JP5500960B2 - Fine grain austenitic stainless steel sheet with excellent stress corrosion cracking resistance and workability - Google Patents
Fine grain austenitic stainless steel sheet with excellent stress corrosion cracking resistance and workability Download PDFInfo
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- 230000007797 corrosion Effects 0.000 title claims description 87
- 238000005260 corrosion Methods 0.000 title claims description 87
- 238000005336 cracking Methods 0.000 title claims description 83
- 229910000963 austenitic stainless steel Inorganic materials 0.000 title claims description 41
- 239000013078 crystal Substances 0.000 claims description 65
- 229910000831 Steel Inorganic materials 0.000 claims description 55
- 239000010959 steel Substances 0.000 claims description 55
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 claims description 20
- 239000007864 aqueous solution Substances 0.000 claims description 10
- 238000009835 boiling Methods 0.000 claims description 10
- 229910001629 magnesium chloride Inorganic materials 0.000 claims description 10
- 229910052802 copper Inorganic materials 0.000 claims description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- 229910052757 nitrogen Inorganic materials 0.000 claims description 8
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 7
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052758 niobium Inorganic materials 0.000 claims description 5
- 229910052710 silicon Inorganic materials 0.000 claims description 5
- 229910052749 magnesium Inorganic materials 0.000 claims description 4
- 239000011777 magnesium Substances 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 238000009864 tensile test Methods 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 230000035882 stress Effects 0.000 description 80
- 238000000137 annealing Methods 0.000 description 38
- 238000005097 cold rolling Methods 0.000 description 30
- 230000000694 effects Effects 0.000 description 29
- 238000004519 manufacturing process Methods 0.000 description 19
- 229910000734 martensite Inorganic materials 0.000 description 19
- 229910001566 austenite Inorganic materials 0.000 description 18
- 239000000463 material Substances 0.000 description 15
- 238000012360 testing method Methods 0.000 description 14
- 230000009466 transformation Effects 0.000 description 12
- 238000012545 processing Methods 0.000 description 10
- 239000011651 chromium Substances 0.000 description 9
- 230000006872 improvement Effects 0.000 description 9
- 229910001220 stainless steel Inorganic materials 0.000 description 9
- 238000005096 rolling process Methods 0.000 description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 238000000034 method Methods 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 238000007670 refining Methods 0.000 description 5
- 238000001816 cooling Methods 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 230000032683 aging Effects 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 230000020169 heat generation Effects 0.000 description 3
- 238000007654 immersion Methods 0.000 description 3
- 230000001771 impaired effect Effects 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 238000005554 pickling Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 239000011573 trace mineral Substances 0.000 description 2
- 235000013619 trace mineral Nutrition 0.000 description 2
- 229910052721 tungsten Inorganic materials 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- CXOWYMLTGOFURZ-UHFFFAOYSA-N azanylidynechromium Chemical compound [Cr]#N CXOWYMLTGOFURZ-UHFFFAOYSA-N 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000000110 cooling liquid Substances 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000000866 electrolytic etching Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
- 229910000859 α-Fe Inorganic materials 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- C—CHEMISTRY; METALLURGY
- 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
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—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
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Heat Treatment Of Steel (AREA)
Description
本発明は、平均結晶粒径が10μm以下の微細粒組織を有する耐応力腐食割れ性と加工性に優れたオーステナイト系ステンレス鋼板に関するものである。 The present invention relates to an austenitic stainless steel sheet having a fine grain structure with an average crystal grain size of 10 μm or less and excellent in stress corrosion cracking resistance and workability.
近年,鉄鋼材料において、結晶粒を微細化することは、合金元素の添加によらず強度・靭性を上昇させる最も有効な方法であることが知られている。オーステナイト系ステンレス鋼においても、非特許文献1および2において、JISG4305に規定するSUS304で加工誘起マルテンサイトからオーステナイトへの相変態を利用した結晶粒の微細化が開示されている。このような方法により、結晶粒径1〜5μmの微細粒組織を形成し,微細化効果として、非特許文献1には降伏強度(0.2%耐力)の上昇,非特許文献2には650〜750℃での超塑性の発現が報告されている。 In recent years, it has been known that refining crystal grains in steel materials is the most effective method for increasing strength and toughness regardless of the addition of alloy elements. Also in austenitic stainless steel, Non-Patent Documents 1 and 2 disclose the refinement of crystal grains using the phase transformation from work-induced martensite to austenite in SUS304 defined in JIS G4305. By such a method, a fine grain structure having a crystal grain size of 1 to 5 μm is formed. As a refinement effect, non-patent document 1 shows an increase in yield strength (0.2% proof stress) and non-patent document 2 shows 650. The development of superplasticity at ˜750 ° C. has been reported.
オーステナイト系ステンレス鋼において、結晶粒の微細化効果を利用したものとして、特許文献1には金属ガスケットとその素材およびそれらの製造方法が開示されている。この公報には、JISG4305に規定するSUS301Lで上述した加工誘起マルテンサイトからオーステナイトへの相変態とクロム窒化物の析出を利用して、結晶粒径5μm以下の微細粒組織とし,調質圧延との組み合わせによりHv500以上の高強度化を図っている。 In austenitic stainless steel, Patent Document 1 discloses a metal gasket, a material thereof, and a method for manufacturing the same as one utilizing a grain refinement effect. In this publication, a fine grain structure having a crystal grain size of 5 μm or less is obtained by utilizing the phase transformation from processing-induced martensite to austenite and precipitation of chromium nitride described in SUS301L defined in JIS G4305. High strength of Hv500 or more is achieved by combination.
従来、オーステナイト系ステンレス鋼の結晶粒微細化は、上述したようなSUS304やSUS301Lにおいて、結晶粒径1〜5μmとして0.2%耐力の上昇や高強度化を指向したものである。 Conventionally, grain refinement of austenitic stainless steel is aimed at increasing 0.2% proof stress and increasing strength in SUS304 and SUS301L as described above with a crystal grain size of 1 to 5 μm.
古くから,オーステナイト系ステンレス鋼板では、塩化物イオンを含む腐食環境で応力腐食割れを発生するという問題がよく知られている。非特許文献3において、その対策としてはNiを含まないフェライト系ステンレス鋼への変更が確実であること,加工性や溶接性の点からフェライト系ステンレス鋼の使用が困難な場合には、高Ni(11.5〜15%)かつSiとCu量を高めたSUSXM15J1系のオーステナイト系ステンレス鋼が有効であると記載されている。 For a long time, it has been well known that austenitic stainless steel sheets cause stress corrosion cracking in a corrosive environment containing chloride ions. In Non-Patent Document 3, as a countermeasure, Ni-containing ferritic stainless steel is surely changed, and when it is difficult to use ferritic stainless steel from the viewpoint of workability and weldability, high Ni is used. It is described that SUSXM15J1 austenitic stainless steel (11.5 to 15%) and having an increased amount of Si and Cu are effective.
孔食や隙間腐食を起点とする応力腐食割れの改善に対して,上述した合金添加は有効に作用する。特許文献2には、Niを9%台、Cuを1.5%超え2.5%未満で添加し,MoおよびNを少量含有させる耐応力腐食割れ性および耐孔食性に優れたオーステナイト系ステンレス鋼が開示されている。特許文献3には、Cr:18〜35%,Ni:25〜50%,Mo:8%以下,Mn:6%以下,N:0.5%以下,C:0.03%以下とする高Crかつ高Niを特徴とする耐応力腐食割れ性に優れたオーステナイト系合金が開示されている。特許文献4では、C:0.08%以下,Si:0.1〜3%,Cr:18〜23%,Ni:8.5〜12%,Mo:0.2〜2%,Cu:0.2〜3.5%,N:0.03〜0.25%とし,かつMnとSとの含有量を調整すること,CuとNを複合添加すること,更に少量のCo,W,V,Nbを添加することによる耐候性、耐隙間腐食性および耐応力腐食割れ性に優れたオーステナイト系ステンレス鋼が開示されている。 The alloy addition described above works effectively for the improvement of stress corrosion cracking starting from pitting corrosion and crevice corrosion. Patent Document 2 discloses an austenitic stainless steel with excellent resistance to stress corrosion cracking and pitting corrosion, in which Ni is added in the order of 9%, Cu is added in an amount exceeding 1.5% and less than 2.5%, and Mo and N are contained in a small amount. Steel is disclosed. In Patent Document 3, Cr: 18 to 35%, Ni: 25 to 50%, Mo: 8% or less, Mn: 6% or less, N: 0.5% or less, C: 0.03% or less An austenitic alloy excellent in stress corrosion cracking resistance characterized by Cr and high Ni is disclosed. In Patent Document 4, C: 0.08% or less, Si: 0.1 to 3%, Cr: 18 to 23%, Ni: 8.5 to 12%, Mo: 0.2 to 2%, Cu: 0 .2 to 3.5%, N: 0.03 to 0.25%, adjusting the contents of Mn and S, adding Cu and N in combination, and further small amounts of Co, W, V , Nb has been disclosed as an austenitic stainless steel excellent in weather resistance, crevice corrosion resistance and stress corrosion cracking resistance.
また、応力腐食割れには粒界型の割れも生じるため,特許文献5〜7には粒界型応力腐食割れの改善について開示されている。特許文献5には、Mo及びNbのいずれか一方,または両方を含むことを特徴とする耐粒界腐食性並びに耐粒界応力腐食割れ性の優れたオーステナイト系ステンレス鋼が示されている。特許文献6,7には、Cを0.03%以下に制約してNを0.15%以下で含有させ,鋼片の加熱温度や時間を調整することで炭化物析出を低減し,粒界近傍のCr欠乏量を軽減することを特徴とする耐粒界応力腐食割れ性に優れたオーステナイト系ステンレス鋼およびその製造方法が開示されている。 In addition, since intergranular cracking also occurs in stress corrosion cracking, Patent Documents 5 to 7 disclose improvement of intergranular stress corrosion cracking. Patent Document 5 discloses an austenitic stainless steel having excellent intergranular corrosion resistance and intergranular stress corrosion cracking resistance, characterized by containing either one or both of Mo and Nb. In Patent Documents 6 and 7, C is limited to 0.03% or less, N is contained at 0.15% or less, and carbide precipitation is reduced by adjusting the heating temperature and time of the steel slab, An austenitic stainless steel excellent in intergranular stress corrosion cracking resistance, characterized by reducing the Cr deficiency in the vicinity, and a method for producing the same are disclosed.
上述した非特許文献3および特許文献2〜7で開示されたオーステナイト系ステンレス鋼は、いずれも8%超のNiを含有し,Cu,Mo,Si,さらには微量元素としてNb,Co,W,V等の添加により耐応力腐食割れ性を改善したものである。
工業生産における焼鈍温度は非特許文献3および4,結晶粒径については非特許文献5で公知である。通常,オーステナイト系ステンレス鋼は1000〜1100℃で焼鈍され,成分を調整しても細粒化の限度は結晶粒度No.10に満たない,すなわち結晶粒径は10μmより大きくなると説明されている。
All of the austenitic stainless steels disclosed in Non-Patent Document 3 and Patent Documents 2 to 7 described above contain more than 8% Ni, Cu, Mo, Si, and Nb, Co, W, and trace elements as trace elements. Stress corrosion cracking resistance is improved by adding V or the like.
The annealing temperature in industrial production is known in Non-Patent Documents 3 and 4, and the crystal grain size is known in Non-Patent Document 5. Usually, austenitic stainless steel is annealed at 1000 to 1100 ° C., and even if the components are adjusted, the limit of refining is the grain size no. It is described that it is less than 10, that is, the crystal grain size is larger than 10 μm.
従来のオーステナイト系ステンレス鋼の結晶粒微細化では、耐応力腐食割れ性に対する結晶粒の微細化効果については全く明らかにされていない。
また、上述したように、通常,オーステナイト系ステンレス鋼は1000〜1100℃で焼鈍され,成分を調整しても結晶粒径は10μmより大きくなると説明されている。特許文献2〜7には、製造方法(焼鈍温度)と結晶粒径は特に記載されていない。従って、特許文献2〜7に開示された鋼も、通常と異なる特別な製造方法を開示していない限りにおいて,その結晶粒径は、非特許文献3と同様に10μmより大きいことが容易に推定できる。
In the conventional grain refinement of austenitic stainless steel, the grain refinement effect on the stress corrosion cracking resistance has not been clarified at all.
Further, as described above, it is usually described that austenitic stainless steel is annealed at 1000 to 1100 ° C., and the crystal grain size becomes larger than 10 μm even if the components are adjusted. Patent Documents 2 to 7 do not specifically describe the production method (annealing temperature) and the crystal grain size. Therefore, the steel disclosed in Patent Documents 2 to 7 is also easily estimated that the crystal grain size is larger than 10 μm as in Non-Patent Document 3, unless a special manufacturing method different from usual is disclosed. it can.
以上に述べたように、オーステナイト系ステンレス鋼において、8%以下のNi量で耐応力腐食割れ性の改善を試みた検討は見当たらない。さらに、8%以下のNi量でかつ高価なMoの添加によらず,結晶粒の微細化効果によりオーステナイト系ステンレス鋼の欠点である応力腐食割れを低減し,加工性との両立を図るという技術思想ならびにそのような開示は全く皆無である。 As described above, in the austenitic stainless steel, there has been no study that attempted to improve the stress corrosion cracking resistance with an Ni amount of 8% or less. Furthermore, technology that reduces stress corrosion cracking, which is a drawback of austenitic stainless steels, due to the refinement effect of crystal grains, and achieves compatibility with workability, regardless of the amount of Ni of 8% or less and expensive addition of Mo. There is no thought or such disclosure at all.
本発明の課題は、8%以下のNi量でかつ高価なMoの添加によらず,オーステナイト系ステンレス鋼の欠点である応力腐食割れを結晶粒の微細化効果により克服し,加工性との両立を図った平均結晶粒径が10μm以下の微細粒組織を有するオーステナイト系ステンレス鋼板を提供することにある。 The object of the present invention is to overcome the stress corrosion cracking, which is a defect of austenitic stainless steel, by the effect of refining crystal grains, regardless of the addition of Ni with an amount of Ni of 8% or less and expensive workability. The object is to provide an austenitic stainless steel sheet having a fine grain structure with an average grain size of 10 μm or less.
(1)質量%にて、C:0.05%以下、Cr:14〜19%、Si:2%以下、Mn:4%以下、Ni:5〜8%,Cu:4%以下,N:0.1%以下,残部Feおよび不可避的不純物からなり,かつ下記のMdが−20〜40の範囲にある鋼成分を有し、平均結晶粒径が6.5μm以下でありかつ15°以上の大傾角粒界の占める比率が80%超であることを特徴とする耐応力腐食割れ性と加工性に優れた微細粒オーステナイト系ステンレス鋼板。
Md=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)−18.2Mo
(1) In mass%, C: 0.05% or less, Cr: 14-19%, Si: 2% or less, Mn: 4% or less, Ni: 5-8%, Cu: 4% or less, N: 0.1% or less, balance Fe and unavoidable impurities, and having a steel component with the following Md in the range of -20 to 40, an average crystal grain size of 6.5 μm or less, and 15 ° or more A fine-grained austenitic stainless steel sheet excellent in stress corrosion cracking resistance and workability, characterized in that the proportion of the large-angle grain boundaries of the steel exceeds 80%.
Md = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29 (Ni + Cu) -18.2Mo
(2)前記鋼成分が、さらに質量%にて、Mo:1%以下、V:1%以下,B:0.010%以下,Nb:0.5%以下,Ti:0.5%以下,希土類元素:0.5%以下,Al:0.5%以下,Mg:0.005%以下,Ca:0.005%以下の1種または2種以上含有していることを特徴とする(1)に記載の耐応力腐食割れ性と加工性に優れた微細粒オーステナイト系ステンレス鋼板。
(3)絞り比1.5〜2.0の範囲で円筒深絞り加工して得られた成形品を、沸騰42%塩化マグネシウム水溶液中に4hr浸漬しても割れが発生しないことを特徴とする(1)または(2)に記載の耐応力腐食割れ性と加工性に優れた微細粒オーステナイト系ステンレス鋼板。絞り比は、ブランク径をポンチ径で割った値とする。
(4)引張試験によって求められる0.2%耐力が400MPa未満,均一伸びが30%超であることを特徴とする(1)から(3)のいずれかに記載の耐応力腐食割れ性と加工性に優れた微細粒オーステナイト系ステンレス鋼板。
(2) The steel component is further in mass%, Mo: 1% or less, V: 1% or less, B: 0.010% or less, Nb: 0.5% or less, Ti: 0.5% or less, One or more rare earth elements: 0.5% or less, Al: 0.5% or less, Mg: 0.005% or less, Ca: 0.005% or less (1) The fine-grained austenitic stainless steel sheet having excellent stress corrosion cracking resistance and workability.
(3) It is characterized in that cracking does not occur even when a molded product obtained by cylindrical deep drawing in a drawing ratio of 1.5 to 2.0 is immersed in a boiling 42% magnesium chloride aqueous solution for 4 hours. A fine-grained austenitic stainless steel sheet excellent in stress corrosion cracking resistance and workability as described in (1) or (2). The aperture ratio is a value obtained by dividing the blank diameter by the punch diameter.
(4) The stress corrosion cracking resistance and processing according to any one of (1) to (3), wherein the 0.2% proof stress obtained by a tensile test is less than 400 MPa and the uniform elongation is more than 30%. Fine-grained austenitic stainless steel sheet with excellent properties.
以下、上記(1)〜(4)の鋼板に係わる発明をそれぞれ本発明という。また、(1)〜(4)の発明を合わせて、本発明ということがある。 Hereinafter, the inventions related to the steel sheets (1) to (4) are referred to as the present invention. The inventions (1) to (4) may be collectively referred to as the present invention.
以上説明したように、本発明の微細粒組織を有するオーステナイト系ステンレス鋼板によれば、8%以下のNi量でかつ高価なMoの添加によらず、オーステナイト系ステンレス鋼の欠点である応力腐食割れを克服し、加工性との両立を図ることができる。 As described above, according to the austenitic stainless steel sheet having a fine grain structure of the present invention, stress corrosion cracking, which is a defect of austenitic stainless steel, regardless of the amount of Ni of 8% or less and expensive addition of Mo. It is possible to overcome the problem and achieve compatibility with workability.
本発明者らは、前記した課題を解決するために、Ni量8%以下のオーステナイト系ステンレス鋼を対象とし,微細粒組織の形成に最適な成分バランスと微細化効果による応力腐食割れの改善作用と加工性との両立について鋭意研究を行い,本発明を完成させた。以下にその代表的な実験結果について説明する。
尚、本発明において、微細粒組織とは、平均結晶粒径が10μm以下であることを意味する。
In order to solve the above-mentioned problems, the present inventors have aimed at an austenitic stainless steel having an Ni content of 8% or less, and have an optimum component balance for the formation of a fine grain structure and an action of improving stress corrosion cracking by a refinement effect. The present invention was completed by earnestly studying the compatibility between the process and workability. The typical experimental results will be described below.
In the present invention, the fine grain structure means that the average crystal grain size is 10 μm or less.
表1に鋼成分を示すオーステナイト系ステンレス鋼を溶製し、3.0mm厚の熱延板を製造した。熱延板焼鈍は1150℃で行い、酸洗して0.5mm厚の冷延板を作製した。冷間圧延は、水冷しながら板温を10℃に保ち,加工発熱を抑制して加工誘起マルテンサイトの生成を促進した。冷延板焼鈍は、加工誘起マルテンサイトからオーステナイトへの相変態を活用して微細粒組織を形成させるために、600〜1050℃,保持時間を1分〜24時間の範囲で変化させた。冷間圧延後、最終焼鈍した鋼板は、酸洗した後、平均結晶粒径の測定,大傾角粒界の占める比率の測定,割れ発生時間の測定に供した。 The austenitic stainless steel which shows a steel component in Table 1 was melted, and a 3.0 mm-thick hot rolled sheet was manufactured. Hot-rolled sheet annealing was performed at 1150 ° C. and pickled to produce a cold-rolled sheet having a thickness of 0.5 mm. In cold rolling, the plate temperature was kept at 10 ° C. while cooling with water, and the generation of processing-induced martensite was promoted by suppressing processing heat generation. In cold-rolled sheet annealing, in order to form a fine grain structure by utilizing the phase transformation from work-induced martensite to austenite, the holding time was changed in the range of 600 to 1050 ° C. and 1 minute to 24 hours. After cold rolling, the final annealed steel sheet was pickled, and then subjected to measurement of the average crystal grain size, measurement of the ratio of the large-angle grain boundary, and measurement of crack generation time.
平均結晶粒径は、板断面を樹脂に埋め込み研磨して硝酸電解エッチングした後,JISG 0551に規定する鋼−結晶粒度の顕微鏡試験方法により求めた。
大傾角粒界の占める比率はEBSP法の粒界マップ表示により測定した。EBSP法では、粒界マップ表示によって15°未満の小傾角粒界と15°以上の大傾角粒界を識別して,全結晶粒界に占める大傾角粒界の比率を算出することができる。ここで,測定倍率は、非特許文献6において,統計的にバルクの性質を反映すると報告されている結晶粒数3000個以上含むように調整した。
The average crystal grain size was determined by a steel-crystal grain size microscopic test method specified in JIS G 0551 after embedding and polishing a plate cross-section in a resin and electrolytic etching with nitric acid.
The ratio of the large tilt grain boundaries was measured by the grain boundary map display of the EBSP method. In the EBSP method, a low-angle grain boundary of less than 15 ° and a large-angle grain boundary of 15 ° or more can be identified by the grain boundary map display, and the ratio of the large-angle grain boundary in all the crystal grain boundaries can be calculated. Here, the measurement magnification was adjusted to include 3000 or more crystal grains, which are reported in Non-Patent Document 6 to statistically reflect bulk properties.
割れ発生時間は、ブランク径67.5mmφ,ポンチ径35mmφ,ダイス径37mmφ,しわ押さえ圧1トンの条件で絞り比(ブランク径をポンチ径で割った値)1.9の円筒深絞り加工を行い、得られた成形品を48hr放置して時効割れの発生しないことを確認したうえで,JIS G 0576に規定する沸騰42%塩化マグネシウム水溶液中に浸漬して割れ発生時間を測定した。 Crack generation time is 1.9 cylinder deep drawing with a drawing ratio (blank diameter divided by punch diameter) of 1.9 under the conditions of blank diameter 67.5 mmφ, punch diameter 35 mmφ, die diameter 37 mmφ, and wrinkle holding pressure 1 ton. The obtained molded product was allowed to stand for 48 hours to confirm that no aging cracks occurred, and then immersed in a boiling 42% magnesium chloride aqueous solution specified in JIS G 0576, and the crack generation time was measured.
(a)図1には、冷延板焼鈍を800℃,4hr保持とした場合の平均結晶粒径と成分バランス(Md)の関係を示している。Mdは下記(1)式のように定義する。図1から、平均結晶粒径は、Mdの上昇とともに小さくなる。Mdの上昇により、冷間圧延で生成する加工誘起マルテンサイトの量は増加する。そのため、Mdの上昇は、前記した非特許文献1および2で述べたように冷間圧延後の焼鈍において、加工誘起マルテンサイトからオーステナイトへの相変態を活用した微細化が促進したものと考えられる。本検討から、目標とする平均結晶粒径10μm以下への微細化には、Mdを−20以上にすることが効果的である。また、MdがSUS304とほぼ同等であっても,Cr,Niを低減してCuを添加した鋼成分(鋼D)の方が、微細化に対して有効であることを確認した。 (A) FIG. 1 shows the relationship between the average crystal grain size and the component balance (Md) when the cold-rolled sheet annealing is held at 800 ° C. for 4 hours. Md is defined as in the following formula (1). From FIG. 1, the average crystal grain size decreases with increasing Md. As the Md increases, the amount of work-induced martensite generated by cold rolling increases. Therefore, it is considered that the increase in Md is promoted by the refinement utilizing the phase transformation from work-induced martensite to austenite in the annealing after cold rolling as described in Non-Patent Documents 1 and 2 described above. . From this study, it is effective to set Md to -20 or more in order to refine the target to an average crystal grain size of 10 μm or less. Moreover, even if Md is substantially equivalent to SUS304, it was confirmed that the steel component (steel D) in which Cr and Ni are reduced and Cu is added is more effective for miniaturization.
Md=551−462(C+N)−9.2Si−8.1Mn−13.7Cr
−29(Ni+Cu)−18.2Mo ・・・(1)
Md = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr
-29 (Ni + Cu) -18.2Mo (1)
(b)図2には、平均結晶粒径(d)の異なる鋼B(i)〜(ii)とSUS316L(iii)を上記の割れ発生時間の測定と同様にして、円筒深絞り加工して得られた成形品(円筒深絞り材)を、沸騰42%塩化マグネシウム水溶液中に4hr浸漬後の外観を示している。さらに、図3には、図2の試験に供した鋼B(i)〜(ii)のミクロ組織の写真を示している。 (B) In FIG. 2, steel B (i) to (ii) and SUS316L (iii) having different average crystal grain diameters (d) are subjected to cylindrical deep drawing in the same manner as the measurement of the crack occurrence time. The appearance of the obtained molded product (cylindrical deep-drawing material) after immersion for 4 hours in a boiling 42% magnesium chloride aqueous solution is shown. Furthermore, in FIG. 3, the photograph of the microstructure of steel B (i)-(ii) used for the test of FIG. 2 is shown.
図2に示すように、平均結晶粒径を3μm(図2(i))まで微細化すると、通常の焼鈍(1050℃,1分保持)で製造した平均結晶粒径28μm(図2(ii))と比較して,円筒深絞り材の沸騰42%塩化マグネシウム水溶液浸漬において割れを発生しない。同試験では、高NiかつMoを含有し,汎用のSUS304(18Cr−8Ni)と比較して応力腐食割れにも抵抗力を示す高価なオーステナイト系ステンレス鋼SUS316L(17Cr−12Ni−2Mo)(図2(iii))と比較した。本結果から、耐応力腐食割れ性(割れ発生時間)は、結晶粒の微細化効果により飛躍的に向上する新規な知見を見出した。 As shown in FIG. 2, when the average crystal grain size is refined to 3 μm (FIG. 2 (i)), the average crystal grain size produced by normal annealing (1050 ° C., 1 minute hold) is 28 μm (FIG. 2 (ii) Compared with), no cracking occurs when the cylindrical deep-drawn material is immersed in a boiling 42% magnesium chloride aqueous solution. In this test, expensive austenitic stainless steel SUS316L (17Cr-12Ni-2Mo) which contains high Ni and Mo and exhibits resistance to stress corrosion cracking compared to general-purpose SUS304 (18Cr-8Ni) (FIG. 2). (Iii)). From these results, the inventors have found a novel finding that the stress corrosion cracking resistance (crack generation time) is remarkably improved by the effect of crystal grain refinement.
(c)図4には、前記した沸騰42%塩化マグネシウム水溶液中での割れ発生時間と平均結晶粒径ならびにMdの関係を示している。なお、図4中の上矢印(↑)は割れ発生時間がプロットされた点より長いことを示す。
Md=29.5(鋼B)の場合、割れ発生時間は、結晶粒の微細化(平均結晶粒径10μm以下)効果により飛躍的に上昇していることが分かる。この理由は、必ずしも明らかでないが、以下のように推定する。応力腐食割れは基本的に粒内割れであり,結晶粒の微細化により割れの起点となる粒内面積率が大幅に減少する。加えて,鉄鋼材料における破壊靭性は、結晶粒微細化により格段に向上することが知られている。これら要因が耐応力腐食割れ性に対しても少なからず効果を発揮したものと思われる。比較としたSUS316Lでは同試験条件において2〜3hr浸漬で割れが発生した。本発明の目標は、同試験条件において割れ発生時間がSUS316Lを明らかに凌駕する,4時間(hr)浸漬することにより割れが発生しないものとした。
(C) FIG. 4 shows the relationship between crack generation time, average crystal grain size and Md in the boiling 42% magnesium chloride aqueous solution. 4 indicates that the crack occurrence time is longer than the plotted point.
In the case of Md = 29.5 (steel B), it can be seen that the crack generation time has increased dramatically due to the effect of refining crystal grains (average crystal grain size of 10 μm or less). The reason is not necessarily clear, but is estimated as follows. Stress corrosion cracking is basically intragranular cracking, and the grain area ratio, which is the starting point of cracking, is greatly reduced by the refinement of crystal grains. In addition, it is known that fracture toughness in steel materials is remarkably improved by crystal grain refinement. These factors seem to have exerted a considerable effect on the stress corrosion cracking resistance. In SUS316L as a comparison, cracks occurred when immersed for 2 to 3 hours under the same test conditions. The target of the present invention was that crack generation time clearly exceeded SUS316L under the same test conditions, and cracking did not occur when immersed for 4 hours (hr).
尚、図4に示す結晶粒微細化により耐応力腐食割れ性が向上した鋼板(鋼B)は、冷間圧延後の冷延板の最終焼鈍を800℃で4時間実施したものと24時間実施したものである。また、図4に示す割れ発生時間が4時間未満で平均結晶粒径10μ超の鋼板は、冷間圧延後の冷延板の最終焼鈍を900℃〜1050℃で1分〜4時間実施したものであり、割れ発生時間が4時間未満で平均結晶粒径10μm以下の鋼板は、冷間圧延後の冷延板の最終焼鈍を800℃で4時間行ったものである。 In addition, the steel plate (steel B) improved in stress corrosion cracking resistance by grain refinement shown in FIG. 4 was subjected to final annealing of the cold-rolled sheet after cold rolling at 800 ° C. for 4 hours and 24 hours. It is a thing. In addition, the steel sheet having a crack generation time of less than 4 hours and an average crystal grain size of more than 10 μm shown in FIG. 4 was obtained by performing final annealing of the cold-rolled sheet after cold rolling at 900 ° C. to 1050 ° C. for 1 minute to 4 hours. The steel sheet having a crack generation time of less than 4 hours and an average crystal grain size of 10 μm or less is obtained by subjecting the cold-rolled sheet after cold rolling to final annealing at 800 ° C. for 4 hours.
(d)耐応力腐食割れ性に対する微細化効果の発現は、成分バランス(Md)の影響を受ける。応力腐食割れを抑制する微細化効果の発現には、Mdを−20〜40の範囲とする必要がある。
図4において、Md=43(鋼A)の場合、割れ発生時間は、微細化しても大きく上昇していない。この理由は、微細化による材料そのものの硬質化,円筒深絞りにおいて多量の加工誘起マルテンサイトを生成し,カップ側壁での残留応力の上昇によって応力腐食割れの抑止効果が発現しなかったものと推定する。本検討から、応力腐食割れを抑制する微細化効果の発現には、Md:40以下が有効である。
(D) The expression of the refinement effect on the stress corrosion cracking resistance is affected by the component balance (Md). In order to develop a refinement effect that suppresses stress corrosion cracking, Md needs to be in the range of -20 to 40.
In FIG. 4, in the case of Md = 43 (steel A), the crack generation time does not increase greatly even if it is miniaturized. The reason for this is that the material itself has been hardened by miniaturization, a large amount of work-induced martensite has been generated in the deep drawing of the cylinder, and the effect of inhibiting stress corrosion cracking has not been manifested due to an increase in residual stress on the cup side wall. To do. From this examination, Md: 40 or less is effective for the expression of the refinement effect which suppresses stress corrosion cracking.
(e)Md値の低いMd=−25(鋼G)の場合、(a)で述べたように微細粒組織の形成が困難になる。そのため,図4において、平均結晶粒径を10μm以下として応力腐食割れを抑制する微細化効果を得ることは困難である。本結果から,応力腐食割れを抑制する微細化効果の発現には、Md:−20以上が効果的である。 (E) In the case of Md = −25 (steel G) having a low Md value, it becomes difficult to form a fine grain structure as described in (a). Therefore, in FIG. 4, it is difficult to obtain a refinement effect that suppresses stress corrosion cracking by setting the average grain size to 10 μm or less. From this result, Md: −20 or more is effective for the expression of the refinement effect for suppressing stress corrosion cracking.
(f)微細粒材の耐応力腐食割れ性には、Mdに加えて,結晶粒界において大傾角粒界が占める比率も影響する。図5は、鋼Bにおける割れ発生時間と15°以上の大傾角粒界の比率との関係を示したグラフである。なお、図5中の上矢印(↑)は割れ発生時間がプロットされた点より長いことを示す。図5に示すように、鋼Bの微細粒材は、15°以上の大傾角粒界の比率が80%超となることで前記(b)および(c)に記載した耐応力腐食割れ性の向上効果が得られる。この理由は、以下のように考えられる。微細粒材は、冷間圧延で加工誘起マルテンサイトを極力多く生成させて,通常より低温の焼鈍で加工誘起マルテンサイトからオーステナイトへの逆変態を活用して製造する。冷間圧延での歪の蓄積が大きいこと,低温焼鈍であることから,焼鈍後の残留歪も大きくなりやすい。このような場合,オーステナイト粒の再結晶が進行途上であり,大傾角粒界と認識されない15°未満の小傾角粒界が多数存在することになる。従って、大傾角粒界の比率が低下することは鋼の残留歪が大きいことを意味し,鋼の残留歪が耐応力腐食割れ性を阻害したものと推定する。 (F) In addition to Md, the ratio of the large-angle grain boundary in the crystal grain boundary affects the stress corrosion cracking resistance of the fine grain material. FIG. 5 is a graph showing the relationship between the crack occurrence time in steel B and the ratio of large-angle boundaries of 15 ° or more. Note that the up arrow (↑) in FIG. 5 indicates that the crack occurrence time is longer than the plotted point. As shown in FIG. 5, the fine grain material of Steel B has the stress corrosion cracking resistance described in (b) and (c) above when the ratio of the large-angle grain boundaries of 15 ° or more exceeds 80%. Improvement effect is obtained. The reason is considered as follows. The fine-grained material is produced by generating as much work-induced martensite as possible by cold rolling and utilizing reverse transformation from work-induced martensite to austenite by annealing at a lower temperature than usual. Due to large strain accumulation during cold rolling and low temperature annealing, residual strain after annealing tends to increase. In such a case, recrystallization of austenite grains is in progress, and there are many small-angle grain boundaries of less than 15 ° that are not recognized as large-angle grain boundaries. Therefore, a decrease in the ratio of the large-angle grain boundaries means that the residual strain of the steel is large, and it is assumed that the residual strain of the steel hinders the stress corrosion cracking resistance.
尚、図5に示す鋼Bは、冷間圧延後の冷延板の最終焼鈍を800℃で10分〜24時間の範囲で変化させて行ったものである。図5に示す大傾角粒界の比率が80%超であるものは、冷間圧延後の冷延板の最終焼鈍を800℃で1時間超で行ったものである。 Steel B shown in FIG. 5 is obtained by changing the final annealing of the cold-rolled sheet after cold rolling at 800 ° C. in the range of 10 minutes to 24 hours. In the case where the ratio of the large-angle grain boundaries shown in FIG. 5 is more than 80%, the final annealing of the cold-rolled sheet after cold rolling is performed at 800 ° C. for more than 1 hour.
(g)結晶粒の微細化は、鋼成分に加えて,製造条件の影響を受ける。加工誘起マルテンサイトからオーステナイトへの相変態を活用するために、冷間圧延において加工誘起マルテンサイト変態を促進させることが効果的である。そのために、冷間圧延で圧下率を大きくしてかつ加工発熱を抑制することが好ましい。さらに、微細粒材で大傾角粒界の比率を上昇させて耐応力腐食割れ性を発現させるために、冷間圧延後に実施する最終焼鈍は、なるべく低温で長時間保持とすることが好ましい。具体的には、最終焼鈍条件を700〜900℃で1時間超とすることが効果的である。また,15°以上の大傾角粒界の比率を上昇させることは0.2%耐力の低下と伸びの上昇にも有効であり,加工性の向上にも寄与する。 (G) Refinement of crystal grains is affected by manufacturing conditions in addition to steel components. In order to utilize the phase transformation from work-induced martensite to austenite, it is effective to promote the work-induced martensite transformation in cold rolling. Therefore, it is preferable that the rolling reduction is increased by cold rolling and the processing heat generation is suppressed. Furthermore, in order to increase the ratio of the large-angle grain boundary with a fine-grained material and to exhibit stress corrosion cracking resistance, it is preferable that the final annealing performed after cold rolling is kept at a low temperature for as long as possible. Specifically, it is effective to set the final annealing condition at 700 to 900 ° C. for more than 1 hour. Further, increasing the ratio of the large tilt grain boundaries of 15 ° or more is effective in reducing the 0.2% proof stress and increasing the elongation, and contributes to the improvement of workability.
本発明者らは、既に、特許文献8において、平均結晶粒径10μm以下の微細粒組織を有するプレス成形用オーステナイト系ステンレス鋼板およびその製造方法を提案している。特許文献8は、深絞り加工後の「時効割れ」=材料の遅れ破壊の改善と目的とし、本発明で改善する「応力腐食割れ」=材料の腐食と溶解が関与する現象とは異なるものである。特許文献8では、前述した応力腐食割れに影響ある15°以上の大傾角粒界の比率については全く検討していない。また、最終の焼鈍時間は実質的に1時間以下である。
本発明は、特許文献8で提案した微細粒鋼の耐応力腐食割れ性を向上させるために,その影響因子である15°以上の大傾角粒界の比率を見出し、最終の焼鈍時間を1時間超にコントロールすることが極めて有効であること知見した。
In the patent document 8, the present inventors have already proposed an austenitic stainless steel sheet for press forming having a fine grain structure with an average crystal grain size of 10 μm or less and a method for producing the same. Patent Document 8 aims to improve “aging cracking” after deep-drawing processing = delayed fracture of material, and is different from the phenomenon involving “stress corrosion cracking” = material corrosion and dissolution improved in the present invention. is there. In Patent Document 8, the ratio of the large tilt grain boundary of 15 ° or more that affects the stress corrosion cracking described above is not studied at all. The final annealing time is substantially 1 hour or less.
In order to improve the stress corrosion cracking resistance of the fine-grained steel proposed in Patent Document 8, the present invention finds a ratio of a large-angle grain boundary of 15 ° or more, which is an influential factor, and sets the final annealing time to 1 hour. It was found that super-control is extremely effective.
前記(1)〜(7)の本発明は、上記(a)〜(g)の知見に基づいて完成されたものである。
以下、本発明の各要件について詳しく説明する。なお、各元素の含有量の「%」表示は「質量%」を意味する。
The present inventions (1) to (7) have been completed based on the findings (a) to (g).
Hereinafter, each requirement of the present invention will be described in detail. In addition, "%" display of the content of each element means "mass%".
(A)鋼成分に関する限定理由を以下に説明する。
本発明のオーステナイト系ステンレス鋼板は、平均結晶粒径10μm以下の微細粒組織を形成して、微細化効果により耐応力腐食割れ性を向上させるために、成分および成分バランス(Md)を規定したものである。
(A) The reason for limitation regarding the steel component will be described below.
The austenitic stainless steel sheet according to the present invention has a component and a component balance (Md) in order to form a fine grain structure with an average crystal grain size of 10 μm or less and improve stress corrosion cracking resistance by a refinement effect. It is.
Cは、オーステナイト生成元素であり、オーステナイト安定度を確保する目的で添加される。多量に添加すると、硬質になり加工性が低下するとともに、炭化物析出を促進して本発明の目的とする耐応力腐食割れ性を阻害する。そのため、上限は0.05%とする。好ましくは0.03%である。下限は、製造性との関係から,0.005%とすることが好ましい。 C is an austenite-forming element and is added for the purpose of ensuring austenite stability. When added in a large amount, it becomes hard and the workability is lowered, and the precipitation of carbide is promoted to inhibit the stress corrosion cracking resistance aimed at by the present invention. Therefore, the upper limit is made 0.05%. Preferably it is 0.03%. The lower limit is preferably 0.005% from the viewpoint of manufacturability.
Crは、十分な耐食性を得るためには14%以上必要であるため、下限は14%とする。好ましくは15%,より好ましくは16%とする。一方、多量に添加すると、硬質化やδフェライトの形成により加工性を低下させる。さらに、本発明の目的とする結晶粒の微細化を阻害する。そのため、上限は19%とする。好ましくは18%である。 Since Cr needs to be 14% or more in order to obtain sufficient corrosion resistance, the lower limit is made 14%. Preferably it is 15%, more preferably 16%. On the other hand, if added in a large amount, the workability is lowered due to hardening or formation of δ ferrite. Furthermore, the refinement | miniaturization of the crystal grain made into the objective of this invention is inhibited. Therefore, the upper limit is 19%. Preferably it is 18%.
Siは、強力な脱酸剤として有効であるが多量に添加すると硬質化するとともに製造性を阻害するため、上限は2%とする。好ましくは1.5%である。一方,本発明の目的とする耐応力腐食割れ性を向上させる作用を持つ。これら作用を得るには、0.5%以上添加することが好ましい。下限は、製造性との関係から,0.1%とすることが好ましい。 Si is effective as a strong deoxidizing agent, but when added in a large amount, it hardens and inhibits manufacturability, so the upper limit is made 2%. Preferably it is 1.5%. On the other hand, it has the effect of improving the stress corrosion cracking resistance which is the object of the present invention. In order to obtain these effects, 0.5% or more is preferably added. The lower limit is preferably 0.1% in terms of manufacturability.
Mnは、オーステナイト生成元素であり、オーステナイト安定度の確保と加工性の向上を目的に添加する。多量に添加するとMnSを形成し、耐食性の低下により本発明の目的とする耐応力腐食割れ性を阻害する。そのため、上限は4%とする。好ましくは、3%とする。下限は、上記目的のために0.5%とすることが好ましい。 Mn is an austenite-forming element and is added for the purpose of ensuring austenite stability and improving workability. When added in a large amount, MnS is formed, and the stress corrosion cracking resistance aimed at by the present invention is hindered due to a decrease in corrosion resistance. Therefore, the upper limit is 4%. Preferably, it is 3%. The lower limit is preferably 0.5% for the above purpose.
Niは、オーステナイト系ステンレス鋼には不可欠な元素であり、オーステナイト安定度および加工性の確保の点から、下限は5%とする。好ましくは6%である。一方、Niは高価で希少な元素であること,本発明の目的とする結晶粒の微細化を阻害する要素も持つことから、上限は8%とする。好ましくは7.5%以下である。 Ni is an indispensable element for austenitic stainless steel, and the lower limit is made 5% from the viewpoint of ensuring austenite stability and workability. Preferably it is 6%. On the other hand, Ni is an expensive and rare element, and also has an element that hinders the refinement of crystal grains targeted by the present invention, so the upper limit is made 8%. Preferably it is 7.5% or less.
Cuは、前記Niと同様に、オーステナイト安定度および軟質化を目的に添加するが、Niを節減して耐応力腐食割れ性の向上と結晶粒の微細化を促進する上でも好ましい元素である。しかし、多量の添加は、熱間加工性を低下させ、Cu金属成分を全く不要とする鋼種の溶鋼の品質、排出されるスラグ品質及びその有効利用に悪影響を及ぼし支障を来すことになる。そのため、上限は4%とする。好ましくは3%である。下限は、上記効果を得るために1%とすることが好ましい。より好ましくは1.5%である。 Like Ni, Cu is added for the purpose of austenite stability and softening. However, Cu is a preferable element for saving Ni and improving stress corrosion cracking resistance and promoting the refinement of crystal grains. However, the addition of a large amount adversely affects the quality of molten steel, the quality of discharged slag and its effective use, which deteriorates hot workability and eliminates the need for Cu metal components. Therefore, the upper limit is 4%. Preferably it is 3%. The lower limit is preferably 1% in order to obtain the above effect. More preferably, it is 1.5%.
Nは、Cと同様にオーステナイト生成元素であり、オーステナイト安定度を確保する目的で添加されるが、多量に添加すると硬質になり加工性が低下する。そのため、上限は0.1%とする。好ましくは0.06%以下である。下限は、製造性との関係から,0.005%とすることが好ましい。より好ましくは、0.01%とする。 N is an austenite-forming element like C, and is added for the purpose of securing austenite stability. However, if added in a large amount, it becomes hard and the workability is lowered. Therefore, the upper limit is made 0.1%. Preferably it is 0.06% or less. The lower limit is preferably 0.005% from the viewpoint of manufacturability. More preferably, the content is 0.01%.
Moは、本発明において必須元素ではないが,耐食性および本発明の目的とする耐応力腐食割れ性を向上させるために適時添加しても良い。しかし、Moは大変高価で希少な元素であるため、添加する場合でも上限は1%とする。好ましくは0.5%である。上記効果を得るため下限は0.1%とすることが好ましい。 Mo is not an essential element in the present invention, but may be added in a timely manner in order to improve the corrosion resistance and the stress corrosion cracking resistance targeted by the present invention. However, since Mo is a very expensive and rare element, even when it is added, the upper limit is made 1%. Preferably it is 0.5%. In order to obtain the above effect, the lower limit is preferably 0.1%.
Vは、本発明において必須元素ではないが,Moに及ばないまでも耐食性および本発明の目的とする耐応力腐食割れ性を向上させるために適時添加しても良い。しかし、Vは高価な元素であるとともに,固溶強化元素であるため加工性を阻害する。そのため、添加する場合でも上限は1%とする。好ましくは0.5%である。上記効果を得るための下限は0.1%とすることが好ましい。 V is not an essential element in the present invention, but may be added as appropriate in order to improve the corrosion resistance and the stress corrosion cracking resistance aimed at by the present invention even if it does not reach Mo. However, V is an expensive element and is a solid solution strengthening element, which impairs workability. Therefore, even when adding, the upper limit is made 1%. Preferably it is 0.5%. The lower limit for obtaining the above effect is preferably 0.1%.
B、希土類元素(REM)は、熱間加工性を向上させるために適時添加しても良い。しかし、Bは0.010%を超えると、製造性や耐食性を著しく損なう場合がある。そのため、添加する場合の上限は0.010%とする。好ましくは0.005%である。添加する場合、Bの下限は0.0005%が好ましい。
一方,希土類元素は、0.5%を超えると、製造性および経済性を損なう場合がある。そのため、希土類元素の上限は0.5%とすることが好ましい。より好ましくは、0.2%である。添加する場合、希土類元素の下限は0.005%が好ましい。
B and rare earth elements (REM) may be added in a timely manner in order to improve hot workability. However, if B exceeds 0.010%, the productivity and corrosion resistance may be significantly impaired. Therefore, the upper limit when adding is 0.010%. Preferably it is 0.005%. When added, the lower limit of B is preferably 0.0005%.
On the other hand, if the rare earth element exceeds 0.5%, the manufacturability and economy may be impaired. Therefore, the upper limit of the rare earth element is preferably 0.5%. More preferably, it is 0.2%. When added, the lower limit of the rare earth element is preferably 0.005%.
Nb、Tiは、炭窒化物を形成してCr炭化物の生成を抑制するため,耐応力腐食割れ性の向上に寄与するため、適時添加しても良い。しかし、多量に添加すると加工性や製造性が低下するため、上限は0.5%とする。好ましくは0.3%である。添加する場合、下限は0.005%が好ましい。より好ましくは0.01%である。 Nb and Ti form carbonitrides and suppress the formation of Cr carbides, and thus contribute to the improvement of stress corrosion cracking resistance. However, if added in a large amount, the workability and manufacturability deteriorate, so the upper limit is made 0.5%. Preferably it is 0.3%. When added, the lower limit is preferably 0.005%. More preferably, it is 0.01%.
Alは、脱酸元素として有効な元素であるため,適時添加しても良い。しかし、過度な添加は加工性や溶接性の低下に繋がるため、上限は0.5%とする。好ましくは0.3%,より好ましくは0.1%である。添加する場合、下限は0.01%が好ましい。 Since Al is an effective element as a deoxidizing element, it may be added as appropriate. However, excessive addition leads to deterioration of workability and weldability, so the upper limit is made 0.5%. Preferably it is 0.3%, more preferably 0.1%. When added, the lower limit is preferably 0.01%.
Mg、Caは、溶鋼中でAlとともに酸化物を形成して脱酸剤として作用するため,適時添加しても良い。CaはSを固定して熱間加工性の改善作用を持つ。しかし、Mg、Caの過度な添加は耐食性や溶接性の低下に繋がるため、上限は0.005%とする。好ましくは、0.002%とする。添加する場合、下限は0.0001%とする。より好ましくは0.0003%とする。 Mg and Ca form an oxide together with Al in the molten steel and act as a deoxidizer, so may be added as appropriate. Ca fixes S and has an effect of improving hot workability. However, excessive addition of Mg and Ca leads to deterioration of corrosion resistance and weldability, so the upper limit is made 0.005%. Preferably, the content is 0.002%. When added, the lower limit is made 0.0001%. More preferably, the content is 0.0003%.
さらに、本発明のオーステナイト系ステンレス鋼は、上記の成分以外に、不可避的不純物の一部としてP,Sを下記の範囲で含有してもよい。P、Sは、熱間加工性や耐食性に有害な元素である。Pは、0.1%以下とするのが好ましい。より好ましくは0.05%以下である。Sは、0.01%以下とするのが好ましい。より好ましくは0.005%以下である。 Furthermore, the austenitic stainless steel of the present invention may contain P and S in the following ranges as a part of inevitable impurities in addition to the above components. P and S are elements harmful to hot workability and corrosion resistance. P is preferably 0.1% or less. More preferably, it is 0.05% or less. S is preferably 0.01% or less. More preferably, it is 0.005% or less.
本発明では、前記した成分範囲に加え,微細粒組織の形成に最適な成分バランスを(1)式に示すMdにより規定した。
Md=551−462(C+N)−9.2Si−8.1Mn−13.7Cr
−29(Ni+Cu)−18.2Mo ・・・(1)
In the present invention, in addition to the component ranges described above, the optimum component balance for the formation of a fine grain structure is defined by Md shown in equation (1).
Md = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr
-29 (Ni + Cu) -18.2Mo (1)
準安定オ−ステナイト系ステンレス鋼はMs点以上の温度でも塑性加工によってマルテンサイト変態を起こす。加工によって変態を生じる上限温度はMd点と呼ばれる。すなわち、Md点はオーステナイトの安定度を示す指標である。
(1)式に示すMdを−20〜40の範囲に設計することにより、本発明の目的とする微細粒組織の形成と微細化効果による耐応力腐食割れ性の向上作用が得られる。Mdが−20未満の場合、上記の(d)(e)で述べたように微細粒組織の形成ならびに耐応力腐食割れ性の発現が困難である。一方,Mdが40を越える場合、上記の(d)(e)で述べたように微細粒組織の形成には有効であるものの,耐応力腐食割れ性の発現を阻害する。好ましいMdの範囲は−5〜35である。
Metastable austenitic stainless steel undergoes martensitic transformation by plastic working even at temperatures above the Ms point. The upper limit temperature that causes transformation by processing is called the Md point. That is, the Md point is an index indicating the stability of austenite.
By designing the Md shown in the formula (1) in the range of -20 to 40, it is possible to obtain the effect of improving the stress corrosion cracking resistance due to the formation of the fine grain structure and the refinement effect as the object of the present invention. When Md is less than −20, it is difficult to form a fine grain structure and develop stress corrosion cracking resistance as described in the above (d) and (e). On the other hand, when Md exceeds 40, as described in the above (d) and (e), it is effective in forming a fine grain structure, but it inhibits the development of stress corrosion cracking resistance. A preferred Md range is -5 to 35.
(B)製造方法を以下に説明する。
本発明の微細粒オーステナイト系ステンレス鋼板を製造する際には、(A)項に述べた鋼成分を有し,平均結晶粒径10μm以下とし、かつ15°以上の大傾角粒界の占める比率を80%超とし,耐応力腐食割れ性を効果的に発現させるために、以下の製造条件とすることが好ましい。
(B) A manufacturing method is demonstrated below.
When producing the fine-grained austenitic stainless steel sheet of the present invention, it has the steel components described in the section (A), the average crystal grain size is 10 μm or less, and the ratio of the large-angle grain boundaries of 15 ° or more is In order to make it more than 80% and to express stress corrosion cracking resistance effectively, it is preferable to set it as the following manufacturing conditions.
熱間圧延までの製造方法は、特に限定するものでなく、公知で良い。
冷間圧延後の最終焼鈍で微細粒組織を形成するには、上記の(g)に記載した通り、冷間圧延で加工誘起マルテンサイト変態を促進させることが有効である。本発明の目的とする平均結晶粒径10μm以下とするには、冷間圧延後に加工誘起マルテンサイト体積率50%以上とすることが効果的である。好ましくは、加工誘起マルテンサイト体積率を60%超とする。冷間圧延後の最終焼鈍条件は、結晶粒の微細化かつ15°以上の大傾角粒界の比率を上昇させるために規定したものである。好ましくは冷間圧延条件も規定する,より好ましくは熱延板焼鈍も考慮するのが良い。
The production method up to hot rolling is not particularly limited and may be known.
In order to form a fine grain structure by final annealing after cold rolling, it is effective to promote work-induced martensitic transformation by cold rolling as described in (g) above. In order to obtain an average crystal grain size of 10 μm or less, which is the object of the present invention, it is effective to set the work-induced martensite volume ratio to 50% or more after cold rolling. Preferably, the processing-induced martensite volume fraction is more than 60%. The final annealing conditions after cold rolling are specified in order to refine crystal grains and increase the ratio of large-angle grain boundaries of 15 ° or more. Preferably, cold rolling conditions are also defined, more preferably hot-rolled sheet annealing should be considered.
熱延板焼鈍は、冷間圧延に供するオーステナイト粒を20μm以上に粗粒化して冷間圧延で加工誘起マルテンサイト変態を促進するために、1050〜1200℃の範囲とすることが好ましい。1050℃未満は、オーステナイト粒径が20μm未満となる場合がある。1200℃超は、焼鈍後の酸洗性など表面品質を阻害する場合がある。また、1200℃超の焼鈍は設備への負荷も大きい。より好ましくは、1080〜1180℃の範囲とする。 In the hot-rolled sheet annealing, in order to coarsen austenite grains used for cold rolling to 20 μm or more and promote work-induced martensitic transformation by cold rolling, it is preferable to set the temperature within a range from 1050 to 1200 ° C. Below 1050 ° C., the austenite grain size may be less than 20 μm. If it exceeds 1200 ° C., surface quality such as pickling after annealing may be impaired. Moreover, annealing over 1200 ° C. has a heavy load on the equipment. More preferably, it is set as the range of 1080-1180 degreeC.
冷間圧延後の最終焼鈍は、平均結晶粒径を10μm以下かつ大傾角粒界の比率を80%超とするために、700〜1050℃の範囲とする。700℃未満は、冷間圧延での歪が蓄積された状態であり,オーステナイト粒の再結晶が不十分となり加工性が著しく低下するとともに,15°以上の大傾角粒界の比率も小さく本発明の目的とする耐応力腐食割れ性を阻害する。好ましくは下限温度を750℃以上とする。1050℃超は、オーステナイトの結晶粒成長が進行し,平均結晶粒径は10μm超となる。好ましくは900℃以下とする。本発明の目標とする大傾角粒界の比率を80%超の微細粒組織を実現するために、より好ましい最終焼鈍温度は、750〜850℃の範囲とする。 The final annealing after the cold rolling is in the range of 700 to 1050 ° C. in order to make the average crystal grain size 10 μm or less and the ratio of the large-angle grain boundary more than 80%. When the temperature is lower than 700 ° C., the strain in cold rolling is accumulated, the austenite grains are insufficiently recrystallized, the workability is remarkably lowered, and the ratio of the large-angle grain boundaries of 15 ° or more is small. Inhibits the intended stress corrosion cracking resistance. Preferably, the lower limit temperature is 750 ° C. or higher. Above 1050 ° C., austenite crystal grain growth proceeds and the average crystal grain size exceeds 10 μm. Preferably it is 900 degrees C or less. In order to realize a fine grain structure having a large tilt grain boundary ratio of 80% or more as a target of the present invention, a more preferable final annealing temperature is in a range of 750 to 850 ° C.
焼鈍時間は、最終焼鈍温度が700〜900℃の場合,オーステナイトの再結晶を促進して15°以上の大傾角粒界の比率を上昇させるために,1時間超とすることが好ましい。より好ましくは2時間以上とする。保持時間の上限は、限定するものではないが、クロム系ステンレスで工業的に公知な箱焼鈍を想定して24時間以下とすることが好ましい。本発明の目標とする大傾角粒界の比率を80%超の微細粒組織を実現するために、より好ましい最終焼鈍時間は、4〜24時間の範囲とする。小規模の焼鈍設備で製造する場合はその限りではなく24時間を超過しても構わない。
最終焼鈍温度が900〜1050℃の場合、焼鈍時間は、結晶粒成長を考慮して,10分以下の短時間保持とすることが好ましい。より好ましくは保持時間を1分以下としても構わない。
When the final annealing temperature is 700 to 900 ° C., the annealing time is preferably more than 1 hour in order to promote the recrystallization of austenite and increase the ratio of the large tilt grain boundaries of 15 ° or more. More preferably, it is 2 hours or more. The upper limit of the holding time is not limited, but it is preferably 24 hours or shorter in consideration of box annealing that is industrially known for chromium-based stainless steel. In order to realize a fine grain structure in which the ratio of the large tilt grain boundary targeted by the present invention is more than 80%, a more preferable final annealing time is set in a range of 4 to 24 hours. When it manufactures with a small-scale annealing equipment, it may not exceed that and may exceed 24 hours.
When the final annealing temperature is 900 to 1050 ° C., the annealing time is preferably maintained for a short time of 10 minutes or less in consideration of crystal grain growth. More preferably, the holding time may be 1 minute or less.
冷間圧延は、加工誘起マルテンサイト変態を促進させるために、圧下率を70%以上,かつ圧延温度50℃以下とすることが好ましい。圧下率70%未満の場合、加工誘起マルテンサイト体積率は50%未満となり、上述したように微細粒組織を形成することが困難となる。より好ましくは圧下率を80%以上とする。上限は特に規定するものではないが、熱延板製造と冷延設備能力を考慮して90%以下が好ましい。圧延温度50℃超の場合、加工誘起マルテンサイト体積率は50%未満となり、前記した通り微細粒組織の形成が困難となる。圧延温度の下限は特に規定するのではないが、工業的には水冷で到達する温度10℃以上が好ましい。小規模の圧延設備で製造する場合はその限りではなく、液体窒素等の冷却で到達する低温(例えば、−200℃)でも構わない。 In cold rolling, in order to promote work-induced martensitic transformation, it is preferable that the rolling reduction is 70% or more and the rolling temperature is 50 ° C. or less. When the rolling reduction is less than 70%, the processing-induced martensite volume fraction is less than 50%, and it becomes difficult to form a fine grain structure as described above. More preferably, the rolling reduction is 80% or more. The upper limit is not particularly specified, but 90% or less is preferable in consideration of hot-rolled sheet production and cold-rolling equipment capacity. When the rolling temperature exceeds 50 ° C., the work-induced martensite volume ratio is less than 50%, and it becomes difficult to form a fine grain structure as described above. The lower limit of the rolling temperature is not particularly defined, but industrially, the temperature reached by water cooling is preferably 10 ° C. or higher. When manufacturing with a small-scale rolling facility, it is not limited thereto, and may be a low temperature (for example, −200 ° C.) reached by cooling liquid nitrogen or the like.
(C)金属組織の限定理由を以下に説明する。
本発明の微細粒オーステナイト系ステンレス鋼板においては、(A)項の鋼成分を有する鋳片を用い,(B)項の好ましい製造条件を実施して、平均結晶粒径を10μm以下かつ15°以上の大傾角粒界の比率を80%超とする。
(C) The reasons for limiting the metal structure will be described below.
In the fine-grained austenitic stainless steel sheet of the present invention, the average crystal grain size is 10 μm or less and 15 ° or more by using the slab having the steel component of (A) and carrying out the preferable production conditions of (B). The ratio of the large tilt grain boundaries is over 80%.
平均結晶粒径10μm超の場合は、本発明の目的とする微細化効果による耐応力腐食割れ性の発現が困難となる。加えて,平均結晶粒径10μm以下であっても,15°以上の大傾角粒界の比率が80%に満たない場合,上記の(f)に記載したように微細化効果による耐応力腐食割れ性の向上を阻害する。本発明の目的とする耐応力腐食割れ性を有効に発現させるには、好ましくは平均結晶粒径を5μm以下かつ15°以上の大傾角粒界の比率を85%以上とする。平均結晶粒径の下限は特に規定するものではないが、非特許文献1および2や特許文献1からも1μm未満とすることは困難である。従って、実用面を考慮して平均結晶粒径は1〜5μmの範囲とすることが好ましい。 When the average crystal grain size exceeds 10 μm, it becomes difficult to develop stress corrosion cracking resistance due to the refinement effect aimed at by the present invention. In addition, even if the average crystal grain size is 10 μm or less, if the ratio of the large angle grain boundaries of 15 ° or more is less than 80%, the stress corrosion cracking resistance due to the refinement effect as described in (f) above. Impairs sex improvement. In order to effectively develop the stress corrosion cracking resistance aimed at by the present invention, the ratio of the large tilt grain boundaries having an average crystal grain size of 5 μm or less and 15 ° or more is preferably 85% or more. The lower limit of the average crystal grain size is not particularly specified, but it is difficult to make it less than 1 μm from Non-Patent Documents 1 and 2 and Patent Document 1. Therefore, in consideration of practical use, the average crystal grain size is preferably in the range of 1 to 5 μm.
15°以上の大傾角粒界の比率は前記したように80%超とし、好ましくは85%超とする。大傾角粒界の比率を上昇させることは、微細粒材において0.2%耐力の低下と伸びの上昇にも有効であり,加工性の向上にも寄与する。本発明の目標とする加工性は、上述した背景から,フェライト系ステンレス鋼を凌駕してSUS304等に代表されるオーステナイト系ステンレス鋼に近いことが好ましい。そのため,0.2%耐力は400MPa未満,均一伸びが30%超であることが好ましい。耐応力腐食割れ性とこれら加工性を両立するために,15°以上の大傾角粒界の比率は85%超が好ましく,より好ましくは90%超とする。なお、本発明においては、機械的性質である0.2%耐力、均一伸びは、JIS13号B引張試験により評価する。 As described above, the ratio of the large tilt grain boundaries of 15 ° or more is more than 80%, preferably more than 85%. Increasing the ratio of the large-angle grain boundaries is effective in reducing the 0.2% proof stress and increasing the elongation of the fine-grained material, and contributes to the improvement of workability. From the background described above, the workability targeted by the present invention is preferably superior to that of ferritic stainless steels and close to that of austenitic stainless steels such as SUS304. Therefore, it is preferable that the 0.2% proof stress is less than 400 MPa and the uniform elongation is more than 30%. In order to satisfy both the stress corrosion cracking resistance and the workability, the ratio of the large tilt grain boundaries of 15 ° or more is preferably more than 85%, more preferably more than 90%. In the present invention, the mechanical properties of 0.2% proof stress and uniform elongation are evaluated by JIS No. 13 B tensile test.
以下に、本発明の実施例について述べる。
表2に鋼成分を示すオーステナイト系ステンレス鋳片を溶製し、熱間圧延を行い板厚4mmの熱延板とした。鋼No.1〜23は、本発明で規定する鋼成分を満たすものである。鋼No.24〜28は、本発明で規定する鋼成分が外れるものである。
Examples of the present invention will be described below.
Austenitic stainless steel slabs having steel components shown in Table 2 were melted and hot-rolled to form hot rolled sheets having a thickness of 4 mm. Steel No. 1-23 satisfy | fills the steel component prescribed | regulated by this invention. Steel No. Nos. 24-28 are for removing the steel components defined in the present invention.
熱延板は焼鈍し,冷間圧延と最終焼鈍は、本発明の好ましい条件に加え,それ以外の条件でも実施した。冷間圧延は、常温で水冷しながら30℃未満となるようにしたもの(<30℃),水冷など実施せず加工発熱により冷延途中50℃を上回る(>50℃)2条件で行った。冷間圧延後、最終焼鈍した鋼板を酸洗した後、平均結晶粒径の測定,EBSP法による15°以上の大傾角粒界比率の測定,耐応力腐食割れ性(割れ発生時間)の測定、機械的性質(0.2%耐力、均一伸び)の測定を行った。 The hot-rolled sheet was annealed, and cold rolling and final annealing were performed under other conditions in addition to the preferable conditions of the present invention. Cold rolling was performed under two conditions that were less than 30 ° C. while cooling with water at room temperature (<30 ° C.), and did not carry out water cooling and exceeded 50 ° C. (> 50 ° C.) in the middle of cold rolling due to processing heat generation. . After cold rolling, pickling the final annealed steel sheet, measuring the average crystal grain size, measuring the large angle grain boundary ratio of 15 ° or more by the EBSP method, measuring the stress corrosion cracking resistance (cracking time), The mechanical properties (0.2% proof stress, uniform elongation) were measured.
各種評価方法は、上述した要領で行った。具体的には、割れ発生時間は、上述した測定方法と同様に、ブランク径67.5mmφ,ポンチ径35mmφ,ダイス径37mmφ,しわ押さえ圧1トンの条件で絞り比(ブランク径をポンチ径で割った値)1.9の円筒深絞り加工を行い、得られた成形品を48hr放置して時効割れの発生しないことを確認したうえで,JIS G 0576に規定する沸騰42%塩化マグネシウム水溶液中に浸漬して割れ(応力腐食割れ)が発生した時間を測定することによって行った。割れの有無は目視判定した。機械的性質はJIS13号B引張試験により評価した。製造条件と特性の関係を表3に示す。 Various evaluation methods were performed as described above. Specifically, the crack generation time is the same as in the measurement method described above, with a blank diameter of 67.5 mmφ, a punch diameter of 35 mmφ, a die diameter of 37 mmφ, and a draw ratio of 1 ton (the blank diameter divided by the punch diameter). 1.9) After performing cylindrical deep drawing of 1.9 and leaving the resulting molded product to stand for 48 hours and confirming that aging cracks do not occur, in a boiling 42% magnesium chloride aqueous solution specified in JIS G 0576 This was carried out by measuring the time when cracking (stress corrosion cracking) occurred after immersion. The presence or absence of cracks was determined visually. The mechanical properties were evaluated by JIS No. 13 B tensile test. Table 3 shows the relationship between manufacturing conditions and characteristics.
試験No.7は、本発明の鋼成分を有し,公知の焼鈍温度で製造したものであり、最終焼鈍温度が高く,平均結晶粒径30μm,大角粒界比率98%,応力腐食割れ発生時間3hrであり、結晶粒微細化による耐応力腐食割れの向上が見られなかったものである。 Test No. 7 has the steel component of the present invention and is manufactured at a known annealing temperature, the final annealing temperature is high, the average crystal grain size is 30 μm, the large-angle grain boundary ratio is 98%, and the stress corrosion cracking occurrence time is 3 hours. The improvement of the stress corrosion cracking resistance due to the refinement of the crystal grains was not observed.
試験No.1〜4,8〜29は、本発明の鋼成分を有し,本発明の好ましい製造条件を実施したものである。これら鋼板は、平均結晶粒径10μm以下でかつ15°以上の大角粒界の比率が80%超であり,応力腐食割れ発生時間は上述で目標とした4hr以上を大きく上回る結果が得られた。さらに、これら鋼板は、0.2%耐力が400MPa未満,均一伸び30%超の機械的性質を有し,耐応力腐食割れ性に加えて上述した好ましい加工性にも到達している。これより、本発明の鋼成分を有し,本発明の好ましい製造条件を実施したオーステナイト系ステンレス鋼板は、微細化効果により優れた耐応力腐食割れ性を発現し,加工性との両立が達成された。 Test No. 1-4 and 8-29 have the steel component of this invention, and implement the preferable manufacturing conditions of this invention. These steel sheets had an average crystal grain size of 10 μm or less and a ratio of large-angle grain boundaries of 15 ° or more exceeding 80%, and the results of stress corrosion cracking generation time significantly exceeded the above-mentioned target of 4 hours or more. Furthermore, these steel sheets have mechanical properties with a 0.2% proof stress of less than 400 MPa and a uniform elongation of more than 30%, and have reached the preferred workability described above in addition to the stress corrosion cracking resistance. As a result, the austenitic stainless steel sheet having the steel components of the present invention and carrying out the preferred production conditions of the present invention exhibits excellent stress corrosion cracking resistance due to the refinement effect, and is compatible with workability. It was.
試験No.5は、本発明の鋼成分を有し、平均結晶粒径が6μmと小さいが、15°以上の大傾角粒界の比率が75%であり、80%に満たない。また,試験No.5は、応力腐食割れ発生時間3hrである。
試験No.6は、本発明の鋼成分を有するものの、本発明の好ましい製造方法から外れるものである。試験No.6は、平均結晶粒径が1μmと小さいが、最終焼鈍温度が低く15°以上の大傾角粒界の比率が80%に満たない。そのため、冷間圧延時の残留歪により耐応力腐食割れ性の向上が見られず、更に,0.2%耐力の上昇に伴う材料の硬質化により加工性も低下した。
Test No. No. 5 has the steel component of the present invention, and the average crystal grain size is as small as 6 μm, but the ratio of large-angle grain boundaries of 15 ° or more is 75%, which is less than 80%. In addition, Test No. 5 is a stress corrosion crack occurrence time of 3 hours.
Test No. Although 6 has the steel component of this invention, it remove | deviates from the preferable manufacturing method of this invention. Test No. No. 6 has an average crystal grain size as small as 1 μm, but the final annealing temperature is low and the ratio of the large-angle grain boundaries of 15 ° or more is less than 80%. For this reason, the stress corrosion cracking resistance was not improved due to the residual strain during cold rolling, and the workability was also lowered due to the hardening of the material accompanying the increase in 0.2% proof stress.
試験No.30,32,34,35,37は、本発明の鋼成分から外れるものの,本発明の好ましい製造方法を実施したものである。試験No.30,32,37は、結晶粒を微細化しても,応力腐食割れ発生時間が4hr未満となり,本発明の目標とする耐応力腐食割れ性の向上が見られなかったものである。試験No.34、35は、本発明の目標とする平均結晶粒10μm以下に到達しなかったものである。 Test No. Although 30, 32, 34, 35, and 37 deviate from the steel components of the present invention, the preferred production method of the present invention was carried out. Test No. In Nos. 30, 32, and 37, even when the crystal grains were refined, the stress corrosion cracking occurrence time was less than 4 hr, and the improvement of the stress corrosion cracking resistance targeted by the present invention was not observed. Test No. Nos. 34 and 35 did not reach the target average grain size of 10 μm or less.
試験No.31,33,36は、鋼成分ならびに好ましい製造方法から外れるものである。これらは、平均結晶粒径28μmまたは30μmであり,従来から公知の成分から、予想どおり本発明の目標とする耐応力腐食割れ性に到達しなかったものである。 Test No. 31, 33, and 36 deviate from the steel components and the preferred manufacturing method. These have an average crystal grain size of 28 μm or 30 μm and did not reach the target stress corrosion cracking resistance of the present invention as expected from the conventionally known components.
本発明によれば、8%以下のNi量でかつ高価なMoの添加によらず,オーステナイト系ステンレス鋼の欠点である応力腐食割れを結晶粒微細化効果により克服し,加工性との両立を図った微細粒オーステナイト系ステンレス鋼板を得ることが出来る。 According to the present invention, the stress corrosion cracking, which is a defect of the austenitic stainless steel, is overcome by the grain refining effect regardless of the amount of Ni of 8% or less and expensive Mo, and the compatibility with workability is achieved. The intended fine-grained austenitic stainless steel sheet can be obtained.
Claims (4)
Md=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)−18.2Mo In mass%, C: 0.05% or less, Cr: 14-19%, Si: 2% or less, Mn: 4% or less, Ni: 5-8%, Cu: 4% or less, N: 0.1 %, With the balance Fe and inevitable impurities, and having a steel component with the following Md in the range of -20 to 40, an average crystal grain size of 6.5 μm or less, and a large tilt angle of 15 ° or more A fine-grained austenitic stainless steel sheet excellent in stress corrosion cracking resistance and workability, characterized in that the proportion occupied by grain boundaries exceeds 80%.
Md = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29 (Ni + Cu) -18.2Mo
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CN102753717A (en) | 2012-10-24 |
WO2011067979A1 (en) | 2011-06-09 |
CN102753717B (en) | 2015-02-11 |
ES2546412T3 (en) | 2015-09-23 |
EP2508639B1 (en) | 2015-08-05 |
KR101411703B1 (en) | 2014-06-25 |
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KR20120093996A (en) | 2012-08-23 |
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