JP2007113068A - Spring material made of high strength and high corrosion resistant stainless steel having excellent bendability - Google Patents

Spring material made of high strength and high corrosion resistant stainless steel having excellent bendability Download PDF

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JP2007113068A
JP2007113068A JP2005305816A JP2005305816A JP2007113068A JP 2007113068 A JP2007113068 A JP 2007113068A JP 2005305816 A JP2005305816 A JP 2005305816A JP 2005305816 A JP2005305816 A JP 2005305816A JP 2007113068 A JP2007113068 A JP 2007113068A
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Kenichi Morimoto
憲一 森本
Seiichi Isozaki
誠一 磯崎
Hiroki Tomimura
宏紀 冨村
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Nippon Steel Nisshin Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a spring material made of stainless steel using metastable austenitic stainless steel as a base and having excellent strength, corrosion resistance, spring properties or the like. <P>SOLUTION: The stainless steel has a composition comprising, by mass, ≤0.15% C, 1.0 to 4.0% Si, ≤5.0% Mn, ≤0.040% P, ≤0.010% S, 4.0 to 10.0% Ni, 13.0 to 18.0% Cr, 0 to 3.5% Cu, 1.0 to 5.0% Mo, ≤0.15% N, ≤0.15% Nb, ≤0.05% Ti, ≤0.20% V, ≤0.015% O, ≤0.70% 2Nb+4Ti+V, and the balance Fe with inevitable impurities, and in which the value of Md(N) defined as Md(N)=580-(520C+2Si+16Mn+16Cr+23Ni+300N+10Mo) is set to the range of 0 to 100. The stainless steel may be as cold-rolled, but is preferably subjected to aging treatment of performing holding at 300 to 500°C for 0 to 20 hr after the cold rolling. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、例えば自動車シートベルトのリトラクターぜんまいバネ等、曲げ加工されて使用され、強度,バネ性及び耐食性を必要とする各種汎用バネに適用されるステンレス鋼性バネ材に関する。   The present invention relates to a stainless steel spring material applied to various general purpose springs which are used after being bent, such as a retractor spring of an automobile seat belt, and which requires strength, springiness and corrosion resistance.

各種汎用バネの素材には、マルテンサイト系ステンレス鋼,加工硬化型ステンレス鋼或いは析出硬化型ステンレス鋼等が従来から使用されている。
マルテンサイト系ステンレス鋼は、高温のオーステナイト状態から急冷してマルテンサイト変態させることによって硬化させた鋼種であり、SUS402J2等がこれに相当する。焼き入れ・焼戻しの調質処理によって高い強度及び靭性が得られるが、Cr含有量が12.0〜14.0%と低いために耐食性が劣り、さらにCを多量に含んでいるために曲げ加工性も悪い場合がある。
Conventionally, martensitic stainless steel, work hardening type stainless steel, precipitation hardening type stainless steel or the like has been used as a material for various general purpose springs.
Martensitic stainless steel is a steel type hardened by quenching from a high-temperature austenite state and transforming into martensite, and SUS402J2 or the like corresponds to this. High strength and toughness can be obtained by tempering treatment of quenching and tempering, but the Cr content is as low as 12.0 to 14.0%, so the corrosion resistance is inferior, and because it contains a large amount of C, it is bent. It may be bad.

加工硬化型オーステナイト系ステンレス鋼は、溶体化処理状態でオーステナイト相を呈し、その後の冷間圧延工程で加工誘起マルテンサイトを生成させて高強度を得ようとするものである。加工硬化型オーステナイト系ステンレス鋼の強度は、冷間加工量やマルテンサイト量に依存するが、冷間加工のみによる強度の調整は非常に困難である。また、冷間加工率を著しく大きくすると良好な曲げ性が得られない場合がある。   Work hardening type austenitic stainless steel exhibits an austenite phase in a solution treatment state, and is intended to obtain high strength by generating work induced martensite in a subsequent cold rolling process. The strength of work-hardening austenitic stainless steel depends on the amount of cold work and the amount of martensite, but it is very difficult to adjust the strength only by cold work. Also, if the cold work rate is significantly increased, good bendability may not be obtained.

析出硬化型ステンレス鋼は、析出硬化能の高い元素を添加し、時効処理により硬化させるもので、Cuを添加したSUS630,Alを添加したSUS631等が代表的である。
Cu添加の析出硬化型ステンレス鋼は、溶体化処理後にマルテンサイト単相を呈し、その後の時効処理により硬化させたものであるが、引張強さは高くても1400N/mm2程度に留まる。
Al添加の析出硬化型ステンレス鋼は、溶体化処理で生じた準安定オーステナイト相を冷間加工等によってマルテンサイトに一部変態させた後、時効処理によって金属間化合物Ni3Alを析出させて硬化させたものである。引張強さを1800N/mm2まで上昇させることが可能であるが、非金属介在物が鋼中に残存しやすく靭性低下を招きやすい。
Precipitation hardening type stainless steel is one in which an element having high precipitation hardening ability is added and hardened by aging treatment. Typical examples include SUS630 to which Cu is added, SUS631 to which Al is added.
The precipitation-added stainless steel with addition of Cu exhibits a martensite single phase after solution treatment and is hardened by subsequent aging treatment, but the tensile strength is at most about 1400 N / mm 2 at most.
Precipitation hardening type stainless steel with addition of Al is obtained by partially transforming the metastable austenite phase generated by solution treatment into martensite by cold working, etc., and then precipitating intermetallic compound Ni 3 Al by aging treatment. It has been made. Although it is possible to increase the tensile strength to 1800 N / mm 2 , nonmetallic inclusions are likely to remain in the steel, leading to a decrease in toughness.

上記の従来鋼種に対し、時効処理による強度上昇を利用した高強度ステンレス鋼が開発されている。例えば特許文献1では、CuとSiを複合添加した準安定オーステナイト系ステンレス鋼に冷間圧延を施して加工誘起マルテンサイトを生成させ、その後の時効処理で引張強さ2000N/mm2,ビッカース硬さ580を得ている。しかしながら、特許文献1で提案されたステンレス鋼は、最適な時効処理温度範囲が比較的狭いため、前記強度レベルを安定して得るには、精度の高い温度制御を必要とし、生産性は必ずしもよくない。
特開昭61−295356号公報
A high-strength stainless steel using the strength increase by aging treatment has been developed with respect to the above-described conventional steel types. For example, in Patent Document 1, a metastable austenitic stainless steel compounded with Cu and Si is cold-rolled to produce work-induced martensite, and then a tensile strength of 2000 N / mm 2 and Vickers hardness are obtained by aging treatment. 580 is obtained. However, since the optimum aging temperature range is relatively narrow, the stainless steel proposed in Patent Document 1 requires highly accurate temperature control in order to stably obtain the strength level, and the productivity is not always good. Absent.
JP-A-61-295356

近年、バネ材は自動車,建築等の各分野で幅広く使用されており、安全基準も年々厳しくなっている。用途によっては素材の耐食性も要求されている。例えば、曲げ加工後に腐食させ、その後引張試験を実施してその破断強度を一つの判断基準としている。素材の耐食性が劣ると、発銹を起点に応力が集中し、切欠き作用によって素材自体の強度低下をもたらす。しかし、現状では要求レベルを満足する強度と耐食性を兼ね備えたバネ用の素材は見当たらない。
本発明は、このような問題を解消すべく案出されたものであり、加工誘起マルテンサイト相+オーステナイト相の二相組織をもつ準安定オーステナイト系ステンレス鋼が優れた強度及び耐食性を呈するとの知見をベースに素材の曲げ加工性を改善し、強度,耐食性及びバネ性等の要求特性を満足するステンレス鋼製バネ材を提供することを目的とする。
In recent years, spring materials have been widely used in various fields such as automobiles and architecture, and safety standards have become stricter year by year. Depending on the application, the corrosion resistance of the material is also required. For example, it is corroded after bending, and then a tensile test is performed to determine its breaking strength as one criterion. If the corrosion resistance of the material is inferior, the stress concentrates on the starting point, and the strength of the material itself is reduced by the notch action. However, at present there are no spring materials that have both strength and corrosion resistance that satisfy the required level.
The present invention has been devised to solve such problems, and the metastable austenitic stainless steel having a two-phase structure of work-induced martensite phase + austenite phase exhibits excellent strength and corrosion resistance. The objective is to provide a stainless steel spring material that improves the bending workability of the material based on the knowledge and satisfies the required properties such as strength, corrosion resistance and spring property.

本発明の曲げ性に優れた高強度高耐食ステンレス鋼製バネ材は、その目的を達成するため、C:0.15質量%以下,Si:1.0〜4.0質量%,Mn:5.0質量%以下,P:0.040質量%以下,S:0.010質量%以下,Ni:4.0〜10.0質量%,Cr:13.0〜18.0質量%,Cu:0〜3.5質量%,Mo:1.0〜5.0質量%,N:0.15質量%以下,Nb:0.15質量%以下,Ti:0.05質量%以下,V:0.20質量%以下,O:0.015質量%以下,2Nb+4Ti+V:0.70質量%以下,残部がFe及び不可避的不純物の組成をもち、Md(N)=580−(520C+2Si+16Mn+16Cr+23Ni+300N+10Mo)と定義されるMd(N)値が0〜100の範囲にあることを特徴とする。   The high-strength, high-corrosion-resistant stainless steel spring material with excellent bendability according to the present invention achieves the object, C: 0.15% by mass or less, Si: 1.0-4.0% by mass, Mn: 5 0.0 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Ni: 4.0-10.0 mass%, Cr: 13.0-18.0 mass%, Cu: 0 to 3.5 mass%, Mo: 1.0 to 5.0 mass%, N: 0.15 mass% or less, Nb: 0.15 mass% or less, Ti: 0.05 mass% or less, V: 0 20% by mass or less, O: 0.015% by mass or less, 2Nb + 4Ti + V: 0.70% by mass or less, with the balance being Fe and inevitable impurities, Md (N) = 580− (520C + 2Si + 16Mn + 16Cr + 23Ni + 300N + 10Mo) Md (N) value is in the range of 0-100 And wherein the Rukoto.

本発明バネ材は、冷延のままでも加工硬化及び加工誘起マルテンサイト変態による変態強化によって硬質化しているが、さらに冷間加工後に300〜500℃で0〜20時間の保持を行う熱処理を施すと、時効硬化によってさらに硬質化することができる。
このステンレス鋼製バネ材としては、JIS Z2248による曲げ試験で曲率Rと板厚tの比R/tが4以下の曲げ特性と、腐食液として35℃の5%NaCl水溶液を用い、当該腐食液を被試験板に15分間噴霧した後、湿度35%で60℃の雰囲気で60分間乾燥し、湿度45%で50℃の雰囲気で180分間湿潤させる処理を1サイクルとし、これを50サイクル実施する腐食試験を行った後に1000N/mm2以上の引張破断強度を有するものが好ましい。
また、JIS H3130で規定される繰返したわみ試験を行ったとき、800N/mm2以上のバネ限界値[Kb0.1]を有するものが好ましい。
The spring material of the present invention is hardened by transformation strengthening by work hardening and work-induced martensite transformation even in cold rolling, and further subjected to heat treatment for 0 to 20 hours at 300 to 500 ° C. after cold working. Further, it can be hardened by age hardening.
As this stainless steel spring material, a bending property in which the ratio R / t of the curvature R to the plate thickness t is 4 or less in a bending test according to JIS Z2248, and a 5% NaCl aqueous solution at 35 ° C. is used as the corrosive solution. Is sprayed on the plate to be tested for 15 minutes, dried in an atmosphere of 35 ° C. and 60 ° C. for 60 minutes, and wetted for 45 minutes in a 45% humidity and 50 ° C. atmosphere for one cycle. Those having a tensile strength at break of 1000 N / mm 2 or more after conducting a corrosion test are preferred.
In addition, when a repeated deflection test specified by JIS H3130 is performed, those having a spring limit value [Kb 0.1 ] of 800 N / mm 2 or more are preferable.

本発明のステンレス鋼製バネ材は、オーステナイト系ステンレス鋼を素材とし、冷間圧延時の加工硬化,変態強化及び時効硬化によって強度が付与され、また析出物の生成を抑制することにより曲げ加工性が改善されている。さらに、腐食環境下に曝されても優れた強度が維持可能な耐食性を有している。
その結果、曲げ加工が必要とされ、さらに強度,バネ性及び耐食性が要求されるバネ用途に最適なステンレス鋼製バネ材として使用される。
The spring material made of stainless steel according to the present invention is made of austenitic stainless steel, is given strength by work hardening during cold rolling, transformation strengthening and age hardening, and also has bending workability by suppressing the formation of precipitates. Has been improved. Furthermore, it has corrosion resistance that can maintain excellent strength even when exposed to a corrosive environment.
As a result, it is used as a spring material made of stainless steel that is optimal for spring applications that require bending and further requires strength, springiness, and corrosion resistance.

本発明者等は、過酷な腐食環境に耐え得るバネ材を得る手段について種々検討した。その結果、オーステナイト系ステンレス鋼を素材とし、「加工硬化」,「変態強化」及び「時効硬化」の現象を利用して強度上昇を図った、加工誘起マルテンサイト相+オーステナイト相の二相組織からなる準安定オーステナイト系ステンレス鋼によって達成されることを見出した。ただし、上記条件のみでは所望の曲げ性や耐食性を満たすことはできない。さらに鋭意検討した結果、成分・組成を細かく調整することで、はじめて所望の強度,バネ性及び耐食性を有するバネ材に最適な準安定オーステナイト系ステンレス鋼が得られる。   The present inventors have studied various means for obtaining a spring material that can withstand a severe corrosive environment. As a result, the austenitic stainless steel was used as a raw material, and the work-induced martensite phase + austenite phase was obtained from the two-phase structure using the phenomena of “work hardening”, “transformation strengthening” and “age hardening”. The metastable austenitic stainless steel is found to be achieved. However, desired bendability and corrosion resistance cannot be satisfied only by the above conditions. As a result of further intensive studies, the metastable austenitic stainless steel optimum for a spring material having desired strength, springiness and corrosion resistance can be obtained for the first time by finely adjusting the components and composition.

前掲のように成分・組成が特定されたステンレス鋼は、加工硬化及び加工誘起マルテンサイト変態による変態強化によって硬質化し、更に冷間加工後の熱処理で時効硬化する。また、時効硬化が促進しやすい成分設計のため、比較的低温・短時間の時効処理で靭性を回復させることができる。比較的低温・短時間の時効処理は、介在物や析出物の生成要因となる成分の制限と合せて、疲労破壊の起点となる粗大析出物の生成防止に有効であり、疲労特性及び耐食性をも向上させる。   The stainless steel whose components and composition are specified as described above hardens by work hardening and transformation strengthening by work-induced martensitic transformation, and further age-hardened by heat treatment after cold working. In addition, because of the component design that facilitates age hardening, the toughness can be recovered by aging treatment at a relatively low temperature for a short time. Aging at a relatively low temperature for a short time is effective in preventing the formation of coarse precipitates that are the starting point of fatigue failure, in combination with the limitations on the components that cause inclusions and precipitates. Also improve.

次いで、本発明のステンレス鋼に含まれる成分,含有量等を説明する。
C:0.15質量%以下
オーステナイト形成元素であり、高温域でのδフェライトの生成を抑え、冷間加工で生じる加工誘起マルテンサイトを強化する合金成分である。しかし、Si含有量の多い本発明の成分系では、Cの固溶限が低下している。そのため、C含有量を多くすると、時効処理で粗大なCr系炭化物が析出し、耐粒界腐食や疲労特性を低下させる原因となる。そこで、C含有量の上限を0.15質量%に設定した。なお、好ましい範囲は0.05〜0.10質量%である。
Next, components, contents and the like contained in the stainless steel of the present invention will be described.
C: 0.15% by mass or less An austenite-forming element, an alloy component that suppresses the formation of δ ferrite in a high temperature range and reinforces work-induced martensite generated in cold work. However, in the component system of the present invention having a high Si content, the solid solubility limit of C is lowered. Therefore, when the C content is increased, coarse Cr-based carbides are precipitated by the aging treatment, which causes a decrease in intergranular corrosion resistance and fatigue characteristics. Therefore, the upper limit of the C content is set to 0.15% by mass. In addition, a preferable range is 0.05-0.10 mass%.

Si:1.0〜4.0質量%
製鋼段階で脱酸剤として添加される合金成分でもある。脱酸剤として添加されるSi含有量は、SUS301,SUS304等の加工硬化型ステンレス鋼にみられるように1.0質量%以下である。これに対し、本発明では、Si含有量を高く設定し、冷間加工時に加工誘起マルテンサイト相の生成を著しく促進させる効果を利用している。また、Siは加工誘起マルテンサイト相を硬質化するとともに、オーステナイト相にも固溶して硬化させ、冷間加工後の強度を上昇させる。さらに、時効処理においてはCuとの相互作用によって時効硬化を促進させる。このようにSiは種々の効果を有しているが、その効果はSi含有量1.0質量%以上で顕著になる。しかし、4.0質量%を超える過剰量のSiが含まれると、高温割れを誘発しやすくなり、製造上でもトラブルが発生しやすくなる。そこで、Si含有量は1.0〜4.0質量%の範囲とした。なお、好ましい範囲は1.0〜3.5質量%である。
Si: 1.0-4.0 mass%
It is also an alloy component added as a deoxidizer in the steelmaking stage. Si content added as a deoxidizer is 1.0 mass% or less so that it may be seen in work hardening type stainless steels, such as SUS301 and SUS304. On the other hand, in this invention, Si content is set high and the effect of remarkably accelerating | stimulating the production | generation of a process induction martensite phase at the time of cold working is utilized. In addition, Si hardens the work-induced martensite phase and also solidifies and hardens in the austenite phase to increase the strength after cold working. Furthermore, in the aging treatment, age hardening is promoted by interaction with Cu. As described above, Si has various effects, but the effect becomes remarkable when the Si content is 1.0 mass% or more. However, when an excessive amount of Si exceeding 4.0% by mass is included, hot cracking is likely to be induced, and troubles are likely to occur in manufacturing. Therefore, the Si content is in the range of 1.0 to 4.0% by mass. In addition, a preferable range is 1.0-3.5 mass%.

Mn:5.0質量%以下
オーステナイト相の安定度を支配する合金成分であり、他の合金成分とのバランスによってMn含有量が定められる。しかし、5.0質量%を超える過剰量のMnが含まれると、冷間圧延時に加工誘起マルテンサイト変態しにくく、変態硬化能が期待できなくなるので、5.0質量%以下とした。なお、好ましいMnの含有量は4.5質量%以下である。
P:0.040質量%以下
固溶強化能の大きな合金成分であるが、曲げ性に悪影響を与えることがあるため、通常許容されている程度の0.040質量%を上限にした。
Mn: 5.0% by mass or less Mn is an alloy component that controls the stability of the austenite phase, and the Mn content is determined by balance with other alloy components. However, if an excessive amount of Mn exceeding 5.0% by mass is contained, the deformation-induced martensite transformation is difficult at the time of cold rolling, and the transformation hardening ability cannot be expected. In addition, preferable content of Mn is 4.5 mass% or less.
P: 0.040% by mass or less Although it is an alloy component having a large solid solution strengthening ability, it may adversely affect the bendability.

S:0.010質量%以下
曲げ加工性低下の原因となる非金属介在物を生成する成分であり、優れた曲げ加工性を得るためには、S含有量を低減して非金属介在物を少なくすることが必要である。そこで、S含有量は0.010質量%を上限にした。
Ni:4.0〜10.0質量%
高温及び室温でオーステナイト相を安定化させる合金成分であるが、室温で準安定オーステナイト相にし、冷間加工で加工誘起マルテンサイト相が生成するようにNi含有量が定められる。4.0質量%未満のNi含有量では、高温域で多量のδフェライトが生成し、室温までの冷却過程でマルテンサイト相が生成するため、オーステナイト単相として存在できなくなる。逆に10.0質量%を超える過剰量のNiが含まれると、冷間加工時に加工誘起マルテンサイト変態しがたく、変態硬化が期待できない。そこで、Ni含有量は4.0〜10.0質量%の範囲とした。なお、好ましい範囲は5.0〜9.5質量%である。
S: 0.010% by mass or less A component that generates non-metallic inclusions that cause a decrease in bending workability. In order to obtain excellent bending workability, the S content is reduced to reduce non-metallic inclusions. It is necessary to reduce it. Therefore, the upper limit of the S content is 0.010% by mass.
Ni: 4.0-10.0 mass%
Although it is an alloy component that stabilizes the austenite phase at high temperatures and room temperature, the Ni content is determined so that it becomes a metastable austenite phase at room temperature and a work-induced martensite phase is generated by cold working. When the Ni content is less than 4.0% by mass, a large amount of δ ferrite is generated in a high temperature region, and a martensite phase is generated in the cooling process to room temperature, so that it cannot exist as an austenite single phase. On the other hand, when an excessive amount of Ni exceeding 10.0% by mass is contained, it is difficult to transform the work-induced martensite during cold working, and transformation hardening cannot be expected. Therefore, the Ni content is in the range of 4.0 to 10.0% by mass. In addition, a preferable range is 5.0-9.5 mass%.

Cr:13.0〜18.0質量%
耐食性の向上に必須の合金成分であり、意図する耐食性を得るには少なくとも13.0質量%のCrを必要とする。しかし、フェライト形成元素であるCrを18.0質量%を超える過剰量添加すると、高温域で多量のδフェライトが生成する。δフェライトの生成はC,N,Ni,Mn,Cu等のオーステナイト形成元素を添加することによってδフェライトの生成は抑えられるが、オーステナイト形成元素を過度に添加すると室温でのオーステナイト相が安定化する。その結果、冷間加工時に加工誘起マルテンサイト変態しなくなり、時効処理後に高強度が得られなくなる。そこで、Cr含有量は13.0〜18.0質量%の範囲とした。なお、好ましい範囲は13.0〜16.5質量%である。
Cr: 13.0 to 18.0 mass%
It is an alloy component essential for improving corrosion resistance, and at least 13.0% by mass of Cr is required to obtain the intended corrosion resistance. However, if an excessive amount of Cr, which is a ferrite forming element, is added in excess of 18.0% by mass, a large amount of δ ferrite is generated in a high temperature range. The formation of δ ferrite can be suppressed by adding austenite-forming elements such as C, N, Ni, Mn, Cu, etc., but if an austenite-forming element is added excessively, the austenite phase at room temperature is stabilized. . As a result, work-induced martensitic transformation does not occur during cold working, and high strength cannot be obtained after aging treatment. Therefore, the Cr content is in the range of 13.0 to 18.0% by mass. In addition, a preferable range is 13.0-16.5 mass%.

Cu:0〜3.5質量%
必要に応じて添加される合金成分であり、Siとの相互作用によって時効処理時に時効硬化を促進させる。時効硬化に及ぼす影響は、Cu含有量の増加に応じて大きくなる。しかし、3.5質量%を超えるCuの過剰添加は、熱間加工性を低下させ、割れ発生の原因となる。そこで、Cu含有量は3.5質量%以下とした。なお、好ましい範囲は1.0〜3.0質量%である。
Cu: 0 to 3.5% by mass
It is an alloy component that is added as necessary, and promotes age hardening during the aging treatment by interaction with Si. The effect on age hardening increases with increasing Cu content. However, excessive addition of Cu exceeding 3.5% by mass reduces hot workability and causes cracking. Therefore, the Cu content is set to 3.5% by mass or less. In addition, a preferable range is 1.0-3.0 mass%.

Mo:1.0〜5.0質量%
耐食性を向上させるとともに、時効処理時に炭窒化物を微細分布させる作用を呈する合金成分である。さらに、本発明では曲げ加工性に悪影響を及ぼす過度の圧延歪を低減するために時効温度を高くするが、Moは高い時効処理温度での急激な歪の解放を抑制する上で非常に有効な元素である。このような作用は、1.0質量%以上のMo添加で顕著に発現する。しかし、5.0質量%を超える過剰量のMoを添加すると、高温域でδフェライトが生成しやすくなる。また、Mo含有量が多くなると、高温での変形抵抗が高くなり、熱間加工性が低下することもある。そこで、Mo含有量は1.0〜5.0質量%の範囲とした。なお、好ましい範囲は1.0〜4.5質量である。
Mo: 1.0-5.0 mass%
It is an alloy component that improves the corrosion resistance and exhibits the function of finely distributing carbonitride during aging treatment. Furthermore, in the present invention, the aging temperature is increased in order to reduce excessive rolling strain that adversely affects bending workability, but Mo is very effective in suppressing the rapid strain release at a high aging temperature. It is an element. Such an effect is remarkably exhibited when 1.0% by mass or more of Mo is added. However, when an excessive amount of Mo exceeding 5.0% by mass is added, δ ferrite is likely to be generated at high temperatures. Further, when the Mo content increases, the deformation resistance at high temperatures increases, and the hot workability may decrease. Therefore, the Mo content is in the range of 1.0 to 5.0 mass%. In addition, a preferable range is 1.0-4.5 mass.

N:0.15質量%以下
オーステナイト形成元素であるとともに、オーステナイト相及びマルテンサイト相の硬質化に極めて有効な合金成分である。しかし、過剰量のN添加は鋳造時にブローホールを発生させることになる。そこで、N含有量は0.15質量%を上限とした。
Nb:0.15質量%以下,Ti:0.05質量%以下
固溶強化により素材強度を高める作用を呈する。しかし、曲げ加工性低下の原因となる析出物を生成させる成分であることから、Nb,Tiの含有量はそれぞれ、0.15質量%,0.05質量%を上限とした。
V:0.2質量%以下
固溶強化により所望の強度を得るために効果的な成分である。しかしその効果は0.20質量%で飽和する。また、曲げ加工性低下の原因となる析出物を生成させる成分でもあるから、V含有量は0.2質量%を上限とした。
O:0.015質量%以下
酸化物系の非金属介在物を形成して鋼の清浄度を低下させ,曲げ加工性に悪影響を及ぼす。このような悪影響は、O含有量を0.015質量%以下に規制することによって抑制できる。
N: 0.15% by mass or less An alloy component that is an austenite-forming element and is extremely effective for hardening the austenite phase and the martensite phase. However, excessive addition of N will cause blow holes during casting. Therefore, the upper limit of the N content is 0.15% by mass.
Nb: 0.15 mass% or less, Ti: 0.05 mass% or less The effect of increasing the material strength by solid solution strengthening is exhibited. However, since it is a component that generates precipitates that cause a decrease in bending workability, the upper limits of the contents of Nb and Ti are 0.15 mass% and 0.05 mass%, respectively.
V: 0.2 mass% or less An effective component for obtaining a desired strength by solid solution strengthening. However, the effect is saturated at 0.20% by mass. Moreover, since it is also a component which produces | generates the precipitate which causes a bending workability fall, V content made the upper limit 0.2 mass%.
O: 0.015% by mass or less Oxide-based non-metallic inclusions are formed to lower the cleanliness of steel and adversely affect bending workability. Such an adverse effect can be suppressed by regulating the O content to 0.015 mass% or less.

2Nb+4Ti+V:0.7質量%以下
製品に存在する析出物は、良好な曲げ加工性を得る上では有害である。上記したように、Nb,Ti,Vはともに析出物を生成させる成分であるため、これらの総量を制限して析出物の生成を抑制する必要がある。本発明者等は、2Nb+4Ti+Vの合計量が0.7質量%を超えると曲げ加工性が低下することを確認した。
ここで、上記式中、Nb,Ti,Vは、それぞれ当該鋼のNb含有量,Ti含有量,V含有量(いずれも質量%で表される値)を意味している。
2Nb + 4Ti + V: 0.7 mass% or less Precipitates present in the product are harmful in obtaining good bending workability. As described above, since Nb, Ti, and V are components that generate precipitates, it is necessary to limit the total amount of these to suppress the formation of precipitates. The inventors of the present invention have confirmed that bending workability deteriorates when the total amount of 2Nb + 4Ti + V exceeds 0.7 mass%.
Here, in the above formula, Nb, Ti, and V mean the Nb content, Ti content, and V content (values expressed in mass%) of the steel, respectively.

Md(N)値:0〜100
本発明では、冷間圧延時に起こる加工誘起マルテンサイト変態を高強度化手段の一つとして積極的に利用している。このため、溶体化処理後の冷間圧延で付与される歪に応じて加工誘起マルテンサイト相が容易に形成されやすいように、オーステナイト相の加工に対する安定度が調整されたものでなくてはならない。本発明では、オーステナイト相の加工に対する安定度を表す指標として、次式で定義されるMd(N)値を採用する。
Md(N)=580−(520C+2Si+16Mn+16Cr+23Ni+300N+10Mo)
ここで、上記式中、C,Si,・・・は、それぞれ当該鋼のC含有量,Si含有量,・・・(いずれも質量%で表される値)を意味している。
本発明では、Md(N)値を0〜100の範囲に限定している。Md(N)値をこの範囲内にすることによって、冷間加工時に適正量の加工誘起マルテンサイト相が生成し、加工硬化及び変態効果による高強度化が可能となる。Md(N)値が0未満の鋼種では、冷間圧延に対するオーステナイト相の安定度が高く、高強度化に寄与する加工誘起マルテンサイト相が十分に生成されない。逆に100を超えるMd(N)値では、比較的低い冷間圧延率で多量の加工誘起マルテンサイト相が生成し、却って製品の曲げ加工性が低下することにもなる。
Md (N) value: 0-100
In the present invention, the processing-induced martensitic transformation that occurs during cold rolling is actively used as one of the means for increasing the strength. For this reason, the stability of the austenite phase must be adjusted so that the work-induced martensite phase is easily formed in accordance with the strain imparted by cold rolling after solution treatment. . In the present invention, an Md (N) value defined by the following equation is adopted as an index representing the stability of austenite phase processing.
Md (N) = 580− (520C + 2Si + 16Mn + 16Cr + 23Ni + 300N + 10Mo)
Here, in the above formulas, C, Si,... Mean the C content, Si content,... (All values expressed in mass%) of the steel.
In the present invention, the Md (N) value is limited to a range of 0 to 100. By setting the Md (N) value within this range, an appropriate amount of work-induced martensite phase is generated during cold working, and high strength can be achieved by work hardening and transformation effects. In a steel type having an Md (N) value of less than 0, the stability of the austenite phase with respect to cold rolling is high, and the work-induced martensite phase contributing to high strength is not sufficiently generated. Conversely, when the Md (N) value exceeds 100, a large amount of work-induced martensite phase is generated at a relatively low cold rolling rate, and the bending workability of the product is also lowered.

冷間圧延後に実施する時効処理では、連続焼鈍炉あるいはバッチ炉を考慮し、また前記のMoの作用を得るために、300〜500℃の温度範囲で0〜20時間の時効処理を行うことが好ましい。なお、時効時間が300℃に満たないと、有効な時効効果が発現しない。また、時効温度が500℃を超え、あるいは時効時間が20時間を超えると、加工誘起マルテンサイト相の一部がオーステナイト相に逆変態し、強度が却って低下する。そのため、冷延後に時効処理を施す場合には、300〜500℃の温度範囲で、0〜20時間の範囲の均熱時間で行うことが好ましい。   In the aging treatment carried out after cold rolling, in consideration of a continuous annealing furnace or a batch furnace, and in order to obtain the above-mentioned effect of Mo, an aging treatment for 0 to 20 hours may be performed in a temperature range of 300 to 500 ° C. preferable. In addition, if the aging time is less than 300 ° C., an effective aging effect is not exhibited. On the other hand, when the aging temperature exceeds 500 ° C. or the aging time exceeds 20 hours, a part of the processing-induced martensite phase is reversely transformed into an austenite phase, and the strength is decreased. Therefore, when performing an aging treatment after cold rolling, it is preferable to carry out the soaking time in the temperature range of 300 to 500 ° C. and in the range of 0 to 20 hours.

表1の組成をもつステンレス鋼を真空溶解炉で溶製し、鍛造,熱延,中間焼鈍を経て板厚0.65mmまで冷間圧延した。冷延鋼帯に1050℃×1分保持の溶体化処理を施した後、水冷した後、板厚0.30mmまで冷間圧延した。さらに冷延板の一部については時効処理を施した。
なお、表1中、鋼種No.1〜5が本発明で規定する化学組成を有する発明対象鋼であり、比較鋼として鋼種No.6〜9及び市販のオーステナイト系バネ用鋼板SUS301(冷延材),析出硬化型バネ用鋼板SUS630(480℃×1hの熱処理材)及びマルテンサイト系バネ用鋼板SUS420J2(1050℃焼入れ→520℃焼戻し材)を用いている。
Stainless steel having the composition shown in Table 1 was melted in a vacuum melting furnace and cold-rolled to a thickness of 0.65 mm through forging, hot rolling and intermediate annealing. The cold-rolled steel strip was subjected to a solution treatment at 1050 ° C. × 1 minute, then water-cooled, and then cold-rolled to a plate thickness of 0.30 mm. Furthermore, an aging treatment was applied to a part of the cold rolled sheet.
In Table 1, steel types Nos. 1 to 5 are steels subject to the invention having the chemical composition defined in the present invention. As comparative steels, steel types No. 6 to 9 and a commercially available austenitic spring steel plate SUS301 (cold rolled material) ), Precipitation hardening type spring steel plate SUS630 (heat treatment material of 480 ° C x 1h) and martensite spring steel plate SUS420J2 (1050 ° C quenching → 520 ° C tempering material).

Figure 2007113068
Figure 2007113068

表1に示すステンレス鋼板の曲げ加工性,引張特性,バネ特性及び腐食試験後の引張破断強度を以下の方法により評価した。
曲げ加工性は、圧延方向に切り出した試験片をJIS‐Z2248に準拠してV曲げ試験し、曲げ加工可能な最小曲げ半径(R)の鋼板板厚(t)に対する比(R/t)を測定した。
引張特性は、JIS‐Z2201に規定されている13B号試験片を用い、JIS‐Z2241に規定されている引張試験法で引張強さを測定した。
The bending workability, tensile properties, spring properties and tensile strength after corrosion test of the stainless steel plate shown in Table 1 were evaluated by the following methods.
For bending workability, a specimen cut in the rolling direction is subjected to a V-bending test according to JIS-Z2248, and the ratio (R / t) of the minimum bending radius (R) to the steel plate thickness (t) that can be bent is determined. It was measured.
For tensile properties, No. 13B test piece specified in JIS-Z2201 was used, and tensile strength was measured by the tensile test method specified in JIS-Z2241.

バネ特性は、圧延方向に切り出した試験片を使用し、JIS‐H3130に準拠して繰返したわみ試験を行ってバネ限界値[Kb0.1]を測定した。
腐食試験後の引張破断強度は、腐食液として35℃の5%NaCl水溶液を用い、当該腐食液を被試験板に15分間噴霧した後、湿度35%で60℃の雰囲気で60分間乾燥し、湿度45%で50℃の雰囲気で180分間湿潤させる処理を1サイクルとし、これを50サイクル実施する腐食試験を行った後に、上記と同じ引張試験法で破断強度を測定した。
表2に、各ステンレス鋼の試験結果を示す。
なお、表中、曲げ加工性は、V曲げ試験でR/tが4以下であったものを○で、R/tが4を超えていたものを×で示した。
For spring characteristics, a test piece cut in the rolling direction was used, a repeated deflection test was performed in accordance with JIS-H3130, and the spring limit value [Kb 0.1 ] was measured.
The tensile strength at break after the corrosion test was determined by using a 5% NaCl aqueous solution at 35 ° C. as the corrosive liquid, spraying the corrosive liquid on the test plate for 15 minutes, and drying for 60 minutes in an atmosphere of 60 ° C. at a humidity of 35%. A treatment of wetting for 180 minutes in an atmosphere of 45% humidity and 50 ° C. was taken as one cycle, and after performing a corrosion test in which this was carried out for 50 cycles, the breaking strength was measured by the same tensile test method as described above.
Table 2 shows the test results of each stainless steel.
In the table, the bending workability was indicated by ◯ when the R / t was 4 or less in the V-bending test, and by × when the R / t exceeded 4.

Figure 2007113068
Figure 2007113068

表2に示す結果に見られるように、本発明鋼は曲げ加工性に優れ、さらに繰返したわみ試験によるバネ限界値[Kb0.1]はいずれも800N/mm2以上であった。また腐食後の引張破断強度は1000N/mm2以上であり、強度と耐食性を兼ね備えたバネ用途に適した材料であることがわかる。
これに対して、比較例のNo.6はMd(N)が低すぎたために加工誘起マルテンサイトが十分に生成されずに、強度が比較的低く十分なバネ限界値が得られなかった。同じくNo.7は2Nb+4Ti+Vが0.70%以上となっていたため、析出物が多く曲げ加工性に劣っていた。No.8はMd(N)が高すぎたために延性・靭性に寄与するオーステナイト量が不十分になって曲げ加工性に劣っていた。さらに、No.9はCr含有量が少なすぎたために耐食性が不十分で、耐食試験後に引張破断強度が低くなっていた。
As can be seen from the results shown in Table 2, the steels of the present invention were excellent in bending workability, and the spring limit values [Kb 0.1 ] by repeated deflection tests were all 800 N / mm 2 or more. Moreover, the tensile fracture strength after corrosion is 1000 N / mm 2 or more, and it can be seen that the material is suitable for spring applications having both strength and corrosion resistance.
On the other hand, in No. 6 of the comparative example, since Md (N) was too low, sufficient work-induced martensite was not generated, and the strength was comparatively low and a sufficient spring limit value could not be obtained. Similarly, No. 7 had 2Nb + 4Ti + V of 0.70% or more, and therefore had many precipitates and was inferior in bending workability. In No. 8, since Md (N) was too high, the amount of austenite contributing to ductility and toughness was insufficient, resulting in poor bending workability. Furthermore, No. 9 had insufficient corrosion resistance because the Cr content was too low, and the tensile strength at break was low after the corrosion resistance test.

以上に説明したように、本発明のステンレス鋼製バネ材はオーステナイト系ステンレス鋼を素材とし、冷間圧延時の加工硬化,変態強化及び時効硬化によって強度が付与されているとともに、腐食環境下に曝されても優れた強度を維持できる耐食性を有している。
したがって、本発明により、自動車シートベルトのリトラクターぜんまいバネ等のような曲げ加工されて使用され、しかも強度,バネ性及び耐食性が要求される用途に最適なバネ材が提供される。
As explained above, the spring material made of stainless steel of the present invention is made of austenitic stainless steel, and is given strength by work hardening, transformation strengthening and age hardening during cold rolling, and in a corrosive environment. It has corrosion resistance that can maintain excellent strength even when exposed.
Therefore, the present invention provides a spring material that is used after being bent and used, such as a retractor spring of an automobile seat belt, and that is required for strength, springiness, and corrosion resistance.

Claims (1)

C:0.15質量%以下,Si:1.0〜4.0質量%,Mn:5.0質量%以下,P:0.040質量%以下,S:0.010質量%以下,Ni:4.0〜10.0質量%,Cr:13.0〜18.0質量%,Cu:0〜3.5質量%,Mo:1.0〜5.0質量%,N:0.15質量%以下,Nb:0.15質量%以下,Ti:0.05質量%以下,V:0.20質量%以下,O:0.015質量%以下,2Nb+4Ti+V:0.70質量%以下,残部がFe及び不可避的不純物の組成をもち、Md(N)=580−(520C+2Si+16Mn+16Cr+23Ni+300N+10Mo)と定義されるMd(N)値が0〜100の範囲にあることを特徴とする曲げ性に優れた高強度高耐食ステンレス鋼製バネ材。   C: 0.15 mass% or less, Si: 1.0-4.0 mass%, Mn: 5.0 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Ni: 4.0-10.0 mass%, Cr: 13.0-18.0 mass%, Cu: 0-3.5 mass%, Mo: 1.0-5.0 mass%, N: 0.15 mass % Or less, Nb: 0.15 mass% or less, Ti: 0.05 mass% or less, V: 0.20 mass% or less, O: 0.015 mass% or less, 2Nb + 4Ti + V: 0.70 mass% or less, and the balance It has a composition of Fe and inevitable impurities, and has a high strength and high bending property characterized by having an Md (N) value defined as Md (N) = 580− (520C + 2Si + 16Mn + 16Cr + 23Ni + 300N + 10Mo) in a range of 0 to 100 Corrosion-resistant stainless steel spring material.
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KR20190004764A (en) * 2016-06-01 2019-01-14 가부시키가이샤 도쿠슈 긴조쿠 엑셀 Metastable austenitic stainless steel strip or steel sheet and manufacturing method thereof
KR102158242B1 (en) 2016-06-01 2020-09-22 가부시키가이샤 도쿠슈 긴조쿠 엑셀 Metastable austenitic stainless steel strip or steel plate and manufacturing method thereof
WO2019176283A1 (en) 2018-03-15 2019-09-19 日鉄ステンレス株式会社 Martensitic stainless steel sheet, method for manufacturing same, and spring member
KR20200130422A (en) 2018-03-15 2020-11-18 닛테츠 스테인레스 가부시키가이샤 Martensitic stainless steel plate and its manufacturing method and spring member
US11499204B2 (en) 2018-03-15 2022-11-15 Nippon Steel Stainless Steel Corporation Martensitic stainless steel sheet, method for manufacturing same, and spring member

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