EP1826285B1 - Martensitic stainless steel - Google Patents
Martensitic stainless steel Download PDFInfo
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- EP1826285B1 EP1826285B1 EP05799225A EP05799225A EP1826285B1 EP 1826285 B1 EP1826285 B1 EP 1826285B1 EP 05799225 A EP05799225 A EP 05799225A EP 05799225 A EP05799225 A EP 05799225A EP 1826285 B1 EP1826285 B1 EP 1826285B1
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- 229910001105 martensitic stainless steel Inorganic materials 0.000 title claims description 43
- 229910000831 Steel Inorganic materials 0.000 claims description 45
- 239000010959 steel Substances 0.000 claims description 45
- 230000014509 gene expression Effects 0.000 claims description 21
- 229910052802 copper Inorganic materials 0.000 claims description 9
- 229910052719 titanium Inorganic materials 0.000 claims description 9
- 229910052791 calcium Inorganic materials 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 7
- 229910052746 lanthanum Inorganic materials 0.000 claims description 7
- 229910052684 Cerium Inorganic materials 0.000 claims description 6
- 229910052749 magnesium Inorganic materials 0.000 claims description 6
- 229910052750 molybdenum Inorganic materials 0.000 claims description 6
- 229910052758 niobium Inorganic materials 0.000 claims description 6
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- 229910052726 zirconium Inorganic materials 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052710 silicon Inorganic materials 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 238000005496 tempering Methods 0.000 description 59
- 239000000463 material Substances 0.000 description 27
- 238000005260 corrosion Methods 0.000 description 26
- 230000007797 corrosion Effects 0.000 description 26
- 239000000523 sample Substances 0.000 description 26
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 24
- 239000010949 copper Substances 0.000 description 18
- 238000000034 method Methods 0.000 description 16
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 16
- 239000007789 gas Substances 0.000 description 15
- 239000011651 chromium Substances 0.000 description 14
- 229910002092 carbon dioxide Inorganic materials 0.000 description 13
- 239000011572 manganese Substances 0.000 description 13
- 229910000734 martensite Inorganic materials 0.000 description 12
- 239000000203 mixture Substances 0.000 description 12
- 239000001569 carbon dioxide Substances 0.000 description 11
- 239000000126 substance Substances 0.000 description 10
- 229910001566 austenite Inorganic materials 0.000 description 8
- 230000009466 transformation Effects 0.000 description 8
- 229910000859 α-Fe Inorganic materials 0.000 description 8
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 7
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 7
- 239000003129 oil well Substances 0.000 description 7
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 238000005266 casting Methods 0.000 description 5
- 238000009864 tensile test Methods 0.000 description 5
- 238000005336 cracking Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000003921 oil Substances 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 239000003518 caustics Substances 0.000 description 3
- 238000005242 forging Methods 0.000 description 3
- 238000005098 hot rolling Methods 0.000 description 3
- 239000011780 sodium chloride Substances 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000011733 molybdenum Substances 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229910001651 emery Inorganic materials 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000001192 hot extrusion Methods 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 229910000765 intermetallic Inorganic materials 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
-
- 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
- C22C38/18—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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the present invention relates to martensitic stainless steel, and more specifically to martensitic stainless steel for use in a corrosive environment including corrosive substances such as hydrogen sulfide, carbon dioxide gas, and chloride ions.
- Martensitic stainless steel having a yield stress (0.2% proof stress) in the range from 758 MPa to 860 MPa hereinafter referred to as "110 ksi grade" and martensitic stainless steel having a strength equal to or higher than the 110 ksi grade have been developed.
- Martensitic stainless steel for oil well must have high corrosion resistance such as SCC (Stress Corrosion Cracking) resistance and SSC (Sulfide Stress Cracking) resistance. This is because oil wells and gas wells exist in corrosive environments that include corrosive substances such as hydrogen sulfide, carbon dioxide gas, and cloride ions. More specifically, martensitic stainless steel for use in oil wells must have high strength, high toughness, and high corrosion resistance.
- Martensitic stainless steel having high strength and high corrosion resistance is disclosed by JP 2003-3243 A .
- the disclosed martensitic stainless steel contains at least 1.5% by mass of Mo and allows higher SSC resistance than conventional martensitic stainless steel to be obtained.
- Fig. 1 shows the relation between the yield stress of martensitic stainless steel with a high Mo content (hereinafter referred to as “high Mo martensitic stainless steel) and the tempering temperature.
- the high Mo martensitic stainless steel in Fig. 1 contains, by mass, 0.016% C, 11.8% Cr, 7.2% Ni, and 2.9% Mo, with the balance being Fe and impurities.
- the gradient of the tempering temperature curve C10 in the yield stress range from 758 MPa to 860 MPa is large.
- the tempering temperature must be about in the range from 580°C to 600°C in order to obtain the 110 ksi grade strength for the high Mo martensitic stainless steel. More specifically, the tempering temperature range ⁇ T that allows the 110 ksi grade strength to be obtained is very small.
- the tempering temperature range ⁇ T is small, the productivity is reduced. In general, several hundred tons of such high Mo martensitic stainless steel is successively produced. In this case, the high Mo martensitic stainless steel is made by a plurality of heats (molten steel produced by a single steel making process) and the chemical compositions of the heats are not completely the same and slightly vary among them. If the tempering temperature range ⁇ T is small, the tempering temperature must be changed every time the chemical composition changes in order to obtain the 110 ksi grade strength for the steel. In short, in order to obtain the 110 ksi grade strength, the tempering temperature must be changed for each of the heats. The necessity of changing the tempering temperature setting in this manner lowers the productivity.
- JP-A 5 156 409 relates to a high-strength martensitic steel having excellent sea water resistance.
- the inventor conducted various experiments and examinations and has obtained the following findings.
- the tempering temperature range that allows the yield stress to be from 758 MPa to 860 MPa can be larger than conventional cases.
- F1 ⁇ 600 because the tempering process is carried out at 600°C or less. If the tempering temperature is set to 600°C or more, microscope carbide or intermetallic compounds in the steel become coarse, and this rather reduces the strength and toughness. Since the tempering temperature is 600°C or less, it is only necessary that F1 be 600°C or more.
- Expression (2) is an expression used to make the steel after tempering martensitic. If the contents of C, Mn, and Ni that are austenite forming elements and the contents of Si, Cr, and Mo that are ferrite forming elements satisfy the relation defined by Expression (2), the structure becomes martensitic, and ⁇ ferrite can be prevented from being produced. Therefore, the strength can be prevented from being lowered, and high toughness can be maintained.
- a tempering temperature curve as curve C1 shown in Fig. 2 can be obtained, and the gradient of the tempering temperature curve in the yield stress range from 758 MPa to 860 MPa can be smaller than that in the conventional cases. Therefore, the tempering temperature range ⁇ T1 that allows the yield stress to be in the range from 758 MPa to 860 MPa is larger than the tempering temperature range ⁇ T2 of the conventional tempering temperature curve C2. Therefore, the decrease in the productivity because of temperature setting changes during operation can be prevented.
- the inventor completed the following invention based on the above-described findings.
- Martensitic stainless steel according to the invention contains, by mass, 0.001% to 0.01% C, at most 0.5% Si, 0.1% to 3.0% Mn, at most 0.04% P, at most 0.01% S, 10% to 15% Cr, 4% to 8% Ni, 2.8% to 5.0% Mo, 0.001% to 0.10% Al, at most 0.07% N, 0% to 0.25% Ti, 0% to 0.25% V, 0% to 0.25% Nb, 0% to 0.25% Zr, 0% to 1.0% Cu, 0% to 0.005% Ca, 0% to 0.005% Mg, 0% to 0.005% La, and 0% to 0.005% Ce, with the balance being Fe and impurities, the steel satisfies Expressions (1) and (2) and has a yield stress in the range from 758 MPa to 860 MPa.
- the gradient of the tempering temperature curve can be reduced by setting the C content to 0.01% or less.
- the A C1 transformation point can be higher than the conventional examples if Expression (1) is satisfied. Therefore, the gradient of the tempering temperature curve is reduced, and the tempering temperature range that allows the yield stress to be in the range from 758 MPa to 860 MPa is increased as compared to the conventional examples.
- the strength can be prevented from being less than 690 MPa (110 ksi) as Expression (2) is satisfied, and the high toughness can be maintained. Since the Mo content is high, high corrosion resistance is obtained.
- the martensitic stainless steel according to the invention preferably contains at least one of 0.005% to 0.25% Ti, 0.005% to 0.25% V, 0.005% to 0.25% Nb, and 0.005% to 0.25% Zr.
- the martensitic stainless steel according to the invention preferably contains 0.05% to 1.0% Cu.
- the martensitic stainless steel according to the invention preferably contains at least one of 0.0002% to 0.005% Ca, 0.0002% to 0.005% Mg, 0.0002% to 0.005% La, and 0.0002% to 0.005% Ce.
- Martensitic stainless steel according to an embodiment of the invention has the following composition.
- % related to each element refers to “% by mass.”
- the C content is excessive, the gradient of the tempering temperature curve becomes steep, and steel having a yield stress in the range from 758 MPa to 860 MPa cannot stably be produced.
- the C content should be limited to a small value. If the C content is less than 0.001%, on the other hand, the manufacturing cost increases. Therefore, the C content is in the range from 0.001% to 0.01%, preferably from 0.001% to 0.008%.
- Silicon is effectively applied as a deoxidizing agent.
- Si hardens steel and therefore an excessive Si content degrades the toughness and workability of the steel.
- Silicon is a ferrite forming element and therefore prevents the steel from becoming martensitic. Therefore, the Si content is not more than 0.5%, preferably 0.3% or less.
- Mn contributes to improvement in the hot workability of the steel. Furthermore, Mn is an austenite forming element and contributes to formation of a martensitic structure. However, an excessive Mn content degrades the toughness. Therefore, the Mn content is in the range from 0.1% to 3.0%, preferably from 0.3% to 1.0%.
- Phosphorus is an impurity and causes SSC to be generated, and therefore the P content is limited as much as possible.
- the P content is 0.04% or less.
- Sulfur is an impurity and lowers the hot workability. Therefore, the S content is limited as much as possible.
- the S content is 0.01% or less.
- Chromium contributes to improvement in corrosion resistance in a wet carbon dioxide gas environment.
- Cr is a ferrite forming element and an excessive Cr content makes it difficult to form tempered martensite, which lowers the strength and the toughness. Therefore, the Cr content is in the range from 10% to 15%, preferably from 11% to 14%.
- Nickel is an austenite forming element and necessary for the structure after tempering to become martensitic. If the Ni content is too small, the structure after the tempering contains much ferrite. On the other hand, an excessive Ni content causes the structure after the tempering to have much austenite. Therefore, the Ni content is in the range from 4% to 8%, preferably from 4% to 7%.
- Molybdenum is a critical element that contributes to improvement in SSC resistance and strength.
- the lower limit for the Mo content to allow high SSC resistance to be obtained is 2.8%.
- Molybdenum is a ferrite forming element and excessive addition of the element prevents the structure from becoming martensitic.
- the upper limit for the Mo content is therefore 5.0%.
- the Mo content is preferably in the range from 2.8% to 4.0%.
- Aluminum is effectively applicable as a deoxidizing agent.
- an excessive Al content causes many inclusions to be generated, and the corrosion resistance is lowered. Therefore, the Al content is from 0.001% to 0.10%, preferably from 0.001% to 0.06%.
- Nitrogen forms a nitride and lowers the corrosion resistance. Therefore, the N content is 0.07% or less.
- the balance consists of Fe and impurities.
- the impurities are mixed in the manufacturing process for various reasons.
- the martensitic stainless steel according to the embodiment further contains at least one of Ti, V, Nb, and Zr if required.
- Ti 0% to 0.25%
- V 0% to 0.25%
- Nb 0% to 0.25%
- Zr 0% to 0.25%
- Ti, V, Nb, and Zr are optional elements. These elements fix C and reduce variations in strength. On the other hand, an excessive content of any of these elements prevents the structure after tempering from becoming martensitic. Therefore, the content of each of these elements is set to the range from 0% to 0.25%, preferably from 0.005% to 0.25%, more preferably from 0.005% to 0.20%.
- the martensitic stainless steel according to the embodiment contains Cu if required.
- Copper is an optional element and an austenite forming element as with Ni suitable for making the structure after tempering martensitic.
- an excessive Cu content lowers the hot workability. Therefore, the Cu content is from 0% to 1.0%, preferably from 0.05% to 1.0%.
- the martensitic stainless steel according to the embodiment further contains at least one of Ca, Mg, La, and Ce if required.
- Ca, Mg, La, and Ce are optional elements. These optional elements contribute to improvement in hot workability. On the other hand, excessive contents of these elements cause coarse oxides to be generated, which lowers the corrosion resistance. Therefore, the contents of these elements are all in the range from 0% to 0.005%, preferably from 0.0002% to 0.005%. Among these elements, Ca and La are elements that particularly contribute to improvement in hot workability.
- the molten steel is formed into a continuos casting material by a continuos casting method.
- the continuos casting material is for example a slab, bloom, or billet.
- the molten steel may be made into ingots by an ingot casting method.
- the slab, bloom, or ingot is formed into billets by hot working. At the time, the billets may be formed by hot rolling or by hot forging.
- the billets produced by the continuos casting or hot working are subjected to further hot working and formed into oil country tubular goods.
- Mannesmann process may be performed as the hot working.
- Ugine-Sejournet hot extrusion process may be employed as the hot working, while a forged pipe making method such as Ehrhardt method may be employed.
- the oil country tubular good after the hot working is subjected to quenching process and tempering process.
- the quenching process is carried out according to a well-known method.
- the quenching temperature is for example from 900°C to 950°C, while other temperature ranges may be employed.
- the lower limit for the tempering temperature is preferably 500°C. If the tempering temperature is too high, retained austenite is precipitated, so that the yield stress cannot be in the range from 758 MPa to 860 MPa. Therefore, the upper limit for the tempering temperature is preferably 600°C.
- the martensitic stainless steel according to the embodiment of the invention satisfies the following Expressions (1) and (2): 922.6 - 554.5 ⁇ C - 50.9 ⁇ Mn + 2944.8 ⁇ P + 1.056 ⁇ Cr - 81.1 ⁇ Ni + 95.8 ⁇ Mo - 125.1 ⁇ Ti - 1584.9 ⁇ Al - 3 76.1 ⁇ N ⁇ 600 30 ⁇ C + 0.5 ⁇ Mn + Ni + 0.5 ⁇ Cu - 1.5 ⁇ Si - Cr - Mo + 7.9 ⁇ 0
- Expression (1) the A c1 transformation point is high, and therefore the gradient of the tempering curve in the yield stress range from 758 MPa to 860 MPa can be reduced.
- Expression (2) the structure can become martensitic in an accelerated manner. Therefore, if both Expressions (1) and (2) are satisfied, the tempering temperature range that allows the yield stress to be in the range from 758 MPa to 860 MPa can be larger than those of the conventional examples. Therefore, a decrease in productivity based on changes in the temperature setting during operation can be reduced.
- the martensitic stainless steel is made into a steel pipe, but the steel may be formed into a steel plate.
- Sample materials having chemical compositions given in Table 1 were produced and each examined for the tempering temperature range that allows the yield stress to be in the range from 758 MPa to 860 MPa. The sample materials were also examined for toughness and corrosion resistance.
- Expressions (1) and (2) are represented as F1 and F2, respectively, and F1 and F2 were obtained for each of the sample materials.
- F1 and F2 were obtained for each of the sample materials.
- "0" is entered in the box for "Ti” in F1 and for those without Cu, "0" is entered in the box for "Cu” in F2.
- F1 and F2 were both within the range according to the invention. More specifically, F1 was 600 or more and F2 was zero or more.
- F1 was less than 600.
- the C content exceeded the upper limit according to the invention.
- F1 was less than 600, and as for the sample material 15, F2 was less than zero.
- the molten steel for the sample materials 1 to 16 were cast into continuous casting materials.
- the produced continuous casting materials were subjected to hot forging and hot rolling and made into a plurality of steel plates each having a thickness of 15 mm, a width of 120 mm, and a length of 1000 mm.
- the steel plates after the hot forging and hot rolling were cooled by air to room temperatures. Using the obtained steel plates, the following tests were conducted.
- the obtained plurality of steel plates were quenched. At the time, the quenching temperature was 910°C. Then, the quenched steel plates were subjected to tempering. At the time, the tempering temperature was varied within the temperature range from 450°C to 650°C. The steel plates after the tempering at various temperatures were subjected to tensile tests. More specifically, a round-bar test piece having a diameter of 6.35 mm and a length of 25.4 mm for the parallel part was produced from each of the steel plates. Using the produced round-bar test pieces, tensile tests were conducted at room temperatures based on JIS Z2241 and the yield stresses were obtained. After the tensile tests, the tempering temperature range ⁇ T in which the yield stress was in the range from 758 MPa to 860 MPa was obtained for each of the sample materials. Note that the 0.2% proof stress was set as the yield stress.
- the tempering temperature ranges of the sample materials that allow the yield stress to be in the range from 758 MPa to 860 MPa are given in Table 2.
- ⁇ T represents the difference between the maximum temperature and the minimum temperature among the tempering temperatures at which the yield stresses of the sample materials are from 758 MPa to 860 MPa.
- the unit is "°C.”
- ⁇ T was 40°C or more for each of the sample materials 1 to 11. Meanwhile, ⁇ T was less than 40°C for the sample materials 12 and 13 because F1 was less than 600 for them.
- the sample material 14 had a high C content, F1 was less than 600, and therefore ⁇ T was less than 40°C.
- the sample materials 15 and 16 each had a high C content, and therefore ⁇ T was less than 40°C.
- Fig. 2 shows the relation between the tempering temperature and the yield stress in the sample materials 1 and 14.
- the gradient of the tempering temperature curve C1 of the sample material 1 whose F1 was 600 or more was small in the yield stress range of 758 MPa to 860 MPa and the tempering temperature range ⁇ T1 was 110°C.
- the gradient of the tempering temperature curve C2 was large in the yield stress range from 758 MPa to 860 MPa, and the tempering temperature range ⁇ T2 was as small as 20°C.
- the toughness tests were conducted as follows. The obtained steel plates were quenched at 910°C and tempered so that the yield stresses become values given in Table 3. From each of the tempered steel plates, a V-notch test piece as wide as 10 mm according to JISZ2202 was produced.
- V-notch test pieces were subjected to Charpy impact tests according to JISZ2242 at -40°C and examined for absorbed energy.
- the unit of the absorbed energy in Table 3 is J. Since the F2 values of the sample materials 1 to 11 are all at least zero, the values of the absorbed energy exceeded 100 J, in other words, high toughness resulted. Meanwhile, the F2 value of the sample material 15 was less than zero, and therefore the absorbed energy was low.
- Corrosion resistance in a wet carbon dioxide gas environment was evaluated by conducting carbon dioxide gas corrosion tests.
- a test piece having a width of 20 mm, a thickness of 3 mm, and a length of 50 mm was cut from each of steel plates quenched and tempered in the same conditions as the above toughness evaluation.
- the surface of each test piece was polished with No. 600 emery paper, then degreased, and dried.
- test pieces were immersed for 720 hours in a 25% NaCl aqueous solution in which CO 2 gas at 9.73 atm and H 2 S at 0.014 atm were saturated. Note that the aqueous solution was kept at 165°C during the tests.
- the test pieces were each examined for quantity loss caused by corrosion. More specifically, the corrosion loss was obtained as a value produced by subtracting the weight of a test piece after the test from the weight of the test piece before the test. The presence/absence of local corrosion at the surfaces of the test pieces was visually inspected. It was determined that the piece had high corrosion resistance in a wet carbon dioxide gas environment if the corrosion loss was less than 7.7 g and there was no local corrosion found.
- the sample materials 1 to 11 each had high corrosion resistance.
- the martensitic stainless steel according to the invention is applicable as a steel material for use in a corrosive environment including corrosive substances such as hydrogen sulfide, carbon dioxide gas, and chloride ions.
- the steel is particularly applicable to steel materials for production facilities, geothermal power generation facilities, and carbon dioxide gas removing facilities, and steel pipes used as oil country tubular goods in a wet hydrogen sulfide environment and a wet carbon dioxide gas environment such as oil wells or gas wells.
Description
- The present invention relates to martensitic stainless steel, and more specifically to martensitic stainless steel for use in a corrosive environment including corrosive substances such as hydrogen sulfide, carbon dioxide gas, and chloride ions.
- As deeper oil wells and gas wells have come to be dug, there has been a demand for stronger and tougher martensitic stainless steel used as a steel material for oil well such as oil country tubular goods. Martensitic stainless steel having a yield stress (0.2% proof stress) in the range from 758 MPa to 860 MPa (hereinafter referred to as "110 ksi grade") and martensitic stainless steel having a strength equal to or higher than the 110 ksi grade have been developed.
- Martensitic stainless steel for oil well must have high corrosion resistance such as SCC (Stress Corrosion Cracking) resistance and SSC (Sulfide Stress Cracking) resistance. This is because oil wells and gas wells exist in corrosive environments that include corrosive substances such as hydrogen sulfide, carbon dioxide gas, and cloride ions. More specifically, martensitic stainless steel for use in oil wells must have high strength, high toughness, and high corrosion resistance.
- Martensitic stainless steel having high strength and high corrosion resistance is disclosed by
JP 2003-3243 A - If the Mo content is high, the tempering temperature range that allows the 110 ksi grade strength to be obtained (hereinafter referred to as "tempering temperature range") is very small.
Fig. 1 shows the relation between the yield stress of martensitic stainless steel with a high Mo content (hereinafter referred to as "high Mo martensitic stainless steel) and the tempering temperature. The high Mo martensitic stainless steel inFig. 1 contains, by mass, 0.016% C, 11.8% Cr, 7.2% Ni, and 2.9% Mo, with the balance being Fe and impurities. With reference toFig. 1 , the gradient of the tempering temperature curve C10 in the yield stress range from 758 MPa to 860 MPa is large. Therefore, the tempering temperature must be about in the range from 580°C to 600°C in order to obtain the 110 ksi grade strength for the high Mo martensitic stainless steel. More specifically, the tempering temperature range ΔT that allows the 110 ksi grade strength to be obtained is very small. - If the tempering temperature range ΔT is small, the productivity is reduced. In general, several hundred tons of such high Mo martensitic stainless steel is successively produced. In this case, the high Mo martensitic stainless steel is made by a plurality of heats (molten steel produced by a single steel making process) and the chemical compositions of the heats are not completely the same and slightly vary among them. If the tempering temperature range ΔT is small, the tempering temperature must be changed every time the chemical composition changes in order to obtain the 110 ksi grade strength for the steel. In short, in order to obtain the 110 ksi grade strength, the tempering temperature must be changed for each of the heats. The necessity of changing the tempering temperature setting in this manner lowers the productivity.
- Note that International Publication No.
WO 2004/57050 JP-A 5 156 409 - It is an object of the invention to provide martensitic stainless steel having a large tempering temperature range that allows a yield stress in the range from 758 MPa to 860 MPa to be obtained.
- The inventor conducted various experiments and examinations and has obtained the following findings.
- (A) If the martensitic stainless steel has such a chemical composition that the transformation point Ac1 of the steel is high, the tempering temperature range that allows the yield stress to be from 758 MPa to 860 MPa increases. If the transformation point Ac1 is lower, austenite forms during high temperature tempering process, which reduces the strength.
- (B) In addition to the increase in the transformation point Ac1, the C content is reduced. In this way, the tempering temperature range that allows the yield stress to be from 758 MPa to 860 MPa even more increases. This is because as the C content is higher, the gradient of the tempering temperature curve in the yield stress range of 758 MPa to 860 MPa increases.
- (C) If the C content is lowered, δ ferrite is more likely to be generated, which affects the strength and toughness of the steel. The 110 ksi grade martensitic stainless steel for use in environments where the atmospheric temperature is less than 0°C must have both high strength and high toughness. If the steel has a composition that allows the structure of the steel to become martensitic even though the transformation point Ac1 is raised and the C content is lowered, δ ferrite can be prevented from forming and the toughness can be prevented from being lowered while the 110 ksi grade strength is maintained.
- As a result of consideration based on these findings, it was found that if the C content is 0.01% or less, and the following Expressions (1) and (2) are satisfied, the tempering temperature range that allows the yield stress to be from 758 MPa to 860 MPa can be larger than conventional cases.
- The left side of Expression (1) (hereinafter the left side of Expression (1) = F1) is an expression used to estimate the Ac1 transformation point of the martensitic stainless steel according to the invention. As described above, if the Ac1 transformation point is high, retained austenite can be prevented from being precipitated during tempering process, so that the yield stress can be prevented from being abruptly lowered. Stated differently, the gradient of the tempering temperature curve in the yield stress range from 758 MPa to 860 MPa can be small.
- Note that F1 ≥ 600 because the tempering process is carried out at 600°C or less. If the tempering temperature is set to 600°C or more, microscope carbide or intermetallic compounds in the steel become coarse, and this rather reduces the strength and toughness. Since the tempering temperature is 600°C or less, it is only necessary that F1 be 600°C or more.
- Expression (2) is an expression used to make the steel after tempering martensitic. If the contents of C, Mn, and Ni that are austenite forming elements and the contents of Si, Cr, and Mo that are ferrite forming elements satisfy the relation defined by Expression (2), the structure becomes martensitic, and δ ferrite can be prevented from being produced. Therefore, the strength can be prevented from being lowered, and high toughness can be maintained.
- Note that if the martensitic stainless steel does not contain optional elements Ti and Cu, the "Ti" and "Cu" in Expressions (1) and (2) are both "0."
- If these expressions are satisfied, a tempering temperature curve as curve C1 shown in
Fig. 2 can be obtained, and the gradient of the tempering temperature curve in the yield stress range from 758 MPa to 860 MPa can be smaller than that in the conventional cases. Therefore, the tempering temperature range ΔT1 that allows the yield stress to be in the range from 758 MPa to 860 MPa is larger than the tempering temperature range ΔT2 of the conventional tempering temperature curve C2. Therefore, the decrease in the productivity because of temperature setting changes during operation can be prevented. - The inventor completed the following invention based on the above-described findings.
- Martensitic stainless steel according to the invention contains, by mass, 0.001% to 0.01% C, at most 0.5% Si, 0.1% to 3.0% Mn, at most 0.04% P, at most 0.01% S, 10% to 15% Cr, 4% to 8% Ni, 2.8% to 5.0% Mo, 0.001% to 0.10% Al, at most 0.07% N, 0% to 0.25% Ti, 0% to 0.25% V, 0% to 0.25% Nb, 0% to 0.25% Zr, 0% to 1.0% Cu, 0% to 0.005% Ca, 0% to 0.005% Mg, 0% to 0.005% La, and 0% to 0.005% Ce, with the balance being Fe and impurities, the steel satisfies Expressions (1) and (2) and has a yield stress in the range from 758 MPa to 860 MPa.
- If the optional elements Ti and Cu are not contained, the "Ti" and "Cu" in Expressions (1) and (2) are both "0." The 0.2 % proof stress corresponds to the yield stress.
- In the martensitic stainless steel according to the invention, the gradient of the tempering temperature curve can be reduced by setting the C content to 0.01% or less. In addition, the AC1 transformation point can be higher than the conventional examples if Expression (1) is satisfied. Therefore, the gradient of the tempering temperature curve is reduced, and the tempering temperature range that allows the yield stress to be in the range from 758 MPa to 860 MPa is increased as compared to the conventional examples.
- The strength can be prevented from being less than 690 MPa (110 ksi) as Expression (2) is satisfied, and the high toughness can be maintained. Since the Mo content is high, high corrosion resistance is obtained.
- The martensitic stainless steel according to the invention preferably contains at least one of 0.005% to 0.25% Ti, 0.005% to 0.25% V, 0.005% to 0.25% Nb, and 0.005% to 0.25% Zr.
- The martensitic stainless steel according to the invention preferably contains 0.05% to 1.0% Cu.
- The martensitic stainless steel according to the invention preferably contains at least one of 0.0002% to 0.005% Ca, 0.0002% to 0.005% Mg, 0.0002% to 0.005% La, and 0.0002% to 0.005% Ce.
- In this way, the hot workability of the martensitic stainless steel is improved. Note that these elements if contained do not affect the effects of the invention described above.
-
-
Fig. 1 shows the relation between the yield stress of a conventional high Mo martensitic stainless steel and the tempering temperature; and -
Fig. 2 shows the relation between the yield stresses of sample materials 1 and 14 according to an embodiment of the invention and the tempering temperature. - Now, an embodiment of the invention will be described in detail in conjunction with the accompanying drawings, in which the same or corresponding portions are denoted by the same reference characters, and their description will not be repeated.
- Martensitic stainless steel according to an embodiment of the invention has the following composition. Hereinafter, "%" related to each element refers to "% by mass."
- If the C content is excessive, the gradient of the tempering temperature curve becomes steep, and steel having a yield stress in the range from 758 MPa to 860 MPa cannot stably be produced. The C content should be limited to a small value. If the C content is less than 0.001%, on the other hand, the manufacturing cost increases. Therefore, the C content is in the range from 0.001% to 0.01%, preferably from 0.001% to 0.008%.
- Silicon is effectively applied as a deoxidizing agent. On the other hand, Si hardens steel and therefore an excessive Si content degrades the toughness and workability of the steel. Silicon is a ferrite forming element and therefore prevents the steel from becoming martensitic. Therefore, the Si content is not more than 0.5%, preferably 0.3% or less.
- Manganese contributes to improvement in the hot workability of the steel. Furthermore, Mn is an austenite forming element and contributes to formation of a martensitic structure. However, an excessive Mn content degrades the toughness. Therefore, the Mn content is in the range from 0.1% to 3.0%, preferably from 0.3% to 1.0%.
- Phosphorus is an impurity and causes SSC to be generated, and therefore the P content is limited as much as possible. The P content is 0.04% or less.
- Sulfur is an impurity and lowers the hot workability. Therefore, the S content is limited as much as possible. The S content is 0.01% or less.
- Chromium contributes to improvement in corrosion resistance in a wet carbon dioxide gas environment. On the other hand, Cr is a ferrite forming element and an excessive Cr content makes it difficult to form tempered martensite, which lowers the strength and the toughness. Therefore, the Cr content is in the range from 10% to 15%, preferably from 11% to 14%.
- Nickel is an austenite forming element and necessary for the structure after tempering to become martensitic. If the Ni content is too small, the structure after the tempering contains much ferrite. On the other hand, an excessive Ni content causes the structure after the tempering to have much austenite. Therefore, the Ni content is in the range from 4% to 8%, preferably from 4% to 7%.
- Molybdenum is a critical element that contributes to improvement in SSC resistance and strength. In the martensitic stainless steel according to the embodiment, the lower limit for the Mo content to allow high SSC resistance to be obtained is 2.8%. Molybdenum is a ferrite forming element and excessive addition of the element prevents the structure from becoming martensitic. The upper limit for the Mo content is therefore 5.0%. The Mo content is preferably in the range from 2.8% to 4.0%.
- Aluminum is effectively applicable as a deoxidizing agent. On the other hand, an excessive Al content causes many inclusions to be generated, and the corrosion resistance is lowered. Therefore, the Al content is from 0.001% to 0.10%, preferably from 0.001% to 0.06%.
- Nitrogen forms a nitride and lowers the corrosion resistance. Therefore, the N content is 0.07% or less.
- Note that the balance consists of Fe and impurities. The impurities are mixed in the manufacturing process for various reasons.
- The martensitic stainless steel according to the embodiment further contains at least one of Ti, V, Nb, and Zr if required.
Ti: 0% to 0.25%
V: 0% to 0.25%
Nb: 0% to 0.25%
Zr: 0% to 0.25% - Note that Ti, V, Nb, and Zr are optional elements. These elements fix C and reduce variations in strength. On the other hand, an excessive content of any of these elements prevents the structure after tempering from becoming martensitic. Therefore, the content of each of these elements is set to the range from 0% to 0.25%, preferably from 0.005% to 0.25%, more preferably from 0.005% to 0.20%.
- The martensitic stainless steel according to the embodiment contains Cu if required.
- Copper is an optional element and an austenite forming element as with Ni suitable for making the structure after tempering martensitic. On the other hand, an excessive Cu content lowers the hot workability. Therefore, the Cu content is from 0% to 1.0%, preferably from 0.05% to 1.0%.
- The martensitic stainless steel according to the embodiment further contains at least one of Ca, Mg, La, and Ce if required.
Ca: 0% to 0.005%
Mg: 0% to 0.005%
La: 0% to 0.005%
Ce: 0% to 0.005% - Note that Ca, Mg, La, and Ce are optional elements. These optional elements contribute to improvement in hot workability. On the other hand, excessive contents of these elements cause coarse oxides to be generated, which lowers the corrosion resistance. Therefore, the contents of these elements are all in the range from 0% to 0.005%, preferably from 0.0002% to 0.005%. Among these elements, Ca and La are elements that particularly contribute to improvement in hot workability.
- Steel having the above-described chemical composition is melted and refined by well-known refining process. Then, the molten steel is formed into a continuos casting material by a continuos casting method. The continuos casting material is for example a slab, bloom, or billet. Alternatively, the molten steel may be made into ingots by an ingot casting method.
- The slab, bloom, or ingot is formed into billets by hot working. At the time, the billets may be formed by hot rolling or by hot forging.
- The billets produced by the continuos casting or hot working are subjected to further hot working and formed into oil country tubular goods. For example, Mannesmann process may be performed as the hot working. Alternatively, Ugine-Sejournet hot extrusion process may be employed as the hot working, while a forged pipe making method such as Ehrhardt method may be employed. The oil country tubular good after the hot working is subjected to quenching process and tempering process. The quenching process is carried out according to a well-known method. The quenching temperature is for example from 900°C to 950°C, while other temperature ranges may be employed.
- In the tempering process, the lower limit for the tempering temperature is preferably 500°C. If the tempering temperature is too high, retained austenite is precipitated, so that the yield stress cannot be in the range from 758 MPa to 860 MPa. Therefore, the upper limit for the tempering temperature is preferably 600°C.
-
- If Expression (1) is satisfied, the Ac1 transformation point is high, and therefore the gradient of the tempering curve in the yield stress range from 758 MPa to 860 MPa can be reduced. If Expression (2) is satisfied, the structure can become martensitic in an accelerated manner. Therefore, if both Expressions (1) and (2) are satisfied, the tempering temperature range that allows the yield stress to be in the range from 758 MPa to 860 MPa can be larger than those of the conventional examples. Therefore, a decrease in productivity based on changes in the temperature setting during operation can be reduced.
- High toughness necessary for steel for use in an oil well can be obtained by satisfying Expression (2).
- Note that if the martensitic stainless steel does not contain Ti and Cu as optional elements, "Ti" and "Cu" in Expressions (1) and (2) are "zero."
- In the above-described example, the martensitic stainless steel is made into a steel pipe, but the steel may be formed into a steel plate.
-
- Steel having the chemical compositions given in Table 1 were melted. As shown in Table 1, the chemical compositions of the sample materials 1 to 11 were within the range of the chemical compositions according to the invention.
- The left sides of Expressions (1) and (2) are represented as F1 and F2, respectively, and F1 and F2 were obtained for each of the sample materials. For the sample materials without Ti, "0" is entered in the box for "Ti" in F1 and for those without Cu, "0" is entered in the box for "Cu" in F2.
- As for all the sample materials 1 to 11, F1 and F2 were both within the range according to the invention. More specifically, F1 was 600 or more and F2 was zero or more.
- As for the sample materials 12 and 13, while the chemical compositions were within the range according to the invention, F1 was less than 600. As for the sample materials 14 to 16, the C content exceeded the upper limit according to the invention. Furthermore, as for the sample material 14, F1 was less than 600, and as for the sample material 15, F2 was less than zero.
- The molten steel for the sample materials 1 to 16 were cast into continuous casting materials. The produced continuous casting materials were subjected to hot forging and hot rolling and made into a plurality of steel plates each having a thickness of 15 mm, a width of 120 mm, and a length of 1000 mm. The steel plates after the hot forging and hot rolling were cooled by air to room temperatures. Using the obtained steel plates, the following tests were conducted.
- To start with, the obtained plurality of steel plates were quenched. At the time, the quenching temperature was 910°C. Then, the quenched steel plates were subjected to tempering. At the time, the tempering temperature was varied within the temperature range from 450°C to 650°C. The steel plates after the tempering at various temperatures were subjected to tensile tests. More specifically, a round-bar test piece having a diameter of 6.35 mm and a length of 25.4 mm for the parallel part was produced from each of the steel plates. Using the produced round-bar test pieces, tensile tests were conducted at room temperatures based on JIS Z2241 and the yield stresses were obtained. After the tensile tests, the tempering temperature range ΔT in which the yield stress was in the range from 758 MPa to 860 MPa was obtained for each of the sample materials. Note that the 0.2% proof stress was set as the yield stress.
- The tempering temperature ranges of the sample materials that allow the yield stress to be in the range from 758 MPa to 860 MPa are given in Table 2.
Table 2 No. ΔT(°C) Inventive Steel 1 110 2 80 3 100 4 110 5 45 6 80 7 50 8 55 9 40 10 110 11 100 Comparative Steel 12 10 13 10 14 20 15 25 16 20 - In Table 2, ΔT represents the difference between the maximum temperature and the minimum temperature among the tempering temperatures at which the yield stresses of the sample materials are from 758 MPa to 860 MPa. The unit is "°C."
- As shown in Table 2, ΔT was 40°C or more for each of the sample materials 1 to 11. Meanwhile, ΔT was less than 40°C for the sample materials 12 and 13 because F1 was less than 600 for them. The sample material 14 had a high C content, F1 was less than 600, and therefore ΔT was less than 40°C. The sample materials 15 and 16 each had a high C content, and therefore ΔT was less than 40°C.
-
Fig. 2 shows the relation between the tempering temperature and the yield stress in the sample materials 1 and 14. As shown inFig. 2 , the gradient of the tempering temperature curve C1 of the sample material 1 whose F1 was 600 or more was small in the yield stress range of 758 MPa to 860 MPa and the tempering temperature range ΔT1 was 110°C. Meanwhile, for the sample material 14 whose F1 was less than 600, the gradient of the tempering temperature curve C2 was large in the yield stress range from 758 MPa to 860 MPa, and the tempering temperature range ΔT2 was as small as 20°C. - The toughness values of the sample materials are given in Table 3.
Table 3 No. F2 yield stress (MPa) absorbed energy at -40°C (J) Inventive Steel 1 0.20 804.0 185 2 0.25 782.0 182 3 0.14 812.0 176 4 0.24 805.0 185 5 0.03 813.0 188 6 0.26 838.0 187 7 0.18 854.0 192 8 0.30 808.0 190 9 0.06 841.0 188 10 0.06 807.0 190 11 0.04 773.0 194 Comparative Steel 12 0.63 848.0 160 13 0.12 815.0 165 14 0.98 851.0 167 15 -1.32 844.0 81 16 0.34 841.0 171 - The toughness tests were conducted as follows. The obtained steel plates were quenched at 910°C and tempered so that the yield stresses become values given in Table 3. From each of the tempered steel plates, a V-notch test piece as wide as 10 mm according to JISZ2202 was produced.
- The produced V-notch test pieces were subjected to Charpy impact tests according to JISZ2242 at -40°C and examined for absorbed energy.
- The unit of the absorbed energy in Table 3 is J. Since the F2 values of the sample materials 1 to 11 are all at least zero, the values of the absorbed energy exceeded 100 J, in other words, high toughness resulted. Meanwhile, the F2 value of the sample material 15 was less than zero, and therefore the absorbed energy was low.
- Corrosion resistance in a wet carbon dioxide gas environment was evaluated by conducting carbon dioxide gas corrosion tests. A test piece having a width of 20 mm, a thickness of 3 mm, and a length of 50 mm was cut from each of steel plates quenched and tempered in the same conditions as the above toughness evaluation. The surface of each test piece was polished with No. 600 emery paper, then degreased, and dried.
- The produced test pieces were immersed for 720 hours in a 25% NaCl aqueous solution in which CO2 gas at 9.73 atm and H2S at 0.014 atm were saturated. Note that the aqueous solution was kept at 165°C during the tests.
- After the tests, the test pieces were each examined for quantity loss caused by corrosion. More specifically, the corrosion loss was obtained as a value produced by subtracting the weight of a test piece after the test from the weight of the test piece before the test. The presence/absence of local corrosion at the surfaces of the test pieces was visually inspected. It was determined that the piece had high corrosion resistance in a wet carbon dioxide gas environment if the corrosion loss was less than 7.7 g and there was no local corrosion found.
- The following SSC tests were conducted to examine SSC resistance in a wet hydrogen sulfide environment. Tensile test pieces each having a diameter of 6.3 mm and a length of 25.4 mm for the parallel part were cut from steel plates quenched and tempered in the same conditions as the above toughness evaluation. The produced tensile test pieces were subjected to proof ring tests based on NACE TM0177-96 Method A. At the time, the test pieces were immersed for 720 hours in a 20% NaCl aqueous solution in which H2S (CO2 bal.) at 0.03 atm was saturated. The pH of the NaCl aqueous solution was 4.5 and the temperature of the aqueous solution was kept at 25°C. After the tests, the presence/absence of crackings was visually inspected.
- The result of the corrosion resistance tests is given in Table 4.
Table 4 No. carbon dioxide gas corrosion tests S S C tests 1 ○ ○ 2 ○ ○ 3 ○ ○ 4 ○ ○ 5 ○ ○ 6 ○ ○ 7 ○ ○ 8 ○ ○ 9 ○ ○ 10 ○ ○ 11 ○ ○ - In Table 4, "○" in the carbon dioxide gas corrosion tests indicates that the corrosion loss was less than 7.7 g and there was no local corrosion. In the SSC corrosion tests, "○" indicates that there was no cracking generated.
- Although the embodiment of the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation. The invention may be embodied in various modified forms as required without departing from the spirit and scope of the invention.
- The martensitic stainless steel according to the invention is applicable as a steel material for use in a corrosive environment including corrosive substances such as hydrogen sulfide, carbon dioxide gas, and chloride ions. The steel is particularly applicable to steel materials for production facilities, geothermal power generation facilities, and carbon dioxide gas removing facilities, and steel pipes used as oil country tubular goods in a wet hydrogen sulfide environment and a wet carbon dioxide gas environment such as oil wells or gas wells.
Claims (5)
- Martensitic stainless steel, comprising, by mass, 0.001% to 0.01% C, at most 0.5% Si, 0.1% to 3.0% Mn, at most 0.04% P, at most 0.01% S, 10% to 15% Cr, 4% to 8% Ni, 2.8% to 5.0% Mo, 0.001% to 0.10% Al, at most 0.07% N, 0% to 0.25% Ti, 0% to 0.25% V, 0% to 0.25% Nb, 0% to 0.25% Zr, 0% to 1.0% Cu, 0% to 0.005% Ca, 0% to 0.005% Mg, 0% to 0.005% La, and 0% to 0.005% Ce, the balance being Fe and impurities, said steel satisfying Expressions (1) and (2) and having a yield stress in the range from 758 MPa to 860 MPa.
where the contents of the elements in percentage by mass are substituted for the characters representing the elements. - The martensitic stainless steel according to claim 1, comprising at least one of 0.005% to 0.25% Ti, 0.005% to 0.25% V, 0.005% to 0.25% Nb, and 0.005% to 0.25% Zr.
- The martensitic stainless steel according to claim 1, comprising 0.05% to 1.0% Cu.
- The martensitic stainless steel according to claim 2, comprising 0.05% to 1.0% Cu.
- The martensitic stainless steel according to any one of claims 1 to 4, comprising at least one of 0.0002% to 0.005% Ca, 0.0002% to 0.005% Mg, 0.0002% to 0.005% La, and 0.0002% to 0.005% Ce.
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US6793744B1 (en) * | 2000-11-15 | 2004-09-21 | Research Institute Of Industrial Science & Technology | Martenstic stainless steel having high mechanical strength and corrosion |
JP2003129190A (en) * | 2001-10-19 | 2003-05-08 | Sumitomo Metal Ind Ltd | Martensitic stainless steel and manufacturing method therefor |
AR042494A1 (en) * | 2002-12-20 | 2005-06-22 | Sumitomo Chemical Co | HIGH RESISTANCE MARTENSITIC STAINLESS STEEL WITH EXCELLENT PROPERTIES OF CORROSION RESISTANCE BY CARBON DIOXIDE AND CORROSION RESISTANCE BY FISURES BY SULFIDE VOLTAGES |
EP1652950B1 (en) * | 2003-07-22 | 2014-10-15 | Nippon Steel & Sumitomo Metal Corporation | Martensitic stainless steel |
-
2004
- 2004-11-19 JP JP2004335241A patent/JP4337712B2/en active Active
-
2005
- 2005-10-26 WO PCT/JP2005/019685 patent/WO2006054430A1/en active Application Filing
- 2005-10-26 US US11/791,015 patent/US20080213120A1/en not_active Abandoned
- 2005-10-26 CN CNB2005800396559A patent/CN100549204C/en not_active Expired - Fee Related
- 2005-10-26 EP EP05799225A patent/EP1826285B1/en active Active
Also Published As
Publication number | Publication date |
---|---|
US20080213120A1 (en) | 2008-09-04 |
EP1826285A1 (en) | 2007-08-29 |
WO2006054430A1 (en) | 2006-05-26 |
JP4337712B2 (en) | 2009-09-30 |
EP1826285A4 (en) | 2009-04-08 |
JP2006144069A (en) | 2006-06-08 |
CN100549204C (en) | 2009-10-14 |
CN101061245A (en) | 2007-10-24 |
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