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    • 专利摘要:
    high strength seamless stainless steel tube for oilfield tubular articles and method for manufacturing the same. a high strength seamless stainless steel tube is provided for oilfield tubular articles, excellent in terms of hot workability, sulphide stress crack resistance and corrosion resistance and a method for making steel tubes. the steel tube has a chemical composition containing cr and ni so that the cr / ni ratio (less than equal) 5.3 is satisfied and a microstructure that mainly includes a tempered martensitic phase, in which a surface layer microstructure includes a phase that looks white when etched with a vilella etching solution, which has a thickness in the direction of the wall thickness from the outer surface of the tube of 10 (mi) m or more and 100 (mi) m or less, and that disperses on the outer surface of the tube in an amount of 50% or more in terms of fraction of area. the chemical composition can be a chemical composition containing, in mass%, c: 0.005% or more and 0.05% or less, si: 0.05% or more and 1.50% or less, mn: 0.2 % or more and 1.8% or less, p: 0.02% or less, s: 0.005% or less, cr: 11% or more and 18% or less, ni: 0.10% or more and 8, 0% or less, hand: 0.6% or more and 3.5% or less, and the remainder being unavoidable and impurities.
    公开号:BR112016027036B1
    申请号:R112016027036-3
    申请日:2015-05-20
    公开日:2021-04-13
    发明作者:Kazuki FUJIMURA；Yasuhide Ishiguro；Tetsu Nakahashi；Hideo Sato
    申请人:Jfe Steel Corporation；
    IPC主号:
    专利说明:

    TECHNICAL FIELD
    [001] The present invention relates to a seamless stainless steel tube of high strength for oilfield tubular articles which can preferably be used for oil wells and gas wells in very severe corrosive environments containing carbon dioxide (CO2) ), chlorine ions (Cl-), and so on, and a method for making the steel pipe, specifically, for improving hot workability, sulfide stress crack resistance, and corrosion resistance. ART FUNDAMENTALS
    [002] Currently, deep oil fields which have never been considered, acid gas fields whose development has been abandoned due to their harsh corrosive environments, and so on are being actively developed on a global scale from the point of view of a steep rise. in the price of crude oil and the depletion of oil resources that is anticipated for the near future. Such oil fields and gas fields are generally found at great depth in the soil and in severe corrosive environments in which the atmosphere has a high temperature and contains CO2, Cl-, and so on. Therefore, as a steel pipe for tubular oilfield articles that are used to drill such oil fields and gas fields, there is a strong demand for a seamless steel pipe that has not only a high strength corresponding to a yield stress greater than 654 MPa (95 ksi), but also excellent resistance to corrosion.
    [003] In response to these requirements, for example, Patent Literature 1 describes excellent martensitic stainless steel in terms of corrosion resistance and resistance to cracking by sulfide stress. The martensitic stainless steel according to Patent Literature 1 is excellent martensitic stainless steel in terms of corrosion resistance and crack resistance by sulfide stress having a chemical composition that contains, in weight%, C: 0.005% to 0, 05%, Si: 0.05% to 0.5%, Mn: 0.1% to 1.0%, P: 0.025% or less, S: 0.015% or less, Cr: 10% to 15%, Ni : 4.0% to 9.0%, Cu: 0.5% to 3%, Mo: 1.0% to 3.0%, Al: 0.005% to 0.2%, and N: 0.005% to 0 , 1%, in which the condition that Ni equivalent is -10 or more is satisfied, and a microstructure including a tempered martensitic phase, a martensitic phase, and a retained austenitic phase, in which the sum of the fraction of a martensitic phase tempered and the fraction of a martensitic phase is 60% to 90%, and Patent Literature 1 states that it is possible to manufacture martensitic stainless steel by performing a two-stage hot treatment that includes a hot treatment at a temperature equal to or less than a temperature at which a the austenitic phase fraction is 80% and a hot treatment at a temperature equal to or less than a temperature in which an austenitic phase fraction is 60%. Patent Literature 1 states that, with this, it is possible to obtain excellent hot workability, tension from 551 MPa to 861 MPa (80 ksi to 110 ksi), improved resistance to corrosion in an aqueous carbon dioxide environment, and resistance to cracks by improved sulfide stress in an aqueous hydrogen sulfide environment.
    [004] In addition, Patent Literature 2 describes a stainless steel tube for tubular oilfield articles. The steel tube according to Patent Literature 2 is a stainless steel tube for tubular oilfield articles excellent in terms of corrosion resistance that has a chemical composition containing, in mass%, C: 0.05% or less, Si: 0.50% or less, Mn: 0.20% to 1.80%, Cr: 14.0% to 18.0%, Ni: 5.0% to 8.0%, Mo: 1 , 5% to 3.5%, Cu: 0.5% to 3.5%, Al: 0.05% or less, V: 0.20% or less, N: 0.01% to 0.15% , and O: 0.006% or less, in which the Cr + 0.65Ni + 0.6Mo + 0.55Cu -20C> 18.5 and Cr + Mo + 0.3Si -43.5C - 0.4Mn - Ni ratios - 0.3Cu -9N <11 are satisfied, and Patent Literature 2 states that it is possible to obtain the steel tube by performing, after a tube manufacturing process has been carried out, a sudden cooling treatment that includes heating to a temperature equal to or higher than the transformation temperature of Ac3 and then cool to room temperature at a cooling rate equal to or greater than that of the cooling of the air and performing a tempering treatment at a temperature equal to or less than the transformation temperature of Ac1. Patent Literature 2 states that, with this, it is possible to obtain a high strength that corresponds to a yield stress greater than 654 MPa (95 ksi) and excellent resistance to corrosion even in a severe corrosive environment containing CO2, Cl-, and so on and having a temperature greater than 180 ° C and less than or equal to 230 ° C.
    [005] In addition, Patent Literature 3 describes a high strength stainless steel tube for tubular oilfield articles excellent in terms of corrosion resistance. The steel tube according to Patent Literature 3 is a steel tube that has a chemical composition containing, in percentage by mass, C: 0.005% to 0.05%, Si: 0.05% to 0.5% , Mn: 0.2% to 1.8%, P: 0.03% or less, S: 0.005% or less, Cr: 15.5% to 18%, Ni: 1.5% to 5%, Mo : 1% to 3.5%, V: 0.02% to 0.2%, N: 0.01% to 0.15%, and O: 0.006% or less, in which the Cr + 0.65Ni ratios + 0.6Mo + 0.55Cu -20C> 19.5 and Cr + Mo + 0.3Si - 43.5C - 0.4Mn - Ni - 0.3Cu -9N> 11.5 are satisfied and, preferably, a microstructure including a martensitic phase as a base phase, a ferrite phase in an amount of 10% to 60% or more in terms of a fraction of volume and, optionally, an austenitic phase retained in an amount of 30% or less in terms of volume fraction. Patent Literature 3 states that, with this, it is possible to obtain improved hot workability so that cracks in a tube manufacturing process are avoided, a high resistance corresponding to a yield stress or greater than 654 MPa (95 ksi) and excellent corrosion resistance even in a harsh corrosive environment that contains CO2, Cl-, and so on and with a temperature of 230 ° C. LIST OF CITATIONS PATENT LITERATURE [PTL 1] Japanese Unexamined Patent Application Publication No. 101755 [PTL 2] Domestic Republic of PCT International Publication for Patent Application No. WO2004-001082 [PTL 3] Patent Application Publication No Examined Japanese N ° 2005-336595 SUMMARY OF THE INVENTION TECHNICAL PROBLEM
    [006] In the case of techniques according to Patent Literature 1 to Patent Literature 3, satisfactory corrosion resistance in relation to a severe corrosive environment is provided by adding a large amount of expensive alloy chemical elements. However, since the addition of a large quantity of chemical alloying elements causes deterioration in hot workability, there is a problem of deterioration in the pipemaking capacity.
    [007] Therefore, an objective of the present invention is, by solving the problems with the conventional techniques described above, to provide a high-strength seamless stainless steel tube for oilfield tubular articles that is inexpensive, excellent in terms of pipe fabrication as a result of being excellent in terms of hot workability, excellent in terms of resistance to cracking by sulfide stress, and excellent in terms of corrosion resistance. Here, the term “high strength” refers to a strength that corresponds to a yield strength greater than 654 MPa (95 ksi). In addition, the term “excellent in terms of corrosion resistance” here refers to a case where when corrosion weight loss is determined after a test piece has been immersed in a test solution, that is, an aqueous solution of NaCl of 20% by mass (having a temperature of 160 ° C and a partial pressure of CO2 of 5.0 MPa) maintained in an autoclave for 720 hours, the corrosion rate is 0.127 mm / year or less. SOLUTION TO THE PROBLEM
    [008] The present inventors, in order to achieve the object described above, diligently conducted investigations regarding the influence of microstructure on corrosion resistance. To date, in the case of a martensitic stainless steel tube, the desired corrosion resistance has been obtained by obtaining the stability of a passivation film as a result of controlling the amount of chemical alloying elements such as Cr, Mo, and Ni in order to be within appropriate ranges, on the assumption that uniform distribution of constituent chemical elements and homogeneous microstructure are obtained. Therefore, differently from the case of conventional techniques, the present inventors, by focusing on the non-homogeneous microstructure, which was never taken into account, tried to improve the corrosion resistance in a stainless steel tube using a non-homogeneous microstructure.
    [009] As a result, it was found that, in the case where a layer having a special microstructure (non-homogeneous microstructure) that is different from an original phase is formed in the outer surface layer of a stainless steel tube, there is an occurrence significant improvement in corrosion resistance. This layer is a layer that includes a phase (white phase) that looks white when subjected to attack with a common Vilella attack solution (picric acid). This white phase has been found to be a phase that mainly includes a martensitic phase, which is less likely to be etched by a Vilella etching solution (picric acid), and which is excellent in terms of corrosion resistance. In addition, from the results of further investigations, it has been found that this white phase is formed as a result of the formation of a chemical composition in which Ni is relatively concentrated as a result of Cr being spent due to surface oxidation.
    [010] Therefore, the present inventors, by conducting further investigations, have found that, by forming a microstructure of the surface layer in which a white phase occupies a portion from the surface to an appropriate depth in the direction of thickness and disperses on the pipe surface in an appropriate amount in terms of fraction of area, it is possible to steadily improve the corrosion resistance of a stainless steel pipe.
    [011] Furthermore, the present inventors have found that, by forming a microstructure of the surface layer in which a white phase occupies a portion from the surface to an appropriate depth in the direction of thickness and disperses on the surface of the tube in a appropriate amount in terms of fraction of area, it is possible to improve the hot workability and the resistance to cracking by sulfide stress.
    [012] In addition, although in the case of conventional manufacturing methods, the oxygen concentration in a heating furnace before a pipe making process is controlled to be at 1% or less to inhibit the oxidation of a surface tube or is left uncontrolled to be approximately 10%, the present inventors have found that, by controlling the oxygen concentration in order to consider an intermediate value between such values, it is possible to form a white phase in the surface layer having a appropriate depth and fraction of area. In addition, the present inventors have found that it is possible to control the depth of a white phase by controlling the temperature of the heating furnace, heating time, and oxygen concentration.
    [013] The present invention has been completed on the basis of the knowledge described above and further investigations. That is, the subject matter of the present invention is as follows. (1) A high strength seamless stainless steel tube for oilfield tubular articles, the steel tube having a chemical composition containing Cr and Ni and a microstructure that mainly includes a tempered martensitic phase, in which the chemical composition satisfies the relational expression (1) below, and in which the surface layer microstructure includes a phase that appears white when subjected to attack with a Vilella attack solution, which has a thickness in the direction of wall thickness from the outer surface of the tube of 10 μm or more, and 100 μm or less, and which disperses on the outer surface of the tube in an amount of 50% or more in terms of fraction of area.
    where Cr and Ni denote respectively the contents (% by mass) of the corresponding chemical elements. (2) The high strength seamless stainless steel tube for oilfield tubular articles according to item (1), the steel tube having the chemical composition containing, in mass%, C: 0.005% or more and 0.05% or less, Si: 0.05% or more and 1.50% or less, Mn: 0.2% or more and 1.8% or less, P: 0.02% or less, S: 0.005% or less, Cr: 11% or more and 18% or less, Ni: 0.10% or more and 8.0% or less, Mo: 0.6% or more and 3.5% or less, and the rest being Fe and unavoidable impurities. (3) The high strength seamless stainless steel tube for oilfield tubular articles according to item (2), the steel tube having the chemical composition additionally containing, in% of mass, one or both selected from V: 0.02% or more and 0.2% or less and N: 0.01% or more and 0.15% or less. (4) Highly seamless stainless steel tube resistance for tubular oilfield articles according to item (2) or (3), the steel tube having the chemical composition containing added mainly, in% of mass, one, or more selected from the group from group A to group D below.Group A: Al: 0.002% or more and 0.050% or lessGroup B: Cu: 3.5% or lessGroup C: one or more selected from Nb: 0.2% or less, Ti: 0.3% or less, Zr: 0.2% or less, W: 3.0% or less, and B: 0.01% or lessGroup D : Ca: 0.01% or less (5) A method for manufacturing a high strength seamless stainless steel tube for oilfield tubular articles, the method including, when a high strength seamless steel tube is manufactured by heating a steel material in a heating oven, by forming the steel material in a seamless steel tube, and by performing a tempering treatment and a quenching treatment in the seamless steel tube, using a material of steel containing Cr and Ni so that the relational expression (1) below is satisfied in terms of% of mass as the steel material, and heating in the heating furnace in an atmosphere having an oxygen concentration of 2% or more and 5% or less in terms of volume fraction at a temperature of 1,250 ° C or higher and 1,300 ° C or lower, and the high strength seamless steel tube having a microstructure that mainly includes a tempered martensitic phase, in which a surface layer microstructure includes a phase that appears white when subjected to attack with a Vilella attack solution, which has a thickness in the direction of the wall thickness from the outer surface of the tube of 10 μm or more and 100 μm or less, and which disperses on the external surface of the tube in an amount of 50% or more in terms of fraction of area.
    where Cr and Ni respectively denote the contents (% by mass) of the corresponding chemical elements. (6) The method of making a high-strength seamless stainless steel tube for oilfield tubular articles according to item (5), the high-strength seamless steel tube having the chemical composition containing, by weight%, C: 0.005% or more and 0.05% or less, Si: 0.05% or more and 1.50% or less, Mn: 0.2% or more and 1.8% or less, P: 0.02% or less, S: 0.005% or less, Cr: 11% or more and 18% or less, Ni: 0.10% or more and 8.0% or less, Mo: 0.6% or more and 3.5% or less, and the remainder being Fe and unavoidable impurities. (7) The method for making a seamless stainless steel tube high strength for oilfield tubular articles according to item (6), the high strength seamless steel tube having the chemical composition additionally containing, by weight%, one or both selected from V: 0, 02% or more and 0.2% or less and N: 0.01% or more and 0.15% or less. (8) Method for manufacturing a high strength seamless stainless steel tube for oilfield tubular articles according to item (6) or (7), the high strength seamless steel tube having the chemical composition additionally containing, by weight%, one or more selected from group A to group D below.Group A: Al: 0.002% or more and 0.050% or lessGroup B: Cu: 3.5% or lessGroup C: one or more selected from Nb: 0.2% or less, Ti: 0.3% or less, Zr: 0.2% or less, W: 3.0% or less , and B: 0.01% or lessGroup D: Ca: 0.01% or less
    [014] Here, the term “white” in the present invention refers to the quality of having a white appearance compared to an original phase when observed using a standard optical microscope under conditions related to brightness and contrast in which it is possible to observe sufficiently the original phase microstructure that was exposed by carrying out the attack. In addition, the term "original phase" refers here to a homogeneous phase that occupies most of the portion within the steel except in the vicinity of the surface.
    [015] In addition, attack with a Vilella attack solution (picric acid) is carried out by immersing a sample in a Vilella reagent (1% by volume - picric acid + 5% by volume at 15% by volume - hydrochloric acid + ethanol) for several seconds after mechanically polishing the sample surface using a leather polishing method. Since the appropriate degree of attack depends on the microstructure and the chemical elements that make up the steel, the immersion time is appropriately controlled so that the microstructure is clearly observed by confirming that the microstructure is exposed using an optical microscope after the attack has been carried out. Furthermore, the term "dispersion" in the present invention refers not only to a state in which a phase having a white appearance is dispersed in the microstructure of the surface layer, but also to a space in which a phase having a white appearance covers the microstructure of the surface layer. ADVANTAGE EFFECTS OF THE INVENTION
    [016] In accordance with the present invention, it is possible to manufacture a seamless high strength stainless steel tube for oilfield tubular articles which has a high strength corresponding to a yield stress of 654 MPa or more, which has excellent strength corrosion even in a severe high temperature corrosive environment containing CO2, Cl-, and so on, and which is excellent in terms of hot workability and resistance to cracking by sulfide stress with low cost and high productivity, which has a marked effect on the industry. BRIEF DESCRIPTION OF THE DRAWINGS
    [017] Figure 1 illustrates one of the examples of the microstructure in the vicinity of the surface layer of the seamless steel tube according to the present invention. DESCRIPTION OF THE MODALITIES
    [018] The seamless steel tube according to the present invention is a steel tube that has the chemical composition of stainless steel containing Cr and Ni so that the following relational expression (1) is satisfied.
    (where Cr and Ni denote respectively the contents (% of mass) of the corresponding chemical elements.)
    [019] In the case where the contents of Cr and Ni do not satisfy the relational expression (1), since there is a decrease in the relative concentration of Ni with respect to Cr, it is not possible to form the microstructure of the desired surface layer, the which makes it impossible to obtain the desired corrosion resistance. Therefore, the contents of Cr and Ni are controlled in order to satisfy the relational expression (1). Here, it is preferable that Cr / Ni is greater than 1.5. With this, it is possible to control the thickness of a white phase (surface layer microstructure) in order to be 100 μm or less. In the case where the thickness of a white phase (surface layer microstructure) is greater than 100 μm, there is a deterioration in hot workability.
    [020] It is preferable that the stainless steel chemical composition of the seamless steel tube according to the present invention contains, specifically, by weight%, C: 0.005% or more and 0.05% or less, Si: 0 , 05% or more and 1.50% or less, Mn: 0.2% or more and 1.8% or less, P: 0.02% or less, S: 0.005% or less, Cr: 11% or more and 18% or less, Ni: 0.10% or more and 8.0% or less, Mo: 0.6% or more and 3.5% or less, and the remainder being Fe and unavoidable impurities, in which Cr and Ni satisfy the relational expression (1) above.
    [021] Next, the reasons for the limitations in the chemical composition of the seamless steel tube according to the present invention will be described. Then,% of mass when describing a chemical composition will be referred to simply as “%.” C: 0.005% or more and 0.05% or less
    [022] C is an important chemical element that is related to the strength of steel, and it is preferable that the C content is 0.005% or more to obtain the desired strength in the present invention. On the other hand, in the case where the C content is greater than 0.05%, there is an occurrence of improvement in the degree of sensitization in a tempering process due to the addition of Ni. Therefore, it is preferable that the C content is limited to 0.005% or more and 0.05% or less. Here, while it is preferable for the C content to be as small as possible from the point of view of improving corrosion resistance, it is more preferable for the C content to be 0.03% or more and 0.05% or less if considering the balance between the improvement of the corrosion resistance and the stable obtaining of resistance.Si: 0.05% or more and 1.50% or less
    [023] Si is a chemical element that functions as a deoxidizing agent, and it is preferable that the Si content is 0.05% or more to achieve such an effect. On the other hand, in the case where the Si content is higher than 1.50%, there is deterioration in resistance to corrosion of CO2, and in a case of deterioration in hot workability. Therefore, it is preferable that the Si content is limited to 0.05% or more and 1.50% or less. It is more preferable that the Si content is 0.10% or more. In addition, it is more preferable that the Si content is 0.50% or less.Mn: 0.2% or more and 1.8% or less
    [024] Mn is a chemical element that has a function of improving resistance, and it is preferable that the Mn content is 0.2% or more in order to obtain the desired resistance in the present invention. On the other hand, in the case where the Mn content is greater than 1.8%, there is a negative effect on the toughness. Therefore, it is preferable that the Mn content is limited to 0.2% or more and 1.8% or less, or more preferably, 0.2% or more and 1.6% or less. P: 0.02% or less
    [025] Since P is a chemical element that has a function of deteriorating all corrosion resistance of CO2, resistance to corrosion cracking under CO2 stress, resistance to pitting corrosion, and resistance to cracking by sulfide stress, it is preferable that the P content is as small as possible in the present invention. However, in the case where the P content is excessively small, there is an increase in refining costs. Therefore, it is preferable that the P content is 0.005% or more, which is within an industrially achievable range at a comparatively low cost. In addition, in the case where the P content is 0.02% or less, the degrees of deterioration in CO2 corrosion resistance, CO2 stress corrosion crack resistance, pitting corrosion resistance, and crack resistance by sulfide stress are acceptable. Therefore, it is preferable that the P content is limited to 0.02% or less, or more preferably 0.01% or less.S: 0.005% or less
    [026] Since S is a chemical element that has a function of significantly deteriorating productivity in a steel pipe fabrication process as a result of significantly deteriorating the hot workability of steel, it is preferable that the S content is as small as possible. However, in the case where the S content is excessively small, there is an increase in refining costs. Therefore, it is preferable that the S content is 0.001% or more, which is within an industrially achievable range at comparatively low cost. Here, in the case where the S content is 0.005% or less, it is possible to manufacture a steel tube using a common manufacturing process. Therefore, it is preferable that the S content is limited to 0.005% or less, or more preferably 0.002% or less. Cr: 11% or more and 18% or less
    [027] Cr is a chemical element that has the function of improving corrosion resistance by forming a protective film on the steel surface and which, specifically, contributes to improving CO2 corrosion resistance and resistance to corrosion cracking. under CO2 tension. In the present invention, it is preferable that the Cr content is 11% or more from the point of view of improving the corrosion resistance at high temperature. On the other hand, in the case where the Cr content is higher than 18%, there is a deterioration in hot workability, and there is a decrease in flow resistance. Therefore, it is preferable that the Cr content be limited to 11% or more and 18% or less, or more preferably 11.5% or more and 18% or less.Ni: 0.10% or more and 8.0 % or less
    [028] Ni is a chemical element that has the function of improving the corrosion resistance of CO2, resistance to corrosion cracking under CO2 stress, resistance to pitting corrosion, and resistance to cracking by sulfide stress by improving the resistance of a protective film formed on the steel surface that improves the strength of the steel by reinforcing a solid solution. Such effects are realized in the case where the Ni content is 0.10% or more. On the other hand, in the case where the Ni content is greater than 8.0%, since there is a deterioration in the stability of a martensitic phase, there is an occurrence of deterioration in resistance. Therefore, it is preferable that the Ni content is limited to 0.10% or more and 8.0% or less, more preferably 2.0% or more and 8.0% or less, or even more preferably 3.5% or more and 7.0% or less.
    [029] Here, it is preferable that the contents of Cr and Ni of the seamless steel tube according to the present invention are controlled so that they fall within the ranges described above and controlled so as to satisfy the relational expression (1) above .Mo: 0.6% or more and 3.5% or less
    [030] Mo is a chemical element that has a function of improving the resistance (resistance to pitting corrosion) to pitting corrosion that is caused by chlorine ions (Cl-). To achieve this effect, it is preferable that the Mo content is 0.6% or more. In the case where the Mo content is less than 0.6%, there is an occurrence of insufficient corrosion resistance in a severe high temperature corrosive environment. On the other hand, in the case where the Mo content is greater than 3.5%, there is an occurrence of deterioration in strength. Here, as Mo is an expensive chemical element, there is an increase in material costs in the case where the Mo content is high. Therefore, it is preferable that the Mo content is limited to 0.6% or more and 3.5% or less, or more preferably 0.6% or more and 2.8% or less.
    [031] Although the chemical composition described above is the basic chemical composition, in addition to the basic chemical composition, one or both selected from V: 0.02% or more and 0.20% or less and N: 0.01% or more and 0.15% or less and / or one, more selected from group A to group D can be added as selective chemical elements.
    [032] One or both selected from V: 0.02% or more and 0.2% or less and N: 0.01% or more and 0.15% or less V and N are both chemical elements that improve the corrosion resistance, and one or both selected from these chemical elements can be selectively added to the present invention.
    [033] V is a chemical element that improves corrosion resistance and crack resistance from stress corrosion and that has a function of improving air resistance. Such effects are sharply realized in the case where the Z content is 0.02% or more. On the other hand, in the case where the V content is greater than 0.2%, there is an occurrence of deterioration in tenacity. Therefore, in the case where V is added, it is preferable that the V content is limited to 0.02% or more and 0.2% or less, or more preferably 0.02% or more and 0.08% or less.
    [034] N is a chemical element that has the function of significantly improving resistance to pitting corrosion. Although N is normally contained in steel as an unavoidable impurity in an amount of less than approximately 0.01%, to achieve such an effect in the present invention, the N content is defined to be 0.01% or more. On the other hand, in the case where the N content is greater than 0.15%, there is deterioration in toughness as a result of the formation of several nitrides. Therefore, in the case where N is particularly added, it is preferable that the N content is limited to 0.01% or more and 0.15% or less. It is more preferable that the N content is 0.02% or more. In addition, it is more preferable that the N content is 0.08% or less. One or more selected from group A to group D
    [035] In the present invention, one or more selected from group A to group D can be added as needed as selective chemical elements. Here, group A consists of Al: 0.002% or more and 0.050% or less, group B consists of Cu: 3.5% or less, group C consists of one or more selected from Nb: 0.2% or less, Ti: 0.3% or less, Zr: 0.2% or less, W: 3.0% or less, and B: 0.01% or less, and group D consists of Ca: 0.01 % or less.
    [036] Group A: Al is a chemical element that functions as a deoxidizing agent, and Al can be added selectively as needed. To achieve this effect, it is preferable that the Al content is 0.002% or more. On the other hand, in the case where the Al content is greater than 0.050%, there is a negative effect on the toughness. Therefore, in the case where group A is added, it is preferable that the content of group A: Al is limited to 0.002% or more and 0.050% or less. It is more preferable that the Al content is 0.03% or less. In the case where Al is not added, it is acceptable for the group A: Al to be contained as an unavoidable impurity and an amount of less than approximately 0.002%. In the case where the content of the group A: Al is limited to less than approximately 0.002%, there is an advantage that there is a significant improvement in resistance to sulphide stress cracking.
    [037] Group B: Cu is a chemical element that has a function of improving the crack resistance of sulfide stress by inhibiting the ingress of hydrogen into the steel as a result of improving the strength of a protective film, and Cu can be selectively added as needed. To achieve this effect, it is preferable that the Cu content is 0.5% or more. However, in the case where the Cu content is greater than 3.5%, there is an occurrence of deterioration in the hot workability due to the CuS grain limit precipitation. Therefore, in the case where group B is added, it is preferable that the content of group B: Cu is limited to 3.5% or less. It is more preferable that the Cu content is 0.5% or more and 2.5% or less.
    [038] Group C: Nb, Ti, Zr, W and B are all chemical elements that improve resistance, and one or more selected from among these chemical elements can be added as needed. To achieve this effect, it is preferable that the Nb content is 0.03% or more, the Ti content is 0.03% or more, the Zr content is 0.03% or more, the content of W is 0.2% or more, and the B content is 0.0005% or more. On the other hand, in the case where the Nb content is greater than 0.2%, the Ti content is greater than 0.3%, the Zr content is greater than 0.2%, the W content is greater than 3.0%, or the B content is greater than 0.01%, there is an occurrence of deterioration in toughness. Therefore, in the case where group C is added, it is preferable that the Nb content is limited to 0.2% or less, the Ti content is limited to 0.3% or less, the Zr content is limited to 0 , 2% or less, the W content is limited to 3.0% or less, and the B content is limited to 0.01% or less.
    [039] Group D: Ca is a chemical element that has the function of submitting the sulfide-based inclusions format to spheroidization, and Ca can be added as needed. Such an effect is sharply realized in the case where the Ca content is 0.0005% or more. On the other hand, in the case where the Ca content is greater than 0.01%, since there is an increase in the amount of CaO, there is a case of deterioration in the corrosion resistance of CO2 and resistance to pitting corrosion. Therefore, in the case where Ca is added, it is preferable that the Ca content is limited to 0.01% or less, or more preferably 0.001% or less.
    [040] The remainder, other than one mentioned above, is Fe and unavoidable impurities. As unavoidable impurities, O: 0.006% or less and N: less than 0.01% are acceptable.
    [041] Here, since O has negative effects on various properties as a result of existing in steel in the form of oxides, it is preferable that the O content is as small as possible to improve the properties. Specifically, in the case where the O content is greater than 0.006%, there is an occurrence of deterioration in hot workability, resistance to corrosion cracking under CO2 stress, resistance to pitting corrosion, resistance to sulphide stress cracking, and tenacity. Therefore, it is preferable that the O content, which is an unavoidable impurity, is 0.006% or less.
    [042] The seamless steel tube according to the present invention has a microstructure that includes a tempered martensitic phase as a main phase in addition to the chemical composition described above. The term "main phase" refers here to a phase that constitutes, in terms of a fraction of volume, 50% or more of the entire microstructure. Examples of second phases other than a tempered martensitic phase include a ferrite phase and a retained austenitic phase which, in terms of volume fraction, make up less than 50% of the entire microstructure. In the case where the second phases constitute, in terms of volume fraction, 50% or more of the entire microstructure, it is not possible to obtain the desired resistance. Here, it is preferable that the phase fraction of the second phase is 40% or less.
    [043] In addition, the seamless steel tube according to the present invention has, on the outer surface layer of the tube, a surface layer microstructure in which a phase (white phase) that appears white when subjected to attack with a Vilella attack solution has a thickness in the direction of wall thickness from the outer surface of the tube of 10 μm or more and disperses on the outer surface of the tube in an amount of 50% or more in terms of fraction of area. The term “outer tube layer” refers here to a region within 100 μm in the direction of wall thickness from the outer surface of the tube. Furthermore, the term "dispersion" in the present invention refers not only to a state in which a phase having a white appearance is dispersed in the surface layer microstructure, but also to a state in which a phase having a white appearance covers the microstructure of surface layer.
    [044] The term "white phase" refers here to a phase that appears white when subjected to attack with a common Vilella attack solution (picric acid). As a result of observation using a scanning electron microscope, it is clarified that this white phase is a phase that mainly includes a martensitic phase and which is excellent in terms of corrosion resistance. By dispersing (forming) such a "white phase" having an appropriate thickness in the direction of wall thickness (10 μm or more and preferably 100 μm or less) in the outer surface layer of the tube, since it is possible to inhibit the ingress of hydrogen through the outer surface of the tube, there is significant improvement in crack resistance by sulfide stress and corrosion resistance (corrosivity in other words corrosion resistance). As an example indicating a state in which a white phase is formed, the photograph of a microstructure in the vicinity of the surface of a seamless steel tube obtained by carrying out an attack with a Vilella attack solution (picric acid) and using a optical microscope is shown in Figure 1. Here, the term “white” in the present invention refers to the quality of having a white appearance compared to an original phase when observed using a standard optical microscope under conditions related to brightness and contrast in that it is possible to sufficiently observe the original phase microstructure that has been exposed by carrying out the attack. In addition, the term “original phase” here refers to a homogeneous phase that occupies most of the portion within the steel except in the vicinity of the surface.
    [045] In the case where the thickness of a white phase in the direction of wall thickness is less than 10 μm, as the thickness of the surface layer microstructure is too small to prevent hydrogen ingress, it is difficult to obtain the desired corrosion resistance. On the other hand, in the case where the thickness is greater than 100 μm, there is a deterioration in hot workability. Here, the thickness of a white phase in the direction of wall thickness is defined as the thickness (maximum thickness) that is obtained under the condition that the maximum thickness value is obtained when engraving with a Vilella etching solution (picric acid) it is performed in several attack times within the range in which an original phase microstructure is exposed.
    [046] Furthermore, in the case where the fraction of area of a white phase on the outer surface of the tube is less than 50%, as the degree of dispersion (coverage factor) on the outer surface layer of the tube is not small, obtain the desired corrosion resistance. Therefore, the fraction of area of a white phase on the outer surface of the tube is limited to 50% or more, or preferably 70% or more.
    [047] Next, the preferred method for making the seamless steel tube according to the present invention will be described.
    [048] A steel material (round ingot manufactured in a continuous casting process) having the chemical composition of stainless steel described above is loaded into a heating furnace to heat the material. In a heating process, since the vicinity of the steel material surface is oxidized, Ni is relatively concentrated as a result of Cr being stretched, which results in a white phase being formed in the surface layer. In order to form the "surface layer microstructure" according to the present invention, it is particularly necessary to control the atmosphere and the heating temperature of the heating oven.
    [049] In the present invention, the oxygen concentration in the atmosphere of the heating furnace is defined to be 2% by volume or more and 5% by volume or less. In the case where the oxygen concentration in the atmosphere of the heating furnace is less than 2% by volume, it is not possible to form the desired white phase. On the other hand, in the case where the oxygen concentration is greater than 5% by volume, since the thickness of a white phase in the direction of wall thickness is greater than 100 μm, there is a deterioration in hot workability. In the present invention, the oxygen concentration can be controlled by controlling, for example, the ratio of the amount of a fuel used in the heating process to the amount of air and the chemical composition of the gas in the heating atmosphere.
    [050] In addition, the heating temperature is defined as being 1,250 ° C or higher and 1,300 ° C or lower. In the case where the heating temperature is below 1,250 ° C, it is not possible to form the desired white phase. On the other hand, in the case where the heating temperature is higher than 1,300 ° C, as the thickness of a white phase in the direction of the wall thickness is greater than 100 μm, there is a deterioration in the hot workability.
    [051] In addition, it is preferable that a maintenance time in a heating process is 2 hours or more and 3 hours or less. In the case where the maintenance time in a heating process is less than 2 hours, there is an occurrence where it is not possible to form the desired white phase. On the other hand, in the case where the maintenance time is more than 3 hours, since the thickness of a white phase in the direction of the wall thickness is greater than 100 μm, there is an occurrence of deterioration in hot workability.
    [052] By carrying out a tube manufacturing process including drilling the heated steel material using a drilling mill such as a perforator to obtain a hollow material having specified dimensions, hot rolling of the hollow material using a mill hot-rolling mill such as a mandrel mill or an elongator, a shutter mill, and a realer, and optionally additionally carrying out, for example, diameter reduction lamination using a reducer, a finishing mill or the like and by performing cooling at a cooling rate equal to or greater than that of air cooling, a seamless steel tube with specified dimensions is obtained. It is not necessary to place specific limitations on the conditions of a pipe making process or cooling conditions, and any of the common conditions can be used.
    [053] In the present invention, a tempering treatment and a quenching treatment are carried out on the seamless steel tube obtained by carrying out the processes described above.
    [054] A tempering treatment is a treatment in which the seamless steel tube is heated to a temperature equal to or greater than the transformation temperature of Ac3 and subsequently cooled to room temperature at a cooling rate equal to or greater than that of air cooling. The seamless tempered steel tube is subsequently subjected to a tempering treatment. Tempering treatment is a treatment in which the seamless steel tube is heated to a temperature equal to or less than the transformation temperature of Ac1 and subsequently cooled to room temperature at a cooling rate equal to or greater than that of air cooling. .
    [055] Here, it is not necessary to impose specific limitations on the specific conditions used for tempering or tempering, and any of the conditions can be used.
    [056] In the following, the present invention will be described in more detail based on examples. EXAMPLES
    [057] By degassing molten steel having the chemical compositions provided in Table 1, and by melting the molten steel in steel ingots having a weight of 100 kg, steel materials were obtained. By heating these steel materials in a heating furnace under the conditions provided in Table 2, the steel materials are then made into tubes by performing hot work using a model seamless rolling mill, and then air, seamless steel tubes (having an outside diameter of 13.9 inchesΦ (3530.6 mm) and a wall thickness of 4.6 inches (1168.4 mm)) were obtained. In Table 2, among the heating conditions of a rotary heating furnace, 100% N2 gas was used in the atmosphere a: inert atmosphere, a mixed gas having an oxygen concentration of 3% by volume and a nitrogen concentration of 97 % was used in atmosphere b: oxidation atmosphere, and a mixed gas having an oxygen concentration of 10% by volume and a nitrogen concentration of 90% was used in atmosphere c: vigorous oxidation atmosphere. By observing the surfaces, internal and external, of seamless steel tubes, obtained in the cooled state after the tube manufacturing process by performing a visual test, it was verified whether cracks occurred or not to assess hot workability. A case where there was a crack having a length of 5 mm or more on the surface of the front or rear end of the tube was evaluated as the case "with" a crack and marked with "x" (unsatisfactory), and the cases except those, were evaluated as the case “without” a crack and marked with “O” (satisfactory).
    [058] Subsequently, the seamless steel tubes obtained were subjected to a tempering treatment and a quenching treatment under the conditions given in Table 2.
    [059] Taking the test pieces from the seamless steel tubes obtained, observation of microstructure, a tensile test, a corrosion test and a sulfide stress crack test were carried out. The test methods were as follows. (9) Observation of microstructure
    [060] Taking a test piece for observation of microstructure from the obtained seamless steel tube, by first polishing a cross section (cross section-C) at a right angle in relation to the direction of the tube axis, by attacking the polished cross section with a Vilella attack solution (1% by volume - picric acid + 5% by volume to 15% by volume - hydrochloric acid + ethanol), and by observing the portion in the vicinity of the tube surface located at different locations (8 locations) in the circumferential direction using an optical microscope (at a magnification of 400 times), the thickness (minimum value) of a white phase in the direction of wall thickness and the phase fractions on the tube surface have been determined. In addition, in the determination described above, a white phase was defined as a phase having a white appearance compared to an original phase when observed using a standard optical microscope under conditions related to brightness and contrast in which it is possible to observe the microstructure sufficiently of the original phase that was exposed by carrying out an attack.
    [061] Here, by observing also an internal microstructure in the regions except the surface layer using an optical microscope (at a magnification of 400 times), and taking photographs, the initial phases were identified and the phase fractions of the individual phases were determined from the microstructure photographs by performing an image analysis. Here, the phase fraction of a retained austenitic phase was determined using an x-ray diffraction method in a central position in the direction of structure. (10) Tensile test
    [062] A round bar type tensile test piece (having a parallel part having a diameter of 6 mmΦ and a length of 80 mm) was taken from the seamless steel tube obtained so that the tensile direction is the direction of the tube axis. As the microstructure of the surface layer was removed from the test piece considered, the test piece was subjected to a heat treatment under a condition in which the conditions of a heating furnace prior to a tube manufacturing process provided in Table 2 were simulated to form a white phase in the surface layer of the test piece, and the treated test piece was then subjected to a tempering treatment and a quenching treatment under the conditions given in Table 2 to control the microstructure of the test piece . Subsequently, by performing a tensile test according to the API (American Petroleum Institute) -5CT prescription, tensile properties (yield stress YS, tensile strength TS and Elongation Elongation) were determined. (11) corrosion
    [063] A corrosion test piece (having a thickness of 3 mm, a width of 30 mm and a length of 40 mm) was taken from the seamless steel tube obtained by machining. Subsequently, as was done in (2), the test piece was subjected to a hot treatment under a condition in which the conditions of a heating furnace provided in Table 2 were simulated to form the white phase in the surface layer of the piece test, the treated test piece was then subjected to a tempering treatment and a quenching treatment under the conditions given in Table 2 to control the microstructure of the test piece, and a corrosion test was then carried out. A corrosion test was carried out by immersing the corrosion test piece in a test solution, that is, an aqueous solution of NaCl at 20% by mass (having a temperature of 160 ° C and a partial pressure of CO2 of 5, 0 MPa) contained in an autoclave for an immersion time of 720 hours. After the corrosion test was carried out, by determining the weight of the corrosion test piece, a corrosion rate was calculated from the difference in weight between before and after the corrosion test. A case where the corrosion rate was 0.127 mm / year or less was assessed as the case of good corrosion resistance and marked with “O” (satisfactory), and cases other than those were assessed as “x” (unsatisfactory). (12) Sulfide stress crack test (SSC)
    [064] A tensile test piece (having a parallel part with a diameter of 6.4 mmΦ and a length of 25.4 mm) was taken from the obtained seamless steel tube and, as was done in (2), the test piece was subjected to a hot treatment under a condition in which the conditions of a heating furnace provided in Table 2 were simulated to form a white phase in the surface layer of the test piece, the treated test piece was then subjected to a tempering treatment and a quenching treatment under the conditions provided in Table 2 to control the microstructure of the test piece, and an SSC test was then carried out according to NACE-TM0177-96 Method A.
    [065] The test piece was subjected to a constant load test while being placed in contact with an aqueous solution of 5% NaCl + 0.5% CH3COOH + CH3COONa (with a temperature of 25 ° C, a pH of 4.0, and an H2S partial pressure of 0.002 MPa). The load tension was 90% -SMYS (Minimum Specified Flow Resistance). A case where crack did not occur after 720 hours was assessed as the case of excellent resistance to sulfide stress crack (SSC resistance) and marked with “O” (satisfactory), and a case where crack occurred was rated as “x” ( unsatisfactory).
    [066] The results obtained are provided in Table 3.





    [067] All examples of the present invention were high strength seamless stainless steel tubes for oilfield tubular articles having a high strength corresponding to a yield stress of 654 MPa or more, excellent hot workability, excellent corrosion resistance even in a severe high temperature corrosive environment containing CO2, Cl-, and so on and having a temperature above 160 ° C, and excellent resistance to cracking by sulfide stress. On the other hand, the comparative examples that were outside the range according to the present invention, had crack resistance by deteriorated sulfide stress (SSC resistance), and steel tube No. 23 additionally had deteriorated hot workability.
    权利要求:
    Claims (11)
    [0001]
    1. High strength seamless stainless steel tube for oilfield tubular articles, the steel tube characterized by the fact that it comprises a chemical composition that contains Cr and Ni and that satisfies the expression (1): Cr / Ni <5.3 ... (1), where Cr and Ni denote the levels (% by mass) of the corresponding chemical elements, respectively; a microstructure that mainly includes a tempered martensitic phase, in which a surface layer microstructure includes a white phase after being subjected to attack with a Vilella attack solution, the white phase having: (i) a thickness in a thickness direction wall from the outer surface of the tube of 10 μm or more, and 100 μm or less, and (ii) being dispersed on the outer surface of the tube in an amount of 50% or more in terms of area fraction.
    [0002]
    2. High strength seamless stainless steel tube for oilfield tubular articles, according to claim 1, characterized by the fact that the chemical composition of the steel tube contains, C: 0.005% or more and 0.05% or less, in% by mass, Si: 0.05% or more and 1.50% or less, in% by mass Mn: 0.2% or more and 1.8% or less, in% by mass, P : 0.02% or less, in mass%, S: 0.005% or less, in mass%, Cr: 11% or more and 18% or less, in mass%, Ni: 2.0% or more and 8.0% or less, in mass%, and Mo: 0.6% or more and 3.5% or less, in mass%, the remainder being Fe and unavoidable impurities.
    [0003]
    3. High-strength seamless stainless steel tube for oilfield tubular articles, according to claim 2, characterized by the fact that the chemical composition additionally comprises one or both selected from V: 0.02% or more and 0 , 2% or less, by weight%, and N: 0.01% or more and 0.15% or less, by weight%.
    [0004]
    4. High-strength seamless stainless steel tube for oilfield tubular articles, according to claim 2, characterized by the fact that the chemical composition additionally comprises one or more selected from the group from group A to group D below: group A: Al: 0.002% or more and 0.050% or less, in mass%, group B: Cu: 3.5% or less, in mass%, group C: one or more selected from Nb: 0.2 % or less, in% by mass, Ti: 0.3% or less, in% by mass, Zr: 0.2% or less, in% by mass, W: 3.0% or less, in% by mass , and B: 0.01% or less, in mass%, and group D: Ca: 0.01% or less, in mass%.
    [0005]
    5. High-strength seamless stainless steel tube for oilfield tubular articles, according to claim 3, characterized by the fact that the chemical composition additionally comprises one or more selected from the group from group A to group D below: group A: Al: 0.002% or more and 0.050% or less, in% in mass group B: Cu: 3.5% or less, in% in mass group C: one or more selected from Nb: 0.2% or less, in% by mass, Ti: 0.3% or less, in% by mass, Zr: 0.2% or less, in% by mass, W: 3.0% or less, in% by mass, and B: 0.01% or less, in mass%, group D: Ca: 0.01% or less, in mass%.
    [0006]
    6. Method for the manufacture of a seamless stainless steel tube of high strength for oilfield tubular articles, the method characterized by the fact that it comprises heating a steel material in a heating furnace in an atmosphere having an oxygen concentration of 2% or more and 5% or less in terms of volume fraction at a temperature of 1,250 ° C or higher and 1,300 ° C or lower, where the steel material contains Cr and Ni and meets the relational expression (1) Cr / Ni <5.3 ... (1), where Cr and Ni denote respectively the contents (% by mass) of the corresponding chemical elements, formation of the steel material in a seamless steel tube, carrying out a cooling treatment abrupt and a tempering treatment in the seamless steel tube where the seamless steel tube has a microstructure including mainly a tempered martensitic phase, a surface layer microstructure includes a white phase after being subjected to attack with a Vilella attack solution, the white phase: (i) having a thickness in one direction of the wall thickness from the outer surface of the tube of 10 μm or more and 100 μm or less, and (ii) being dispersed on the external surface of the tube tube in an amount of 50% or more in terms of fraction of area.
    [0007]
    7. Method for manufacturing a seamless stainless steel tube of high strength for oilfield tubular articles, according to claim 6, characterized by the fact that the chemical composition of the steel material containing, C: 0.005% or more and 0.05% or less,% by mass, Si: 0.05% or more and 1.50% or less,% by mass, Mn: 0.2% or more and 1.8% or less,% by mass , P: 0.02% or less,% by mass, 5: 0.005% or less,% by mass, Cr: 11% or more and 18% or less,% by mass, Ni: 2.0% or more and 8.0% or less,% by mass, Mo: 0.6% or more and 3.5% or less,% by mass, and the remainder being Fe and unavoidable impurities.
    [0008]
    8. Method for manufacturing a seamless stainless steel tube of high strength for oilfield tubular articles, according to claim 7, characterized by the fact that the chemical composition of the steel material additionally comprises one or both selected from of V: 0.02% or more and 0.2% or less,% by mass and N: 0.01% or more and 0.15% or less,% by mass.
    [0009]
    9. Method for manufacturing a seamless stainless steel tube of high strength for oilfield tubular articles, according to claim 7, characterized by the fact that the chemical composition of the steel material additionally comprises one or more selected from among group A to group D below: group A: Al: 0.002% or more and 0.050% or less,% by mass, group B: Cu: 3.5% or less,% by mass, group C: one or more selected from among Nb: 0.2% or less,% by mass, Ti: 0.3% or less,% by mass, Zr: 0.2% or less,% by mass, W: 3.0% or less,% by weight mass, and B: 0.01% or less,% by mass, and group D: Ca: 0.01% or less,% by mass.
    [0010]
    10. Method for manufacturing a high-strength seamless stainless steel tube for oilfield tubular articles, according to claim 8, characterized by the fact that the chemical composition of the steel material additionally comprises one or more selected from among group A to group D below: group A: Al: 0.002% or more and 0.050% or less,% in massagroup B: Cu: 3.5% or less,% in massagroup C: one or more selected from Nb: 0, 2% or less,% by mass, Ti: 0.3% or less,% by mass, Zr: 0.2% or less,% by mass, W: 3.0% or less,% by mass, and B : 0.01% or less,% by mass and group D: Ca: 0.01% or less,% by mass.
    [0011]
    11. Method for manufacturing a high-strength seamless stainless steel tube for oilfield tubular articles, according to claim 6, characterized by the fact that the heating maintenance time is 2 hours or more and 3 hours hours or less.
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    法律状态:
    2019-08-20| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2021-02-09| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-04-13| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 20/05/2015, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2014-105039|2014-05-21|
    JP2014105039|2014-05-21|
    PCT/JP2015/002535|WO2015178022A1|2014-05-21|2015-05-20|High-strength stainless steel seamless pipe for oil well, and method for producing same|
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