JP4327030B2 - Low Ni austenitic stainless steel with excellent overhanging and rust resistance - Google Patents
Low Ni austenitic stainless steel with excellent overhanging and rust resistance Download PDFInfo
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- 229910000963 austenitic stainless steel Inorganic materials 0.000 title claims description 33
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 title claims description 14
- 238000005482 strain hardening Methods 0.000 claims description 25
- 229910001566 austenite Inorganic materials 0.000 claims description 15
- 229910001220 stainless steel Inorganic materials 0.000 claims description 11
- 239000010935 stainless steel Substances 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 9
- 229910052799 carbon Inorganic materials 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 229910018553 Ni—O Inorganic materials 0.000 claims 1
- 229910052742 iron Inorganic materials 0.000 claims 1
- 229910000831 Steel Inorganic materials 0.000 description 18
- 239000010959 steel Substances 0.000 description 18
- 239000000463 material Substances 0.000 description 14
- 230000000694 effects Effects 0.000 description 9
- 229910000734 martensite Inorganic materials 0.000 description 7
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- 238000005554 pickling Methods 0.000 description 6
- 230000009466 transformation Effects 0.000 description 6
- 238000000137 annealing Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 238000005728 strengthening Methods 0.000 description 5
- 238000009864 tensile test Methods 0.000 description 5
- 238000000465 moulding Methods 0.000 description 4
- 229910052698 phosphorus Inorganic materials 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 238000002791 soaking Methods 0.000 description 3
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 229910021591 Copper(I) chloride Inorganic materials 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000004035 construction material Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- OXBLHERUFWYNTN-UHFFFAOYSA-M copper(I) chloride Chemical compound [Cu]Cl OXBLHERUFWYNTN-UHFFFAOYSA-M 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000005347 demagnetization Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 230000005389 magnetism Effects 0.000 description 1
- 230000005415 magnetization Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 125000000896 monocarboxylic acid group Chemical group 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
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Description
本発明は、省Ni型のオ−ステナイト系ステンレス鋼であって、軟質で適度な加工硬化性を有し張出し性に優れるとともに,良好な耐発銹性を兼備した低Niオ−ステナイト系ステンレス鋼に関する。 The present invention is a Ni-saving austenitic stainless steel, which is soft, has an appropriate work-hardening property, has excellent overhanging properties, and has good galling resistance. Related to steel.
オ−ステナイト系ステンレス鋼は、JISG4305に規定される300系(SUS304,SUS316,SUS301等)や200系(SUS201,SUS202等)のものがある。 As the austenitic stainless steel, there are 300 series (SUS304, SUS316, SUS301, etc.) and 200 series (SUS201, SUS202, etc.) defined in JIS G4305.
300系のオ−ステナイト系ステンレス鋼は、Mnが2.0質量%以下,Niが6〜15質量%程度含まれる。SUS304に代表されるNi系のオ−ステナイト系ステンレス鋼は、良好な加工性を有し耐食性にも優れる。特に、SUS304は、オ−ステナイト相が準安定であり,成形加工中にマルテンサイト変態を生じて加工硬化が大きくなるために、張出し性が良好である。しかし、SUS304は、高価なNiを多量に含むことから原料コストが高いという欠点がある。 300 series austenitic stainless steel contains 2.0 mass% or less of Mn and about 6 to 15 mass% of Ni. Ni-based austenitic stainless steel typified by SUS304 has good workability and excellent corrosion resistance. In particular, SUS304 has a good overhanging property because the austenite phase is metastable and a martensitic transformation occurs during the molding process to increase work hardening. However, SUS304 has a drawback that the raw material cost is high because it contains a large amount of expensive Ni.
他方、200系のオ−ステナイト系ステンレス鋼は、NiをMnで置換した高Mnステンレス鋼であり、CやNを多く含むために強度が高く非磁性である。また、Ni系のオ−ステナイト系ステンレス鋼と比較して原料コストが安価である。しかし、SUS201やSUS202等に代表される高Mnステンレス鋼は、焼鈍状態において300系と比較して強度が高いために冷間加工性やプレス成形性に劣るという問題がある。 On the other hand, the 200-series austenitic stainless steel is a high Mn stainless steel in which Ni is replaced with Mn, and has a high strength and is nonmagnetic because it contains a large amount of C and N. Moreover, the raw material cost is low compared with Ni-type austenitic stainless steel. However, high Mn stainless steel represented by SUS201, SUS202, and the like has a problem that it is inferior in cold workability and press formability because it is higher in strength than 300 series in the annealed state.
オ−ステナイト系ステンレス鋼の加工性を改善する手段に関し、Mnが3%未満,Niが6%以上を含む300系については従来から多くの検討がなされている。例えば、特許文献1,特許文献2,特許文献3,特許文献4,特許文献5等に開示されているように、プレス成形性等の加工性改善には、Cuの添加が有効に作用することが知られている。
With respect to means for improving the workability of austenitic stainless steel, many studies have been made on the 300 series containing Mn of less than 3% and Ni of 6% or more. For example, as disclosed in
他方、200系のオ−ステナイト系ステンレス鋼は、電子機器用シャフト材,自転車スポ−クス用線,建築,建材用釘等の高強度非磁性が要求される部材への適用が主体である。そのため、高Mnステンレス鋼は、高強度非磁性化の更なる向上に関し、多くの検討がなされている。例えば、特許文献6,特許文献7等には、高強度・非磁性化には、高N化とあわせてMnやCrの増加を抑制してNb,Mo,Pの微量添加が有効に作用することが開示されている。 On the other hand, the 200 series austenitic stainless steel is mainly applied to members requiring high-strength non-magnetism such as shaft materials for electronic equipment, wires for bicycle spokes, nails for construction, and building materials. Therefore, many studies have been made on high Mn stainless steel for further improvement of high strength non-magnetization. For example, in Patent Document 6, Patent Document 7 and the like, to increase the strength and demagnetization, the addition of a small amount of Nb, Mo, and P effectively works by suppressing the increase in Mn and Cr in conjunction with increasing N. It is disclosed.
上述した通り、低Niオ−ステナイト系ステンレス鋼は、SUS304に代表されるNi系のステンレス鋼が使用されるプレス成形用途へ適応するための加工性の改善を意図したものでない。すなわち、SUS304と同等以上の優れた張出し性を具備した低Niオ−ステナイト系ステンレス鋼は未だ出現していないのが現状である。 As described above, the low Ni austenitic stainless steel is not intended to improve the workability for adapting to the press forming application in which the Ni stainless steel represented by SUS304 is used. That is, the present situation is that a low Ni austenitic stainless steel having an overhanging property equivalent to or better than that of SUS304 has not yet appeared.
本発明は、上述した低Niオ−ステナイト系ステンレス鋼の加工性を改善すべく案出されたものであり、C+NやMn等の元素,オ−ステナイト安定度の指標Md30値(℃),積層欠陥エネルギ−の生成指標SFE(mJ/m2)が特定条件を満足するよう成分設計を行うことにより、SUS304と同等以上の張出し性を具備し,SUS304と遜色ない耐発銹性を有する低Niオ−ステナイト系ステンレス鋼を提供することを目的とする。 The present invention has been devised to improve the workability of the above-described low Ni austenitic stainless steel, elements such as C + N and Mn, an austenite stability index Md30 value (° C.), lamination By designing the components so that the defect energy generation index SFE (mJ / m 2 ) satisfies a specific condition, the Ni is low Ni having an overhanging property equal to or higher than that of SUS304 and having an anti-fogging property comparable to that of SUS304. An object is to provide an austenitic stainless steel.
(1)本発明の低Niオ−ステナイト系ステンレス鋼は、その目的を達成するために、質量%で、C+N:0.03〜0.20%,Si:1%以下,Mn:2〜7%,Cr:10〜16%,Ni:1〜6%,Cu:1〜3%,残部Feおよび不可避的不純物からなり、オ−ステナイト安定度の指標Md30値と積層欠陥エネルギ−の生成指標SFEが下記を満足するように成分設計されていることを特徴とする。
30<Md30<65,40<SFE<70
Md30(℃):497−462(C+N)−9.2Si−8.1Mn−13.7Cr−20(Ni+Cu)−18.5Mo
SFE(mJ/m2):6.2Ni+18.6Cu+0.7Cr+3.2Mn+9.3Mo−53
(2)この低Niオ−ステナイト系ステンレス鋼は、良好な耐発銹性を得るために、S:0.0025質量%以下、P:0.040質量%以下とすることができる。
(3)この低Niオ−ステナイト系ステンレス鋼は、良好な耐発銹性を得るために、Moを0.3〜3.0質量%含むことができる。
(4)高い加工率で張出し加工ができるプレス成形性を確保するには、C+Nが0.2質量%以下,引張試験で求められる0.2%耐力が300MPa未満,真応力−対数伸び歪曲線で公称歪10%と30%の勾配である加工硬化指数nが0.40〜0.60,伸びを45%以上とする。
(1) The low Ni austenitic stainless steel of the present invention is, in mass%, C + N: 0.03 to 0.20%, Si: 1% or less, Mn: 2 to 7 in order to achieve the object. %, Cr: 10 to 16%, Ni: 1 to 6%, Cu: 1 to 3%, balance Fe and inevitable impurities, and austenite stability index Md30 value and stacking fault energy generation index SFE Is designed to satisfy the following conditions.
30 <Md30 <65, 40 <SFE <70
Md30 (° C): 497-462 (C + N) -9.2Si-8.1Mn-13.7Cr-20 (Ni + Cu) -18.5Mo
SFE (mJ / m 2 ): 6.2Ni + 18.6Cu + 0.7Cr + 3.2Mn + 9.3Mo-53
(2) This low Ni austenitic stainless steel can be made to have S: 0.0025 mass% or less and P: 0.040 mass% or less in order to obtain good galling resistance.
(3) This low Ni austenitic stainless steel can contain 0.3 to 3.0% by mass of Mo in order to obtain good cracking resistance.
(4) In order to ensure press formability that can be stretched at a high processing rate, C + N is 0.2% by mass or less, 0.2% proof stress obtained by a tensile test is less than 300 MPa, and true stress-logarithmic elongation strain curve The work hardening index n, which is a gradient of 10% nominal strain and 30%, is 0.40 to 0.60, and the elongation is 45% or more.
本発明の低Niオ−ステナイト系ステンレス鋼は、C+N:0.03〜0.20%,Mn:2〜7%,30<Md30<65,40<SFE<70とする成分設計を採用しているため、0.2%耐力が300MPa未満の軟質で適度な加工硬化性を有し,高い加工率で張出し加工ができる優れたプレス成形性を有する。必要に応じて、SやPの不純物元素を低減し,Moを添加することにより、更に良好な耐発銹性を兼備することができる。従って、従来の低Niオ−ステナイト系ステンレス鋼ではなし得なかった成形加工が可能であり、良好な耐発銹性を兼備することから、SUS304に代表されるNi系ステンレス鋼が使用されている成形加工用の材料として広範囲な分野で適用可能である。 The low Ni austenitic stainless steel of the present invention adopts a component design such that C + N: 0.03 to 0.20%, Mn: 2 to 7%, 30 <Md30 <65, 40 <SFE <70. Therefore, it has a soft and moderate work curability with a 0.2% proof stress of less than 300 MPa, and an excellent press formability capable of being stretched at a high processing rate. If necessary, the impurity elements of S and P can be reduced and Mo can be added to further improve the rust resistance. Therefore, it is possible to perform the forming process that could not be achieved with the conventional low Ni austenitic stainless steel, and since it has good galling resistance, Ni stainless steel represented by SUS304 is used. It can be applied in a wide range of fields as a material for molding.
本発明の低Niオ−ステナイト系ステンレス鋼は、C+N,Mn,オ−ステナイト安定度の指標Md30値(℃),積層欠陥エネルギ−の生成指標SFE(mJ/m2)が適正範囲を満足する成分設計を採用することにより、SUS304と同等以上の張出し性を具備している。必要に応じて、SやPの不純物元素を低減し,Moを添加することにより、更に良好な耐発銹性を得ることができる。 In the low Ni austenitic stainless steel of the present invention, C + N, Mn, austenite stability index Md30 value (° C.), stacking fault energy generation index SFE (mJ / m 2 ) satisfy an appropriate range. By adopting the component design, it has an overhang property equal to or higher than that of SUS304. If necessary, the impurity element of S or P can be reduced and Mo can be added to obtain even better weathering resistance.
以下、本発明の低Niオ−ステナイト系ステンレス鋼の成分設計に関する作用効果とその限定理由を説明する。 Hereafter, the effect regarding the component design of the low Ni austenitic stainless steel of this invention and the reason for the limitation are demonstrated.
C+N:0.03〜0.20%
CやNは、オ−ステナイト相の安定化やδフェライト相の生成抑制に有効な元素である。他方、これら元素は、固溶強化により鋼材の0.2%耐力を上昇させて加工性を低下させる。そこで、C+Nの上限は0.20%とした。NはCと比較して0.2%耐力を上昇させる作用が大きいために、NはCより低く設計することが好ましい。本発明が目的とする高い加工率で張出し加工などのプレス成形が要求される用途には、C+Nを0.20%以下(N<C)に設計することにより、鋼材の0.2%耐力を300MPa未満に軟質化することが有効である。好ましくは、C+Nを0.15%以下とする。
C + N: 0.03 to 0.20%
C and N are effective elements for stabilizing the austenite phase and suppressing the formation of the δ ferrite phase. On the other hand, these elements increase the 0.2% proof stress of the steel material by solid solution strengthening and reduce workability. Therefore, the upper limit of C + N is set to 0.20%. Since N has a large effect of increasing the proof stress by 0.2% compared to C, it is preferable to design N to be lower than C. For applications that require press forming such as overhanging at a high processing rate that is the object of the present invention, the C + N is designed to be 0.20% or less (N <C), so that the 0.2% proof stress of the steel material can be achieved. It is effective to soften to less than 300 MPa. Preferably, C + N is 0.15% or less.
しかし、C+Nが0.03%未満の場合、オ−ステナイト相を確保することが困難になるばかりでなく,CやNを低減するための製鋼コストの負担を招く。従って、C+Nの下限は0.03%とする。好ましくは0.08%以上とする。 However, when C + N is less than 0.03%, not only is it difficult to secure the austenite phase, but also the burden of steelmaking costs for reducing C and N is caused. Therefore, the lower limit of C + N is 0.03%. Preferably it is 0.08% or more.
Mn:2〜7%
Mnは溶製時の脱酸剤として使用されることに加え,Niの代替としてのオ−ステナイト形成元素として有効に作用する。本発明では、これらの作用を得るためにMnは2%以上添加する。好ましくは3%以上である。他方、Mnの添加はS系介在物の増加をもたらし,耐発銹性を阻害するという問題がある。さらに、Mnの添加量が多いと、オ−ステナイト相が安定となり、成形加工中のマルテンサイト変態(α‘相の生成)が抑制されて張出し性が低下することが分かった。従って、本発明では、耐発銹性の確保と良好な張出し性を得るために、Mnの上限は7%とする。好ましくは6.5%以下である。
Mn: 2-7%
In addition to being used as a deoxidizer during melting, Mn effectively acts as an austenite forming element as a substitute for Ni. In the present invention, 2% or more of Mn is added to obtain these effects. Preferably it is 3% or more. On the other hand, the addition of Mn causes an increase in S-based inclusions, and there is a problem that the rust resistance is inhibited. Furthermore, it was found that when the amount of Mn added is large, the austenite phase becomes stable, the martensite transformation (formation of α ′ phase) during the molding process is suppressed, and the stretchability is lowered. Therefore, in the present invention, the upper limit of Mn is set to 7% in order to secure the rust resistance and obtain the good overhanging property. Preferably it is 6.5% or less.
オ−ステナイト安定度の指標:Md30値(℃)
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。加工によって変態点を生じる上限温度はMd値と呼ばれる。すなわち、Md値はオ−ステナイトの安定度を示す指標である。そして、引張変形によって30%の歪を与えたとき、50%のマルテンサイトが生じる温度をMd30値という。Md30=497−462(C+N)−9.2Si−8.1Mn−13.7Cr−20(Ni+Cu)−18.5Mo と定義するMd30値(℃)を本発明の低Niオ−ステナイト系ステンレス鋼において30℃〜65℃の範囲に設計することにより、本発明が目的とする張出し性が確保されることを見出した。
Austenite stability index: Md30 value (° C)
Metastable austenitic stainless steel undergoes martensitic transformation by plastic working even at temperatures above the Ms point. The upper limit temperature at which the transformation point is generated by processing is called the Md value. That is, the Md value is an index indicating the stability of austenite. The temperature at which 50% martensite is generated when 30% strain is applied by tensile deformation is referred to as the Md30 value. In the low Ni austenitic stainless steel of the present invention, the Md30 value (° C.) defined as Md30 = 497-462 (C + N) -9.2Si-8.1Mn-13.7Cr-20 (Ni + Cu) -18.5Mo It has been found that by designing in the range of 30 ° C. to 65 ° C., the desired overhanging property of the present invention is secured.
Md30値が30℃より小さい場合、オ−ステナイト安定度が高いために鋼材の加工誘起マルテンサイト変態が抑制されて加工硬化が小さくなり張出し性が低下する。他方、Md30値が65℃を越える場合、加工誘起マルテンサイトの生成量(α‘相)が多くなり過度な強度上昇により鋼材の伸びが低下する。そのため、良好な張出し性は得られない。Md30値が30〜65℃の場合,本発明の低Niオ−ステナイト系ステンレス鋼は、加工誘起マルテンサイト変態により適度な加工硬化能を有し、良好な張出し性を得ることができる。 When the Md30 value is smaller than 30 ° C., since the austenite stability is high, the work-induced martensitic transformation of the steel material is suppressed, the work hardening is reduced, and the stretchability is lowered. On the other hand, when the Md30 value exceeds 65 ° C., the production amount (α ′ phase) of work-induced martensite increases and the elongation of the steel material decreases due to an excessive increase in strength. Therefore, good overhanging property cannot be obtained. When the Md30 value is 30 to 65 ° C., the low Ni austenitic stainless steel of the present invention has an appropriate work hardening ability due to work-induced martensitic transformation and can obtain good stretchability.
積層欠陥エネルギ−の生成指標:SFE(mJ/m2)
bcc構造の普通鋼に比較して、fcc構造をもつオ−ステナイト系ステンレス鋼は、積層欠陥が生成しやすいために加工硬化が大きい。本発明では、高い加工率で張出し加工などのプレス成形を可能にするために、積層欠陥が生成し難い転位の交差すべりが容易な成分設計を採用している。
Generation index of stacking fault energy: SFE (mJ / m 2 )
Compared to ordinary steel having a bcc structure, an austenitic stainless steel having an fcc structure has a greater work hardening because stacking faults are easily generated. In the present invention, in order to enable press forming such as overhanging at a high processing rate, a component design is adopted in which dislocation crossing that is difficult to generate stacking faults is easy.
近年、ステンレス鋼板は複雑な形状の製品を冷間加工で製造することが多くなっている。このような場合、加工硬化が大きい鋼材は加工の途中に中間焼鈍の工程を挟んで軟化させながら繰り返して大きな加工度を得ることが必要になる。加工硬化が小さい鋼材であれば中間焼鈍の工程を省略して製品加工が可能になり、製品コストの低減に大きく寄与する。本発明者らは、このような観点から、良好な張出し性を得るに必要な加工硬化を担保しつつ,過度な加工硬化を抑制するために、積層欠陥エネルギ−(SFE)に及ぼす成分の影響を検討した。その結果、SFE(mJ/m2):6.2Ni+18.6Cu+0.7Cr+3.2Mn+9.3Mo−53 と定義されるSFEを40〜70の範囲に調整するとき、本発明が目的とする優れた張出し性が発現することを見出した。 In recent years, stainless steel sheets are often produced by cold working of products having complicated shapes. In such a case, it is necessary to repeatedly obtain a high degree of workability for a steel material having a high work hardening while being softened with an intermediate annealing step in the middle of the work. If the steel is low in work hardening, the intermediate annealing process can be omitted, and the product can be processed. This greatly contributes to the reduction in product cost. From these viewpoints, the present inventors have the influence of the component on the stacking fault energy (SFE) in order to suppress excessive work hardening while ensuring work hardening necessary for obtaining good stretchability. It was investigated. As a result, when the SFE defined as SFE (mJ / m 2 ): 6.2Ni + 18.6Cu + 0.7Cr + 3.2Mn + 9.3Mo-53 is adjusted to a range of 40 to 70, the excellent extensibility desired by the present invention is achieved. Was found to be expressed.
SFEが40未満の場合、低Niオ−ステナイト系ステンレス鋼は積層欠陥が生成しやすく加工硬化が大きくなり、本発明が目的とする張出し性が得られなくなる。このとき、引張試験で求められる加工硬化指数n値(真応力−対数伸び歪曲線で公称歪10%と30%の勾配)は0.60を超える。他方、SFEが70を超える場合、加工硬化が小さくn値は0.40未満となる。このとき、実用のプレス成形では張出し性が低下するという問題がある。従って、本発明では、引張試験で求められるn値は0.40〜0.60の範囲であることが好ましい。 When the SFE is less than 40, the low Ni austenitic stainless steel is liable to generate stacking faults, and the work hardening becomes large, and the overhanging property intended by the present invention cannot be obtained. At this time, the work hardening index n value (true stress-logarithmic elongation strain curve, nominal strain of 10% and 30% slope) obtained by a tensile test exceeds 0.60. On the other hand, when SFE exceeds 70, work hardening is small and n value will be less than 0.40. At this time, there is a problem that the stretchability is lowered in practical press molding. Therefore, in this invention, it is preferable that n value calculated | required by a tensile test is the range of 0.40-0.60.
本発明のC+N:0.03〜0.20%,Mn:2〜7%,Md30値:30〜65℃,SFE:40〜70(mJ/m2)に調整された低Niオ−ステナイト系ステンレス鋼材は、0.2%耐力が300MPa未満の軟質で適度な加工硬化性を有し,高い加工率で張出し加工ができる優れたプレス成形性を有する。また、良好な耐発銹性を兼備している。以下、本発明のCとN,Mnを除く他の合金元素は次の範囲で選定される。 Low Ni austenite system adjusted to C + N: 0.03 to 0.20%, Mn: 2 to 7%, Md30 value: 30 to 65 ° C., SFE: 40 to 70 (mJ / m 2 ) The stainless steel material is soft with a 0.2% proof stress of less than 300 MPa, has an appropriate work hardening property, and has an excellent press formability capable of being stretched at a high processing rate. It also has good rust resistance. Hereinafter, other alloy elements except C, N, and Mn of the present invention are selected in the following range.
Si:1%以下
Siは溶製時の脱酸剤として有効であり、その効果を得るために0.1%以上添加することが好ましい。より好ましくは0.3%以上である。また、Siは固溶強化およびSFEを低下させて加工硬化を助長する元素である。そのため、本発明の300MPa未満の0.2%耐力を得るために上限は1%以下である。好ましくは0.7%以下である。
Si: 1% or less Si is effective as a deoxidizing agent at the time of melting, and in order to obtain the effect, it is preferable to add 0.1% or more. More preferably, it is 0.3% or more. Si is an element that promotes work hardening by reducing solid solution strengthening and SFE. Therefore, the upper limit is 1% or less in order to obtain 0.2% proof stress of less than 300 MPa of the present invention. Preferably it is 0.7% or less.
Cr:10〜16%
Crはステンレス鋼に要求される耐食性を得るために必要な合金元素であり、10%以上必要である。好ましくは12%以上である。他方、Crは固溶強化およびSFEを低下させて加工硬化を助長する元素である。そのため、本発明の300MPa未満の0.2%耐力,加工硬化指数n値が0.60未満を得るために上限は16%以下である。好ましくは15%以下である。
Cr: 10 to 16%
Cr is an alloying element necessary for obtaining the corrosion resistance required for stainless steel, and 10% or more is necessary. Preferably it is 12% or more. On the other hand, Cr is an element that promotes work hardening by reducing solid solution strengthening and SFE. Therefore, the upper limit is 16% or less in order to obtain a 0.2% yield strength and work hardening index n value of less than 0.60 of the present invention less than 300 MPa. Preferably it is 15% or less.
Ni:1〜6%
Niは高価な元素であり,6%を超える300系のオ−ステナイト系ステンレス鋼は原料コストの上昇を招く。従って、Niは6%以下である。好ましくは5.5%以下である。Niはオ−ステナイト系ステンレス鋼に必要な元素であり、更に,延性を確保するのに有効な元素である。そのため、下限は1%とする。好ましくは2%以上である。
Ni: 1-6%
Ni is an expensive element, and 300-series austenitic stainless steel exceeding 6% causes an increase in raw material costs. Therefore, Ni is 6% or less. Preferably it is 5.5% or less. Ni is an element necessary for austenitic stainless steel, and is also an element effective for ensuring ductility. Therefore, the lower limit is 1%. Preferably it is 2% or more.
Cu:1〜3%
Cuは、NiやMnの代替としてのオ−ステナイト形成元素として有効に作用する。本発明ではこれらの作用を得るためにCuは1%以上添加する。さらに、Cuは軟質化に有効な元素であり,本発明で定義するMd30値やSFEの調整に有効な合金元素である。本発明ではこれら作用を得るために、好ましくは1.5%以上とする。しかし、過剰量のCu添加は製鋼時のCu汚染や熱間脆性を誘発する問題がある。また、SFEが過度に上昇して張出し性の低下を招く。そのため、Cuの上限は3%以下とする。
Cu: 1-3%
Cu acts effectively as an austenite forming element as a substitute for Ni and Mn. In the present invention, in order to obtain these effects, Cu is added in an amount of 1% or more. Furthermore, Cu is an element effective for softening, and is an alloy element effective for adjusting the Md30 value and SFE defined in the present invention. In the present invention, in order to obtain these effects, the content is preferably 1.5% or more. However, excessive addition of Cu has a problem of inducing Cu contamination and hot brittleness during steelmaking. Moreover, SFE rises excessively and causes a reduction in overhanging property. Therefore, the upper limit of Cu is 3% or less.
Mo:0.3〜3%
必要に応じて添加される元素であり、耐発銹性の向上に有効な元素である。また、本発明で定義するMd30値やSFEの調整にも有効な元素である。これら作用を得るためには、Moは0.3%以上添加することが好ましい。しかし、Moは高価な元素であり、過剰な添加はコスト上昇を招く。また、δフェライトの生成や固溶強化により強度上昇する。そのため、Moの上限は3%以下とすることが好ましい。
Mo: 0.3-3%
It is an element that is added as necessary, and is an element that is effective in improving the rust resistance. It is also an element effective for adjusting the Md30 value and SFE defined in the present invention. In order to obtain these effects, it is preferable to add Mo by 0.3% or more. However, Mo is an expensive element, and excessive addition causes an increase in cost. In addition, the strength increases due to the formation of δ ferrite and solid solution strengthening. Therefore, the upper limit of Mo is preferably 3% or less.
S:0.0025%以下
MnS等の介在物を形成する不純物元素であり、耐発銹性を阻害する場合がある。そのため、耐発銹性の要求が高い場合は、Sを0.0025%以下とすることが好ましい。より好ましくは、0.0020%以下である。
S: 0.0025% or less An impurity element that forms inclusions such as MnS, and may impair the rust resistance. Therefore, when the requirement for rust resistance is high, it is preferable to set S to 0.0025% or less. More preferably, it is 0.0020% or less.
P:0.040%以下
Pは不純物元素であり,耐発銹性を低下させる場合がある。そのため、耐発銹性の要求が高い場合は、Pを0.040%以下とすることが好ましい。より好ましくは0.0035%以下である。
P: 0.040% or less P is an impurity element and may reduce the rust resistance. Therefore, when the requirement for rust resistance is high, it is preferable to set P to 0.040% or less. More preferably, it is 0.0035% or less.
表1の化学組成を有するステンレス鋼を溶製し、加熱温度1200℃の熱間圧延により板厚4.0mmの熱延鋼板を製造した。熱延鋼板を1120℃,均熱時間2分で焼鈍し、酸洗後に板厚1.5mmまで冷間圧延し、更に1080℃,均熱時間2分の中間焼鈍を施し、酸洗後,板厚0.7mmの冷延鋼板とし、最終焼鈍を1080℃,均熱時間1分で実施した(焼鈍酸洗材)。 Stainless steel having the chemical composition shown in Table 1 was melted, and a hot-rolled steel sheet having a thickness of 4.0 mm was manufactured by hot rolling at a heating temperature of 1200 ° C. Hot-rolled steel sheet was annealed at 1120 ° C for 2 minutes, soaking, cold-rolled to 1.5 mm after pickling, further subjected to intermediate annealing at 1080 ° C for 2 minutes, soaking, and pickled, A cold-rolled steel sheet having a thickness of 0.7 mm was used, and final annealing was performed at 1080 ° C. and a soaking time of 1 minute (annealing pickling material).
焼鈍酸洗材からJIS13B引張試験片を切り出し,引張試験により0.2%耐力,引張強度,伸び,加工硬化指数nを測定した。加工硬化指数nは、公称歪10%と30%に相当する真歪ε10,ε30における真応力δ10,δ30を求め、次式に従って加工硬化指数n値を算出した。
n値=ln(ε30/ε10)/ln(δ30/δ10)
A JIS13B tensile test piece was cut out from the annealed pickling material, and 0.2% proof stress, tensile strength, elongation, and work hardening index n were measured by a tensile test. For the work hardening index n, true stresses δ 10 and δ 30 at true strains ε 10 and ε 30 corresponding to nominal strains of 10% and 30% were obtained, and the work hardening index n value was calculated according to the following equation.
n value = ln (ε 30 / ε 10 ) / ln (δ 30 / δ 10 )
張出し性は、焼鈍酸洗材から90mm角の試験片を切り出し,JISZ2247に規定するエリクセン試験(B法:しわ押さえ圧1ton負荷)により評価した。また、絞り張出し複合成形性は、JISZ2249に準拠したコニカルカップ試験(13型)により評価した。
The overhanging property was evaluated by an Erichsen test (Method B:
耐発銹性は、焼鈍酸洗材から100mm角の試験片を切り出し,JISZ2371に準拠するキャス試験(50℃,5%NaCl+0.26g/L CuCl2+CH3COOH,pH3.0,100hr噴霧)により評価した。 The rust resistance was obtained by cutting a 100 mm square test piece from the annealed pickling material and performing a cast test (50 ° C., 5% NaCl + 0.26 g / L CuCl 2 + CH 3 COOH, pH 3.0, 100 hr spraying) in accordance with JISZ2371. evaluated.
焼鈍酸洗材の0.2%耐力,引張強度,伸び,n値,エリクセン値,CCV値,キャス試験の発銹状況を表1に併記して示す。鋼No.1〜6は、本発明で規定した低Niオ−ステナイト系ステンレス鋼の成分設計条件を満足しており、0.2%耐力が300MPa未満,伸びが45%以上,加工硬化指数nが0.4〜0.6の機械的性質を有し,本発明が目標とするSUS304と同等以上のエリクセン値,CCV値が得られた。さらに、S,Pを低減してMoを添加した鋼No.1,3〜6はSUS304と同等の耐発銹性が得られた。鋼No.7〜14は、Md30値とSFEの片方あるいは両者が本発明の規定する条件から外れるために、本発明が目標とする加工性(SUS304と同等以上のエリクセン値とCCV値)が得られなかったものである。鋼No.15は加工性の比較となるSUS304である。鋼No.16〜26は、本発明が規定する成分範囲を満足しないものであり、目標とする加工性や耐発銹性が得られなかったものである。
鋼材のエリクセン値とCCV値に及ぼすオ−ステナイト安定度の指標Md30値の影響について検討した結果を図1および図2に示す。図1および図2に示すように、30<Md30<65に制御することによって、本発明が目標とするSUS304と同等以上の張出し性が得られることが確認できた。 The results of examining the influence of the austenite stability index Md30 value on the Erichsen value and CCV value of steel are shown in FIGS. As shown in FIG. 1 and FIG. 2, it was confirmed that by controlling to 30 <Md30 <65, an overhang property equal to or higher than SUS304 targeted by the present invention can be obtained.
また、積層欠陥エネルギ−の生成指標SFEと加工硬化指数nとの関係を検討した結果、図3に見られるように、40<SFE<70にすることによって、本発明が目標とするn値が得られることが確認できた。 Further, as a result of examining the relationship between the stacking fault energy generation index SFE and the work hardening index n, as shown in FIG. 3, by setting 40 <SFE <70, the target n value of the present invention is It was confirmed that it was obtained.
本発明の低Niオ−ステナイト系ステンレス鋼は、従来の低Niオ−ステナイト系ステンレス鋼ではなし得なかった成形加工が可能であり、良好な耐発銹性も兼備することから、SUS304に代表されるNi系ステンレス鋼が使用されている成形加工用の材料として広範囲な分野で適用可能である。 The low Ni austenitic stainless steel of the present invention is representative of SUS304 because it can be formed and cannot be formed by conventional low Ni austenitic stainless steel, and also has good galling resistance. It can be applied in a wide range of fields as a forming material using Ni-based stainless steel.
Claims (4)
30<Md30<65,40<SFE<70
Md30(℃):497−462(C+N)−9.2Si−8.1Mn−13.7Cr−20(Ni+Cu)−18.5Mo
SFE(mJ/m2):6.2Ni+18.6Cu+0.7Cr+3.2Mn+9.3Mo−53 In mass%, C + N: 0.03 to 0.20%, Si: 1% or less, Mn: 2 to 7%, Cr: 10 to 16%, Ni: 1 to 6%, Cu: 1 to 3%, balance Low Ni-O which is excellent in overhanging property and galling resistance, and is characterized by comprising an austenite stability index Md30 value and a stacking fault energy generation index SFE consisting of Fe and inevitable impurities. Stenitic stainless steel.
30 <Md30 <65, 40 <SFE <70
Md30 (° C): 497-462 (C + N) -9.2Si-8.1Mn-13.7Cr-20 (Ni + Cu) -18.5Mo
SFE (mJ / m 2 ): 6.2Ni + 18.6Cu + 0.7Cr + 3.2Mn + 9.3Mo-53
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