WO2022162824A1 - 鋼材 - Google Patents
鋼材 Download PDFInfo
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- WO2022162824A1 WO2022162824A1 PCT/JP2021/002997 JP2021002997W WO2022162824A1 WO 2022162824 A1 WO2022162824 A1 WO 2022162824A1 JP 2021002997 W JP2021002997 W JP 2021002997W WO 2022162824 A1 WO2022162824 A1 WO 2022162824A1
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- Prior art keywords
- steel
- content
- steel material
- sulfides
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 397
- 239000010959 steel Substances 0.000 title claims abstract description 397
- 239000000463 material Substances 0.000 title claims abstract description 246
- 239000000203 mixture Substances 0.000 claims abstract description 59
- 239000000126 substance Substances 0.000 claims abstract description 55
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims abstract description 47
- 229910052761 rare earth metal Inorganic materials 0.000 claims abstract description 32
- 239000012535 impurity Substances 0.000 claims abstract description 15
- 150000003568 thioethers Chemical class 0.000 claims description 113
- 229910052742 iron Inorganic materials 0.000 abstract description 3
- 239000002245 particle Substances 0.000 abstract 1
- 238000012360 testing method Methods 0.000 description 118
- 239000011572 manganese Substances 0.000 description 115
- 239000011575 calcium Substances 0.000 description 103
- 238000000034 method Methods 0.000 description 76
- 239000011651 chromium Substances 0.000 description 55
- 230000008569 process Effects 0.000 description 40
- 238000004519 manufacturing process Methods 0.000 description 33
- 229910000734 martensite Inorganic materials 0.000 description 32
- 238000010791 quenching Methods 0.000 description 28
- 230000000171 quenching effect Effects 0.000 description 28
- 229910001566 austenite Inorganic materials 0.000 description 27
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 26
- 230000000717 retained effect Effects 0.000 description 26
- 238000005261 decarburization Methods 0.000 description 23
- 239000010955 niobium Substances 0.000 description 23
- 230000000694 effects Effects 0.000 description 21
- 238000005496 tempering Methods 0.000 description 21
- 238000009864 tensile test Methods 0.000 description 21
- 239000010949 copper Substances 0.000 description 20
- 239000011777 magnesium Substances 0.000 description 20
- 238000007670 refining Methods 0.000 description 18
- 239000007789 gas Substances 0.000 description 17
- 238000010438 heat treatment Methods 0.000 description 17
- 239000010936 titanium Substances 0.000 description 16
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 description 15
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 14
- 230000009467 reduction Effects 0.000 description 14
- 239000002893 slag Substances 0.000 description 14
- 238000011156 evaluation Methods 0.000 description 12
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 11
- 230000015572 biosynthetic process Effects 0.000 description 10
- 229910052804 chromium Inorganic materials 0.000 description 10
- 229910052802 copper Inorganic materials 0.000 description 10
- 230000007423 decrease Effects 0.000 description 10
- 238000002156 mixing Methods 0.000 description 10
- 229910052698 phosphorus Inorganic materials 0.000 description 10
- 238000005096 rolling process Methods 0.000 description 10
- 239000002344 surface layer Substances 0.000 description 10
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 9
- 229910052748 manganese Inorganic materials 0.000 description 9
- 238000005259 measurement Methods 0.000 description 9
- 229910052750 molybdenum Inorganic materials 0.000 description 9
- 229910052710 silicon Inorganic materials 0.000 description 9
- 229910052717 sulfur Inorganic materials 0.000 description 9
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 8
- 229910052759 nickel Inorganic materials 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 7
- 238000002441 X-ray diffraction Methods 0.000 description 7
- -1 hydrogen sulfide ions Chemical class 0.000 description 7
- 239000003921 oil Substances 0.000 description 7
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 6
- 229910052791 calcium Inorganic materials 0.000 description 6
- 238000005336 cracking Methods 0.000 description 6
- 229910052749 magnesium Inorganic materials 0.000 description 6
- 229910052758 niobium Inorganic materials 0.000 description 6
- 150000004767 nitrides Chemical class 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- 239000012085 test solution Substances 0.000 description 6
- 229910052721 tungsten Inorganic materials 0.000 description 6
- 229910000851 Alloy steel Inorganic materials 0.000 description 5
- 239000001569 carbon dioxide Substances 0.000 description 5
- 229910002092 carbon dioxide Inorganic materials 0.000 description 5
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 5
- 238000009776 industrial production Methods 0.000 description 5
- 239000002994 raw material Substances 0.000 description 5
- 229910052719 titanium Inorganic materials 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 229910052796 boron Inorganic materials 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 230000014759 maintenance of location Effects 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 239000003129 oil well Substances 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
- 239000011347 resin Substances 0.000 description 4
- 229920005989 resin Polymers 0.000 description 4
- 229920006395 saturated elastomer Polymers 0.000 description 4
- 239000011780 sodium chloride Substances 0.000 description 4
- 229910052720 vanadium Inorganic materials 0.000 description 4
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 235000013339 cereals Nutrition 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000006378 damage Effects 0.000 description 3
- 229910001105 martensitic stainless steel Inorganic materials 0.000 description 3
- 230000007246 mechanism Effects 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 238000002161 passivation Methods 0.000 description 3
- 238000003303 reheating Methods 0.000 description 3
- 238000009628 steelmaking Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- 241000209094 Oryza Species 0.000 description 2
- 235000007164 Oryza sativa Nutrition 0.000 description 2
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 239000003518 caustics Substances 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 229910052801 chlorine Inorganic materials 0.000 description 2
- 238000007872 degassing Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
- 229910052700 potassium Inorganic materials 0.000 description 2
- 238000011946 reduction process Methods 0.000 description 2
- 235000009566 rice Nutrition 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 239000001632 sodium acetate Substances 0.000 description 2
- 235000017281 sodium acetate Nutrition 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910052726 zirconium Inorganic materials 0.000 description 2
- 229910000859 α-Fe Inorganic materials 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
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910052765 Lutetium Inorganic materials 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
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- VVTSZOCINPYFDP-UHFFFAOYSA-N [O].[Ar] Chemical compound [O].[Ar] VVTSZOCINPYFDP-UHFFFAOYSA-N 0.000 description 1
- 239000008186 active pharmaceutical agent Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 238000000921 elemental analysis Methods 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- OHSVLFRHMCKCQY-UHFFFAOYSA-N lutetium atom Chemical compound [Lu] OHSVLFRHMCKCQY-UHFFFAOYSA-N 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 239000003595 mist 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
- 239000011574 phosphorus Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 229910052706 scandium Inorganic materials 0.000 description 1
- SIXSYDAISGFNSX-UHFFFAOYSA-N scandium atom Chemical compound [Sc] SIXSYDAISGFNSX-UHFFFAOYSA-N 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
Classifications
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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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- 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
-
- 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
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
-
- 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
-
- 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
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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
- C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
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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
- 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")
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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
- C21D2211/004—Dispersions; Precipitations
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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
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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
- C21D6/004—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
- C21D6/007—Heat treatment of ferrous alloys containing Co
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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
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- 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
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires 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
- 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
- C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
Definitions
- the present disclosure relates to steel materials, and more particularly to steel materials suitable for use in sour environments containing hydrogen sulfide and carbon dioxide gas.
- Oil wells and gas wells have an environment containing a large amount of corrosive substances.
- Corrosive substances are, for example, corrosive gases such as hydrogen sulfide (H 2 S) gas and carbonic acid (CO 2 ) gas.
- H 2 S hydrogen sulfide
- CO 2 carbonic acid
- an environment containing hydrogen sulfide and carbon dioxide is referred to as a "sour environment.”
- the temperature of the sour environment is about room temperature to 200° C., depending on the depth of the well.
- normal temperature means 24 ⁇ 3°C.
- chromium is effective in improving the carbon dioxide corrosion resistance of steel. Therefore, in an oil well environment containing a large amount of carbon dioxide, depending on the partial pressure and temperature of carbon dioxide, API L80 13Cr steel (regular 13Cr steel), super 13Cr steel with reduced C content, etc. A martensitic stainless steel material containing about 13% by mass of Cr is used.
- Patent Document 1 JP-A-10-503809
- Patent Document 2 JP-A-2000-192196
- Patent Document 3 JP-A-8-246107
- Patent Document 4 JP-A-2012-136742
- Patent Document 1 has, in weight percent, C: 0.005 to 0.05%, Si ⁇ 0.50%, Mn: 0.1 to 1.0%, P ⁇ 0.03%, S ⁇ 0 .005%, Mo: 1.0 to 3.0%, Cu: 1.0 to 4.0%, Ni: 5 to 8%, Al ⁇ 0.06%, and the balance consists of Fe and impurities , Cr+1.6Mo ⁇ 13, and 40C+34N+Ni+0.3Cu ⁇ 1.1Cr ⁇ 1.8Mo ⁇ 10.5.
- the microstructure of the martensitic stainless steel in this document is a tempered martensitic structure.
- Patent Document 1 describes that the SSC resistance can be enhanced by containing 1.0 to 3.0% of Mo.
- Patent Document 2 has, in weight percent, C: 0.001 to 0.05%, Si: 0.05 to 1%, Mn: 0.05 to 2%, P: 0.025% or less, S: 0.01% or less, Cr: 9-14%, Mo: 3.1-7%, Ni: 1-8%, Co: 0.5-7%, sol. Al: 0.001 to 0.1%, N: 0.05% or less, O (oxygen): 0.01% or less, Cu: 0 to 5%, W: 0 to 5%, and the balance is Fe and inevitable impurities.
- Mo is contained, the Ms point is lowered. Therefore, by containing Co together with Mo, the decrease in the Ms point is suppressed and the microstructure is made into a martensite single-phase structure.
- Patent Literature 2 describes that this can improve the SSC resistance while maintaining the strength of 80 ksi or more (552 MPa or more).
- the chemical composition of the martensitic stainless steel of Patent Document 3 is, in weight percent, C: 0.005% to 0.05%, Si: 0.05% to 0.5%, Mn: 0.1% to 1. 0%, P: 0.025% or less, S: 0.015% or less, Cr: 12-15%, Ni: 4.5%-9.0%, Cu: 1%-3%, Mo: 2 % to 3%, W: 0.1% to 3%, Al: 0.005 to 0.2%, N: 0.005% to 0.1%, and the balance consists of Fe and unavoidable impurities .
- the above chemical composition further satisfies 40C+34N+Ni+0.3Cu+Co-1.1Cr-1.8Mo-0.9W ⁇ -10.
- the martensitic stainless seamless steel pipe of Patent Document 4 contains, in % by mass, C: 0.01% or less, Si: 0.5% or less, Mn: 0.1 to 2.0%, and P: 0.03%. Below, S: 0.005% or less, Cr: 14.0 to 15.5%, Ni: 5.5 to 7.0%, Mo: 2.0 to 3.5%, Cu: 0.3 to 3 .5%, V: 0.20% or less, Al: 0.05% or less, N: 0.06% or less, and the balance consists of Fe and unavoidable impurities.
- the martensitic stainless seamless steel pipe of this document has a yield strength of 655 to 862 MPa and a yield ratio of 0.90 or more.
- Patent Document 4 describes that , excellent SSC resistance can be obtained.
- Patent Documents 1 to 4 propose a means of improving SSC resistance in a sour environment by adjusting the element content in the chemical composition.
- the SSC resistance of steel materials in a sour environment may be enhanced by means other than the means proposed in the above patent documents.
- the purpose of the present disclosure is to provide a steel material with excellent SSC resistance.
- the steel according to the present disclosure is The chemical composition, in mass %, C: 0.035% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, sol. Al: 0.005 to 0.100%, N: 0.001 to 0.020%, Ni: 5.00 to 7.50%, Cr: 10.00 to 14.00%, Cu: less than 0.01 to 1.50%, Mo: 1.50-3.50%, V: 0.01 to 1.00%, Ti: 0.02 to 0.30%, Co: 0.01-0.50%, Ca: 0.0003 to 0.0030%, O: 0.0050% or less, W: 0 to 1.50%, Nb: 0 to 0.50%, B: 0 to 0.0050%, Mg: 0-0.0050%, Rare earth element (REM): 0 to 0.020%, and The remainder consists of Fe and impurities, Among the inclusions in the steel material, Mn sulfide having a Mn content of 10% or more,
- the steel material according to the present disclosure has excellent SSC resistance.
- the inventors investigated steel materials with excellent SSC resistance in a sour environment.
- the inventors first studied the chemical composition of steel that can have excellent SSC resistance in a sour environment. As a result, in mass %, C: 0.035% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, sol.
- the present inventors investigated the cause of the deterioration of the SSC resistance in the steel material having the chemical composition described above. As a result, the present inventors obtained the following findings.
- the present inventors have found that, in the case of a steel material having the above-described chemical composition, by suppressing the formation of large-sized Mn sulfides, surface dents caused by dissolution of Mn sulfides are suppressed, It was thought that the SSC resistance of steel could be improved. Therefore, the present inventors thought that if the above chemical composition further contains 0.0003 to 0.0030% by mass of Ca, the formation of large-sized Mn sulfides can be suppressed. That is, in mass %, C: 0.035% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, sol.
- the present inventors found that if the steel material having the chemical composition described above not only suppresses the formation of large-sized Mn sulfides but also suppresses the formation of large-sized Ca sulfides, 110 ksi It was thought that excellent SSC resistance in a sour environment could be obtained even in the case of having a yield strength of 758 MPa or more. Therefore, the present inventors have found that if the total number of large-sized Mn sulfides and large-sized Ca sulfides per unit area is suppressed, the yield strength is 110 ksi or more (758 MPa or more). Further investigation was conducted to see if excellent SSC resistance could be obtained even in such cases.
- the total of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more was 0.50/mm 2 or less. It has been found that excellent SSC resistance in a sour environment can be obtained even if the steel has a yield strength of 110 ksi or more (758 MPa or more).
- the steel material according to the present embodiment is a steel material having a Cr content of 10.00% or more. It was completed from the viewpoint of suppressing the dent of The steel material according to this embodiment has the following configuration.
- [1] is steel, The chemical composition, in mass %, C: 0.035% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, sol. Al: 0.005 to 0.100%, N: 0.001 to 0.020%, Ni: 5.00 to 7.50%, Cr: 10.00 to 14.00%, Cu: less than 0.01 to 1.50%, Mo: 1.50-3.50%, V: 0.01 to 1.00%, Ti: 0.02 to 0.30%, Co: 0.01-0.50%, Ca: 0.0003 to 0.0030%, O: 0.0050% or less, W: 0 to 1.50%, Nb: 0 to 0.50%, B: 0 to 0.0050%, Mg: 0-0.0050%, Rare earth element (REM): 0 to 0.020%, and The remainder consists of Fe and impurities, Among the inclusions in the steel material, Mn sulfide having a Mn content of 10% or more, an S
- the chemical composition is B: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, and Rare earth element (REM): 0.001 to 0.020%, containing one or more selected from the group consisting of steel.
- REM Rare earth element
- the steel material according to any one of [1] to [4],
- the steel material is a seamless steel pipe for oil country tubular goods, steel.
- C 0.035% or less Carbon (C) is inevitably contained. That is, the C content is over 0%. C enhances the hardenability of the steel material and enhances the strength of the steel material. However, if the C content exceeds 0.035%, the strength of the steel material becomes too high and the SSC resistance of the steel material decreases even if the contents of other elements are within the ranges of the present embodiment. Therefore, the C content is 0.035% or less.
- the C content is preferably as low as possible. However, excessively reducing the C content increases the production cost. Therefore, considering industrial production, the preferred lower limit of the C content is 0.001%, more preferably 0.003%, still more preferably 0.007%, still more preferably 0.008% and more preferably 0.009%.
- the upper limit of the C content is preferably 0.030%, more preferably 0.025%, still more preferably 0.020%, still more preferably 0.018%, still more preferably 0.016 %, more preferably 0.015%.
- Si Silicon
- Si Silicon
- the lower limit of the Si content is preferably 0.01%, more preferably 0.05%, still more preferably 0.10%, still more preferably 0.15%, still more preferably 0.20 %, more preferably 0.25%.
- a preferred upper limit of the Si content is 0.70%, more preferably 0.60%, still more preferably 0.50%, still more preferably 0.45%.
- Mn 1.00% or less Manganese (Mn) is inevitably contained. That is, the Mn content is over 0%. Mn enhances the hardenability of the steel material and increases the strength of the steel material. However, if the Mn content is too high, Mn will form a large number of coarse Mn sulfides. In a sour environment, coarse MnS present in the vicinity of the surface layer of the steel material may dissolve. At this time, dents are formed as traces of dissolved MnS. This dent becomes the starting point of SSC, and SSC may occur.
- Mn Manganese
- the Mn content is 1.00% or less.
- a preferred lower limit for the Mn content is 0.01%, more preferably 0.05%, still more preferably 0.10%, and still more preferably 0.15%.
- a preferred upper limit of the Mn content is 0.80%, more preferably 0.70%, still more preferably 0.60%, still more preferably 0.50%.
- Phosphorus (P) is an unavoidable impurity. That is, the P content is over 0%. P segregates at grain boundaries and makes SSC more likely to occur. If the P content exceeds 0.030%, the SSC resistance of the steel is remarkably lowered even if the contents of other elements are within the range of the present embodiment. Therefore, the P content is 0.030% or less.
- a preferable upper limit of the P content is 0.025%, more preferably 0.020%, and still more preferably 0.018%. The lower the P content is, the better. However, if the P content is excessively reduced, the manufacturing cost will increase. Therefore, considering industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.002%, and still more preferably 0.003%.
- S 0.0050% or less Sulfur (S) is an unavoidable impurity. That is, the S content is over 0%. Like P, S also segregates at grain boundaries, making it easier for SSC to occur. If the S content exceeds 0.0050%, the SSC resistance of the steel is remarkably lowered even if the content of other elements is within the range of the present embodiment. Therefore, the S content is 0.0050% or less.
- the preferred upper limit of the S content is 0.0040%, more preferably 0.0030%, still more preferably 0.0025%, still more preferably 0.0020%, still more preferably 0.0015 %. It is preferable that the S content is as low as possible. However, excessively reducing the S content increases the manufacturing cost. Therefore, considering industrial production, the preferred lower limit of the S content is 0.0001%, more preferably 0.0002%, and still more preferably 0.0003%.
- sol. Al 0.005-0.100%
- Aluminum (Al) deoxidizes steel. sol. If the Al content is less than 0.005%, the above effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, sol. If the Al content exceeds 0.100%, coarse oxides are formed and the toughness of the steel is reduced even if the content of other elements is within the range of the present embodiment. Therefore, sol.
- the Al content is 0.005-0.100%. sol.
- the lower limit of the Al content is preferably 0.010%, more preferably 0.013%, still more preferably 0.015%, still more preferably 0.018%. sol.
- a preferable upper limit of the Al content is 0.080%, more preferably 0.060%, still more preferably 0.055%, still more preferably 0.050%.
- the Al content means the content of acid-soluble Al.
- N 0.001 to 0.020% Nitrogen (N) combines with Ti to form fine Ti nitrides. Fine TiN suppresses coarsening of crystal grains due to the pinning effect. As a result, the strength of the steel material increases. If the N content is less than 0.001%, the above effect cannot be sufficiently obtained even if the other element content is within the range of the present embodiment. On the other hand, if the N content exceeds 0.020%, coarse nitrides are formed to lower the toughness of the steel material even if the content of other elements is within the range of the present embodiment. Therefore, the N content is 0.001-0.020%.
- the lower limit of the N content is preferably 0.002%, more preferably 0.003%, still more preferably 0.004%, still more preferably 0.005%.
- a preferred upper limit of the N content is 0.018%, more preferably 0.016%, still more preferably 0.014%, still more preferably 0.012%.
- Nickel (Ni) is an austenite-forming element and converts the structure after quenching into martensite. This increases the strength of the steel material. Ni also forms sulfides on the passive film in sour environments. Ni sulfide suppresses contact of chloride ions (Cl - ) and hydrogen sulfide ions (HS - ) with the passive film, and suppresses destruction of the passive film by chloride ions and hydrogen sulfide ions. do. Therefore, the SSC resistance of the steel is enhanced. If the Ni content is less than 5.00%, the above effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment.
- the Ni content is 5.00-7.50%.
- a preferable lower limit of the Ni content is 5.10%, more preferably 5.20%, further preferably 5.30%.
- a preferable upper limit of the Ni content is 7.40%, more preferably 7.30%, and still more preferably 7.20%.
- Chromium (Cr) forms a passivation film on the surface of the steel material and enhances the SSC resistance of the steel material. If the Cr content is less than 10.00%, the above effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, if the Cr content exceeds 14.00%, even if the content of other elements is within the range of the present embodiment, ⁇ (delta) ferrite is likely to form in the steel material, and the toughness of the steel material is reduced. do. Therefore, the Cr content is 10.00-14.00%.
- the preferred lower limit of the Cr content is 10.50%, more preferably 11.00%, still more preferably 11.50%, still more preferably 12.00%, still more preferably 12.20 %.
- the preferred upper limit of the Cr content is 13.80%, more preferably 13.60%, still more preferably 13.50%, still more preferably 13.45%, still more preferably 13.40 %.
- Cu 0.01 to less than 1.50%
- Copper (Cu) is an austenite-forming element like Ni, and converts the structure after quenching into martensite. If the Cu content is less than 0.01%, the above effect cannot be sufficiently obtained. On the other hand, if the Cu content is 1.50% or more, the above effect is saturated and the manufacturing cost increases. Therefore, the Cu content is between 0.01 and less than 1.50%.
- a preferable lower limit of the Cu content is 0.05%, more preferably 0.10%, and still more preferably 0.15%.
- a preferable upper limit of the Cu content is 1.40%, more preferably 1.25%, and still more preferably 1.00%.
- Mo 1.50-3.50% Molybdenum (Mo) forms sulfides on passive films in sour environments. Mo sulfide prevents chloride ions (Cl - ) and hydrogen sulfide ions (HS - ) from coming into contact with the passive film, and prevents the passive film from being destroyed by chloride ions and hydrogen sulfide ions. do. Therefore, the SSC resistance of the steel is enhanced. Mo also forms a solid solution in the steel material to increase the strength of the steel material. If the Mo content is less than 1.50%, the above effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment.
- the Mo content is 1.50-3.50%.
- the lower limit of the Mo content is preferably 1.60%, more preferably 1.70%, still more preferably 1.80%.
- a preferable upper limit of the Mo content is 3.40%, more preferably 3.30%, and still more preferably 3.20%.
- V Vanadium (V) enhances the hardenability of steel and enhances the strength of steel. If the V content is less than 0.01%, the above effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, if the V content exceeds 1.00%, the hardenability of the steel material becomes excessively high and the SSC resistance of the steel material decreases even if the contents of other elements are within the ranges of the present embodiment. Therefore, the V content is 0.01-1.00%.
- a preferable lower limit of the V content is 0.02%, more preferably 0.03%.
- the upper limit of the V content is preferably 0.70%, more preferably 0.50%, still more preferably 0.30%, still more preferably 0.20%, still more preferably 0.15 %, more preferably 0.10%.
- Titanium (Ti) combines with C and/or N to form carbides or nitrides. In this case, the pinning effect suppresses coarsening of crystal grains and increases the strength of the steel material. If the Ti content is less than 0.02%, the above effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, if the Ti content exceeds 0.30%, even if the content of other elements is within the range of the present embodiment, ⁇ ferrite is likely to form, and the toughness of the steel decreases. Therefore, the Ti content is 0.02-0.30%. A preferred lower limit for the Ti content is 0.05%, more preferably 0.07%. The upper limit of the Ti content is preferably 0.25%, more preferably 0.20%, still more preferably 0.18%, still more preferably 0.16%.
- Co 0.01-0.50% Cobalt (Co) forms sulfides on passivation films in sour environments.
- Co sulfide suppresses contact of chloride ions (Cl - ) and hydrogen sulfide ions (HS - ) with the passive film, and suppresses destruction of the passive film by chloride ions and hydrogen sulfide ions. do. Therefore, the SSC resistance of the steel is enhanced.
- Co further enhances the hardenability of the steel material and ensures a stable high strength of the steel material, especially during industrial production. Specifically, Co suppresses the formation of retained austenite and suppresses variations in the strength of the steel material.
- the Co content is 0.01-0.50%.
- the lower limit of the Co content is preferably 0.02%, more preferably 0.04%, still more preferably 0.08%, still more preferably 0.10%.
- the upper limit of the Co content is preferably 0.48%, more preferably 0.45%, still more preferably 0.40%, still more preferably 0.35%.
- Ca 0.0003-0.0030% Calcium (Ca) combines with S in the steel material to form Ca sulfide and suppresses the formation of Mn sulfide.
- Mn sulfide having an equivalent circle diameter of 1.0 ⁇ m or more exists in the surface layer of the steel material, the Mn sulfide in the surface layer may dissolve in a sour environment. In this case, dents are formed at the traces of the dissolved Mn sulfide. The dents formed on the surface of the steel material are likely to be the origin of SSC.
- Ca suppresses the formation of Mn sulfides and lowers the number density of Mn sulfides having an equivalent circle diameter of 1.0 ⁇ m or more.
- the SSC resistance of the steel is enhanced. If the Ca content is less than 0.0003%, the above effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, if the Ca content exceeds 0.0030%, Ca sulfide having an equivalent circle diameter of 2.0 ⁇ m or more is excessively generated even if the content of other elements is within the range of the present embodiment.
- Ca sulfide having an equivalent circle diameter of 2.0 ⁇ m or more exists in the surface layer of the steel material, it may melt in a sour environment to form dents on the surface of the steel material, like the Mn sulfide described above. In this case, the SSC resistance of the steel is lowered.
- the Ca content is 0.0003-0.0030%.
- the lower limit of the Ca content is preferably 0.0005%, more preferably 0.0007%, still more preferably 0.0009%.
- the upper limit of the Ca content is preferably 0.0029%, more preferably 0.0028%, still more preferably 0.0027%, still more preferably 0.0026%.
- Oxygen (O) is an unavoidable impurity. That is, the O content is over 0%. O forms oxides to lower the toughness of the steel material. If the O content exceeds 0.0050%, the toughness of the steel material is remarkably lowered even if the content of other elements is within the range of the present embodiment. Therefore, the O content is 0.0050% or less.
- the upper limit of the O content is preferably 0.0045%, more preferably 0.0040%, still more preferably 0.0035%, still more preferably 0.0030%. It is preferable that the O content is as low as possible. However, excessively reducing the O content increases the production cost. Therefore, considering industrial production, the lower limit of the O content is preferably 0.0001%, more preferably 0.0002%.
- the remainder of the chemical composition of the steel material according to this embodiment consists of Fe and impurities.
- the impurities are those that are mixed from ore, scrap, or the manufacturing environment as raw materials when industrially producing steel materials, and are not intentionally included. It means that it is permissible within a range that does not adversely affect the steel material.
- the chemical composition of the steel material according to this embodiment may further contain W instead of part of Fe.
- W 0-1.50% Tungsten (W) is an optional element and may not be contained. That is, the W content may be 0%.
- W stabilizes the passive film in a sour environment and inhibits destruction of the passive film by chloride ions and hydrogen sulfide ions. Therefore, the SSC resistance of the steel is enhanced. If even a small amount of W is contained, the above effect can be obtained to some extent. However, if the W content exceeds 1.50%, W combines with C to form coarse carbides. In this case, even if the contents of the other elements are within the range of the present embodiment, the toughness of the steel material is lowered. Therefore, the W content is 0-1.50%.
- the preferred lower limit of the W content is 0.01%, more preferably 0.05%, still more preferably 0.10%, still more preferably 0.30%, still more preferably 0.50 %.
- a preferable upper limit of the W content is 1.45%, more preferably 1.40%, and still more preferably 1.37%.
- the chemical composition of the steel material according to this embodiment may further contain Nb instead of part of Fe.
- Niobium (Nb) is an optional element and may not be contained. That is, the Nb content may be 0%. When included, Nb combines with C and/or N to form Nb carbides, Nb carbonitrides. In this case, the pinning effect suppresses coarsening of crystal grains and increases the strength of the steel material. If even a small amount of Nb is contained, the above effect can be obtained to some extent. However, if the Nb content exceeds 0.50%, Nb carbides and/or Nb carbonitrides are excessively generated even if the content of other elements is within the range of the present embodiment, and the toughness of the steel material deteriorates. descend. Therefore, the Nb content is 0-0.50%.
- the lower limit of the Nb content is preferably 0.01%, more preferably 0.05%, still more preferably 0.10%, still more preferably 0.15%.
- a preferable upper limit of the Nb content is 0.45%, more preferably 0.40%, and still more preferably 0.35%.
- the chemical composition of the steel material according to this embodiment may further contain B, Mg, and rare earth elements (REM) instead of part of Fe.
- REM rare earth elements
- B 0 to 0.0050% Boron (B) is an optional element and may not be contained. That is, the B content may be 0%. When contained, B forms a solid solution in the steel material and enhances the hot workability of the steel material. If even a small amount of B is contained, the above effect can be obtained to some extent. However, if the B content exceeds 0.0050%, coarse B nitrides are formed even if the content of other elements is within the range of the present embodiment, and the toughness of the steel material is lowered. Therefore, the B content is 0-0.0050%.
- the lower limit of the B content is preferably 0.0001%, more preferably 0.0002%, still more preferably 0.0003%, still more preferably 0.0004%.
- a preferable upper limit of the B content is 0.0040%, more preferably 0.0030%, and still more preferably 0.0020%.
- Mg 0-0.0050%
- Mg Magnesium
- the Mg content may be 0%.
- Mg controls the morphology of inclusions and enhances the hot workability of the steel. If even a small amount of Mg is contained, the above effect can be obtained to some extent. However, if the Mg content exceeds 0.0050%, coarse oxides are produced. In this case, even if the contents of the other elements are within the range of the present embodiment, the toughness of the steel material is lowered. Therefore, the Mg content is 0-0.0050%.
- a preferable lower limit of the Mg content is 0.0001%, more preferably 0.0002%, and still more preferably 0.0003%.
- a preferable upper limit of the Mg content is 0.0040%, more preferably 0.0035%, still more preferably 0.0030%, still more preferably 0.0025%.
- Rare earth element 0-0.020%
- a rare earth element (REM) is an optional element and may not be contained. That is, the REM content may be 0%. When included, REM, like Mg, controls the morphology of inclusions and enhances the hot workability of the steel. The above effect can be obtained to some extent if REM is contained even in a small amount. However, if the REM content exceeds 0.020%, coarse oxides are produced. In this case, even if the contents of the other elements are within the range of the present embodiment, the toughness of the steel material is lowered. Therefore, the REM content is 0-0.020%.
- a preferable lower limit of the REM content is 0.001%, more preferably 0.003%, and still more preferably 0.005%.
- a preferred upper limit for the REM content is 0.019%, more preferably 0.018%, and still more preferably 0.017%.
- REM refers to scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanoid (La) with atomic number 57 to atomic number 71.
- Sc scandium
- Y yttrium
- La lanthanoid
- REM refers to scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanoid (La) with atomic number 57 to atomic number 71.
- Y yttrium
- La lanthanoid
- REM content in this specification is the total content of these elements.
- the yield strength of the steel material is preferably 758 MPa or higher (110 ksi or higher), more preferably 862 MPa or higher (125 ksi or higher).
- the preferred chemical composition according to the yield strength to be obtained is as follows.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the lower limits of the C content are 0.002% and 0.002%. 005%, 0.007%, 0.008% or 0.009%.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the lower limit of the Ni content is 5.10%, 5.20%, Alternatively, it is preferably 5.30%.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the upper limit of the Ni content is 7.00%, 6.80%, It is preferably 6.50% or less than 6.50%.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the lower limit of the Mo content is 1.60%, 1.70%, Alternatively, it is preferably 1.80%.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the upper limit of the Mo content is 3.20%, 3.00%, It is preferably 2.80%, 2.50% or less than 2.50%.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the lower limits of the Ni content are 5.50% and 6.00%. , 6.30%, 6.50% or more than 6.50%.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the upper limit of the Ni content is 7.40%, 7.30%, or 7.20% is preferred.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the lower limit of the Mo content is 1.80%, 2.10%, or 2. 30% is preferred.
- the chemical composition of the steel material satisfies all the ranges of the above-mentioned element contents, and the upper limit of the Mo content is 3.40%, 3.30%, or 3.20% is preferred.
- Mn sulfide and Ca sulfide in steel are defined as follows.
- Mn sulfide inclusions having a Mn content of 10% or more and an S content of 10% or more in mass% when the mass% of inclusions is 100%
- Ca sulfide mass% of inclusions is 100%, inclusions having a Ca content of 20% or more, an S content of 10% or more, and an Mn content of less than 10% by mass
- the total number density (pieces/mm 2 ) of Mn sulfides and Ca sulfides of a size that easily dissolves in a sour environment and forms dents in the surface layer is reduced.
- Mn sulfides in the steel are present extending in the longitudinal direction (rolling direction) of the steel.
- Ca sulfides in the steel are spherical. Therefore, Mn sulfide and Ca sulfide differ in the size at which a dent, which is the starting point of SSC, is likely to be formed.
- the equivalent circle diameter is defined as the diameter when the area of the Mn sulfide and the Ca sulfide is converted into a circle.
- the unit of Mn sulfide with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfide with an equivalent circle diameter of 2.0 ⁇ m or more The number per area correlates with SSC resistance in sour environments.
- the total number of Mn sulfides and Ca sulfides per unit area (1 mm 2 ) is defined as the total number density (pieces/mm 2 ).
- the total number density of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more is defined as a total number density ND (Number Density).
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more is 0.50/mm 2 or less.
- the total number of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more is 0.50/mm 2 or less.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more is 0.50 / mm 2 or less, is within the range of the present embodiment, the number density of Mn sulfides and Ca sulfides having a size that is easy to dissolve in a sour environment is sufficiently low. Therefore, dents are less likely to form on the surface layer of the steel material even in a sour environment. As a result, the SSC resistance of the steel is sufficiently enhanced.
- a preferable upper limit of the total number density ND of Mn sulfides having an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides having an equivalent circle diameter of 2.0 ⁇ m or more is 0.48/mm 2 , more preferably 0.47. number/mm 2 , more preferably 0.46 number/mm 2 , still more preferably 0.45 number/mm 2 , still more preferably 0.44 number/mm 2 , still more preferably 0 0.43/mm 2 , more preferably 0.42/mm 2 .
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more can be measured by the following method. Specifically, a test piece is taken from an arbitrary position on the steel material. When the steel material is a steel pipe, a test piece is taken from the thickness center position. If the steel material is a steel bar with a circular cross section, a test piece is taken from the R/2 position. In addition, in this specification, the R/2 position means the central position of the radius R in the cross section perpendicular to the longitudinal direction of the steel bar. When the steel material is a steel plate, a test piece is taken from the thickness center position.
- the sampled test piece is embedded in resin.
- the steel material is a steel pipe
- the surface including the pipe axial direction and the thickness direction is used as the observation surface.
- the surface of the test piece including the axial direction (longitudinal direction) and the radial direction is used as the observation surface.
- the observation plane is a plane including the longitudinal direction (rolling direction) and the plate thickness direction. Polish the observation surface of the resin-filled steel material. Any 10 fields of view are observed on the observation surface after polishing. The number of inclusions is obtained in each field of view. The area of each field of view is 36 mm 2 (6 mm ⁇ 6 mm).
- EDS analysis element concentration analysis
- the acceleration voltage is 20 kV
- the elements to be analyzed are N, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zr, Nb and
- the inclusion Based on the EDS analysis results of each inclusion, identify whether the inclusion is Mn sulfide or Ca sulfide. When the Mn content is 10% or more and the S content is 10% or more in mass %, the inclusion is specified as "Mn sulfide”. When the Ca content is 20% or more, the S content is 10% or more, and the Mn content is less than 10%, the inclusion is specified as "Ca sulfide”.
- the total number of Mn sulfides having an equivalent circle diameter of 1.0 ⁇ m or more among the Mn sulfides identified in the 10 fields of view is determined. Furthermore, the total number of Ca sulfides having an equivalent circle diameter of 2.0 ⁇ m or more is determined among the Ca sulfides measured in the 10 fields of view. Based on the total number of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more, the total number of Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more, and the total area of 10 fields of view, the equivalent circle diameter is 1.0 ⁇ m.
- the total number density ND (pieces/mm 2 ) of Mn sulfides of 0 ⁇ m or more and Ca sulfides of 2.0 ⁇ m or more in equivalent circle diameter is determined.
- the total number density ND can be measured using a scanning electron microscope equipped with a composition analysis function (SEM-EDS device).
- SEM-EDS device for example, an inclusion automatic analysis device manufactured by FEI (ASPEX), trade name: Metals Quality Analyzer, can be used.
- the microstructure of the steel material according to this embodiment is mainly martensite.
- martensite includes not only fresh martensite but also tempered martensite.
- "mainly composed of martensite” means that the volume fraction of martensite is 80% or more in the microstructure.
- the remainder of the microstructure is retained austenite. That is, in the steel material of this embodiment, the volume fraction of retained austenite is 0 to 20%.
- the volume fraction of retained austenite is preferably as low as possible.
- a preferable lower limit of the volume fraction of martensite in the microstructure of the steel material of the present embodiment is 85%, more preferably 90%. More preferably, the microstructure of the steel material is martensite single phase.
- the volume fraction of retained austenite is 0 to 20% in the microstructure of the steel material of the present embodiment.
- the upper limit of the volume fraction of retained austenite is preferably 15%, more preferably 10%.
- the microstructure of the steel material of the present embodiment may be martensite single phase. Therefore, the volume fraction of retained austenite may be 0%.
- the volume fraction of retained austenite is more than 0 to 20%, more preferably more than 0 to 15%, and more preferably more than 0 to 10%.
- the volume fraction (vol.%) of martensite in the microstructure of the steel material of this embodiment is determined by subtracting the volume fraction (vol.%) of retained austenite determined by the method described below from 100%.
- the volume fraction of retained austenite is determined by an X-ray diffraction method. Specifically, a test piece is taken from an arbitrary position on the steel material. When the steel material is a steel pipe, a test piece is taken from the thickness center position. If the steel material is a steel bar, the specimen is taken from the R/2 position. When the steel material is a steel plate, a test piece is taken from the thickness center position. The size of the test piece is not particularly limited. The specimen is for example 15 mm x 15 mm x 2 mm thick. In this case, when the steel material is a steel pipe, the thickness direction of the test piece is the pipe radial direction. When the steel material is a steel bar, the thickness direction of the test piece is the radial direction.
- the thickness direction of the test piece is the plate thickness direction.
- each of the ⁇ -phase (200) plane, the ⁇ -phase (211) plane, the ⁇ -phase (200) plane, the ⁇ -phase (220) plane, and the ⁇ -phase (311) plane The X-ray diffraction intensity of is measured, and the integrated intensity of each surface is calculated.
- the target of the X-ray diffractometer is Mo (MoK ⁇ ray) and the output is 50 kV-40 mA.
- V ⁇ 100/ ⁇ 1+(I ⁇ R ⁇ )/(I ⁇ R ⁇ ) ⁇ (I) where I ⁇ is the integrated intensity of the ⁇ phase.
- R ⁇ is the crystallographically calculated value of the ⁇ phase.
- I ⁇ is the integrated intensity of the ⁇ phase.
- R ⁇ is the crystallographically calculated value of the ⁇ phase.
- R ⁇ on the (200) plane of the ⁇ phase is 15.9
- R ⁇ on the (211) plane of the ⁇ phase is 29.2
- R ⁇ on the (200) plane of the ⁇ phase is 35.9. 5.
- R ⁇ on the (220) plane of the ⁇ phase be 20.8
- R ⁇ on the (311) plane of the ⁇ phase be 21.8.
- the obtained numerical value is rounded off to the first decimal place.
- volume fraction of martensite 100 - volume fraction of retained austenite (%)
- the yield strength of the steel material according to this embodiment is not particularly limited.
- the yield strength of the steel material is preferably 758 MPa or more (110 ksi or more), more preferably 862 MPa or more (125 ksi or more).
- the upper limit of the yield strength is not particularly limited, the upper limit of the yield strength of the steel material of the present embodiment is, for example, less than 1069 MPa (less than 155 ksi).
- a more preferable upper limit of the yield strength of the steel material is 1000 MPa.
- yield strength means 0.2% offset yield strength (MPa) obtained by a tensile test at room temperature (24 ⁇ 3°C) in accordance with ASTM E8/E8M (2013). Specifically, the yield strength is obtained by the following method. A tensile test piece is taken from an arbitrary position on the steel material. When the steel material is a steel pipe, a tensile test piece is taken from the thickness center position. If the steel material is a steel bar, a tensile specimen is taken from the R/2 position. When the steel material is a steel plate, a tensile test piece is taken from the central position of the plate thickness. The size of the tensile test piece is not particularly limited.
- the tensile test piece is, for example, a round bar tensile test piece having a parallel portion diameter of 8.9 mm and a parallel length of 35.6 mm.
- the longitudinal direction of the parallel portion of the tensile test piece is parallel to the longitudinal direction (rolling direction) of the steel material.
- a tensile test is performed at room temperature (24 ⁇ 3°C) in accordance with ASTM E8/E8M (2013) to determine the 0.2% offset yield strength (MPa).
- the obtained 0.2% offset yield strength is defined as yield strength (MPa).
- the steel material according to this embodiment has excellent SSC resistance.
- the SSC resistance of the steel material according to this embodiment can be evaluated by an SSC resistance evaluation test at room temperature.
- the SSC resistance evaluation test is conducted according to NACE TM0177-2005 Method A.
- a round bar test piece is taken from the steel material according to this embodiment.
- a round bar test piece is taken from the thickness center position.
- a round bar test piece is taken from the R/2 part.
- a round bar test piece is taken from the center position of the plate thickness.
- the size of the round bar test piece is not particularly limited.
- the round bar test piece for example, has a parallel portion diameter of 6.35 mm and a parallel portion length of 25.4 mm.
- the axial direction of the round bar test piece is parallel to the longitudinal direction (rolling direction) of the steel material.
- the test solution is a 0.17 mass % sodium chloride aqueous solution with a pH of 3.0.
- a test solution is prepared by adding acetic acid to an aqueous solution containing 0.17 mass % sodium chloride and 0.41 g/L sodium acetate to adjust the pH to 3.0.
- a stress equivalent to 90% of the actual yield stress is applied to the round-bar test piece sampled as described above.
- the test solution at 24° C. is poured into the test container so that the stress-loaded round bar test piece is immersed to form a test bath. After degassing the test bath, 0.03 bar H 2 S gas and 0.97 bar CO 2 gas are blown into the test bath to saturate the test bath with H 2 S gas.
- a test bath saturated with H 2 S gas is held at 24° C. for 720 hours. After holding for 720 hours, the surface of the parallel portion of the test piece is observed with a magnifying glass having a magnification of 10 times to confirm the presence or absence of cracks. If there is a portion suspected of cracking by observation with a magnifying glass, the cross section of the portion suspected of cracking is observed with a 100x optical microscope to confirm the presence or absence of cracking.
- the steel material according to this embodiment is a steel pipe, a round bar (solid material), or a steel plate.
- the steel pipe may be a seamless steel pipe or a welded steel pipe.
- Steel pipes are, for example, steel pipes for oil country tubular goods.
- a steel pipe for oil country tubular goods means a steel pipe for oil country tubular goods.
- Oil country tubular goods are, for example, casings, tubings, drill pipes, etc. used for drilling oil wells or gas wells, extracting crude oil or natural gas, and the like.
- the steel material of the present embodiment is a seamless steel pipe for oil country tubular goods.
- each element in the chemical composition is within the range of the present embodiment, and Mn sulfide having an equivalent circle diameter of 1.0 ⁇ m or more and Mn sulfide having an equivalent circle diameter of 2
- the total number of Ca sulfides of 0 ⁇ m or more is 0.50/mm 2 or less.
- the steel material according to this embodiment has excellent SSC resistance.
- An example of the steel manufacturing method of the present embodiment includes a process of manufacturing a material (steelmaking process), a process of hot working the material to manufacture an intermediate steel material (hot working process), and quenching the intermediate steel material. and a step of performing tempering (heat treatment step). Each step will be described below.
- the steelmaking process includes a process of manufacturing molten steel (refining process) and a process of manufacturing materials by casting using molten steel (material manufacturing process).
- a deoxidizing agent is added to the ladle to reduce Cr 2 O 3 in the slag and recover Cr in the molten steel (Cr reduction treatment step).
- the rough decarburization refining step and the Cr reduction treatment step are performed by, for example, an electric furnace method, a converter method, or an AOD (Argon Oxygen Decarburization) method.
- slag is removed from the molten steel (slag removal treatment step).
- the decarburization reaction is suppressed because Cr lowers the C activity. Therefore, the molten steel after the slag removal process is further subjected to finishing decarburization treatment (finish decarburization refining process).
- finish decarburization refining process decarburization is performed under reduced pressure. If the decarburization treatment is performed under reduced pressure, the CO gas partial pressure (P CO ) in the atmosphere is lowered, and the oxidation of Cr in molten steel is suppressed. Therefore, if the decarburization treatment is performed under reduced pressure, the C concentration in the molten steel can be further reduced while suppressing the oxidation of Cr.
- the finish decarburization refining step and the Cr reduction treatment step after the finish decarburization refining step may be performed, for example, by a VOD (Vacuum Oxygen Decarburization) method or an RH (Ruhrstahl-Heraeus) method.
- the molten steel in the ladle is subjected to final composition adjustment and temperature adjustment of the molten steel before the raw material manufacturing step (component adjustment step).
- the component adjustment step is performed by, for example, LT (Ladle Treatment).
- Ca is added to the molten steel in the second half of the component adjustment process.
- the time from adding Ca to uniformly dispersing Ca in the molten steel is defined as "uniform mixing time" ⁇ .
- ⁇ is the stirring power density of molten steel at LT and is defined by equation (B).
- Q is the top-blowing gas flow rate (Nm 3 /min).
- W is the molten steel mass (t).
- T is the molten steel temperature (K).
- H is the depth of molten steel in the ladle (steel bath depth) (m).
- the molten steel temperature in the ladle is kept at 1500-1700°C. Furthermore, Ca is put into the molten steel, and the holding time after uniform mixing time has passed is defined as "holding time t" (seconds). In this case, in this embodiment, the retention time t after the uniform mixing time has passed is set to 60 seconds or longer.
- the holding time t is less than 60 seconds, the Ca added to the molten steel cannot sufficiently reform the Mn sulfides in the molten steel. In this case, large-sized Mn sulfides remain in the steel material. Therefore, the number per unit area of Mn sulfides having an equivalent circle diameter of 1.0 ⁇ m or more is excessively increased in the steel material. As a result, the total number density ND (pieces/mm 2 ) of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50 pieces/mm 2 put away.
- Mn sulfide reacts with Ca to progress reformation, and although the number of Mn sulfides having an equivalent circle diameter of 1.0 ⁇ m or more per unit area decreases, Ca sulfide generated by combining with S It remains in the molten steel without being sufficiently absorbed by the slag.
- the total number density ND (pieces/mm 2 ) of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50 pieces/mm 2 put away.
- the Ca added to the molten steel sufficiently reforms the Mn sulfides in the molten steel and reduces the large-sized Mn sulfides. Therefore, the number of Mn sulfides having an equivalent circle diameter of 1.0 ⁇ m or more per unit area is sufficiently reduced. Furthermore, it is possible to ensure sufficient time for the large-sized Ca sulfides generated by combining with S to float in the molten steel and be absorbed by the slag. Therefore, the number of Ca sulfides having an equivalent circle diameter of 2.0 ⁇ m or more per unit area is sufficiently reduced.
- the total number density ND (pieces/mm 2 ) of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more is 0.50 pieces/mm 2 or less.
- the holding time t after the uniform mixing time it is preferable to set the holding time t after the uniform mixing time to 60 seconds or longer.
- the upper limit of the retention time t after the uniform mixing time has elapsed is not particularly limited, but is, for example, 3600 seconds.
- a raw material (a slab or an ingot) is manufactured using the molten steel manufactured by the refining process described above.
- a slab is produced by a continuous casting method using molten steel.
- the slab may be a slab, a bloom, or a billet.
- molten steel may be used as an ingot by an ingot casting method.
- the slab or ingot may be further subjected to blooming rolling or the like to produce a billet.
- the material is manufactured by the above steps.
- the material is hot worked to produce an intermediate steel material.
- the steel material is a steel pipe
- the intermediate steel material corresponds to the base pipe.
- the material is heated in a heating furnace.
- the heating temperature is not particularly limited, it is, for example, 1100 to 1300.degree.
- a billet extracted from a heating furnace is subjected to hot working to produce a blank pipe (seamless steel pipe), which is an intermediate steel material.
- the method of hot working is not particularly limited, and a known method may be used.
- the Mannesmann process is carried out as hot working to produce a mother tube. In this case, the round billet is pierced and rolled by a piercing machine.
- the piercing ratio is not particularly limited, but is, for example, 1.0 to 4.0.
- the pierced-rolled round billet is further hot-rolled by a mandrel mill, a reducer, a sizing mill, or the like to form a mother pipe.
- the cumulative area reduction rate in the hot working process is, for example, 20 to 70%.
- a blank tube may be manufactured from a billet by other hot working methods.
- a blank pipe may be manufactured by forging such as the Ehrhardt method.
- a blank pipe is manufactured by the above steps.
- the material is first heated in a heating furnace.
- the heating temperature is not particularly limited, it is, for example, 1100 to 1300.degree.
- the raw material extracted from the heating furnace is subjected to hot working to produce a steel bar as an intermediate steel material.
- Hot working is, for example, blooming by a blooming mill or hot rolling by a continuous rolling mill.
- a horizontal stand having a pair of grooved rolls arranged vertically and a vertical stand having a pair of grooved rolls arranged horizontally are arranged alternately.
- the material is first heated in a heating furnace.
- the heating temperature is not particularly limited, it is, for example, 1100 to 1300.degree.
- the raw material extracted from the heating furnace is subjected to hot rolling using a blooming mill and a continuous rolling mill to produce a steel plate as an intermediate steel material.
- the intermediate steel material produced by hot working may be air-cooled (As-Rolled).
- the intermediate steel material produced by hot working may also be directly quenched after hot working without being cooled to room temperature, or may be quenched after supplementary heating (reheating) after hot working. good too.
- stress relief annealing When quenching is performed directly after hot working, or when quenching is performed after reheating after hot working, stress relief annealing (SR processing) may be implemented.
- the heat treatment process includes a quenching process and a tempering process.
- the intermediate steel material produced in the hot working process is quenched (quenching process). Quenching is performed by a well-known method. Specifically, the intermediate steel material after the hot working process is charged into a heat treatment furnace and held at the quenching temperature. The quenching temperature is above the A C3 transformation point, eg, 900-1000°C. After holding the intermediate steel material at the quenching temperature, it is rapidly cooled (quenched). Although the holding time at the quenching temperature is not particularly limited, it is, for example, 10 to 60 minutes. The quenching method is, for example, water cooling. The quenching method is not particularly limited.
- the blank pipe When the intermediate steel material is a blank pipe, for example, the blank pipe may be quenched by being immersed in a water tank or an oil bath, or by shower cooling or mist cooling, cooling water may be poured onto the outer surface and/or the inner surface of the blank pipe. or by jetting to rapidly cool the tube.
- quenching may be performed immediately after hot working without cooling the intermediate steel material to room temperature, or the temperature of the mother tube after hot working may be Quenching may be performed after the steel is charged into a reheating furnace and held at the quenching temperature before the temperature drops.
- the intermediate steel material is further subjected to a tempering process.
- the tempering process adjusts the yield strength of the steel material.
- the tempering temperature is 540-620.degree.
- the holding time at the tempering temperature is not particularly limited, it is, for example, 10 to 180 minutes. It is well known to those skilled in the art that the yield strength of steel materials can be adjusted by appropriately adjusting the tempering temperature according to the chemical composition. Preferably, tempering conditions are adjusted so that the yield strength of the steel material is 758 MPa or more (110 ksi or more).
- the steel material of this embodiment can be manufactured by the above steps. It is not limited to the steel material manufacturing method of the present embodiment.
- the content of each element in the chemical composition is within the range of the present embodiment, and the total number of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more in the steel material
- the steel material production method of the present embodiment is not limited to the above-described production method.
- Example 1 the SSC resistance of steel materials having a yield strength of 125 ksi or more (yield strength of 862 MPa or more) was investigated. Specifically, molten steel having the chemical composition shown in Table 1 was produced.
- "-" in Table 1 means that the content of the corresponding element was below the detection limit.
- the W content of Test No. 1 was rounded to the third decimal place, meaning that it was 0%. It means that the Nb content of Test No. 1 was 0%, rounded to the third decimal place.
- the B content of Test No. 1 was rounded to the fifth decimal place, meaning that it was 0%. It means that the Mg content of Test No. 1 was 0%, rounded to the fifth decimal place. It means that the REM content of Test No. 1 was 0%, rounded to the fourth decimal place.
- the molten steel of test numbers 1 to 23 was produced as follows. Molten steel containing Cr was placed in a ladle, and a known crude decarburization refining process and Cr reduction process were carried out by the AOD method. After the Cr reduction treatment step, a slag removal treatment step was performed to remove slag from the molten steel. Furthermore, a well-known finishing decarburization refining step and a Cr reduction treatment step were carried out by the VOD method.
- the LT performed the final composition adjustment of the molten steel in the ladle and the temperature adjustment of the molten steel before the material manufacturing process.
- the molten steel temperature was 1500 to 1700°C in all cases.
- Ca was added to the molten steel.
- Table 2 the retention time t (seconds) after the homogeneous mixing time had elapsed after the addition of Ca was adjusted.
- a billet with an outer diameter of 310 mm was manufactured using molten steel of test numbers 1 to 23. After heating the manufactured billet to 1250° C., it was hot-rolled by the Mannesmann method to manufacture a blank pipe (seamless steel pipe) having an outer diameter of 244.48 mm and a wall thickness of 13.84 mm.
- Quenching and tempering were performed on the tube with test numbers 1 to 23.
- the quenching temperature was set to 920° C. and the holding time at the quenching temperature was set to 10 minutes for each of the tube blanks of test numbers 1 to 23.
- Tempering was performed on the blank pipes of test numbers 1 to 23 after quenching.
- the tempering temperature was adjusted in the range of 540 to 580° C. for each test number so that the steel material (seamless steel pipe) after tempering had a yield strength of 862 MPa or more.
- the holding time at the tempering temperature was 30 minutes for all test numbers.
- the martensite volume fraction in the microstructure of the steel materials (seamless steel pipes) of test numbers 1 to 23 was obtained by the following method.
- each of the ⁇ -phase (200) plane, the ⁇ -phase (211) plane, the ⁇ -phase (200) plane, the ⁇ -phase (220) plane, and the ⁇ -phase (311) plane was measured, and the integrated intensity of each surface was calculated.
- the target of the X-ray diffractometer was Mo (MoK ⁇ ray) and the output was 50 kV-40 mA.
- V ⁇ 100/ ⁇ 1+(I ⁇ R ⁇ )/(I ⁇ R ⁇ ) ⁇ (I)
- I ⁇ the integrated intensity of the ⁇ phase.
- R ⁇ is the crystallographically calculated value of the ⁇ phase.
- I ⁇ is the integrated intensity of the ⁇ phase.
- R ⁇ is the crystallographically calculated value of the ⁇ phase.
- R ⁇ on the (200) plane of the ⁇ phase is 15.9
- R ⁇ on the (211) plane of the ⁇ phase is 29.2
- R ⁇ on the (200) plane of the ⁇ phase is 35.9. 5.
- R ⁇ on the (220) plane of the ⁇ phase was set to 20.8, and R ⁇ on the (311) plane of the ⁇ phase was set to 21.8.
- the obtained numerical value was rounded off to the first decimal place.
- volume fraction (%) of retained austenite obtained by the above-described X-ray diffraction method
- volume fraction (vol.%) of martensite in the microstructures of the steel materials of test numbers 1 to 23 is obtained by the following formula. rice field.
- Volume fraction of martensite 100 - volume fraction of retained austenite (%)
- the obtained martensite volume fractions of Test Nos. 1 to 23 are shown in Table 2 in the column of "Martensite volume fraction (%)".
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more in steel materials (seamless steel pipes) of test numbers 1 to 23 is determined by the following method. It was measured. A test piece was taken from the thickness center position of the steel material of each test number. The sampled test piece was embedded in resin. Among the surfaces of the test piece, the surface including the pipe axial direction and the wall thickness direction was used as the observation surface. The observation surface of the resin-filled steel material was polished. Arbitrary 10 visual fields were observed in the observation surface after polishing. The number of inclusions was determined in each field of view. The area of each field of view was 36 mm 2 (6 mm ⁇ 6 mm).
- EDS analysis For each inclusion in the field of view, an elemental concentration analysis (EDS analysis) was performed to identify the type of inclusion.
- the acceleration voltage is 20 kV
- the elements to be analyzed are N, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zr, Nb and
- the inclusions were Mn sulfides or Ca sulfides. Specifically, when the Mn content was 10% or more and the S content was 10% or more in mass%, the inclusion was identified as "Mn sulfide”. When the Ca content was 20% or more, the S content was 10% or more, and the Mn content was less than 10%, the inclusion was specified as "Ca sulfide”.
- the equivalent circle diameter is 1.0 ⁇ m.
- the total number density ND (pieces/mm 2 ) of Mn sulfides of 0 ⁇ m or more and Ca sulfides of 2.0 ⁇ m or more in equivalent circle diameter was determined.
- the obtained total number density ND of test numbers 1 to 23 is shown in Table 2, "total number density ND (pieces/mm 2 )" column.
- Test Nos. 1 to 23 A tensile test was performed on steel materials (seamless steel pipes) of test numbers 1 to 23 in accordance with ASTM E8/E8M (2013). Specifically, a round bar tensile test piece was taken from the thickness center position of the steel material of each test number. The parallel portion of the round bar tensile test piece had a diameter of 8.9 mm and a length of 35.6 mm. The longitudinal direction of the round bar tensile test piece was parallel to the longitudinal direction (rolling direction) of the steel material. Using round bar tensile test pieces of test numbers 1 to 23, a tensile test was performed at normal temperature (25° C.) in the atmosphere to obtain 0.2% offset yield strength (MPa). The obtained 0.2% offset yield strength was defined as the yield strength (MPa). The obtained yield strengths of Test Nos. 1 to 23 are shown in Table 2, "YS (MPa)" column.
- the test solution was a 0.17 mass % sodium chloride aqueous solution with a pH of 3.0.
- a test solution was prepared by adding acetic acid to an aqueous solution containing 0.17 mass % sodium chloride and 0.41 g/L sodium acetate to adjust the pH to 3.0.
- a stress equivalent to 90% of the actual yield stress was applied to the round bar test piece.
- the test solution at 24° C. was poured into the test container so that the stress-loaded round-bar test piece was immersed therein to form a test bath. After degassing the test bath, 0.03 bar H 2 S gas and 0.97 bar CO 2 gas were blown into the test bath to saturate the test bath with H 2 S gas. A test bath saturated with H 2 S gas was held at 24° C.
- the steel materials of Test Nos. 1 to 16 had appropriate chemical compositions. Furthermore, the martensite volume fraction in the microstructure was 80% or more, and the yield strength was 862 MPa or more (125 ksi or more). Furthermore, the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more was 0.50/mm 2 or less. As a result, the steel materials of test numbers 1 to 16 had excellent SSC resistance.
- test numbers 17 and 18 the S content was too high in the chemical composition of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel materials of test numbers 17 and 18 did not have excellent SSC resistance.
- test number 19 the Ca content was too low in the chemical composition of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel material of test number 19 did not have excellent SSC resistance.
- test number 20 the Ca content was too high in the chemical composition of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel material of test number 20 did not have excellent SSC resistance.
- test numbers 21 to 23 the holding time t after the uniform mixing time was too short in the manufacturing process of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel materials of test numbers 21 to 23 did not have excellent SSC resistance.
- Example 2 the SSC resistance of steel materials having a yield strength of 110 ksi class (yield strength of 758 MPa to less than 862 MPa) was investigated. Specifically, molten steel having the chemical composition shown in Table 3 was produced. "-" in Table 3 means that the content of the corresponding element was below the detection limit, as in Table 1 described in Example 1.
- the molten steels of Test Nos. 24-46 were produced in the same manner as the molten steels of Test Nos. 1-23 of Example 1 as follows. Molten steel containing Cr was placed in a ladle, and a known crude decarburization refining process and Cr reduction process were carried out by the AOD method. After the Cr reduction treatment step, a slag removal treatment step was performed to remove slag from the molten steel. Furthermore, a well-known finishing decarburization refining step and a Cr reduction treatment step were carried out by the VOD method.
- the LT performed the final composition adjustment of the molten steel in the ladle and the temperature adjustment of the molten steel before the material manufacturing process.
- the molten steel temperature was 1500 to 1700°C in all cases.
- Ca was added to the molten steel.
- Table 4 the retention time t (seconds) after the uniform mixing time had elapsed after the addition of Ca was adjusted.
- a billet with an outer diameter of 310 mm was manufactured using molten steel with test numbers 24 to 46. After heating the manufactured billet to 1250° C., it was hot-rolled by the Mannesmann method to manufacture a blank pipe (seamless steel pipe) having an outer diameter of 244.48 mm and a wall thickness of 13.84 mm.
- Quenching and tempering were performed on the tube with test numbers 24 to 46.
- the quenching temperature was set to 920° C. and the holding time at the quenching temperature was set to 10 minutes for each of the tube blanks of test numbers 24 to 46.
- Tempering was performed on the blank pipes of test numbers 24 to 46 after quenching.
- the tempering temperature was adjusted in the range of 580 to 620° C. for each test number so that the steel material (seamless steel pipe) after tempering had a yield strength of 758 to less than 862 MPa (110 ksi grade).
- the holding time at the tempering temperature was 30 minutes for all test numbers.
- Test Nos. 24 to 46 Steel materials (seamless steel pipes) of test numbers 24 to 46 were subjected to a tensile test in the same manner as in Example 1 according to ASTM E8/E8M (2013). The obtained yield strengths of Test Nos. 24 to 46 are shown in Table 4, "YS (MPa)" column.
- SSC resistance evaluation test The SSC resistance evaluation test was performed in the same manner as in Example 1 for the steel materials (seamless steel pipes) of test numbers 24 to 46. When no cracks were observed even when the surface of the round bar test piece was observed with a loupe of 10 times and an optical microscope of 100 times, it was judged that excellent SSC resistance was obtained ("SSC resistance in Table 4 ” column with “E (Excellent)”). When cracks were confirmed, it was judged that excellent SSC resistance was not obtained (denoted as "B (Bad)" in the "SSC resistance” column in Table 4).
- the steel materials of Test Nos. 24 to 40 had appropriate chemical compositions. Furthermore, the martensite volume fraction in the microstructure was 80% or more, and the yield strength was 758 to less than 862 MPa (110 ksi grade). Furthermore, the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more was 0.50/mm 2 or less. As a result, the steel materials of test numbers 24 to 40 exhibited excellent SSC resistance.
- test numbers 41 and 42 the S content was too high in the chemical composition of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel materials of test numbers 41 and 42 did not have excellent SSC resistance.
- test number 43 the Ca content was too low in the chemical composition of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel material of test number 43 did not have excellent SSC resistance.
- test number 44 the Ca content was too high in the chemical composition of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel material of test number 44 did not have excellent SSC resistance.
- test numbers 45 and 46 the holding time t after the uniform mixing time was too short in the manufacturing process of the steel material.
- the total number density ND of Mn sulfides with an equivalent circle diameter of 1.0 ⁇ m or more and Ca sulfides with an equivalent circle diameter of 2.0 ⁇ m or more exceeded 0.50/mm 2 .
- the steel materials of test numbers 45 and 46 did not have excellent SSC resistance.
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Abstract
Description
化学組成が、質量%で、
C:0.035%以下、
Si:1.00%以下、
Mn:1.00%以下、
P:0.030%以下、
S:0.0050%以下、
sol.Al:0.005~0.100%、
N:0.001~0.020%、
Ni:5.00~7.50%、
Cr:10.00~14.00%、
Cu:0.01~1.50%未満、
Mo:1.50~3.50%、
V:0.01~1.00%、
Ti:0.02~0.30%、
Co:0.01~0.50%、
Ca:0.0003~0.0030%、
O:0.0050%以下、
W:0~1.50%、
Nb:0~0.50%、
B:0~0.0050%、
Mg:0~0.0050%、
希土類元素(REM):0~0.020%、及び、
残部がFe及び不純物、からなり、
前記鋼材中の介在物のうち、Mn含有量が10%以上であり、S含有量が10%以上であり、円相当径が1.0μm以上のMn硫化物と、Ca含有量が20%以上であり、S含有量が10%以上であり、Mn含有量が10%未満であり、円相当径が2.0μm以上のCa硫化物との合計が0.50個/mm2以下である。
鋼材であって、
化学組成が、質量%で、
C:0.035%以下、
Si:1.00%以下、
Mn:1.00%以下、
P:0.030%以下、
S:0.0050%以下、
sol.Al:0.005~0.100%、
N:0.001~0.020%、
Ni:5.00~7.50%、
Cr:10.00~14.00%、
Cu:0.01~1.50%未満、
Mo:1.50~3.50%、
V:0.01~1.00%、
Ti:0.02~0.30%、
Co:0.01~0.50%、
Ca:0.0003~0.0030%、
O:0.0050%以下、
W:0~1.50%、
Nb:0~0.50%、
B:0~0.0050%、
Mg:0~0.0050%、
希土類元素(REM):0~0.020%、及び、
残部がFe及び不純物、からなり、
前記鋼材中の介在物のうち、Mn含有量が10%以上であり、S含有量が10%以上であり、円相当径が1.0μm以上のMn硫化物と、Ca含有量が20%以上であり、S含有量が10%以上であり、Mn含有量が10%未満であり、円相当径が2.0μm以上のCa硫化物との合計が0.50個/mm2以下である、
鋼材。
[1]に記載の鋼材であって、
前記化学組成は、
W:0.01~1.50%を含有する、
鋼材。
[1]又は[2]に記載の鋼材であって、
前記化学組成は、
Nb:0.01~0.50%を含有する、
鋼材。
[1]~[3]のいずれか1項に記載の鋼材であって、
前記化学組成は、
B:0.0001~0.0050%、
Mg:0.0001~0.0050%、及び、
希土類元素(REM):0.001~0.020%、からなる群から選択される1種以上を含有する、
鋼材。
[1]~[4]のいずれか1項に記載の鋼材であって、
前記鋼材は、油井管用継目無鋼管である、
鋼材。
本実施形態の鋼材の化学組成は、次の元素を含有する。
炭素(C)は不可避に含有される。つまり、C含有量は0%超である。Cは、鋼材の焼入れ性を高めて鋼材の強度を高める。しかしながら、C含有量が0.035%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の強度が高くなりすぎて鋼材の耐SSC性が低下する。したがって、C含有量は0.035%以下である。C含有量はなるべく低い方が好ましい。しかしながら、C含有量を過剰に低減すれば、製造コストが高くなる。したがって、工業生産を考慮すれば、C含有量の好ましい下限は0.001%であり、さらに好ましくは0.003%であり、さらに好ましくは0.007%であり、さらに好ましくは0.008%であり、さらに好ましくは0.009%である。C含有量の好ましい上限は0.030%であり、さらに好ましくは0.025%であり、さらに好ましくは0.020%であり、さらに好ましくは0.018%であり、さらに好ましくは0.016%であり、さらに好ましくは0.015%である。
シリコン(Si)は不可避に含有される。つまり、Si含有量は0%超である。Siは鋼を脱酸する。しかしながら、Si含有量が1.00%を超えれば、他の元素含有量が本実施形態の範囲内であっても、脱酸効果が飽和し、かつ、鋼材の熱間加工性が低下する。したがって、Si含有量は1.00%以下である。Si含有量の好ましい下限は0.01%であり、さらに好ましくは0.05%であり、さらに好ましくは0.10%であり、さらに好ましくは0.15%であり、さらに好ましくは0.20%であり、さらに好ましくは0.25%である。Si含有量の好ましい上限は0.70%であり、さらに好ましくは0.60%であり、さらに好ましくは0.50%であり、さらに好ましくは0.45%である。
マンガン(Mn)は不可避に含有される。つまり、Mn含有量は0%超である。Mnは鋼材の焼入れ性を高めて鋼材の強度を高める。しかしながら、Mn含有量が高すぎれば、Mnは、粗大なMn硫化物を多数形成する。サワー環境において、鋼材の表層近傍に存在する粗大なMnSは溶解する場合がある。このとき、溶解したMnSの跡である凹みが形成される。この凹みがSSCの起点となり、SSCが発生する場合がある。Mn含有量が1.00%を超えれば、他の元素含有量が本実施形態の範囲内であっても、溶解したMnSの跡である凹みが生成し、耐SSC性が低下する。したがって、Mn含有量は1.00%以下である。Mn含有量の好ましい下限は0.01%であり、さらに好ましくは0.05%であり、さらに好ましくは0.10%であり、さらに好ましくは0.15%である。Mn含有量の好ましい上限は0.80%であり、さらに好ましくは0.70%であり、さらに好ましくは0.60%であり、さらに好ましくは0.50%である。
燐(P)は、不可避に含有される不純物である。つまり、P含有量は0%超である。Pは、結晶粒界に偏析し、SSCを発生しやすくする。P含有量が0.030%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の耐SSC性が顕著に低下する。したがって、P含有量は0.030%以下である。P含有量の好ましい上限は0.025%であり、さらに好ましくは0.020%であり、さらに好ましくは0.018%である。P含有量はなるべく低い方が好ましい。しかしながら、P含有量を過剰に低減すれば、製造コストが高くなる。したがって、工業生産を考慮すれば、P含有量の好ましい下限は0.001%であり、さらに好ましくは0.002%であり、さらに好ましくは0.003%である。
硫黄(S)は、不可避に含有される不純物である。つまり、S含有量は0%超である。SもPと同様に結晶粒界に偏析し、SSCを発生しやすくする。S含有量が0.0050%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の耐SSC性が顕著に低下する。したがって、S含有量は0.0050%以下である。S含有量の好ましい上限は0.0040%であり、さらに好ましくは0.0030%であり、さらに好ましくは0.0025%であり、さらに好ましくは0.0020%であり、さらに好ましくは0.0015%である。S含有量はなるべく低い方が好ましい。しかしながら、S含有量を過剰に低減すれば、製造コストが高くなる。したがって、工業生産を考慮すれば、S含有量の好ましい下限は0.0001%であり、さらに好ましくは0.0002%であり、さらに好ましくは0.0003%である。
アルミニウム(Al)は鋼を脱酸する。sol.Al含有量が0.005%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、sol.Al含有量が0.100%を超えれば、他の元素含有量が本実施形態の範囲内であっても、粗大な酸化物が生成して、鋼材の靭性が低下する。したがって、sol.Al含有量は0.005~0.100%である。sol.Al含有量の好ましい下限は0.010%であり、さらに好ましくは0.013%であり、さらに好ましくは0.015%であり、さらに好ましくは0.018%である。sol.Al含有量の好ましい上限は0.080%であり、さらに好ましくは0.060%であり、さらに好ましくは0.055%であり、さらに好ましくは0.050%である。本明細書でいうsol.Al含有量は、酸可溶Alの含有量を意味する。
窒素(N)は、Tiと結合して微細なTi窒化物を形成する。微細なTiNはピンニング効果により結晶粒の粗大化を抑制する。その結果、鋼材の強度が高まる。N含有量が0.001%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、N含有量が0.020%を超えれば、他の元素含有量が本実施形態の範囲内であっても、粗大な窒化物が形成して鋼材の靭性が低下する。したがって、N含有量は0.001~0.020%である。N含有量の好ましい下限は0.002%であり、さらに好ましくは0.003%であり、さらに好ましくは0.004%であり、さらに好ましくは0.005%である。N含有量の好ましい上限は0.018%であり、さらに好ましくは0.016%であり、さらに好ましくは0.014%であり、さらに好ましくは0.012%である。
ニッケル(Ni)は、オーステナイト形成元素であり、焼入れ後の組織をマルテンサイト化する。これにより、鋼材の強度が高まる。Niはさらに、サワー環境において不働態皮膜上に硫化物を形成する。Ni硫化物は、塩化物イオン(Cl-)や硫化水素イオン(HS-)が不働態皮膜に接触するのを抑制し、不働態皮膜が塩化物イオンや硫化水素イオンにより破壊されるのを抑制する。そのため、鋼材の耐SSC性が高まる。Ni含有量が5.00%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、Ni含有量が7.50%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材中の水素拡散係数が低下する。鋼材中の水素拡散係数が低下すれば、鋼材の耐SSC性が低下する。したがって、Ni含有量は5.00~7.50%である。Ni含有量の好ましい下限は5.10%であり、さらに好ましくは5.20%であり、さらに好ましくは5.30%である。Ni含有量の好ましい上限は7.40%であり、さらに好ましくは7.30%であり、さらに好ましくは7.20%である。
クロム(Cr)は、鋼材の表面に不働態皮膜を形成して、鋼材の耐SSC性を高める。Cr含有量が10.00%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、Cr含有量が14.00%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材中にδ(デルタ)フェライトが生成しやすくなり、鋼材の靭性が低下する。したがって、Cr含有量は10.00~14.00%である。Cr含有量の好ましい下限は10.50%であり、さらに好ましくは11.00%であり、さらに好ましくは11.50%であり、さらに好ましくは12.00%であり、さらに好ましくは12.20%である。Cr含有量の好ましい上限は13.80%であり、さらに好ましくは13.60%であり、さらに好ましくは13.50%であり、さらに好ましくは13.45%であり、さらに好ましくは13.40%である。
銅(Cu)はNiと同様にオーステナイト形成元素であり、焼入れ後の組織をマルテンサイト化する。Cu含有量が0.01%未満であれば、上記効果が十分に得られない。一方、Cu含有量が1.50%以上であれば、上記効果が飽和し、製造コストが高くなる。したがって、Cu含有量は0.01~1.50%未満である。Cu含有量の好ましい下限は0.05%であり、さらに好ましくは0.10%であり、さらに好ましくは0.15%である。Cu含有量の好ましい上限は1.40%であり、さらに好ましくは1.25%であり、さらに好ましくは1.00%である。
モリブデン(Mo)は、サワー環境において不働態皮膜上に硫化物を形成する。Mo硫化物は、塩化物イオン(Cl-)や硫化水素イオン(HS-)が不働態皮膜に接触するのを抑制し、不働態皮膜が塩化物イオンや硫化水素イオンにより破壊されるのを抑制する。そのため、鋼材の耐SSC性が高まる。Moはさらに、鋼材中に固溶して鋼材の強度を高める。Mo含有量が1.50%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果は十分に得られない。一方、Mo含有量が3.50%を超えれば、他の元素含有量が本実施形態の範囲内であっても、オーステナイトが安定化しにくくなる。その結果、マルテンサイトを主体とするミクロ組織が安定的に得られにくくなる。したがって、Mo含有量は1.50~3.50%である。Mo含有量の好ましい下限は1.60%であり、さらに好ましくは1.70%であり、さらに好ましくは1.80%である。Mo含有量の好ましい上限は3.40%であり、さらに好ましくは3.30%であり、さらに好ましくは3.20%である。
バナジウム(V)は、鋼材の焼入れ性を高め、鋼材の強度を高める。V含有量が0.01%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、V含有量が1.00%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の焼入れ性が過剰に高くなり、鋼材の耐SSC性が低下する。したがって、V含有量は0.01~1.00%である。V含有量の好ましい下限は0.02%であり、さらに好ましくは0.03%である。V含有量の好ましい上限は0.70%であり、さらに好ましくは0.50%であり、さらに好ましくは0.30%であり、さらに好ましくは0.20%であり、さらに好ましくは0.15%であり、さらに好ましくは0.10%である。
チタン(Ti)は、C及び/又はNと結合して炭化物又は窒化物を形成する。この場合、ピンニング効果により結晶粒の粗大化が抑制され、鋼材の強度が高まる。Ti含有量が0.02%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、Ti含有量が0.30%を超えれば、他の元素含有量が本実施形態の範囲内であっても、δフェライトが生成しやすくなり、鋼材の靭性が低下する。したがって、Ti含有量は0.02~0.30%である。Ti含有量の好ましい下限は0.05%であり、さらに好ましくは0.07%である。Ti含有量の好ましい上限は0.25%であり、さらに好ましくは0.20%であり、さらに好ましくは0.18%であり、さらに好ましくは0.16%である。
コバルト(Co)は、サワー環境において不働態皮膜上に硫化物を形成する。Co硫化物は、塩化物イオン(Cl-)や硫化水素イオン(HS-)が不働態皮膜に接触するのを抑制し、不働態皮膜が塩化物イオンや硫化水素イオンにより破壊されるのを抑制する。そのため、鋼材の耐SSC性が高まる。Coはさらに、鋼材の焼入れ性を高め、特に工業生産時において、鋼材の安定した高強度を確保する。具体的には、Coは残留オーステナイトの生成を抑制し、鋼材の強度のばらつきを抑制する。Co含有量が0.01%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、Co含有量が0.50%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性が低下する。したがって、Co含有量は0.01~0.50%である。Co含有量の好ましい下限は0.02%であり、さらに好ましくは0.04%であり、さらに好ましくは0.08%であり、さらに好ましくは0.10%である。Co含有量の好ましい上限は0.48%であり、さらに好ましくは0.45%であり、さらに好ましくは0.40%であり、さらに好ましくは0.35%である。
カルシウム(Ca)は、鋼材中のSと結合してCa硫化物を生成し、Mn硫化物の生成を抑制する。鋼材の表層に、円相当径が1.0μm以上のMn硫化物が存在する場合、サワー環境において、表層のMn硫化物が溶解する場合がある。この場合、溶解したMn硫化物の跡には凹みが形成される。鋼材表面に形成されるこの凹みがSSCの発生の起点となりやすい。CaはMn硫化物の生成を抑制し、円相当径が1.0μm以上のMn硫化物の個数密度を低下させる。その結果、鋼材の耐SSC性が高まる。Ca含有量が0.0003%未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。一方、Ca含有量が0.0030%を超えれば、他の元素含有量が本実施形態の範囲内であっても、円相当径が2.0μm以上のCa硫化物が過剰に生成する。円相当径が2.0μm以上のCa硫化物が鋼材の表層に存在する場合、上述のMn硫化物と同様に、サワー環境において溶解して、鋼材の表面に凹みを形成する場合がある。この場合、鋼材の耐SSC性が低下する。したがって、Ca含有量は0.0003~0.0030%である。Ca含有量の好ましい下限は0.0005%であり、さらに好ましくは0.0007%であり、さらに好ましくは0.0009%である。Ca含有量の好ましい上限は0.0029%であり、さらに好ましくは0.0028%であり、さらに好ましくは0.0027%であり、さらに好ましくは0.0026%である。
酸素(O)は不可避に含有される不純物である。つまり、O含有量は0%超である。Oは、酸化物を形成して、鋼材の靭性が低下する。O含有量が0.0050%を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性が顕著に低下する。したがって、O含有量は0.0050%以下である。O含有量の好ましい上限は0.0045%であり、さらに好ましくは0.0040%であり、さらに好ましくは0.0035%であり、さらに好ましくは0.0030%である。O含有量はなるべく低い方が好ましい。しかしながら、O含有量を過剰に低減すれば、製造コストが高くなる。したがって、工業生産を考慮すれば、O含有量の好ましい下限は0.0001%であり、さらに好ましくは0.0002%である。
本実施形態による鋼材の化学組成はさらに、Feの一部に代えて、Wを含有してもよい。
タングステン(W)は任意元素であり、含有されなくてもよい。つまり、W含有量は0%であってもよい。含有される場合、Wはサワー環境において不働態皮膜を安定化して、不働態皮膜が塩化物イオンや硫化水素イオンにより破壊されるのを抑制する。そのため、鋼材の耐SSC性が高まる。Wが少しでも含有されれば、上記効果がある程度得られる。しかしながら、W含有量が1.50%を超えれば、WはCと結合して、粗大な炭化物を形成する。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の靱性が低下する。したがって、W含有量は0~1.50%である。W含有量の好ましい下限は0.01%であり、さらに好ましくは0.05%であり、さらに好ましくは0.10%であり、さらに好ましくは0.30%であり、さらに好ましくは0.50%である。W含有量の好ましい上限は1.45%であり、さらに好ましくは1.40%であり、さらに好ましくは1.37%である。
ニオブ(Nb)は任意元素であり、含有されなくてもよい。つまり、Nb含有量は0%であってもよい。含有される場合、NbはC及び/又はNと結合してNb炭化物、Nb炭窒化物を形成する。この場合、ピンニング効果により結晶粒の粗大化が抑制され、鋼材の強度が高まる。Nbが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Nb含有量が0.50%を超えれば、他の元素含有量が本実施形態の範囲内であっても、Nb炭化物及び/又はNb炭窒化物が過剰に生成して鋼材の靭性が低下する。したがって、Nb含有量は0~0.50%である。Nb含有量の好ましい下限は0.01%であり、さらに好ましくは0.05%であり、さらに好ましくは0.10%であり、さらに好ましくは0.15%である。Nb含有量の好ましい上限は0.45%であり、さらに好ましくは0.40%であり、さらに好ましくは0.35%である。
ボロン(B)は任意元素であり、含有されなくてもよい。つまり、B含有量は0%であってもよい。含有される場合、Bは鋼材に固溶して鋼材の熱間加工性を高める。Bが少しでも含有されれば、上記効果がある程度得られる。しかしながら、B含有量が0.0050%を超えれば、他の元素含有量が本実施形態の範囲内であっても、粗大なB窒化物が生成して、鋼材の靭性が低下する。したがって、B含有量は0~0.0050%である。B含有量の好ましい下限は0.0001%であり、さらに好ましくは0.0002%であり、さらに好ましくは0.0003%であり、さらに好ましくは0.0004%である。B含有量の好ましい上限は0.0040%であり、さらに好ましくは0.0030%であり、さらに好ましくは0.0020%である。
マグネシウム(Mg)は任意元素であり、含有されなくてもよい。つまり、Mg含有量は0%であってもよい。含有される場合、Mgは介在物の形態を制御して、鋼材の熱間加工性を高める。Mgが少しでも含有されれば、上記効果がある程度得られる。しかしながら、Mg含有量が0.0050%を超えれば、粗大な酸化物が生成する。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の靱性が低下する。したがって、Mg含有量は0~0.0050%である。Mg含有量の好ましい下限は0.0001%であり、さらに好ましくは0.0002%であり、さらに好ましくは0.0003%である。Mg含有量の好ましい上限は0.0040%であり、さらに好ましくは0.0035%であり、さらに好ましくは0.0030%であり、さらに好ましくは0.0025%である。
希土類元素(REM)は任意元素であり、含有されなくてもよい。つまり、REM含有量は0%であってもよい。含有される場合、REMはMgと同様に、介在物の形態を制御して、鋼材の熱間加工性を高める。REMが少しでも含有されれば、上記効果がある程度得られる。しかしながら、REM含有量が0.020%を超えれば、粗大な酸化物が生成する。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の靱性が低下する。したがって、REM含有量は0~0.020%である。REM含有量の好ましい下限は0.001%であり、さらに好ましくは0.003%であり、さらに好ましくは0.005%である。REM含有量の好ましい上限は0.019%であり、さらに好ましくは0.018%であり、さらに好ましくは0.017%である。
本実施形態の鋼材において、鋼材中の介在物のうち、Mn硫化物、及び、Ca硫化物を次のとおり定義する。
Mn硫化物:介在物の質量%を100%とした場合に、質量%でMn含有量が10%以上であり、S含有量が10%以上である介在物
Ca硫化物:介在物の質量%を100%とした場合に、質量%でCa含有量が20%以上であり、S含有量が10%以上であり、Mn含有量が10%未満である介在物
円相当径が1.0μm以上のMn硫化物及び円相当径が2.0μm以上のCa硫化物の総個数密度NDは次の方法により測定できる。具体的には、鋼材の任意の位置から試験片を採取する。鋼材が鋼管である場合、肉厚中央位置から試験片を採取する。鋼材が断面円形の棒鋼である場合、R/2位置から試験片を採取する。なお、本明細書において、R/2位置とは、棒鋼の長手方向に垂直な断面において、半径Rの中央位置を意味する。鋼材が鋼板である場合、板厚中央位置から試験片を採取する。
本実施形態による鋼材のミクロ組織は、マルテンサイトを主体とする。本明細書において、マルテンサイトとは、フレッシュマルテンサイトだけでなく、焼戻しマルテンサイトも含む。また、本明細書において、マルテンサイトが主体とは、ミクロ組織において、マルテンサイトの体積率が80%以上であることを意味する。ミクロ組織の残部は、残留オーステナイトである。つまり、本実施形態の鋼材において、残留オーステナイトの体積率は0~20%である。残留オーステナイトの体積率はなるべく低い方が好ましい。本実施形態の鋼材のミクロ組織中のマルテンサイトの体積率の好ましい下限は85%であり、さらに好ましくは90%である。さらに好ましくは、鋼材のミクロ組織は、マルテンサイト単相である。
本実施形態の鋼材のミクロ組織におけるマルテンサイトの体積率(vol.%)は、以下に示す方法で求めた残留オーステナイトの体積率(vol.%)を、100%から差し引いて求める。
Vγ=100/{1+(Iα×Rγ)/(Iγ×Rα)} (I)
ここで、Iαはα相の積分強度である。Rαはα相の結晶学的理論計算値である。Iγはγ相の積分強度である。Rγはγ相の結晶学的理論計算値である。なお、本明細書において、α相の(200)面でのRαを15.9、α相の(211)面でのRαを29.2、γ相の(200)面でのRγを35.5、γ相の(220)面でのRγを20.8、γ相の(311)面でのRγを21.8とする。なお、残留オーステナイトの体積率は、得られた数値の小数第一位を四捨五入する。
マルテンサイトの体積率=100-残留オーステナイトの体積率(%)
本実施形態による鋼材の降伏強度は、特に限定されない。鋼材の好ましい降伏強度は758MPa以上(110ksi以上)であり、さらに好ましくは862MPa以上(125ksi以上)である。降伏強度の上限は特に限定されないが、本実施形態の鋼材の降伏強度の上限は、たとえば、1069MPa未満(155ksi未満)である。鋼材のさらに好ましい降伏強度の上限は1000MPaである。
本実施形態による鋼材は、優れた耐SSC性を有する。本実施形態による鋼材の耐SSC性は、常温での耐SSC性評価試験により評価できる。耐SSC性評価試験は、NACE TM0177-2005 Method Aに準拠した方法で実施する。
本実施形態による鋼材は、鋼管、丸棒(中実材)、又は鋼板である。鋼管は継目無鋼管であってもよいし、溶接鋼管であってもよい。鋼管はたとえば、油井管用鋼管である。油井管用鋼管は、油井管用途の鋼管を意味する。油井管はたとえば、油井又はガス井の掘削、原油又は天然ガスの採取等に用いられるケーシング、チュービング、ドリルパイプ等である。好ましくは、本実施形態の鋼材は、油井管用継目無鋼管である。
本実施形態の鋼材の製造方法の一例を説明する。なお、以下に説明する製造方法は一例であって、本実施形態の鋼材の製造方法はこれに限定されない。つまり、上述の構成を有する本実施形態の鋼材が製造できれば、以下に説明する製造方法に限定されない。ただし、以下に説明する製造方法は、本実施形態の鋼材を製造する好適な製造方法である。
製鋼工程では、溶鋼を製造する工程(精錬工程)と、溶鋼を用いて鋳造法により素材を製造する工程(素材製造工程)とを含む。
精錬工程では初めに、Crを含有する溶鋼を取鍋に収納して、取鍋内の溶鋼に対して、大気圧下で脱炭処理を実施する(粗脱炭精錬工程)。粗脱炭精錬工程での脱炭処理により、スラグが生成する。粗脱炭精錬工程後の溶鋼の液面には、脱炭処理により生成したスラグが浮上している。粗脱炭精錬工程において、溶鋼中のCrが酸化してCr2O3が生成する。Cr2O3はスラグ中に吸収される。そこで、取鍋に脱酸剤を添加して、スラグ中のCr2O3を還元し、Crを溶鋼中に回収する(Cr還元処理工程)。粗脱炭精錬工程及びCr還元処理工程はたとえば、電気炉法、転炉法、又は、AOD(Argon Oxygen Decarburization)法により実施する。Cr還元処理工程後、溶鋼からスラグを除滓する(除滓処理工程)。
τ=800×ε-0.4 (A)
ここで、εはLTにおける溶鋼の撹拌動力密度であり、式(B)により定義される。
ε=28.5(Q/W)×T×log(1+H/1.48) (B)
ここで、Qは上吹きガス流量(Nm3/min)である。Wは溶鋼質量(t)である。Tは溶鋼温度(K)である。Hは取鍋内の溶鋼の深さ(鋼浴深さ)(m)である。
上述の精錬工程により製造された溶鋼を用いて、素材(鋳片又はインゴット)を製造する。具体的には、溶鋼を用いて連続鋳造法により鋳片を製造する。鋳片はスラブでもよいし、ブルームでもよいし、ビレットでもよい。又は、溶鋼を用いて造塊法によりインゴットとしてもよい。鋳片又はインゴットに対してさらに、分塊圧延等を実施して、ビレットを製造してもよい。以上の工程により、素材を製造する。
熱間加工工程では、素材を熱間加工して中間鋼材を製造する。鋼材が鋼管である場合、中間鋼材は素管に相当する。初めに、素材を加熱炉で加熱する。加熱温度は特に限定されないが、たとえば、1100~1300℃である。加熱炉から抽出されたビレットに対して熱間加工を実施して、中間鋼材である素管(継目無鋼管)を製造する。熱間加工の方法は、特に限定されず、周知の方法でよい。たとえば、熱間加工としてマンネスマン法を実施し、素管を製造する。この場合、穿孔機により丸ビレットを穿孔圧延する。穿孔圧延する場合、穿孔比は特に限定されないが、たとえば、1.0~4.0である。穿孔圧延された丸ビレットをさらに、マンドレルミル、レデューサ、サイジングミル等により熱間圧延して素管にする。熱間加工工程での累積の減面率はたとえば、20~70%である。
熱処理工程は、焼入れ工程及び焼戻し工程を含む。
熱処理工程では、初めに、熱間加工工程で製造された中間鋼材に対して、焼入れを実施する(焼入れ工程)。焼入れは周知の方法で実施する。具体的には、熱間加工工程後の中間鋼材を熱処理炉に装入し、焼入れ温度で保持する。焼入れ温度はAC3変態点以上であり、たとえば、900~1000℃である。中間鋼材を焼入れ温度で保持した後、急冷(焼入れ)する。焼入れ温度での保持時間は特に限定されないが、たとえば、10~60分である。焼入れ方法はたとえば、水冷である。焼入れ方法は特に制限されない。中間鋼材が素管である場合、たとえば、水槽又は油槽に浸漬して素管を急冷してもよいし、シャワー冷却又はミスト冷却により、素管の外面及び/又は内面に対して冷却水を注いだり、噴射したりして、素管を急冷してもよい。
焼入れ後の中間鋼材に対してさらに、焼戻し工程を実施する。焼戻し工程では、鋼材の降伏強度を調整する。本実施形態では、焼戻し温度を540~620℃とする。焼戻し温度での保持時間は特に限定されないが、たとえば、10~180分である。化学組成に応じて焼戻し温度を適宜調整することにより、鋼材の降伏強度を調整することができることは当業者に周知である。好ましくは、鋼材の降伏強度が758MPa以上(110ksi以上)となるように焼戻し条件を調整する。
上述の焼戻し後の試験番号1~23の鋼材に対して、ミクロ組織観察試験、総個数密度ND測定試験、引張試験、及び、耐SSC性評価試験を実施した。
試験番号1~23の鋼材(継目無鋼管)のミクロ組織におけるマルテンサイト体積率を、次の方法により求めた。初めに、各試験番号の鋼材のミクロ組織中の残留オーステナイトの体積率を、X線回折法により求めた。具体的には、各試験番号の鋼材(継目無鋼管)の肉厚中央位置から試験片を採取した。試験片の大きさは、15mm×15mm×厚さ2mmであった。試験片の厚さ方向を、管径方向とした。得られた試験片を用いて、α相の(200)面、α相の(211)面、γ相の(200)面、γ相の(220)面、γ相の(311)面の各々のX線回折強度を測定し、各面の積分強度を算出した。X線回折強度の測定において、X線回折装置のターゲットをMoとし(MoKα線)、出力を50kV-40mAとした。算出後、α相の各面と、γ相の各面との組合せ(2×3=6組)ごとに式(I)を用いて残留オーステナイトの体積率Vγ(%)を算出した。そして、6組の残留オーステナイトの体積率Vγの平均値を、残留オーステナイトの体積率(%)と定義した。
Vγ=100/{1+(Iα×Rγ)/(Iγ×Rα)} (I)
ここで、Iαはα相の積分強度である。Rαはα相の結晶学的理論計算値である。Iγはγ相の積分強度である。Rγはγ相の結晶学的理論計算値である。なお、本明細書において、α相の(200)面でのRαを15.9、α相の(211)面でのRαを29.2、γ相の(200)面でのRγを35.5、γ相の(220)面でのRγを20.8、γ相の(311)面でのRγを21.8とした。なお、残留オーステナイトの体積率は、得られた数値の小数第一位を四捨五入した。
マルテンサイトの体積率=100-残留オーステナイトの体積率(%)
得られた試験番号1~23のマルテンサイトの体積率を、表2の「マルテンサイト体積率(%)」欄に示す。
試験番号1~23の鋼材(継目無鋼管)中における、円相当径が1.0μm以上のMn硫化物及び円相当径が2.0μm以上のCa硫化物の総個数密度NDは次の方法により測定した。各試験番号の鋼材の肉厚中央位置から試験片を採取した。採取した試験片を樹脂埋めした。試験片の表面のうち、管軸方向及び肉厚方向を含む面を観察面とした。樹脂埋めされた鋼材の観察面を研磨した。研磨後の観察面のうち、任意の10視野を観察した。各視野において、介在物の個数を求めた。各視野の面積は36mm2(6mm×6mm)とした。
試験番号1~23の鋼材(継目無鋼管)について、ASTM E8/E8M(2013)に準拠して、引張試験を実施した。具体的には、各試験番号の鋼材の肉厚中央位置から、丸棒引張試験片を採取した。丸棒引張試験片の平行部の直径は8.9mmであり、平行部の長さは35.6mmであった。丸棒引張試験片の長手方向は、鋼材の長手方向(圧延方向)と平行であった。試験番号1~23の丸棒引張試験片を用いて、常温(25℃)、大気中にて引張試験を実施して、0.2%オフセット耐力(MPa)を求めた。求めた0.2%オフセット耐力を降伏強度(MPa)と定義した。得られた試験番号1~23の降伏強度を、表2の「YS(MPa)」欄に示す。
試験番号1~23の鋼材(継目無鋼管)の耐SSC性評価試験を次の方法で実施した。各試験番号の鋼材の肉厚中央位置から、丸棒試験片を採取した。丸棒試験片の平行部の直径は6.35mmであり、平行部の長さは25.4mmであった。丸棒試験片の長手方向は、鋼材の長手方向(管軸方向)と平行であった。
表1及び表2を参照して、試験番号1~16の鋼材は、その化学組成が適切であった。さらに、ミクロ組織中のマルテンサイト体積率は80%以上であり、降伏強度は862MPa以上(125ksi以上)であった。さらに、円相当径が1.0μm以上のMn硫化物及び円相当径が2.0μm以上のCa硫化物の総個数密度NDが0.50個/mm2以下であった。その結果、試験番号1~16の鋼材は、優れた耐SSC性が得られた。
上述の実施例1と同様に、焼戻し後の試験番号24~46の鋼材に対して、ミクロ組織観察試験、総個数密度ND測定試験、引張試験、及び、耐SSC性評価試験を実施した。
試験番号24~46の鋼材(継目無鋼管)のミクロ組織におけるマルテンサイト体積率を、上述の実施例1と同様の方法により求めた。得られた試験番号24~46のマルテンサイトの体積率を、表4の「マルテンサイト体積率(%)」欄に示す。
試験番号24~46の鋼材(継目無鋼管)中における、円相当径が1.0μm以上のMn硫化物及び円相当径が2.0μm以上のCa硫化物の総個数密度NDは、実施例1と同様の方法により測定した。求めた試験番号24~46の総個数密度NDを表4の「総個数密度ND(個/mm2)」欄に示す。
試験番号24~46の鋼材(継目無鋼管)について、ASTM E8/E8M(2013)に準拠して、実施例1と同様の方法で引張試験を実施した。得られた試験番号24~46の降伏強度を、表4の「YS(MPa)」欄に示す。
試験番号24~46の鋼材(継目無鋼管)について、実施例1と同様の方法で耐SSC性評価試験を実施した。丸棒試験片の表面を10倍のルーペ及び100倍の光学顕微鏡で観察しても割れが確認されなかった場合、優れた耐SSC性が得られたと判断した(表4中の「耐SSC性」欄に「E(Excellent)」と表記)。割れが確認された場合、優れた耐SSC性が得られなかったと判断した(表4中の「耐SSC性」欄に「B(Bad)」と表記)。
表3及び表4を参照して、試験番号24~40の鋼材は、その化学組成が適切であった。さらに、ミクロ組織中のマルテンサイト体積率は80%以上であり、降伏強度は758~862MPa未満(110ksi級)であった。さらに、円相当径が1.0μm以上のMn硫化物及び円相当径が2.0μm以上のCa硫化物の総個数密度NDが0.50個/mm2以下であった。その結果、試験番号24~40の鋼材は、優れた耐SSC性が得られた。
Claims (5)
- 鋼材であって、
化学組成が、質量%で、
C:0.035%以下、
Si:1.00%以下、
Mn:1.00%以下、
P:0.030%以下、
S:0.0050%以下、
sol.Al:0.005~0.100%、
N:0.001~0.020%、
Ni:5.00~7.50%、
Cr:10.00~14.00%、
Cu:0.01~1.50%未満、
Mo:1.50~3.50%、
V:0.01~1.00%、
Ti:0.02~0.30%、
Co:0.01~0.50%、
Ca:0.0003~0.0030%、
O:0.0050%以下、
W:0~1.50%、
Nb:0~0.50%、
B:0~0.0050%、
Mg:0~0.0050%、
希土類元素(REM):0~0.020%、及び、
残部がFe及び不純物、からなり、
前記鋼材中の介在物のうち、Mn含有量が10%以上であり、S含有量が10%以上であり、円相当径が1.0μm以上のMn硫化物と、Ca含有量が20%以上であり、S含有量が10%以上であり、Mn含有量が10%未満であり、円相当径が2.0μm以上のCa硫化物との合計が0.50個/mm2以下である、
鋼材。 - 請求項1に記載の鋼材であって、
前記化学組成は、
W:0.01~1.50%を含有する、
鋼材。 - 請求項1又は請求項2に記載の鋼材であって、
前記化学組成は、
Nb:0.01~0.50%を含有する、
鋼材。 - 請求項1~請求項3のいずれか1項に記載の鋼材であって、
前記化学組成は、
B:0.0001~0.0050%、
Mg:0.0001~0.0050%、及び、
希土類元素(REM):0.001~0.020%、からなる群から選択される1種以上を含有する、
鋼材。 - 請求項1~請求項4のいずれか1項に記載の鋼材であって、
前記鋼材は、油井管用継目無鋼管である、
鋼材。
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