JP6821097B1 - Martensitic stainless steel for high hardness and corrosion resistance with excellent cold workability and its manufacturing method - Google Patents
Martensitic stainless steel for high hardness and corrosion resistance with excellent cold workability and its manufacturing method Download PDFInfo
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- 229910001105 martensitic stainless steel Inorganic materials 0.000 title claims abstract description 39
- 238000004519 manufacturing process Methods 0.000 title claims description 14
- 238000005260 corrosion Methods 0.000 title abstract description 32
- 230000007797 corrosion Effects 0.000 title abstract description 32
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 239000000126 substance Substances 0.000 claims abstract description 5
- 238000000137 annealing Methods 0.000 claims description 47
- 238000001816 cooling Methods 0.000 claims description 21
- 238000007711 solidification Methods 0.000 claims description 14
- 230000008023 solidification Effects 0.000 claims description 14
- 238000010438 heat treatment Methods 0.000 claims description 11
- 239000006104 solid solution Substances 0.000 claims description 8
- 229910052742 iron Inorganic materials 0.000 claims description 7
- 238000005266 casting Methods 0.000 claims description 6
- 239000000463 material Substances 0.000 abstract description 17
- 229910052782 aluminium Inorganic materials 0.000 abstract description 6
- 229910052748 manganese Inorganic materials 0.000 abstract description 5
- 229910052710 silicon Inorganic materials 0.000 abstract description 5
- 229910052804 chromium Inorganic materials 0.000 abstract description 4
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 4
- 229910052750 molybdenum Inorganic materials 0.000 abstract description 3
- 229910052759 nickel Inorganic materials 0.000 abstract description 3
- 229910000831 Steel Inorganic materials 0.000 description 39
- 239000010959 steel Substances 0.000 description 39
- 239000000047 product Substances 0.000 description 37
- 230000000694 effects Effects 0.000 description 21
- 238000010791 quenching Methods 0.000 description 19
- 230000000171 quenching effect Effects 0.000 description 19
- 238000005482 strain hardening Methods 0.000 description 19
- 239000000203 mixture Substances 0.000 description 18
- 230000000052 comparative effect Effects 0.000 description 13
- 238000000034 method Methods 0.000 description 13
- 229910001220 stainless steel Inorganic materials 0.000 description 13
- 239000010935 stainless steel Substances 0.000 description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 11
- 230000014759 maintenance of location Effects 0.000 description 9
- 238000012545 processing Methods 0.000 description 9
- 229920006395 saturated elastomer Polymers 0.000 description 9
- 229910052799 carbon Inorganic materials 0.000 description 8
- 238000010273 cold forging Methods 0.000 description 7
- 229910000734 martensite Inorganic materials 0.000 description 7
- 238000000354 decomposition reaction Methods 0.000 description 6
- 238000005098 hot rolling Methods 0.000 description 6
- 230000006835 compression Effects 0.000 description 5
- 238000007906 compression Methods 0.000 description 5
- 229910052761 rare earth metal Inorganic materials 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 239000012467 final product Substances 0.000 description 3
- 229910052755 nonmetal Inorganic materials 0.000 description 3
- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000005097 cold rolling Methods 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000010583 slow cooling Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229910052765 Lutetium Inorganic materials 0.000 description 1
- OFOBLEOULBTSOW-UHFFFAOYSA-N Propanedioic acid Natural products OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- QZPSXPBJTPJTSZ-UHFFFAOYSA-N aqua regia Chemical compound Cl.O[N+]([O-])=O QZPSXPBJTPJTSZ-UHFFFAOYSA-N 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 238000012669 compression test Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 210000001787 dendrite Anatomy 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 229910052745 lead Inorganic materials 0.000 description 1
- OHSVLFRHMCKCQY-UHFFFAOYSA-N lutetium atom Chemical compound [Lu] OHSVLFRHMCKCQY-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 1
- 239000011976 maleic acid Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001737 promoting effect Effects 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
- 229910052711 selenium Inorganic materials 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- 229910052714 tellurium Inorganic materials 0.000 description 1
- QEMXHQIAXOOASZ-UHFFFAOYSA-N tetramethylammonium Chemical compound C[N+](C)(C)C QEMXHQIAXOOASZ-UHFFFAOYSA-N 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- VZCYOOQTPOCHFL-UHFFFAOYSA-N trans-butenedioic acid Natural products OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 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
- 229910052725 zinc Inorganic materials 0.000 description 1
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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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—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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- 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
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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Abstract
冷間加工性に優れる高硬度・高耐食性マルテンサイト系ステンレス鋼の軟化焼鈍材は、質量%で、C:0.15〜0.70%、Si:2.0%以下、Mn:1.5%以下、S:0.01%未満、P:0.05%以下、Ni:1.5%以下、Cr:10.5〜16.0%、Mo:0.9〜3.0%,N:0.14%以下、Al:0.008〜1.0を含有し、O:0.001〜0.008%以下を含有し、残部Feおよび不純物からなる化学成分を有し、C+N/2:0.14〜0.70%であり、かつ、1μm以上の炭窒化物が1600μm2中に10個以上であり、酸化物の平均直径サイズが1〜5μmであり、Hv硬さ≦(60C+170)である。The softened annealed material of high hardness and high corrosion resistance martensitic stainless steel with excellent cold workability is C: 0.15 to 0.70%, Si: 2.0% or less, Mn: 1.5 in mass%. % Or less, S: less than 0.01%, P: 0.05% or less, Ni: 1.5% or less, Cr: 10.5 to 16.0%, Mo: 0.9 to 3.0%, N : 0.14% or less, Al: 0.008 to 1.0, O: 0.001 to 0.008% or less, has a chemical component consisting of the balance Fe and impurities, and C + N / 2 : 0.14 to 0.70%, 10 or more carbonitrides of 1 μm or more in 1600 μm2, average diameter size of oxides of 1 to 5 μm, Hv hardness ≦ (60C + 170) Is.
Description
本発明は、冷間加工用の部品に関して、軟化特性に優れて強冷間加工が可能な高硬度・高耐食部品用のマルテンサイト系ステンレス鋼及びその製造方法に関するものである。 The present invention relates to a martensitic stainless steel for high hardness and high corrosion resistant parts which is excellent in softening characteristics and capable of strong cold working, and a method for producing the same.
近年、高硬度・高耐食マルテンサイト系ステンレス鋼のニーズが高く、自動車部品やねじ締結部品等の多くに使用されている(特許文献1〜4)。これら高硬度・高耐食マルテンサイト系ステンレス鋼部品、特に、大型の自動車部品等において、複雑形状に冷間鍛造等の冷間加工によって成型される。このため、冷間加工前に軟化焼鈍を行って鋼を軟質化した上で冷間加工を行い、冷間加工後に焼き入れを行い、高硬度・高耐食マルテンサイト系ステンレス鋼となる。焼入れ後のマルテンサイト系ステンレス鋼において、鋼中のC含有量が高いほど高硬度の鋼を得ることができる。同様に、軟化焼鈍後のステンレス鋼においても、鋼中のC含有量が高いほど硬度が高くなることが知られている。そのような状況の中、軟化焼鈍後のステンレス鋼において、C量(質量%)に依存して(60C+170)以下のHv硬さ、好ましくは(60C+160)以下のHv硬さの軟化状態であることが望まれる。 In recent years, there has been a high demand for martensitic stainless steel with high hardness and high corrosion resistance, and it is used in many automobile parts, screw fastening parts, etc. (Patent Documents 1 to 4). These high hardness and high corrosion resistant martensitic stainless steel parts, especially large automobile parts, are molded into a complicated shape by cold working such as cold forging. For this reason, the steel is softened by softening and annealing before cold working, and then cold working is performed, and then quenching is performed after cold working to obtain high hardness and high corrosion resistant martensitic stainless steel. In the martensitic stainless steel after quenching, the higher the C content in the steel, the higher the hardness of the steel can be obtained. Similarly, it is known that the hardness of stainless steel after softening and annealing increases as the C content in the steel increases. Under such circumstances, the stainless steel after softening and annealing is in a softened state having an Hv hardness of (60C + 170) or less, preferably (60C + 160) or less, depending on the amount of C (mass%). Is desired.
しかしながら、高硬度・高耐食マルテンサイト系ステンレス鋼には、C,N,Mo,Ni等合金元素が多く添加されているため、軟化焼鈍で十分に軟質化して優れた冷間加工性(冷間鍛造性)を確保することが難しい。例えば、特許文献5には冷間鍛造性を向上させるための成分設計と軟化焼鈍技術が提案されているが、本発明に求められる水準まで軟質化できていない。 However, since a large amount of alloying elements such as C, N, Mo, and Ni are added to the high hardness and high corrosion resistant martensitic stainless steel, it is sufficiently softened by softening annealing and has excellent cold workability (cold). It is difficult to secure forgeability). For example, Patent Document 5 proposes a component design and a softening annealing technique for improving cold forging property, but the softening has not been achieved to the level required for the present invention.
このように従来の技術では、高硬度・高耐食マルテンサイト系ステンレス鋼を軟化焼鈍で十分に軟質化させて複雑形状へ冷間加工(冷間鍛造)することができない。 As described above, with the conventional technology, it is not possible to sufficiently soften a martensitic stainless steel having high hardness and high corrosion resistance by soft annealing and cold work (cold forging) into a complicated shape.
本発明の解決すべき課題は、複雑形状の冷間加工、もしくは冷間鍛造部品用素材として、軟質化特性を著しく改善した高硬度・高耐食性用途のマルテンサイト系ステンレス鋼及びその製造方法を安価に提供することである。なお、本発明が対象とする、軟化焼鈍後のステンレス鋼においては、鋼組織はフェライトと炭化物からなり、マルテンサイト組織ではない。一方、本発明のステンレス鋼を冷間加工した後に焼き入れを行い、最終製品はマルテンサイト組織を有していることから、本発明のステンレス鋼をマルテンサイト系ステンレス鋼と呼ぶこととする。 The problem to be solved by the present invention is to inexpensively produce martensitic stainless steel for high hardness and high corrosion resistance, which has significantly improved softening characteristics, as a material for cold working or cold forged parts having a complicated shape. Is to provide to. In the stainless steel after softening and annealing, which is the subject of the present invention, the steel structure is composed of ferrite and carbide, and is not a martensite structure. On the other hand, since the stainless steel of the present invention is cold-worked and then hardened and the final product has a martensitic structure, the stainless steel of the present invention is referred to as a martensitic stainless steel.
本発明者等は、上記課題を解決するために種々検討した結果、成分調整された高耐食高硬度用途のマルテンサイト系ステンレス鋼において、2次脱酸生成物である酸化物のサイズと組成を制御し、且つ、高温の軟化焼鈍により微細な炭窒化物の分散状態を制御することで、(60C+170)以下のHv硬さまで軟質化して冷間加工性が著しく向上する知見を得た。また、転位や結晶粒界をピン止めしないような微細な脱酸生成物組成をAl含有系に制御するとより好ましい。 As a result of various studies to solve the above problems, the present inventors have determined the size and composition of oxides, which are secondary deoxidizing products, in martensitic stainless steels for high corrosion resistance and high hardness whose components have been adjusted. It was found that by controlling and controlling the dispersed state of fine carbonitride by softening and annealing at high temperature, the hardness is softened to Hv hardness of (60C + 170) or less and the cold workability is remarkably improved. Further, it is more preferable to control the fine deoxidized product composition that does not pin the dislocations and grain boundaries to the Al-containing system.
本発明は、上記知見に基づいてなされたものであり、その要旨とするところは以下の通りである。
(1)質量%で、
C:0.15%超0.70%以下
Si:2.0%以下、
Mn:1.5%以下、
S:0.01%未満、
P:0.05%以下、
Ni:1.5%以下、
Cr:10.5〜16.0%、
Mo:0.9〜3.0%、
N:0.14%以下、
Al:0.008〜1.0%、
O:0.001〜0.008%を含有し、
残部Feおよび不純物からなる化学成分を有し、
C+N/2:0.16〜0.70%であり、
かつ、1.0μm以上の炭窒化物が1600μm2中に10個以上であり、2次脱酸生成物である酸化物の平均直径サイズが1〜5μmであり、前記酸化物の平均Al濃度が15〜40質量%であり、(a)式で示されるHv硬さであることを特徴とするマルテンサイト系ステンレス鋼。
Hv≦60C+170 ・・・・・・・・・・・・・・・・・・・(a)
C:C含有量(質量%)
(2)前記Feの一部に替えて、更に質量%で、
Cu:1.5%以下、
W:1.5%以下、
Co:1.5%以下
B:0.01%以下、
Sn:0.3%以下、
Sb:0.3%以下の内、1種類以上を含有することを特徴とする本発明のマルテンサイト系ステンレス鋼。
(3)前記Feの一部に替えて、更に質量%で、
Nb:0.1%以下、
Ti:0.1%以下、
V:0.2%以下、
Ta:0.2%以下の内、1種類以上を含有することを特徴とする本発明のマルテンサイト系ステンレス鋼。
(4)前記Feの一部に替えて、更に質量%で、
Mg:0.01%以下、
Ca:0.01%以下、
Hf:0.01%以下、
REM:0.01%以下の内、1種類以上を含有することを特徴とする本発明のマルテンサイト系ステンレス鋼。
The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) By mass%
C: More than 0.15% 0.70% or less Si: 2.0% or less,
Mn: 1.5% or less,
S: less than 0.01%,
P: 0.05% or less,
Ni: 1.5% or less,
Cr: 10.5 to 16.0%,
Mo: 0.9-3.0%,
N: 0.14% or less,
Al: 0.008 to 1.0%,
O: Contains 0.001 to 0.008%,
It has a chemical component consisting of the balance Fe and impurities,
C + N / 2: 0.16 to 0.70%,
In addition, there are 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 , the average diameter size of the oxide as the secondary deoxidizing product is 1 to 5 μm, and the average Al concentration of the oxide is A martensitic stainless steel having an Hv hardness of 15 to 40% by mass and represented by the formula (a).
Hv ≤ 60C + 170 ... (a)
C: C content (mass%)
(2) Instead of a part of the Fe, further by mass%
Cu: 1.5% or less,
W: 1.5% or less,
Co: 1.5% or less B: 0.01% or less,
Sn: 0.3% or less,
Sb: The martensitic stainless steel of the present invention, which comprises one or more of 0.3% or less.
(3) Instead of a part of the Fe, further by mass%
Nb: 0.1% or less,
Ti: 0.1% or less,
V: 0.2% or less,
Ta: The martensitic stainless steel of the present invention, which comprises one or more of 0.2% or less.
(4) Instead of a part of the Fe, further by mass%
Mg: 0.01% or less,
Ca: 0.01% or less,
Hf: 0.01% or less,
REM: The martensitic stainless steel of the present invention, which comprises one or more of 0.01% or less .
(5)鋳造時の凝固時の平均冷却速度が5〜500℃/sであり、
軟化焼鈍処理として、
870℃よりも高く、C濃度と下記(b)式で表される炭化物の固溶温度:Tよりも20〜120℃低い温度範囲で1〜48hの熱処理を施し、引き続き平均60℃/h以下の冷却速度でTよりも250℃低い温度まで除冷することを特徴とする本発明のマルテンサイト系ステンレス鋼の製造方法。
log(C) = −6100/(T+273) + 4 ・・・・・(b)
(b)式で「C」はC濃度(質量%)、「T」は炭化物の固溶温度(℃)を意味する。
( 5 ) The average cooling rate during solidification during casting is 5 to 500 ° C./s.
As a softening annealing treatment
Heat treatment is performed for 1 to 48 hours in a temperature range higher than 870 ° C., C concentration and solid solution temperature of carbide represented by the following formula (b): 20 to 120 ° C. lower than T, and the average is 60 ° C./h or less. The method for producing martensitic stainless steel of the present invention, which comprises cooling to a temperature 250 ° C. lower than T at the cooling rate of.
log (C) = -6100 / (T + 273) + 4 ... (b)
In the formula (b), "C" means the C concentration (mass%), and "T" means the solid solution temperature (° C.) of the carbide .
本発明によれば、複雑部品形状に強冷間鍛造(冷間加工)もしくはニアネット成形が可能となり、自動車用等の冷間鍛造(冷間加工)による部品コストの大幅な低減効果を発揮できる高硬度・高耐食性マルテンサイト系ステンレス鋼の軟化焼鈍材を提供できる。 According to the present invention, strong cold forging (cold working) or near net forming can be performed on a complicated part shape, and the effect of significantly reducing the part cost by cold forging (cold working) for automobiles and the like can be exhibited. It is possible to provide a softened annealed material of martensitic stainless steel having high hardness and high corrosion resistance.
以下に本発明の各要件について説明する。なお、以下の説明における(%)は特に断りがない限り、質量(%)である。 Each requirement of the present invention will be described below. In the following description, (%) is mass (%) unless otherwise specified.
本発明が対象とする、冷間加工性に優れる高硬度・高耐食性用途のマルテンサイト系ステンレス鋼は、鋼を軟化焼鈍することで軟質化したステンレス鋼であり、鋼組織はフェライトと炭窒化物からなる。軟質化した本発明のステンレス鋼を素材として冷間加工を行い、その後に焼き入れ処理を行って高硬度化し、最終製品とする。なお、後述の本発明の成分組成を含有することにより、焼き入れ処理により大半がマルテンサイト組織となり、マルテンサイト系ステンレス鋼とすることができる。具体的には、1000〜1200℃からの焼き入れ処理で組織の約8割以上がマルテンサイト組織になる鋼である。 The martensitic stainless steel for high hardness and high corrosion resistance, which is the object of the present invention and has excellent cold workability, is a stainless steel softened by softening and annealing the steel, and the steel structure is ferrite and carbon nitride. Consists of. The softened stainless steel of the present invention is used as a material for cold working, and then quenching is performed to increase the hardness to obtain a final product. By containing the component composition of the present invention described later, most of the steel has a martensitic structure by quenching, and a martensitic stainless steel can be obtained. Specifically, it is a steel in which about 80% or more of the structure becomes a martensite structure by quenching treatment from 1000 to 1200 ° C.
《鋼の必須成分組成》
本発明の軟質による冷間加工性向上の効果は、製品の焼入れ処理後の硬さで500Hv以上になる高硬度・高耐食マルテンサイト系ステンレス鋼で著しく発揮される。最高焼入れで500Hv未満の鋼については従来の技術で冷間加工性を十分に確保でき本発明の効果が不明瞭になる。そのため、焼入れ硬さを支配するC,N,C+N/2の含有量を限定し、本発明の効果が明瞭な範囲を規定する。<< Essential composition of steel >>
The effect of improving cold workability due to the softness of the present invention is remarkably exhibited in high hardness and high corrosion resistant martensitic stainless steel having a hardness of 500 Hv or more after quenching of the product. For steels with a maximum quenching of less than 500 Hv, the cold workability can be sufficiently ensured by the conventional technique, and the effect of the present invention becomes unclear. Therefore, the content of C, N, C + N / 2, which controls the quenching hardness, is limited, and the range in which the effect of the present invention is clear is defined.
Cを0.15%超、C+N/2を0.16%超に限定する。焼入れ後の硬度確保のためである。しかしながら、Cを0.70%超、C+N/2を0.70超含有させると粗大な炭化物や微細な窒化物により冷間加工性が劣化するため、上限を該値に規定する。500Hv以上の焼入れ硬さを安定的に得て、軟質化効果が発揮するCの好ましい範囲は0.16〜0.40%、C+N/2の好ましい範囲は0.18〜0.45%である。 C is limited to more than 0.15% and C + N / 2 is limited to more than 0.16%. This is to ensure hardness after quenching. However, if C is contained in an amount of more than 0.70% and C + N / 2 is contained in an amount of more than 0.70, the cold workability is deteriorated due to coarse carbides and fine nitrides. Therefore, the upper limit is specified in the value. The preferred range of C, which stably obtains a quenching hardness of 500 Hv or more and exerts a softening effect, is 0.16 to 0.40%, and the preferable range of C + N / 2 is 0.18 to 0.45%. ..
Nは上述した焼入れ硬さに加えて製品の耐食性の確保のために含有させることができる。しかしながら、Nを0.14%超含有させるとブローホールの生成のため鋳造が困難となり、鋳造できても鋼中に粗大な炭窒化物が生成し、冷間加工性が劣化するため上限を0.14%にする。好ましい範囲は0.02〜0.11%である。更に好ましくは、0.04〜0.10%である。 N can be contained in order to ensure the corrosion resistance of the product in addition to the quenching hardness described above. However, if N is contained in excess of 0.14%, casting becomes difficult due to the formation of blow holes, and even if casting is possible, coarse carbonitrides are formed in the steel and cold workability deteriorates, so the upper limit is 0. .14%. The preferred range is 0.02 to 0.11%. More preferably, it is 0.04 to 0.10%.
Siは、軟化焼鈍時のフェライト組織の固溶強化、及び炭窒化物の微細分散により冷間加工性を劣化させる元素であるため、含有量を2.0%以下に限定する。好ましくは、0.7%以下である。Si含有量を0.01%以上とすると好ましい。Siは含有しなくても良い。 Since Si is an element that deteriorates cold workability due to solid solution strengthening of the ferrite structure during softening and annealing and fine dispersion of carbonitride, the content is limited to 2.0% or less. Preferably, it is 0.7% or less. The Si content is preferably 0.01% or more. Si may not be contained.
Mnは、軟化焼鈍後の強度を上昇させて冷間加工性を劣化させるため、含有量を1.5%以下に限定する。Mn含有量を0.01%以上とすると好ましい。Mnは含有しなくても良い。 The content of Mn is limited to 1.5% or less in order to increase the strength after softening and annealing and deteriorate the cold workability. The Mn content is preferably 0.01% or more. Mn may not be contained.
Sは、硫化物を形成して冷間加工性を劣化させるため、含有量を0.01%未満に限定する。好ましくは0.007%以下である。 The content of S is limited to less than 0.01% because it forms sulfide and deteriorates cold workability. It is preferably 0.007% or less.
Pは、粒界偏析して冷間加工性を劣化させるため、含有量を0.05%以下に限定する。 The content of P is limited to 0.05% or less because it segregates at grain boundaries and deteriorates cold workability.
Niは、マルテンサイト系ステンレス鋼の製品の靭性、耐食性を向上させる元素であるため、含有させてもよい。しかしながら、1.5%を超えて含有させると軟化焼鈍後の硬度が(60C+170)のHv硬さ以下に軟質化せずに冷間加工性が劣化する。そのため、1.5%以下に限定する。好ましくは、1.3%以下である。Ni含有量を0.01%以上とすると好ましい。Niは含有しなくても良い。 Since Ni is an element that improves the toughness and corrosion resistance of martensitic stainless steel products, it may be contained. However, if it is contained in excess of 1.5%, the hardness after softening and annealing does not soften below the Hv hardness of (60C + 170), and the cold workability deteriorates. Therefore, it is limited to 1.5% or less. It is preferably 1.3% or less. The Ni content is preferably 0.01% or more. Ni does not have to be contained.
Crは、ステンレス鋼の高耐食性の機能を得るための基本元素であり、10.5%以上を含有させる。しかしながら、16.0%を超えて含有させると、焼入れ後に本発明の特徴である高硬度の製品硬さを得ることができず、また、従来の技術で冷間加工性を確保できる。そのため、16.0%以下に限定する。好ましいCrの範囲は、11.0〜15.0%である。 Cr is a basic element for obtaining the function of high corrosion resistance of stainless steel, and contains 10.5% or more. However, if it is contained in an amount of more than 16.0%, the high hardness of the product, which is a feature of the present invention, cannot be obtained after quenching, and cold workability can be ensured by the conventional technique. Therefore, it is limited to 16.0% or less. The preferred Cr range is 11.0 to 15.0%.
Moは、高耐食性マルテンサイト系ステンレス鋼を得るため含有させる。なお、軟化焼鈍時に炭窒化物の粗大化を阻害して、素材を軟化し難くする元素であり、本発明の軟質・高冷間加工性の効果が明瞭になる0.9%以上に限定する。0.9%未満では公知の軟化焼鈍方法で冷間加工性が確保でき、本発明の有効性が明瞭でなくなるとともに耐食性が不足する。一方、3.0%を超えて過度に含有させると本発明の手法でも軟化し難くなり、焼鈍時に炭窒化物が粗大化せず、冷間加工性が劣化する。そのため、3.0%以下に限定する。好ましい範囲は、1.0〜2.5%である。 Mo is included to obtain highly corrosion resistant martensitic stainless steel. It should be noted that it is an element that inhibits the coarsening of the carbonitride during softening annealing and makes it difficult to soften the material, and is limited to 0.9% or more at which the effect of the soft and highly cold workability of the present invention becomes clear. .. If it is less than 0.9%, cold workability can be ensured by a known softening and annealing method, the effectiveness of the present invention becomes unclear, and corrosion resistance is insufficient. On the other hand, if it is excessively contained in excess of 3.0%, it becomes difficult to soften even by the method of the present invention, the carbonitride does not become coarse during annealing, and the cold workability deteriorates. Therefore, it is limited to 3.0% or less. The preferred range is 1.0 to 2.5%.
Alは、脱酸で脱酸生成物を低減させて、分解・微細化を抑制するのに有効な元素であるため0.008%以上含有させる。しかしながら、1.0%を超えて添加しても脱酸効果は飽和するばかりか粗大な酸化物が生成して冷間加工性を著しく劣化させる。そのため、上限を1.0%に限定する。好ましくは、0.01〜0.2%である。 Al is an element effective for reducing deoxidation products by deoxidation and suppressing decomposition and miniaturization, and therefore contains 0.008% or more. However, even if it is added in excess of 1.0%, not only the deoxidizing effect is saturated but also coarse oxides are generated, which significantly deteriorates the cold workability. Therefore, the upper limit is limited to 1.0%. It is preferably 0.01 to 0.2%.
Oは、Al含有鋼での微細な脱酸生成物(酸化物)の組成やサイズに大きく影響を与える。後述する凝固速度を制御すると共にO含有量を制御すると、製品の脱酸生成物の平均直径が5μm超と過度に粗大化することを防止して冷間加工割れに対して実質的に無害化し、且つ、熱間圧延時に酸化物が1μm未満サイズに分解・微細化することを抑制する。そのため、鋼中のOを0.001〜0.008%に制御する。OはT.Oを意味する。Oが0.001%未満の場合、工業的な実施が困難となり、0.008%を超えて含有させると粗大な酸化物が生成するため冷間加工性が低下していく。好ましくは、0.001〜0.006%である。 O has a great influence on the composition and size of fine deoxidizing products (oxides) in Al-containing steel. By controlling the solidification rate and the O content, which will be described later, it is possible to prevent the average diameter of the deoxidized product of the product from becoming excessively coarse, exceeding 5 μm, and to make it substantially harmless to cold rolling cracks. In addition, it suppresses the decomposition and miniaturization of oxides to a size of less than 1 μm during hot rolling. Therefore, O in steel is controlled to 0.001 to 0.008%. O is T.I. Means O. If O is less than 0.001%, industrial implementation becomes difficult, and if it is contained in excess of 0.008%, coarse oxides are generated, so that cold workability is lowered. It is preferably 0.001 to 0.006%.
《1.0μm以上の炭窒化物が1600μm2中に10個以上》
本発明のマルテンサイト系ステンレス鋼(軟化焼鈍後)の炭窒化物の分布は、マルテンサイト系ステンレス鋼の軟化焼鈍時の軟化挙動(軟化焼鈍後の軟質化特性)に影響を与える。軟化焼鈍後の鋼中の炭窒化物が微細分散していると、軟化焼鈍後の冷間加工において、転位や結晶粒界の動きをピンニングして冷間加工し難い。炭窒化物サイズは大きい方がよく、1600μm2中に1.0μm以上の炭窒化物個数が10個以上であれば、1.0μm未満の微細な炭窒化物が減少するため、Hv≦(60C+170)の軟質化特性が得られる。
図1に、13Cr−2Mo−0.2C−0.1N系鋼を公知の方法(650℃−4hの低温焼鈍)で軟化焼鈍した場合の金属組織を示す。ラスマルテンサイト組織の界面にサブミクロンの棒状炭化物が析出しており、軟化焼鈍して軟質化した後もHv硬さで305あり、冷間加工性に劣る。一方、後述の本発明の方法で軟化焼鈍した鋼の例を図2に示す。図2において、1600μm2中に1.0μmサイズ以上の炭窒化物が10個以上あり、Hv≦60C+170まで軟質化している。
炭窒化物サイズは大きい方がよく、1600μm2中に1μm以上のサイズの炭窒化物個数が10個以上で軟質化特性が得られている。好ましくは、1600μm2中に2μm以上のサイズ以上の炭窒化物が10個以上である。ここで炭窒化物サイズとは、炭窒化物の(長径+短径)/2を示す。<< 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 >>
The distribution of carbon nitride in the martensitic stainless steel (after softening and annealing) of the present invention affects the softening behavior (softening characteristics after softening and annealing) of the martensitic stainless steel during softening and annealing. If the carbonitride in the steel after softening annealing is finely dispersed, it is difficult to perform cold working by pinning dislocations and movements of grain boundaries in cold working after softening annealing. The larger the size of the carbonitride is, the better, and if the number of carbonitrides of 1.0 μm or more is 10 or more in 1600 μm 2 , fine carbonitrides of less than 1.0 μm are reduced, so Hv ≦ (60C + 170). ) Softening characteristics are obtained.
FIG. 1 shows the metallographic structure when 13Cr-2Mo-0.2C-0.1N steel is softened and annealed by a known method (low temperature annealing at 650 ° C.-4h). Submicron rod-shaped carbides are precipitated at the interface of the lath martensite structure, and even after being softened and annealed, the Hv hardness is 305, which is inferior in cold workability. On the other hand, FIG. 2 shows an example of steel softened and annealed by the method of the present invention described later. In FIG. 2, there are 10 or more carbonitrides having a size of 1.0 μm or more in 1600 μm 2 , which are softened to Hv ≦ 60C + 170.
The larger the size of the carbonitride, the better, and the number of carbonitrides having a size of 1 μm or more in 1600 μm 2 is 10 or more, and the softening property is obtained. Preferably, 1600 .mu.m carbonitride or more sizes 2μm in 2 is 10 or more. Here, the carbonitride size indicates the carbonitride (major diameter + minor diameter) / 2.
前記本発明の好適な鋼成分組成を有するとともに、後述する好適な軟化焼鈍条件を用いて軟化焼鈍を行うことにより、1.0μm以上の炭窒化物が1600μm2中に10個以上となる鋼を実現することができる。A steel having the suitable steel composition of the present invention and having 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 can be obtained by performing softening annealing using the suitable softening annealing conditions described later. It can be realized.
《酸化物の平均直径サイズが1〜5μm》
本発明のマルテンサイト系ステンレス鋼(軟化焼鈍後)の凝固時に生成する2次脱酸生成物である酸化物のサイズは、マルテンサイト系ステンレス鋼の軟化焼鈍時の軟化挙動(軟化焼鈍後の軟質化特性)に影響を与え、この酸化物の平均直径サイズが1μm未満に微細化していると、軟化焼鈍後の冷間加工において、転位や結晶粒界の動きをピンニングして冷間加工し難く、Hv≦(60C+170)の軟質化特性も得られない。酸化物サイズが大きい方がよく、平均直径サイズが1μm以上であれば軟質化特性が得られる。一方、酸化物の平均直径サイズが5μm超になると冷間加工時の割れの起点となるため冷間加工性が劣化する。好ましくは2〜4μmである。ここで2次脱酸生成物である酸化物のサイズとは、2次脱酸生成物の(長径+短径)/2を示し、平均サイズとは任意にサンプリングした30個の平均値を示す。酸化物の評価において、1次脱酸生成物と2次脱酸生成物との区別は、溶鋼中で生成する15μm超のサイズの粗大なものを1次脱酸生成物と判定し、15μm以下のサイズを凝固中に全面に晶出する2次脱酸生成物として判定する。<< Average diameter size of oxide is 1 to 5 μm >>
The size of the oxide, which is a secondary deoxidizing product produced during solidification of the martensitic stainless steel of the present invention (after softening and annealing), is the softening behavior of the martensitic stainless steel during softening and annealing (softness after softening and annealing). If the average diameter size of this oxide is reduced to less than 1 μm, it will be difficult to perform cold working by pinning dislocations and movements of grain boundaries in cold working after softening annealing. , Hv ≦ (60C + 170) softening characteristics cannot be obtained either. The larger the oxide size, the better, and if the average diameter size is 1 μm or more, softening characteristics can be obtained. On the other hand, when the average diameter size of the oxide exceeds 5 μm, it becomes the starting point of cracks during cold working, so that the cold workability deteriorates. It is preferably 2 to 4 μm. Here, the size of the oxide as the secondary deoxidizing product indicates the secondary deoxidizing product (major axis + minor axis) / 2, and the average size indicates the average value of 30 arbitrarily sampled pieces. .. In the evaluation of oxides, the distinction between the primary deoxidizing product and the secondary deoxidizing product is that a coarse product having a size of more than 15 μm produced in molten steel is judged to be a primary deoxidizing product and is 15 μm or less. Is determined as a secondary deoxidizing product that crystallizes over the entire surface during solidification.
前記本発明の好適な鋼成分組成を有し、特にAl含有量を本発明範囲とするとともに、後述する凝固条件を好適化することにより、酸化物の平均直径サイズを1〜5μmとすることができる。 The average diameter size of the oxide can be set to 1 to 5 μm by having the suitable steel composition of the present invention, particularly setting the Al content within the range of the present invention, and optimizing the solidification conditions described later. it can.
《(a)式で示されるHv硬さ》
以上詳述したように、公知技術よりも軟質化して複雑形状へ冷間加工して効果が著しく発揮されるためには、本発明のステンレス鋼(軟化焼鈍後)のHv硬さについて、下記(a)式で示されるHv硬さに限定する。更に、Hv≦(60C+160)のHv硬さになると、複雑形状の大型部品への冷間鍛造も可能となり、飛躍的に工業的・経済的な効果が大きくなるため、好ましくは、(60C+160)以下のHv硬さ以下である。
Hv≦60C+170 ・・・・・・・・・・・・・・・・(a)
C:C含有量(質量%)<< Hv hardness represented by equation (a) >>
As described in detail above, the Hv hardness of the stainless steel (after softening and annealing) of the present invention is described below in order to be softer than known techniques and cold-worked into a complicated shape to exert a remarkable effect. a) Limited to the Hv hardness represented by the equation. Further, when the Hv hardness is Hv ≦ (60C + 160), cold forging of a large part having a complicated shape becomes possible, and the industrial and economic effect is dramatically increased. Therefore, it is preferably (60C + 160) or less. Hv hardness or less.
Hv ≦ 60C + 170 ・ ・ ・ ・ ・ (a)
C: C content (mass%)
《酸化物の平均Al濃度》
脱酸生成物は熱間圧延時に分解・微細化するため軟化焼鈍時の素材の軟質化を抑制する。そのため、脱酸元素であるAl量、さらにO量や凝固速度の調整によって脱酸生成物の組成を制御することで、脱酸生成物の熱間圧延時の分解・微細化を抑制でき、転位や結晶粒界をピン止めせずに冷間加工割れを誘発しないサイズに安定的に制御することができ、軟質化を促進することができるので好ましい。具体的には、酸化物の平均Al濃度を15〜40質量%とすることにより、脱酸生成物を熱的に安定化して、熱間圧延時の1μm未満サイズへの分解・微細化の抑制に寄与する。
酸化物中の平均組成とは、非金属介在物中のS元素を除いてOを含めて質量%で換算して求めた値である。Al含有の熱力学的に安定(熱間圧延時に分解して微細化しない)な脱酸生成物を生成させることにより、軟化焼鈍後の冷間加工時に、転位や結晶粒界の動きをピンニングし難くするので、軟化焼鈍時の軟質化促進に有効である。<< Average Al concentration of oxide >>
Since the deoxidized product decomposes and becomes finer during hot rolling, it suppresses the softening of the material during softening and annealing. Therefore, by controlling the composition of the deoxidized product by adjusting the amount of Al, which is a deoxidizing element, the amount of O, and the solidification rate, it is possible to suppress the decomposition and refinement of the deoxidized product during hot rolling, and dislocations. It is preferable because it can be stably controlled to a size that does not induce cold rolling cracks without pinning the grain boundaries and the grain boundaries, and softening can be promoted. Specifically, by setting the average Al concentration of the oxide to 15 to 40% by mass, the deoxidized product is thermally stabilized, and decomposition and miniaturization to a size of less than 1 μm during hot rolling are suppressed. Contribute to.
The average composition in the oxide is a value obtained by converting in mass% including O excluding the S element in the non-metal inclusions. By generating an Al-containing thermodynamically stable deoxidizing product (which does not decompose and become finer during hot rolling), dislocations and grain boundary movements are pinned during cold working after softening annealing. Since it makes it difficult, it is effective in promoting softening during softening annealing.
《選択的含有成分》
本発明のステンレス鋼は、上述してきた元素以外は、Feおよび不純物からなる化学成分から構成される。さらに、前記成分組成に加え、Feの一部に替えて、選択的に以下に示す元素を含有しても良い。<< Selective ingredients >>
The stainless steel of the present invention is composed of chemical components composed of Fe and impurities other than the elements described above. Further, in addition to the above-mentioned component composition, the following elements may be selectively contained in place of a part of Fe.
Cuは、製品の耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、1.5%を超えて含有させても、その効果は飽和し、冷間加工性を劣化させるため、含有量は1.5%以下とする。好ましくは、0.35%以下である。 Cu may be contained if necessary in order to improve the corrosion resistance of the product. However, even if the content exceeds 1.5%, the effect is saturated and the cold workability is deteriorated, so the content is set to 1.5% or less. Preferably, it is 0.35% or less.
Co,Wは、製品の靭性や耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ1.5%を超えて含有させても、その効果は飽和し、冷間加工性を劣化させるため、含有量は1.5%以下とする。好ましくは、1.0%以下である。 Co and W may be contained as necessary in order to improve the toughness and corrosion resistance of the product. However, even if each content exceeds 1.5%, the effect is saturated and the cold workability is deteriorated, so the content is set to 1.5% or less. Preferably, it is 1.0% or less.
Bは、製品の靭性を向上させるため、必要に応じて含有させてもよい。しかしながら、0.01%を超えて含有させても、その効果は飽和するし、逆に粗大なボライドを生成して冷間加工性を劣化させるため、含有量は0.01%以下とする。好ましくは、0.006%以下である。 B may be contained if necessary in order to improve the toughness of the product. However, even if the content exceeds 0.01%, the effect is saturated, and conversely, coarse boride is generated and the cold workability is deteriorated. Therefore, the content is set to 0.01% or less. Preferably, it is 0.006% or less.
Sn,Sbは、製品の耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ0.3%を超えて含有させても、その効果は飽和するし、熱間製造性が著しく劣化させるため、含有量は0.3%以下とする。好ましくは、0.1%以下である。 Sn and Sb may be contained as necessary in order to improve the corrosion resistance of the product. However, even if each content exceeds 0.3%, the effect is saturated and the hot manufacturability is significantly deteriorated. Therefore, the content is set to 0.3% or less. Preferably, it is 0.1% or less.
Nb,Tiは、製品の靭性や耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ0.1%を超えて含有させても、その効果は飽和するし、逆に粗大な炭窒化物を生成して冷間加工性が劣化させるため、含有量は0.1%以下とする。好ましくは、0.06%以下である。 Nb and Ti may be contained as necessary in order to improve the toughness and corrosion resistance of the product. However, even if each content exceeds 0.1%, the effect is saturated, and conversely, coarse carbonitride is generated and the cold workability is deteriorated. Therefore, the content is 0.1% or less. And. Preferably, it is 0.06% or less.
V,Taは、製品の靭性や耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ0.2%を超えて含有させても、その効果は飽和するし、逆に粗大な炭窒化物を生成して冷間加工性が劣化させるため、含有量は0.2%以下とする。好ましくは、0.1%以下である。 V and Ta may be contained as necessary in order to improve the toughness and corrosion resistance of the product. However, even if each content exceeds 0.2%, the effect is saturated, and conversely, coarse carbonitride is generated and the cold workability is deteriorated, so that the content is 0.2% or less. And. Preferably, it is 0.1% or less.
Mg,Ca,Hf,REMは、脱酸生成物の熱力学的な安定度を増加して軟化焼鈍時の軟質化に効果があるため、必要に応じて含有させてもよい。しかしながら、それぞれ0.01%を超えて添加しても、その効果は飽和するし、逆に粗大な酸化物を生成して冷間加工性を劣化させるため、含有量を0.01%以下とする。好ましくは、0.005%以下である。
REM(希土類元素)は、一般的な定義に従い、スカンジウム(Sc)、イットリウム(Y)の2元素と、ランタン(La)からルテチウム(Lu)までの15元素(ランタノイド)の総称を指す。単独で含有させてもよいし、混合物であってもよい。Mg, Ca, Hf, and REM may be contained as necessary because they increase the thermodynamic stability of the deoxidized product and are effective in softening during softening and annealing. However, even if each is added in excess of 0.01%, the effect is saturated, and conversely, coarse oxides are generated and cold workability is deteriorated. Therefore, the content is set to 0.01% or less. To do. Preferably, it is 0.005% or less.
REM (rare earth element) is a general term for two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu), according to a general definition. It may be contained alone or as a mixture.
本発明のステンレス鋼が含有する不純物について、代表的な不純物としては、Zn,Bi,Pb,Ge,Se,Ag,Se,Te等が挙げられ、通常、鉄鋼の製造プロセスで不純物として、0.1%程度の範囲で混入する。
また、任意添加元素について、代表的なものを上記(3)〜(5)で規定しているが、本明細書中に記載されていない元素であっても、本発明の効果を損なわない範囲で含有させることができる。Regarding the impurities contained in the stainless steel of the present invention, typical impurities include Zn, Bi, Pb, Ge, Se, Ag, Se, Te, etc., and usually, as impurities in the steel manufacturing process, 0. Mix in the range of about 1%.
In addition, although typical optional additive elements are defined in (3) to (5) above, even elements not described in the present specification do not impair the effects of the present invention. Can be contained in.
《マルテンサイト系ステンレス鋼の製造方法》
次に、本発明のマルテンサイト系ステンレス鋼の製造方法について説明する。
第一に、軟化焼鈍処理条件について説明する。
前記のように、1.0μm以上の炭窒化物が1600μm2中に10個以上となる鋼として軟質化するためには、前記本発明の好適な鋼成分組成を有するとともに、軟化焼鈍処理として、870℃以上の高温で、かつ、(b)式で計算される炭化物の固溶温度:Tよりも20〜120℃低い温度範囲で1〜48hの保定熱処理を施し、引き続き平均60℃/h以下の冷却速度で徐冷することが好ましい。保定熱処理時間が1hよりも短いと炭素窒化物サイズが微細となり、軟質化が期待できず、逆に48hよりも長いと効果は飽和するし、工業的に経済合理性を失う。そのため、保定熱処理時間を1〜48hに限定する。好ましい範囲は、2〜10hである。なお、(b)式でC量による炭化物の固溶温度を計算できる。
log(C)=―6100/(T+273)+4 ・・・・・(b)
(b)式で「C」はC濃度(質量%)、「T」は炭化物の固溶温度(℃)を意味する。<< Manufacturing method of martensitic stainless steel >>
Next, the method for producing the martensitic stainless steel of the present invention will be described.
First, the softening and annealing treatment conditions will be described.
As described above, in order to soften the carbonitride of 1.0 μm or more into 10 or more steels in 1600 μm 2 , it has the suitable steel component composition of the present invention and is used as a softening annealing treatment. Solid solution temperature of carbide calculated by Eq. (B) at a high temperature of 870 ° C. or higher: A retention heat treatment of 1 to 48 h is performed in a
log (C) = -6100 / (T + 273) +4 ... (b)
In the formula (b), "C" means the C concentration (mass%), and "T" means the solid solution temperature (° C.) of the carbide.
保定熱処理温度が870℃もしくは(T−120)℃よりも低温になると炭窒化物サイズが微細になり、軟質化が期待できず、逆に(T−20)℃よりも高温で保定熱処理を実施するとフィルム状の粒界炭化物となり、冷間加工性が劣化する。なお、保定熱処理温度の好ましい範囲は、900℃以上で、かつ、Tよりも30〜100℃低い温度である。 When the retention heat treatment temperature becomes lower than 870 ° C or (T-120) ° C, the carbide size becomes finer and softening cannot be expected. On the contrary, the retention heat treatment is performed at a temperature higher than (T-20) ° C. Then, it becomes a film-like grain boundary carbide, and the cold workability deteriorates. The preferred range of the retention heat treatment temperature is 900 ° C. or higher and 30 to 100 ° C. lower than T.
保定熱処理温度からの徐冷の冷却速度について、平均60℃/hを超える冷却速度で徐冷すると、炭窒化物が微細となり、軟質化が期待できない。 Regarding the cooling rate of slow cooling from the retention heat treatment temperature, if the cooling rate is slowed down at an average cooling rate of more than 60 ° C./h, the carbonitride becomes fine and softening cannot be expected.
徐冷終了温度について、(T−250)℃まで徐冷しなかった場合、炭窒化物の微細化や硬質なマルテンサイト組織の生成により軟質化が期待できない。そのため、(T−250)℃よりも低い温度まで徐冷することが好ましい。なお、(T−250)℃よりも低い温度では特に冷却速度は規定しなくともよい。 When the slow cooling end temperature is not slowly cooled to (T-250) ° C., softening cannot be expected due to the refinement of the carbonitride and the formation of a hard martensite structure. Therefore, it is preferable to slowly cool to a temperature lower than (T-250) ° C. The cooling rate does not have to be specified at a temperature lower than (T-250) ° C.
上記の本発明の軟化焼鈍方法で炭化物サイズ、分散状態が決まるため、本発明の焼鈍方法の後に従来の焼鈍方法を適用しても効果は継続されるので、従来の焼鈍方法と組み合わせてもよい。 Since the carbide size and dispersion state are determined by the above-mentioned softening annealing method of the present invention, the effect is continued even if the conventional annealing method is applied after the annealing method of the present invention, and therefore, it may be combined with the conventional annealing method. ..
次に、本発明のマルテンサイト系ステンレス鋼の製造方法のうち、鋳造時の製造条件について説明する。
鋼中の微細な2次脱酸生成物である酸化物は凝固時に生成する。酸化物が熱力学的に不安定な場合、熱間圧延等の熱加工で分解・微細化が進み、軟化焼鈍時に転位や結晶粒界の動きをピンニングして軟化を阻害する。マルテンサイト系ステンレス鋼の場合、Al,O含有量の適正制御に加え、鋳造時の平均冷却速度を5〜500℃/sの範囲とすることにより、凝固時に生じる2次脱酸生成物の平均サイズが1μm以上5μm以下となって分解・微細化を抑制することによって軟質化することができる。一方、平均冷却速度が5℃/sよりも遅くなると脱酸生成物が5μmを超えて粗大化し、本発明の軟質化効果が不明瞭となるばかりか、冷間加工性も劣化する。一方、500℃/sよりも平均冷却速度が大きいと2次脱酸生成物のAl濃度が15%以下に低下して熱力学的に不安定となって1μm未満への分解・微細化が進み、素材の軟質化を促進し難くなる。そのため、本発明で規定する軟質化し易い微細な熱力学的に安定な酸化物のサイズを得るには5〜500℃/sの平均冷却速度で凝固させることが必要になる。好ましくは10℃/s以上、400℃/s未満である。Next, among the methods for producing martensitic stainless steel of the present invention, the production conditions at the time of casting will be described.
Oxides, which are fine secondary deoxidizing products in steel, are formed during solidification. When the oxide is thermodynamically unstable, it is decomposed and refined by thermal processing such as hot rolling, and dislocations and movements of grain boundaries are pinned during softening annealing to inhibit softening. In the case of martensitic stainless steel, in addition to proper control of Al and O contents, the average cooling rate during casting is set in the range of 5 to 500 ° C / s, so that the average of secondary deoxidation products generated during solidification It can be softened by suppressing decomposition and miniaturization when the size is 1 μm or more and 5 μm or less. On the other hand, when the average cooling rate is slower than 5 ° C./s, the deoxidized product becomes coarser than 5 μm, the softening effect of the present invention becomes unclear, and the cold workability also deteriorates. On the other hand, if the average cooling rate is higher than 500 ° C./s, the Al concentration of the secondary deoxidizing product decreases to 15% or less, becomes thermodynamically unstable, and decomposition and miniaturization to less than 1 μm progress. , It becomes difficult to promote the softening of the material. Therefore, it is necessary to solidify at an average cooling rate of 5 to 500 ° C./s in order to obtain a fine thermodynamically stable oxide size that is easily softened as defined in the present invention. It is preferably 10 ° C./s or more and less than 400 ° C./s.
以上説明した本発明によれば、軟質化特性を有して複雑形状に強冷間加工できる高硬度・高耐食性マルテンサイト系ステンレス鋼の軟化焼鈍材を安価に提供できる。 According to the present invention described above, it is possible to inexpensively provide a softened annealed material of high hardness and high corrosion resistance martensitic stainless steel which has softening characteristics and can be strongly cold-worked into a complicated shape.
<実施例1>
150kgの真空溶解炉にて表1〜表3に示す化学組成の鋼を約1600℃で溶解した後、鋳型に鋳造した。なお、Al,Si,Mn等の脱酸元素添加量と脱酸元素の溶鋼への投入から鋳型への出鋼時間でO量を変化させた。鋳型として、各種サイズ(φ20〜φ250mm)、材質(鉄系,マグネシア系,シリカ系)のものを用いることにより、凝固時の平均冷却速度を変化させた。なお、凝固時の平均冷却速度は、同じ条件で溶解・凝固させたSUS304のサンプルの鋳片の断面の1/4部および中央部の2次デンドライトアーム間隔:λを測定し、その平均値で平均冷却速度(℃/s)=(110/λ)2.2を見積もった。
その後、1200℃加熱後に熱間鍛造して直径14mmの棒鋼に熱間加工し、常温まで空冷した。その後、軟化焼鈍を行うに際し、表4〜表6に示す各温度で5hの保定熱処理を施し、20℃/hで650℃まで徐冷した。そして、軟質化状況、冷間加工性および炭窒化物や微細酸化物の状態に及ぼす成分の影響について調査した。表4〜表6に製造条件および評価結果について示す。<Example 1>
Steels having the chemical compositions shown in Tables 1 to 3 were melted at about 1600 ° C. in a 150 kg vacuum melting furnace and then cast into a mold. The amount of O was changed depending on the amount of deoxidizing elements added such as Al, Si, and Mn and the time from the addition of the deoxidizing elements to the molten steel to the delivery time to the mold. By using various sizes (φ20 to φ250 mm) and materials (iron-based, magnesia-based, silica-based) as the mold, the average cooling rate during solidification was changed. The average cooling rate during solidification is the average value obtained by measuring the secondary dendrite arm spacing: λ in the 1/4 part of the cross section and the central part of the slab of the SUS304 sample melted and solidified under the same conditions. The average cooling rate (° C./s) = (110 / λ) 2.2 was estimated.
Then, after heating at 1200 ° C., it was hot forged, hot-worked into a steel bar having a diameter of 14 mm, and air-cooled to room temperature. Then, when the softening annealing was performed, a retention heat treatment for 5 hours was performed at each temperature shown in Tables 4 to 6, and the temperature was gradually cooled to 650 ° C. at 20 ° C./h. Then, the influence of the components on the softening condition, cold workability and the state of carbonitride and fine oxide was investigated. Tables 4 to 6 show the manufacturing conditions and evaluation results.
軟質化について、前記棒鋼を長手方向中心断面に埋め込み研磨し、荷重1kgで断面の直径の1/4部および中心部のHv硬さを測定し、その平均値で評価し、表4〜表6に示した。表中、Hvの右隣に(a)式右辺(60C+170)の値を示している。 For softening, the steel bar was embedded in the central cross section in the longitudinal direction and polished, and the Hv hardness of 1/4 of the diameter of the cross section and the central part was measured with a load of 1 kg and evaluated by the average value. Tables 4 to 6 It was shown to. In the table, the value of the right side (60C + 170) of the equation (a) is shown on the right side of Hv.
冷間加工性は、φ8mm,高さ12mmの圧縮試験片を作成し、高さ方向に10/sの歪み速度で端面圧縮加工を施し、割れなく冷間圧縮加工が可能か否かで判断した。なお、鋼材の冷間加工性はC量(質量%)に依存し、C量が高いほど冷間加工性が低下する性質があるため、限界加工率をC量の式として規定する。(85−50C)%の限界加工率で冷間圧縮加工が可能であれば「B」、割れが発生した場合を「X」、さらに(90−50C)%の限界加工率で冷間圧縮加工が可能であれば「A」で評価した。本発明鋼では全てBまたはAであり、優れた冷間加工性を示していた。なお、加工率とは、(12−H)/12×100(%)であり、Hは冷間圧縮加工後の試験片の厚さ(mm)である。 For cold workability, a compression test piece with a diameter of 8 mm and a height of 12 mm was prepared, end face compression processing was performed at a strain rate of 10 / s in the height direction, and it was judged whether or not cold compression processing was possible without cracking. .. The cold workability of the steel material depends on the amount of C (mass%), and the higher the amount of C, the lower the cold workability. Therefore, the limit workability is defined as the formula for the amount of C. "B" if cold compression processing is possible at the limit processing rate of (85-50C)%, "X" if cracks occur, and cold compression processing at the limit processing rate of (90-50C)% Was evaluated as "A" if possible. All of the steels of the present invention were B or A, and showed excellent cold workability. The processing rate is (12-H) / 12 × 100 (%), and H is the thickness (mm) of the test piece after cold compression processing.
炭窒化物の分散状態は、埋め込み研磨面を王水にてエッチングし、SEM・EDSにて評価した。1600μm2中に直径1μmサイズ以上の炭窒化物が10個以上ある場合を「B」、1600μm2中に直径2μmサイズ以上の炭窒化物が10個以上ある場合を「A」、それ以外を「X」で評価した。本発明鋼では全てBまたはAであり、優れた冷間加工性に資する炭窒化物の分散状態を示していた。なお、サイズの直径とは(長径+短径)/2で計算される。炭窒化物とはEDS分析にてCr、Fe、C、Nを主体とする析出物である。The dispersed state of the carbonitride was evaluated by SEM / EDS after etching the embedded polished surface with aqua regia. "B" if the 1600 .mu.m carbonitride or more in diameter 1μm size during 2 is 10 or more, "A" if the carbonitride above diameter 2μm size in 1600 .mu.m 2 is 10 or more, the rest " It was evaluated by "X". In the steel of the present invention, all of them were B or A, and showed a dispersed state of the carbonitride which contributed to excellent cold workability. The diameter of the size is calculated by (major axis + minor axis) / 2. The carbonitride is a precipitate mainly composed of Cr, Fe, C, and N in EDS analysis.
酸化物の平均サイズおよび酸化物の組成の評価については、炭窒化物の影響を除くため1150℃から空冷の焼入れ処理した材料を用いて評価した。表層を#500研磨した鋼材を非水溶液中(3%のマレイン酸+1%のテトラメチルアンモニウムクロイド+残部メタノール)で電解(100mV定電圧)して、マトリックスを溶解し、フィルターでろ過して、酸化物を抽出した。その後、フィルター上に残った酸化物について、SEM・EDSにて、任意に30個の酸化物の直径サイズを測定して平均直径サイズを算出した。酸化物とはEDS分析にてOとAl,Mn,Si,Fe,Cr,Ti等の組成が主体の非金属介在物を意味する。直径のサイズとは(長径+短径)/2で計算される。観察される介在物のうち15μm以下のサイズのものを、2次脱酸生成物であるとして上記酸化物サイズの判定に用いた。
また、任意に20個の酸化物を選定して組成分析を実施した。なお、熱間鍛造材についても同様に酸化物の組成分析を実施し、本焼入れ処理で酸化物の状態が変化していないことを確認している。EDS分析にてOとAl,Mn,Si,Fe,Cr,Ti等の組成が主体の非金属介在物を酸化物とし、Sを除いたものの合計を100%換算し、Alの質量%を算出した。The average size of the oxide and the composition of the oxide were evaluated using a material hardened by air cooling from 1150 ° C. in order to eliminate the influence of the carbonitride. A steel material whose surface layer is # 500 polished is electrolyzed (100 mV constant voltage) in a non-aqueous solution (3% maleic acid + 1% tetramethylammonium cloid + residual methanol) to dissolve the matrix, filtered with a filter, and oxidized. The thing was extracted. Then, for the oxides remaining on the filter, the diameter sizes of 30 oxides were arbitrarily measured by SEM / EDS to calculate the average diameter size. Oxide means a non-metal inclusion mainly composed of O and Al, Mn, Si, Fe, Cr, Ti and the like in EDS analysis. The diameter size is calculated by (major axis + minor axis) / 2. Among the observed inclusions, those having a size of 15 μm or less were regarded as secondary deoxidation products and used for determining the oxide size.
In addition, composition analysis was carried out by arbitrarily selecting 20 oxides. In addition, the composition analysis of the oxide was also carried out for the hot forged material, and it was confirmed that the state of the oxide did not change during the main quenching treatment. In EDS analysis, non-metal inclusions mainly composed of O and Al, Mn, Si, Fe, Cr, Ti, etc. are used as oxides, and the total excluding S is converted to 100% to calculate the mass% of Al. did.
粗大な酸化物の評価について、前記の埋め込み研磨材を光学顕微鏡にて観察し、長径が30μm以上の粗大な酸化物がある場合、表6の備考欄に「粗大酸化物」と記載した。 Regarding the evaluation of the coarse oxide, the above-mentioned embedded abrasive was observed with an optical microscope, and when there was a coarse oxide having a major axis of 30 μm or more, it was described as “coarse oxide” in the remarks column of Table 6.
本発明のマルテンサイト系ステンレス鋼は、高硬度・高耐食性用途であり、冷間加工後に焼き入れ処理を施して最終製品とした段階で、高硬度・高耐食性を具備していることが要求される。
高硬度特性については、冷間加工後にT+50℃の温度から空冷の焼き入れを行い、Hv硬さ評価を行った。Hv500以上であれば本発明の要件を具備しえいる。実施例において、焼き入れ後にHv500未満の場合に表6の備考欄に「焼き入れ硬さ不足」と記載した。
耐食性特性については、冷間加工後にT+50℃の温度から空冷の焼き入れを行い、表面を#500研磨後にJISの中性塩水噴霧試験で24hの塩水噴霧で耐食性評価を行い、赤錆が発生しなければ良好な耐食性を具備している。実施例において、赤錆びが発生した場合(端部除く)に表6の備考欄に「耐食性不足」と記載した。The martensitic stainless steel of the present invention is used for high hardness and high corrosion resistance, and is required to have high hardness and high corrosion resistance at the stage of quenching after cold working to make a final product. To.
For the high hardness characteristics, after cold working, air-cooled quenching was performed from a temperature of T + 50 ° C., and Hv hardness was evaluated. If it is Hv500 or higher, the requirements of the present invention can be satisfied. In the examples, when the Hv was less than 500 after quenching, "insufficient quenching hardness" was described in the remarks column of Table 6.
Regarding the corrosion resistance characteristics, after cold working, air-cooling quenching is performed from a temperature of T + 50 ° C., and after polishing the surface with # 500, corrosion resistance is evaluated by spraying salt water for 24 hours in the JIS neutral salt spray test, and red rust must occur. It has good corrosion resistance. In the examples, when red rust occurred (excluding the end portion), "insufficient corrosion resistance" was described in the remarks column of Table 6.
表4、表5の本発明例は1〜63である。製品の硬さについて、本発明例ではHv硬さで(60C+170)以下が得られており、また、大半で好ましいHv硬さである(60C+160)以下が得られた。冷間加工性について、本発明鋼では全てBまたはAであり、優れた冷間加工性に資する炭窒化物の分散状態を示していた。 Examples of the present invention in Tables 4 and 5 are 1 to 63. Regarding the hardness of the product, in the example of the present invention, the Hv hardness was (60C + 170) or less, and in most cases, the preferable Hv hardness (60C + 160) or less was obtained. Regarding the cold workability, all of the steels of the present invention were B or A, indicating a dispersed state of the carbonitride that contributes to excellent cold workability.
発明例1〜3、7〜15,17〜50、52は、Al含有量が0.01〜0.2%、O含有量が0.001〜0.006の好適範囲にあり、軟質化に資する酸化物状態を示していた。また、1〜5μmサイズの酸化物の平均Al濃度は15〜40質量%の好適範囲にある。 Inventive Examples 1 to 3, 7 to 15, 17 to 50, 52 have an Al content of 0.01 to 0.2% and an O content of 0.001 to 0.006 in a preferable range for softening. It showed a contributing oxide state. The average Al concentration of an oxide having a size of 1 to 5 μm is in a preferable range of 15 to 40% by mass.
一方、表6に示す比較例1〜22では、鋼の成分組成が本発明から外れ、あるいは凝固速度が本発明の好適条件から外れており、炭窒化物の分布状態、酸化物平均サイズが本発明の規定範囲を満たしておらず、所要の特性を満足していないことがわかる。
比較例1、3、5は凝固冷却速度が速く、比較例19はAlが過少であり、いずれも酸化物の平均直径サイズが過小であるため、Hvが高くなり、冷間加工性が不良であった。比較例2、4、6は凝固冷却速度が遅く、酸化物の平均直径サイズが過大であるため、冷間加工性が不良であった。
比較例8〜10、13、17、18、21は、それぞれC、Si、Mn、Ni、Mo、Al、C+N/2が過多であり、Hvが高くなり、冷間加工性が不良であった。加えて比較例9、17は炭窒化物の分散状態も不良であった。
比較例7はCが過少であり、比較例15はCrが過多であり、焼入れ硬さ不足となった。比較例14はCrが過少であり、比較例16はMoが過少であり、耐食性不足となった。
比較例18はAlが過多であり、比較例22はOが過多であり、粗大な酸化物が形成されるとともに、冷間加工性が不良であった。On the other hand, in Comparative Examples 1 to 22 shown in Table 6, the composition of the steel is out of the present invention, or the solidification rate is out of the preferable conditions of the present invention, and the distribution state of the carbonitride and the average oxide size are the present. It can be seen that the specified range of the invention is not satisfied and the required characteristics are not satisfied.
In Comparative Examples 1, 3 and 5, the solidification cooling rate is high, and in Comparative Example 19, Al is too small, and the average diameter size of the oxide is too small in each case, so that Hv is high and cold workability is poor. there were. In Comparative Examples 2, 4 and 6, the solidification cooling rate was slow and the average diameter size of the oxide was excessive, so that the cold workability was poor.
In Comparative Examples 8 to 10, 13, 17, 18, and 21, C, Si, Mn, Ni, Mo, Al, and C + N / 2, respectively, were excessive, Hv was high, and cold workability was poor. .. In addition, in Comparative Examples 9 and 17, the dispersed state of the carbonitride was also poor.
In Comparative Example 7, C was too small, and in Comparative Example 15, Cr was too much, resulting in insufficient quenching hardness. In Comparative Example 14, Cr was too small, and in Comparative Example 16, Mo was too small, resulting in insufficient corrosion resistance.
In Comparative Example 18, Al was excessive, and in Comparative Example 22, O was excessive, coarse oxides were formed, and cold workability was poor.
<実施例2>
次に、軟化焼鈍材の製造方法の影響を調査した。前述で製造した本発明鋼Cの熱間鍛造材のφ14mm棒鋼について、種々の条件で軟化焼鈍を施し、軟質化、冷間加工性および炭窒化物の状態に及ぼす製造方法の影響について調査した。なお、軟化焼鈍時には微細酸化物の状態は変化しないため本実施例では酸化物の調査は実施していない。表7に軟化焼鈍材の製造方法と調査結果を示す。<Example 2>
Next, the influence of the manufacturing method of the softened annealed material was investigated. The φ14 mm steel bar of the hot forged material of the steel C of the present invention produced above was softened and annealed under various conditions, and the influence of the manufacturing method on the softening, cold workability and the state of the carbonitride was investigated. Since the state of fine oxides does not change during softening and annealing, the oxides were not investigated in this example. Table 7 shows the manufacturing method and survey results of the softened annealed material.
発明例7、53〜55、57〜63ではいずれも優れた冷間加工性に資する炭窒化物の分散状態を示し、冷間鍛造性に優れていた。発明例63では、表5の備考に「軟化焼鈍追加」と記載したように、本発明条件での軟化焼鈍を実施した後に、従来の850℃−2h保定後、30℃/hで700℃まで徐冷して脱炉する軟化焼鈍を付与している例である。品質は良好であり、本発明の効果が引き継がれている。 In Invention Examples 7, 53 to 55, 57 to 63, all of them showed a dispersed state of the carbonitride contributing to excellent cold workability, and were excellent in cold forging property. In Invention Example 63, as described in the remarks in Table 5, "additional softening annealing", after the softening annealing under the conditions of the present invention, after the conventional 850 ° C.-2h retention, up to 700 ° C. at 30 ° C./h. This is an example in which soft annealing is applied to slowly cool and degas. The quality is good and the effects of the present invention are inherited.
一方、比較例22〜26では、軟化焼鈍条件が本発明の規定範囲を満たしておらず、本発明の炭窒化物の分散状態やHv硬さ、優れた冷間加工性を満足していないことがわかる。 On the other hand, in Comparative Examples 22 to 26, the softening and annealing conditions did not satisfy the specified range of the present invention, and did not satisfy the dispersed state of the carbonitride of the present invention, the Hv hardness, and the excellent cold workability. I understand.
以上の各実施例から明らかなように、本発明により、冷間加工性に優れる高硬度・高耐食用途のマルテンサイト系ステンレス鋼の軟化焼鈍材を安定的に提供することができ、冷間加工で大量生産することで部品の製造コストを大幅に低減でき、産業上極めて有用である。 As is clear from each of the above examples, according to the present invention, it is possible to stably provide a softened annealed material of martensitic stainless steel for high hardness and high corrosion resistance, which is excellent in cold workability, and cold working. Mass production in stainless steel can significantly reduce the manufacturing cost of parts, which is extremely useful in industry.
Claims (5)
C:0.15〜0.70%
Si:2.0%以下、
Mn:1.5%以下、
S:0.01%未満、
P:0.05%以下、
Ni:1.5%以下、
Cr:10.5〜16.0%、
Mo:0.9〜3.0%、
N:0.01〜0.14%、
Al:0.008〜1.0%、
O:0.001〜0.008%を含有し、
残部Feおよび不純物からなる化学成分を有し、
C+N/2:0.16〜0.70%であり、
かつ、1.0μm以上の炭窒化物が1600μm2中に10個以上であり、2次脱酸生成物である酸化物の平均直径サイズが1〜5μmであり、前記酸化物の平均Al濃度が15〜40質量%であり、(a)式で示されるHv硬さであることを特徴とするマルテンサイト系ステンレス鋼。
Hv≦60C+170 ・・・・・・・・・・・・・・・・(a)
C:C含有量(質量%) By mass%
C: 0.15 to 0.70%
Si: 2.0% or less,
Mn: 1.5% or less,
S: less than 0.01%,
P: 0.05% or less,
Ni: 1.5% or less,
Cr: 10.5 to 16.0%,
Mo: 0.9-3.0%,
N: 0.01-0.14%,
Al: 0.008 to 1.0%,
O: Contains 0.001 to 0.008%,
It has a chemical component consisting of the balance Fe and impurities,
C + N / 2: 0.16 to 0.70%,
In addition, there are 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 , the average diameter size of the oxide as the secondary deoxidizing product is 1 to 5 μm, and the average Al concentration of the oxide is A martensitic stainless steel having an Hv hardness of 15 to 40% by mass and represented by the formula (a).
Hv ≦ 60C + 170 ・ ・ ・ ・ ・ (a)
C: C content (mass%)
Cu:1.5%以下、
W:1.5%以下、
Co:1.5%以下
B:0.01%以下、
Sn:0.3%以下、
Sb:0.3%以下の内、1種類以上を含有することを特徴とする請求項1に記載のマルテンサイト系ステンレス鋼。 Instead of a part of the Fe, in% by mass,
Cu: 1.5% or less,
W: 1.5% or less,
Co: 1.5% or less B: 0.01% or less,
Sn: 0.3% or less,
The martensitic stainless steel according to claim 1, wherein Sb: contains one or more of 0.3% or less.
Nb:0.1%以下、
Ti:0.1%以下、
V:0.2%以下、
Ta:0.2%以下の内、1種類以上を含有することを特徴とする請求項1または請求項2に記載のマルテンサイト系ステンレス鋼。 Instead of a part of the Fe, in% by mass,
Nb: 0.1% or less,
Ti: 0.1% or less,
V: 0.2% or less,
The martensitic stainless steel according to claim 1 or 2, wherein Ta: contains one or more of 0.2% or less.
Mg:0.01%以下、
Ca:0.01%以下、
Hf:0.01%以下、
REM:0.01%以下の内、1種類以上を含有することを特徴とする請求項1〜請求項3のいずれか1項に記載のマルテンサイト系ステンレス鋼。 Instead of a part of the Fe, in% by mass,
Mg: 0.01% or less,
Ca: 0.01% or less,
Hf: 0.01% or less,
REM: The martensitic stainless steel according to any one of claims 1 to 3, wherein the martensitic stainless steel contains one or more of 0.01% or less.
軟化焼鈍処理として、
870℃よりも高く、C濃度と下記(b)式で表される炭化物の固溶温度:Tよりも20〜120℃低い温度範囲で1〜48hの熱処理を施し、引き続き平均60℃/h以下の冷却速度でTよりも250℃低い温度まで除冷することを特徴とする請求項1〜請求項4のいずれか1項に記載のマルテンサイト系ステンレス鋼の製造方法。
log(C) = −6100/(T+273) + 4 ・・・・・(b)
(b)式で「C」はC濃度(質量%)、「T」は炭化物の固溶温度(℃)を意味する。 The average cooling rate during solidification during casting is 5 to 500 ° C./s.
As a softening annealing treatment
Heat treatment is performed for 1 to 48 hours in a temperature range higher than 870 ° C., C concentration and solid solution temperature of carbide represented by the following formula (b): 20 to 120 ° C. lower than T, and the average is 60 ° C./h or less. The method for producing a martensitic stainless steel according to any one of claims 1 to 4 , wherein the cold is cooled to a temperature 250 ° C. lower than T at the cooling rate of.
log (C) = -6100 / (T + 273) + 4 ... (b)
In the formula (b), "C" means the C concentration (mass%), and "T" means the solid solution temperature (° C.) of the carbide.
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