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    • 专利摘要:
    LOW ALLOY OIL WELL STEEL TUBE AND METHOD FOR MANUFACTURING THE SAME. It is a low alloy oil well steel tube which has an elastic limit of 965 MPa (140 ksi) or more and which exhibits excellent SSC resistance which is provided in a stable manner. The low alloy oil well steel tube according to the present invention includes a chemical composition consisting, in% by weight, in C: 0.40 to 0.65%, Si: 0.05 to 0 , 50%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.0020% or less, Cu: 0.15% or less, Cr: 0.40 to 1.50% , Mo: 0.50 to 2.50%, V: 0.05 to 0.25%, Ti: 0 to less than 0.01%, Nb: 0.01 to 0.2%, Al sol .: 0.010 at 0.100%, N: 0.006% or less, B: 0 to 0.0015%, and Ca: 0 to 0.003%, the balance being Fe and impurities; and a structure consisting of tempered martensite and 0 less than 2% in the volume ratio of retained austenite, and a grain size number of a previous austenite grain in the structure is 9.0 or more, and in tempered martensite, an equivalent circular diameter of a substructure surrounded by a boundary that has a difference in crystal orientation of 15 ° or more among a packet boundary, a block boundary (...).
    公开号:BR112016000543B1
    申请号:R112016000543-0
    申请日:2014-07-23
    公开日:2020-11-17
    发明作者:Tomohiko Omura；Yuji Arai；Keiichi Kondo
    申请人:Nippon Steel Corporation；
    IPC主号:
    专利说明:

    TECHNICAL FIELD
    [0001] The present invention relates to an oil well steel tube and a method for making it and, more specifically, it relates to a used low alloy oil well steel tube, for example , for a liner or piping for an oil well or a gas well and a method for making the same. BACKGROUND OF THE TECHNIQUE
    [0002] With the increase in depth of oil wells and gas wells (hereinafter, oil wells and gas wells are collectively and simply referred to as “oil wells”), there is a need to increase the rigidity of pipes steel from oil well. Conventionally, the 551 MPa (80 ksi) oil well steel tube (yield limit of 551 to 654 MPa (ie 80 to 95 ksi)) and the 654 MPa (95 ksi) yield limit (yield limit) 654 to 758 MPa ie 95 to 758 MPa (110 ksi)) has been widely used. However, recently, 758 MPa (110 ksi) oil well steel tubes (yield limit of 758 to 862 MPa, that is, 110 to 125 ksi) are put into use.
    [0003] Many of the newly developed deep wells contain hydrogen sulfide, which is corrosive. Therefore, oil well steel tubes are required to have not only high rigidity, but also resistance to corrosion under sulfide-assisted stress (hereinafter referred to as SSC resistance).
    [0004] As a measure to improve the SSC resistance of a conventional 654 to 758 MPa (95 to 110 ksi) oil well steel tube, known methods include cleaning the steel and making the steel structure more slim. For example, Patent Application Publication No. JP 62-253720 proposes the method to improve resistance to SSC by reducing impurity elements, such as Mn and P. Patent Application Publication No. JP 59- 232220 proposes the method to improve the resistance to SSC by performing hardening twice by grain refinement.
    [0005] In response to the need to increase the rigidity of oil well steel tubes, recently, 862 MPa (125 ksi) oil well steel tubes (yield limit of 862 to 965 MPa) are placed in use. In addition, there is an increasing need for oil well steel tubes that have a yield limit of 965 MPa (yield limit of 140 ksi) or more.
    [0006] Sulfide-assisted stress (SSC) corrosion is more likely to occur as the stiffness is higher. Therefore, 965 MPa (140 ksi) or more oil well steel tubes need to have additionally improved SSC resistance compared to conventional 658 MPa (95 ksi) class 758 oil well steel tubes MPa (110 ksi) and the classification 862 MPa (125 ksi).
    [0007] Patent Application Publications No. JP 6-322478, JP 8-311551, JP 11-335731, JP 2000-178682, JP 2000-256783, JP 2000-297344, JP 2000-119798, JP 2005- 350754 and JP 2006-265657 each propose a measure to improve the SSC resistance of steel for a highly rigid oil well tube.
    [0008] Patent Application Publication No. JP 6-322478 proposes the method to improve the SSC resistance of a steel product of 862 MPa (125 ksi) grade by providing a thinner steel structure by heat treatment with use of induction heating. Patent Application Publication No. JP 8-311551 proposes the method to improve the SSC resistance of a steel tube of the 758 to 965 MPa (110 to 140 ksi) classifications by intensifying the hardness using the direct tempering process and increasing the tempering temperature. Patent Application Publication No. JP 11-335731 proposes the method to improve the SSC resistance of a low alloy steel of grades 758 to 965 MPa (110 to 140 ksi) by making the adjustment to provide the chemical composition of ideal alloy. Patent Application Publications No. JP 2000-178682, JP 2000-256783 and JP 2000-297344 each propose a method for improving the SSC resistance of a steel for a low alloy oil well pipe classifications 758 to 965 MPa (110 to 140 ksi) controlling the carbide shapes. Patent Application Publication No. JP 2000-119798 proposes the method to delay a time of occurrence of SSC in a steel product from the ratings of 758 to 862 MPa (110 to 125 ksi) by precipitating a large amount of fine V carbides. Patent Application Publication No. JP 2005-350754 proposes the method to improve the SSC resistance of an oil well steel tube of the classification 862 MPa (125 ksi) or more, controlling the displacement density and the hydrogen diffusion coefficient to desired values. Patent Application Publication No. JP 2006-265657 proposes the method to improve the SSC resistance of a steel for an oil well tube of the classification 862 MPa (125 ksi) or more by producing a bainite structure of single phase, which is supplied containing a high C content in the steel and, during the water cooling, interrupting the water cooling to 400 to 600 ° C and performing the isothermal transformation heat treatment (treatment by austempera) at 400 to 600 ° C. PREVIOUS TECHNICAL DOCUMENTS PATENT DOCUMENTS
    [0009] Patent Literature 1: Unexamined Patent Application Publication No. Jp: 62-253720
    [0010] Patent Literature 2: Unexamined Patent Application Publication No. Jp: 59-232220
    [0011] Patent Literature 3: Unexamined Patent Application Publication No. jp: β-322478
    [0012] Patent Literature 4: Unexamined Patent Application Publication No. jp: 8-311551
    [0013] Patent Literature 5: Publication of Unexamined Patent Application No. jp. 11_335731
    [0014] Patent Literature 6: Unexamined Patent Application Publication No. jp. 2000-178682
    [0015] Patent Literature 7: Publication of Unexamined Patent Application No. jp. 2000-256783
    [0016] Patent Literature 8: Publication of Unexamined Patent Application No. jp. 2000-297344
    [0017] Patent Literature 9: Unexamined Patent Application Publication No. jp: 2000-119798
    [0018] Patent Literature 10: Unexamined Patent Application Publication No. jp: 2005-350754
    [0019] Patent Literature 11: Unexamined Patent Application Publication No. Jp: 2006-265657 SUMMARY OF THE INVENTION
    [0020] However, any of the techniques revealed in the patent documents may fail to provide an oil well steel tube that has a yield limit of 965 MPa (140 ksi) or more and that displays, in a stable manner, excellent resistance to SSC.
    [0021] It is an objective of the present invention to provide a low alloy oil well steel tube that has a yield limit of 965 MPa (140 ksi) or more and which exhibits excellent resistance to SSC in a stable manner.
    [0022] The low alloy oil well steel tube according to the present invention includes a chemical composition consisting, in% by weight, in C: 0.40 to 0.65%, Si: 0, 05 to 0.50%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.0020% or less, Cu: 0.15% or less, Cr: 0.40 to 1 , 50%, Mo: 0.50 to 2.50%, V: 0.05 to 0.25%, Ti: 0 to less than 0.01%, Nb: 0.01 to 0.2%, Al sol .: 0.010 to 0.100%, N: 0.006% or less, B: 0 to 0.0015%, and Ca: 0 to 0.003%, the balance being Fe and impurities, and a structure consisting of tempered martensite and 0 less than 2% in the volumetric fraction of retained austenite. A grain size number of a previous austenite grain in the structure is 9.0 or more, and in tempered martensite, an equivalent circular diameter of a substructure surrounded by a boundary that has a crystal orientation difference of 15 ° or more among a packet limit, a block limit and a lath limit is 3 pm or less.
    [0023] The method for making a low alloy oil well steel tube according to the present invention includes a hot work step of performing a hot work on a primary material that has the chemical composition described above to form a magnifying glass, a final tempering step of quenching the magnifying glass in which a cooling rate, when a magnifying glass temperature is between 500 ° C and 100 ° C, is set to 1 ° C / s less than 15 ° The temperature of the magnifying glass at which cooling is stopped is set to 100 ° C or less, and a step of tempering the tempered magnifying glass.
    [0024] The low alloy oil well steel tube according to the present invention has a yield limit of 965 MPa (140 ksi) or more and exhibits excellent resistance to SSC in a stable manner. BRIEF DESCRIPTION OF THE DRAWINGS
    [0025] Figure 1 illustrates an austenite grain boundary map of a structure whose substructures have a grain diameter of 2.6 pm.
    [0026] Figure 2 illustrates a high-angle grain boundary map of a structure whose substructures have a grain diameter of 2.6 pm.
    [0027] Figure 3 illustrates an austenite grain boundary map of a structure whose substructures have a grain diameter of 4.1 pm.
    [0028] Figure 4 is a high-angle grain boundary map of a structure whose substructures have a grain diameter of 4.1 pm. DESCRIPTION OF THE MODALITIES
    [0029] An embodiment of the present invention will be described in detail below. In the present description, "%" means "mass%", unless otherwise noted.
    [0030] The present inventors researched and studied the SSC resistance of low-alloy oil well steel tubes that have a yield limit of 965 MPa or more and obtained the following checks.
    [0031] (1) In order to provide a high rigidity, low-alloy oil well steel tube that exhibits excellent SSC resistance in a stable manner, it is effective to use steel that has a high C content of 0 , 40% or more. The reasons for this are indicated below.
    [0032] In general, a low alloy oil well steel tube is adjusted to have a metal structure that mainly includes tempered martensite, by quenching and tempering after hot rolling. Conventionally, it is believed that, as carbides are more spheroidized in the tempering process, SSC resistance is further improved. Precipitating carbides mainly include cementite, and the rest of the carbides include alloy carbides (Mo carbides, V carbides and Nb carbides, and Ti carbides, if Ti is contained). If carbides precipitate at a grain boundary, since carbides are flatter, SSC is more likely to occur with these carbides as the starting point. In other words, since carbides are closer to a spherical shape, carbides at the grain boundary are less likely to cause SSC, and then resistance to SSC is intensified. So, in order to improve resistance to SSC, spheroidization of carbides, in particular cementite, is desirable.
    [0033] It is known that carbides can be spheroidized by tempering at the maximum possible temperature. However, the high temperature tempering decreases the displacement density inside the steel tube. The decrease in displacement density, per se, is effective for intensifying SSC resistance. However, in general, this can cause a decrease in stiffness. A displacement serves as a trapping site for hydrogen, so if the displacement density is high, it is difficult to provide excellent resistance to SSC in a stable manner. Containing alloying elements that enhance the resistance to softening by tempering, such as Mo and V, is effectively to suppress the decrease in stiffness caused by tempering at high temperature. However, such an effect has a limit.
    [0034] If 0.40% or more of C is contained, the spheroidization of carbides, in particular cementite, is accelerated and, in addition, many carbides precipitate in steel. Then, the steel can be reinforced by resistance to precipitation, regardless of the displacement density. In other words, tempering a low-alloy steel that has a high C content under suitable tempering conditions allows for the expectation of ensuring rigidity by precipitation resistance resulting from the precipitation of many carbides and guaranteeing resistance to SSC resulting from the spheroidization of carbides.
    [0035] According to what has been described above, if a C content is 0.40% or more, a large amount of carbides will precipitate and disperse and then the steel stiffness can be further intensified by resistance to precipitation, regardless of displacement density. In addition, if a C content is 0.40% or more, the concentration of the alloying elements in the cementite decreases and the cementite is spheroidized. Then, SSC resistance is stabilized, while high rigidity is achieved. In addition, if a C content is 0.40% or more, the volumetric fraction of martensite in the structure increases. Since the volume fraction of martensite is higher, the displacement density after tempering decreases further, and then the resistance to SSC is also stabilized.
    [0036] In order to reach the flow limit of 965 MPa or more, it is preferable that the structure consists substantially of the tempered martensite of single phase; and the volumetric fraction of austenite retained for the entire structure (hereinafter referred to as the volumetric fraction of austenite retained) (%) is as low as possible. If the structure contains any phase other than tempered martensite (for example, bainite), the high rigidity mentioned above cannot be achieved. In addition, if the volumetric fraction of austenite retained is high, the stiffness varies. Consequently, the structure of a low alloy oil well steel tube must be a structure consisting of tempered martensite and 0 to less than 2% in the volumetric fraction of retained austenite.
    [0037] (2) In order to provide a low alloy oil well steel tube that has a high stiffness of 965 MPa or more and that exhibits a stable resistance to SSC, the tempered martensite structure is makes it thinner. The tempered martensite contains a plurality of prior austenite grains, a plurality of packages, a plurality of blocks and a plurality of slats. More specifically, the tempered martensite contains a plurality of prior austenite grains, and each prior austenite grain includes a plurality of packages. Each package includes a plurality of plate-like blocks, and each block includes a plurality of strips.
    [0038] Among the regions of tempered martensite defined by the limits, such as the package limits, the block limits and the lath limits, a region surrounded by a high angle grain limit is defined as "substructure." In addition, among the respective limits mentioned above (packet limits, block limits and lath limits), limits that have a crystal orientation difference of 15 ° or more are defined as “angle grain limits high."
    [0039] Since the previous austenite grains and the substructures of a low alloy oil well steel tube that has a yield limit of 965 MPa or more are finer, excellent resistance to SSC can be provided in a stable manner. More specifically, if the grain size number of the previous austenite grains that conform to ASTM E112 is 9.0 or more and the equivalent circular diameter of the substructures is 3 pm or less, a low oil well steel tube alloy which has a high stiffness of 965 MPa or more and which exhibits stable SSC resistance can be provided.
    [0040] (3) In order to make the equivalent circular diameter of the substructures 3 pm or less, preferably, the final tempering conditions during the manufacturing process are controlled. More specifically, in the final temper, the cooling rate for a magnifying glass temperature range of 500 to 100 ° C is adjusted to 1 ° C / s or more, and the magnifying glass temperature at which cooling is stopped (hereinafter referred to as coma cooling interruption temperature) is set to 100 ° C or less.
    [0041] (4) Before final tempering, intermediate heat treatment can be carried out. More specifically, the magnifying glass subjected to hot lamination is embedded in a point that is an Ai point or more (an Ad point or an AM point). In this case, since austenite is produced in the structure, the previous austenite grains are further refined, providing excellent resistance to SSC.
    [0042] Based on the above checks, the present inventors have completed the following invention.
    [0043] The low alloy oil well steel tube according to the present invention includes a chemical composition consisting, in% by weight, in C: 0.40 to 0.65%, Si: 0, 05 to 0.50%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.0020% or less, Cu: 0.15% or less, Cr: 0.40 to 1 , 50%, Mo: 0.50 to 2.50%, V: 0.05 to 0.25%, Ti: 0 to less than 0.01%, Nb: 0.01 to 0.2%, Al sol .: 0.010 to 0.100%, N: 0.006% or less, B: 0 to 0.0015%, and Ca: 0 to 0.003%, the balance being Fe and impurities, and a structure consisting of tempered martensite and 0 less than 2% in the volumetric fraction of austenite retained, and a grain size number of a previous austenite grain in the structure is 9.0 or more, and, in tempered martensite, an equivalent circular diameter of a substructure surrounded by a limit that has a crystal orientation difference of 15 ° or more out of a packet limit, a block limit and a slat limit is 3 pm or less.
    [0044] The method for making the low alloy oil well steel tube according to the present invention includes a hot work step of performing a hot work on a primary material that has the chemical composition described above to form a magnifying glass, a final tempering step of quenching the magnifying glass, in which a cooling rate for the magnifying glass between 500 ° C and 100 ° C is set to 1 ° C / s less than 15 ° C / s and the temperature the magnifying glass on which cooling is stopped is set to 100 ° C or less; and a step of tempering the tempered loupe.
    [0045] The above manufacturing method can additionally include an intermediate heat treatment step of soaking the magnifying glass at a temperature of a point Ai or more, after the hot work step and before the final tempering step.
    [0046] The low alloy oil well steel tube, according to the present invention, and the method for manufacturing it will be described in detail below. CHEMICAL COMPOSITION
    [0047] The low alloy oil well steel tube, according to the present invention, has the following chemical composition.
    [0048] C: 0.40 to 0.65%
    [0049] The low alloy oil well steel tube according to the present invention has a carbon content (C) that is higher than that of conventional low alloy oil well steel tubes. As a result of a large amount of C being contained, a large amount of fine carbides is dispersed in the steel, and the steel's stiffness is thus intensified. Examples of carbides include cementite and alloy carbides (for example, Mo carbides, V carbides, Nb carbides and Ti carbides). In addition, the substructures become thinner, and resistance to SSC thus increases. If the C content is excessively low, the effect mentioned above cannot be achieved. On the other hand, if the C content is excessively high, the hardness of the steel in the as-quenched condition decreases, resulting in an increase in the susceptibility of corrosion to tempering. So, the C content is 0.40 to 0.65%. The lower limit of the C content is preferably 0.50%, more preferably more than 0.50%, even more preferably 0.55%. The upper limit of the C content is preferably 0.62%, more preferably 0.60%.
    [0050] Si: 0.05 to 0.50%
    [0051] Silicon (Si) deoxides steel. If the Si content is excessively low, this effect cannot be achieved. On the other hand, if the Si content is excessively high, resistance to SSC decreases. So, the Si content is 0.05 to 0.50%. The lower limit of the Si content is preferably 0.10%, more preferably 0.20%. The upper limit of the Si content is preferably 0.40%, more preferably 0.35%.
    [0052] Mn: 0.10 to 1.00%
    [0053] Manganese (Mn) deoxides steel. If the Mn content is excessively low, this effect cannot be achieved. On the other hand, if the Mn content is excessively high, manganese is segregated at the grain limits, along with impurity elements, such as phosphorus (P) and sulfur (S). As a result, the SSC resistance of the steel decreases. So, the Mn content is 0.10 to 1.00%. The lower limit of the Mn content is preferably 0.20%, more preferably 0.28%. The upper limit of the Mn content is preferably 0.80%, more preferably 0.50%.
    [0054] P: 0.020% or less
    [0055] Phosphorus (P) is an impurity. Phosphorus is segregated at the grain boundaries and thus decreases the SSC resistance of steel. Therefore, the P content is preferably as low as possible. So, the P content is 0.020% or less. The P content is preferably 0.015% or less, more preferably 0.012% or less.
    [0056] S: 0.0020% or less
    [0057] Sulfur (S) is an impurity, as well as phosphorus. Sulfur is segregated at the grain boundaries and thus decreases the SSC resistance of steel. Therefore, the S content is preferably as low as possible. So, the S content is 0.0020% or less. The S content is preferably 0.0015% or less, more preferably 0.0010% or less.
    [0058] Cu: 0.15% or less
    [0059] Copper (Cu) is an impurity. Copper weakens steel and thus decreases the SSC resistance of steel. Therefore, the Cu content is preferably as low as possible. So, the Cu content is 0.15% or less. The upper limit of the Cu content is preferably less than 0.03%, more preferably 0.02%, even more preferably 0.01%.
    [0060] Cr: 0.40 to 1.50%
    [0061] Chromium (Cr) intensifies the hardness of the steel and the rigidity of the steel. On the other hand, if an excessive amount of Cr is contained, the hardness of the steel decreases and the SSC resistance of the steel decreases. So, the Cr content is 0.40 to 1.50%. The lower limit of the Cr content is preferably 0.45%. The upper limit of the Cré content, preferably 1.30%, more preferably 1.00%.
    [0062] Mo: 0.50 to 2.50%
    [0063] Molybdenum (Mo), as described above, forms carbides and, thus, intensifies the resistance to softening by tempering and, consequently, contributes to the intensification of resistance to SSC by tempering at high temperature. If the Mo content is excessively low, this effect cannot be achieved. On the other hand, if the Mo content is excessively high, the above effect is saturated. So, the Mo content is 0.50 to 2.50%. The lower limit of the Mo content is preferably 0.60%, more preferably 0.65%. The upper limit of the Mo content is 2.0%, more preferably 1.6%.
    [0064] V: 0.05 to 0.25%
    [0065] Vanadium (V), as described above, forms carbides and, thus, intensifies the resistance to softening by tempering and, consequently, contributes to the intensification of resistance to SSC by tempering at high temperature. If the V content is excessively low, this effect cannot be achieved. On the other hand, if the V content is too high, the hardness of the steel decreases. So, the V content is 0.05 to 0.25%. The lower limit of the V content is preferably 0.07%. The upper limit of the V content is preferably 0.15%, more preferably 0.12%.
    [0066] Nb: 0.01 to 0.2%
    [0067] Niobium (Nb) combines with C and / or N to form carbides, nitrides or carbonitrides. These precipitates (carbides, nitrides and carbonitrides) subject the substructures of a steel to grain refinement due to the pinning effect and, thus, intensify the SSC resistance of the steel. If the Nb content is excessively low, this effect cannot be achieved. On the other hand, if the Nb content is excessively high, the excess nitrides are produced and, thus, destabilize the SSC resistance of the steel. So, the Nb content is 0.01 to 0.2%. The lower limit of the Nb content is preferably 0.012%, more preferably 0.015%. The upper limit of the Nb content is preferably 0.10%, more preferably 0.05%.
    [0068] Al sol .: 0.010 to 0.100%
    [0069] Aluminum (Al) deoxides steel. If the Al content is excessively low, steel deoxidation is insufficient, resulting in a decrease in the SSC resistance of the steel. On the other hand, if the Al content is excessively high, oxidations are produced, resulting in a decrease in the SSC resistance of the steel. So, the Al content is 0.010 to 0.100%. The lower limit of the Al content is preferably 0.015%, more preferably 0.020%. The upper limit of the Al content is preferably 0.080%, more preferably 0.050%. In this description, the content of "Al" means the content of "Al soluble in acid," that is, "Al sol.".
    [0070] N: 0.006% or less
    [0071] Nitrogen (N) is an impurity. Nitrogen forms a nitride and thus destabilizes the SSC resistance of steel. Therefore, the N content is preferably as low as possible. So, the N content is 0.006% or less. The N content is preferably 0.005% or less, more preferably 0.004% or less.
    [0072] The chemical composition balance of the low alloy oil well steel tube is Fe and impurities. The impurities referred to in this document are elements that are mixed from ore and scrap used as raw materials for steel or from, for example, the environment in the manufacturing process. IN RELATION TO OPTIONAL ELEMENTS
    [0073] The low alloy oil well steel tube may additionally contain Ti instead of a part of Fe.
    [0074] Ti: 0 less than 0.01%
    [0075] Titanium (Ti) is an optional element. Ti forms nitrides and, thus, submits steel to grain refinement. Ti additionally suppresses the surface corrosion of a casting, which is occasionally generated during continuous casting. During continuous casting, the dissolved N combines with Al in a casting, the nitrides of Al precipitate due to induction of deformation. In this case, the surface of the casting becomes prone to corroding. Ti, preferably, combines with dissolved N to form nitrides of Ti, and thus suppress the precipitation of nitrides of Al. Then, the surface corrosion of the casting during continuous casting is suppressed. Even if only a small amount of Ti is contained, these effects can be achieved. However, if the Ti content is excessively high, the TiN becomes coarse and thus destabilizes the SSC resistance of the steel. So, the Ti content is 0 less than 0.01%. The lower limit of the Ti content is preferably 0.001%, more preferably 0.003%. The upper limit of the Ti content is preferably 0.008%, more preferably 0.006%.
    [0076] The low alloy oil well steel tube may additionally contain B instead of a part of Fe.
    [0077] B: 0 to 0.0015%
    [0078] Boron (B) is an optional element. Boron intensifies the hardness and intensifies the stiffness of the steel. Even if only a small amount of B is contained, the above effect can be achieved. However, if the B content is excessively high, M23CB6 is formed at the grain boundaries, resulting in a decrease in the SSC resistance of the steel. Therefore, a low content of B is preferred, even if B is contained. So, the B content is 0 to 0.0015% or less. The lower limit of the B content is preferably 0.0003%, more preferably 0.0005%. The upper limit of the B content is preferably 0.0012%, more preferably 0.0010%.
    [0079] The low alloy oil well steel tube may additionally contain Ca instead of a part of Fe.
    [0080] Ca: 0 to 0.003%
    [0081] Calcium (Ca) is an optional element. Calcium combines with S in a steel to form sulfides and thus improves the shapes of inclusions and intensifies the hardness of the steel. Even if only a small amount of Ca is contained, the above effect can be achieved. On the other hand, if the Ca content is excessively high, this effect is saturated. So, the Ca content is 0 to 0.003%. The lower limit of the Ca content is preferably 0.0005%, more preferably 0.0010%. The upper limit of the Ca content is preferably 0.0025%, more preferably 0.0020%. STRUCTURE (MICROSTRUCTURE)
    [0082] The structure of the low alloy oil well steel tube according to the present invention mainly includes tempered martensite. More specifically, the matrix in the structure consists of tempered martensite and 0 less than 2% in the volumetric fraction of retained austenite.
    [0083] For low alloy oil well steel tube, according to the present invention, the quench cooling rate is restricted from the perspective of preventing quench corrosion due to the relatively high C content in the steel . Then, the retained austenite can remain in the steel tube after quenching. In the final product (state after tempering), the retained austenite causes great variation in stiffness. Therefore, the volumetric fraction of austenite retained is preferably as low as possible. The volumetric fraction of austenite retained is preferably less than 1%. The steel tube of low-alloy oil well, according to the present invention, has more preferably a structure consisting of tempered martensite, with the volumetric fraction of austenite retained being 0%.
    [0084] The volumetric fraction of austenite retained is measured as follows, using X-ray diffractometry. A sample that includes a central part in the wall thickness of a steel tube from produced oil well is collected. The surface of the collected sample is chemically polished. The chemically polished surface is subjected to X-ray diffraction using a CoKa ray as an incident X-ray. From the integrated surface intensities of the surface (211), the surface (200) and the surface (110) of ferrite, and the integrated surface intensities of the surface (220), the surface (200) and the surface (111) of austenite, the volumetric fraction of austenite retained is determined and obtained. PREVIOUS AUSTENITE GRAIN GRAIN SIZE
    [0085] The grain size number of the previous austenite grains in the above structure is 9.0 or more. The grain size number of the previous austenite grains referred to in this description is measured in accordance with ASTM E112. If the grain size number of previous austenite grains is 9.0 or more, the steel exhibits excellent resistance to SSC, even if the steel has a yield limit of 965 MPa (140 ksi) or more. If the grain size number of the previous austenite grains is less than 9.0, the steel has low resistance to SSC, where the steel has the previously mentioned stiffness. The grain size number of the preceding austenite grains is preferably more than 9.0, more preferably 10.0 or more.
    [0086] The grain size number of the previous austenite grains can be measured using a steel product after quenching and before tempering (which is called as-quenched product) or it can also be measured with use of a tempered steel product. The alternate use of these steel products does not provide any change in the size of the previous austenite grains. SUBSTRUCTURE SIZE
    [0087] As described above, the tempered martensite contains a plurality of previous austenite grains, a plurality of packages, a plurality of blocks and a plurality of slats. Among the regions of tempered martensite that are defined by the limits that are packet limits, block limits and lath limits, the equivalent circular diameter of a substructure surrounded by a limit with a crystal orientation difference of 15 ° or more (limit angle grain) is 3 pm or less.
    [0088] The SSC resistance of a steel that has a high stiffness of 965 MPa or more depends not only on the size of the previous austenite grain, but also on the size of the substructure. If the grain size number of the previous austenite grains is 9.0 or more and the equivalent circular diameter of the substructures is 3 pm or less, a low-alloy oil well steel tube that has a high stiffness of 965 MPa or more and which exhibits stably excellent resistance to SSC can be provided. The equivalent circular diameter of the substructures is preferably 2.5 pm or less, more preferably 2.0 pm or less.
    [0089] The equivalent circular diameter of the substructures is measured by the following method. A sample that includes an observation surface of 25 pm to 25 pm, with the center in the wall thickness as the center being collected from an arbitrary transverse surface of a low alloy oil well steel tube (a perpendicular surface axial direction of the low alloy oil well steel tube).
    [0090] The observation surface is subjected to crystal orientation analysis by backscattered electron diffraction imaging (EBSP). Then, based on the results of the analysis, the limits that have a difference in crystal orientation of 15o or more are plotted on the observation surface to identify a substructure.
    [0091] The equivalent circular diameter of each of the specified substructures is measured. The equivalent circular diameter means a diameter of a circle in which the area of the substructure is converted into a circle having the same area. The equivalent circular diameter can be measured, for example, using the method of measuring the interception length of the crystal grain medium defined in document JIS G 0551 to obtain the grain size of the medium. The mean of the equivalent circular diameters obtained from the respective substructures is defined as the equivalent circular diameter of the substructures referred to in the present description.
    [0092] Figures 1 and 2 each illustrate an exemplary structure, whose equivalent circular diameter of the substructures is 2.6 pm. Figure 1 is a grain boundary map of anterior austenite, and Figure 2 is a high angle grain boundary map. The structure is one obtained from a steel that has a previous austenite grain size number of 10.5 and that contains C: 0.51%, Si: 0.31%, Mn: 0.47%, P : 0.012%, S: 0.0014%, Cu: 0.02%, Cr: 1.06%, Mo: 0.67%, V: 0.098%, Ti: 0.008%, Nb: 0.012%, Ca: 0 , 0018%, B: 0.0001%, Al sol .: 0.029% and N: 0.0034%, the balance being Fe and impurities.
    [0093] Figures 3 and 4 each illustrate an exemplary structure, whose grain diameter of the substructures is 4.1 pm. Figure 3 is a grain boundary map of anterior austenite, and Figure 4 is a high angle grain boundary map. The structure is one obtained from a steel that has a previous austenite grain size number of 11.5 and that contains C: 0.26%, Si: 0.19%, Mn: 0.82%, P : 0.013%, S: 0.0008%, Cu: 0.01%, Cr: 0.52%, Mo: 0.70%, V: 0.11%, Ti: 0.018%, Nb: 0.013%, Ca : 0.0001%, B: 0.0001%, Al sol .: 0.040% and N: 0.0041%, the balance being Fe and impurities. ELASTIC LIMIT
    [0094] The low alloy oil well steel tube, according to the present invention, has a flow limit of 965 MPa or more (140 ksi or more). The yield limit is defined based on the 0.2% yield limit. Although the upper limit of the yield limit is not specifically limited, the upper limit of the yield limit is, for example, 1,150 MPa. YIELD RATE
    [0095] The low alloy oil well steel tube according to the present invention, which has the chemical composition and structure described above, has YR yield rate (= YS yield limit / TS tensile strength) 0.90 or more. If the YR yield rate is less than 0.90, a phase other than tempered martensite (eg bainite) is contained in the structure. In this case, resistance to SSC decreases. The YR yield rate of the low alloy oil well steel tube according to the present invention is 0.90 or more, and the structure consists of the single phase of tempered martensite, or tempered martensite and 0 unless 2% of retained austenite. Therefore, the low alloy oil well steel tube, according to the present invention, has a high yield limit (965 MPa or more), as well as excellent resistance to SSC. MANUFACTURING METHOD
    [0096] An example of the method of manufacturing the low alloy oil well steel tube according to the present invention will be described. In this example, a method of making seamless steel pipe (low alloy oil well steel pipe) will be described.
    [0097] A steel having the chemical composition described above is melted and refined by a well-known method. Subsequently, the molten steel becomes a continuously melted material by the continuous casting process. The continuously melted material can be, for example, a plate, a semi-finished material or a billet. In addition, molten steel can become an ingot through the ingot production process.
    [0098] The plate, the semi-finished material or the ingot are hot worked on a billet. The billet can be formed by hot rolling or hot forging.
    [0099] The billet is hot worked to produce a magnifying glass. First, the billet is heated in a heating oven. The billet extracted from the heating furnace is subjected to hot work to produce a magnifying glass (seamless steel tube). For example, the Mannesmann process is performed like hot work to produce a magnifying glass. In this case, a round billet is laminated by drilling using a drilling machine. The perforated rolled round billet is additionally hot rolled in a magnifying glass using, for example, a mandrel mill, a reducer or a dimensioning mill. The loupe can be produced from the billet by another hot work process.
    [00100] The hot-worked loupe is subjected to tempering for at least one reheating and tempering.
    [00101] A tempering temperature, in tempering, is a well-known temperature (temperature of an Ac3 point or more). The upper limit of the tempering temperature is preferably 900 ° C or less. In that case, the previous austenite grains become additionally finer.
    [00102] Tempering can be carried out once or a plurality of times. A magnifying glass temperature at which cooling during the final quench (ie, cooling interruption temperature) is interrupted is 100 ° C or less. If the cooling interruption temperature is higher than 100 ° C, the equivalent circular diameter of the substructures becomes greater than 3 pm.
    [00103] In addition, in the final temper, the cooling rate, when the magnifying glass temperature is between 500 ° C and 100 ° C, is adjusted to 1 ° C / s less than 15 ° C / s. If the cooling rate for the temperature range mentioned above is less than 1 ° C / s, the equivalent circular diameter of the substructures becomes greater than 3 pm. Furthermore, in the structure, not only martensite, but also bainite is produced. On the other hand, if the cooling rate is 15 ° C / s or more, quench corrosion is likely to occur. If the cooling rate, when the magnifying glass temperature is between 500 ° C and 100 ° C, is 1 ° C / s less than 15 ° C / s, the equivalent circular diameter of the substructures becomes 3.0 pm or less and temper corrosion is less likely to occur. The lower limit of the cooling rate is preferably 2 ° C / s, more preferably 3 ° C / s.
    [00104] After the final tempering is carried out, tempering is carried out at a tempering temperature of less than the Aci point. The tempering temperature is arbitrarily adjusted according to the chemical composition of the magnifying glass and the desired flow limit. The tempering temperature is preferably 650 ° C to 700 ° C, and the impregnation period for the tempering temperature is preferably 15 to 120 minutes. The volumetric fraction of austenite retained can also be reduced by adjusting the tempering temperature. As a result of the tempering, the flow limit of the loupe becomes 965 MPa or more. Tempering and tempering can be performed a plurality of times.
    [00105] The low alloy oil well steel tube according to the present invention is produced by the manufacturing process described above. INTERMEDIATE HEAT TREATMENT PROCESS
    [00106] In the manufacturing method described above, tempering is carried out after hot work. However, another heat treatment (intermediate heat treatment) can be carried out after hot work.
    [00107] For example, the hot-worked loupe can be subjected to normalization. More specifically, the hot-worked loupe is kept at a temperature that is higher than an A3 point (eg 850 ° C to 950 ° C) for a given period of time and then allowed to cool naturally . The maintenance period is, for example, 15 to 120 minutes. For normalization, in general, after hot work, the magnifying glass is cooled to normal temperature and then heated to the point of Acs or more. However, in the present invention, normalization can be performed by keeping the magnifier as it is at a temperature of the point Acs or more after hot work.
    [00108] If normalization is performed, the grains (previous austenite grains) of the steel are further refined. More specifically, if the standard magnifier is tempered, the grain size number of the previous austenite grains in the post-cooling material (as-quenched) becomes 10.0 or more.
    [00109] In addition, instead of the normalization described above, tempering can be performed. In that case, as described above, tempering is performed a plurality of times.
    [00110] In addition, the intermediate heat treatment provides an effect similar to the above effect, even if it is a heat treatment in a two-phase temperature range, ferrite + austenite (hereinafter referred to as “two-phase heating”). In intermediate heat treatment, if at least part of the steel structure is transformed into austenite, an effect that is favorable to grain refinement can be achieved. Consequently, in the intermediate heat treatment, it is preferred that at least the magnifying glass is soaked at a temperature of the point Ac1 or higher.
    [00111] If the intermediate heat treatment is carried out before the final quench, the previous austenite grains are further refined and the resistance to SSC is further intensified.
    [00112] As described above, the cooling stop temperature in the final temper is set to 100 ° C or less, and the cooling rate, when the magnifying glass temperature is between 500 ° C and 100 ° C, is set to 1 ° C / s less than 15 ° C / s, whereby the grain size number of the previous austenite grains becomes 9.0 or more and the equivalent circular diameter of the substructures becomes 3.0 pm or less. Then, a low alloy oil well steel tube that has a yield limit of 965 MPa or more and that exhibits excellent SSC resistance can be provided in a stable manner. EXAMPLE
    [00113] Steel ingots A to K, which have the respective chemical compositions indicated in table 1, were produced.
    * indicates that the relevant content is outside the scope of the claims in this application.
    [00114] The symbol in table 1 indicates that the content is substantially "0"%. Referring to Table 1, the chemical compositions of steels A to H were within the scope of the present invention. On the other hand, the C content in steel I was less than the lower limit of the C content in the present invention. The Ti content in steel J was more than the upper limit of the Ti content in the present invention. The Mn content in K steel was more than the upper limit of the Mn content in the present invention.
    [00115] After the respective ingots were heated, the seamless steel tubes, each with an outer diameter of 244.5 mm and a wall thickness 10 of 13.8 mm, were produced by hot work (perforation lamination ). The seamless steel tubes were subjected to intermediate heat treatment and final quenching by reheating the tubes to the temperatures indicated in table 2.


    * indicates that the relevant value or steel is within the scope of the claims in this application. 9E / ZZ
    [00116] The “intermediate heat treatment” column in table 2 indicates the levels of intermediate heat treatments performed for seamlessly worked seamless steel tubes from the respective test numbers. More specifically, the “Type” column in the “intermediate heat treatment” column indicates the type of heat treatment performed (normalization, tempering or heating of the biphasic region). For example, in the case of number 2, it is indicated that the normalization was carried out at a heat treatment temperature of 920 ° C, since the method of intermediate heat treatment and cooling was natural cooling. In the case of number 3, it is indicated that the quenching was carried out at a quenching temperature of 920 ° C, and the forced cooling was carried out with the use of steam spray. In the case of number 4, it is indicated that the relevant seamless steel tube was heated to a temperature that is the point Ad or more and then allowed to cool naturally, in the case of number 7, it is indicated that the magnifying glass it is immersed in a tempered oil tank for reinforced cooling and, in the case of number 18, it is indicated that the magnifying glass is immersed in a water tank for reinforced cooling.
    [00117] The “final temper” column, in table 2, indicates the final temper levels achieved for the seamless steel tube of the respective test numbers, which was subjected to the respective intermediate heat treatments. More specifically, the “cooling rate” column indicates cooling rates (° C / s) when the temperatures of the respective seamless steel tubes were between 500 ° C and 100 ° C.
    [00118] In table 2, the symbol in the “intermediate heat treatment” column indicates that no intermediate heat treatment has been carried out for the relevant number. PREVIOUS AUSTENITE GRAIN SIZE TEST
    [00119] With the use of seamless steel tubes (after-cooling products (as-quenched)) subjected to the final quench, a previous austenite grain size test was conducted. More specifically, the samples were collected by cutting the post-cooling products (as-quenched) in the direction of wall thickness. Then, the samples were embedded in resin, and a surface of each sample corresponding to the cut surface perpendicular to the axial direction of the seamless steel tube (hereinafter referred to as the observation surface) was incised with the use of picric acid. The notched observation surface was observed, and the grain size number of the previous austenite grains was determined in accordance with ASTM E112. REFERENCE
    [00120] The seamless steel tubes submitted to the final temper were 10 subjected to tempering, at the respective tempering temperatures (° C), for the impregnation period (minutes) indicated in table 3 to adjust the seamless steel tubes of the numbers in order to have a yield limit of 965 MPa (140 ksi) or more.

    EVALUATION TEST FOR SEAMLESS STEEL PIPES SUBMITTED TO TEMPERING MICRO-STRUCTURE OBSERVATION TEST AND VOLUMETRIC FRACTION MEASUREMENT TEST OF RETENTED AUSTENITE
    [00121] The following microstructure observation test was conducted for the seamless steel tube of each number, which was subjected to tempering. A central part in the wall thickness of a cross section of each seamless steel tube (surface perpendicular to the axial direction of the seamless steel tube) was carved using nital. Three arbitrary visual fields (each with an area of 100 pm x 100 pm) in the central part notched in the wall thickness were observed. For observation, a scanning electron microscope (SEM) was used. As a result of the carving, the tempered martensite was confirmed.
    [00122] The results of the microstructure observation are shown in table 3. The symbol “M” in the table means that the microstructure of the relevant number consists of tempered martensite or tempered martensite and retained austenite. The “B” symbol in the Table means that the microstructure of the relevant number is a bainite structure.
    [00123] In each of the numbers 1 to 21, the microstructure was a structure consisting of tempered martensite or tempered martensite and retained austenite. At number 22, a bainite structure was observed.
    [00124] By means of the X-ray diffractometry mentioned above, the volumetric fraction (%) of the austenite retained in each steel was measured. More specifically, a sample that includes a central part in the wall thickness of each seamless steel tube was collected. The surfaces of the collected sample were chemically polished. The chemically polished surface was subjected to X-ray diffraction using a CoKa ray, as an incident X-ray. By forming the integrated surface intensities of the surface (211), surface (200) and surface (110) of ferrite and the integrated surface intensities of the surface (220), surface (200) and surface (111) of austenite, the volumetric fraction (%) of retained austenite was determined.
    [00125] The results of the determination are shown in table 3. In each of the numbers, the volumetric fraction of austenite retained was less than 2%. TEST FOR MEASURING EQUIVALENT CIRCULAR DIAMETER OF SUBSTRUCTURES
    [00126] The seamless steel tube of each number, which was subjected to tempering, was subjected to crystal orientation analysis using EBSP by the method described above to obtain the equivalent circular diameter of the substructures. ELASTIC LIMIT TEST:
    [00127] From each of the seamless steel tubes subjected to tempering, a round bar tension test specimen that has a parallel part measurement of 6 mm outside diameter and 40 mm in length was collected. The parallel part was parallel to the axial direction of the seamless steel tube. Using each of the round bar tension test specimens collected, a stress test was conducted at normal temperature (25 ° C) to obtain the yield limit YS (0.2% of proof effort) (MPa) and the tensile strength TS (MPa). As a result, as shown in table 3, the flow limit was 965 MPa (140 ksi) or more in each of the numbers. SSC RESISTANCE TEST
    [00128] The following constant load tension test was performed for the seamless steel tube of each number. From the seamless steel tube of each number, three test specimens of rounded bar tension, each of which includes a parallel part extending in the axial direction, were collected. The parallel part of each rounded bar strain test specimen measured 6.35 mm in outer diameter and 25.4 mm in length. A constant load voltage test was conducted at normal temperature (24 ° C) in a test bath based on the NACE TM0177 A method. For the test bath, an aqueous solution of 5% NaCI + 0.5% CH3COOH charged with a 0.01 MPa (0.1 bar) hydrogen sulfide gas (the balance being CO2 gas) was used. Under the condition of pH 3.5, a constant load that is 90% of the yield limit measured in the stress test was imposed on each of the test specimens (three in total) in the test bath. It was determined that no SSC occurred if the test specimen did not rupture even after the passage of 720 hours, and it was determined that SSC occurred if the test specimen ruptured during the test (i.e., within 720 hours). TEST RESULTS
    [00129] Table 3 indicates the test results. The “NF” symbol in the “SSC resistance test” column in Table 3 indicates that the relevant test specimen did not break even after 720 hours had passed (that is, no SSC occurred). The “F” symbol indicates that the relevant test specimen was interrupted during the test (ie, SSC has occurred).
    [00130] In each of the numbers 1 to 4, 6a10e12a17, the chemical composition of the primary material was within the scope of the present invention and the production conditions (the cooling rate and the cooling stop temperature in the final quench) were appropriate . Then, the structure consisted of tempered martensite and 0 less than 2% retained austenite, and the grain size number of the previous austenite grains was 9.0 or more. In addition, the equivalent circular diameter of the substructures was 3.0 pm or less. In addition, the YR yield rate was 0.90 or more. Then, in the SSC resistance test, none of the three test specimens broke and excellent resistance to SSC was obtained in a stable manner.
    [00131] In particular, in each of the numbers 2 to 4, 6 to 8, 10, 12 to 14,16 and 17, the normalization, tempering or heating of the biphasic band was carried out as the intermediate heat treatment. So, the grain size number of the previous austenite grains in the seamless steel tube for each of these numbers was 10.0 or more, which is higher than those in numbers 1, 9 and 15, in which no treatment intermediate thermal was performed.
    [00132] On the other hand, in each of numbers 5 and 11, although the chemical composition of the primary material and the cooling rate in the final quench were appropriate, the temperature of the cooling interruption was more than 100 ° C. Then, the equivalent circular diameter of the substructures was more than 3.0 pm, and in the SSC resistance test, all of the three test specimens broke.
    [00133] In number 18, the C content in the primary material was excessively low. In addition, the cooling rate in the final quench was more than 15 ° C / s. Since the C content was low, no quench corrosion occurred, but the equivalent circular diameter of the substructures was more than 3.0 pm, and in the SSC resistance test, all of the three test specimens broke.
    [00134] At number 19, the Ti content in the primary material was excessively high. Then, in the SSC resistance test, two of the three test specimens broke, and the SSC resistance was unstable.
    [00135] At number 20, the Mn content in the primary material was excessively high. Then, in the SSC resistance test, two of the three test specimens broke, and the SSC resistance was unstable.
    [00136] In number 21, although the chemical composition of the primary material was within the scope of the present invention, the cooling rate in the final temper was excessively high. Then, quench corrosion occurred.
    [00137] In number 22, although the chemical composition of the primary material was within the scope of the present invention, the cooling rate in the final temper was excessively low. Then, the structure becomes a bainite structure, and the YR yield rate was less than 0.90. Then, in the SSC resistance test, all of the three test specimens broke.
    [00138] Although the embodiment of the present invention has been described above, the embodiment described above is a mere illustration for carrying out the present invention. Therefore, the present invention is not limited to the modality, and the present invention can be carried out with the modality arbitrarily modified, without departing from the spirit of the modality.
    权利要求:
    Claims (3)
    [0001]
    1. Low alloy oil well steel tube CHARACTERIZED by the fact that it comprises: a chemical composition consisting, in% by weight, in C: 0.40 to 0.65%, Si: 0.05 to 0, 50%, Mn: 0.10 to 1.00%, P: 0.020% or less, S: 0.0020% or less, Cu: 0.15% or less, Cr: 0.40 to 1.50%, Mo: 0.50 to 2.50%, V: 0.05 to 0.25%, Ti: 0 to less than 0.01%, Nb: 0.01 to 0.2%, sol. Al: 0.010 to 0.100%, N: 0.006% or less, B: 0 to 0.0015%, and Ca: 0 to 0.003%, the balance being Fe and impurities; and a structure consisting of tempered martensite and 0 less than 2% in the volumetric fraction of retained austenite, where the steel pipe has a yield limit of 965 MPa or more; wherein a grain size number of a previous austenite grain in the structure is 9.0 or more; and where, in tempered martensite, an equivalent circular diameter of a substructure surrounded by a boundary that has a difference in crystal orientation of 15 ° or more, within a packet boundary, a block boundary and a slat boundary is 3 pm or less.
    [0002]
    2. Method for making a low alloy oil well steel tube CHARACTERIZED by the fact that it comprises: a hot work step of performing a hot work on a primary material that has the chemical composition as defined in claim 1 for form a magnifying glass; a final hardening step of quenching the loupe, in which a cooling rate, when a loupe temperature is between 500 ° C and 100 ° C, is set to 1 ° C / s less than 15 ° C / s, and the magnifying glass temperature at which cooling is stopped is set to 100 ° C or less; and a step of tempering the cooled loupe.
    [0003]
    3. Method according to claim 2, characterized in that the method additionally comprises an intermediate heat treatment step of soaking the magnifying glass at a temperature of a point Ai or more, after the hot working step and before of the final tempering step.
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    同族专利:
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    JPWO2015011917A1|2017-03-02|
    EP3026139A1|2016-06-01|
    CN105492642A|2016-04-13|
    WO2015011917A1|2015-01-29|
    EP3026139B1|2018-11-21|
    JP5880787B2|2016-03-09|
    US20160160307A1|2016-06-09|
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    法律状态:
    2018-11-06| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-07-09| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2019-09-03| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |
    2020-02-04| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2020-06-02| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2020-11-17| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 23/07/2014, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2013-155674|2013-07-26|
    JP2013155674|2013-07-26|
    PCT/JP2014/003858|WO2015011917A1|2013-07-26|2014-07-23|Low-alloy steel pipe for oil well and production method therefor|
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