JP4207137B2 - High hardness and high corrosion resistance stainless steel - Google Patents
High hardness and high corrosion resistance stainless steel Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、高い硬さと耐食性がともに要求される部材、部品、例えば板ばね、コイルばね、フラッパーバルブ、メタルガスケット、カミソリ刃等の刃物類、等に使用されるのに適した高硬度高耐食ステンレス鋼に関するものである。
【0002】
【従来の技術】
従来より、高硬度と耐食性を必要とする上記の用途には、主としてCを0.5%前後含む13Cr系のマルテンサイト系ステンレス鋼が使用されている。これらのステンレス鋼は焼鈍で軟化させた状態で冷間加工を加えて所定の寸法にした後、焼入れ焼戻しという熱処理を行うことで製造される。この熱処理によってCを含む硬いマルテンサイト相が得られるため、非常に高い硬さを得ることができる。しかし、高硬度を得るために焼入れ焼戻しという熱処理を必要とするため、素材の製造工程が多く、製造工程が複雑であるという問題があった。
また、必要とする硬さがあまり高くない用途には、SUS304、SUS201のようなオーステナイト系ステンレス鋼を冷間加工したものが使用されている。これらはオーステナイト組織の素材を冷間加工することで転位を多く導入して加工硬化するとともに、一部のオーステナイト相が加工誘起マルテンサイト変態することによって強化される。しかし、これらは上記のマルテンサイト系ステンレス鋼並みの高硬度を得るには、オーステナイトが安定なため、かなり強加工を行っても十分な高硬度が得られないという問題があった。
【0003】
【発明が解決しようとする課題】
そこで、最近、焼入れ焼戻しといった複雑な熱処理を必要とせず、主として冷間加工によって強化することでマルテンサイト系ステンレス鋼並みの高硬度が得られるステンレス鋼が望まれている。
本発明の目的は、複雑な熱処理を必要とせずに主として冷間加工によって高硬度が得られ、かつ実用上問題ないレベルの高耐食を有するステンレス鋼を提供することである。
【0004】
【課題を解決するための手段】
本発明者は、オーステナイト系ステンレス鋼について、冷間加工によって高硬度を得るべく、鋭意検討を行なった。その結果、冷間加工後の硬さは加工誘起で変態するマルテンサイト量と関係があり、マルテンサイト量が多い方が硬さが高くなるが、所望の加工誘起マルテンサイトの量を得るには、個々の成分を限定した上で、加工誘起マルテンサイト変態のしやすさに関係するNi当量の適正化が必要であることを見出した。また、耐食性を高めるためには、耐食性を向上させる元素であるCr、Mo、Cu、Nの適正化が必要であり、さらにはそれぞれの合金元素に依存する製造性、硬さ、耐食性に基づいた合金添加量の最適化が必要であり、これらの要件を満たす合金を検討し本発明に到達した。
【0005】
すなわち、本発明の第1発明は、重量%にて、C 0.01〜0.10%、Si 3.0%以下、Mn 5.0%を超え10.0%%以下、Ni 1.0〜7.0%、Cr 12.0〜18.0%、MoまたはWの1種または2種が、Mo+1/2Wで3.0%以下(0%を含む)、Cu 2.0%以下(0%を含む)、N 0.02〜0.15%、残部が実質的にFeからなり、かつ(1)式で示されるA値が23.58〜27、(2)式で示されるB値が25.15以上であって、オーステナイト相中に加工誘起マルテンサイト相を体積%で30%以上含むことを特徴とする高硬度高耐食ステンレス鋼。
A=Ni+0.65Cr+0.98Mo+0.49W+1.05Mn+0.35Si+Cu+12.6(C+N)…………(1)
(ただし、選択元素のうち無添加の元素はゼロとして計算)
B=Cr+3.3Mo+1.65W+Cu+30N …………(2)
(ただし、選択元素のうち無添加の元素はゼロとして計算)
【0006】
また第2発明は、重量%にて、C 0.01〜0.10%、Si 1.0%未満、Mn 5.0%を超え7.0%%以下、Ni 2.0〜7.0%、Cr 12.0〜18.0%、MoまたはWの1種または2種が、Mo+1/2Wで1.0〜3.0%、Cu 2.0%以下(0%を含む)、N 0.02〜0.15%、残部が実質的にFeからなり、かつ(1)式で示されるA値が23.58〜27、(2)式で示されるB値が25.15以上であって、オーステナイト相中に加工誘起マルテンサイト相を体積%で30%以上含むことを特徴とする高硬度高耐食ステンレス鋼。
A=Ni+0.65Cr+0.98Mo+0.49W+1.05Mn+0.35Si+Cu+12.6(C+N)…………(1)
(ただし、選択元素のうち無添加の元素はゼロとして計算)
B=Cr+3.3Mo+1.65W+Cu+30N …………(2)
(ただし、選択元素のうち無添加の元素はゼロとして計算)
【0007】
本発明の第3発明は、第1発明ないし第2発明のいずれかに記載の鋼組成に、V、Ti、Nbのうち1種または2種以上を合計で0.2%以下含むことを特徴とする高硬度高耐食ステンレス鋼であり、また、第1発明ないし第3発明のいずれかに記載の鋼組成に、B、Mg、Ca、Alのうち1種または2種以上を合計で0.10%以下含有することができる。
【0008】
【発明の実施の形態】
本発明は、加工誘起マルテンサイト変態のしやすさと、耐食性を向上させる元素であるCr、Mo、Cu、Nの添加量の最適化を図るために、合金元素のバランスを最適化することが本発明の特徴の一つである。
先ず、Ni、Cr、Mo、W、Mn、Si、Cu、C、Nの元素は、個々の成分範囲を満足するだけでなく、高硬度および良好な耐食性を得るためには、本発明鋼において規定した式を満足する必要がある。
(1)式に示すA値は、本発明鋼のNi当量を示しており、この式のA値の大小が加工誘起マルテンサイト相の生成し易さを左右する重要な指標である。A値は、加工誘起マルテンサイトへの変態しやすさに影響する各元素の重量%に各元素の効果に応じてそれぞれ係数を付した値を足したものである。実験の結果、本発明鋼では、このA値が27を越えると加工誘起マルテンサイトが生成しにくくなり、十分な高硬度が得られにくくなることから、(1)式に示すA値の上限を27とし、A値を23.58〜27の範囲に規定した。
【0009】
(2)式に示すB値は、本発明鋼の耐食性を左右する重要な指標であり、耐孔食性を直接的に向上させる元素であるCr、Mo、W、Cu、Nの重量%に各元素の効果の寄与の程度を示す係数を付した値の和で示している。本発明鋼では、このB値が15より小さいと、良好な耐孔食性が得られないので、(2)式に示すB値を25.15以上とした。
【0010】
以下に本発明鋼の各元素の作用について述べる。
Cは、オーステナイト系ステンレス鋼において、オーステナイト生成元素であり、固溶化処理後にオーステナイト組織を得るために有効である。また冷間加工によって加工誘起変態したマルテンサイト組織を強化し、硬度を高めるのに有効であるが、0.10%を越えて添加すると基地に固溶してオーステナイト相が安定になりすぎ、加工誘起変態が起こりにくくなったり、オーステナイト結晶粒界にCrの炭化物を形成し、基地のCr量を減少させて耐食性を劣化させる原因になる。一方、0.01%より少ないと、冷間加工後に十分な硬さが得られなくなるだけでなく、デルタフェライトが多く生成して耐食性、硬さ、および熱間加工性を低下させることから、Cの含有量を0.01%〜0.10%とした。
【0011】
Siは、脱酸のために少量添加するが、3.0%を越えて添加してもより一層の向上効果がみられず、Cr炭化物をオーステナイト結晶粒界に多く生成して耐食性が劣化することから、3.0%以下とした。望ましくは1.0%未満がよい。
Mnは、オーステナイト生成元素であり、固溶化処理後にオーステナイト組織を得るために有効である。また、A値で規定したNi当量の制御においてはNiの一部をMnに置換してMnを多くできることから、Niと比べると原料が安価なMnを多く添加することで、コストを安くできるという利点もある。
また、オーステナイト相中へのNの固溶度を増加させ、Nの添加を容易にする。換言すれば、N添加を安定して行う(つまりNによる鋳造欠陥をつくらない)ために非常に有効である。したがって、N含有鋼においてはMnを高くする必要があるが10.0%を超えて添加すると、耐食性が劣化する一方、5.0%以下では十分な効果が得られないことから、5.0%を超え10.0%以下とした。望ましくは、5.0%を超え7.0%以下がよい。
【0012】
Niは、Mnと同じくオーステナイト生成元素であり、固溶化処理後にオーステナイト組織を得るために有効である。1.0%より少ないと十分な効果が得られず、一方、7.0%を超えて添加するとオーステナイト相が安定になりすぎ、加工誘起マルテンサイト変態が起こりにくくなるため、十分な高硬度が得にくくなることから、1.0〜7.0%とした。望ましくは、2.0〜7.0%がよい。
Crは、不動態皮膜を形成することで耐食性、特に耐孔食性を高める効果を有する重要な元素である。12.0%より少ないと十分な耐食性が得られず、一方、18.0%を越えて添加するとデルタフェライトを生成しやすくなり、耐食性および熱間加工性を劣化させるので、12.0〜18.0%とした。
【0013】
Moは、不動態皮膜を強化することによって耐食性を高めるのに非常に有効な元素であり、耐食性を重視する場合は添加することが望ましい。WもMoと同様、耐食性を高めるのに有効であるが、W単独ではその効果は小さく、Wを添加する場合は、Moの一部を当量のW(1/2Wが当量のMoに相当)で置換する形で添加するのが望ましい。3.0%を越えて添加するとデルタフェライトを生成し、逆に耐食性を劣化させるだけでなく、熱間加工性、冷間鍛造性も劣化させるので、3.0%以下とした。
【0014】
Cuは、少量添加することで耐食性を高めるのに有効な元素であり、また、オーステナイト相の加工硬化指数を小さくして冷間加工性を向上させる効果があるので、冷間加工によって製造する場合に添加するのが望ましい。2.0%を超えて添加すると熱間加工性が劣化しやすいことから、Cuは2.0%以下とした。
Nは、オーステナイト相およびマルテンサイト相中に固溶して硬さを高めるとともに、耐食性を高めるのに非常に有効な元素である。0.05%より少ないと十分な効果が得られず、一方、0.15%を越えて添加すると、鋼塊の健全性を害して製造性を劣化させることから、0.05%〜0.15%とした。望ましいNの範囲は、0.05〜0.12%である。
【0015】
V、Ti、Nbは必ずしも添加する必要はないが、一次炭化物を形成することで結晶粒を微細化して硬さおよび延性を向上させるのに有効な元素であり、1種または2種以上を必要に応じて添加する。これらのうち、1種または2種以上が合計で、0.2%を越えて添加すると粗大な一次炭化物を形成し、冷間加工性を害することから1種または2種以上を合計で0.2%以下とするのがよい。
【0016】
B、Mg、Ca、Alは、必ずしも添加する必要はないが、酸化物、硫化物を形成することで、結晶粒界に偏析するS、Oを低減し、熱間加工性を向上させるのに有効であり、1種または2種以上を必要に応じて添加する。B、Mg、Ca、Alのうちの1種または2種以上が合計で、0.10%を越えて添加してもより一層の向上効果が得られず、逆に清浄度を低下させて熱間加工性、冷間加工性を害するので、B、Mg、Ca、Alのうちの1種または2種以上を合計で、0.10%以下とするのがよい。
また、不純物元素であるPについては、通常の溶解工程で混入するレベルなら問題ないので特に規定はしないが、耐食性の点からは低い方が望ましい。
本発明鋼は上記の成分範囲を満足しただけでは、所望の高硬度が得られず、冷間圧延、冷間引抜、冷間鍛造等の冷間加工を加えることによって、加工誘起マルテンサイトを生成させる必要がある。加工誘起マルテンサイト相が体積率で30%より少ないと、十分な高硬度が得られないことから、加工誘起マルテンサイト相の体積率は30%以上とした。
【0017】
本発明鋼は、冷間加工を加えることによって高硬度を得ることができる。適正な冷間加工によって所望の量の加工誘起マルテンサイトを生成させることで、ビッカース硬さを500以上とすることができる。
また、本発明鋼は、硬さを低下させずに延性、ばね特性等の向上のために、必要に応じて、冷間加工後に400〜600℃で時効処理を行うことができる。
【0018】
【実施例】
以下、実施例に基づいて本発明を説明する。表1に示す化学成分を持つ鋼を真空溶解によって溶解し、10kgの鋼塊を得た。ここで、鋼No.1,4,6,9,14は組成、A値、B値および冷間加工後の加工誘起マルテンサイト相量がいずれも本発明の限定範囲内にある本発明鋼であり、No.31〜35は組成、A値、B値、冷間加工後の加工誘起マルテンサイト相量のいずれか、またはいくつかが本発明の限定範囲からはずれた比較鋼、No.36は従来の焼入れ焼戻し鋼の一種SUS420J2であり、それ以外は参考例である。No.1〜35の鋼を熱間鍛造、熱間圧延によって厚さ2mmの板材にし、1050℃に加熱後、空冷の固溶化処理を行なった。その後、50〜70%の圧下率で冷間圧延した。No.36の鋼は950℃から焼入れた後、300℃で焼戻しを行った。
【0019】
上記の加工誘起マルテンサイト相量はX線回折法によって測定した。硬さについては、冷間圧延した板の縦断面でビッカース硬さを測定することによって求めた。耐食性については、JIS Z2371に規定される35℃の5%塩水による塩水噴霧試験を100時間行い、発錆の有無で評価した。これらの結果を表2に示す。ここで耐食試験による発錆の有無については、発錆のなかったものを○印、発錆したものを×印を付して示した。
また、参考例No.2、本発明鋼No.4および従来鋼No.36については、50℃の5%硫酸、20%硝酸、20%塩酸、20%水酸化ナトリウム溶液中での耐食試験を行い、試験後の重量減を測定し、水溶液中での耐食性を評価した。
【0020】
【表1】
【0021】
【表2】
【0022】
【表3】
【0023】
表2からわかるように、本発明鋼No.1,4,6,9,14はいずれも冷間加工後のビッカース硬さが500以上の高硬度を示している。また、本発明鋼は塩水噴霧試験による発錆もみられず、高い硬度と良好な耐食性を持つことがわかる。
これに対して、組成、A値、B値、冷間加工後の加工誘起マルテンサイト相量のいずれか一つ以上が本発明に規定した範囲から外れる比較鋼No.31〜35および従来鋼No.36は、硬さ、塩水噴霧による耐食性の一つ以上の特性が本発明鋼に比べて悪いことがわかる。
特にA値および加工誘起マルテンサイト相量が規定した範囲から外れる比較鋼No.32〜34は硬さが低く、高硬度が得られない。またB値が規定した範囲から外れる比較鋼No.31は発錆がみられており、耐食性が不十分である。
【0024】
また、図1に本発明鋼と従来鋼の硫酸、硝酸、塩酸、水酸化ナトリウム溶液中での耐食性を比較して示す。図1より、本発明鋼は、各種酸、アルカリ水溶液に浸漬後の腐食減量が従来鋼より小さく、各種酸、アルカリ水溶液に対する耐食性が、従来鋼より優れていることがわかる。
また、表3に、参考例No.2、本発明鋼No.4の冷間加工前の固溶化処理状態の常温引張特性を示すが、本発明鋼は固溶化処理状態のビッカース硬さが300以下と低く、伸び、絞りが大きい値を示している。このことから、本発明鋼は冷間加工性が良好であり、冷間成形も容易であることがわかる。
【0025】
【発明の効果】
以上説明したように、本発明の高硬度高耐食ステンレス鋼は、高硬度を持ち、かつ耐食性に優れることから、高い硬さと耐食性がともに要求される部材、部品、例えば板ばね、コイルばね、フラッパーバルブ、メタルガスケット、カミソリ刃等の刃物類、等に用いれば、寿命が向上し、工業上顕著な効果を有する。
【図面の簡単な説明】
【図1】耐食性を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention provides a high hardness and high corrosion resistance suitable for use in members and parts that require both high hardness and corrosion resistance, such as blades, coil springs, flapper valves, metal gaskets, blades such as razor blades, etc. It relates to stainless steel.
[0002]
[Prior art]
Conventionally, 13Cr-based martensitic stainless steel mainly containing about 0.5% of C has been used for the above-mentioned applications requiring high hardness and corrosion resistance. These stainless steels are manufactured by performing a heat treatment called quenching and tempering after applying cold working to a predetermined size after annealing and softening. Since a hard martensite phase containing C is obtained by this heat treatment, a very high hardness can be obtained. However, since heat treatment called quenching and tempering is required to obtain high hardness, there are many manufacturing processes of the material, and there is a problem that the manufacturing process is complicated.
For applications where the required hardness is not so high, austenitic stainless steels such as SUS304 and SUS201 are cold-worked. These are strengthened by cold-working the austenitic structure material to introduce and disperse many dislocations and to cause some austenitic phases to undergo work-induced martensitic transformation. However, they have a problem that austenite is stable in order to obtain the same high hardness as the martensitic stainless steel described above, and therefore, a sufficiently high hardness cannot be obtained even if considerably hardened.
[0003]
[Problems to be solved by the invention]
Therefore, recently, there is a demand for stainless steel that does not require complicated heat treatment such as quenching and tempering, and that can obtain high hardness similar to martensitic stainless steel by strengthening mainly by cold working.
An object of the present invention is to provide a stainless steel having a high level of corrosion resistance, which has high hardness obtained mainly by cold working without requiring a complicated heat treatment and has no practical problem.
[0004]
[Means for Solving the Problems]
The inventor has intensively studied austenitic stainless steel in order to obtain high hardness by cold working. As a result, the hardness after cold working is related to the amount of martensite transformed by processing induction, and the higher the amount of martensite, the higher the hardness, but to obtain the desired amount of processing-induced martensite. The present inventors have found that it is necessary to optimize the Ni equivalent related to the ease of processing-induced martensite transformation after limiting individual components. In addition, in order to improve the corrosion resistance, it is necessary to optimize Cr, Mo, Cu, and N, which are elements that improve the corrosion resistance, and further based on the manufacturability, hardness, and corrosion resistance depending on each alloy element. The alloy addition amount needs to be optimized, and an alloy satisfying these requirements has been studied and the present invention has been achieved.
[0005]
That is, according to the first invention of the present invention, in terms of% by weight, C 0.01 to 0.10%, Si 3.0% or less, Mn over 5.0% and 10.0% or less, Ni 1.0 -7.0%, Cr 12.0-18.0%, 1 or 2 types of Mo or W is 3.0% or less (including 0%) at Mo + 1 / 2W, Cu 2.0% or less ( N is 0.02 to 0.15%, the balance is substantially made of Fe, and the A value represented by the formula (1) is 23.58 to 27 , and B is represented by the formula (2). A high-hardness, high-corrosion-resistant stainless steel having a value of 25.15 or more and containing a work-induced martensite phase in an austenite phase of 30% or more by volume.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among selected elements)
[0006]
Further, the second invention is, in terms of% by weight, C 0.01 to 0.10%, Si less than 1.0%, Mn exceeding 5.0% and 7.0% or less, Ni 2.0 to 7.0. %, Cr 12.0 to 18.0%, one or two of Mo or W is Mo + 1 / 2W, 1.0 to 3.0%, Cu 2.0% or less (including 0%), N 0.02 to 0.15%, the balance is substantially made of Fe, and the A value represented by the formula (1) is 23.58 to 27 , and the B value represented by the formula (2) is 25.15 or more. A high-hardness, high-corrosion-resistant stainless steel characterized by containing a work-induced martensite phase in a volume of 30% or more in the austenite phase.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among selected elements)
[0007]
A third invention of the present invention is characterized in that the steel composition according to any one of the first and second inventions includes one or more of V, Ti and Nb in a total amount of 0.2% or less. In addition, the steel composition according to any one of the first to third aspects of the present invention includes one or more of B, Mg, Ca, and Al in a total of 0.001. It can contain 10% or less .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is to optimize the balance of alloy elements in order to optimize the ease of processing-induced martensite transformation and the amount of addition of Cr, Mo, Cu, and N, which are elements that improve corrosion resistance. This is one of the features of the invention.
First, the elements Ni, Cr, Mo, W, Mn, Si, Cu, C and N not only satisfy the individual component ranges, but also in the steel of the present invention in order to obtain high hardness and good corrosion resistance. It is necessary to satisfy the specified formula.
The A value shown in the formula (1) indicates the Ni equivalent of the steel of the present invention, and the magnitude of the A value in this formula is an important index that affects the ease of forming the work-induced martensite phase. The A value is obtained by adding a value obtained by adding a coefficient according to the effect of each element to the weight% of each element that affects the ease of transformation to work-induced martensite. As a result of the experiment, in the steel of the present invention, when this A value exceeds 27, it becomes difficult to form work-induced martensite and it becomes difficult to obtain a sufficiently high hardness, so the upper limit of the A value shown in the formula (1) is limited. 27, and the A value was specified in the range of 23.58 to 27 .
[0009]
The B value shown in the formula (2) is an important index that influences the corrosion resistance of the steel of the present invention, and the weight value of Cr, Mo, W, Cu, and N, which are elements that directly improve the pitting corrosion resistance. It is shown as a sum of values with coefficients indicating the degree of contribution of elemental effects. In the steel of the present invention, when this B value is smaller than 15, good pitting corrosion resistance cannot be obtained, so the B value shown in the formula (2) is set to 25.15 or more .
[0010]
The action of each element of the steel of the present invention will be described below.
C is an austenite-forming element in austenitic stainless steel, and is effective for obtaining an austenite structure after solution treatment. It is effective for strengthening the martensite structure that has been induced by cold working and increasing the hardness, but if added over 0.10%, the austenite phase becomes too stable due to solid solution in the matrix. Induced transformation is less likely to occur, or Cr carbide is formed at the austenite grain boundaries, reducing the amount of Cr in the matrix and deteriorating corrosion resistance. On the other hand, if the content is less than 0.01%, not only the sufficient hardness cannot be obtained after cold working, but also a large amount of delta ferrite is generated, which decreases the corrosion resistance, hardness, and hot workability. The content of was made 0.01% to 0.10%.
[0011]
Si is added in a small amount for deoxidation, but even if added over 3.0%, a further improvement effect is not seen, and a large amount of Cr carbide is generated at the austenite grain boundaries, resulting in deterioration of corrosion resistance. Therefore, it was set to 3.0% or less. Desirably, it is less than 1.0%.
Mn is an austenite generating element and is effective for obtaining an austenite structure after the solution treatment. In addition, in the control of the Ni equivalent defined by the A value, Mn can be increased by substituting part of Ni with Mn. Therefore, the cost can be reduced by adding more Mn, which is cheaper than Ni. There are also advantages.
In addition, the solid solubility of N in the austenite phase is increased, and the addition of N is facilitated. In other words, it is very effective for stably adding N (that is, not producing casting defects due to N). Therefore, it is necessary to increase Mn in the N-containing steel, but if it is added over 10.0%, the corrosion resistance is deteriorated. On the other hand, if it is 5.0% or less, a sufficient effect cannot be obtained. % And 10.0% or less. Desirably, it is more than 5.0% and 7.0% or less.
[0012]
Ni is an austenite-forming element like Mn, and is effective for obtaining an austenite structure after solution treatment. If the amount is less than 1.0%, a sufficient effect cannot be obtained. On the other hand, if the amount exceeds 7.0%, the austenite phase becomes too stable, and the processing-induced martensite transformation hardly occurs. Since it becomes difficult to obtain, it was set to 1.0 to 7.0%. Desirably, 2.0 to 7.0% is good.
Cr is an important element having an effect of improving corrosion resistance, particularly pitting corrosion resistance, by forming a passive film. If it is less than 12.0%, sufficient corrosion resistance cannot be obtained. On the other hand, if it is added in excess of 18.0%, delta ferrite is likely to be formed, and the corrosion resistance and hot workability are deteriorated. 0.0%.
[0013]
Mo is an element that is very effective for enhancing the corrosion resistance by strengthening the passive film, and it is desirable to add it when importance is attached to the corrosion resistance. W is also effective for enhancing the corrosion resistance like Mo, but the effect of W alone is small, and when W is added, a part of Mo is equivalent to W (1/2 W corresponds to equivalent Mo) It is desirable to add in the form of replacing with. If added over 3.0%, delta ferrite is generated, and not only the corrosion resistance is deteriorated, but also hot workability and cold forgeability are deteriorated.
[0014]
Cu is an element effective for enhancing corrosion resistance when added in a small amount, and has the effect of improving the cold workability by reducing the work hardening index of the austenite phase. It is desirable to add to. If hot addition exceeds 2.0%, the hot workability tends to deteriorate, so Cu was made 2.0% or less.
N is an element that is very effective for increasing the hardness and increasing the corrosion resistance while dissolving in the austenite phase and the martensite phase. 0.0 less than 5% and no sufficient effect is obtained, whereas, when added in excess of 0.15%, from degrading the productivity and impair the integrity of the steel ingot, 0.0 5% 0.15%. A desirable range of N is 0.05 to 0.12%.
[0015]
V, Ti and Nb do not necessarily need to be added, but are effective elements to refine the crystal grains and improve the hardness and ductility by forming primary carbides, and one or more are required Add as appropriate. Among these, one or more types are added in total, and if added in excess of 0.2%, coarse primary carbides are formed, and cold workability is impaired. It should be 2% or less.
[0016]
B, Mg, Ca, and Al are not necessarily added, but by forming oxides and sulfides, S and O segregated at the grain boundaries are reduced, and hot workability is improved. It is effective, and 1 type, or 2 or more types is added as needed. Even if one or more of B, Mg, Ca, and Al are added in total exceeding 0.10%, a further improvement effect cannot be obtained. Since the hot workability and the cold workability are impaired, it is preferable that one or more of B, Mg, Ca, and Al be 0.10% or less in total.
Further, P, which is an impurity element, is not particularly specified as long as it is a level mixed in a normal melting process, and is not particularly specified, but is preferably lower in terms of corrosion resistance.
The steel of the present invention does not achieve the desired high hardness only by satisfying the above component ranges, and generates work-induced martensite by applying cold working such as cold rolling, cold drawing, cold forging, etc. It is necessary to let If the work-induced martensite phase is less than 30% in volume ratio, sufficient high hardness cannot be obtained. Therefore, the volume ratio of the work-induced martensite phase is set to 30% or more.
[0017]
The steel of the present invention can obtain high hardness by applying cold working. By generating a desired amount of processing-induced martensite by appropriate cold processing, the Vickers hardness can be set to 500 or more.
In addition, the steel of the present invention can be subjected to aging treatment at 400 to 600 ° C. after cold working, if necessary, in order to improve ductility, spring characteristics, etc. without reducing the hardness.
[0018]
【Example】
Hereinafter, the present invention will be described based on examples. Steel having chemical components shown in Table 1 was melted by vacuum melting to obtain a 10 kg steel ingot. Here, Steel No. Nos. 1 , 4, 6 , 9, and 14 are steels of the present invention in which the composition, A value, B value, and work induced martensite phase amount after cold working are all within the limited range of the present invention. Nos. 31 to 35 are comparative steels having a composition, A value, B value, work-induced martensite phase amount after cold working, or some of them being out of the limited range of the present invention, No. 31-35. 36 Ri kind SUS420J2 der conventional quenched and tempered steel, otherwise Ru Reference Example der. No. 1 to 35 steel was made into a plate having a thickness of 2 mm by hot forging and hot rolling, heated to 1050 ° C., and then subjected to air cooling solid solution treatment. Then, cold rolling was performed at a reduction rate of 50 to 70%. No. The 36 steel was quenched from 950 ° C. and then tempered at 300 ° C.
[0019]
The amount of work-induced martensite phase was measured by an X-ray diffraction method. About hardness, it calculated | required by measuring Vickers hardness in the longitudinal cross-section of the cold-rolled board. About corrosion resistance, the salt spray test by 5% salt water of 35 degreeC prescribed | regulated to JISZ2371 was done for 100 hours, and it evaluated by the presence or absence of rusting. These results are shown in Table 2. Here, with respect to the presence or absence of rusting by the corrosion resistance test, those that did not rust were marked with ○, and those that rusted were marked with ×.
Reference Example No. 2. Invention steel No. 2 4 and conventional steel no. For 36, a corrosion resistance test was conducted in 5% sulfuric acid, 20% nitric acid, 20% hydrochloric acid, and 20% sodium hydroxide solution at 50 ° C., and the weight loss after the test was measured to evaluate the corrosion resistance in an aqueous solution. .
[0020]
[Table 1]
[0021]
[Table 2]
[0022]
[Table 3]
[0023]
As can be seen from Table 2, steel No. 1 of the present invention. 1 , 4, 6 , 9, and 14 all show a high hardness of 500 or more after the Vickers hardness after cold working. In addition, it can be seen that the steel of the present invention does not show rusting by the salt spray test and has high hardness and good corrosion resistance.
On the other hand, comparative steel No. 1 in which any one or more of the composition, the A value, the B value, and the work-induced martensite phase amount after cold working deviate from the range defined in the present invention. 31-35 and conventional steel No. No. 36 shows that one or more characteristics of hardness and corrosion resistance by salt spray are worse than the steel of the present invention.
In particular, the comparative steel no. Nos. 32-34 have low hardness, and high hardness cannot be obtained. In addition, comparative steel no. No. 31 is rusted and has insufficient corrosion resistance.
[0024]
FIG. 1 shows a comparison of the corrosion resistance of the steel of the present invention and conventional steel in sulfuric acid, nitric acid, hydrochloric acid, and sodium hydroxide solutions. FIG. 1 shows that the steel of the present invention has smaller corrosion weight loss after immersion in various acid and alkaline aqueous solutions than that of conventional steel, and is superior in corrosion resistance to various acid and alkaline aqueous solutions.
In Table 3, Reference Example No. 2. Invention steel No. 2 4 shows the room temperature tensile properties of the solution treatment state before cold working, but the steel of the present invention has a low Vickers hardness of 300 or less in the solution treatment state, and shows a large value of elongation and drawing. This shows that the steel of the present invention has good cold workability and is easy to cold form.
[0025]
【The invention's effect】
As described above, the high hardness and high corrosion resistance stainless steel of the present invention has high hardness and excellent corrosion resistance. Therefore, members and parts that require both high hardness and corrosion resistance, such as leaf springs, coil springs, and flappers. When used for blades such as valves, metal gaskets, razor blades, etc., the service life is improved, and there is a remarkable industrial effect.
[Brief description of the drawings]
FIG. 1 is a diagram showing corrosion resistance.
Claims (4)
A=Ni+0.65Cr+0.98Mo+0.49W+1.05Mn+0.35Si+Cu+12.6(C+N)…………(1)
(ただし、選択元素のうち無添加の元素はゼロとして計算)
B=Cr+3.3Mo+1.65W+Cu+30N …………(2)
(ただし、選択元素のうち無添加の元素はゼロとして計算)By weight%, C 0.01 to 0.10%, Si 3.0% or less, Mn 5.0% to 10.0% or less, Ni 1.0 to 7.0%, Cr 12.0 to 18.0%, one or two of Mo or W are Mo + 1 / 2W of 3.0% or less (including 0%), Cu 2.0% or less (including 0%), N 0.05 to 0.15%, the balance consists of Fe and inevitable impurities, and the A value represented by the formula (1) is 23.58 to 27 , the B value represented by the formula (2) is 25.15 or more, A high-hardness, high-corrosion-resistant stainless steel characterized by containing a work-induced martensite phase in an austenite phase of 30% or more by volume.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among the selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among the selected elements)
A=Ni+0.65Cr+0.98Mo+0.49W+1.05Mn+0.35Si+Cu+12.6(C+N)…………(1)
(ただし、選択元素のうち無添加の元素はゼロとして計算)
B=Cr+3.3Mo+1.65W+Cu+30N …………(2)
(ただし、選択元素のうち無添加の元素はゼロとして計算)By weight%, C 0.01 to 0.10%, Si less than 1.0%, Mn over 5.0% and 7.0% or less, Ni 2.0 to 7.0%, Cr 12.0 ˜18.0%, one or two of Mo or W are Mo + 1 / 2W, 1.0 to 3.0%, Cu 2.0% or less (including 0%), N 0.05 to 0.00. 15%, the balance is Fe and inevitable impurities, and the A value represented by the formula (1) is 23.58 to 27 , the B value represented by the formula (2) is 25.15 or more, and the austenite phase A high-hardness, high-corrosion-resistant stainless steel characterized by containing a work-induced martensite phase at 30% or more by volume.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among the selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among the selected elements)
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DE10046181C2 (en) * | 2000-09-19 | 2002-08-01 | Krupp Thyssen Nirosta Gmbh | Process for producing a steel strip or sheet consisting predominantly of Mn austenite |
FR2827876B1 (en) * | 2001-07-27 | 2004-06-18 | Usinor | AUSTENITIC STAINLESS STEEL FOR COLD DEFORMATION THAT CAN BE FOLLOWED BY MACHINING |
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JP3899018B2 (en) * | 2002-11-29 | 2007-03-28 | 東洋鋼鈑株式会社 | Gasket material, manufacturing method thereof, and gasket |
JP4498847B2 (en) * | 2003-11-07 | 2010-07-07 | 新日鐵住金ステンレス株式会社 | Austenitic high Mn stainless steel with excellent workability |
DE102005030413C5 (en) * | 2005-06-28 | 2009-12-10 | Technische Universität Bergakademie Freiberg | High-strength austenitic-martensitic lightweight steel and its use |
US8052703B2 (en) * | 2005-06-29 | 2011-11-08 | Boston Scientific Scimed, Inc. | Medical devices with cutting elements |
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