CN115298340A - High-strength steel sheet for acid-resistant line, method for producing same, and high-strength steel pipe using high-strength steel sheet for acid-resistant line - Google Patents
High-strength steel sheet for acid-resistant line, method for producing same, and high-strength steel pipe using high-strength steel sheet for acid-resistant line Download PDFInfo
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- CN115298340A CN115298340A CN202180020748.6A CN202180020748A CN115298340A CN 115298340 A CN115298340 A CN 115298340A CN 202180020748 A CN202180020748 A CN 202180020748A CN 115298340 A CN115298340 A CN 115298340A
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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Abstract
The present invention provides a high-strength steel sheet for acid-resistant pipelines, which is excellent not only in HIC resistance, but also in SSCC resistance in a severer corrosive environment and SSCC resistance in an environment with a low hydrogen sulfide partial pressure of less than 1 bar. The high-strength steel sheet for acid-resistant pipelines of the present invention is characterized by having the following composition: contains, in mass%, C:0.020 to 0.080%, si:0.01 to 0.50%, mn:0.50 to 1.80%, P:0.015% or less, S:0.0015% or less, al: 0.010-0.080%, N:0.0010 to 0.0080%, mo:0.01 to 0.50% and Ca:0.0005 to 0.0050%, the balance being Fe and unavoidable impurities, the magnetite content in the scale present on the steel sheet surface being 50% or more, the maximum Vickers hardness at 0.25mm below the steel sheet surface being 230HV or less, and the tensile strength being 520MPa or more.
Description
Technical Field
The present invention relates to a high-strength steel sheet for acid-resistant pipelines, which is suitable for pipelines in the fields of construction, marine structures, shipbuilding, civil engineering, and construction industrial machines and has excellent uniformity of material quality in the steel sheet, and a method for producing the same. The present invention also relates to a high-strength steel pipe using the high-strength steel sheet for acid-resistant line.
Background
Generally, a steel pipe is manufactured by forming a steel plate manufactured by a heavy plate mill or a hot rolling mill into a steel pipe by UOE forming, press bending, roll forming, or the like.
Among them, pipelines used for transporting crude oil and natural gas containing Hydrogen Sulfide are required to have so-called acid resistance such as Hydrogen Induced Cracking resistance (HIC resistance) and Sulfide Stress Corrosion Cracking resistance (SSCC resistance) in addition to strength, toughness, weldability, and the like. Among them, HIC is a phenomenon in which hydrogen ions generated by a corrosion reaction are adsorbed on the surface of steel, and hydrogen in an atomic state enters the inside of steel, diffuses and accumulates around nonmetallic inclusions such as MnS in the steel and a hard 2 nd phase structure, molecular hydrogen is cracked due to its internal pressure, and it has been considered as a problem in pipelines having a relatively low strength level compared to oil country tubular goods, and therefore a large number of countermeasure techniques have been disclosed. On the other hand, it is known that SSCC occurs in a high hardness region of a welded portion, and generally, it has not been considered as a problem in a high-strength seamless steel pipe for an oil well or a line pipe having a relatively low hardness. However, in recent years, the environment for crude oil and natural gas production has become more severe, and it has been reported that SSCC occurs even in the base material portion of the pipeline in an environment where the partial pressure of hydrogen sulfide is high or the pH is low, and importance has been pointed out that the SSCC resistance in a more severe corrosive environment is improved by controlling the hardness of the inner surface portion of the steel pipe. In addition, in an environment where the partial pressure of hydrogen sulfide is relatively low, micro cracks called fissures may occur, and SSCC may occur.
Generally, when manufacturing a high-strength steel sheet for a pipeline, a so-called TMCP (Thermo-Mechanical Control Process) technique combining controlled rolling and controlled cooling is applied. In order to increase the strength of a steel sheet using the TMCP technique, it is effective to control the increase in the cooling rate during cooling. However, when the controlled cooling is performed at a high cooling rate, the surface layer portion of the steel sheet is rapidly cooled, and thus the hardness of the surface layer portion is higher than that of the inside of the steel sheet. Further, work hardening occurs when the steel sheet is formed into a tubular shape, and therefore the hardness of the surface layer portion is further increased, and the SSCC resistance is lowered.
In order to solve the above-mentioned problems, for example, patent documents 1 and 2 disclose a method of controlled cooling at a high cooling rate by reheating the surface after rolling and before the bainite transformation in the surface layer portion is completed. Patent documents 3 and 4 disclose methods for producing steel plates for pipelines, in which the surface of a steel plate after accelerated cooling is heated to a temperature higher than the internal temperature using a high-frequency induction heating apparatus, thereby reducing the hardness of the surface layer portion.
On the other hand, if the scale thickness on the steel sheet surface varies, the cooling rate of the steel sheet below the surface also varies during cooling. On the other hand, patent documents 5 and 6 disclose methods for descaling a steel sheet immediately before cooling, reducing cooling unevenness due to uneven scale thickness, and improving the shape of the steel sheet.
Documents of the prior art
Patent document
Patent document 1: japanese patent No. 3951428
Patent document 2: japanese patent No. 3951429
Patent document 3: japanese patent laid-open publication No. 2002-327212
Patent document 4: japanese patent No. 3711896
Patent document 5: japanese patent laid-open publication No. 9-57327
Patent document 6: japanese patent No. 3796133
Disclosure of Invention
However, according to the studies of the present inventors, it has been found that the high-strength steel sheets obtained by the manufacturing methods described in patent documents 1 to 6 have room for improvement from the viewpoint of SSCC resistance in a more severe corrosive environment. The reason for this is as follows.
In the manufacturing methods described in patent documents 1 to 4, the conditions for controlled cooling of the steel sheet have not been sufficiently optimized, and as a result, a locally high-hardness portion is formed in the surface layer portion of the steel sheet.
In the methods described in patent documents 5 and 6, the shape of the steel sheet is improved by removing scale, reducing surface defects due to indentation of scale during hot straightening, and reducing unevenness in the cooling stop temperature of the steel sheet. However, the descaling conditions were not optimized from the viewpoint of improving SSCC resistance. In addition, cooling conditions for reducing the hardness of the surface layer portion of the steel sheet are not considered at all.
In patent documents 1 to 6, the conditions for avoiding such a micro-crack as a crack in an environment where the partial pressure of hydrogen sulfide is relatively low are not clarified.
In view of the above problems, an object of the present invention is to provide a high-strength steel sheet for acid-resistant pipelines which is excellent not only in HIC resistance but also in SSCC resistance in a severer corrosive environment and SSCC resistance in an environment with a low hydrogen sulfide partial pressure of less than 1bar, and an advantageous method for producing the same. Further, an object of the present invention is to provide a high-strength steel pipe using the high-strength steel sheet for acid-resistant pipelines.
The present inventors have conducted intensive studies to solve the above problems and found that, for further improvement of the SSCC resistance of a high-strength steel pipe, it is not sufficient to merely suppress the hardness of the surface layer portion as in the conventional case. That is, in the conventional technique, even if the hardness of the surface layer portion is suppressed as a whole, a local high-hardness portion is actually generated in the extreme surface layer portion as close as possible to the surface of the steel sheet in the surface layer portion, and SSCC is generated with this portion as a starting point. Therefore, the present inventors have repeatedly conducted a large number of experiments on the composition of the steel sheet, the properties of the scale present on the surface of the steel sheet, and the production conditions of the steel sheet in order to obtain a high-strength steel sheet in which no locally high-hardness portion is present at the extreme surface portion, specifically, at a position 0.25mm below the surface of the steel sheet.
As a result, it was found that the formation of a scale mainly composed of magnetite on the surface of the steel sheet using a predetermined composition is a necessary condition for obtaining a high-strength steel sheet having no portion having locally high hardness at a position of 0.25mm below the surface of the steel sheet. Further, it was found that in order to form a scale mainly composed of magnetite on the surface of the steel sheet, it is necessary to optimize the conditions for removing the scale in the hot rolling step and to set the cooling stop temperature in the controlled cooling within a predetermined range. Further, as a requirement concerning the production conditions, it was found that the cooling rate at 0.25mm below the surface of the steel sheet needs to be strictly controlled and the conditions thereof were successfully established. The present invention has been made based on the above findings.
That is, the gist of the present invention is as follows.
[1] A high-strength steel sheet for acid-resistant pipelines, characterized by having the following composition: contains, in mass%, C:0.020 to 0.080%, si:0.01 to 0.50%, mn:0.50 to 1.80%, P:0.015% or less, S:0.0015% or less, al: 0.010-0.080%, N:0.0010 to 0.0080%, mo:0.01 to 0.50% and Ca:0.0005 to 0.0050%, the remainder consisting of Fe and unavoidable impurities,
the ratio of magnetite in the oxide scale present on the surface of the steel sheet is 50% or more,
the maximum Vickers hardness at 0.25mm below the surface of the steel sheet is 230HV or less,
the tensile strength is 520MPa or more.
[2] The high-strength steel sheet for acid-resistant line according to the above [1], wherein the above-mentioned composition further contains, in mass%, a metal selected from the group consisting of Cu:0.30% or less, ni:0.10% or less and Cr:0.50% or less of 1 or more.
[3] The high-strength steel sheet for acid-resistant pipelines according to the above [1] or [2], wherein the above-mentioned composition further contains, in mass%, a component selected from the group consisting of Nb:0.005 to 0.1%, V:0.005 to 0.1%, ti:0.005 to 0.1%, zr:0.0005 to 0.02%, mg:0.0005 to 0.02% and REM: more than 1 of 0.0005 to 0.02 percent.
[4] A method for producing a high-strength steel sheet for acid-resistant line, characterized by heating a steel sheet having the composition described in any one of the above [1] to [3] to a temperature of 1000 to 1300 ℃,
then, the steel sheet is hot-rolled to produce a steel sheet, and descaling with a discharge pressure of 10MPa or more is performed in 50% or more passes of the hot-rolling pass,
thereafter, the steel sheet was subjected to controlled cooling under the following conditions:
steel sheet surface temperature at the start of cooling: (Ar) 3 At a temperature of-10 ℃ or higher,
average cooling rate from 750 ℃ to 550 ℃ with a thermometer of a steel plate at 0.25mm from the surface of the steel plate: 20 to 100 ℃/s of the mixture,
average cooling rate from 750 ℃ to 550 ℃ with average thermometer of steel plate: 15 ℃/sec or more, and
with a steel plate thermometer at 0.25mm below the surface of the steel plate, cooling stop temperature: 250-550 ℃.
[5] A high-strength steel pipe using the high-strength steel sheet for acid-resistant pipelines according to any one of [1] to [3 ].
The high-strength steel sheet for acid-resistant pipelines and the high-strength steel pipe using the same according to the present invention are excellent not only in HIC resistance, but also in SSCC resistance in a severer corrosive environment and SSCC resistance in an environment with a low hydrogen sulfide partial pressure of less than 1 bar. Further, according to the method for producing a high-strength steel sheet for acid-resistant line of the present invention, it is possible to produce a high-strength steel sheet for acid-resistant line which is excellent not only in HIC resistance but also in SSCC resistance in a severe corrosive environment and SSCC resistance in an environment with a low hydrogen sulfide partial pressure of less than 1 bar.
Drawings
FIG. 1 is a schematic diagram illustrating a method for collecting a test piece used for evaluation of SSCC resistance in examples.
Detailed Description
Hereinafter, the high-strength steel sheet for acid-resistant line according to the present invention will be specifically described.
[ composition of ingredients ]
First, the composition of the high-strength steel sheet of the present invention and the reasons for the limitation thereof will be described. In the following description, units represented by% are all mass% unless otherwise specified.
C：0.020～0.080％
C effectively contributes to the improvement of strength, but if the content is less than 0.020%, sufficient strength cannot be secured. Therefore, the C content is 0.020% or more, preferably 0.025% or more. On the other hand, if the C content exceeds 0.080%, the hardness of the surface layer portion and the center segregation portion is increased at the time of accelerated cooling, and therefore SSCC resistance and HIC resistance are deteriorated. In addition, toughness is also deteriorated. Therefore, the C content is 0.080% or less, preferably 0.070% or less.
Si：0.01～0.50％
Si is added for deoxidation, and if the content is less than 0.01%, the deoxidation effect is insufficient. Therefore, the Si content is 0.01% or more, preferably 0.05% or more. On the other hand, if the Si content exceeds 0.50%, toughness and weldability deteriorate. Therefore, the Si content is 0.50% or less, preferably 0.45% or less.
Mn：0.50～1.80％
While Mn effectively contributes to the improvement of strength and toughness, if the content is less than 0.50%, the effect of addition thereof is not sufficiently exhibited. Therefore, the Mn content is 0.50% or more, preferably 0.80% or more. On the other hand, if the Mn content exceeds 1.80%, the hardness of the surface layer portion and the center segregation portion increases at the time of accelerated cooling, and therefore SSCC resistance and HIC resistance deteriorate. In addition, weldability also deteriorates. Therefore, the Mn content is 1.80% or less, preferably 1.70% or less.
P: less than 0.015%
P is an inevitable impurity element, and deteriorates weldability, and also increases the hardness of the surface layer portion and the center segregation portion, thereby deteriorating SSCC resistance and HIC resistance. If the P amount exceeds 0.015%, the tendency becomes remarkable, so the P amount is 0.015% or less, preferably 0.008% or less. The lower the amount of P, the better, but from the viewpoint of refining cost, it is preferably 0.001% or more.
S: less than 0.0015%
S is an unavoidable impurity element, and becomes an MnS inclusion in steel, thereby deteriorating HIC resistance. Therefore, the S content is 0.0015% or less, preferably 0.0010% or less. The lower the S content, the better, but from the viewpoint of refining cost, it is preferably 0.0002% or more.
Al：0.010～0.080％
Al is added as a deoxidizer, but if the content is less than 0.010%, the effect is not sufficiently exhibited. Therefore, the Al content is 0.010% or more, preferably 0.015% or more. On the other hand, if the Al content exceeds 0.080%, the cleanliness of the steel is reduced and the toughness is deteriorated. Therefore, the Al content is 0.080% or less, preferably 0.070% or less.
N：0.0010～0.0080％
N effectively contributes to the improvement of strength, but when the content is less than 0.0010%, sufficient strength cannot be secured. Therefore, the N content is 0.0010% or more, preferably 0.0015% or more. On the other hand, if the N amount exceeds 0.0080%, the hardness of the surface layer portion and the center segregation portion at the time of accelerated cooling is increased, and therefore SSCC resistance and HIC resistance are deteriorated. In addition, toughness also deteriorates. Accordingly, the N content is 0.0080% or less, preferably 0.0070% or less.
Mo：0.01～0.50％
Mo is an element effective for improving toughness and strength, and is an element effective for improving SSCC resistance regardless of the partial pressure of hydrogen sulfide. The present inventors have found that when a steel sheet containing Mo is subjected to an SSCC test, the surface of the steel sheet after the test is smoother than the surface of the steel sheet containing no Mo after the SSCC test. The mechanism is not clear, and this is considered to be due to the correlation with the improvement in SSCC resistance. In order to obtain this effect, the Mo content must be 0.01% or more, preferably 0.10% or more. On the other hand, if the Mo amount exceeds 0.50%, hardenability becomes excessive, so that hardness of the surface layer portion and the center segregation portion at the time of accelerated cooling is improved, and SSCC resistance and HIC resistance are deteriorated. In addition, weldability also deteriorates. Therefore, the Mo amount is 0.50% or less, preferably 0.40% or less.
Ca：0.0005～0.0050％
Ca is an element effective for improving HIC resistance by controlling the morphology of sulfide-based inclusions, but if the content is less than 0.0005%, the effect is not sufficiently exhibited. Therefore, the amount of Ca is 0.0005% or more, preferably 0.0008% or more. On the other hand, if the amount of Ca exceeds 0.0050%, the above-mentioned effects are not only saturated, but also the cleanliness of the steel is reduced, thereby deteriorating the HIC resistance. Therefore, the Ca content is 0.0050% or less, preferably 0.0045% or less.
While the basic components of the composition of the present invention have been described above, in the present invention, 1 or more species selected from Cu, ni and Cr may be optionally contained in the following ranges in order to further improve the strength and toughness of the steel sheet.
Cu: less than 0.30%
Cu is an element effective for improving toughness and strength, and the amount of Cu is preferably 0.05% or more in order to obtain the effect. However, if the Cu content exceeds 0.30%, in an environment with a low hydrogen sulfide partial pressure of less than 1bar, micro cracks called fissures are likely to be generated, and therefore, SSCC resistance is deteriorated. Therefore, when Cu is added, the amount of Cu is 0.30% or less, preferably 0.25% or less.
Ni: less than 0.10%
Ni is an element effective for improving toughness and strength, and the amount of Ni is preferably 0.01% or more in order to obtain this effect. However, if the Ni content exceeds 0.10%, in an environment with a low hydrogen sulfide partial pressure of less than 1bar, micro cracks called fissures are likely to be generated, and therefore, the SSCC resistance is deteriorated. Therefore, when Ni is added, the Ni content is 0.10% or less, preferably 0.05% or less.
Cr: less than 0.50%
Cr is an element effective for obtaining sufficient strength even with low C, as in Mn, and the amount of Cr is preferably 0.05% or more in order to obtain this effect. However, if the Cr content exceeds 0.50%, the hardenability becomes excessive, and therefore the hardness of the surface layer portion and the center segregation portion during accelerated cooling is increased, and the SSCC resistance and the HIC resistance are deteriorated. In addition, weldability also deteriorates. Therefore, when Cr is added, the Cr amount is 0.50% or less, preferably 0.45% or less.
In the present invention, the component composition may further contain 1 or more selected from Nb, V, ti, zr, mg and REM in the following ranges as desired.
Is selected from Nb:0.005 to 0.1%, V:0.005 to 0.1%, ti:0.005 to 0.1%, zr:0.0005 to 0.02%, mg:0.0005 to 0.02% and REM: more than 1 of 0.0005-0.02%
Nb, V, and Ti are elements that may be optionally added to improve the strength and toughness of the steel sheet. The effect is not sufficiently exhibited when the content of each element is less than 0.005%. Therefore, when these elements are added, the content of each element is preferably 0.005% or more. On the other hand, if the content of these elements exceeds 0.1%, the toughness of the weld is deteriorated. Therefore, when these elements are added, the content of each element is preferably 0.1% or less.
Zr, mg and REM are elements that may be added arbitrarily to improve toughness by making crystal grains finer or to improve crack resistance by controlling inclusion properties. If the content of each element is less than 0.0005%, the effect is not sufficiently exhibited. Therefore, when these elements are added, the content of each element is preferably 0.0005% or more. On the other hand, if the content of these elements exceeds 0.02%, the effect thereof is saturated. Therefore, when these elements are added, the content of each element is preferably 0.02% or less.
The present invention relates to a technique for improving the SSCC resistance of a high-strength steel pipe using a high-strength steel sheet for acid-resistant line, but it is needless to say that the high-strength steel pipe must satisfy the HIC resistance at the same time as the acid resistance, and it is preferable that the CP value obtained from the following formula (1) is 1.00 or less, for example. Elements not added are substituted for 0.
CP＝4.46[％C]+2.37[％Mn]/6+(1.74[％Cu]+1.7[％Ni])/15+(1.18[％Cr]+1.95[％Mo]+1.74[％V])/5+22.36[％P]···(1)
Wherein [% X ] represents the content (% by mass) of the X element in the steel.
Here, the CP value is a formula designed by estimating the material of the center segregation portion from the content of each alloy element, and the hardness of the center segregation portion increases as the CP value of the formula (1) increases and the concentration of the component in the center segregation portion increases. Therefore, the occurrence of cracking in the HIC test can be suppressed by setting the CP value obtained in the above formula (1) to 1.00 or less. In addition, when the hardness of the center segregation portion is lower as the CP value is lower and higher HIC resistance is required, the upper limit thereof may be 0.95.
The remainder of the elements other than the above elements is composed of Fe and unavoidable impurities. However, the inclusion of other trace elements is not hindered as long as the action and effect of the present invention are not impaired. For example, O is an element inevitably contained in steel, and is allowable in the present invention as long as the content thereof is 0.0050% or less, preferably 0.0040% or less.
[ Structure of Steel sheet ]
Next, the steel structure of the high-strength steel sheet for acid-resistant line according to the present invention will be described. In order to reduce the hardness of the surface layer portion, the steel structure of the surface layer portion is preferably a bainite phase. In particular, the maximum hardness of 0.25mm below the surface of the steel sheet is kept constant or less, and in order to improve SSCC resistance, the steel structure of 0.25mm below the surface of the steel sheet is preferably a bainite phase. In order to achieve high strength with a tensile strength of 520MPa or more, the steel structure of the entire steel sheet including the portions other than the surface layer portion is preferably a bainite phase. Specifically, the microstructure at the center of the plate thickness may be a bainite phase, which represents "a portion other than the surface portion".
Here, the bainite phase contains a structure called bainitic ferrite or granular ferrite which is transformed at the time of accelerated cooling or after accelerated cooling and contributes to transformation strengthening. In the bainite phase, when different types of structures such as ferrite, martensite, pearlite, island martensite, and retained austenite are mixed, the strength is decreased, the toughness is deteriorated, and the surface hardness is increased, and therefore, the smaller the structure fraction other than the bainite phase is, the better. However, when the area fraction of the structure other than the bainite phase is sufficiently low, the influence thereof is negligible, and a certain amount is allowable. Specifically, in the present invention, if the total of the steel structures other than bainite (ferrite, martensite, pearlite, island martensite, retained austenite, and the like) is less than 10% by area ratio, it does not have a large influence, and therefore it is allowable, and more preferably less than 5%.
[ Scale on Steel sheet surface ]
In the high-strength steel sheet of the present invention, it is important to control the magnetite content in the scale present on the surface of the steel sheet after cooling to 50% or more from the viewpoint of further improving the SSCC resistance. Generally, the scale on the surface of the steel sheet after controlled cooling is composed of wolframite (FeO) and magnetite (Fe) 3 O 4 ) And hematite (Fe) 2 O 3 ) And (4) forming. The present inventors have found that when the magnetite ratio is 50%, a locally high-hardness portion is formed at a position 0.25mm below the surface of the steel sheet, and as a result, the maximum value of the vickers hardness at a position 0.25mm below the surface of the steel sheet exceeds 230HV. In other words, in order to set the maximum Vickers hardness at 0.25mm below the surface of the steel sheet to 230HV or less, it is necessary to set the magnetite ratio to at least 50% or more. The upper limit of the magnetite ratio is not particularly limited, and the magnetite ratio may be 100% or less, or 95% or less.
[ hardness of the extreme surface layer portion ]
In the high-strength steel sheet of the present invention, it is important that the maximum value of Vickers hardness (HV 0.5) at 0.25mm below the surface of the steel sheet is 230HV or less. By satisfying this condition, excellent SSCC resistance can be obtained even in a more severe corrosive environment and an environment with a low hydrogen sulfide partial pressure of less than 1 bar. When the maximum value of the Vickers hardness at 0.25mm below the surface of the steel sheet exceeds 230HV, local high-hardness portions are present in the extreme surface layer of the steel sheet, resulting in deterioration of SSCC resistance from the portions. Here, "the maximum value of Vickers hardness (HV 0.5) at 0.25mm below the surface of the steel sheet" means that the Vickers hardness (HV 0.5) at a position 0.25mm below the surface of the steel sheet at 100 points is measured at equal intervals in the sheet width direction on a cross section perpendicular to the rolling direction of the steel sheet, and the maximum value among the measured values is taken. Here, the measurement is performed with HV0.5 instead of HV10 which is generally used, because the indentation becomes smaller by the measurement with HV0.5, the hardness information of the position closer to the surface and the hardness information more sensitive to the microstructure can be obtained. When the measurement is carried out at a value smaller than HV0.5, the indentation size is too small, and the measurement unevenness increases. The reason why the evaluation is made not by the average hardness but by the highest hardness is as follows. That is, if there is a locally hard position, the crack is likely to spread, and therefore, in order to examine crack progress sensitivity with high accuracy, it is more appropriate to perform evaluation based on the highest hardness at which the locally hard position can be detected.
[ tensile Strength ]
The high-strength steel sheet of the present invention is a steel sheet for steel pipes having a strength of API 5L at X60 level or higher, and therefore has a tensile strength of 520MPa or higher.
[ thickness of Steel plate ]
The high-strength steel sheet of the present invention has a thickness of 14 to 39 mm.
[ production method ]
Hereinafter, a method and conditions for manufacturing the high-strength steel sheet for acid-resistant line will be described in detail. The production method of the present invention is a method of heating a steel sheet having the above-described composition, hot rolling the heated steel sheet to produce a steel sheet, and then controlled cooling the steel sheet under predetermined conditions.
[ slab heating temperature ]
Heating temperature of the plate blank: 1000-1300 deg.C
If the slab heating temperature is less than 1000 ℃, the solid solution of carbides becomes insufficient, and the amount of solid solution strengthening becomes small, so that the necessary strength cannot be obtained. Therefore, the slab heating temperature is 1000 ℃ or more, preferably 1030 ℃ or more. On the other hand, if the slab heating temperature exceeds 1300 ℃, the crystal grains are extremely coarsened and the toughness deteriorates. Therefore, the slab heating temperature is 1300 ℃ or less, preferably 1250 ℃ or less. The temperature is the furnace temperature of the heating furnace, and the slab is heated to the temperature at the center.
[ Oxidation skin ]
In the present invention, it is important to remove scale with a discharge pressure of 10MPa or more in rolling passes of 50% or more of the number of rolling passes in hot rolling in the hot rolling step. The "rolling pass" referred to herein includes both the rolling pass of rough rolling and the rolling pass of finish rolling in the hot rolling step. Specifically, in a rolling pass of 50% or more of the number of rolling passes in hot rolling, descaling at a pressure of 10MPa or more is sprayed onto the surface of a slab (steel sheet) at a position before the introduction of the slab into the rolling pass. This descaling condition is one of the requirements for suppressing the non-uniform formation of scale and controlling the magnetite content in the scale present on the steel sheet surface to 50% or more after cooling. The "position before the slab is introduced into the rolling pass" is a position within 3m, preferably within 1.5m, from the position of the roll shaft of the rolling mill corresponding to the rolling pass in the longitudinal direction of the hot rolling line. The number of passes of rough rolling may be arbitrarily set in a general range, and is not particularly limited, but is preferably 2 to 12, for example. The number of finish rolling passes may be arbitrarily set in a general range, and is not particularly limited, but is preferably 5 to 15, for example. The descaling method can be performed by a standard method, for example, by spraying high-pressure water onto the surface of the slab from a plurality of descaling nozzles arranged in the width direction of the hot rolling line. In each descaling, the conditions other than the ejection pressure (for example, the amount of water, the distance between the nozzle and the slab, and the nozzle angle) may be general conditions.
If the discharge pressure is less than 10MPa, the oxide scale cannot be removed uniformly, and the hematite increases, so that the magnetite ratio cannot be made 50% or more. Therefore, the discharge pressure is 10MPa or more, preferably 15MPa or more. The higher the discharge pressure, the better, but the larger the equipment, the preferable is 25MPa or less.
When the number of descaling was less than 50% of the number of rolling passes, the amount of hematite increased, and as a result, the magnetite ratio could not be made 50% or more. Therefore, the number of descaling times is 50% or more, preferably 60% or more of the number of rolling passes. The upper limit of the number of times of descaling is not particularly limited, and may be 100% of the number of rolling passes, that is, descaling may be performed before all the rolling passes.
[ Rolling finish temperature ]
In the hot rolling step, in order to obtain high base metal toughness, it is preferable that the rolling end temperature is as low as possible, but on the other hand, the rolling efficiency is low, and therefore, the rolling end temperature of the steel sheet surface temperature needs to be set in consideration of the required base metal toughness and rolling efficiency. From the viewpoint of improving strength and HIC resistance, it is preferable that the rolling end temperature be Ar as measured as the surface temperature of the steel sheet 3 Above the transformation point. Here, ar 3 The transformation point is a ferrite transformation starting temperature during cooling, and can be obtained from the composition of steel by the following formula, for example. The surface temperature of the steel sheet may be measured by a radiation thermometer or the like.
Ar 3 (℃)＝910－310[％C]－80[％Mn]－20[％Cu]－15[％Cr]－55[％Ni]－80[％Mo]
Wherein [% X ] represents the content (mass%) of the X element in the steel.
[ Cooling Start temperature for controlled Cooling ]
Cooling start temperature: measured as a steel sheet surface temperature meter of (Ar) 3 -10 ℃) or higher
If the steel sheet surface temperature at the start of cooling is low, the amount of ferrite generated before controlled cooling increases. In particular from less than (Ar) 3 When cooling was started at a temperature of-10 deg.C, ferrite was generated in an amount exceeding 5% by area fraction, the decrease in strength was increased, and HIC resistance was deteriorated. Therefore, the steel sheet surface temperature at the start of cooling is (Ar) 3 -10 ℃) or higher. The steel sheet surface temperature at the start of cooling is equal to or lower than the rolling end temperature.
[ control of Cooling Rate of Cooling ]
In order to achieve high strength and to set the maximum Vickers hardness at 0.25mm below the surface of the steel sheet to 230HV or less, it is necessary to control the cooling rate at 0.25mm below the surface of the steel sheet.
Average cooling rate from 750 ℃ to 550 ℃ with a steel plate thermometer at 0.25mm below the surface of the steel plate: 20-100 ℃/second
It is important to minimize the generation of high-temperature phase change phase at an average cooling rate of 750 ℃ to 550 ℃ of a steel plate thermometer 0.25mm below the surface of the steel plate, and the lower the cooling rate, the lower the maximum hardness can be. The temperature region from 750 ℃ to 550 ℃ is an important temperature region in bainite transformation, and therefore it becomes important to control the cooling rate in this temperature region. When the average cooling rate exceeds 100 ℃/sec, the ratio of low-temperature phase change phase is high and the maximum value of vickers hardness at 0.25mm below the surface of the steel sheet exceeds 230HV, thereby suppressing the generation of scale unevenness, and the SSCC resistance after pipe making deteriorates. Therefore, the average cooling rate is 100 ℃/sec or less, preferably 80 ℃/sec or less. When the average cooling rate is less than 20 ℃/sec, ferrite and pearlite are generated and the strength is insufficient. Therefore, the average cooling rate is 20 ℃/sec or more.
In the cooling at 550 ℃ or less with respect to a steel sheet thermometer at 0.25mm below the surface of the steel sheet, it is preferable to increase the water density from the viewpoint of performing cooling in a stable nucleate boiling state. In order to prevent the formation of a local high-hardness portion in the extremely surface portion of the steel sheet by performing stable cooling in the nucleate boiling state, the average cooling rate from 550 ℃ to the cooling stop temperature with a steel sheet thermometer 0.25mm below the surface of the steel sheet is preferably 110 ℃/sec or more, and more preferably 150 ℃/sec or more. In addition, from the viewpoint of more reliably suppressing the generation of high-hardness portions, the average cooling rate is preferably 200 ℃/sec or less.
Average cooling rate from 750 ℃ to 550 ℃ with average thermometer of steel plate: 15 ℃/second or more
If the average cooling rate from 750 ℃ to 550 ℃ on an average thermometer of a steel sheet is less than 15 ℃/sec, the fraction of phases other than the bainite phase increases, resulting in a decrease in strength and deterioration in HIC resistance. Therefore, the average cooling rate at the average thermometer for steel sheet is 15 ℃/sec or more. From the viewpoint of the difference between the strength and hardness of the steel sheet, the average cooling rate by the average thermometer of the steel sheet is preferably 20 ℃/sec or more. The upper limit of the average cooling rate is not particularly limited, but the average cooling rate is preferably 80 ℃/sec or less in order to prevent excessive generation of low-temperature transformation products.
The temperature of the steel sheet at 0.25mm below the surface of the steel sheet and the average temperature of the steel sheet cannot be directly measured physically, and the temperature distribution in the sheet thickness profile can be obtained in real time by differential calculation using a process computer, for example, based on the surface temperature at the start of cooling measured by a radiation thermometer and the surface temperature at the stop of target cooling. The temperature at 0.25mm below the surface of the steel sheet in the temperature distribution is referred to as "steel sheet temperature at 0.25mm below the surface of the steel sheet" in the present specification, and the average value of the temperatures in the sheet thickness direction in the temperature distribution is referred to as "steel sheet average temperature" in the present specification.
[ Cooling stop temperature ]
Cooling stop temperature: the cooling stop temperature of 250 to 550 ℃ is one of the requirements for controlling the ratio of magnetite to scale present on the surface of the steel sheet to 50% or more after cooling, with a thermometer of the steel sheet at 0.25mm below the surface of the steel sheet. If the cooling stop temperature exceeds 550 ℃, the bainite transformation is incomplete and sufficient strength cannot be obtained. When the cooling stop temperature is less than 250 ℃, the content of wolframite increases, and as a result, the magnetite content cannot be made 50% or more. As a result, the maximum Vickers hardness at 0.25mm below the surface of the steel sheet exceeded 230HV, and the SSCC resistance after pipe making was therefore deteriorated. Further, the hardness of the center segregation portion also increases, and the HIC resistance also deteriorates. Therefore, the cooling stop temperature is 250 to 550 ℃ based on a steel plate thermometer 0.25mm below the surface of the steel plate.
[ high-Strength Steel pipe ]
The high-strength steel sheet of the present invention may be formed into a tubular shape by press bending, roll forming or UOE forming, and then welded at the butt joint portion to produce a high-strength steel pipe (UOE steel pipe, electric seam steel pipe, spiral steel pipe, etc.) for acid-resistant line suitable for transportation of crude oil or natural gas.
For example, UOE steel pipes are manufactured by beveling the end portions of steel plates, forming the steel pipes into a steel pipe shape by C-press, U-press, or O-press forming, seam welding the butt portions by inner surface welding and outer surface welding, and, if necessary, performing a pipe expansion process. The welding method may be any method as long as sufficient joint strength and joint toughness are obtained, and submerged arc welding is preferably used from the viewpoint of excellent welding quality and production efficiency. Further, after the steel sheet is formed into a tubular shape by press bending, the butt portion is seam welded to obtain a steel pipe, and the steel pipe is also subjected to pipe expansion.
Examples
Steels having the compositions shown in table 1 were produced into slabs by a continuous casting method, heated to the temperatures shown in table 2, and hot-rolled at the rolling completion temperatures shown in table 2 to produce steel sheets having the thicknesses shown in table 2. The hot rolling step was performed for 10 to 25 passes in total of 2 to 12 passes in rough rolling and 5 to 15 passes in finish rolling, and the descaling at the discharge pressure shown in table 2 was performed in the rolling passes at the ratio shown in table 2. Thereafter, the steel sheet was subjected to controlled cooling using a water-cooling type controlled cooling apparatus under the conditions shown in table 2.
[ determination of tissue ]
The microstructure of the obtained steel sheet was observed with an optical microscope. Samples for microstructure observation were collected from the widthwise central portions of the steel sheets. These samples were mirror-polished in a cross section parallel to the rolling length direction, and then were subjected to nital etching. Thereafter, photographs were taken at 5 fields of view of the polished surface of each sample at random at a magnification in the range of 400 to 1000 times using an optical microscope, and the area fraction of each phase was calculated by image analysis processing. The types of the structure at a position of 0.25mm below the surface of the steel sheet and the structure at the center of the sheet thickness, and the area ratios of phases other than the bainite phase are shown in Table 3.
[ measurement of Magnetite ratio in oxide Scale ]
Scale was collected from the surface of the obtained steel sheet. The scale was collected at 9 positions in total, namely, at the center in the width direction and at both ends in the width direction of the steel sheet at each of the front end, the center, and the tail end in the longitudinal direction of the steel sheet, and at each position, 0.5g or more of scale was collected. The scale collected at each site was subjected to phase identification by X-ray diffraction (XRD: X-ray diffraction) method, and quantitative analysis (i.e., determination of magnetite Ratio) was performed by using Reference Intensity Ratio (RIR: reference Intensity Ratio) method. The average value of the magnetite ratios of the scale of 9 sites is shown in table 3 as "magnetite ratio" in the present invention.
[ measurement of tensile Strength ]
Tensile test was conducted using a total thickness test piece in a direction perpendicular to the rolling direction as a tensile test piece, and the yield strength and the tensile strength were measured. The results are shown in Table 3.
[ measurement of Vickers hardness ]
The Vickers hardness at 100 points (HV 0.5) was measured at a position 0.25mm below the surface of the steel sheet according to JIS Z2244 on a cross section perpendicular to the rolling direction, and the maximum hardness, the average value, and the standard deviation σ were determined. The maximum hardness, the average value, and the value of 3 σ are shown in table 3.
[ evaluation of SSCC resistance ]
The SSCC resistance was evaluated by using a part of each of these steel sheets to produce a pipe. The pipe making is a process of chamfering the end of a steel plate, forming the end into a steel pipe shape by C-press, U-press, or O-press, and then seam welding the butt joint between the inner surface and the outer surface by submerged arc welding, followed by a pipe expansion step. As shown in FIG. 1, a sample cut out from the obtained steel pipe was flattened, and then a 5X 15X 115mm SSCC test piece was sampled from the inner surface of the steel pipe. In this case, a test piece including both the welded portion and the base material was used, except for a test piece of only the base material without the welded portion. The inner surface of the surface to be inspected is directly covered with a black skin so as to leave the outermost layer. For the stress of 90% of the actual yield strength (0.5% ys) of each steel pipe loaded by the adopted SSCC test piece, NACE specification TM0177 Solution a Solution was used at a hydrogen sulfide partial pressure: 1bar was carried out according to the 4-point bending SSCC test of EFC16 specification. In addition, NACE specification TM0177 Solution B Solution was used at hydrogen sulfide partial pressure: 0.1bar + partial pressure of carbon dioxide: 0.9bar was carried out according to the 4-point bending SSCC test of EFC16 specification. Further using NACE specification TM0177 Solution a Solution at hydrogen sulfide partial pressure: 2bar + partial pressure of carbon dioxide: 3bar was carried out according to the 4-point bending SSCC test with EFC16 specification. After 720 hours of immersion, in both the test piece of the base material including only the welded portion and the test piece including both the welded portion and the base material, it was judged that the SSCC resistance was good when no crack was observed, and it was judged that the other test piece was poor when a crack was generated. The results are shown in Table 3.
[ evaluation of HIC resistance ]
HIC resistance was measured using NACE specification TM0177 Solution a Solution at hydrogen sulfide partial pressure: 1bar was investigated by means of the HIC test after 96 hours of immersion. In addition, NACE specification TM0177 Solution B Solution was used at hydrogen sulfide partial pressure: 0.1bar + partial pressure of carbon dioxide: 0.9bar was investigated by means of the HIC test after immersion for 96 hours. For HIC resistance, the case where the Crack Length Ratio (CLR: crack Length Ratio) in the HIC test was 10% or less was judged as excellent, the case where the Crack Length Ratio exceeded 10% and was 15% or less was judged as good, and the case where the Crack Length Ratio exceeded 15% was judged as insufficient. The results are shown in Table 3.
The scope of the invention is the tensile strength of the high-strength steel sheet for acid-resistant pipelines: 520MPa or more, a bainite structure having a microstructure at both a 0.25mm position and a t/2 position below the surface, a maximum hardness of HV0.5 at 0.25mm below the surface of 230 or less, no cracking observed in the SSCC test, and a Cracking Length Ratio (CLR) in the HIC test of 15% or less.
As shown in tables 2 and 3, nos. 1 to 6 and 30 to 31 are examples of the invention in which the composition and production conditions satisfy the suitable range of the present invention. The tensile strength of the steel sheet is 520MPa or more, and the SSCC resistance and the HIC resistance are good.
In contrast, the composition of the steel sheets of Nos. 7 to 18 is outside the scope of the present invention. No.7, no.9 and No.12 have insufficient solid-solution strengthening and low strength. The highest hardness of HV0.5 of No.8, no.10, no.11, no.13, no.15, no.18 exceeds 230, and therefore, SSCC resistance and HIC resistance are poor. Since the steel sheet of No.14 does not contain Mo, the SSCC resistance is deteriorated in a very severe corrosive environment such as a partial pressure of hydrogen sulfide of 2 Bar. Since the steel sheet of No.16 had an excessive Cu content, the SSCC resistance in an environment where the partial pressure of hydrogen sulfide was low was deteriorated. Since the steel sheet of No.17 contained too much Ni, the SSCC resistance in an environment where the partial pressure of hydrogen sulfide was low was deteriorated.
The samples Nos. 19 to 29 are comparative examples in which the composition of the components falls within the range of the present invention, but the production conditions are outside the range of the present invention. Since the slab of No.19 was heated at a low temperature, homogenization of the microstructure and solid solution of carbide were insufficient, and the strength was low. The spray pressure of scale removal of Nos. 20 and 28 was less than 10MPa, and therefore, scale unevenness occurred, the magnetite ratio was less than 50%, and the highest hardness of HV0.5 exceeded 230, and therefore, SSCC resistance and HIC resistance were poor. The ratio of the number of descaling times in the rolling passes of Nos. 21 and 29 was less than 50%, and therefore the magnetite ratio was less than 50%, and the maximum hardness of HV0.5 exceeded 230, and therefore the SSCC resistance and HIC resistance were poor. No.22 had a low cooling initiation temperature and had a lamellar structure in which ferrite was precipitated, and therefore had low strength and deteriorated HIC resistance. The controlled cooling condition of No.23 was outside the range of the present invention, and the microstructure was ferrite + bainite, and thus low in strength and deteriorated in HIC resistance. The average cooling rate of 750 → 550 ℃ at 0.25mm below the surface of steel sheet of No.24 exceeds 100 ℃/sec, so the proportion of low-temperature phase change phase becomes high, and the maximum hardness of HV0.5 at 0.25mm below the surface of steel sheet exceeds 230, so SSCC resistance is poor. No.25 has a low cooling stop temperature, the magnetite ratio is less than 50%, and the maximum hardness of HV0.5 exceeds 230, so that the SSCC resistance is poor. No.26 has a high cooling stop temperature and does not have complete bainite transformation, so that a sufficient strength is not obtained. In addition, no.26 had a cooling stop temperature of 560 ℃ and had no controlled cooling (accelerated cooling) performed in a temperature range of 550 ℃ or lower, and the column "cooling rate at 550 ℃ or lower (0.25 mm below the surface of the steel sheet)" in table 2 was left blank. Since the average cooling rate of 750 → 550 ℃ at 0.25mm below the surface of the steel sheet of No.27 exceeds 100 ℃/sec, the cooling stop temperature is low, the magnetite ratio is less than 50%, the maximum hardness of HV0.5 exceeds 230, and the SSCC resistance is poor.
Industrial availability
According to the present invention, it is possible to provide a high-strength steel sheet for acid-resistant line which is excellent not only in HIC resistance but also in SSCC resistance in a more severe corrosive environment and SSCC resistance in an environment with a low hydrogen sulfide partial pressure of less than 1 bar. Therefore, a steel pipe (e.g., an electric seam steel pipe, a spiral steel pipe, and a UOE steel pipe) produced by cold rolling the steel sheet can be suitably used for transporting crude oil and natural gas containing hydrogen sulfide, which require acid resistance.
Claims (5)
1. A high-strength steel sheet for acid-resistant pipelines, characterized by having the following composition: contains, in mass%, C:0.020 to 0.080%, si:0.01 to 0.50%, mn:0.50 to 1.80%, P:0.015% or less, S:0.0015% or less, al: 0.010-0.080%, N:0.0010 to 0.0080%, mo:0.01 to 0.50% and Ca:0.0005 to 0.0050%, the remainder consisting of Fe and unavoidable impurities,
the ratio of magnetite in the oxide scale present on the surface of the steel sheet is 50% or more,
the maximum Vickers hardness at a position 0.25mm below the surface of the steel sheet is 230HV or less,
the tensile strength is 520MPa or more.
2. The high-strength steel sheet for acid-resistant pipelines according to claim 1, wherein the composition further contains, in mass%, a metal selected from the group consisting of Cu:0.30% or less, ni:0.10% or less and Cr:0.50% or less of 1 or more.
3. The high-strength steel sheet for acid-resistant pipelines according to claim 1 or 2, wherein the composition further contains, in mass%, a metal selected from the group consisting of Nb:0.005 to 0.1%, V:0.005 to 0.1%, ti:0.005 to 0.1%, zr:0.0005 to 0.02%, mg:0.0005 to 0.02% and REM: more than 1 of 0.0005 to 0.02 percent.
4. A method for producing a high-strength steel sheet for acid-resistant line use, characterized by heating a steel sheet having the composition of any one of claims 1 to 3 to a temperature of 1000 to 1300 ℃,
then, the steel sheet is hot-rolled to produce a steel sheet, descaling with a discharge pressure of 10MPa or more is performed in 50% or more passes of the hot-rolling pass,
thereafter, the steel sheet was subjected to controlled cooling under the following conditions:
the surface temperature of the steel sheet at the start of cooling was (Ar) 3 At a temperature of-10 ℃ or higher,
the average cooling speed from 750 ℃ to 550 ℃ of a steel plate thermometer at a position 0.25mm below the surface of the steel plate is 20-100 ℃/s,
an average cooling rate from 750 ℃ to 550 ℃ with an average thermometer of a steel sheet of 15 ℃/sec or more, an
The cooling stop temperature of a steel plate thermometer at a position 0.25mm below the surface of the steel plate is 250-550 ℃.
5. A high-strength steel pipe using the high-strength steel sheet for acid-resistant line defined in any one of claims 1 to 3.
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| JP2020-056573 | 2020-03-26 | ||
| JP2020056573 | 2020-03-26 | ||
| PCT/JP2021/011238 WO2021193383A1 (en) | 2020-03-26 | 2021-03-18 | High-strength steel sheet for sour-resistant line pipe, manufacturing method thereof, and high-strength steel pipe made using high-strength steel sheet for sour-resistant line pipe |
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| CN115298340A true CN115298340A (en) | 2022-11-04 |
| CN115298340B CN115298340B (en) | 2023-10-31 |
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| EP (1) | EP4129510A1 (en) |
| JP (1) | JP7264269B2 (en) |
| KR (1) | KR20220137970A (en) |
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| WO2023233734A1 (en) * | 2022-06-03 | 2023-12-07 | Ｊｆｅスチール株式会社 | High-strength steel sheet for sour gas equipment, and high-strength steel pipe using same |
| JP7332078B1 (en) * | 2022-06-03 | 2023-08-23 | Ｊｆｅスチール株式会社 | High-strength steel plate for sour gas equipment and high-strength steel pipe using the same |
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| Publication number | Publication date |
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| BR112022019204A2 (en) | 2022-11-08 |
| WO2021193383A1 (en) | 2021-09-30 |
| JPWO2021193383A1 (en) | 2021-09-30 |
| CN115298340B (en) | 2023-10-31 |
| JP7264269B2 (en) | 2023-04-25 |
| EP4129510A1 (en) | 2023-02-08 |
| KR20220137970A (en) | 2022-10-12 |
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