JP2008038191A - Austenitic stainless steel and its production method - Google Patents
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本発明は、高耐力、ばね性および加工性に優れたオーステナイト系ステンレス鋼とその製造方法に関するものである。 The present invention relates to an austenitic stainless steel excellent in high yield strength, springiness and workability and a method for producing the same.
近年、電気製品は軽量化が進んでおり、使用されるステンレス鋼板の部品も薄肉化が求められている。そのため、加工性を損なわずに強度を向上させた材料が求められることが多い。また、一部の部品では、ばね性を求められることもあり、耐力の高い材料が必要となる。これらの用途には、従来技術では、軽圧下の調質圧延を施した準安定オーステナイト系ステンレス鋼板、例えばSUS304-1/2Hが広く使用されている。 In recent years, the weight of electric products has been reduced, and the use of thin stainless steel plate parts is also required. Therefore, a material having improved strength without impairing workability is often required. In addition, in some parts, a spring property may be required, and a material having a high yield strength is required. In these applications, metastable austenitic stainless steel sheets subjected to temper rolling under light pressure, such as SUS304-1 / 2H, are widely used in the prior art.
加工性を損なわずにステンレス鋼板の強度を上げる手段として、(a) C、N、Mo添加などによる固溶強化、(b) 軽圧下の調質圧延による加工硬化、(c) 低温焼鈍による結晶粒の微細化[例えば、特開平０７−２１６４５０、特開２０００−２７３５３８]などがある。 (A) Solid solution strengthening by adding C, N, Mo, etc., (b) Work hardening by temper rolling under light pressure, (c) Crystal by low temperature annealing There are grain refinements [for example, JP 07-216450, JP 2000-273538].
固溶強化元素については、過剰添加は材料の焼鈍状態での強度を上げるため、薄板を製造する場合、冷間圧延の負荷が高く、場合によっては、途中で再焼鈍を行う必要があり、製造コストが高くなる。 For solid solution strengthening elements, excessive addition increases the strength of the material in the annealed state, so when manufacturing a thin plate, the load of cold rolling is high, and in some cases, it is necessary to re-anneal in the middle, manufacturing Cost increases.
軽圧下の調質圧延については、圧下率が低いため、薄板になると圧延前の表面肌の影響を受け、表面に模様が発生することがある。また、圧延方向(Ｔ方向)と圧延直角方向(Ｌ方向)で特性が異なるといった、異方性の問題もある。さらに、準安定オーステナイト系ステンレス鋼板では、圧延により、加工誘起マルテンサイト相が誘起されるため、磁性を帯びるようになる。 For temper rolling under light reduction, since the reduction ratio is low, a thin plate may be affected by the surface skin before rolling, and a pattern may be generated on the surface. In addition, there is an anisotropy problem that the characteristics are different between the rolling direction (T direction) and the direction perpendicular to the rolling direction (L direction). Furthermore, in a metastable austenitic stainless steel sheet, since a work induction martensite phase is induced by rolling, it becomes magnetized.
低温焼鈍については、前述の先行技術に記載のように、焼鈍温度が650〜900℃あるいは700〜950℃と低いため、均一な再結晶組織を得るためには長時間の焼鈍を行う必要がある。例えば、一般的なオーステナイト系ステンレス鋼の最終仕上焼鈍(焼鈍温度：1100〜1200℃程度)に比べ、焼鈍に長時間を要するため、生産性が低く、製造コストが高くなる。また、大気焼鈍の場合、焼鈍温度が低いため、表面が十分に酸化されず、模様（油模様など）が発生しやすい、というような問題があった。
本発明はこれら従来技術の問題点を解決するためになされたものであり、その課題は、熱延板焼鈍後の冷間圧延性を損なうことなく、最終製品の高耐力および優れたばね性を実現し、しかも表面状態に優れ、異方性が小さく、更に軽圧延後も磁性を帯びるというようなこともないオーステナイト系ステンレス鋼とその製造方法を提供することにある。 The present invention has been made to solve these problems of the prior art, and the task is to achieve high yield strength and excellent springiness of the final product without impairing the cold rolling property after hot-rolled sheet annealing. And it is providing the austenitic stainless steel which is excellent in a surface state, has small anisotropy, and is not magnetized even after light rolling, and its manufacturing method.
請求項１に記載の発明は、質量%で、C：0.10%以下、Si：1.0%以下、Mn：3.0〜8.0%、P：0.10%以下、S：0.010%以下、Ni：2.0〜5.0%、Cr：16.0〜20.0%、Mo：0.40%以下、Cu：1.0〜3.0%、N：0.10〜0.30%を含有し、残部がＦｅおよび不可避的不純物からなる化学組成を有し、以下の数式を満足することを特徴とするオーステナイト系ステンレス鋼である。
Ａ値＝136+731C+47.6Si-1.9Mn-3.4Ni+4.2Cr+17.5Mo-7.7Cu+945N≦500
Ｂ値＝0.8×Ａ値＋12×d-1/2−4≧470
0.001≦d≦0.026
ここで、dは平均結晶粒径（mm）である。
Invention of Claim 1 is mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 3.0-8.0%, P: 0.10% or less, S: 0.010% or less, Ni: 2.0-5.0% , Cr: 16.0-20.0%, Mo: 0.40% or less, Cu: 1.0-3.0%, N: 0.10-0.30%, with the chemical composition consisting of Fe and unavoidable impurities as the balance, An austenitic stainless steel characterized by satisfaction.
A value = 136 + 731C + 47.6Si-1.9Mn-3.4Ni + 4.2Cr + 17.5Mo-7.7Cu + 945N ≦ 500
B value = 0.8 × A value + 12 × d −1/2 −4 ≧ 470
0.001 ≦ d ≦ 0.026
Here, d is an average crystal grain size (mm).
Ａ値は、焼鈍板の0.2%耐力：Ｎ／ｍｍ2(以下、耐力と記す)を化学成分組成との関係で表した値であり、Ａ値を５００以下とすることにより、冷間加工性を確保することができる。 The A value is a value representing the 0.2% proof stress of the annealed sheet: N / mm 2 (hereinafter referred to as proof stress) in relation to the chemical composition, and by making the A value 500 or less, cold workability is achieved. Can be secured.
Ｂ値は、焼鈍板の耐力について、化学成分組成に加えて、さらに結晶粒径の影響も入れて表した値であり、Ｂ値を470以上とすることにより、SUS 304-1/2Hの耐力のJIS規格(JIS G 4313)を満足し、加工性と強度の両方を必要とする用途への適用が可能となる。
なお、Ａ値、Ｂ値及び平均結晶粒径dの請求範囲を図示すると、図１のようになる。
The B value is a value that represents the yield strength of the annealed plate in addition to the chemical composition, and also includes the influence of the crystal grain size. By setting the B value to 470 or more, the yield strength of SUS 304-1 / 2H It satisfies the JIS standard (JIS G 4313) and can be applied to applications that require both workability and strength.
In addition, FIG. 1 illustrates the claims of the A value, the B value, and the average crystal grain size d.
請求項２に記載の発明は、請求項１に記載のオーステナイト系ステンレス鋼において、更にＣ値が以下の数式を満足するオーステナイト系ステンレス鋼である。
Ｃ値＝551-462 (C+N)-9.2Si-18.5Mn-29(Ni+Cu)-13.7Cr-18.5Mo-68Nb＜−40
The invention described in claim 2 is the austenitic stainless steel according to claim 1, wherein the C value further satisfies the following mathematical formula.
C value = 551-462 (C + N) -9.2Si-18.5Mn-29 (Ni + Cu) -13.7Cr-18.5Mo-68Nb <-40
Ｃ値は、焼鈍板に冷間加工を加えたときの加工誘起マルテンサイト相の生成量の程度を表す指標であり、Ｃ値が−40未満であれば、例えば30%程度の冷間加工を行ったときにマルテンサイト相の生成がなく非磁性を保つことができ、非磁性が要求される部材(例えば、ハードディスク押えばね等の電子部品)に適用することが可能となる。 The C value is an index representing the degree of formation of a work-induced martensite phase when cold working is applied to an annealed plate. If the C value is less than −40, for example, cold work of about 30% is performed. When this is done, no martensite phase is generated and non-magnetism can be maintained, so that it can be applied to members that require non-magnetism (for example, electronic parts such as hard disk pressing springs).
請求項３に記載の発明は、前記オーステナイト系ステンレス鋼の製造方法であって、質量%で、C：0.10%以下、Si：1.0%以下、Mn：3.0〜8.0%、P：0.10%以下、S：0.010%以下、Ni：2.0〜5.0%、Cr：16.0〜20.0%、Mo：0.40%以下、Cu：1.0〜3.0%、N：0.10〜0.30%を含有し、残部がFeおよび不可避的不純物からなり、Ａ値およびＣ値が下記式を満足する化学組成のオーステナイト系ステンレス鋼を熱間圧延し、次いで焼鈍、冷間圧延を行い、然る後、900〜1100℃で仕上焼鈍を行うことによって、Ｂ値および平均結晶粒径(d)が下記式を満足するようにしたことを特徴とする。
Ａ値=136+731C+47.6Si-1.9Mn-3.4Ni+4.2Cr+17.5Mo-7.7Cu+945N≦500
Ｃ値＝551-462 (C+N)-9.2Si-18.5Mn-29(Ni+Cu)-13.7Cr-18.5Mo-68Nb＜−40
Ｂ値＝0.8×Ａ値＋12×d-1/2−4≧470
0.001≦d≦0.026
ここで、dは平均結晶粒径（mm）である。
Invention of Claim 3 is a manufacturing method of said austenitic stainless steel, Comprising: By mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 3.0-8.0%, P: 0.10% or less, S: 0.010% or less, Ni: 2.0-5.0%, Cr: 16.0-20.0%, Mo: 0.40% or less, Cu: 1.0-3.0%, N: 0.10-0.30%, the balance being Fe and inevitable impurities Austenitic stainless steel having a chemical composition satisfying the following formula with A value and C value is hot-rolled, followed by annealing and cold rolling, and then finish annealing at 900 to 1100 ° C. The B value and the average crystal grain size (d) satisfy the following formula.
A value = 136 + 731C + 47.6Si-1.9Mn-3.4Ni + 4.2Cr + 17.5Mo-7.7Cu + 945N ≦ 500
C value = 551-462 (C + N) -9.2Si-18.5Mn-29 (Ni + Cu) -13.7Cr-18.5Mo-68Nb <-40
B value = 0.8 × A value + 12 × d −1/2 −4 ≧ 470
0.001 ≦ d ≦ 0.026
Here, d is an average crystal grain size (mm).
本発明によれば、固溶強化元素を適量添加しかつＡ値を500以下とするとともに、冷間圧延後の低温焼鈍により結晶粒を微細化してＢ値を470以上とすることにより、冷間圧延性を損なわずに仕上焼鈍状態で高耐力、高ばね性かつ冷間加工性に優れた材料を提供することができる。しかも最終工程は低温焼鈍を行うだけであるから、従来の調質圧延を施した準安定オーステナイト系ステンレス鋼板(SUS304-1/2H)に比べて異方性が小さく表面品質の良好な材料を得ることができ、幅広い用途へ適用することが可能である。 According to the present invention, an appropriate amount of a solid solution strengthening element is added and the A value is 500 or less, and the crystal grains are refined by low-temperature annealing after cold rolling to obtain a B value of 470 or more. It is possible to provide a material having high yield strength, high spring property, and excellent cold workability in the finish annealing state without impairing the rollability. In addition, since the final process is only low-temperature annealing, a material with low surface anisotropy and low anisotropy is obtained as compared to conventional temper rolled metastable austenitic stainless steel sheet (SUS304-1 / 2H). It can be applied to a wide range of uses.
また、Ｃ値を−40未満にすることで、加工誘起マルテンサイト相の生成を抑制することが出来るので、製品加工前だけでなく、製品加工時においてある程度の冷間加工を施しても、非磁性を保つことができ、そのために加工後の製品に対する非磁性が要求される用途への適用も可能である。 In addition, by making the C value less than −40, it is possible to suppress the formation of the processing-induced martensite phase, so that not only before the product processing but also by applying a certain amount of cold processing at the time of product processing, The magnetism can be maintained, and therefore, it can be applied to uses that require non-magnetism for the processed product.
以下、本発明のオーステナイトステンレス鋼およびその製造方法について詳細に説明する。まず、本発明のオーステナイトステンレス鋼における化学組成の限定理由について説明する。なお、化学組成はすべて質量%で示す。 Hereinafter, the austenitic stainless steel of the present invention and the manufacturing method thereof will be described in detail. First, the reason for limiting the chemical composition in the austenitic stainless steel of the present invention will be described. All chemical compositions are expressed in mass%.
C:0.10%以下
Cは固溶強化元素であるため、含有量を高くすることは、耐力を上昇させるためには効果的と言えるが、過剰に添加すると、Crと炭化物を生成することにより、耐食性を劣化させる。特に低温にて焼鈍を行う場合、Cr炭化物が粒界に生成し、耐食性を劣化させる。よってCによる固溶強化は最低限とし、0.10%以下とした。
C: 0.10% or less
Since C is a solid solution strengthening element, it can be said that increasing the content is effective for increasing the yield strength. However, when added in excess, the corrosion resistance is deteriorated by producing Cr and carbides. In particular, when annealing is performed at a low temperature, Cr carbide is generated at the grain boundary, and the corrosion resistance is deteriorated. Therefore, the solid solution strengthening by C is minimized, and it is set to 0.10% or less.
Si:1.0%以下
Siは溶解時の脱酸剤の役割をすると同時に耐食性を増加させる効果もある。また、Siも固溶強化元素であり、耐力を上昇させるために効果的と言えるが、1%を超える添加は熱間加工性を害するだけでなくσ相生成を助長するので好ましくない。このため、その上限を1.0%とした。
Si: 1.0% or less
Si plays the role of a deoxidizing agent at the time of dissolution and also has an effect of increasing the corrosion resistance. Si is also a solid solution strengthening element, and it can be said that it is effective for increasing the yield strength. However, addition of more than 1% is not preferable because it not only harms hot workability but also promotes σ phase formation. For this reason, the upper limit was made 1.0%.
P：0.10%以下
Pは耐食性や熱間加工性を劣化させるため、その上限を0.10%とした。
P: 0.10% or less
P degrades corrosion resistance and hot workability, so its upper limit was made 0.10%.
S：0.010%以下
Sは、介在物を増加させ、また耐発銹性を低下させる。また、熱間加工性を著しく低下させるため、その上限を0.010%とした。
S: 0.010% or less
S increases inclusions and reduces rust resistance. Further, the upper limit is made 0.010% in order to significantly reduce the hot workability.
Mn：3.0〜8.0%
Mnはオーステナイト形成元素あり、加工誘起マルテンサイト相の生成を抑制し、加工硬化を低くすることができるため、冷間圧延性の向上に有利となる。また、Mnの添加により、有益な固溶強化元素であるNの固溶度が上がる。さらにMnは酸化スケールの生成を促進させる効果があり、低温にて大気焼鈍を行う場合においても、十分に酸化スケール層が生成し、焼鈍前の油汚れなどを起因とする模様が発生しにくい。これらの効果を得るためには3.0%以上が必要であるが、Mnの過剰添加は酸化による肌荒れを起こし、また製品の耐食性を低下させる恐れがあるため、上限を8.0%とした。
Mn: 3.0-8.0%
Mn is an austenite-forming element and can suppress the formation of a work-induced martensite phase and lower work hardening, which is advantageous for improving cold rollability. Further, the addition of Mn increases the solid solubility of N, which is a useful solid solution strengthening element. Further, Mn has an effect of promoting the generation of oxide scale, and even when atmospheric annealing is performed at a low temperature, a sufficient oxide scale layer is generated, and a pattern caused by oil stains before annealing is hardly generated. In order to obtain these effects, 3.0% or more is necessary, but excessive addition of Mn causes rough skin due to oxidation and may reduce the corrosion resistance of the product, so the upper limit was set to 8.0%.
Ni：2.0〜5.0%
Niはオーステナイト形成元素であり、オーステナイト組織の安定化や、良好な熱間加工性や冷間加工性を得るためには、Mn添加ステンレス鋼においても必要とされる元素であり、2.0%以上は添加する必要がある。しかし、Ni価格は高価であるため、その上限を5.0%、下限を2.0%とした。
Ni: 2.0-5.0%
Ni is an austenite-forming element, and is an element required for Mn-added stainless steel to stabilize the austenite structure and to obtain good hot workability and cold workability. It is necessary to add. However, since the Ni price is expensive, the upper limit is set to 5.0% and the lower limit is set to 2.0%.
Cr：16.0〜20.0%
Crはステンレス鋼の耐食性を高めるのにもっとも有効な元素のひとつであるが、そのためには13.0%以上の添加が必要である。しかし、SUS304と同等の耐食性を得るためには16.0%以上は必要であり、下限を16.0%とした。また20.0%を超える添加は、δフェライトの生成や熱間加工性の低下をもたらし好ましくない。よって、Crの上限を20.0%とした。
Cr: 16.0-20.0%
Cr is one of the most effective elements for enhancing the corrosion resistance of stainless steel, but for that purpose, addition of 13.0% or more is necessary. However, in order to obtain the same corrosion resistance as SUS304, 16.0% or more is necessary, and the lower limit was set to 16.0%. Addition in excess of 20.0% is undesirable because it results in the formation of δ ferrite and a decrease in hot workability. Therefore, the upper limit of Cr is set to 20.0%.
Mo：0.40%以下
Moは有力な固溶強化元素であり、Crと並んで、ステンレス鋼の耐食性を高めるのにも有効な元素であるが、その添加はコストを大きくするため、上限を0.40%とした。
Mo: 0.40% or less
Mo is a powerful solid solution strengthening element, and is an element that is effective in increasing the corrosion resistance of stainless steel along with Cr, but its addition is made 0.40% in order to increase the cost.
Cu：1.0〜3.0%
Cuは耐力を上昇させるためには、不利な元素であるが、材料を軟質化させ、加工硬化を抑える効果があるため、冷間圧延性を高めるためには必要である。また、加工誘起マルテンサイト相の生成を抑制する効果もある。このような効果を有効に発揮させるためには1.0%以上が必要である。しかし、3.0%を超える添加は熱間加工性を悪くするため、上限を3.0%とした。
Cu: 1.0-3.0%
Cu is an unfavorable element for increasing the proof stress, but it is necessary for enhancing the cold rolling property because it has the effect of softening the material and suppressing work hardening. In addition, there is an effect of suppressing the formation of a processing-induced martensite phase. In order to exhibit such an effect effectively, 1.0% or more is necessary. However, addition exceeding 3.0% deteriorates hot workability, so the upper limit was made 3.0%.
N：0.10〜0.30%
NはCと同様に有効な固溶強化元素である。また、耐食性の向上にも効果がある。C量を抑えているため、固溶強化を考えた場合、Nは最低0.10%の添加が必要である。しかし、過剰の添加は熱間加工性を悪化させるため、上限を0.30%とした。
N: 0.10 to 0.30%
N is an effective solid solution strengthening element like C. It is also effective in improving corrosion resistance. Since the amount of C is suppressed, N should be added at least 0.10% when considering solid solution strengthening. However, excessive addition deteriorates hot workability, so the upper limit was made 0.30%.
次に、Ａ値、Ｂ値について、詳細に説明する。
まず、Cr−Mn−Niオーステナイト系ステンレス鋼について、各成分の含有量を表１(表１の数字は質量%)に示す範囲内で変化させた多数の焼鈍板(結晶粒径20〜40μm)の耐力を測定した。そして、耐力と化学成分組成との関係式を求めた結果、Ａ値(＝計算耐力値)として、以下の関係式を得ることができた。
Ａ値(＝計算耐力値)＝136+731C+47.6Si-1.9Mn-3.4Ni+4.2Cr+17.5Mo-7.7Cu+945N
また、図２は上記Ａ値と実測耐力との相関を表す図であり、相関係数R2＝は0.94であり、極めて高い相関を示している。
ここで、寄与率の高いC、N、Si、Moの添加量を高めることにより、耐力は上昇し、逆にMn、Ni、Cuの添加量を上げると、耐力は低下することがわかる。
First, for Cr-Mn-Ni austenitic stainless steel, a number of annealed plates (crystal grain size 20-40 μm) in which the content of each component was changed within the range shown in Table 1 (the numbers in Table 1 are mass%). The proof stress was measured. And as a result of calculating | requiring the relational expression of proof stress and a chemical component composition, the following relational expressions were able to be obtained as A value (= calculation proof stress value).
A value (= calculated proof stress value) = 136 + 731C + 47.6Si-1.9Mn-3.4Ni + 4.2Cr + 17.5Mo-7.7Cu + 945N
FIG. 2 is a diagram showing the correlation between the A value and the measured proof stress, and the correlation coefficient R 2 = 0.94, indicating a very high correlation.
Here, it can be seen that by increasing the amount of C, N, Si, and Mo having a high contribution rate, the yield strength increases, and conversely, when the amount of addition of Mn, Ni, and Cu increases, the yield strength decreases.
上述のＡ値は化学成分だけによる耐力の計算式であることから、更に結晶粒径をも取り入れた計算式を求めるための実験を行った。結晶粒径1〜40μmの焼鈍材について、耐力を測定し、耐力がＡ値と結晶粒径でどのように整理することができるか検討した結果、以下のＢ値の式を得ることができた。
Ｂ値(＝計算耐力値)＝0.8×Ａ値＋12×d-1/2−4
ここで、dは平均結晶粒径（mm）である。なお、本発明においては、平均結晶粒径dの測定方法はJIS G 0511による。
また、図３は上記Ｂ値と実測耐力との相関を表す図であり、相関係数R2＝は0.91である。
Since the above-mentioned A value is a calculation formula for the yield strength based only on chemical components, an experiment was performed to obtain a calculation formula that also incorporated the crystal grain size. As a result of measuring the yield strength of the annealed material having a crystal grain size of 1 to 40 μm and examining how the yield strength can be arranged by the A value and the crystal grain size, the following formula of the B value was obtained. .
B value (= calculated proof stress value) = 0.8 x A value + 12 x d -1/2 -4
Here, d is an average crystal grain size (mm). In the present invention, the average crystal grain size d is measured according to JIS G 0511.
FIG. 3 is a diagram showing the correlation between the B value and the measured yield strength, and the correlation coefficient R 2 = 0.91.
固溶強化により強度を上げすぎると、熱延板焼鈍後の冷間圧延での負荷が高くなり、冷間圧延性が低下する。よって固溶強化による耐力を表すＡ値は500以下を満足することとする。また、加工硬化を抑制するために、Cuを1.0%以上添加することとする。Ａ値が500を超える場合、再加熱なしでは板厚3mmの熱延焼鈍板を一度の冷間圧延で板厚0.8mm以下まで圧延できないため、製造コストの増大につながる。 If the strength is increased too much by solid solution strengthening, the load in cold rolling after the hot-rolled sheet annealing becomes high, and the cold rollability deteriorates. Therefore, the A value representing the yield strength by solid solution strengthening satisfies 500 or less. Further, in order to suppress work hardening, Cu is added by 1.0% or more. When the A value exceeds 500, a hot-rolled annealed sheet having a thickness of 3 mm cannot be rolled to a thickness of 0.8 mm or less by a single cold rolling without reheating, leading to an increase in manufacturing cost.
Ｂ値は、本発明に係る結晶粒を微細化したオーステナイト系ステンレス鋼製品の耐力を表しており、Ｂ値が、SUS304-1/2HのJIS規格である470以上であれば、固溶強化および結晶粒微細化により焼鈍状態で高耐力の材料を得ることができ、加工性と強度の両方を必要とする用途への適用が可能となる。 The B value represents the proof stress of the austenitic stainless steel product in which the crystal grains according to the present invention are refined. If the B value is 470 or higher, which is the JIS standard of SUS304-1 / 2H, By refining crystal grains, a material having a high yield strength can be obtained in an annealed state, and application to applications that require both workability and strength becomes possible.
結晶粒径については、Ａ値≦500かつＢ値≧470を満たすためには、Ｂ値の計算式から、平均結晶粒径dの上限は0.026mmとなる。また、サブミクロンの超微細粒を得るためには、より低温の長時間の仕上焼鈍が必要であり、焼鈍工程への負荷が高いため、平均結晶粒径dの下限は0.001mmとする。 Regarding the crystal grain size, in order to satisfy A value ≦ 500 and B value ≧ 470, the upper limit of the average crystal grain size d is 0.026 mm from the formula for calculating the B value. Further, in order to obtain submicron ultrafine grains, it is necessary to perform annealing at a lower temperature for a longer time, and the load on the annealing process is high. Therefore, the lower limit of the average crystal grain size d is set to 0.001 mm.
本発明におけるＡ値、Ｂ値及び平均結晶粒径dの許容範囲を図で表すと、図１のとおりであり、これらの数値をこの範囲とすることで、高耐力であるにも関わらず熱延板焼鈍後の冷間圧延での負荷が小さくて冷間圧延が容易となる。 The permissible ranges of the A value, B value, and average crystal grain size d in the present invention are shown in FIG. 1, and by setting these values within this range, the heat resistance is high in spite of high proof stress. The cold rolling is easy because the load in cold rolling after sheet annealing is small.
次に、Cr−Mn−Niオーステナイト系ステンレス鋼について、磁性を有する加工誘起マルテンサイト（α'）の生成量に及ぼす化学成分の影響を調査した。図４は、冷間圧下率30%の加工におけるα'の生成量とＣ値の関係を示した実験データである。ここで、Ｃ値は、焼鈍板に冷間加工を加えたときの加工誘起マルテンサイトの生成量の程度を表す指標であり、化学成分により以下の式で計算される。
Ｃ値＝551-462 (C+N)-9.2Si-18.5Mn-29(Ni+Cu)-13.7Cr-18.5Mo-68Nb
図４から、Ｃ値を−40未満にすれば、α'の生成量を2%以下に抑えることができ、磁石に吸い付かない程度の非磁性が得られる。
Next, the influence of chemical components on the amount of magnetically induced work-induced martensite (α ′) in the Cr—Mn—Ni austenitic stainless steel was investigated. FIG. 4 is experimental data showing the relationship between the amount of α ′ produced and the C value in the machining with a cold reduction rate of 30%. Here, the C value is an index that represents the degree of generation of work-induced martensite when cold working is applied to the annealed plate, and is calculated by the following equation depending on the chemical component.
C value = 551-462 (C + N) -9.2Si-18.5Mn-29 (Ni + Cu) -13.7Cr-18.5Mo-68Nb
From FIG. 4, if the C value is less than −40, the amount of α ′ generated can be suppressed to 2% or less, and non-magnetism that does not attract the magnet can be obtained.
このように、本発明に係るオーステナイト系ステンレス鋼は、仕上焼鈍後にある程度の冷間加工（例えば、板厚減少率30%程度）を施しても、加工誘起マルテンサイト相の生成が抑えられ、非磁性を保つことができる。これにより高耐力を必要とし且つ仕上焼鈍後の冷間加工に対しても非磁性を保つことが必要な部材(例えばハードディスク押えばね等の電子部品)に適用することが可能となる。 As described above, the austenitic stainless steel according to the present invention suppresses the formation of a work-induced martensite phase even if a certain amount of cold working (for example, a sheet thickness reduction rate of about 30%) is performed after finish annealing. Can maintain magnetism. As a result, it is possible to apply to a member (for example, an electronic component such as a hard disk pressing spring) that requires high proof stress and needs to maintain non-magnetism even during cold working after finish annealing.
次に、製造方法について詳細に説明する。本発明に係るオーステナイト系ステンレス鋼の製造方法は、所定の化学組成を有するオーステナイト系ステンレス鋼を熱間圧延し、次いで焼鈍、冷間圧延を行い、その後、900〜1100℃で仕上焼鈍を行うことを特徴としている。最後の仕上焼鈍により、組織は微細結晶粒の再結晶組織となり、高耐力、ばね性および加工性に優れたオーステナイト系ステンレス鋼が得られる。 Next, the manufacturing method will be described in detail. The method for producing an austenitic stainless steel according to the present invention includes hot rolling an austenitic stainless steel having a predetermined chemical composition, followed by annealing and cold rolling, followed by finish annealing at 900 to 1100 ° C. It is characterized by. By the final finish annealing, the structure becomes a recrystallized structure of fine crystal grains, and an austenitic stainless steel excellent in high yield strength, spring property and workability is obtained.
本発明においては、固溶強化の助力により、それほど結晶粒を微細化させずに、高耐力が得られるため、仕上焼鈍温度は900〜1,100℃でよく、長時間の焼鈍を必要としない。例えば焼鈍時間は、板厚0.6mmの場合、従来技術の低温焼鈍の方法(焼鈍温度は例えば650〜900℃)では在炉時間約45secであるのに対し、本発明の方法では約25secの在炉時間で処理することが可能であり、焼鈍工程にかかる負荷が軽減し、製造コストの低減が図られるという効果がある。 In the present invention, high yield strength can be obtained without refining the crystal grains so much with the aid of solid solution strengthening, so the finish annealing temperature may be 900 to 1,100 ° C. and does not require long-time annealing. For example, when the plate thickness is 0.6 mm, the annealing time is about 45 seconds in the conventional low temperature annealing method (annealing temperature is, for example, 650 to 900 ° C.), whereas in the method of the present invention, the current is about 25 seconds. It is possible to perform processing in the furnace time, and there is an effect that the load on the annealing process is reduced and the manufacturing cost is reduced.
仕上焼鈍温度は、900℃未満では均一微細な再結晶粒とするためには焼鈍に長時間を要し製造コストが増大する。一方1100℃を超えると結晶粒の成長が速くなり、微細な結晶粒を得ることが困難となり、高耐力の材料を得ることができない。 If the final annealing temperature is less than 900 ° C., it takes a long time for annealing to obtain uniform fine recrystallized grains, and the manufacturing cost increases. On the other hand, when the temperature exceeds 1100 ° C., the growth of crystal grains becomes fast and it becomes difficult to obtain fine crystal grains, and a material with high yield strength cannot be obtained.
（1)実施例１
固溶強化および結晶粒微細化による耐力の上昇について、成分の異なる５種類の鋼種(鋼種a〜e)で３種類の結晶粒径の材料について耐力を求めた。表２にこれら材料の化学成分、平均結晶粒径、Ａ値、Ｂ値、Ｃ値および耐力を示す。鋼種a、c、dでは、結晶粒径5μm以下で目標の470N/mm2以上の耐力を得ることができる。一方、比較材である鋼種e（SUS304）では、2μm以下まで結晶粒を微細化させないと470N/mm2以上の耐力を得ることができなかった。
With regard to the increase in yield strength due to solid solution strengthening and grain refinement, the yield strength was determined for materials of three types of crystal grain sizes in five types of steel (steel types a to e) having different components. Table 2 shows the chemical composition, average crystal grain size, A value, B value, C value, and yield strength of these materials. For steel types a, c, and d, a target proof stress of 470 N / mm 2 or more can be obtained with a crystal grain size of 5 μm or less. On the other hand, with the steel grade e (SUS304) as a comparative material, a yield strength of 470 N / mm 2 or more could not be obtained unless the crystal grains were refined to 2 μm or less.
（2)実施例２
表２に示す化学成分を有する鋼種a（開発鋼）および比較材の鋼種e（SUS304）について、板厚3mmの熱延焼鈍板から板厚１mmまで冷間圧延を行い、その後1000〜1200℃で焼鈍を行い、耐力および結晶粒径の変化を調査した。鋼種aは、鋼種eに比べてＡ値(計算耐力値）が約150高い。焼鈍試験結果は図５に示すとおりであり、同じ結晶粒径で比較した場合、鋼種aは、鋼種eに比べて耐力が約150Ｎ／mm2高いことが分かる。即ち、固溶強化により、鋼種aは鋼種eに比べて耐力を上昇させていることが確認できる。また、結晶粒微細化により、さらに耐力を上昇させることが可能である。鋼種aは、固溶強化および結晶粒微細化により、SUS304-1/2HのJIS規格を満足することができる。
(2) Example 2
For steel grade a (developed steel) having the chemical composition shown in Table 2 and comparative steel grade e (SUS304), cold rolling is performed from a hot-rolled annealed sheet with a thickness of 3 mm to a thickness of 1 mm, and then at 1000 to 1200 ° C. Annealing was performed and changes in proof stress and crystal grain size were investigated. Steel type a has an A value (calculated proof stress value) about 150 higher than steel type e. The results of the annealing test are as shown in FIG. 5, and it can be seen that when compared with the same crystal grain size, the strength of steel type a is higher by about 150 N / mm 2 than that of steel type e. That is, it can be confirmed that the strength of steel type a is higher than that of steel type e by solid solution strengthening. Further, the yield strength can be further increased by refining the crystal grains. Steel type a can satisfy JIS standard of SUS304-1 / 2H by solid solution strengthening and crystal grain refinement.
（3)実施例３
表２に示す化学成分を有する鋼種ａ(開発鋼種)について、板厚3mmの熱延焼鈍板から板厚0.3mmまで冷間圧延を行い、その後960℃で焼鈍し、各種特性を調査した。以下に開発鋼種の特性を示す。
●冷間圧延性；開発鋼種は、途中で中間焼鈍を行わずに、板厚3mmの熱延焼鈍板から板厚0.3mmまで冷間圧延することができた。
●組織；開発鋼種のミクロ組織を図６に示す。平均結晶粒径3μmの再結晶組織が得られた。
●機械的特性（表３）；開発鋼種は高耐力（600N/mm2）、かつ良好な加工性（伸び：38%）を有する。また、SUS 304-1/2H（調質圧延材)に比べて耐力の異方性が小さい。
●バネ限界値：Ｋｂ（表４、図７）； 開発鋼種（鋼種a）は、SUS304-1/2H仕上（調質圧延材）に比べて、バネ限界値が高く、異方性も小さい。また、L方向については、SUS304 H仕上（調質圧延材）に比べて高いバネ限界値を有する。
●透磁率（図８）；開発鋼種（鋼種a）の透磁率は、60%の冷間圧下率においても極めて低い値を維持している。
●低温熱処理特性（図９）；SUS 304-1/2Hでは、500℃を超える温度で熱処理を行うと、マルテンサイトの焼き戻しにより軟化するが、開発鋼種（鋼種a）は、500℃以上においても軟化しない。また、調質圧延材と同様にバネ限界値も高くなる。
About the steel type a (development steel type) which has the chemical composition shown in Table 2, it cold-rolled from the hot rolled annealing board of 3 mm in thickness to 0.3 mm in thickness, and then annealed at 960 degreeC, and investigated the various characteristics. The characteristics of the developed steel types are shown below.
● Cold Rollability: The developed steel grade could be cold rolled from a hot rolled annealed sheet with a thickness of 3mm to a thickness of 0.3mm without intermediate annealing.
● Microstructure: Figure 6 shows the microstructure of the developed steel grade. A recrystallized structure with an average crystal grain size of 3 μm was obtained.
● Mechanical properties (Table 3): The developed steel has high yield strength (600 N / mm 2 ) and good workability (elongation: 38%). Moreover, the anisotropy of the proof stress is small compared with SUS 304-1 / 2H (tempered rolled material).
● Spring limit value: Kb (Table 4, Fig. 7); The developed steel grade (steel grade a) has a higher spring limit value and less anisotropy than SUS304-1 / 2H finish (tempered rolled material). In the L direction, the spring limit value is higher than that of SUS304H finish (tempered rolled material).
● Permeability (Fig. 8): The permeability of the developed steel grade (steel grade a) remains extremely low even at a cold reduction of 60%.
● Low-temperature heat treatment characteristics (Fig. 9): SUS 304-1 / 2H softens due to tempering of martensite when heat-treated at temperatures exceeding 500 ° C, but the developed steel grade (steel grade a) is 500 ° C or higher. Does not soften. In addition, the spring limit value increases as in the case of the temper rolled material.
Claims (3)
Ａ値=136+731C+47.6Si-1.9Mn-3.4Ni+4.2Cr+17.5Mo-7.7Cu+945N≦500
Ｂ値＝0.8×Ａ値＋12×d-1/2−4≧470
0.001≦d≦0.026
ここで、dは平均結晶粒径（mm）。 In mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 3.0 to 8.0%, P: 0.10% or less, S: 0.010% or less, Ni: 2.0 to 5.0%, Cr: 16.0 to 20.0%, Mo : 0.40% or less, Cu: 1.0 to 3.0%, N: 0.10 to 0.30%, with the balance being a chemical composition consisting of Fe and inevitable impurities, and satisfying the following formula: Stainless steel.
A value = 136 + 731C + 47.6Si-1.9Mn-3.4Ni + 4.2Cr + 17.5Mo-7.7Cu + 945N ≦ 500
B value = 0.8 × A value + 12 × d −1/2 −4 ≧ 470
0.001 ≦ d ≦ 0.026
Here, d is an average crystal grain size (mm).
Ｃ値＝551-462 (C+N)-9.2Si-18.5Mn-29(Ni+Cu)-13.7Cr-18.5Mo-68Nb＜−40 2. The austenitic stainless steel according to claim 1, wherein the C value satisfies the following mathematical formula.
C value = 551-462 (C + N) -9.2Si-18.5Mn-29 (Ni + Cu) -13.7Cr-18.5Mo-68Nb <-40
Ａ値=136+731C+47.6Si-1.9Mn-3.4Ni+4.2Cr+17.5Mo-7.7Cu+945N≦500
Ｃ値＝551-462 (C+N)-9.2Si-18.5Mn-29(Ni+Cu)-13.7Cr-18.5Mo-68Nb＜−40
Ｂ値＝0.8×Ａ値＋12×d-1/2−4≧470
0.001≦d≦0.026
ここで、dは平均結晶粒径（mm）。
In mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 3.0 to 8.0%, P: 0.10% or less, S: 0.010% or less, Ni: 2.0 to 5.0%, Cr: 16.0 to 20.0%, Mo : 0.40% or less, Cu: 1.0 to 3.0%, N: 0.10 to 0.30%, the balance is Fe and inevitable impurities, A value and C value of the austenitic stainless steel satisfying the following formula And then annealing and cold rolling, followed by finish annealing at 900 to 1100 ° C. so that the B value and average crystal grain size (d) satisfy the following formula: A method for producing an austenitic stainless steel.
A value = 136 + 731C + 47.6Si-1.9Mn-3.4Ni + 4.2Cr + 17.5Mo-7.7Cu + 945N ≦ 500
C value = 551-462 (C + N) -9.2Si-18.5Mn-29 (Ni + Cu) -13.7Cr-18.5Mo-68Nb <-40
B value = 0.8 × A value + 12 × d −1/2 −4 ≧ 470
0.001 ≦ d ≦ 0.026
Here, d is an average crystal grain size (mm).
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