WO2017038178A1 - ステンレス鋼管及びその製造方法 - Google Patents
ステンレス鋼管及びその製造方法 Download PDFInfo
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- WO2017038178A1 WO2017038178A1 PCT/JP2016/066277 JP2016066277W WO2017038178A1 WO 2017038178 A1 WO2017038178 A1 WO 2017038178A1 JP 2016066277 W JP2016066277 W JP 2016066277W WO 2017038178 A1 WO2017038178 A1 WO 2017038178A1
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 51
- 239000010935 stainless steel Substances 0.000 title claims abstract description 51
- 238000004519 manufacturing process Methods 0.000 title description 17
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 76
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 24
- 239000000203 mixture Substances 0.000 claims abstract description 19
- 239000000126 substance Substances 0.000 claims abstract description 19
- 239000012535 impurity Substances 0.000 claims abstract description 10
- 229910000831 Steel Inorganic materials 0.000 claims description 51
- 239000010959 steel Substances 0.000 claims description 51
- 230000000717 retained effect Effects 0.000 claims description 39
- 238000005496 tempering Methods 0.000 claims description 38
- 238000010791 quenching Methods 0.000 claims description 28
- 230000000171 quenching effect Effects 0.000 claims description 28
- 229910052759 nickel Inorganic materials 0.000 claims description 11
- 229910052796 boron Inorganic materials 0.000 claims description 7
- 239000000463 material Substances 0.000 claims description 7
- 229910052791 calcium Inorganic materials 0.000 claims description 6
- 229910052749 magnesium Inorganic materials 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 6
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 229910052710 silicon Inorganic materials 0.000 claims description 5
- 229910052782 aluminium Inorganic materials 0.000 claims description 4
- 229910052758 niobium Inorganic materials 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 229910052717 sulfur Inorganic materials 0.000 claims description 4
- 229910052719 titanium Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 239000013078 crystal Substances 0.000 abstract description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 21
- 239000011651 chromium Substances 0.000 description 18
- 238000005260 corrosion Methods 0.000 description 14
- 230000007797 corrosion Effects 0.000 description 14
- 239000011575 calcium Substances 0.000 description 13
- 230000000694 effects Effects 0.000 description 13
- 239000011572 manganese Substances 0.000 description 13
- 239000010949 copper Substances 0.000 description 12
- 238000010438 heat treatment Methods 0.000 description 11
- 239000011777 magnesium Substances 0.000 description 11
- 238000001816 cooling Methods 0.000 description 10
- 239000010955 niobium Substances 0.000 description 10
- 239000010936 titanium Substances 0.000 description 10
- 238000005336 cracking Methods 0.000 description 9
- 238000010586 diagram Methods 0.000 description 9
- 238000005096 rolling process Methods 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- 229910000859 α-Fe Inorganic materials 0.000 description 7
- 230000007423 decrease Effects 0.000 description 6
- 229910001105 martensitic stainless steel Inorganic materials 0.000 description 6
- 238000003303 reheating Methods 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 4
- 230000035945 sensitivity Effects 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000003921 oil Substances 0.000 description 2
- 239000003129 oil well Substances 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 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
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- -1 Vanadium (V) forms carbides Chemical class 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
Images
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- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
- C21D9/085—Cooling or quenching
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- 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
-
- 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
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- 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
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
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- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
- C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
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- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
-
- 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
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- 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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- 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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- 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
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- 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
- C21D2211/001—Austenite
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- 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 a stainless steel pipe and a manufacturing method thereof.
- Steel pipes used for the extraction and transportation of oil, natural gas, etc. are required to have corrosion resistance and strength according to the usage environment.
- Reeling is a construction method in which steel pipes are welded on land and wound up in a coil shape, wound on a ship, laid on the seabed while being uncoiled on the ship. In reeling, a steel pipe with a low yield ratio is required because plastic deformation is applied to the steel pipe.
- Japanese Patent Application Laid-Open No. 3-120337 describes a martensitic stainless steel for oil wells having excellent resistance to sulfide stress corrosion cracking and containing Cr: 8 to 15%, Ni: 2 to 8%, etc. by weight. Has been.
- Japanese Patent Application Laid-Open No. 10-130785 discloses martensite for oil wells having excellent resistance to sulfide stress corrosion cracking and hot workability containing Cr: 7 to 14%, Ni: 0 to 8%, etc. by weight. Stainless steel is described.
- JP-A-2002-105604 discloses an austenite phase containing Cr: 10 to 14%, Ni: 0.2 to 7.0%, etc., having a martensite phase as a main phase and an area ratio of 5% or more.
- a high Cr martensitic stainless steel pipe for line pipes having a corrosion resistance and weldability having a structure including it is described.
- Japanese Patent Application Laid-Open No. 2001-107199 contains Cr: 9 to 15%, Ni: 0.5 to 9%, etc., and the sum of the retained austenite ratio in the base material after tempering + the fresh martensite ratio is 25% or less.
- a martensitic stainless steel with stable magnetic properties is described.
- Japanese Patent Application Laid-Open No. 2001-107198 describes martensitic stainless steel mainly composed of a tempered martensite structure containing a retained austenite phase of 15 to 40% in volume fraction.
- Japanese Patent Application Laid-Open No. 2001-226749 describes a low yield ratio martensitic stainless steel which has a retained austenite phase with a volume fraction of 4% or more and has a yield ratio of 90% or less and excellent in corrosion resistance.
- Japanese Patent Application Laid-Open No. 2001-303206 describes a stainless steel for coiled tubing that includes a retained austenite phase with a volume fraction of 2% or more and is excellent in fatigue resistance and corrosion resistance.
- JP 2000-226614 describes martensitic stainless steel that simultaneously improves strength, stress corrosion cracking resistance, and toughness while maintaining corrosion resistance.
- JP-A-2001-107198, JP-A-2001-226749, JP-A-2001-303206, and JP-A-2000-226614 described above describe that tempering is performed in a two-phase region. Yes.
- JP-A-2001-303206 mentioned above describes a steel pipe having a yield ratio reduced to 75%. However, in order to perform reeling stably, it is preferable to further reduce the yield ratio.
- the transport pipeline is used by circumferential welding of multiple steel pipes. In that case, it is preferable to use an overmatched joint in which the strength of the weld metal is higher than that of the base metal.
- the steel pipe used for the transportation pipeline is required to have strength according to the use environment. On the other hand, if the strength is too high, it is difficult to obtain an overmatch joint. Therefore, the strength of the steel pipe used by welding needs to be adjusted to a predetermined range.
- An object of the present invention is to provide a stainless steel pipe having a predetermined range of strength and a low yield ratio, and a method for manufacturing the same.
- the stainless steel pipe according to an embodiment of the present invention has a chemical composition of mass%, C: 0.02% or less, Si: 0.05 to 1.00%, Mn: 0.1 to 1.0%, P : 0.030% or less, S: 0.002% or less, Ni: 5.5 to 8%, Cr: 10 to 14%, Mo: 2 to 4%, V: 0.01 to 0.10%, Ti : 0.05 to 0.3%, Nb: 0.1% or less, Al: 0.001 to 0.1%, N: 0.05% or less, Cu: 0.5% or less, Ca: 0 to 0 0.008%, Mg: 0 to 0.05%, B: 0 to 0.005%, balance: Fe and impurities, and the structure is a martensite phase and a residual austenite phase with a volume fraction of 12 to 18%. Including.
- the martensite phase has prior austenite grains having a grain size number based on ASTM E112 and less than 8.0.
- the stainless steel pipe has a yield strength of 550 to
- the method of manufacturing a stainless steel pipe according to an embodiment of the present invention has a chemical composition of mass%, C: 0.02% or less, Si: 0.05 to 1.00%, Mn: 0.1 to 1.0. %, P: 0.030% or less, S: 0.002% or less, Ni: 5.5-8%, Cr: 10-14%, Mo: 2-4%, V: 0.01-0.10 %, Ti: 0.05 to 0.3%, Nb: 0.1% or less, Al: 0.001 to 0.1%, N: 0.05% or less, Cu: 0.5% or less, Ca: 0 to 0.008%, Mg: 0 to 0.05%, B: 0 to 0.005%, balance: a process of hot working Fe and impurities steel to form a raw tube, and the hot working after a step of hardening the blank tube from a temperature of 940 ⁇ 980 ° C.
- T is a tempering temperature expressed in ° C.
- t is a tempering time expressed in minutes.
- a stainless steel pipe having a predetermined range of strength and a low yield ratio can be obtained.
- FIG. 1 is a block diagram illustrating an example of a production line.
- FIG. 2 is a flowchart showing a manufacturing process of a stainless steel pipe.
- FIG. 3 shows the change in temperature with respect to the time of the workpiece being manufactured.
- FIG. 4 is a scatter diagram showing the relationship between the volume fraction of retained austenite phase and the yield strength.
- FIG. 5 is a scatter diagram showing the relationship between the volume fraction of retained austenite phase and the yield ratio.
- FIG. 6 is a scatter diagram showing the relationship between the value of T + 15.39ln (t) and the volume fraction of retained austenite phase.
- the inventors have adjusted a heat treatment condition of a stainless steel pipe containing Cr: 10 to 14%, Ni: 5.5 to 8%, etc., and a method capable of realizing a low yield ratio within a predetermined yield strength range. investigated.
- the lower limit of the yield strength range was 550 MPa from the viewpoint of securing the strength of the 80 ksi grade, and the upper limit was 700 MPa from the viewpoint of enabling the production of an overmatched joint. On that basis, the goal was to reduce the yield ratio to 75% or less.
- stainless steel pipes containing Cr: 10-14%, Ni: 5.5-8%, etc. contain a retained austenite phase with a volume fraction of 12-18%, and the martensite phase conforms to ASTM E112. It was found that a yield stress of 550 to 700 MPa and a yield ratio of 75% or less can be obtained if the former austenite grains having a grain size number of less than 8.0 are included.
- the above structure is obtained by quenching the hot-worked pipe in-line from a temperature of 940 to 980 ° C., and quenching the steel pipe at a temperature of Ac 1 point to Ac 3 point according to the following formula (1). It was found to be obtained by tempering under the conditions shown. 680 ⁇ T + 15.39ln (t) ⁇ 720 (1)
- T is a tempering temperature expressed in ° C.
- t is a tempering time expressed in minutes.
- the stainless steel pipe according to the present embodiment has a chemical composition described below.
- “%” of the element content means mass%.
- C 0.02% or less Carbon (C) improves the strength of steel.
- C content exceeds 0.02%, the hardness of the heat-affected zone increases and the toughness and sulfide stress corrosion cracking resistance (SSC resistance) decreases. Therefore, the C content is 0.02% or less.
- the upper limit of the C content is preferably 0.015%.
- the lower limit of the C content is preferably 0.001%.
- Si 0.05 to 1.00% Silicon (Si) deoxidizes steel. If the Si content is less than 0.05%, this effect cannot be obtained sufficiently. On the other hand, if the Si content exceeds 1.00%, the formation of ⁇ ferrite is promoted, and the SSC resistance, toughness, and hot workability of the steel are reduced. Therefore, the Si content is 0.05 to 1.00%.
- the lower limit of the Si content is preferably 0.10%, more preferably 0.15%.
- the upper limit of the Si content is preferably 0.50%, more preferably 0.40%.
- Mn 0.1 to 1.0%
- Manganese (Mn) fixes S and improves the hot workability of steel. Mn also stabilizes austenite and suppresses the formation of ⁇ ferrite. If the Mn content is less than 0.1%, this effect cannot be obtained sufficiently. On the other hand, if the Mn content exceeds 1.0%, Mn is segregated in the steel and the toughness is lowered. Therefore, the Mn content is 0.1 to 1.0%.
- the lower limit of the Mn content is preferably 0.2%, more preferably 0.25%.
- the upper limit of the Mn content is preferably 0.8%, more preferably 0.7%.
- Phosphorus (P) is an impurity. P segregates at the grain boundaries and lowers the SSC resistance and toughness of the steel. For this reason, the P content is preferably as low as possible. Therefore, the P content is 0.030% or less. The P content is preferably 0.025% or less.
- S 0.002% or less Sulfur (S) is an impurity. S decreases the hot workability of steel. Therefore, the S content is preferably as low as possible. Therefore, the S content is 0.002% or less. The S content is preferably 0.001% or less.
- Ni 5.5-8% Nickel (Ni) improves the corrosion resistance of steel. Ni is also a strong austenite-forming element, stabilizing austenite and suppressing the formation of ⁇ ferrite. If the Ni content is less than 5.5%, this effect cannot be sufficiently obtained. On the other hand, if the Ni content exceeds 8%, the hot workability of the steel decreases. Therefore, the Ni content is 5.5 to 8%.
- the Ni content is preferably higher than 6.0%.
- the lower limit of the Ni content is more preferably 6.1%.
- the upper limit of the Ni content is preferably 7.5%, more preferably 7.0%.
- Chromium (Cr) improves the corrosion resistance of steel. If the Cr content is less than 10%, this effect cannot be obtained sufficiently. On the other hand, if the Cr content exceeds 14%, the formation of ⁇ ferrite is promoted, and the SSC resistance, toughness, and hot workability of the steel are reduced. Therefore, the Cr content is 10 to 14%.
- the lower limit of the Cr content is preferably 10.5%, more preferably 11%.
- the upper limit of the Cr content is preferably 13%, more preferably 12.5%.
- Mo 2-4% Molybdenum (Mo) improves the corrosion resistance of steel. Mo also suppresses the grain boundary segregation of P and improves the toughness of the steel. Further, Mo is an element effective for generating a retained austenite phase. However, when the Mo content is less than 2%, this effect cannot be sufficiently obtained. On the other hand, if the Mo content exceeds 4%, the formation of ⁇ ferrite is promoted, and the SSC resistance, toughness, and hot workability of the steel decrease. Therefore, the Mo content is 2 to 4%. The lower limit of the Mo content is preferably 2.2%. The upper limit of the Mo content is preferably 3.5%, more preferably 3%.
- V 0.01 to 0.10% Vanadium (V) forms carbides and improves the strength of the steel. If the V content is less than 0.01%, this effect cannot be sufficiently obtained. On the other hand, if the V content exceeds 0.10%, the weld cracking sensitivity of the steel increases. Therefore, the V content is 0.01 to 0.10%.
- the lower limit of the V content is preferably 0.02%, more preferably 0.03%.
- the upper limit of the V content is preferably 0.08%, more preferably 0.07%.
- Ti 0.05 to 0.3% Titanium (Ti) forms carbides and improves the strength of the steel. If the Ti content is less than 0.05%, this effect cannot be sufficiently obtained. On the other hand, if the Ti content exceeds 0.3%, the weld cracking sensitivity of the steel increases. Therefore, the Ti content is 0.05 to 0.3%.
- the lower limit of the Ti content is preferably 0.06%, and more preferably 0.08%.
- the upper limit of the Ti content is preferably 0.25%, more preferably 0.20%.
- Niobium (Nb) forms carbides and improves the strength of the steel. This effect can be obtained if Nb is contained even a little.
- the Nb content is 0.1% or less.
- the lower limit of the Nb content is preferably 0.001%.
- the upper limit of the Nb content is preferably 0.08%, more preferably 0.05%.
- Al 0.001 to 0.1%
- Aluminum (Al) deoxidizes steel. If the Al content is less than 0.001%, this effect cannot be sufficiently obtained. On the other hand, when the Al content exceeds 0.1%, inclusions increase and the toughness of the steel decreases. Therefore, the Al content is 0.001 to 0.1%.
- the lower limit of the Al content is preferably 0.01%.
- the upper limit of the Al content is preferably 0.08%, more preferably 0.06%.
- N 0.05% or less Nitrogen (N) increases the hardness of the weld heat-affected zone and decreases toughness and resistance to sulfide stress corrosion cracking (SSC resistance). Therefore, it is preferable that the N content is as small as possible. Therefore, the N content is 0.05% or less.
- the upper limit of the N content is preferably 0.03%, and more preferably 0.02%. From the viewpoint of cost, the lower limit of the N content is preferably 0.001%.
- Cu 0.5% or less Copper (Cu) is not necessarily contained positively. Since Cu is an effective element for improving the corrosion resistance in an acidic environment containing both carbon dioxide gas and hydrogen sulfide, an appropriate amount of Cu may be contained. In order to acquire the effect, it is preferable to make it contain 0.05% or more. On the other hand, if the Cu content exceeds 0.5%, the hardness of the heat-affected zone increases. Therefore, the Cu content is 0.5% or less. The lower limit of the Cu content is more preferably 0.08%. The upper limit of the Cu content is preferably 0.4%.
- the balance of the chemical composition of the stainless steel pipe according to this embodiment is Fe and impurities.
- the impurity here refers to an element mixed from ore and scrap used as a raw material of steel, or an element mixed from the environment of the manufacturing process.
- the chemical composition of the stainless steel pipe according to the present embodiment may further contain one or more elements selected from the group consisting of Ca, Mg, and B instead of a part of Fe. All of these elements improve the hot workability of steel. Ca, Mg, and B are all selective elements. That is, the chemical composition of the stainless steel pipe according to the present embodiment may not include some or all of these elements.
- Ca 0 to 0.008% Calcium (Ca) improves the hot workability of steel. This effect can be obtained if Ca is contained even a little. On the other hand, if the Ca content exceeds 0.008%, coarse oxides are formed and the toughness of the steel is lowered. Therefore, the Ca content is 0 to 0.008%.
- the lower limit of the Ca content is preferably 0.001%.
- the upper limit of the Ca content is preferably 0.005%.
- Mg 0 to 0.05%
- Magnesium (Mg) improves the hot workability of steel. This effect can be obtained if Mg is contained even a little.
- Mg content exceeds 0.05%, a coarse oxide is formed and the toughness of the steel is lowered. Therefore, the Mg content is 0 to 0.05%.
- the lower limit of the Mg content is preferably 0.001%.
- the upper limit of the Ca content is preferably 0.03%.
- B 0 to 0.005% Boron (B) improves the hot workability of steel. If B is contained even a little, this effect can be obtained. On the other hand, if the B content exceeds 0.005%, the weld cracking sensitivity of the steel increases. Therefore, the B content is 0 to 0.005%.
- the lower limit of the B content is preferably 0.0005%.
- the upper limit of the B content is preferably 0.003%.
- the structure of the stainless steel pipe according to the present embodiment is mainly composed of a martensite phase and includes a retained austenite phase having a volume fraction of 12 to 18%.
- the martensite phase has prior austenite grains having a grain size number based on ASTM E112 of less than 8.0.
- the yield ratio is reduced by setting the volume fraction of the residual austenite phase to 12% or more and the grain size number of the prior austenite grains of the martensite phase to less than 8.0. It can be reduced to 75% or less.
- the volume fraction of the retained austenite phase can be adjusted by heat treatment as will be described later.
- the volume fraction of the retained austenite phase also depends on the balance of the content of austenite forming elements such as C, Mn, Ni and Cu and the content of ferrite forming elements such as Si, Cr, Mo and V. Especially, the influence of Ni content is large.
- the volume fraction of the retained austenite phase is measured as follows using an X-ray diffraction method.
- a sample including the central thickness of the tempered stainless steel pipe is collected.
- the surface of the collected sample is polished.
- X-ray diffraction is performed on the polished surface using CoK ⁇ rays as incident X-rays. From the integrated intensities of the (211), (200), and (110) planes of ferrite (bcc structure) and the integrated intensities of the (220), (200), and (111) planes of austenite (fcc structure).
- the volume fraction of retained austenite is quantitatively determined.
- the volume fraction of the retained austenite phase is 12-18%.
- the lower limit of the volume fraction of the retained austenite phase is preferably 13%.
- the upper limit of the volume fraction of the retained austenite phase is preferably 17%.
- the grain size number of the prior austenite grains in the martensite phase is measured by electron beam backscatter diffraction (EBSD) as follows. A sample is taken from the central position of the thickness of the cross section of the stainless steel pipe after tempering (cross section perpendicular to the axial direction of the steel pipe). The old austenite grain boundary is specified by EBSD in the observation range of 90 ⁇ 90 ⁇ m 2 using the collected sample, and the crystal grain size number is obtained according to ASTM E112.
- EBSD electron beam backscatter diffraction
- the grain size number of the prior austenite grains in the martensite phase is 8.0 or more, the amount of retained austenite phase generated tends to increase. Therefore, the grain size number of the prior austenite grains in the martensite phase is less than 8.0.
- the upper limit of the grain size number of the prior austenite grains in the martensite phase is preferably 7.8.
- the stainless steel according to the present embodiment has a yield strength of 550 to 700 MPa.
- the upper limit of the yield strength is set to 700 MPa because when the yield strength exceeds 700 MPa, it becomes difficult to form an overmatch joint.
- FIG. 1 is a block diagram showing an example of a production line.
- the production line includes a heating furnace 1, a piercing machine 2, a stretch rolling mill 3, a constant diameter rolling mill 4, an auxiliary heating furnace 5, a water cooling device 6, and a tempering device 7.
- a transport roller 10 is disposed between the devices. In the manufacturing method according to the example of FIG. 1, hot working, quenching, and tempering are all performed inline.
- FIG. 2 is a flowchart showing the manufacturing process of the stainless steel pipe according to the present embodiment.
- FIG. 3 is a diagram showing a change in temperature with respect to time of a workpiece (steel material or raw pipe) being manufactured.
- A1 indicates Ac 1 point when the workpiece is heated, and Ar 1 point when the workpiece is cooled.
- A3 indicates Ac 3 point when the workpiece is heated, and Ar 3 point when the workpiece is cooled.
- the heating furnace 1 is, for example, a walking beam furnace or a rotary furnace.
- the steel material is, for example, a round billet.
- the steel material may be manufactured by a continuous casting apparatus such as round CC, or may be manufactured by hot working (forging or split rolling) an ingot or slab.
- a preferred heating temperature is 1100 ° C. to 1300 ° C.
- the hot steel material is hot-worked into a raw pipe (S2 and S3). Specifically, a round billet is pierced and rolled by a piercing machine 2 to form a raw pipe (piercing and rolling step: S2). Furthermore, the piercing-rolled element pipe is rolled by the drawing mill 3 and the constant diameter rolling machine 4 (stretching rolling process and regular rolling process: S3).
- the raw tube manufactured by hot working is continuously quenched in-line (quenching step: S5). If necessary, a reheating step (S4) may be performed between the drawing and rolling step (S3) and the quenching step (S5).
- the hot-worked raw tube is heated to a predetermined temperature of 940 ° C. or higher by the auxiliary heating furnace 5.
- the reheating step (S4) can be omitted when quenching in the subsequent quenching step is possible without being performed. However, even in that case, it is preferable to perform the reheating step (S4) in order to make the temperature of the raw tube uniform.
- the raw tube manufactured by hot working or the reheated raw tube is quenched in-line by the water cooling device 6 (quenching step: S5).
- quenching in-line includes both the case of quenching immediately after hot working and the case of quenching after reheating by the auxiliary heating furnace 5 after hot working.
- the water cooling device 6 is, for example, a laminar water flow device and / or a jet water flow device.
- the cooling rate is preferably 5 ° C./second or more.
- the structure of the tube immediately before water cooling is almost austenite single phase.
- the temperature (quenching temperature) of the raw tube immediately before water cooling is increased, the particle size of the austenite phase increases.
- the austenite phase is cooled with water to become a martensite phase, and further tempered to become a martensite phase.
- the size of the prior austenite grains is not significantly affected by tempering. Therefore, the size of the prior austenite grains in the martensite phase is largely determined by the quenching conditions. That is, the size of the prior austenite grains of the martensite phase contained in the structure of the stainless steel pipe after tempering can be controlled by the quenching conditions.
- in-line quenching is offline quenching (after hot working, the temperature of the tube is lowered to about room temperature, and then it is again heated to a predetermined temperature and quenched.
- hot working Compared with the above-mentioned equipment, the size of the prior austenite grains can be easily increased.
- the quenching temperature is 940 to 980 ° C.
- the quenched pipe is tempered by the tempering device 7 (tempering step: S6). Specifically, the quenched pipe is charged into a furnace having a temperature of Ac 1 to Ac 3 (tempering temperature), and a predetermined time (tempering time) so as to satisfy the following formula (1). Hold.
- the tempering temperature is the average temperature in the furnace.
- the tempering time is the time (in-furnace time) from when the raw tube is charged into the furnace until it is extracted.
- the tempered tube is usually cooled by air cooling. 680 ⁇ T + 15.39ln (t) ⁇ 720 (1)
- T is a tempering temperature expressed in ° C.
- t is a tempering time expressed in minutes.
- ln (t) is the natural logarithm of t.
- the tempering temperature By setting the tempering temperature to Ac 1 point to Ac 3 point, a part of the martensite phase is reversely transformed into the austenite phase. While being kept at the tempering temperature, the austenite stabilizing element is concentrated in the reverse transformed austenite phase. Many of the reverse-transformed austenite phases retain the austenite phase after cooling and become a retained austenite phase.
- the volume fraction of the retained austenite phase can be made 12 to 18% if the tempering temperature and the tempering time satisfy the formula (1).
- a plurality of stainless steel pipes having various chemical compositions were manufactured, and the relationship between mechanical properties and retained austenite amount was investigated.
- each manufactured round billet was heated to 1100-1300 ° C. in a heating furnace. Subsequently, each round billet was pierced and rolled by a piercing machine into a raw pipe. Subsequently, each raw tube was stretched and rolled by a mandrel mill. Subsequently, each raw pipe was drawn and rolled (constant diameter rolling) with a sizer to produce a stainless steel pipe having an outer diameter of 273.1 mm and a wall thickness of 14.3 mm.
- the yield strength and tensile strength of each stainless steel pipe were measured according to ASTM A370. The yield ratio was determined by dividing the yield strength value by the tensile strength value. Furthermore, the volume fraction of the retained austenite phase of each stainless steel pipe was measured by X-ray diffraction. The results are shown in Table 2 above. In Table 2, “YS” is the yield strength (MPa), “TS” is the tensile strength (MPa), “YR” is the yield ratio (%), and “residual ⁇ amount” is the volume fraction of the retained austenite phase. (%) Is shown respectively.
- the old austenite grains in the martensite phase were measured by EBSD.
- the results are shown in the column of “Old austenite grain size number” in Table 2. “-” In the same column indicates that the crystal grain size number is not measured. In all the stainless steel pipes of “invention steel”, the crystal grain size number of the prior austenite grains was less than 8.0.
- the test numbers E1, F1, J1, K1, M1 to P1, E2, F2, J2, K2, M2 to P2, A3, and D5 are suitable for quenching conditions, tempering temperature and tempering.
- These stainless steel tubes had a volume fraction of retained austenite phase of 12-18%.
- These stainless steel pipes had a yield strength of 550 to 700 MPa and a yield ratio of 75% or less.
- the stainless steel pipes with test numbers A1 to D1, H1, I1, A2 to D2, H2, I2, B3 to E3, A4 to C4, and A5 to C5 had a yield ratio higher than 75%. This is probably because the tempering temperature and the tempering time did not satisfy the formula (1), or the chemical composition did not satisfy the specified range, and the volume fraction of the retained austenite phase was less than 12%.
- the stainless steel pipes with test numbers Q1 and Q2 had a yield strength lower than 550 MPa. This is probably because the quenching temperature was low, the prior austenite grain size was refined, and the amount of retained austenite phase produced increased.
- the stainless steel pipes with test numbers G1, L1, G2, and L2 had a yield strength lower than 550 MPa. This is probably because the volume fraction of the retained austenite phase was higher than 18%. The reason why the volume fraction of the retained austenite phase was higher than 18% is considered that the tempering temperature and the tempering time did not satisfy the formula (1).
- FIG. 4 is a scatter diagram showing the relationship between the volume fraction of retained austenite phase and the yield strength in a target whose chemical composition and quenching temperature conditions satisfy the predetermined ranges. From this figure, it is understood that a yield strength of 550 to 700 MPa can be obtained if the volume fraction of the retained austenite phase is larger than 10% and not larger than 18%.
- FIG. 5 is a scatter diagram showing the relationship between the volume fraction of the retained austenite phase and the yield ratio in a case where the chemical composition and the quenching temperature condition satisfy the predetermined ranges. From this figure, it is understood that when the volume fraction of the retained austenite phase is 12% or more, a yield ratio of 75% or less can be obtained.
- FIG. 6 is a scatter diagram showing the relationship between the value of T + 15.39 ln (t) and the volume fraction of residual austenite phase in the case where the chemical composition and the quenching temperature condition satisfy the predetermined ranges. From FIG. 6, it can be seen that if the value of T + 15.39ln (t) is 680 to 720, the volume fraction of the retained austenite phase can be 12 to 18%.
Abstract
Description
680≦T+15.39ln(t)≦720・・・(1)
ここで、Tは℃で表した焼戻し温度であり、tは分で表した焼戻し時間である。
680≦T+15.39ln(t)≦720・・・(1)
ここで、Tは℃で表した焼戻し温度であり、tは分で表した焼戻し時間である。
本実施形態によるステンレス鋼管は、以下に説明する化学組成を有する。以下の説明において、元素の含有量の「%」は、質量%を意味する。
炭素(C)は、鋼の強度を向上させる。一方、C含有量が0.02%を超えると、熱影響部の硬さが上昇して靱性及び耐硫化物応力腐食割れ性(耐SSC性)が低下する。したがって、C含有量は0.02%以下である。C含有量の上限は、好ましくは0.015%である。C含有量の下限は、好ましくは0.001%である。
シリコン(Si)は、鋼を脱酸する。Si含有量が0.05%未満では、この効果が十分に得られない。一方、Si含有量が1.00%を超えると、δフェライトの形成が促進されて鋼の耐SSC性、靱性、及び熱間加工性が低下する。したがって、Si含有量は0.05~1.00%である。Si含有量の下限は、好ましくは0.10%であり、さらに好ましくは0.15%である。Si含有量の上限は、好ましくは0.50%であり、さらに好ましくは0.40%である。
マンガン(Mn)は、Sを固定して鋼の熱間加工性を向上させる。Mnはまた、オーステナイトを安定化させてδフェライトの生成を抑制する。Mn含有量が0.1%未満では、この効果が十分に得られない。一方、Mn含有量が1.0%を超えると、Mnが鋼中で偏析し、靱性が低下する。したがって、Mn含有量は0.1~1.0%である。Mn含有量の下限は、好ましくは0.2%であり、さらに好ましくは0.25%である。Mn含有量の上限は、好ましくは0.8%であり、さらに好ましくは0.7%である。
燐(P)は不純物である。Pは粒界に偏析して鋼の耐SSC性及び靱性を低下させる。そのため、P含有量はなるべく低い方が好ましい。したがって、P含有量は0.030%以下である。P含有量は、好ましくは0.025%以下である。
硫黄(S)は不純物である。Sは鋼の熱間加工性を低下させる。そのため、S含有量はなるべく低い方が好ましい。したがって、S含有量は0.002%以下である。S含有量は、好ましくは0.001%以下である。
ニッケル(Ni)は、鋼の耐食性を向上させる。Niはまた、強力なオーステナイト形成元素であり、オーステナイトを安定化させてδフェライトの生成を抑制する。Ni含有量が5.5%未満では、この効果が十分に得られない。一方、Ni含有量が8%を超えると、鋼の熱間加工性が低下する。したがって、Ni含有量は5.5~8%である。Ni含有量は、好ましくは6.0%よりも高い。Ni含有量の下限は、さらに好ましくは6.1%である。Ni含有量の上限は、好ましくは7.5%であり、さらに好ましくは7.0%である。
クロム(Cr)は、鋼の耐食性を向上させる。Cr含有量が10%未満では、この効果が十分に得られない。一方、Cr含有量が14%を超えると、δフェライトの形成が促進されて鋼の耐SSC性、靱性、及び熱間加工性が低下する。したがって、Cr含有量は10~14%である。Cr含有量の下限は、好ましくは10.5%であり、さらに好ましくは11%である。Cr含有量の上限は、好ましくは13%であり、さらに好ましくは12.5%である。
モリブデン(Mo)は、鋼の耐食性を向上させる。Moはまた、Pの粒界偏析を抑制して鋼の靱性を向上させる。また、Moは残留オーステナイト相の生成に効果のある元素であるが、Mo含有量が2%未満では、この効果が十分に得られない。一方、Mo含有量が4%を超えると、δフェライトの形成が促進されて鋼の耐SSC性、靱性、及び熱間加工性が低下する。したがって、Mo含有量は2~4%である。Mo含有量の下限は、好ましくは2.2%である。Mo含有量の上限は、好ましくは3.5%であり、さらに好ましくは3%である。
バナジウム(V)は、炭化物を形成して鋼の強度を向上させる。V含有量が0.01%未満では、この効果が十分に得られない。一方、V含有量が0.10%を超えると、鋼の溶接割れ感受性が高くなる。したがって、V含有量は0.01~0.10%である。V含有量の下限は、好ましくは0.02%であり、さらに好ましくは0.03%である。V含有量の上限は、好ましくは0.08%であり、さらに好ましくは0.07%である。
チタン(Ti)は、炭化物を形成して鋼の強度を向上させる。Ti含有量が0.05%未満では、この効果が十分に得られない。一方、Ti含有量が0.3%を超えると、鋼の溶接割れ感受性が高くなる。したがって、Ti含有量は0.05~0.3%である。Ti含有量の下限は、好ましくは0.06%であり、さらに好ましくは0.08%である。Ti含有量の上限は、好ましくは0.25%であり、さらに好ましくは0.20%である。
ニオブ(Nb)は、炭化物を形成して鋼の強度を向上させる。Nbが少しでも含有されていれば、この効果が得られる。一方、Nb含有量が0.1%を超えると、鋼の溶接割れ感受性が高くなる。したがって、Nb含有量は0.1%以下である。Nb含有量の下限は、好ましくは0.001%である。Nb含有量の上限は、好ましくは0.08%であり、さらに好ましくは0.05%である。
アルミニウム(Al)は、鋼を脱酸する。Al含有量が0.001%未満では、この効果が十分に得られない。一方、Al含有量が0.1%を超えると、介在物が多くなり鋼の靱性が低下する。したがって、Al含有量は0.001~0.1%である。Al含有量の下限は、好ましくは0.01%である。Al含有量の上限は、好ましくは0.08%であり、さらに好ましくは0.06%である。
窒素(N)は、溶接熱影響部の硬さを上昇させて靱性及び耐硫化物応力腐食割れ性(耐SSC性)を低下させる。そのため、N含有量はなるべく少ない方が好ましい。したがって、N含有量は0.05%以下である。N含有量の上限は、好ましくは0.03%であり、さらに好ましくは0.02%である。コストの観点から、N含有量の下限は、好ましくは0.001%である。
銅(Cu)は、必ずしも積極的に含有させる必要はない。Cuは、炭酸ガスと硫化水素の両方を含む酸性環境中での耐食性を向上させるのに有効的な元素であるので、Cuを適量含有させてもよい。その効果を得るには、0.05%以上含有させるのが好ましい。一方、Cu含有量が0.5%を超えると、熱影響部の硬さが高くなる。したがって、Cu含有量は0.5%以下である。Cu含有量の下限は、より好ましくは0.08%である。Cu含有量の上限は、好ましくは0.4%である。
カルシウム(Ca)は、鋼の熱間加工性を向上させる。Caが少しでも含有されていれば、この効果が得られる。一方、Ca含有量が0.008%を超えると、粗大な酸化物が形成されて鋼の靱性が低下する。したがって、Ca含有量は0~0.008%である。Ca含有量の下限は、好ましくは0.001%である。Ca含有量の上限は、好ましくは0.005%である。
マグネシウム(Mg)は、鋼の熱間加工性を向上させる。Mgが少しでも含有されていれば、この効果が得られる。一方、Mg含有量が0.05%を超えると、粗大な酸化物が形成されて鋼の靱性が低下する。したがって、Mg含有量は0~0.05%である。Mg含有量の下限は、好ましくは0.001%である。Ca含有量の上限は、好ましくは0.03%である。
硼素(B)は、鋼の熱間加工性を向上させる。Bが少しでも含有されていれば、この効果が得られる。一方、B含有量が0.005%を超えると、鋼の溶接割れ感受性が高くなる。したがって、B含有量は0~0.005%である。B含有量の下限は、好ましくは0.0005%である。B含有量の上限は、好ましくは0.003%である。
本実施形態によるステンレス鋼管の組織は、マルテンサイト相を主体とし、体積分率で12~18%の残留オーステナイト相を含む。マルテンサイト相は、ASTM E112に準拠した結晶粒度番号が8.0未満の旧オーステナイト粒を有する。
以下、本実施形態によるステンレス鋼管の製造方法の一例を説明する。ただし、本実施形態によるステンレス鋼管の製造方法は、これに限定されない。
680≦T+15.39ln(t)≦720・・・(1)
ここで、Tは℃で表した焼戻し温度であり、tは分で表した焼戻し時間である。ln(t)は、tの自然対数である。
表1に示す化学組成を有する複数の溶鋼を電気炉で製造した。溶鋼からインゴットを製造した。インゴットを熱間鍛造して、丸ビレットを製造した。なお、表1中の「‐」は、含有量が不純物レベルであることを示す。
Claims (3)
- 化学組成が、質量%で、
C :0.02%以下、
Si:0.05~1.00%、
Mn:0.1~1.0%、
P :0.030%以下、
S :0.002%以下、
Ni:5.5~8%、
Cr:10~14%、
Mo:2~4%、
V :0.01~0.10%、
Ti:0.05~0.3%、
Nb:0.1%以下、
Al:0.001~0.1%、
N :0.05%以下、
Cu:0.5%以下、
Ca:0~0.008%、
Mg:0~0.05%、
B :0~0.005%、
残部:Fe及び不純物であり、
組織が、マルテンサイト相と、体積分率で12~18%の残留オーステナイト相とを含み、
前記マルテンサイト相は、ASTM E112に準拠した結晶粒度番号で8.0未満の旧オーステナイト粒を有し、
550~700MPaの降伏強度を有する、ステンレス鋼管。 - 請求項1に記載のステンレス鋼管であって、
前記化学組成が、質量%で、
Ca:0.001~0.008%、
Mg:0.001~0.05%、及び
B :0.0005~0.005%、
からなる群から選択される1又は2以上の元素を含有する、ステンレス鋼管。 - 化学組成が、質量%で、C:0.02%以下、Si:0.05~1.00%、Mn:0.1~1.0%、P:0.030%以下、S:0.002%以下、Ni:5.5~8%、Cr:10~14%、Mo:2~4%、V:0.01~0.10%、Ti:0.05~0.3%、Nb:0.1%以下、Al:0.001~0.1%、N:0.05%以下、Cu:0.5%以下、Ca:0~0.008%、Mg:0~0.05%、B:0~0.005%、残部:Fe及び不純物である鋼材を熱間加工して素管にする工程と、
前記熱間加工後、前記熱間加工とインラインで前記素管を940~980℃の温度から焼入れする工程と、
前記焼入れされた素管をAc1点~Ac3点の温度で、下記式(1)に示す条件で焼戻しする工程とを備える、ステンレス鋼管の製造方法。
680≦T+15.39ln(t)≦720・・・(1)
ここで、Tは℃で表した焼戻し温度であり、tは分で表した焼戻し時間である。
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EP3690072A4 (en) * | 2017-09-29 | 2020-08-05 | JFE Steel Corporation | MARTENSITE BASED STAINLESS STEEL SEAMLESS PIPE FOR OIL WELL PIPING, AND METHOD OF MANUFACTURING THE SAME |
JP2021021087A (ja) * | 2019-07-24 | 2021-02-18 | 日本製鉄株式会社 | ステンレス鋼管の製造方法 |
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CN113584407A (zh) * | 2020-04-30 | 2021-11-02 | 宝山钢铁股份有限公司 | 一种高强度耐高温腐蚀马氏体不锈钢及其制造方法 |
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