tempered and tempered seamless steel pipe, process to produce a tempered and tempered seamless steel

专利摘要:
SEASONED AND TEMPERED SEAMLESS STEEL TUBE, PROCESS TO PRODUCE A SEASONED AND TEMPERED SEAMLESS STEEL TUBE, CURVED STEEL Tempered and tempered seamless steel pipe having an EP wall thickness above or equal to 6 mm and below or equal at 35 mm, where the steel tube has a chemical composition consisting of 0.050-0.090% p C, 0.80-1.65% p Mn, 0.10-0.45% p Si, 0.10-0 , 60% p Cr, 0.05-0.45% p Ni, 0.05-0.40% p Mo, 0.020-0.040% p Al, 0.0030-0.0090% p N, 0.0008- 0.0050% p Ca, 0.000-0.040% p Nb, 0.000-0.020% p Ti, 0.000-0.070% p V, 0.000-0.030% p Zr, 0.000-0.030% p Ta, based on the weight of the composition , the rest being iron and impurities; where the content of (V + Nb) is less than 0.07% w; where, by defining a first parameter P1 = (60 x C) + Cr + [5 x e (35 Mo / WT)] + 50 x (V + Nb), the chemical composition satisfies a first condition P1 (equal less) 14, 5; where the tempered and tempered steel tube has, at medium thickness and possibly also on the inner surface of the tube, a microstructure comprising, in volumetric percentage, tempered bainite above or equal to 40% and ferrite (VF) below or equal at 60%, and has a distance of up to 2 mm, starting from both the external and internal surfaces of the (...).
公开号:BR102014008356B1
申请号:R102014008356-1
申请日:2014-04-07
公开日:2020-12-01
发明作者:Ettore Anelli；Emanuele Paravicini Bagliani；Stefano Fare；José Enrique Garcia Gonzales；Victor Blancas Garcia；Hèctor Manuel Quintanilla Carmona
申请人:Dalmine S.P.A；
IPC主号:

专利说明:

FIELD OF THE INVENTION
[0001] The present invention relates to seamless steel tubes with medium walls having a thickness greater than or equal to 6 mm and less than or equal to 35 mm, and also refers to a method for the manufacture of seamless steel tubes . Said steel tubes, suitable for inline tubes, flow lines and risers for use in the oil and gas industry, also include calenders suitable for hot bending. ANTERIORITY
[0002] The exploitation of oil and gas reserves on the high seas in remote regions of the world is increasingly moving away from the conditions where relatively traditional piping solutions can be used and moving towards more demanding environments. These can incorporate a combination of very challenging factors including, for example, locations in deep water, wells of higher temperatures and pressures, more corrosive products and lower design temperatures. These conditions, when added to the rigorous criteria of weldability and toughness already associated with the specifications of tubes for applications in oil and gas exploration in the high seas, place even more demands on materials and supply capacity.
[0003] These requirements are evident in the development of projects involving aggressive environments and operating under high pressure. For example, most manufacturers of seamless line tubes are able to produce X60, X65 and X70 grade tubes according to the American Petroleum Institute (API) 5L and the standards of the International Organization for Standards (ISO) ) 3183, with resistance to sulfide brittleness (SSC) and hydrogen-induced cracking (HIC). However, the compensation of mechanical strength and toughness, combined with the need for resistance to sulfide embrittlement (SSC) and hydrogen-induced cracking (HIC), like acid resistance, proved difficult to achieve. In particular, tempered and tempered seamless support tubes (T&R) of API 5L of grade X60, X65 and X70 typically exhibit maximum values of hardness, measured at 1.5-2.0 mm deep on the surfaces of the tubes (according to API 5L- ISO 3183), below 250 HV10, but above 235HV10, where new projects now require smaller values to make the material weldable and resistant to SSC, according to Region 3 in NACE MR-0175. These lower values of maximum hardness cannot be consistently achieved with current chemical compositions and processes.
[0004] In addition, pipe collapsing operations, especially when line pipes are installed using the bobiba placement method, cause repeated plastic flexing and straightening deformation cycles. These cyclic loads, producing both cold work and the Bauschinger effect, can affect the final stress-resistance properties of the material.
[0005] The winding currently applied to a growing group of tubular geometries, the present limit being given by tubes with an external diameter (DE) of 40.64cm (16 ’’) and wall thickness (DP) of 35 mm. Other pipe installation techniques, for example, J-lay, S-lay and S-lay steep also introduce plastic tension.
[0006] Accumulated plastic stress, combined with aging, can reduce the ductility and toughness of the tubular material. Therefore, stress and ductility aging tests should be performed following specified procedures when the piping must be exposed to more than 2% of the plastic stress during installation (as recommended by DNV OS-F101. 2012). The plastic deformation of the tube can also decrease the fracture resistance by sulfide stress corrosion, but it is commonly assumed that if normal levels of hardness are maintained after tensioning, there will be sufficient control over the risk of sulfide stress fracture in service .
[0007] In the past, various types of high strength steel for line pipes have been developed in the field of seamless T&R tubes. These seamless tubes combine both mechanical resistance and good weldability in their surroundings. However, these seamless tubes exhibit chemical compositions that prevent the reduction of hardness during tempering. Therefore, in the vicinity of the tube surface, where very high cooling rates are exposed during the internal and external tempering using water and where high hardness values are obtained after treatment due to the formation of a predominantly martensitic microstructure, there is a risk that the maximum hardness values over the entire thickness of the pipe wall remain above 235 HV10 and less preferably above 240 HV10, even after tempering with high temperature and long exposure time.
[0008] The concept of alloy applied to tempered and tempered seamless tubes (T&R) of grade X65 / X70 by some producers of seamless line tubes and based on microalloys with vanadium and niobium. However, individual hardness values are not systematically below 235 HV10 over the entire wall thickness.
[0009] In addition, in the case of hot-induced folds produced from high-strength seamless T&R tubes, it is more difficult to develop the required grade, combined with good impact resistance and low values of surface hardness, concomitant with good resistance to HIC and SSC. This problem is predominantly associated with the process conditions used during the heat treatment of the folds that are necessarily different from those of the seamless tube. In particular, the fold tempering process is less effective. This problem cannot be solved using high hardness steel (that is, with a higher content of chemical elements), as weldability is impaired, toughness is negatively affected and the risk of hardness peaks is increased.
[0010] WO2013 / 002418, EP1918395A1, US2012 / 267014A1, US2013 / 000790A1 and EP1627931A1 are described as examples of manufacturing processes for the related steel tubes.
[0011] WO2013 / 002418 describes tempering and tempering conditions adjusted to have a yield stress greater than 450 MPa and Vickers HV5 hardness (load of 5 kgf = 49 N), measured on the outside and inside of a tube, equal or less than 250 HV5 by performing a superficial decarburization during heating before tempering and / or a grinding operation of the tube while tempering in order to decrease the surface hardness to target values. The depth of superficial decarburization is 2.5-3.0 mm, while the surface layer removed mechanically is 0.3-0.7 mm.
[0012] EP1918395A1 describes low carbon steel and a process for manufacturing seamless steel tubes where immediately after thermoforming the tempering and tempering process is carried out, or else they are placed in a treatment oven and exposed to a temperature not lower than the point Ac3 and finally quenched and tempered. Thus, the EP1918395A1 process performs a continuous treatment right after thermoforming operations, while the tube is still at temperatures above Ar3 (that is, without the transformation from austenite to ferrite phase). Tempering includes reheating below Ac1 followed by air cooling. Such a process, carried out using the low-carbon steels described, produces particle sizes defined in the Japanese standard KIS G0551 (1988) that correspond to values of the previous austenitic particle size (average linear intersection, ASTM E112) greater than 32 nm . As a disadvantage, these high values of anterior austenic particle size (AGS) for these low carbon contents mean greater hardness of the apo consequently with very high hardness values obtained after tempering, where, also after tempering, no maximum hardness values below 250 HV10 can be guaranteed at 1.5 mm depth of the pipe surface. In addition, coarse previous austenitic particle sizes lead to low toughness, since the impact energy values and shear area are negatively affected by coarse grain populations.
[0013] US2013 / 000790A1 describes that the apo tube is subjected, immediately after hot rolling and before tempering and tempering, to an S4 annealing step (Fig. 5) and / or to an accelerated cooling step with S5 water with a cooling rate of at least 100 ° C / min and a cooling stop temperature of 550 ° to 450 ° C in order to avoid the precipitation of carbonitrides. After this accelerated and interrupted cooling, the tubes have very poor grain growth inhibition. Therefore, in these tubes a coarse austenitic particle size (AGS) greater than 25 pm is expected, which means greater hardness of the apo with consequently maximum hardness values of 250 HV10 or greater at 1.5 mm in depth of the tube surface. Thus, low SSC resistance is also expected for these materials in the vicinity of the pipe surfaces.
[0014] US2012 / 267014A1 describes a process for producing a seamless steel pipe for line pipe capable of improving toughness. The tube is subjected, after hot rolling and before austenitization, tempering and tempering, to an additional reheating step S4 (Fig. 4) and / or to an accelerated cooling step with water with a cooling rate of at least 10 ° C / s. This accelerated cooling with water from the hot rolled tube is stopped when the surface temperature of the tube reaches a maximum of 450 ° C. The water-cooled stop temperature is preferably at least 300 ° C, more preferably at least 350 ° C, and even more preferably at least 400 ° C, so room temperature is not reached. Disadvantageously, coarse austenite grain size (TGA), more than 25pm, is expected in these tubes. In addition, the pipes produced with this process are not suitable for severe applications with line pipes, where resistance to very acidic environments and weldability are required.
[0015] Finally, EP1627931A1 describes a seamless tube with a composition of steel without Ca and having both V and Nb as fundamental elements, with a content (V + Nb) greater than 0.07%. Disadvantageously, this high content of V and Nb contributes to the resistance to tempering of bainite and martensite with precipitation hardening, increasing the difficulty in maintaining the maximum hardness below or equal to 235 HV10, close to the outer and inner surfaces of the tube. Furthermore, the control of the shape of inclusions and the improvement of resistance to HIC by the formation of thin and substantially round sulfides is not guaranteed due to the absence of Ca.
[0016] Therefore, new solutions must be found, outside the conventional standard for adding (micro) alloys followed so far for seamless T&R tubes and hot induction bends, for high performance grades X60Q, X65Q and X70Q of seamless tubes of medium walls, with maximum hardness less than or equal to 235 HV10 and very good impact resistance at low temperatures (<-60 ° C). SUMMARY OF THE INVENTION
[0017] The main objective of the present invention is to produce a tempered and tempered medium wall seamless steel tube that offers a combination of consistently low maximum hardness values also close to the inner and outer surfaces of the tubes, excellent low temperature toughness, corrosion resistance (in an acid service environment, containing H2S) and good weldability.
[0018] An additional objective of the present invention is to provide a process for manufacturing said seamless steel tube.
[0019] The present invention proposes to achieve the aforementioned objectives by producing a tempered and tempered seamless steel tube which, according to claim 1, has a wall thickness (EP) greater than or equal to 6 mm and less than or equal to at 35 mm; where the steel tube has a chemical composition consisting of 0.050-0.090% (mass) of C, 0.80-1.65% (mass) of Mn, 0.100.45% (mass) of Si, 0 , 10-0.60% (mass) of Cr, 0.05-0.45% (mass) of Ni, 0.05-0.40% (mass) of Mo, 0.020-0.040% (mass) of Al , 0.0030-0.0090% (mass) of N, 0.0008-0.0050% (mass) of Ca, 0.000-0.040% (mass) of Nb, 0.000-0.020% (mass) of Ti, 0.000 -0.070% (mass) of V, 0.000-0.030% (mass) of Zr, 0.0000.030% (mass) of Ta, 0.00-0.25% (mass) of Cu, 0.000-0.003% ( mass) of S, 0.000-0.018% (mass) of P, 0.0000-0.0005% (mass) of B based on the mass composition, the remainder being iron and impurities; where at least one of Nb and V is present, the content of (V + Nb) being less than 0.07%; where, by defining a first parameter P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb), the chemical composition satisfies a first condition 10 <P1 <14.5 ; where the tempered and tempered steel pipe has, in intermediate thickness and possibly also on the inner surface of the pipe, a microstructure consisting of, in volumetric percentage, an amount of tempered bainite greater than or equal to 40% and of ferrite (VF) less or equal to 60%; and has, at a distance of up to 2 mm from both the inner and outer surface of the tube, or possibly only from the outer surface, a microstructure consisting of, in volumetric percentage, an amount of tempered martensite less than 70%, bainite tempering greater than 30% and traces of ferrite less than or equal to 10%; where the microstructure of the quenched and tempered apo tube has a previous austenitic particle size, measured by the ASTM E112 standard, less than 25 pm; and where the maximum hardness values, measured at 1.5-2.0 mm deep from the internal and external surfaces, are not greater than 235 HV10.
[0020] A second aspect of the invention relates to a manufacturing process of said seamless apo tube where, according to claim 18, the following steps are provided: a) thermoforming of a seamless apo tube having a chemical composition of according to claim 1 and an EP wall thickness greater than or equal to 6 mm and less than or equal to 35 mm; b) refrigeration of the seamless support tube with air until room temperature is reached; c) heating of the seamless apo tube, with a first heating rate between 0.1 ° C / s and 10 ° C / s, for an austenitization temperature above the transformation point Ac3, in an interval between 880 ° C and 980 ° C, providing a residence time between 180s and 5400s; d) temper of the seamless apo tube with a cooling rate in the range of 20 to 80 ° C / s in the intermediate thickness of the tube, or in the intermediate thickness and on the inner surface of the tube, and with a cooling rate of 100- 200 ° C / s in the vicinity of the inner and outer surfaces of the tube or only in the vicinity of the outer surface; e) heating the seamless steel tube, with a second heating rate between 0.1 ° C / s and 10 ° C / s, to a temperature within a predetermined interval, providing a residence time at said tempering temperature between 600 s and 7200 s; where said predetermined range is calculated with a tolerance of ± 20 ° C using the following equation:
where a is a parameter whose value is 1.75, 1.90 or 2.15 if the degree to be reached is X60, X65 or X70, respectively.
[0021] The tempered and tempered seamless steel tubes (T&R) of the Invention are suitable for line tubes, line tubes and risers of grades X60Q, X65Q and X70Q, and preferably have an external diameter (OD) between 3 1 / 2 ”(89 mm) and 28” (711 mm).
[0022] After manufacture, the seamless tube of medium walls can be subjected to folding operations and heat treatments to obtain folds of grades X60Q, X65Q and X70Q with low maximum hardness and improved toughness at low temperatures. Said folds have a yield stress of 415 to 635 MPa; maximum hardness values, measured at 1.5-2.0 mm of surface depth, less than 235 HV10 or equal to 235 HV10; good toughness under impact at low temperatures (minimum impact energy of 150 J for CVN transverse tests performed on standard-sized species at - 40 ° C), while having good resistance to HIC and SSC concomitantly.
[0023] By setting the parameter P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb), the steel tube of the Invention allows to reach the requirements of low maximum hardness (in particular in the part of thickness close to the inner and outer surfaces of the tube), the specified minimum yield stresses (SMYS), toughness and corrosion resistance when satisfying the following condition: P1 = (60 x C) + Cr + [ 5 xe (35 x Mo / EP)] + 50 x (V + Nb) <14.5, preferably P1 <13.5, where the symbols of the chemical elements represent the value of mass percentage (% mass) and EP and the value of the wall thickness in mm.
[0024] Furthermore, by setting the parameter P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V), the preferred modalities of the Invention allow to obtain a hardening for guarantee the minimum specified stress properties in intermediate thicknesses if the parameter P2 satisfies the conditions summarized in the following table:
where in parameter P2 the s ^ cakes for the chemical elements represent the value of mass percentage (% mass).
[0025] The steel tubes manufactured in accordance with the present invention exhibit: • Flow stress, YS: minimum of 415 MPa (60.2 ksi) and maximum of 635 MPa (92.1 ksi); • Tensile strength, UTS: minimum of 520 MPa (75.4 ksi) and maximum of 760 MPa (110.2 ksi); • Stretching, not less than 18%; • YS / UTS ratio not greater than 0.90; • Maximum hardness (measured between 1.5 mm and 2.0 mm in depth of the tube surface) not greater than 235 HV10, preferably not greater than 230 HV10, and more preferably not greater than 225 HV10; • Minimum impact energy of 200 J / 150 J (average / individual) and a minimum of 85% average shear area for both longitudinal and transverse Charpy V-notch (CVN) tests performed on standard specimens at -40 ° C according to ASTM A 370; • Ductil-Fragil Transformation Temperature (ASTM E23) less than or equal to around -60 ° C; • Resistance to Hydrogen-Induced Fissure, evaluated according to NACE TM0284-2003 standard item No. 21215, using a NACE solution and a 96-hour duration test, with the following HIC parameters (average in three sections of three bodies of proof): o Crack Length Ratio, CLR <10% o Crack Thickness Ratio, CTR <3% o Crack Sensitivity Ratio, CSR <0.5% • Resistance to Sulfide Fragility Cracking (SSC ), evaluated according to ASTM G39, using test solution A NACE TM0177 and duration of 720 hours, with no failure at 90% of the true flow stress (AYS).
[0026] All the features were achieved through the metallurgical design adapted from tubes by means of laboratory tests and industrial sorting. The results show that the manufacture of seamless T&R tubes and folds with a maximum hardness of not more than 235 HV10, preferably not more than 230 HV10, and more preferably not more than 225 HV10, is possible with at least a given dimensional range: diameter external (OD) ranging from 3 1/2 ”(89 mm) to 28” (711 mm), and wall thickness (EP) from 6 mm to 35 mm.
[0027] In particular, the steel tubes of the Invention have maximum hardness, measured at 1.5-2.0 mm in depth of the internal and external surfaces, not greater than 235 HV10 for grade X70Q, not greater than 230 HV10 for grade X65Q, and not greater than 225 HV10 for grade X60Q.
[0028] The term "tube" as used here, refers to a hollow, elongated member that can be erect or have folds or curves and be formed in a predetermined shape, and any additional formation required to consolidate the formed tubular product in your desired location. The tube may have a substantially cylindrical external and internal surface, although other shapes and cross sections are also contemplated.
[0029] The term "room temperature" as used here has its common meaning known to those skilled in the art and can include temperatures between about 16 ° C (60 ° F) to about 32 ° C (90 ° F) .
[0030] Regarding the composition of the steel, the term "optional element" refers to an element that is possibly added to the mandatory elements that define the essential chemical composition of the steel tubes of the Invention. Each optional element can be added to further improve the properties of the steel tubes. The optional elements in the action of the seamless tubes of the Invention are: vanadium (V), niobium (Nb), titanium (Ti), zirconium (Zr) and tantalum (Ta).
[0031] In particular, vanadium and niobium are optional elements that, if present, must satisfy the condition (V + Nb) <0.07%. In some preferred embodiments, at least one of V and Nb is present and the (V + Nb) content is less than 0.07%, preferably less than or equal to 0.055%. In seamless steel tubes of the technique, higher content of vanadium and niobium caused maximum hardness values greater than 235HV10, particularly in the vicinity of the tube surfaces, even if the average hardness value over the entire wall thickness has been less than 235HV10. The term "average hardness" means the average value of the hardness values measured over the wall thickness of the tube.
[0032] The term "element of impurity", on the contrary, refers to an element not provided in the design of the steel composition in order to achieve the referred objectives of the Invention. However, the said element may be present as impurity or traces, because, depending on the manufacturing processes, its presence may be inevitable. In order to optimize the properties of the steel tubes of the Invention, the content of each impurity element was appropriately limited.
[0033] Such impurity elements can be: copper (Cu), sulfur (S), phosphorus (P) and boron (B).
[0034] The maximum value of all impurities in the formulation of the steel is advantageously less than or equal to 0.30% (mass), preferably equal to 0.27% (mass). The dependent claims describe preferred embodiments of the Invention).
[0035] The terms "approximately", "around" and "substantially" as used herein represent an amount equal to or close to the reported amount that still performs a desired function or achieves a desired result. For example, the terms "approximately", "around" and "substantially" may refer to an amount that is less than 20%, less than 5% and less than 1% of the reported amount, respectively. BRIEF DESCRIPTION OF THE FIGURES
[0036] Advantages and additional features of the present invention will be more apparent in the light of the Detailed Description of seamless steel tubes and their manufacturing process, illustrated by means of non-limiting examples, with the aid of the attached illustrations, where:
[0037] Figure 1 is a flow chart of the process according to the Invention. DETAILED DESCRIPTION OF PREFERENTIAL MODALITIES OF THE INVENTION
[0038] The seamless steel tube, subject of the present invention, was designed so as to have not only the average hardness value over the entire wall thickness, but also the maximum hardness values below or equal to 235 HV10 , preferably below or equal to 230 HV10, and more preferably not greater than 225 HV10, also in the vicinity of both the inner and outer surfaces of the tube, combined with good toughness at low temperatures, resistance to sulfide brittleness (SSC) and cracking hydrogen induced (HIC), allowing the use of the tube in sour service environments. Said maximum hardness values were measured at 1.5-2.0 mm in depth on both the inner and outer surfaces of the tubes, according to ISO 3183.
[0039] Seamless tubes according to the invention can be used, for example, as line tubes, flow lines and risers for use in the oil and gas industry. These tubes have a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm and, overall, have a predominant microstructure of bainite, as will be explained in more detail later. Said tubes have a minimum yield stress of at least 415 MPa (60ksi), involving the mechanical properties corresponding to different degrees: X60Q (minimum yield stress of 415 MPa = 60.2 ksi), X65Q (minimum yield stress of 450 MPa = 65 ksi) and X70Q (minimum flow stress of 485 MPa = 70 ksi).
[0040] As discussed in detail below, through a combination of steel composition and heat treatment, a final microstructure is achieved that enhances the selected mechanical properties of interest in seamless tubes with medium walls.
[0041] The steel composition of the present invention comprises carbon (C), manganese (Mn), silicon (Si), chromium (Cr), nickel (Ni), molybdenum (Mo), nitrogen (N), aluminum ( Al) and calcium (Ca). In addition, one or more of the following elements can be optionally added: niobium (Nb), vanadium (V), titanium (Ti), zirconium (Zr) and tantalum (Ta). The rest of the composition comprises iron (Fe) and possible impurities. The concentration of said impurities is reduced to the least amount possible. Said impurities can include copper (Cu), sulfur (S), phosphorus (P) and boron (B).
[0042] The hardness of the steel, that is, the relative ability of the steel to form bainite and martensite when tempered, has been improved through chemical composition. In particular, the addition of elements such as Mo, Mn, Cr and Ni in the intervals described below are effective to promote predominantly the formation of bainite instead of ferrite.
[0043] Three stages are considered as the crack fracture initiation process: (I) formation of the fracture origin by breaking the cementite, (II) propagation of the crack in the cementite in the matrix and formation of a crack, and (III) propagation cracking across the boundaries between high angle grains, with both a low content per unit volume of cementite particles and a high frequency of high angle (finely divided) boundaries leading to better resistance to impact at low temperatures.
[0044] The low carbon content prevents the formation of an excessive number of coarse particles of cementite, but reduces the hardness and increases the transformation temperatures. Therefore, the decrease in C has to be combined with suitable additions of Mn, Cr, Ni and Mo to reduce temperatures and maintain fine particle size.
Preferred actions have been identified as having: - limitation of vanadium content plus the content of niobium (V + Nb) to values less than 0.07%, preferably 0.055%; - carbon content from 0.050 to 0.090%, where the lower the carbon content in the water the higher the content of other alloying elements such as Mn, Mo, Cr and Ni.
[0046] As an advantage, the combination of chemical elements is optimized in order to keep the maximum hardness value low and induce good weldability, maintaining the equivalent carbon CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.26% to 0.43%. Furthermore, preferably the equivalent carbon values (CEpcm = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB) are in the range of 0 , 14 to 0.22. The symbols of the chemical elements of the Ceiiw and CEpcm equivalent carbons represent the value of the respective mass percentage (% mass).
[0047] Advantageously, the requirements for appropriately reduced maximum hardness values (over the entire thickness of the tube), the minimum flow stress, toughness and corrosion resistance can be consistently guaranteed if parameter P1 defined by equation 1: P1 = (60 x C) + Cr + [5 x and (35 x Mo / EP)] + 50 x (V + Nb) (Equation 1) satisfies the condition P1 <14.5, preferably P1 <13.5.
[0048] Advantageously, P1 is greater than or equal to 10.0.
[0049] The steel tubes of the Invention have a U-shaped hardness profile along the wall thickness, with the highest values on the internal and external surfaces and the lowest values on the intermediate thickness. A suitable hardening to guarantee the minimum specified stress properties is achieved if parameter P2 defined by equation 2 P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V) (Equation 2) satisfy the minimum values summarized in the following table as a function of grade and wall thickness:

[0050] Advantageously P2 and less than or equal to 4.0.
[0051] The symbol "x" in equations 1, 2 and the equivalent carbon formula CEpcm is a multiplication sign. In equations 1 and 2 in both the CEpcm and Ceiiw formulas, the symbols for the chemical elements represent the value of mass percentage (mass%).
[0052] Table 1 illustrates some preferred modalities of the composition of the August, in mass percentage (% mass): Table 1 - Intervals of compositions of Ages (mass percentage)

(*) M = Mandatory; O = Optional; I = impurity
[0053] An additional preferred mode (Composition 5) of the apo composition has the same ranges as Composition 3, except for the maximum value of Nb, which is equal to 0.005% (mass).
[0054] Carbon (C) is a mandatory element whose addition to the apo increases its resistance at no additional cost and refines the microstructure, reducing transformation temperatures. If the C content is less than around 0.050%, it is difficult to obtain the desired resistance in the tubes. On the other hand, if the apo composition has a C content greater than around 0.090%, the maximum hardness is above 235 HV10, the toughness is impaired and the weldability decreases, making any welding process more difficult and expensive . Therefore, the C content of the apo formulation is selected within the range of 0.050% to 0.090%, and preferably within the range of 0.060% to 0.085%.
[0055] Manganese (Mn) is a mandatory element whose addition in the formulation of steel is effective to increase the hardness, mechanical resistance and toughness of the steel. If the Mn content of the steel composition is less than around 0.80% and it is difficult to obtain the desired mechanical strength. However, if the Mn content in the steel exceeds 1.65% bonding structures are exposed, and both the toughness and resistance to HIC / SSC decrease. Therefore, the Mn content of the steel composition is selected within the range of 0.80% to 1.65%, preferably between 0.90% and 1.35% and more preferably between 1.00% and 1.30% . In a preferred embodiment, the Mn content is greater than or equal to 1.00% and less than or equal to 1.25%.
[0056] Silicon (Si) is a mandatory element whose addition in the formulation of the steel confers a deoxidizing effect during the manufacturing process and also increases the mechanical resistance (for example, reinforcement of solid solution). If the Si content of the steel composition is less than 0.10%, the water is little deoxidized during manufacture and exhibits a high level of microinclusions. If the Si content of the steel formulation exceeds 0.45%, both the toughness and machinability of the steel will decrease. A Si content greater than around 0.45% is also recognized as having a detrimental effect on the surface quality when the water is processed at high temperatures (for example, temperatures greater than around 1000 ° C) in oxidizing atmospheres, because the adhesion of the oxide surface (scale) is increased due to the formation of phialite and the risk of defect on the surface is greater. Thus, the Si content in the steel composition is selected within the range of 0.10% to 0.45%, preferably between 0.10% and 0.35%, and more preferably within the range of 0.10% to 0.30%.
[0057] Chromium (Cr) is a mandatory element whose adherence in the formulation of the auger increases the hardness, decreases the transformation temperatures and increases the resistance to the annealing of the auger. Thus, the addition of Cr is desirable to reach high levels of strength and toughness. If the Cr content of the steel composition is less than 0.10%, it is difficult to obtain the desired strength and toughness. On the other hand, if the Cr content exceeds about 0.60%, the cost is excessive and the toughness decreases due to facilitated precipitation of coarse carbides at the grain boundaries. Additionally, the weldability of the resulting steel is reduced, making the welding process more difficult and expensive. Therefore, the Cr content of the composition of the auger is selected within the range of 0.10% to 0.60%, preferably between 0.10% and 0.40%, and more preferably between 0.20% and 0.40 %. In a preferred embodiment, the Cr content is greater than or equal to 0.30% and less than or equal to 0.40%.
[0058] The nickel (Ni) is a mandatory element whose addition increases the resistance and tenacity of the steel. However, when the Ni addition exceeds 0.45%, a more adherent scale is observed, with a greater risk of forming surface defects. Furthermore, the nickel content greater than 1% is recognized as having a harmful effect on sulfide brittleness (SSC). Instead, if the Ni content is less than 0.05%, the effect on toughness and strength becomes negligible. Therefore, the Ni content of the augmentation formulation can vary within the range of 0.05% to 0.45%, preferably between 0.20% and 0.40%, and more preferably between 0.25% and 0.35 %. In a preferred embodiment, the Ni content is greater than or equal to 0.25% and less than or equal to 0.35%.
[0059] Molybdenum (Mo) is a mandatory element whose addition in the formulation of the steel improves the hardness, the hardening by solid solution and the fine precipitation. Mo assists in delaying sweetening during tempering, promoting the formation of very fine MC and M2C precipitates. These particles are substantially uniformly distributed in the matrix and also act as beneficial hydrogen capture sites, slowing down the diffusion of elemental hydrogen to dangerous capture sites, usually located at the boundaries between the grains, which behave as sites of nucleation of cracks. Mo also reduces phosphorus segregation at the grain boundaries, improving resistance to intergranular fracture, with beneficial effects also on resistance to SSC, since high-strength products that suffer from hydrogen embrittlement exhibit an intergranular fracture morphology. By increasing the Mo content, the desired strength is achieved at higher tempering temperatures, which promote better levels of toughness. In order to exert the mentioned effect, the Mo content of the steel formulation is greater than or equal to 0.05%. However, for Mo contents greater than 0.40%, weldability is reduced. As the alloy with Mo iron is expensive, the Mo content is selected within the range of 0.05% to 0.40%, preferably between 0.07% to 0.40% and more preferably between 0.10% and 0.35%. In a preferred embodiment, the Mo content is greater than or equal to 0.25% and less than or equal to 0.35%.
[0060] Niobium (Nb) is an optional element whose addition to the steel is used to further refine the size of the austenitic grain during hot rolling and reheating before tempering, as it prevents movement of the grain boundaries by acting so much in the solid solution as in the form of carbides and fine nitrides.
[0061] Nb increases the resistance of the water by hardening the dispersion of particles and can contribute to generate high hardness values in bainite and martensite after tempering. These fine, rounded particles are substantially uniformly distributed in the matrix and also act as hydrogen capture sites, beneficially delaying the diffusion of atomic hydrogen to hazardous capture sites, usually in the border regions of the grains, which behave as sites of grains. nucleation of cracks. If the Nb content is greater than 0.040%, a coarse distribution of precipitates is formed which impairs toughness. In addition, if the Nb content is greater than 0.040% it can promote the formation of brittle zones in the heat affected zone (HAZ) in the welded perimeter. Thus, the Nb content in the formulation of the steel is selected to be less than or equal to around 0.040% (with 0.000% possibility included), preferably less than or equal to 0.035%, and more preferably less than or equal to 0.030%. In a preferred embodiment, the Nb content is greater than or equal to 0.020% and less than or equal to 0.030%. In an additionally preferred embodiment, the Ni content is less than or equal to 0.005% (with 0.000% possibility included).
[0062] Vanadium (V) is an optional element whose addition to the steel composition increases the resistance due to the precipitation of very fine carbonitrides during tempering. However, if a significant volumetric fraction of vanadium carbide particles is formed, difficulties in maintaining high levels of toughness and maximum hardness values less than or equal to 235 HV10 occur after tempering. Therefore, the V content of the steel composition is maintained to be less than or equal to 0.070% (with 0.000% possibility included). In a preferred embodiment, the V content is less than or equal to 0.040%, preferably less than or equal to 0.030%.
[0063] Both vanadium and niobium contribute to the resistance to tempering of bainite and martensite through precipitation hardening, increasing the difficulty in maintaining the maximum hardness less than or equal to the value of 235 HV10, in particular, near the external surfaces and internal to the tube, where the presence of significant amounts of martensite cannot be excluded. Therefore, the sum of vanadium and niobium content of the steel composition should be less than 0.07%, preferably less than or equal to 0.055%. Advantageously, at least one of vanadium and niobium must be present.
[0064] Titanium (Ti) is an optional element whose addition in the formulation of the steel is provided to refine the austenitic grain size in high temperature processes, forming nitrides and carbonitrides. When titanium is present in concentrates greater than 0.020%, coarse particles of TiN are formed which impair toughness. Accordingly, the Ti content of the steel composition is less than or equal to 0.020% (with 0.000% possibility included), preferably less than or equal to 0.015%. In an alternative steel modality, titanic (Ti) is a mandatory element with content selected as being greater than or equal to 0.006% and less than or equal to 0.020%, preferably greater than or equal to 0.006% and less than or equal to 0.015%.
[0065] Aluminum (Al) is a mandatory element whose addition in the formulation of steel has a deoxidizing effect during the manufacturing process and can refine the grain of steel. Therefore, the Al content is greater than or equal to 0.020%. If the Al content of the formulation is greater than around 0.040%, coarse precipitates of AlN may be formed which impair the toughness and / or oxides rich in Al (for example, non-metallic inclusions) which impair the resistance to HIC and SSC. Therefore the Al content of the water is selected to be within the range of 0.020% and 0.040%, preferably between 0.020% and 0.035%. In a preferred embodiment, the Al content is greater than or equal to 0.020% and less than or equal to 0.035.
[0066] Nitrogen (N) is a mandatory element whose presence in the formulation of the steel contributes to form carbonitrides of Nb, Mo and Ti, and helps to achieve the minimum mechanical resistance. However, if the N content exceeds 0.0090%, the steel's toughness can be degraded. Furthermore, when the nitrogen content is above such a threshold value, the response to stress aging is prevented due to the increase in the flow stress / tensile stress and ductile / brittle transition temperature. Thus, the N content in the formulation of the steel is selected in the range of 0.0030% to 0.0090%, preferably between 0.0030% and 0.0070%. In a preferred embodiment, the N content is greater than or equal to 0.0030% and less than or equal to 0.0060%.
[0067] Copper (Cu) is an element of impurity that is not necessary in the modalities of steel compositions. However, depending on the manufacturing process, the presence of copper may be unavoidable. Thus, the copper content is limited to the lowest possible level, in order to keep the risks of hot cracking (hot cracks) and the formation of defects induced by sticky scale at very low levels. For example, the Cu content of the steel formulation is less than or equal to 0.25% (0.00% possibility included), preferably less than or equal to 0.20%, and more preferably less than or equal to 0 , 15%. Among the possible impurities, copper is the element that can be present in larger mass% and its eventual presence is due to the manufacturing process. These maximum limits are typical of a steel production route based on the Electric Arc Furnace (EAF) using scrap as a raw material. Intense recycling is now a common practice in the world for the production of flat and long / tubular products, and this practice can determine the presence of copper as an impurity at the levels mentioned above.
[0068] Sulfur (S) is an impurity element that can decrease both the toughness and handling of the water, as well as the resistance to HIC / SSC. Therefore, the sulfur content in the water is kept as low as possible. For example, the S content in the formulation is less than or equal to 0.0030% (0.00% possibility included), preferably less than or equal to 0.0020%, and more preferably less than or equal to 0.0015 %.
[0069] Phosphorus (P) is an impurity element that can reduce the toughness and resistance to HIC / SSC of high strength steel. Therefore, the phosphorus content is kept as low as possible. For example, the P content in the composition may be less than or equal to about 0.018% (0.00% possibility included), preferably less than or equal to about 0.015% and, more preferably, less than or equal to about 0.012%. In a preferred embodiment, the P content is less than or equal to 0.011%.
[0070] Calcium (Ca) is a mandatory element whose addition in the formulation of steel helps to control the shape of inclusions and to improve resistance to HIC by forming thin and substantially round sulfides. To provide these benefits, the calcium content in the formulation is selected to be greater than or equal to around 0.0008%. However, if the Ca content exceeds 0, 0050% the effect of the addition of Ca is saturated and increases the risk of formation of aggregates of calcium-rich non-metallic inclusions that reduce resistance to HIC and SSC. Therefore, the Ca content in the steel formulation is selected to be in the range of 0.0008% to 0.0050%, preferably between 0.0008% and 0.0030%. In a preferred embodiment, the Ca content is greater than or equal to 0.0015% and less than or equal to 0.0030%. In an additionally preferred embodiment, the Ca content is greater than or equal to 0.0010% and less than or equal to 0.0030%.
[0071] Boron (B) is an impurity element whose presence in the composition of the steel is undesirable, since it increases the hardness of the steel and the hardness in the HAZ. The upper limit of the boron content to avoid malefic effects is around 0.0005%. Therefore, the maximum B content in the steel composition is selected to be less than or equal to 0.0005% (0.00% possibility included).
[0072] Zirconium (Zr) and tantalum (Ta) are optional elements that act as strong carbide and nitride builders, as well as Nb and Ti. These elements can optionally be added to the steel composition in order to produce carbonitrides Zr and Ta fines that increase the mechanical resistance of the action by hardening the dispersion of particles and that also act as beneficial hydrogen capture sites, delaying the diffusion of atomic hydrogen to dangerous capture sites. If the content of Zr or Ta is greater than or equal to 0.030%, a coarse distribution of precipitates is formed which can impair the toughness of the steel. Zirconium also acts as a deoxidizing element in steel and combines with sulfur; however, calcium is preferred if the addition to the steel is to promote non-metallic globular inclusions. Therefore, the content of Zr and Ta in the formulation of the steel is selected to be less than or equal to 0.030% (0.00% possibility included), preferably less than or equal to 0.015% and more preferably less than or equal to 0.010% .
[0073] A process for the manufacture of seamless steel tubes, object of the present invention, is schematically illustrated in the flowchart of Figure 1. The process includes steel 102 manufacturing operations; thermoforming operations 104; heat treatment operations 106, including austenitization 106A, tempera 106B and tempering 106C; and finishing operations 110. Known methodologies may be included in the steelmaking operations to prepare the compositions in Table 1 and in the thermoforming operations to produce a seamless steel pipe that has a wall thickness in the range of 6 to 35 mm.
[0074] Steel fabrication operations 102 preferably comprise the manufacture of steel and the production of a solid metal billet capable of being drilled and laminated to form a metal tubular product. Selected scrap of steel, cast iron and sponge iron can be used to prepare the raw material for the formulation of steel. Other sources of iron and / or steel can be used for the preparation of the steel composition.
[0075] Primary steelmaking can be carried out using an electric arc furnace to melt it, reduce phosphorous and other impurities, and reach the selected temperature. Stamping and deoxidation can be carried out in addition to the addition of alloying elements.
[0076] One of the main goals of the steel manufacturing process is to refine iron by removing impurities. In particular, sulfur and phosphorus are harmful to water as they degrade the mechanical properties and resistance to HIC and SSC. In one embodiment, a secondary steelmaking can be carried out in a pan oven and cutting station after the primary steelmaking to perform specific purification steps.
[0077] During these operations very low levels of sulfur in the water are achieved, treatments of inclusion of calcium and flotation of inclusions are carried out. The flotation of inclusions can be carried out by bubbling inert gases in the pan oven to force the flotation of inclusions and impurities. This technique produces a fluid slag capable of absorbing impurities and inclusions. In this way, a high quality steel is provided which has the desired composition with a low content of inclusions.
[0078] Following the production of molten steel as having a composition within the ranges of Table 1, it is shaped like a solid cylindrical billet having a substantially uniform diameter along the longitudinal axis. For example, cylindrical billets with diameters ranging from 190 mm to about 420 mm can be produced in this way.
The billet is then manufactured and transformed into a tubular product through thermoforming processes 104. A solid, cylindrical billet of clean water can be heated to a temperature of around 1200 ° C to 1340 ° C, preferably around 1280 ° C. For example, the billet can be reheated by a rotary smelting furnace. The billet is additionally subject to thermo-drilling and rolling operations. In the rolling mill, the billet is drilled, for example, using the Mannessmann effect, and a thermal deformation process is used to substantially reduce the outer diameter and wall thickness of the tube, while the length is substantially increased. The drilling process can be carried out at temperatures ranging from about 1200 ° C to about 1300 ° C.
[0080] The hollow bars obtained are subjected to hot rolling at temperatures in the range between about 1000 ° C and about 1200 ° C in a retained mandrel roller mill or equivalent mill.
[0081] The precise dimensioning can be carried out by a dimensioning mill.
[0082] The seamless tubes are, after thermoforming and before austenitization, tempering and tempering cooled directly in air, preferably stagnant air, to approximately room temperature in a cooling bed. The air-cooled tubes have a microstructure of ferrite and perlite, due to the relatively low cooling rate during cooling in stagnant air between 800 ° C and 500 ° C, with that rate being around 0.5-2 ° C / s, depending on the thickness. Furthermore, air-cooled tubes already contain fine precipitates (for example, Nb and / or V carbonitrides) formed during air cooling, which are very effective in inhibiting the growth of austenitic grain during reheating (austenitization) before of the seasoning. For example, tubes with an outside diameter (OD) between about 3 1/2 and 16 inches can be formed in this way.
[0083] Alternatively, after hot rolling the tubes can be heated continuously, without cooling to room temperature, by an intermediate oven to provide uniform temperature, with the precise dimensioning being able to be conducted by a dimensioning mill. Then, the seamless tubes are immediately cooled in air, preferably stagnant air, to room temperature in a cooling bed.
[0084] In the case of a pipe with final OD greater than around 16 inches, the pipes produced by a medium sized mill can be processed by a rotating expansion mill. For example, medium-sized tubes can be reheated by a mobile beam oven at a temperature in the range of about 1150 ° C to about 1250 ° C, expanded to the desired diameter by an expansion mill at a temperature in between around 1100 ° C to around 1200 ° C, and reheated continuously before final design.
[0085] In a non-limiting example, a solid bar can be thermoformed as discussed above in a tube having an outside diameter within the range of 3 1/2 to around 28 inches and a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm.
[0086] The final microstructure of the formed tube is determined by the composition of the steel provided in the steel manufacturing operations 102 and in the heat treatments performed in operations 106. The composition and the microstructure, in turn, reveal the properties of the formed tube.
[0087] The thermal treatment operations 106, performed after the tube has been cooled in air to around room temperature, include austenitization, tempering and tempering (T + R).
[0088] In this way the process of the Invention conducts a temper outside the continuous process (or reheating temper) which involves cooling the tube to room temperature, and then heating the tube until the phase transformation to austenite completely occurs, and finally perform tempering and tempering (reheating below Ac1, transformation point of austenite, followed by air cooling).
[0089] This tempera of the Invention outside the continuous process, through the austenite-ferrite-austenite transformation, promotes the refinement of the austenitic grains and makes them more uniform, when compared with the microstructure of the tempered material in the continuous process.
[0090] A consequence of this process is that the average size of anterior austenitic grains (AGS), measured as the linear interstice measured by the ASTM E112 standard, and <25 pm, corresponding to the number of previous austenitic grain size equal to 7.3 according to Japanese standard JIS G0551 or the same standard ASTM E112, allowing to achieve better toughness.
[0091] The austenitization operation includes reheating the tube around room temperature (reached after thermoforming by means of cooling air) to a temperature that austensitizes the tube followed by rapid cooling.
[0092] In particular, a heating of the support tube is conducted seamlessly, with a heating rate of between 0.1 ° C / s and 10 ° C / s, to an austenitization temperature above the transformation point Ac3, in an interval between 880 ° C and 980 ° C, providing a residence time between 180 s and 5400 s.
[0093] This heating of the austenitization operation is carried out in a gas oven provided with burners. The source of heat during reheating for austenitization and combustion of natural gas (CH4). Thus, oxygen is consumed during combustion, but advantageously its concentration in the oven is less than 10%. Typically the oxygen content is in the range of 0.5 to 4% and the decarbonization process is quite limited, with typical decarbonization depths from 0.05 mm to 0.15 mm (maximum value).
[0094] For example, the austenitization oven temperatures can be selected in order to allow the tube to reach the desired austenitization temperature with a tolerance lower than around +/- 30 ° C. The austenitization temperatures must be above the transformation point Ac3, preferably in the range between 900 ° C and 960 ° C, more preferably between 910 ° C and 930 ° C. The heating rate can be selected between 0.1 ° C / s and 8 ° C. The residence time, the time when the tube reaches the desired final temperature minus 10 ° C until the outlet of the oven tube, can be selected in the range between 300 s to 3600 s. Austenitization temperatures and residence times can be selected depending on the chemical composition, wall thickness, and desired austenitic grain size. At the exit of the oven, the tube can be peeled, for example, with pressurized water, to remove surface oxides and then it is quickly moved, preferably in less than 120 s, to a tempering system, for example, a tempering system with water.
[0095] In the 106B tempering operations, an internal and external cooling is used to reach, at an average thickness, the desired cooling rates, greater than about 20 ° C / s, preferably in the range between 20 ° C / s and 80 ° C / s. In one embodiment, such a cooling rate is in the range between 50 ° C / s and 80 ° C / s. Otherwise, in the vicinity of the inner and outer surfaces of the tube, in particular at 1.5-2 mm in depth, the cooling rate is in the range between 100 ° C / s and 200 ° C / s.
[0096] Alternatively, in the 106B tempering operations, an external cooling is applied to achieve, in the intermediate thickness and also on the inner surface of the tube, the desired cooling rates, greater than about 20 ° C / s, preferably in the range between 20 ° C / s and 80 ° C / s. in one embodiment, such a cooling rate is in the range of 50 ° C / s to 80 ° C / s. instead, in the vicinity of the outer surface of the tube, in particular at 1.5-2 mm deep from these surfaces, the cooling rate is in the range between 100 and 200 ° C / s. In case the wall thickness is less than about 25 mm, an external temper by means of water jet rings can be applied.
[0097] For example, a seasoning with water can be performed by immersing the tube in a tank containing agitated water. The tube is quickly rotated during cooling to make the heat transfer high and uniform and to avoid distortions. Additionally, in order to remove the steam generated inside the tube, an internal jet of water is used. The water temperature may not be higher than around 40 ° C, preferably less than around 30 ° C during tempering operations 10 6B.
[0098] Advantageously, the tube is rotating during immersion in the water tank and a jet of water is ejected by a nozzle into the tube in order to remove steam and prevent the formation of film. In this way, uniform and effective cooling is conducted, as the heating process with the formation of a gaseous film is avoided. In fact, in the case of heating, the heat transfer is not so homogeneous along the tube and low cooling rates are obtained in the intermediate thickness, with the risk that the flow stress will not be achieved.
[0099] After the aforementioned tempera operations 106B, the seamless steel tubes, with chemical composition according to one of the modalities of Table 1 and with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm, promote in its global microstructure the formation of a volumetric percentage of bainite greater than 40%, preferably greater than 50% and more preferably greater than 80%, and less than or equal to 90%.
[00100] Particularly, in the intermediate thickness (and possibly also on the inner surface of the tube), the microstructure of the tempered steel tube comprises a volumetric percentage of bainite greater than or equal to 40% and of ferrite (VF), for example, polygonal ferrite fine, less than or equal to 60%, with smaller amounts of MA constituents (islands of high carbon martensite and retained ferrite). Preferably the content of bainite is greater than or equal to 50% and that of ferrite (VF) less than or equal to 50%. More preferably, the bainite content is greater than or equal to 80% and that of ferrite (VF) less than or equal to 20%. MA constituents are present in volumetric fractions of up to approximately 12%.
[00101] Advantageously, at distances of up to approximately 2 mm from the outer and inner surfaces of the steel tubes (or possibly at distances of up to approximately 2 mm from the outer surface only), the microstructure of the tempered steel tube is constituted by of martensite with volumetric percentages less than 70%, preferably less than 40%, and more preferably less than 20% (measured according to ASTM E562-08) and constituted of bainite with volumetric percentages greater than 30%, preferably greater than 60%, more preferably greater than 80%. Ferrite scraps of up to 10% may be present in the apo with less hardening. Martensite and bainite can be formed at temperatures below 450 ° C and 600 ° C, respectively, after reheating in austenitizing temperatures in the range of 900 ° C to 960 ° C for residence times between 300 s and 3600 s, and cooling at rates greater than or equal to 20 ° C / s, preferably in the range of 20 to 80 ° C / s in the intermediate thickness, in the case of external and internal tempera, or both in the intermediate thickness and in the inner surface of the tube, in the case of external tempera only.
[00102] Additionally, the average size of the previous austenitic grain, measured by the ASTM E112 standard, is advantageously less than 25 pm (linear intersection).
[00103] The average size of regions separated by high angle boundaries (i.e., packing size) is advantageously less than 9 pm, preferably less than 7 pm and more preferably less than 5 pm. Said packaging size is measured as the average linear intersection in images obtained by Scanning Electron Microscopy (SEM) using the Backscattered Electron Diffraction signal (EBSD), and considering the high angle boundaries those with a degree of disorder> 15 ° .
[00104] After the tempering operation 106B the tube is introduced into another furnace for tempering operations 106C, comprising heating the seamless steel tube to a tempering temperature in the range between 600 ° C and 680 ° C, and providing a residence time at said temperature between 600 s and 7200 s.
[00105] Tolerances for the selected tempering temperature are around ± 15 ° C. The tube can be heated at a rate between about 0.1 ° C / s to about 10 ° C / s for the selected tempering temperature. The tube is additionally maintained at the selected tempering temperature for a time preferably between 600 s and 5400 s.
[00106] The tempering temperature can be selected within the range of around 600 ° C to around 680 ° C depending on the chemical composition of the steel and the degree to be achieved.
[00107] The optimum tempering temperature can be calculated with a tolerance of ± 20 ° C, preferably ± 10 ° C, using the following equation 3:
where a is a parameter that has a value of 1.75, 1.90 or 2.15 if the degree to be achieved is X60Q, X65Q or X70Q, respectively. The "x" symbol is a multiplication sign and the chemical element symbols represent the mass percentage value.
[00108] For example, if the tempering temperature calculated using equation 3 is equal to 647 ° C (according to the chemical composition of example 2, see below, for an X60 grade steel tube), the optimal range tempering and from 627 ° C to 667 ° C, where the tempering temperature can be chosen within this optimal range.
[00109] Particularly, in the intermediate thickness (and possibly also on the inner surface of the tube), the microstructure of the tempered and tempered steel tube comprises in volumetric percentage a content of bainite greater than or equal to 40% and of ferrite (VF), for example, fine polygonal ferrite, less than or equal to 60%, while the MA constituents are now absent since during the tempering the MA islands decompose into ferrite and carbides, with such a decomposition requiring temperatures greater than 550 ° C and being necessary for not impair the toughness of the final product. Preferably, the tempered bainite content is greater than or equal to 50% and that of ferrite (VF) is less than or equal to 50%. Most preferably the content of tempered bainite is greater than or equal to 80% and that of ferrite (VF) is less than or equal to 20%.
[00110] Advantageously, at distances of up to approximately 2 mm from the external and internal surfaces of the apo tubes (or possibly up to distances of approximately 2 mm from the external surface only), the microstructure of the quenched and tempered apo tube comprises tempered martensite with volumetric percentages less than 70%, preferably less than 40% and more preferably less than 20% (measured according to ASTM E562-08) and tempered bainite in volumetric percentage greater than 30%, preferably greater than 60% and more preferably greater than 80%. Ferrite rags of up to 10% may be present in the rooms with less hardening.
[00111] After tempering, the microstructure still has a previous austenitic grain size, measured by the ASTM E112 standard, advantageously less than 25 pm (linear intersection).
[00112] The average size of regions separated by high angle boundaries (i.e., packing size) is advantageously less than 9 pm, preferably less than 7 pm, more preferably less than 5 pm. By forming a microstructure including tempered bainite, as opposed to a banded microstructure (e.g., ferrite-perlite), the HIC resistance of the apo tube is further increased. Said packaging size is measured as the linear linear intersection of the images obtained by Scanning Electron Microscopy (SEM) using the Backscattered Electron Diffraction (EBSD) signal, and considering the high angle boundaries those with a degree of disorder> 15 ° .
The quenched microstructure may also include the presence of fine precipitates of the MX or M2X type (where M and Mo, Nb, or Cr and X and C or N) with size less than 40 nm, in addition to precipitates of the type M3C with an average diameter of around 80 nm to around 400 nm (measured by Transmission Electron Microscopy).
[00114] Finishing operations 110 may include, but are not limited to, grinding and hot bending operations.
[00115] The rectification can be carried out at temperatures below the tempering temperature and above around 450 ° C.
[00116] The bending of tempered and tempered seamless tubes can be done by hot induction. The hot induction bend is a thermal deformation process that is concentrated in a narrow area, referred to as the hot pattern, which is defined by an induction spiral (eg heating ring) and a cooling ring that sprays water on the external surface of the structure to be folded. A straight tube (mother) is pushed from the rear, while the front is tightened on an arm constrained to describe a circular trajectory. This constraint causes a bending moment in the entire structure, but the tube is only and plastically deformed substantially in the area corresponding to the hot print. The cooling ring performs two simultaneous tasks: defining the zone under plastic deformation and continuously cooling the hot fold.
[00117] The diameter of both the heating and cooling ring is around 20 mm to about 60 mm greater than the outer diameter (OD) of the mother tube. The bending temperature, for example, in the range 800-870 ° C, both on the outside surface and inside the tube, can be continuously measured by pyrometers. The bending rate is preferably within the range of 10-25 mm / min.
[00118] In a conventional fabrication, folds can be subjected to residual stress relief treatment after folding by a tempering treatment at a relatively low temperature to achieve the final mechanical properties.
[00119] However, it is recognized that the continuous tempering and tempering operations performed during finishing operations 110 may produce a microstructure that is different from that obtained from operations outside the tempering and tempering operations 106B, 106C. Therefore, as discussed above, in order to substantially restore the microstructure obtained after operations 106B and 106C, the folds are advantageously subjected to tempering and tempering outside the continuous process. The folds can be reheated in an oven at a rate within the range of 0.05 ° C / s to approximately 1 ° C / s at a temperature between 900 ° C and 960 ° C, and then quickly immersed in a cooling tank with stirred water and then tempered in an oven. Tempering after bending can be carried out at a temperature within the range of around 600 ° C to around 680 ° C. The tube can be reheated at a rate within the range of about 0.05 ° C / s to approximately 1 ° C / s. A residence time of between 600 s to 5400 s can be employed after reaching the desired tempering temperature.
[00120] The steel tubes of the present invention, with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm, with chemical composition according to Table 1, being subject to the aforementioned manufacturing process including operations of austenitization, tempering and tempering, and having the aforementioned microstructure after tempering, they can cover grades X60Q and / or X65Q and / or X70Q.
[00121] An X65Q grade steel pipe, with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm and the composition and microstructure discussed above, has the following properties: • Flow stress, YS: minimum 450 MPa (65.3 ksi) and a maximum of 600 MPa (87 ksi); • Tensile strength, UTS: minimum of 535 MPa (77.6 ksi) and maximum of 760 MPa (110.2 ksi); • Elongation, not less than 20%, with reference to a test piece with a circular cross-section of 12.5 mm in diameter; • YS / UTS ratio not greater than 0.88; • Maximum hardness (measured at 1.5 mm in depth of the tube surface) not greater than 230 HV10, preferably not greater than 225 HV10; • Minimum impact energy of 200 J / 150 J (average / individual) and a minimum of 85% average shear area for both longitudinal and transverse Charpy V-notch (CVN) tests performed on standard specimens or bodies small size tests, when applicable, at -40 ° C according to ISO 148-1; • Ductil-Fragil Transformation Temperature (ASTM E23) less than or equal to around -60 ° C; • HIC resistance, assessed according to the NACE Standard TM0284-2003 item No. 21215, using a NACE solution and a 96-hour duration test, with the following HIC parameters (averaged over three sections of three specimens) : o Crack Length Ratio, CLR <10% o Crack Thickness Ratio, CTR <3% o Crack Sensitivity Ratio, CSR <0.5% • SSC resistance, evaluated according to ASTM G39, using solution -test A NACE TM0177 and duration of 720 hours, with no failure at 90% of the true flow stress (AYS).
[00122] An X60Q grade steel tube, with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm and the composition and microstructure discussed above, has the following properties: • Flow stress, YS: minimum 415 MPa (60.2 ksi) and a maximum of 565 MPa (81.9 ksi); • Resistance to cheating, UTS: minimum of 520 MPa (75.4 ksi) and maximum of 760 MPa (110.2 ksi); • Elongation, not less than 20%, with reference to a test piece with a circular cross-section of 12.5 mm in diameter; • YS / UTS ratio not greater than 0.87; • Maximum hardness (measured between 1.5 mm and 2.0 mm in depth of the tube surface) not greater than 225 HV10; • Minimum impact energy of 200 J / 150 J (average / individual) and a minimum of 85% average shear area for both longitudinal and transverse Charpy V-notch (CVN) tests performed on standard specimens or bodies small size tests, when applicable, at -40 ° C in accordance with ASTM A 37 0; • Ductil-Fragil Transformation Temperature (ASTM E23) less than or equal to around -60 ° C; • HIC resistance, assessed in accordance with NACE TM0284-2003 item No. 21215, using a NACE A solution and a 96-hour duration test, with the following HIC parameters (averaged over three sections of three specimens) : o Crack Length Ratio, CLR <10% o Crack Thickness Ratio, CTR <3% o Crack Sensitivity Ratio, CSR <0.5% • Resistance to Sulfide Fragility Cracking (SSC), assessed according to ASTM G39, using test solution A NACE TM0177 and lasting 720 hours, with no failure at 90% of the true flow stress (AYS).
[00123] An X70Q grade steel tube, with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm and the composition and microstructure discussed above, has the following properties: • Flow stress, YS: minimum 485 MPa (70.3 ksi) and a maximum of 635 MPa (92.1 ksi); • Tensile strength, UTS: minimum of 570 MPa (83.82 ksi) and maximum of 760 MPa (110.2 ksi); • Elongation, not less than 18%, with reference to a test piece with a circular cross-section of 12.5 mm in diameter; • YS / UTS ratio not greater than 0.90; • Maximum hardness (measured between 1.5 mm and 2.0 mm in depth of the tube surface) not greater than 235 HV10; • Minimum impact energy of 200 J / 150 J (average / individual) and a minimum of 85% average shear area for both longitudinal and transverse Charpy V-notch (CVN) tests performed on standard specimens or bodies small size tests, when applicable, at -40 ° C in accordance with ASTM A 37 0; • Ductil-Fragil Transformation Temperature (ASTM E23) less than or equal to around -60 ° C; • Resistance to Hydrogen-Induced Fissure, evaluated according to NACE TM0284-2003 standard item No. 21215, using a NACE solution and a 96-hour duration test, with the following HIC parameters (average in three sections of three bodies of proof): o Crack Length Ratio, CLR <10% o Crack Thickness Ratio, CTR <3% o Crack Sensitivity Ratio, CSR <0.5% • SSC resistance, assessed according to ASTM G39 , using the NACE TM0177 test solution and lasting 720 hours, with no failure at 90% of the true flow stress (AYS).
[00124] In order to achieve these results, the microstructural limitations on the ferrite content, in the intermediate thickness (and possibly also on the inner surface of the tube, in the case of external tempering only), must be in accordance with the following table:

[00125] In addition, folds of grade X70Q and X65Q with EP greater than or equal to 6 mm and less than or equal to 35 mm and the formulations and microstructures discussed above have the same properties as the tube of grade X70Q and X65Q, respectively, with maximum hardness (measured between 1.5 mm and 2.0 mm of surface depth) not greater than 235 HV10, more preferably not greater than 230 HV10.
[00126] Otherwise, folds of grade X60Q having EP greater than or equal to 6 mm and less than or equal to 35 mm and the formulations and microstructures discussed above have the same properties as the tube of grade X60Q, with maximum hardness (measured between 1 , 5 mm and 2.0 mm of surface depth) not greater than 230 HV10, more preferably not greater than 225 HV10.
[00127] A first preferred embodiment of steel tubes according to the Invention has the following chemical composition: Table 2
(*) M = Mandatory; O = Optional; I = Impurity CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.26% to 0.37%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.14% to 0.18%. P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb) in the range 10 to 14.5; P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)>2.0; Nb + V <0.07%, preferably <0.055%.
[00128] Advantageously, after thermoforming, the steel pipe is subjected to the following steps: - cooling the steel pipe in air, preferably stagnant air, until it reaches room temperature; - heating of the steel pipe, with heating rate between 0.1 ° C / s and 10 ° C / s, for a austenitization temperature in the range between 900 ° C and 960 ° C, providing a residence time of between 180 s 3600 s; - internal and external tempering (tempering with water in a tank) of the steel pipe, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular 1.5-2 mm deep from said surfaces; or external tempering (by water jet rings) of the steel pipe, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and on the inner surface of the pipe and a cooling rate of 100-200 ° C / s in the vicinity of the outer surface of the tube, in particular 1.5-2 mm deep from said outer surface. - heating of the steel pipe, with a heating rate between 0.1 ° C / s and 10 ° C / s, up to a tempering temperature between 600 ° C and 680 ° C and providing a residence time at the said tempering temperature between 600 s and 5400 s.
[00129] Said first preferred modality of seamless steel tubes comprises the following tubes: - steel tubes grade X60Q having a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm, respecting the conditions P2 > 2.00 for wall thickness less than 20 mm and P2> 2.20 for wall thickness greater than or equal to 20 mm; - X65Q grade steel tubes having a wall thickness of less than 20 mm, respecting the condition P2> 2.10.
[00130] In an alternative mode, the titanic content is in the range of 0.006-0.0015%.
[00131] A second preferred embodiment of the steel tubes according to the invention has the following chemical composition: Table 3

(*) M = Mandatory; O = Optional; I = Impurity and meets the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.36% to 0.43%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.18% to 0.21%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb) in the range of 10 to 14.5; P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)>2.30; Nb + V <0.07%, preferably <0.055%.
[00132] Advantageously, after thermoforming, the steel tube is subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until it reaches room temperature; - heating of the steel pipe, with heating rate between 0.1 ° C / s and 10 ° C / s, for a austenitization temperature in the range between 900 ° C and 960 ° C, providing a residence time of between 180 s 3600 s; - internal and external tempering (tempering with water in a tank) of the steel pipe, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular 1.5-2 mm deep from said surfaces; - heating of the steel pipe, with a heating rate between 0.1 ° C / s and 10 ° C / s, up to a tempering temperature between 600 ° C and 680 ° C and providing a residence time at the said tempering temperature between 600 s and 5400 s.
[00133] Said second preferred embodiment of seamless steel tubes comprises X65Q steel tubes with a wall thickness greater than or equal to 20 mm and less than or equal to 35 mm.
[00134] In an alternative modality the titanic content is in the range of 0.006-0.0015%.
[00135] A third preferred embodiment of the steel tubes according to the invention has the following chemical composition: Table 4

(*) M = Mandatory; O = Optional; I = Impurity and satisfies the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.37% to 0.43%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.18% to 0.21%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb) in the range of 12 to 14.5; P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)> 2.30.
[00136] Advantageously, after thermoforming, the apo tube is subjected to the following steps: - cooling the apo tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with heating rate between 0.1 ° C / s and 10 ° C / s, for an austenitization temperature in the range between 900 ° C and 960 ° C, providing a residence time of between 180 s 3600 s; - internal and external tempering (tempering with water in a tank) of the apo tube, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular 1.5-2 mm deep from said surfaces; or external tempera (by external water jet rings) of the apo tube, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the outer surface of the tube, in particular 1.5-2 mm deep from said outer surface; - heating of the steel pipe, with a heating rate between 0.1 ° C / s and 10 ° C / s, up to a tempering temperature between 600 ° C and 680 ° C and providing a residence time at the said tempering temperature between 600 s and 5400 s.
[00137] Said third preferred embodiment of seamless steel tubes comprises: - X70Q steel tubes with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm with P2> 2.35 for a smaller wall thickness than 20 mm and P2> 2.45 for a wall thickness greater than or equal to 20 mm. - X65Q steel tubes with a wall thickness greater than or equal to 20 mm and less than or equal to 35 mm with the condition P2> 2.3.
[00138] In an alternative modality the titanium content is in the range of 0.006-0.0015%.
[00139] A fourth preferred embodiment of the steel tubes according to the Invention has the following chemical composition: Table 5
(*) M = Mandatory; O = Optional; I = Impurity and satisfies the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.26% to 0.36%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 +5 x B in the range of 0.14% to 0.18%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb) in the range of 10 to 14.5; P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)>2.00; Nb + V <0.07%, preferably <0.055%.
[00140] Advantageously, after thermoforming, the steel pipe is subjected to the following steps: - cooling the steel pipe in air, preferably stagnant air, until it reaches room temperature; - heating of the steel pipe, with heating rate between 0.1 ° C / s and 10 ° C / s, for a austenitization temperature in the range between 900 ° C and 960 ° C, providing a residence time of between 180 s 3600 s; - internal and external tempering (tempering with water in a tank) of the steel pipe, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular 1.5-2 mm deep from said surfaces; or external tempering (by external water jet rings) of the steel pipe, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the outer surface of the tube, in particular 1.5-2 mm deep from said outer surface; - heating of the steel pipe, with a heating rate between 0.1 ° C / s and 10 ° C / s, up to a tempering temperature between 600 ° C and 680 ° C and providing a residence time at the said tempering temperature between 600 s and 5400 s.
[00141] Said fourth preferred modality of seamless steel tubes comprises: - X60Q steel tubes with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm with P2> 2.00 for a smaller wall thickness than 20 mm and P2> 2.20 for a wall thickness greater than or equal to 20 mm. - X65Q steel tubes with a wall thickness of less than 20 mm and respecting the condition P2> 2.1.
[00142] A fifth preferred embodiment of the steel tubes according to the Invention has the following chemical composition: Table 6
(*) M = Mandatory; O = Optional; I = Impurity and satisfies the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15) in the range of 0.31% to 0.41%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5 x B in the range of 0.15% to 0.20%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb) in the range 11 to 14.5; P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)>2.30; Nb + V <0.07%, preferably <0.055%.
[00143] Advantageously, after thermoforming, the steel tube is subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until it reaches room temperature; - heating of the steel pipe, with heating rate between 0.1 ° C / s and 10 ° C / s, for a austenitization temperature in the range between 900 ° C and 960 ° C, providing a residence time of between 180 s 3600 s; - internal and external tempering (tempering with water in a tank) of the steel pipe, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular 1.5-2 mm deep from said surfaces; - heating of the steel pipe, with a heating rate between 0.1 ° C / s and 10 ° C / s, up to a tempering temperature between 600 ° C and 680 ° C and providing a residence time at the said tempering temperature between 600 s and 5400 s.
[00144] Said fifth preferred embodiment of seamless steel tubes comprises: - X65Q steel tubes with a wall thickness greater than or equal to 20 mm and less than or equal to 35 mm.
[00145] A sixth preferred embodiment of the steel tubes according to the Invention has the following chemical composition: Table 7
(*) M = Mandatory; O = Optional; I = Impurity and satisfies the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.37% to 0.43%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 +5 x B in the range of 0.16% to 0.22%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / EP)] + 50 x (V + Nb) in the range of 12.5 to 14.5; P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)>2.30; Nb + V <0.07%, preferably <0.055%.
[00146] Advantageously, after thermoforming, the steel tube is subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until it reaches room temperature; - heating of the steel pipe, with heating rate between 0.1 ° C / s and 10 ° C / s, for a austenitization temperature in the range between 900 ° C and 960 ° C, providing a residence time of between 180 s 3600 s; - internal and external tempering (tempering with water in a tank) of the steel pipe, reaching a cooling rate of 20-80 ° C / s in the intermediate thickness and a cooling rate of 100-200 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular 1.5-2 mm deep from said surfaces; - heating of the steel pipe, with a heating rate between 0.1 ° C / s and 10 ° C / s, up to a tempering temperature between 600 ° C and 680 ° C and providing a residence time at the said tempering temperature between 600 s and 5400 s.
[00147] Said sixth preferred mode of seamless steel tubes comprises: - X70Q steel tubes with a wall thickness greater than or equal to 6 mm and less than or equal to 35 mm with P2> 2.35 for a smaller wall thickness than 20 mm and P2> 2.45 for a wall thickness greater than or equal to 20 mm. - X65Q steel tubes with wall thickness greater than 20 mm and less than 35 mm with condition P2> 2.30. EXAMPLES
[00148] Some examples according to the present invention are described below. In each example, the chemical composition of the selected steel is indicated, the process parameters with respect to the austenitization, tempering and tempering steps, the microstructure along the thickness of the tube wall and the maximum hardness value detected over the entire thickness . In all examples the maximum hardness value is below 235 HV10, with yield stress, toughness and corrosion resistance satisfying at least one of grades X60Q, X65Q and X70Q.
[00149] The methodology used for the characterization of T&R tubes and folds are summarized here: - The microstructural constituents along the wall thickness were analyzed by optical microscopy after etching of Nital 2% etching. The previous austenitic grain size was measured after polishing and etching with Winsteard's solution, based on picric acid in a solution saturated with water. The grain size was measured according to the ASTM E112 standard with the method of the measured linear interspace. - High angle domains (packaging size) were analyzed by Backscattered Electron Diffraction (EBSD), applying the ASTM E112 standard linear intercept method to determine the average packaging size. - The Hydrogen Induced Fissure (HIC) test was conducted according to the standard NACE TM 02-84 / 2011. - The four-point flexion test (FPBT) was conducted according to the ASTM G39 standard, using the A NACE TM 0284/2011 solution. - The stress tests were carried out according to the ASTM A370 standard, using round specimens with ½ inch in diameter, collected in the intermediate thickness in both the longitudinal and transverse directions. - The toughness was tested by the Charpy V-Notch impact tests, conducted according to the ASTM A370 standard. The specimens were obtained both in the intermediate thickness and 2 mm from the outer diameter, in a transverse direction. Temperatures between -40 ° C and -120 ° C were tested and the 50% fracture transition temperature (FATT) value was used as a parameter to characterize the toughness of the material. - The hardness was tested with four notches per sector at 1.5 mm (-0 to +0.5 mm) of OD (external diameter), in the intermediate thickness and at 1.5 mm (-0 to +0.5 mm ) of the ID (internal diameter), following the specifications of ISO 3183 and DNV-OS-F101. Four specimens obtained at 90 ° were tested along the circumference of the rear and front of three tubes per batch of heat treatment. - The mechanical properties after stress aging were performed after the application of multiple stress cycles to large full-thickness specimens, which were subsequently subjected to aging treatments according to DNV offshore F101, at 250 ° C for 1h . the stress cycles were composed of the following steps: a) Compression to -3% of the absolute stress, b) Discharge to stress 0, c) Displacement of stress to + 3% of the relative stress, d) Discharge to stress 0, e) Repeat the steps a) to d) five times, ending in tension. The full-thickness specimens were subsequently machined to prepare the specimens for tensile, Charpy, HIC and FPBT tests. Example 1
[00150] An apo with the following chemical composition was selected: 0.08% C, 1.04% Mn, 0.24% Si, 0.12% Cr, 0.26% Ni, 0.13% Mo, 0.025 % Al, 0.0008% Ca, 0.020% Nb, 0.002% Ti, 0.03% V, 0.0045% N, the remainder being iron and impurities; with said impurities being 0.17% Cu, 0.0020% S, 0.0012% P, 0.0002% B; and with P1 = 13.7; P2 = 2.24; CEIIW = 0.34%; and CEPCM = 0.17%.
[00151] A seamless apo tube with a wall thickness of 20 mm was thermoformed.
[00152] The said thermoformed apo tube was subjected to the following steps: - cooling the apo tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with a heating rate of 0.3 ° C / s, for an austenitization temperature of 920 ° C, providing a residence time of 1200 s; - temper in a tank, reaching a cooling rate of about 50 ° C / s in the intermediate thickness and a cooling rate of around 120 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular at 1 , 5-2 mm deep from said surfaces; - heating the apo tube, with a heating rate of 0.2 ° C / s, to a tempering temperature of 635 ° C and providing a residence time at said tempering temperature of 2400 s.
[00153] The average resulting microstructure of the steel tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite around 65% and ferrite (VF) around 35%; - at a distance of up to 2 mm from the inner and outer surfaces of the steel tube, tempered martensite equal to around 10%, ferrite equal to 10% and tempered bainite equal to around 80%.
[00154] The previous average austenitic grain size, measured according to ASTM E112, is equal to 14 pm. The packaging size is 5.5 pm.
[00155] The maximum hardness value, measured at 1.5-2.0 mm in depth of the internal and external surfaces, is equal to 212 HV10 (<225 HV10).
[00156] The minimum and maximum values of yield stress were 446 MPa and 483 MPa, respectively.
[00157] The minimum and maximum tensile strength values were equal to 536 MPa and 584 MPa respectively.
[00158] The minimum and maximum% elongation after rupture were 29.6% and 34.1%, respectively.
[00159] The average impact energy at -60 ° C was 331 J, with a minimum value of 32 6 J and a minimum shear area of 100%.
[00160] The average for 50% FATT was at -105 ° C.
[00161] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00162] Flexural tests with four points at 90% of SMYS passed without fail after 720 h of tests.
[00163] This support tube meets grade X60Q. Example 2
[00164] An apo with the following chemical composition was selected: 0.08% C, 1.10% Mn, 0.27% Si, 0.14% Cr, 0.15% Ni, 0.09% Mo, 0.029 % Al, 0.0014% Ca, 0.001% Nb, 0.011% Ti, 0.04% V, 0.0048% N, the remainder being iron and impurities; with said impurities being 0.17% Cu, 0.0012% S, 0.013% P, 0.0001% B; and with P1 = 12.8; P2 = 2.32; CEIIW = 0.34%; and CEPCM = 0.17%.
[00165] A seamless apo tube with a wall thickness of 20 mm was thermoformed.
[00166] The said thermoformed apo tube was subjected to the following steps: - cooling the apo tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with a heating rate of 0.3 ° C / s, for an austenitization temperature of 920 ° C, providing a residence time of 1200 s; - temper in a tank, reaching a cooling rate of about 50 ° C / s in the intermediate thickness and a cooling rate of around 130 ° C / s in the vicinity of the inner and outer surfaces of the pipe, in particular 1 , 5-2 mm deep from said surfaces; - heating the apo tube, with a heating rate of 0.25 ° C / s, to a tempering temperature of 635 ° C and providing a residence time at said tempering temperature of 2400 s.
[00167] The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite around 90% and ferrite around 10%; - at a distance of up to 2 mm from the inner and outer surfaces of the support tube, tempered martensite equal to around 40% and tempered bainite equal to around 60%.
[00168] The previous average austenitic grain size, measured according to ASTM E112, is equal to 22 pm. The packaging size is 6.5 pm.
[00169] The maximum hardness value, measured at 1.5-2.0 mm in depth of the internal and external surfaces, is equal to 218 HV10 (<225 HV10).
[00170] The minimum and maximum values of yield stress were 432 MPa and 454 MPa, respectively.
[00171] The minimum and maximum tensile strength values were equal to 540 MPa and 574 MPa respectively.
[00172] The minimum and maximum% elongation after rupture were 24% and 30%.
[00173] The average impact energy at -60 ° C was 324 J, with a value of 282 J. The average shear area was 98% with a minimum shear area of 90%.
[00174] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00175] Four point flexural tests at 90% of SMYS passed without fail after 720 h of tests.
[00176] This steel tube meets grade X60Q. Example 3
[00177] A steel with the following chemical composition was selected: 0.075% C, 1.01% Mn, 0.27% Si, 0.38% Cr, 0.30% Ni, 0.33% Mo, 0.031% Al , 0.0010% Ca, 0.024% Nb, 0.005% Ti, 0.003% V, 0.0047% N, the remainder being iron and impurities; with said impurities being 0.09% Cu, 0.001% S, 0.011% P, 0.0002% B; and with P1 = 14.2; P2 = 2.50; CEIIW = 0.41%; and CEPCM = 0.19%.
[00178] A seamless steel tube with a wall thickness of 25 mm was thermoformed.
[00179] The thermoformed apo tube was subjected to the following steps: - cooling the apo tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with a heating rate of 0.3 ° C / s, for an austenitization temperature of 920 ° C, providing a residence time of 1200 s; - temper in a tank, reaching a cooling rate of 35 ° C / s in the intermediate thickness and a cooling rate of around 130 ° C / s in the vicinity of the inner and outer surfaces of the pipe, in particular at 1.5 -2 mm depth of said surfaces; - heating of the apo tube, with a heating rate of 0.2 ° C / s, to a tempering temperature of 650 ° C and providing a residence time at the said tempering temperature of 2400 s.
[00180] The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 100%; - at a distance of up to 2 mm from the inner and outer surfaces of the support tube, tempered martensite equal to around 50% and tempered bainite equal to around 50%.
[00181] The previous average austenitic grain size, measured according to ASTM E112, is equal to 23 pm. The packaging size is equal to 5.7 pm.
[00182] The maximum hardness value, measured at 1.5-2.0 mm in depth of the internal and external surfaces, is equal to 230 HV10).
[00183] The minimum and maximum values of yield stress were 513 MPa and 559 MPa, respectively.
[00184] The minimum and maximum values of resistance to cheating were 599 MPa and 638 MPa respectively.
[00185] The minimum and maximum% elongation after rupture were 30% and 32%, respectively.
[00186] The average impact energy at -60 ° C was 337 J, with a minimum value of 190 J. The average shear area was 99% with a minimum shear area of 70%.
[00187] The mean value of 50% FATT was -100 ° C.
[00188] After stress aging, the measured value for yield stress was 551 MPa, the value of resistance to cheating was 622 MPa, the yield / trap ratio was 0.88, the elongation value was 34% and 50% Average FATT was at -100 ° C. all mechanical properties were in accordance with grade X70, both before and after aging.
[00189] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%, both in the T&R material and in the tensioned and aged material.
[00190] Four point flexural tests at 90% of SMYS passed without fail after 720 h of tests, both in T&R material and in tensioned and aged material.
[00191] This steel tube meets grade X70Q. Example 4
[00192] A steel with the following chemical composition was selected: 0.076% C, 1.15% Mn, 0.25% Si, 0.14% Cr, 0.22% Ni, 0.12% Mo, 0.031% Al, 0 .0013% Ca, 0.024% Nb, 0.002% Ti, 0.007% V, 0.0048% N, the remainder being iron and impurities; such impurities being 0.16% Cu, 0.0012% S, 0.013% P, 0.0001% B; and where P1 = 13.6; P2 = 2.30; CEIIW = 0.35%; and CEPCM = 0.17%.
[00193] A seamless steel tube was thermoformed, having a wall thickness of 11 mm.
[00194] Such thermoformed steel tube was subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until reaching room temperature; - heating the steel tube, with a heating rate of 0.4 ° C / s, up to an austenitization temperature of 920 ° C and providing a residence time of 600 s; - external temperature by water rings, reaching a cooling rate of 50 ° C / s in the intermediate thickness and also on the inner surface of the tube, and a cooling rate of around 130 ° C / s in the vicinity of the inner surface the tube, in particular 1.5-2 mm deep from said surface; - heating of the apo tube, with a heating rate of 0.25 ° C / s, to a tempering temperature of 620 ° C and providing a residence time of 2400 s at said tempering temperature. - The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness and on the inner surface of the tube, tempered bainite equal to around 65% and ferrite equal to around 35%; - at a distance of up to 2 mm starting from the outer surface of the apo tube, tempered martensite equal to around 50%, tempered bainite equal to around 45% and finally polygonal ferrite equal to around 5%. - average grain size of previous austenite, measured according to ASTM E112, and equal to 16 pm. The packing size is 6.0 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 218 HV10 (<230 HV10). - The minimum and maximum flow resistance values were 448 MPa and 518 MPa, respectively. - The minimum and maximum values of the resistance to cheating were equal to 539 and 592 MPa, respectively. - The minimum and maximum elongation% after rupture was 29.8% and 34.2%. - The average impact energy at -60 ° C was 348 J, with a minimum value of 246 J. The average shear area was 96% with a minimum shear area of 80%. At - 40 ° C the minimum impact energy was 304 J, with a minimum shear area of 100%.
[00195] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00196] Four point flexural tests at 90% of SMYS passed without fail after 720 h of tests.
[00197] This aqo grade satisfies the X60Q. Example 5
[00198] A steel with the following chemical composition was selected: 0.084% C, 1.15% Mn, 0.25% Si, 0.16% Cr, 0.30% Ni, 0.18% Mo, 0.025% Al , 0.0010% Ca, 0.025% Nb, 0.002% Ti, 0.03% V, 0.0055% N, the remainder being iron and impurities; such impurities being 0.12% Cu, 0.001% S, 0.011% P, 0.0001% B; and where P1 = 14.0; P2 = 2.48; CEIIW = 0.38%; and CEPCM = 0.18%.
[00199] A seamless steel tube was thermoformed, having a wall thickness of 31.8 mm.
[00200] Such thermoformed steel tube was subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with a heating rate of 0.2 ° C / s, up to an austenitization temperature of 920 ° C and providing a residence time of 600 s; - temper in a tank, reaching a cooling rate of around 20 ° C / s in the intermediate thickness and a cooling rate of around 140 ° C / s in the vicinity of the inner and outer surfaces of the pipe, in particular the 1.5-2 mm in depth from such surfaces; - heating the apo tube, with a heating rate of 0.2 ° C / s, to a tempering temperature of 640 ° C and providing a residence time of 3600 s at said tempering temperature. - The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 75% and ferrite equal to around 25%; - at a distance of up to 2 mm starting from the external and internal surfaces of the apo tube, tempered martensite equal to around 60% and tempered bainite equal to around 40%. - The average grain size of the previous austenite, measured according to ASTM E112, is equal to 15 pm. The packaging size is 5.8 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 228 HV10 (<230 HV10). - The minimum and maximum flow resistance values were 480 MPa and 501 MPa, respectively. - The minimum and maximum values of tensile strength were 578 and 590 MPa, respectively. - The minimum and maximum elongation% after rupture was 28% and 33%. - The average impact energy at -60 ° C was 335 J, with a minimum value of 290 J. The average shear area was 98% with a minimum shear area of 90%.
[00201] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00202] Flexural tests with four points at 90% of SMYS passed without fail after 720 h of tests.
[00203] This steel meets grade X65Q. Example 6
[00204] A steel with the following chemical composition was selected: 0.081% C, 0.94% Mn, 0.24% Si, 0.11% Cr, 0.05% Ni, 0.069% Mo, 0.029% Al , 0.0012% Ca, 0.012% Ti, 0.054% V, 0.0052% N, the remainder being iron and impurities; such impurities being 0.11% Cu, 0.0012% S, 0.010% P; and where P1 = 13.7; P2 = 2.12; CEIIW = 0.29%; and CEPCM = 0.16%.
[00205] A seamless steel tube was thermoformed, having a wall thickness of 12.7 mm.
[00206] Such thermoformed steel tube was subjected to the following steps: - cooling the apo tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with a heating rate of 0.4 ° C / s, up to an austenitization temperature of 900 ° C and providing a residence time of 900 s; - temper in a tank, reaching a cooling rate of around 75 ° C / s in the intermediate thickness and a cooling rate of around 100 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular the 1.5-2 mm in depth from such surfaces; - heating of the apo tube, with a heating rate of 0.23 ° C / s, to a tempering temperature of 640 ° C and providing a residence time of 27 00 s at said tempering temperature. - The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 50% and ferrite equal to around 50%; - at a distance of up to 2 mm starting from the outer and inner surfaces of the apo tube, tempered martensite equal to around 10%, tempered bainite equal to around 80% and ferrite equal to around 10%. - The average grain size of previous austenite, measured according to ASTM E112, is equal to 15-17 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 196 HV10 (<225 HV10) - The minimum and maximum values of the flow resistance were equal to 440 MPa and 487 MPa, respectively. - The minimum and maximum values of tensile strength were 529 and 565 MPa, respectively. - The minimum and maximum% elongation after rupture was 38% and 45%. - The average impact energy at -50 ° C was 326 J, with a minimum value of 253 J. The average shear area was 100% with a minimum shear area of 100%.
[00207] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00208] The flexion tests with four points at 90% of AYS passed without fail after 720 h of tests.
[00209] This aqo grade satisfies the X60Q. Example 7
[00210] A steel with the following chemical composition was selected: 0. 085% C, 0.93% Mn, 0.24% Si, 0.16% Cr, 0.05% Ni, 0. 085% Mo, 0.030 % Al, 0.0011% Ca, 0.011% Ti, 0.053% V, 0.0050% N, the remainder being iron and impurities; such impurities being 0.127% Cu, 0.0016% S, 0.008% P; and where P1 = 13.9; P2 = 2.21; CEIIW = 0.31%; and CEPCM = 0.17%.
[00211] A seamless steel tube was thermoformed, having a wall thickness of 15.9 mm.
[00212] Such thermoformed steel tube was subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until reaching room temperature; - heating the steel tube, with a heating rate of 0.3 ° C / s, up to an austenitization temperature of 900 ° C and providing a residence time of 900 s; - temper in a tank, reaching a cooling rate of around 65 ° C / s in the intermediate thickness and a cooling rate of around 100 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular the 1.5-2 mm in depth from such surfaces; - heating the steel tube, with a heating rate of 0.15 ° C / s, to a tempering temperature of 635 ° C and providing a residence time of 27 00 s at said tempering temperature. - The average microstructure resulting from the steel tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 65% and ferrite equal to around 35%; - at a distance of up to 2 mm starting from the external and internal surfaces of the steel tube, tempered martensite equal to around 10%, tempered bainite equal to around 80% and ferrite equal to around 10%. - The average grain size of previous austenite, measured according to ASTM E112, is equal to 15-17 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 228 HV10 (<230 HV10) - The minimum and maximum values of the flow resistance were equal to 459 MPa and 490 MPa, respectively. - The minimum and maximum tensile strength values were equal to 543 and 574 MPa, respectively. - The minimum and maximum elongation% after rupture was 45% and 47%. - The average impact energy at -50 ° C was 329 J, with a minimum value of 287 J. The average shear area was 97% with a minimum shear area of 85%.
[00213] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00214] Four point flexural tests at 90% of AYS passed without fail after 720 h of tests.
[00215] This steel meets grade X65Q. Example 8
[00216] A steel with the following chemical composition was selected: 0.06% C, 1.24% Mn, 0.26% Si, 0.30% Cr, 0.26% Ni, 0.112% Mo, 0.029% Al , 0.0014% Ca, 0.012% Ti, 0.059% V, 0.0058% N, the remainder being iron and impurities; such impurities being 0.10% Cu, 0.0005% S, 0.008% P; and where P1 = 12.7; P2 = 2.52; CEIIW = 0.38%; and CEPCM = 0.17%.
[00217] A seamless steel tube was thermoformed, having a wall thickness of 25.4 mm.
[00218] Such thermoformed steel tube was subjected to the following steps: - cooling the apo tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with a heating rate of 0.3 ° C / s, up to an austenitization temperature of 900 ° C and providing a residence time of 900 s; - temper in a tank, reaching a cooling rate of around 30 ° C / s in the intermediate thickness and a cooling rate of around 100 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular the 1.5-2 mm in depth from such surfaces; - heating of the apo tube, with a heating rate of 0.15 ° C / s, to a tempering temperature of 650 ° C and providing a residence time of 27 00 s at said tempering temperature. - The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 70% and ferrite equal to around 30%; - at a distance of up to 2 mm starting from the outer and inner surfaces of the apo tube, tempered martensite equal to around 10%, tempered bainite equal to around 80% and ferrite equal to around 10%. - The average grain size of previous austenite, measured according to ASTM E112, is equal to 15-17 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 219 HV10 (<230 HV10) - The minimum and maximum values of flow resistance were equal to 476 MPa and 508 MPa, respectively. - The minimum and maximum values of the tensile strength were equal to 558 and 589 MPa, respectively. - The minimum and maximum% elongation after rupture was 54% and 60%. - The average impact energy at -40 ° C was 433 J, with a minimum value of 461 J. The average shear area was 100% with a minimum shear area of 100%. - FATT 50% was below -70 ° C.
[00219] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00220] Flexion tests with four points at 90% of AYS passed without fail after 720 h of tests.
[00221] This steel meets grade X65Q. Example 9
[00222] A steel with the following chemical composition was selected: 0.06% C, 1.30% Mn, 0.25% Si, 0.35% Cr, 0.38% Ni, 0.139% Mo, 0.025% Al , 0.0018% Ca, 0.012% Ti, 0.059% V, 0.0068% N, the remainder being iron and impurities; such impurities being 0.137% Cu, 0.0011% S, 0.013% P; and where P1 = 12.8; P2 = 2.67; CEIIW = 0.42%; and CEPCM = 0.18%.
[00223] A seamless steel tube was thermoformed, having a wall thickness of 30 mm.
[00224] Such thermoformed steel tube was subjected to the following steps: - cooling the apo tube in air, preferably stagnant air, until reaching room temperature; - heating of the apo tube, with a heating rate of 0.35 ° C / s, up to an austenitization temperature of 900 ° C and providing a residence time of 900 s; - temper in a tank, reaching a cooling rate of around 25 ° C / s in the intermediate thickness and a cooling rate of around 100 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular the 1.5-2 mm in depth from such surfaces; - heating the apo tube, with a heating rate of 0.15 ° C / s, to a tempering temperature of 635 ° C and providing a residence time of 3600 s at said tempering temperature. - The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 90% and ferrite equal to around 10%; - at a distance of up to 2 mm starting from the outer and inner surfaces of the apo tube, tempered martensite equal to around 5-10%, tempered bainite equal to around 90% and ferrite equal to around 0 -5%. - The average grain size of previous austenite, measured according to ASTM E112, is equal to 15-20 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 234 HV10 (<235 HV10). - The minimum and maximum flow resistance values were equal to 506 MPa and 523 MPa, respectively. - The minimum and maximum values of tensile strength were 592 and 609 MPa, respectively. - The minimum and maximum elongation% after rupture was 29% and 31%. (round specimen) - The average impact energy at -40 ° C was 450 J, with a minimum value of 425 J. The average shear area was 100% with a minimum shear area of 100%. - FATT 50% was below -60 ° C.
[00225] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00226] Flexural tests with four points at 90% of AYS passed without fail after 720 h of tests.
[00227] This steel meets grade X70Q. Example 10
[00228] A steel with the following chemical composition was selected: 0.06% C, 1.30% Mn, 0.27% Si, 0.35% Cr, 0.38% Ni, 0.21% Mo, 0.025 % Al, 0.0017% Ca, 0.012% Ti, 0.059% V, 0.0055% N, the remainder being iron and impurities; such impurities being 0.127% Cu, 0.0007% S, 0.011% P; and where P1 = 13.2; P2 = 2.72; CEIIW = 0.43%; and CEPCM = 0.18%.
[00229] A seamless steel tube was thermoformed, having a wall thickness of 32.5 mm.
[00230] Such thermoformed steel tube was subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until reaching room temperature; - heating of the steel pipe, with a heating rate of 0.38 ° C / s, up to an austenitization temperature of 900 ° C and providing a residence time of 900 s; - temper in a tank, reaching a cooling rate of around 23 ° C / s in the intermediate thickness and a cooling rate of around 100 ° C / s in the vicinity of the inner and outer surfaces of the tube, in particular the 1.5-2 mm in depth from such surfaces; - heating the steel tube, with a heating rate of 0.15 ° C / s, to a tempering temperature of 660 ° C and providing a residence time of 3600 s at said tempering temperature. - The average microstructure resulting from the steel tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 95% and ferrite equal to around 5%; - at a distance of up to 2 mm starting from the outer and inner surfaces of the steel tube, tempered martensite equal to around 5-10%, tempered bainite equal to around 90% and ferrite equal to around 0 -5%. - The average grain size of previous austenite, measured according to ASTM E112, is equal to 15-20 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 217 HV10 (225 HV10). - The minimum and maximum flow resistance values were equal to 506 MPa and 534 MPa, respectively. - The minimum and maximum values of tensile strength were 601 and 611 MPa, respectively. - The minimum and maximum elongation% after rupture was 27% and 33%. (round specimen). - The average impact energy at -40 ° C was 382 J, with a minimum value of 278 J. The average shear area was 98% with a minimum shear area of 85%. - FATT 50% was around -60 ° C.
[00231] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00232] The four point flexion tests at 90% of AYS passed without fail after 720 h of tests.
[00233] This aqo grade satisfies the X70Q. Example 11
[00234] Steel tubes having an external diameter of 323.9 mm and a wall thickness of 25 mm, made according to the procedure described in example 3, were selected to produce T&R bends of the same wall thickness.
[00235] The following composition was used: 0.075% C, 1.01% Mn, 0.27% Si, 0.38% Cr, 0.30% Ni, 0.33% Mo, 0.031% Al, 0.0010 % Ca, 0.024% Nb, 0.005% Ti, 0.003% V, 0.0047% N, the remainder being iron and impurities; such impurities being 0.09% Cu, 0.001% S, 0.011% P, 0.0002% B. and being P1 = 14.2; P2 = 2.50; CEIIW = 0.41%; and CEPCM = 0.19%.
[00236] The steel tube was subjected to the following steps: - thermoinduction of the curvature at a temperature between 800 and 870 ° C and adaptation to a curvature rate between 10 and 25 mm / min. The curvatures were produced with a radius equal to three times the outer diameter and tangent length of 1 m; - heating of the curvature, with a heating rate of 0.15 ° C / s, up to an austenitization temperature of around 920 ° C and providing a residence time of around 600 s; - temper in a tank, reaching a cooling rate of around 20 ° C / s in the intermediate thickness in the body of the curvature and a cooling rate of around 150 ° C / s in the vicinity of the inner and outer surfaces of the tube , in particular at 1.5-2 mm in depth from such surfaces; - heating of the curvature, with a heating rate of 0.05 ° C / s, up to a tempering temperature of around 660 ° C and providing a residence time of around 600 s at said tempering temperature.
[00237] The average microstructure resulting from the steel tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 75% and ferrite (VF) equal to around 25%, - at a distance of up to 2 mm starting from the outer and inner surfaces of the steel tube, tempered martensite equal to around 60% and tempered bainite equal to around 40%.
[00238] The average grain size of previous austenite, measured according to ASTM E112, is equal to 20 pm. the average packaging size is 6.5 µm.
[00239] The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 230 HV10 (<235 HV10).
[00240] The minimum and maximum flow resistance values were 518 MPa and 539 MPa, respectively.
[00241] The minimum and maximum values of the resistance to trapping were 611 MPa and 621 MPa, respectively.
[00242] The minimum and maximum elongation% after rupture was 28.0% and 30.0%, respectively.
[00243] The average impact energy at -60 ° C was 287 J with a minimum value of 274 J and an average shear area of 100%.
[00244] The 50% average FATT was around -90 ° C.
[00245] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00246] Four point flexural tests at 90% of SMYS passed without fail after 720 h of tests.
[00247] This curvature of the steel pipe satisfies the grade X70Q. Example 12
[00248] A steel with the following chemical composition was selected: 0.076% C, 1.10% Mn, 0.26% Si, 0.35% Cr, 0.25% Ni, 0.25% Mo, 0.025% Al , 0.0010% Ca, 0.025% Nb, 0.0045% N, the remainder being iron; and where P1 = 13.6; P2 = 2.53; CEIIW = 0.40%; and CEPCM = 0.18%.
[00249] A seamless steel tube was thermoformed, having a wall thickness of 22 mm.
[00250] Such thermoformed steel tube was subjected to the following steps: - cooling the steel tube in air, preferably stagnant air, until reaching room temperature; - heating the steel tube, with a heating rate of 0.35 ° C / s, up to an austenitization temperature of 920 ° C and providing a residence time of 900 s; - temper in a tank, reaching a cooling rate of around 45 ° C / s in the intermediate thickness and a cooling rate of around 120 ° C / s in the vicinity of the inner and outer surfaces of the pipe, in particular the 1.5-2 mm in depth from such surfaces; - heating of the apo tube, with a heating rate of 0.15 ° C / s, to a tempering temperature of 650 ° C and providing a residence time of 3600 s at said tempering temperature. - The average microstructure resulting from the apo tube comprises, in volumetric percentage: - in the intermediate thickness, tempered bainite equal to around 85% and ferrite equal to around 15%; - at a distance of up to 2 mm starting from the outer and inner surfaces of the apo tube, tempered martensite equal to around 15%, tempered bainite equal to around 80% and ferrite equal to around 5%. - The average grain size of the previous austenite, measured according to ASTM E112, is equal to 16-18 pm. - The maximum hardness value, measured at 1.5-2.0 mm in depth from the internal and external surfaces, is equal to 220 HV10 (<225 HV10). - The minimum and maximum values of the flow resistance were 491 MPa and 497 MPa, respectively. - The minimum and maximum values of the resistance to cheating were equal to 589 and 595 MPa, respectively. - The minimum and maximum elongation% after rupture was 27% and 31%. (round specimen). - The average impact energy at -40 ° C was 375 J, with a minimum value of 315 J. The average shear area was 100%. - FATT 50% was around -80 ° C.
[00251] Hydrogen-induced crack tests passed with CLR% = 0%, CTR% = 0% and CSR% = 0%.
[00252] Four point flexion tests at 90% of AYS passed without fail after 720 h of tests.
[00253] This steel tube meets grades X65Q, X60Q and X70Q.

权利要求:
Claims (26)
[0001]
1. Tempered and tempered seamless steel pipe characterized by an elastic limit of 415 MPa to 635 MPa and an EP wall thickness greater than or equal to 6 mm and less than 35 mm, in which the steel pipe has a chemical composition consisting of: 0.050-0.090% w C; 0.80-1.65% p Mn; 0.10-0.45% p Si; 0.10-0.60% p Cr; 0.05-0.45% p Ni; 0.05-0.40% w Mo; 0.020-0.040% p Al; 0.0030-0.0090% p N; 0.0008-0.0050% p Ca; 0.000-0.040% p Nb; 0.000-0.020% p Ti; 0.000-0.070% p V; 0.000-0.030% p Zr; 0.000-0.030% p Ta; 0.00-0.25% p Cu; 0.000-0.003% p S; 0.000-0.018% p P; and 0.0000-0.0005% p B; The rest being Fe; wherein at least Nb and V are present, the content of (V + Nb) being less than 0.07% w; where, by defining a first parameter P1 = (60 x C) + Cr + [5 x e (35 x Mo / WT)] + 50 x (V + Nb), the chemical composition satisfies a first condition 10 <P1 <14, 5; where the tempered and tempered steel tube has, at an average thickness, a microstructure comprising, in volumetric percentage, tempered bainite above or equal to 40% and ferrite (VF) below or equal to 60%, and has a distance of up to 2 mm, starting from the outer surface only, a microstructure comprising, in volumetric percentage, tempered martensite below 70% tempered bainite above 30% and ferrite traces less than or equal to 10%, in which the microstructure of the tempered and tempered seamless steel tube has an average grain size of authenticity measured by the ASTM E112 standard less than 25 pm; and in which maximum hardness values, measured at 1.5-2.0 mm deep from the external and internal surfaces, are not greater than 235 HV10.
[0002]
2. Tempered and tempered seamless steel tube according to claim 1, characterized by defining a second parameter P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V), the chemical composition satisfies a second condition P2> 2.
[0003]
3. Tempered and tempered seamless steel pipe according to claim 2, characterized in that the second condition, as a function of grade and wall thickness (EP), is:
[0004]
4. Tempered and tempered seamless steel tube according to claim 1, characterized in that at a distance of up to 2 mm starting from the outer surface of the steel tube, the microstructure comprises tempered martensite below 40% and tempered bainite above 60%.
[0005]
5. Tempered and tempered seamless steel tube according to claim 1, characterized in that at a distance of up to 2 mm starting from the outer surface of the steel tube, the microstructure comprises tempered martensite below 20% and tempered baianite above 80%.
[0006]
6. Tempered and tempered seamless steel tube according to claim 1, characterized in that at an average thickness, the microstructure comprises tempered bainite above or equal to 50% and ferrite (VF) below or equal to 50%.
[0007]
7. Tempered and tempered seamless steel tube according to claim 1, characterized in that at an average thickness, the microstructure comprises tempered bainite above or equal to 80% and ferrite (VF) below or equal to 20%.
[0008]
8. Tempered and tempered seamless steel tube according to claim 1, characterized in that the (V + Nb) content is less than 0.055% w.
[0009]
9. Tempered and tempered seamless steel tube according to claim 1, characterized in that at an average thickness the microstructure comprises ferrite (VF) less than or equal to 60% for a tube of grade X60, ferrite (VF) less than or equal to 40% for an X65 grade pipe, ferrite (VF) less than or equal to 20% for an X70.8 grade pipe.
[0010]
10. Tempered and tempered seamless steel tube according to claim 1, characterized in that CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15) is in the range of 0 , 26% to 0.43%, and CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB will be in the 0.14 range % up to 0.22%.
[0011]
11. Tempered and tempered seamless steel tube according to claim 1, characterized in that the chemical composition consists of: 0.050-0.090% w C; 0.90-1.35% p Mn; 0.10-0.35% p Si; 0.10-0.40% p Cr; 0.05-0.40% p Ni; 0.07-0.40% w Mo; 0-0.070% p V; 0.020-0.040% p Al; 0.0008-0.0030% p Ca; 0.000-0.035% p Nb; 0.000-0.015% p Ti; 0.0030-0.0070% p N; 0.00-0.20% p Cu; 0.000-0.002% p S; 0.000-0.015% p P; 0.0000-0.0005% p B; 0.000-0.015% p Zr; and 0.000-0.015% p Ta; the rest being iron.
[0012]
12. Tempered and tempered seamless steel tube according to claim 11, characterized in that the chemical composition consists of: 0.060-0.085% wc; 1.00-1.30% p Mn; 0.10-0.30% p Si; 0.20-0.40% p Cr; 0.20-0.40% p Ni; 0.10-0.35% w Mo; 0.000-0.070% p V; 0.020-0.040% p Al; 0.0015-0.0030% p Ca; 0.000-0.030% p Nb; 0.000-0.015% p Ti; 0.0030-0.0070% p N; 0.00-0.15% p Cu; 0.000-0.0015% p S; 0.000-0.012% p P; 0.0000-0.0005% p B; 0.000-0.010% p Zr; and 0.000-0.010% p Ta; the rest being iron.
[0013]
13. Tempered and tempered seamless steel tube according to claim 12, characterized in that the chemical composition consists of: 0.060-0.085% wc; 1.00-1.25% p Mn; 0.10-0.30% p Si; 0.30-0.40% p Cr; 0.25-0.35% p Ni; 0.25-0.35% w Mo; 0.000-0.040% p V; 0.020-0.035% p Al; 0.0010-0.0030% p Ca; 0.020-0.030% p Nb; 0.000-0.015% p Ti; 0.0030-0.0060% p N; 0.00-0.15% p Cu; 0.000-0.0015% p S; 0.000-0.011% p P; 0.0000-0.0005% p B; 0.000-0.010% p Zr and 0.000-0.010% p Ta; the rest being iron.
[0014]
Hardened and tempered seamless steel tube according to claim 1, characterized in that the chemical composition consists of: 0.050-0.090% wc; 0.90-1.30% p Mn; 0.10-0.35% p Si; 0.10-0.25% p Cr; 0.08-0.30% p Ni; 0.08-0.15% w Mo; 0.000-0.045% p V; 0.020-0.040% p Al; 0.0008-0.0030% p Ca; 0.000-0.035% p Nb; 0.000-0.015% p Ti; 0.0030-0.0070% p N; 0.00-0.20% p Cu; 0.000-0.002% p S; 0.000-0.015% p P; 0.0000-0.0001% p B; and 0.000-0.010% p Zr; 0.000-0.010% p Ta, the rest being iron; and satisfy the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.26% to 0.37%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5 x B in the range of 0.14% to 0.18%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / WT)] + 50 x (V + Nb) in the range of 10 to 14.5; and P2 = (9 x C) + (1, 2 x Mn) + Cr + (0.7 x Mo) + (2 x V)> 2.0.
[0015]
15. Tempered and tempered seamless steel tube according to claim 1, characterized in that the chemical composition consists of: 0.060-0.090% w C; 0.95-1.30% p Mn; 0.10-0.35% p Si; 0.10-0.30% p Cr; 0.20-0.40% p Ni; 0.14-0.25% w Mo; 0.000-0.045% p V; 0.020-0.040% p Al; 0.0008-0.0030% p Ca; 0.000-0.035% p Nb; 0.000-0.015% p Ti; 0.0030-0.0070% p N; 0.00-0.20% p Cu; 0.000-0.002% p S; 0.000-0.015% p P; 0.0000-0.0001% p B; 0.000-0.010% p Zr; and 0.000-0.010% p Ta; the rest being iron; and satisfy the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.36% to 0.43%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.18% to 0.21%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / WT)] + 50 x (V + Nb) in the range of 10 to 14.5; and P2 = (9 x C) + (1, 2 x Mn) + Cr + (0.7 x Mo) + (2 x V)> 2.30.
[0016]
16. Tempered and tempered seamless steel tube according to claim 1, characterized in that the chemical composition consists of: 0.060-0.090% w C; 0.95-1.30% p Mn; 0.10-0.35% p Si; 0.20-0.40% p Cr; 0.25-0.40% p Ni; 0.25-0.35% w Mo; 0.000-0.010% p V; 0.020-0.040% p Al; 0.0008-0.0030% p Ca; 0.020-0.035% p Nb; 0.000-0.015% p Ti; 0.0030-0.0070% p N; 0.00-0.20% p Cu; 0.000-0.002% p S; 0.000-0.015% p P; 0.0000-0.0001% p B; 0.000-0.010% p Zr; and 0.000-0.010% p Ta; the rest being iron; and satisfy the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.37% to 0.43%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.18% to 0.21%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / WT)] + 50 x (V + Nb) in the range of 12 to 14.5; and P2 = (9 x C) + (1, 2 x Mn) + Cr + (0.7 x Mo) + (2 x V)> 2.30.
[0017]
17. Tempered and tempered seamless steel tube according to claim 1, characterized in that the chemical composition consists of: 0.060-0.090% w C; 0.90-1.20% p Mn; 0.10-0.35% p Si; 0.10-0.25% p Cr; 0.05-0.20% p Ni; 0.05-0.15% w Mo; 0.000-0.070% p V; 0.020-0.040% p Al; 0.0008-0.0030% p Ca; 0.000-0.005% p Nb; 0.005-0.015% p Ti; 0.0030-0.0090% p N; 0.00-0.20% p Cu; 0.000-0.003% p S; 0.000-0.015% p P; 0.0000-0.0001% p B; 0.000-0.010% p Zr; and 0.000-0.010% p Ta; the rest being iron; and satisfy the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.26% to 0.36%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.14% to 0.18%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / WT)] + 50 x (V + Nb) in the range of 10 to 14.5; and P2 = (9 x C) + (1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)> 2.00.
[0018]
18. Tempered and tempered seamless steel tube according to claim 1, characterized in that the chemical composition consists of: 0.060-0.090% w C; 0.95-1.30% p Mn; 0.10-0.35% p Si; 0.10-0.40% p Cr; 0.05-0.40% p Ni; 0.07-0.25% w Mo; 0.000-0.070% p V; 0.020-0.040% p Al; 0.0008-0.0030% p Ca; 0.000-0.005% p Nb; 0.005-0.015% p Ti; 0.0030-0.0080% p N; 0.00-0.20% p Cu; 0.000-0.003% p S; 0.000-0.015% p P; 0.0000-0.0001% p B; 0.000-0.010% p Zr and 0.000-0.010% p Ta; the rest being iron; and satisfy the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15) in the range of 0.31% to 0.41%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.15% to 0.20%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / WT)] + 50 x (V + Nb) in the range 11 to 14.5; and P2 = (9 x C) + (1, 2 x Mn) + Cr + (0.7 x Mo) + (2 x V)> 2.30.
[0019]
19. Tempered and tempered seamless steel tube according to claim 1, characterized in that the chemical composition consists of: 0.060-0.090% w C; 1.00-1.30% p Mn; 0.10-0.35% p Si; 0.20-0.40% p Cr; 0.20-0.40% p Ni; 0.10-0.25% w Mo; 0.000-0.070% p V; 0.020-0.040% p Al; 0.0008-0.0030% p Ca; 0.000-0.005% p Nb; 0.005-0.015% p Ti; 0.0030-0.0070% p N; 0.00-0.15% p Cu; 0.000-0.003% p S; 0.000-0.012% p P; 0.0000-0.0001% p B; 0.000-0.010% p Zr; e, 0.000-0.010% p Ta; the rest being iron; and satisfy the following additional conditions: CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 in the range of 0.37% to 0.43%; CEPCM = C + Si / 30 + Mn / 20 + Cr / 20 + Cu / 20 + Ni / 60 + Mo / 15 + V / 10 + 5xB in the range of 0.16% to 0.22%; P1 = (60 x C) + Cr + [5 x e (35 x Mo / WT)] + 50 x (V + Nb) in the range of 12.5 to 14.5; and P2 = (9 x C) + ( 1.2 x Mn) + Cr + (0.7 x Mo) + (2 x V)> 2.30.
[0020]
20. Process for producing a quenched and tempered seamless steel pipe characterized by comprising: Hot forming a seamless steel pipe with an EP wall thickness greater than or equal to 6mm and less than 35mm and a chemical composition consisting of: 0.050-0.090% p C; 0.80-1.65% p Mn; 0.10-0.45% p Si; 0.10-0.60% p Cr; 0.05-0.45% p Ni; 0.05-0.40% w Mo; 0.020-0.040% p Al; 0.0030-0.0090% p N; 0.0008-0.0050% p Ca; 0.000-0.040% p Nb; 0.000-0.020% p Ti; 0.000-0.070% p V; 0.000-0.030% p Zr; 0.000-0.030% p Ta; 0.00-0.25% p Cu; 0.000-0.003% p S; 0.000-0.018% p P; and 0.0000-0.0005% p B; the rest being Fe; cool the seamless steel tube in air to decrease to reach room temperature; heat the seamless steel tube with a first heating rate between 0.1 ° C / s and 10 ° C / s, to a austenitization temperature above the transformation point Ac3, in a range between 880 ° C and 980 ° C , and provide a soak time between 180s and 5400s; temper the seamless steel tube with a cooling rate in the range of 20 to 80 ° C / s or medium thickness and an inner surface of the tube, and with a cooling rate of 100-200 ° C / s in the proximity to the inner and outer surfaces of the tube or in the vicinity of the outer surface only, and heat the seamless steel tube with a second heating rate between 0.1 ° C / s and 10 ° C / s, to a tempering temperature comprised in a predetermined range, and provide a retention time at said tempering temperature between 600s and 7200s, where the predetermined range is calculated with a tolerance of ± 20 ° C using the following equation:
[0021]
21. Process according to claim 20, characterized in that the heating takes place in a furnace fed with gas, provided with at least one burner, in which the oxygen concentration is less than 10%.
[0022]
22. Process according to claim 21, characterized in that the oxygen concentration is in the range of 0.5% to 4%.
[0023]
23. Process according to claim 21, characterized in that the outlet of the furnace tube fed with gas is immediately descaled by high water pressure and moved to less than 120 seconds in a water tempering system.
[0024]
24. Curved AQO, obtainable by a seamless steel tube according to claim 1, characterized by having maximum hardness values, measured at 1.5 mm to 2 mm in depth from the surface, not greater than 235 HV10.
[0025]
25. Curved AQO according to claim 24, characterized in that it has maximum hardness values, measured at 1.5 mm to 2 mm in depth from the surface, not greater than 230 HV10.
[0026]
26. Seamless tempered and tempered steel tube according to claim 1, characterized by the fact that the microstructure has, at a distance of up to 2 mm, from the inner surface of the tube, a microstructure comprising, in percentage of volume, tempered martensite less than 70%, tempered bainite greater than 30% and traces of ferrite less than or equal to 10%.

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AU2014201976B2|2017-12-07|

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法律状态:
2016-02-16| B03A| Publication of an application: publication of a patent application or of a certificate of addition of invention|

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2018-11-13| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|

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2019-10-08| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|

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2020-07-28| B09A| Decision: intention to grant|

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2020-12-01| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 07/04/2014, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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EP13162724.2A|EP2789701A1|2013-04-08|2013-04-08|High strength medium wall quenched and tempered seamless steel pipes and related method for manufacturing said steel pipes|

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EP13162724.2|2013-04-08|

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EP14163364.4|2014-04-03|

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EP14163364.4A|EP2789703B1|2013-04-08|2014-04-03|High strength medium wall quenched and tempered seamless steel pipes and related method for manufacturing said steel pipes|

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