JP2014189876A - Steel for spring excellent in corrosion resistance and steel material for spring - Google Patents
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本発明は、耐腐食特性に優れたばね用鋼およびばね用鋼材に関するものであり、腐食環境下での耐食性に優れることが必要な用途で用いられる、ばねに適用されるものである。さらに、詳しくは、鋼中に存在して鋼の腐食の起点となるマンガン硫化物を改質し、耐食性を向上させた、ばね用鋼およびばね用鋼材に関するものである。 The present invention relates to a spring steel and a spring steel material excellent in corrosion resistance characteristics, and is applied to a spring used in applications that require excellent corrosion resistance in a corrosive environment. More specifically, the present invention relates to a spring steel and a spring steel material that are improved in corrosion resistance by modifying manganese sulfide that is present in steel and is a starting point of corrosion of steel.
例えば、ばね、歯車、無段変速機、軸受などのエンジン、足回り、および動力伝達部品等の機械構造用部品は、使用環境化下において、耐食性が求められるケースがある。錆びの発生と腐食疲労特性、水素脆化特性が密接関係すると考えられているためである。 For example, engine structural parts such as springs, gears, continuously variable transmissions, bearings, etc., suspensions, and power transmission parts may be required to have corrosion resistance under the environment of use. This is because the occurrence of rust, corrosion fatigue characteristics, and hydrogen embrittlement characteristics are considered to be closely related.
これらの要求に応えるために、耐食性を向上させる方法として、めっき、表面改質（窒化等）、被膜処理等の様々な鋼材表面処理が施されている場合がある（非特許文献１、２）。一方、鋼材自体の耐食性を向上させるに、ステンレスに見られるように合金酸化物による不動態被膜を形成させるためにＣｒ、Ｎｉを多量に添加する方法が考えられる（非特許文献３）。 In order to meet these demands, various steel surface treatments such as plating, surface modification (nitriding, etc.), coating treatment, etc. may be applied as a method for improving corrosion resistance (Non-patent Documents 1 and 2). . On the other hand, in order to improve the corrosion resistance of the steel material itself, a method of adding a large amount of Cr and Ni to form a passive film made of an alloy oxide as seen in stainless steel can be considered (Non-patent Document 3).
これらのいずれのケースにおいても、工程増もしくは合金添加による製造コストの上昇が不可欠であり、安価に鋼材および鋼部品の耐食性を向上させる技術は存在していなかった。 In any of these cases, it is indispensable to increase the manufacturing cost by increasing the number of processes or adding an alloy, and there has been no technology for improving the corrosion resistance of steel materials and steel parts at low cost.
また、例えば、特許文献１には、ＴｉおよびＺｒを添加した、水素侵入抑制効果を有するボルトに適した高強度合金鋼として、Ｔｉ系およびＺｒ系介在物を多量に含有させることで遅れ破壊の原因となる水素侵入の抑制を図ることが開示されているが、硫化物の改質により耐食性を向上させる技術的な思想、および、同技術を実現させるための条件、即ち、硫化物を改質させるためのＮ濃度とＴｉ、Ｚｒ、さらにＮｂ、Ｖ、Ｓ濃度等の関係は示されていない。また、例えば、特許文献２には、Ｔｉを含有する硫化物について規定した高強度ボルト用鋼が開示されているが、微細なＴｉＣを多量に生成させるために、Ｔｉを含む硫化物が少ない方が遅れ破壊特性を向上させるために好ましいことが示されており、本発明のようにＴｉを含む硫化物を多量に生成させて、耐食性を向上させる技術思想および成分条件とは全く逆の発想である。さらに、例えば、特許文献３には、固溶Ｓを極力鋼中に残さずにＴｉ硫化物に変え、固溶Ｎも極力Ｔｉ窒化物に変え、さらに十分量のＴｉ炭化物を形成することで耐水素脆化特性を向上させたＴｉ添加のばね用鋼があるが、この場合のＴｉ添加はＴｉ系の炭化物・窒化物・硫化物などを微細分散させ、鋼中に侵入した水素を効率よくトラップでき、水素が旧オーステナイト粒界を拡散移行することを抑制でき、水素脆化を防止できるために用いられており、硫化物の改質に関しては言及されていないものである。 Further, for example, in Patent Document 1, as a high-strength alloy steel suitable for a bolt having an effect of suppressing hydrogen intrusion to which Ti and Zr are added, delayed fracture is caused by containing a large amount of Ti-based and Zr-based inclusions. Although it has been disclosed to suppress the hydrogen intrusion that causes it, the technical idea of improving the corrosion resistance by reforming the sulfide and the conditions for realizing the technology, that is, reforming the sulfide The relationship between the N concentration and Ti, Zr, Nb, V, S concentration, and the like for the purpose is not shown. Further, for example, Patent Document 2 discloses a steel for high-strength bolts specified for sulfides containing Ti. However, in order to produce a large amount of fine TiC, there is less sulfide containing Ti. It is shown that it is preferable for improving delayed fracture characteristics, and it is a concept that is completely opposite to the technical idea and component conditions for improving corrosion resistance by producing a large amount of sulfide containing Ti as in the present invention. is there. Further, for example, in Patent Document 3, the solid solution S is changed to Ti sulfide without leaving it in the steel as much as possible, the solid solution N is also changed to Ti nitride as much as possible, and a sufficient amount of Ti carbide is formed. There are Ti-added spring steels with improved hydrogen embrittlement characteristics. In this case, Ti addition finely disperses Ti carbides, nitrides, sulfides, etc., and traps hydrogen that has penetrated into the steel efficiently. It can be used to suppress diffusion and transfer of hydrogen through the prior austenite grain boundaries and prevent hydrogen embrittlement, and is not mentioned regarding the reforming of sulfides.
本発明は上記の実情を鑑み、特に、ばね用鋼において、鋼中の非金属介在物として存在し、鋼の腐食の起点として作用すると考えられるマンガン硫化物（以降はＭｎＳと表記）を改質し、耐食性を向上させることにより、耐腐食疲労特性、耐水素脆化特性を向上させた、ばね用鋼およびばね用鋼材を提供することが本発明の課題である。 In view of the above circumstances, the present invention improves manganese sulfide (hereinafter referred to as MnS), which is considered to be a non-metallic inclusion in steel and act as a starting point for corrosion of steel, particularly in spring steel. It is an object of the present invention to provide a spring steel and a spring steel material having improved corrosion resistance and hydrogen embrittlement resistance by improving corrosion resistance.
鋼部品表面の耐食性を向上させる方法の一つとして、腐食の起点を低減させて局部電池反応を抑制させることが挙げられる。鋼材の腐食の起点としては鋼材中に非金属介在物として存在するＭｎＳが知られている。このＭｎＳは湿潤環境において加水分解しピットを生成させるとともに溶解してイオン化することに起因して酸性化し、局部電池反応が進行するためである。即ち、腐食は、このＭｎＳが溶解した局部から徐々に広がっていくことにより進行する。 One method for improving the corrosion resistance of the steel part surface is to reduce the starting point of corrosion and suppress the local battery reaction. As a starting point of corrosion of steel materials, MnS existing as nonmetallic inclusions in steel materials is known. This is because MnS is hydrolyzed in a wet environment to generate pits and is acidified due to dissolution and ionization, and the local battery reaction proceeds. That is, the corrosion proceeds by gradually spreading from the local area where the MnS is dissolved.
腐食を抑制させる方策の一つに、硫化物を難水溶化なものに改質させてＳ２−化を抑制し、局部電池反応を抑制させることが挙げられる。そこで、鋼材に合金元素を添加し、鋼中に存在する硫化物をＭｎＳから、他の合金系の硫化物に改質させ、錆びの発生状況を検討し、最適な合金について評価を個なった。その結果、鋼中に含有させるＳ濃度に応じて、ある一定量以上のＺｒを含有させると、ＭｎＳがもはや存在しなくなるとともに、ＺｒＳと考えられる硫化物が生成されること、この改質硫化物は難水溶性であり、耐食特性に優れていることを知見した。 One of the measures for suppressing the corrosion is to modify the sulfide to be slightly water-soluble so as to suppress S 2− conversion and to suppress the local battery reaction. Therefore, an alloying element was added to the steel material, and the sulfide existing in the steel was modified from MnS to other alloy-based sulfides, and the occurrence of rust was examined, and the optimum alloy was evaluated. . As a result, when a certain amount or more of Zr is contained depending on the S concentration contained in the steel, MnS is no longer present, and sulfides considered to be ZrS are produced. Was found to be poorly water-soluble and excellent in corrosion resistance.
本発明は上記の知見に基づいて完成したものであり、その発明の要旨は以下の通りである。 The present invention has been completed based on the above findings, and the gist of the present invention is as follows.
（１） 化学成分が、質量％で、
Ｃ：０．４〜１．２％、
Ｓｉ：０．０２〜３．０％、
Ｍｎ：０．３５〜２．５％、
Ａｌ：０．００１〜０．５％、
Ｎ：０．００３〜０．０１５％、
Ｚｒ：０．１〜０．５％、
を含有し、
Ｓ：０．０３０％以下、
Ｐ：０．０３％以下、
Ｏ：０．００５０％以下
に制限し、
下記（１）式を満たし、残部がＦｅ及び不可避的不純物よりなることを特徴とする耐腐食特性に優れたばね用鋼。
Ｚｒ／９１．２−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１ ・ ・ ・（１）
ここで、Ｚｒ、Ｓ、Ｎは、それぞれ鋼中質量％である。
(1) The chemical component is mass%,
C: 0.4 to 1.2%
Si: 0.02-3.0%,
Mn: 0.35 to 2.5%,
Al: 0.001 to 0.5%,
N: 0.003 to 0.015%,
Zr: 0.1 to 0.5%,
Containing
S: 0.030% or less,
P: 0.03% or less,
O: limited to 0.0050% or less,
A spring steel excellent in corrosion resistance characterized by satisfying the following formula (1) and the balance being Fe and inevitable impurities.
Zr / 91.2− (S / 32.1 + N / 14.0) ≧ 0.001 (1)
Here, Zr, S, and N are each mass% in steel.
（２） さらに、化学成分が、質量％で、
Ｂ：０．００５％以下、
Ｗ：０．５％以下、
Ｍｏ：１．０％以下、
Ｃｒ：２．０％以下、
Ｖ：０．０５〜１．０％、
Ｎｂ：０．００５〜０．３％、
Ｃｕ：２．０％以下、
Ｎｉ：２．０％以下
の内の１種または２種以上を含有し、下記（２）式を満たすことを特徴とする上記（１）項に記載の耐腐食特性に優れたばね用鋼。
Ｚｒ／９１．２＋Ｎｂ／９２．９＋Ｖ／５０．９−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１ ・ ・ ・（２）
ここで、Ｚｒ、Ｎｂ、Ｖ、Ｓ、Ｎは、それぞれ鋼中質量％である。
(2) Furthermore, the chemical component is mass%,
B: 0.005% or less,
W: 0.5% or less,
Mo: 1.0% or less,
Cr: 2.0% or less,
V: 0.05-1.0%
Nb: 0.005-0.3%
Cu: 2.0% or less,
Ni: A spring steel having excellent corrosion resistance as described in the above item (1), which contains one or more of 2.0% or less and satisfies the following formula (2).
Zr / 91.2 + Nb / 92.9 + V / 50.9− (S / 32.1 + N / 14.0) ≧ 0.001 (2)
Here, Zr, Nb, V, S, and N are respectively mass% in steel.
（３） さらに、化学成分が、質量％で、
Ｃａ：０．０１％以下、
Ｍｇ：０．０１％以下、
Ｔｅ：０．１％以下、
の内の１種または２種以上を含有することを特徴とする上記（１）または（２）項に記載の耐腐食特性に優れたばね用鋼。
(3) Furthermore, the chemical component is mass%,
Ca: 0.01% or less,
Mg: 0.01% or less,
Te: 0.1% or less,
A spring steel having excellent corrosion resistance as described in (1) or (2) above, comprising one or more of the above.
（４） 上記（１）〜（３）項のいずれかに記載の鋼からなり、表面において、ＥＰＭＡ分析により、ＭｎとＳが１μｍ２以上のスポットで同時検出される点が、０．２５ｍｍ２あたり２５箇所以下であることを特徴とする耐腐食特性に優れたばね用鋼材。 (4) It is made of the steel according to any one of the above items (1) to (3), and the point that Mn and S are simultaneously detected at a spot of 1 μm 2 or more by EPMA analysis on the surface is 0.25 mm 2. A steel material for springs with excellent corrosion resistance, characterized by having 25 or less per hole.
本発明の腐食環境下での耐食特性に優れたばね用鋼および鋼材は、自動車のエンジン部品や足回り部品として使用されるばねに適用でき、腐食環境下において、従来よりも高い耐食特性、すなわち、耐腐食疲労、および耐水素脆化特性を有する、ばねを提供できる。また、ばね以外にも、歯車、無段変速機、ハブ、軸受等の部品を提供することができ、これにより自動車の耐久性向上、および低コスト化等に大きく寄与する。 The spring steel and steel material excellent in corrosion resistance in a corrosive environment of the present invention can be applied to a spring used as an engine part or an undercarriage part of an automobile. A spring having corrosion fatigue resistance and hydrogen embrittlement resistance can be provided. In addition to springs, parts such as gears, continuously variable transmissions, hubs, and bearings can be provided, which greatly contributes to improving the durability and cost of automobiles.
本発明は、高い耐食特性を要求される、ばね鋼において、上記の鋼中に存在する腐食の起点となる硫化物をＭｎＳから、他の合金系の硫化物に改質させ、この改質硫化物は難水溶性であり、耐食特性に優れているとの知見をもとに鋼材中に存在する硫黄（Ｓ）、窒素（Ｎ）の濃度に応じて、Ｚｒを適正に添加して鋼を作成することで、耐腐食特性に優れたばね用鋼およびばね用鋼材に係る本発明を完成したものである。 The present invention is a spring steel that requires high corrosion resistance, and the sulfide that is the starting point of corrosion existing in the steel is modified from MnS to a sulfide of another alloy system. Depending on the concentration of sulfur (S) and nitrogen (N) present in the steel based on the knowledge that the product is poorly water-soluble and has excellent corrosion resistance, Thus, the present invention relating to spring steel and spring steel material excellent in corrosion resistance is completed.
先ず、本発明のばね用鋼の必須化学成分の規定理由を説明する。ここで、成分についての％は質量％を表す。 First, the reasons for defining the essential chemical components of the spring steel of the present invention will be described. Here,% about a component represents the mass%.
（Ｃ：０．４〜１．２％）
Ｃは、鋼の強度を得るために重要な元素であり、特に、高周波焼入れの前組織としてのフェライト分率を低減し、高周波焼入れ時の硬化能を向上させ、硬化層深さを大きくするために必要な元素である。０．４％未満ではフェライト分率が高く、調質時の硬化が不足するので下限を０．４％とした。好ましくは０．４５％以上、より好ましくは０．５％以上である。また、本鋼材は軸受鋼および浸炭処理した材料に適用した場合においても有効であり、浸炭処理した表面炭素濃度として上限を１．２％とした。
(C: 0.4-1.2%)
C is an important element for obtaining the strength of steel, and in particular, to reduce the ferrite fraction as a structure before induction hardening, to improve the hardening ability during induction hardening, and to increase the hardened layer depth. It is a necessary element. If it is less than 0.4%, the ferrite fraction is high, and the hardening during tempering is insufficient, so the lower limit was made 0.4%. Preferably it is 0.45% or more, More preferably, it is 0.5% or more. This steel material is also effective when applied to bearing steel and carburized material, and the upper limit of carburized surface carbon concentration is set to 1.2%.
（Ｓｉ：０．０２〜３．０％）
Ｓｉは焼入層の軟化抵抗を向上させることにより、面疲労強度を向上させる効果がある。その効果を得るには０．０２％以上とすることが好ましい。しかし、３．０％を超えると製造性が著しく低下するため３．０％を上限とした。ただし上限を２．３％以下とするのが製造性の観点からより好適である。
(Si: 0.02-3.0%)
Si has the effect of improving the surface fatigue strength by improving the softening resistance of the hardened layer. In order to acquire the effect, it is preferable to set it as 0.02% or more. However, if it exceeds 3.0%, the productivity is remarkably lowered, so 3.0% was made the upper limit. However, the upper limit is preferably 2.3% or less from the viewpoint of manufacturability.
（Ｍｎ：０．３５〜２．５％）
Ｍｎは、焼入れ性向上により疲労強度を向上させるのに有効な元素である。焼入れ焼戻しでの焼入れ性確保、ひいては鋼材強度を確保する観点から、ある一定の濃度を確保する必要があり、その観点から０．３５％以上の添加が必要である。また、製造性の観点から、上限を２．５％とした。ただし上限を２．０％以下とするのがより好適である。
(Mn: 0.35 to 2.5%)
Mn is an element effective for improving fatigue strength by improving hardenability. From the viewpoint of ensuring hardenability by quenching and tempering, and thus ensuring the strength of the steel material, it is necessary to ensure a certain concentration, and from that viewpoint, addition of 0.35% or more is necessary. From the viewpoint of manufacturability, the upper limit is set to 2.5%. However, the upper limit is more preferably 2.0% or less.
また、上述したようにＭｎよりも硫化物生成傾向の強い、Ｔｉ等の合金元素が含まれない場合は、鋼中のＳを化合してＭｎＳを生成する。このＭｎＳが加水分解して腐食の起点となることから、ＭｎＳの生成を抑制される合金元素の添加が本発明の特徴である。 Further, as described above, when an alloy element such as Ti, which has a stronger tendency to produce sulfide than Mn, is not included, M in the steel is combined to produce MnS. Since this MnS is hydrolyzed and becomes a starting point of corrosion, the addition of an alloy element that suppresses the formation of MnS is a feature of the present invention.
（Ａｌ：０．００１〜０．５％）
Ａｌは、脱酸材として溶鋼中に固溶する酸素を酸化させて除去させる働きをもつとともに、窒化物として鋼中に析出分散することにより、高周波焼入処理時のオーステナイト組織の細粒化に有効に働き、さらに焼入れ性を高めて硬化層深さを大きくする元素である。そのため０．００１％以上は必要である。なお、脱酸材として利用し酸素を充分に除去させるには０．０１％以上とすることが好ましい。しかし、０．５％を超えると析出物が粗大化して鋼を脆化させるため上限を０．５％とした。
(Al: 0.001 to 0.5%)
Al has the function of oxidizing and removing oxygen dissolved in molten steel as a deoxidizer, and it precipitates and disperses in steel as a nitride, thereby reducing the austenite structure during induction hardening. It is an element that works effectively and further increases the hardenability by increasing the hardenability. Therefore, 0.001% or more is necessary. In order to sufficiently remove oxygen by using it as a deoxidizer, the content is preferably 0.01% or more. However, if it exceeds 0.5%, the precipitate becomes coarse and the steel becomes brittle, so the upper limit was made 0.5%.
（Ｎ：０．００３〜０．０１５％）
Ｎは溶鋼へ大気の窒素が固溶するなどの機構を通して、鋼中に不可避的に存在する元素であるが、合金元素の適切な選択と熱処理条件により窒化物を生成させ、結晶粒のピン止め等に活用することもできる。Ｎの下限値は特に指定するものではないが、不可避的に混入する最低のレベルとして０．００３％を下限値として設定した。また、本発明は鋼材製造段階での硫化物の改質を手段としたものであり、Ｎの濃度範囲はバルクの窒素濃度で表現することを注釈しておく。すなわち、鋼材の表面硬化処理方法の一つである、窒化処理を活用したプロセス（軟窒化等の窒化処理、および、窒化処理後の高周波焼入れなど）では表層の窒素濃度が高くなることがあるが、この窒化処理に伴う窒素濃度上昇分は本発明の成分範囲の対象外とする。バルクの窒素濃度については製造性を考慮し、０．０１５％を上限値として設定した。なおＮが低いほど製造性が良好になる傾向にあり、好ましい上限は０．０１％である。
(N: 0.003-0.015%)
N is an element that is unavoidably present in the steel through a mechanism such as the dissolution of atmospheric nitrogen into the molten steel. Nitride is generated by appropriate selection of alloy elements and heat treatment conditions, and crystal grains are pinned. It can also be used for other purposes. The lower limit value of N is not particularly specified, but 0.003% is set as the lower limit value as the lowest level inevitably mixed. Further, it is noted that the present invention is based on the modification of sulfide in the steel material production stage, and the concentration range of N is expressed by a bulk nitrogen concentration. That is, in a process utilizing nitriding, which is one of steel surface hardening methods (nitriding such as soft nitriding, and induction hardening after nitriding), the nitrogen concentration in the surface layer may increase. Therefore, the increase in nitrogen concentration accompanying this nitriding treatment is not covered by the component range of the present invention. The bulk nitrogen concentration was set to 0.015% as an upper limit in consideration of manufacturability. In addition, it exists in the tendency for productivity to become favorable, so that N is low, and a preferable upper limit is 0.01%.
（Ｚｒ：０．１〜０．５％）
Ｚｒは適切な条件で添加することにより硫化物ＺｒＳ等の難水溶性のＺｒ系硫化物を生成させる。このＺｒ系硫化物の生成により、鋼材の腐食の起点となるＭｎＳの生成を低減することになり、結果的にＭｎＳの加水分解に伴う腐食を抑制させる。適切な条件とは本発明の請求項に示すように、
(a) Ｚｒが鋼中のＮおよびＳを窒化物および硫化物として生成させるのに充分な量の添加を意味し、Ｎｂ、Ｖ等のＺｒ以外で窒化物生成傾向の強い元素が無い場合は、
Ｚｒ≧Ｓ×９１．２／３２．１＋Ｎ×９１．２／１４．０＋０．００１×９１．２、
即ち、Ｚｒ／９１．２−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１・ ・ ・（１）
(b) Ｎｂ、Ｖ等を含有する場合は、
Ｚｒ／９１．２＋Ｎｂ／９２．９＋Ｖ／５０．９≧Ｓ／３２．１＋Ｎ／１４．０＋０．００１×９１．２、
即ち、Ｚｒ／９１．２＋Ｎｂ／９２．９＋Ｖ／５０．９−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１ ・ ・ ・（２）
が条件である。
(Zr: 0.1 to 0.5%)
Zr is added under appropriate conditions to form a poorly water-soluble Zr-based sulfide such as sulfide ZrS. Generation of this Zr-based sulfide reduces the generation of MnS, which is the starting point of corrosion of steel materials, and consequently suppresses corrosion associated with hydrolysis of MnS. Appropriate conditions, as indicated in the claims of the present invention,
(a) Zr means the addition of an amount sufficient to form N and S in the steel as nitrides and sulfides, and when there is no element with a strong tendency to form nitrides other than Zr such as Nb and V ,
Zr ≧ S × 91.2 / 32.1 + N × 91.2 / 14.0 + 0.001 × 91.2,
That is, Zr / 91.2- (S / 32.1 + N / 14.0) ≧ 0.001 (1)
(b) When containing Nb, V, etc.
Zr / 91.2 + Nb / 92.9 + V / 50.9 ≧ S / 32.1 + N / 14.0 + 0.001 × 91.2,
That is, Zr / 91.2 + Nb / 92.9 + V / 50.9− (S / 32.1 + N / 14.0) ≧ 0.001 (2)
Is a condition.
Ｚｒ濃度の範囲に関しては、上式の関係を満足させることが第一の条件であり、特に下限については明確に決められるものではないが、Ｚｒを添加する場合にその効果が確実に得られる０．１％をＺｒ濃度の下限値とした。尚、式（１）および式（２）を充分に満足し、耐食性が向上する機能を充分に発揮させるには、Ｚｒ濃度は０．１１％以上が望ましい。より好ましくは０．１３％以上、さらに好ましくは０．１５％以上である。また、Ｚｒ濃度の上限については極端に製造性を損なわない範囲で設定すると０．５％である。ただし、本発明の対象鋼のうち最も適用するケースが多いと考えるばね鋼を想定するとＺｒ濃度の好ましい上限は０．２％である。 Regarding the range of the Zr concentration, the first condition is to satisfy the relationship of the above formula, and the lower limit is not specifically determined. However, when Zr is added, the effect is surely obtained. .1% was the lower limit of the Zr concentration. In order to sufficiently satisfy the expressions (1) and (2) and to fully exhibit the function of improving the corrosion resistance, the Zr concentration is desirably 0.11% or more. More preferably, it is 0.13% or more, More preferably, it is 0.15% or more. The upper limit of the Zr concentration is 0.5% when it is set within a range that does not significantly impair the productivity. However, when the spring steel considered to be the most applicable among the target steels of the present invention is assumed, the preferable upper limit of the Zr concentration is 0.2%.
（Ｓ：０．０３０％以下、Ｐ：０．０３％以下、Ｏ：０．００５０％以下）
Ｓ、Ｐ、Ｏはいずれも鋼中に不可避的に混入する不純物であり、濃度を低減させることが望ましい。ただし、鋼材製造プロセスにおいて、これらの濃度を必要以上に低減させるには予備処理等、雰囲気制御、処理時間管理等の様々なコストアップの原因となるので、経済性を大きく損なわない程度の濃度範囲が産業上の観点から重要である。この視点に立って各々の元素の上限値を設定したところ、それぞれＳ：０．０３０％、Ｐ：０．０３％、Ｏ：０．００５０％という結論に至った。なお、Ｓは一部の用途で被削性改善のために意図的に添加することがあるが、本発明では、被削性改善のもととなっているＭｎＳを低減させることになるので、必要以上のＳ添加は意図しない。また、Ｐについては破断面形状制御等、Ｐ添加による脆化を活用した鋼部品も存在し、一部に本発明の上限値以上の鋼材が存在する可能性はある。
(S: 0.030% or less, P: 0.03% or less, O: 0.0050% or less)
S, P, and O are all impurities inevitably mixed in the steel, and it is desirable to reduce the concentration. However, in the steel material manufacturing process, reducing these concentrations more than necessary can cause various cost increases such as pretreatment, atmosphere control, treatment time management, etc., so the concentration range does not significantly impair the economy. Is important from an industrial point of view. From this point of view, when the upper limit value of each element was set, it was concluded that S: 0.030%, P: 0.03%, and O: 0.0050%, respectively. In some applications, S may be intentionally added to improve machinability, but in the present invention, since MnS that is the basis of machinability improvement is reduced, Unnecessary addition of S is not intended. In addition, there are steel parts that utilize embrittlement due to the addition of P, such as fracture surface shape control, and there is a possibility that some steel materials exceed the upper limit of the present invention.
Ｚｒ／９１．２＋Ｎｂ／９２．９＋Ｖ／５０．９≧Ｓ／３２．１＋Ｎ／１４．０＋０．００１×９１．２、
即ち、Ｚｒ／９１．２＋Ｎｂ／９２．９＋Ｖ／５０．９−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１ ・ ・ ・（２）、ここで、Ｚｒ、Ｎｂ、Ｖ、Ｓ、Ｎは、それぞれ鋼中質量％である。）
各元素の濃度で除算する分母の値はそれぞれの元素の原子量であり、上式は各元素の原子数の比率を示すものである。式(1)は、Ｚｒ／９１．２−（Ｓ／３２．１＋Ｎ／１４．０）については、Ｚｒが窒化物ＺｒＮ、硫化物ＺｒＳとして消費されても、Ｚｒ量が０．００１以上であることを表わすものである。さらに、式(2)のＺｒ／９１．２＋Ｎｂ／９２．９＋Ｖ／５０．９−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１については、Ｎｂ、ＶがそれぞれＮｂＮ、ＶＮといった窒化物を形成し、固溶のＮを低減させたうえで、Ｚｒが窒化物ＺｒＮ、硫化物ＺｒＳとして消費されても、Ｚｒ量が耐食性を発揮させるに十分であることを表わすものである。Ｚｒ量が０．００１以上であることは、硫化物が全てＺｒＳとなり、従来鋼における代表的な硫化物であるＭｎ硫化物（ＭｎＳ）は生成されないことを意味するものである。さらに、ＭｎＳが抑制されることにより、ＭｎＳ起因の腐食が抑制されることを意味し、本発明の耐食性に優れた効果が発揮されることになる。
Zr / 91.2 + Nb / 92.9 + V / 50.9 ≧ S / 32.1 + N / 14.0 + 0.001 × 91.2,
That is, Zr / 91.2 + Nb / 92.9 + V / 50.9− (S / 32.1 + N / 14.0) ≧ 0.001 (2), where Zr, Nb, V, S, N Are mass% in steel, respectively. )
The value of the denominator divided by the concentration of each element is the atomic weight of each element, and the above formula indicates the ratio of the number of atoms of each element. Formula (1) shows that for Zr / 91.2- (S / 32.1 + N / 14.0), the amount of Zr is 0.001 or more even when Zr is consumed as nitride ZrN or sulfide ZrS. It represents. Furthermore, for Zr / 91.2 + Nb / 92.9 + V / 50.9− (S / 32.1 + N / 14.0) ≧ 0.001 in the formula (2), nitrides such that Nb and V are NbN and VN, respectively. This shows that even if Zr is consumed as nitride ZrN and sulfide ZrS after reducing the solid solution N, the amount of Zr is sufficient to exhibit corrosion resistance. When the amount of Zr is 0.001 or more, all the sulfides become ZrS, which means that Mn sulfide (MnS), which is a typical sulfide in conventional steel, is not generated. Furthermore, by suppressing MnS, it means that corrosion caused by MnS is suppressed, and the effect excellent in the corrosion resistance of the present invention is exhibited.
次に選択的に添加する元素について説明する。 Next, elements to be selectively added will be described.
（Ｂ：０．００５％以下、Ｗ：０．５％以下、Ｍｏ：１．０％以下、Ｃｒ：２．０％以下、Ｖ：０．０５〜１．０％、Ｎｂ：０．００５〜０．３％、Ｃｕ：２．０％以下、Ｎｉ：２．０％以下の内の１種または２種以上）
本発明は、鋼材を強化する等のために、さらに、上記成分の内の１種または２種以上を添加できる。
(B: 0.005% or less, W: 0.5% or less, Mo: 1.0% or less, Cr: 2.0% or less, V: 0.05 to 1.0%, Nb: 0.005 0.3%, Cu: 2.0% or less, Ni: 2.0% or less, one or more)
In the present invention, one or more of the above components can be added to strengthen the steel material.
（Ｂ：０．００５％以下）
Ｂは鋼の焼入れ性を向上させ、鋼材強化に用いられる元素である。Ｂによる焼入れ性向上効果を確実に発揮させるには０．０００３％以上の添加が好ましい。なお、０．０００３％未満のＢを添加する場合はＢ添加効果を明確に見極めることが難しいことから、不可避不純物としてみなしても差し支えない。また、０．００５％を超えて添加してもその効果は飽和するため、上限を０．００５％とした。
(B: 0.005% or less)
B is an element that improves the hardenability of steel and is used for strengthening steel. Addition of 0.0003% or more is preferable in order to reliably exhibit the effect of improving the hardenability by B. In addition, when adding less than 0.0003% of B, it is difficult to clearly determine the effect of adding B, so that it may be regarded as an inevitable impurity. Further, even if added over 0.005%, the effect is saturated, so the upper limit was made 0.005%.
（Ｗ：０．５％以下）
Ｗは炭化物を生成させ、析出強化機構による鋼材強化に用いられる元素である。Ｗによる析出強化の効果を確実に発揮させるには０．００２５％以上の添加が好ましい。なお、０．００２５％未満のＷを添加する場合はＷ添加効果を明確に見極めることが難しいことから、不可避不純物としてみなしても差し支えない。また、０．５％を超えて添加すると製造コスト上昇が著しくなり、産業上の利用が難しいことから上限を０．５％とした。
(W: 0.5% or less)
W is an element that generates carbides and is used for strengthening steel by a precipitation strengthening mechanism. Addition of 0.0025% or more is preferable in order to ensure the effect of precipitation strengthening by W. In addition, when adding less than 0.0025% W, it is difficult to clearly determine the effect of W addition, and therefore, it may be regarded as an inevitable impurity. Further, if added over 0.5%, the production cost rises remarkably, and industrial use is difficult, so the upper limit was made 0.5%.
（Ｍｏ：１．０％以下）
Ｍｏは炭化物を生成させ、析出強化機構による鋼材強化に用いられる元素である。Ｍｏによる析出強化の効果を確実に発揮させるには０．０５％以上の添加が好ましい。なお、０．０５％未満のＭｏを添加する場合はＭｏ添加効果を明確に見極めることが難しいことから、不可避不純物としてみなしても差し支えない。また、１．０％を超えて添加すると製造コスト上昇が著しくなり、産業上の利用が難しいことから上限を１．０％とした。好ましくは上限を０．５％とする。
(Mo: 1.0% or less)
Mo is an element that generates carbides and is used for strengthening steel by a precipitation strengthening mechanism. In order to ensure the effect of precipitation strengthening by Mo, addition of 0.05% or more is preferable. In addition, when adding less than 0.05% Mo, it is difficult to clearly determine the Mo addition effect, and therefore, it may be regarded as an inevitable impurity. On the other hand, if the content exceeds 1.0%, the production cost rises remarkably and the industrial application is difficult, so the upper limit was made 1.0%. Preferably, the upper limit is 0.5%.
（Ｃｒ：２．０％以下）
Ｃｒは焼入層軟化抵抗を向上させ、疲労強度が向上する効果がある。その効果を得るには０．０１％以上とすることが好ましい。また、２．０％を超えると加工性が悪化するため２．０％を上限とした。好ましくは上限を１．３％とする。
(Cr: 2.0% or less)
Cr has the effect of improving the hardened layer softening resistance and improving the fatigue strength. In order to acquire the effect, it is preferable to set it as 0.01% or more. Further, if over 2.0%, the workability deteriorates, so 2.0% was made the upper limit. Preferably, the upper limit is 1.3%.
（Ｖ：０．０５〜１．０％）
Ｖは窒化物、炭化物、及び端窒化物を生成させ、析出強化機構による鋼材強化、結晶粒のピンニングよる組織微細化制御に用いられる元素である。Ｖによるこれらの効果を確実に発揮させるには０．０５％以上の添加が必要である。なお、０．０５％未満のＶを添加する場合はＶ添加効果を明確に見極めることが難しいことから、不可避不純物としてみなしても差し支えない。また、１．０％を超えて添加すると製造コスト上昇が著しくなり、産業上の利用が難しいことから上限を１．０％とした。好ましくは上限を０．１％とする。
(V: 0.05-1.0%)
V is an element that generates nitrides, carbides, and end nitrides, and is used for strengthening the steel by a precipitation strengthening mechanism and controlling the refinement of the structure by pinning of crystal grains. Addition of 0.05% or more is necessary to ensure that these effects of V are exhibited. In addition, when adding less than 0.05% V, it is difficult to clearly determine the effect of adding V, and therefore, it may be regarded as an inevitable impurity. On the other hand, if the content exceeds 1.0%, the production cost rises remarkably and the industrial application is difficult, so the upper limit was made 1.0%. Preferably, the upper limit is 0.1%.
（Ｎｂ：０．００５〜０．３％）
Ｎｂは窒化物、炭化物、及び端窒化物を生成させ、析出強化機構による鋼材強化、結晶粒のピンニングよる組織微細化制御に用いられる元素である。Ｎｂによるこれらの効果を確実に発揮させるには０．００５％以上の添加が必要である。なお、０．００５％未満のＮｂを添加する場合はＮｂ添加効果を明確に見極めることが難しいことから、不可避不純物としてみなしても差し支えない。また、０．３％以上を添加すると製造性が極端に悪化し、産業上の利用が難しいことから上限を０．３％とした。好ましくは上限を０．０５％とする。
(Nb: 0.005-0.3%)
Nb is an element that generates nitrides, carbides, and edge nitrides, and is used for strengthening a steel material by a precipitation strengthening mechanism and controlling structure refinement by pinning of crystal grains. Addition of 0.005% or more is necessary to reliably exhibit these effects of Nb. In addition, when adding Nb of less than 0.005%, it is difficult to clearly determine the Nb addition effect, and therefore, it may be regarded as an inevitable impurity. Further, if 0.3% or more is added, the productivity is extremely deteriorated and the industrial use is difficult, so the upper limit was made 0.3%. Preferably, the upper limit is 0.05%.
（Ｃｕ：２．０％以下）
Ｃｕは市中のスクラップ鉄を鋼材原料とする場合に不可避的に混入する場合があるが、鋼材に含有し、安定さび形成などに利用される。その効果を確実に発揮するには０．０１％以上の添加が好ましい。ただし、Ｎｉ添加とのバランスにもよるが、同時に鋼材に焼き割れ等の疵の原因となり、過度の添加は回避する必要がある。その観点から、２．０％以下とした。
(Cu: 2.0% or less)
Cu may be inevitably mixed when scrap steel in the city is used as a raw material for steel, but is contained in the steel and used for forming stable rust. Addition of 0.01% or more is preferable in order to reliably exhibit the effect. However, although depending on the balance with the addition of Ni, it causes a flaw such as burn cracking in the steel at the same time, and it is necessary to avoid excessive addition. From that point of view, it was made 2.0% or less.
（Ｎｉ：２．０％以下）
Ｎｉは鋼材に含有し、靭性の向上に効果をもたらす。また、Ｃｕ濃度とのバランスにもよるがＣｕ添加鋼にＮｉを適用添加することにより、鋼材中のＣｕ相の融点が上昇し、焼き割れを防止することにも有効である。これらの効果を確実に発揮するには０．０１％以上の添加が好ましい。一方で、過度に添加すると添加すると製造コスト上昇が著しくなり、産業上の利用が難しくなる。これらを鑑み、２．０％以下とした。
(Ni: 2.0% or less)
Ni is contained in the steel material and brings about an effect of improving toughness. Further, although depending on the balance with the Cu concentration, by adding Ni to the Cu-added steel, the melting point of the Cu phase in the steel material is increased, which is effective in preventing burning cracks. Addition of 0.01% or more is preferable in order to reliably exhibit these effects. On the other hand, if added excessively, if added, the manufacturing cost rises remarkably, and industrial utilization becomes difficult. In view of these, the content was made 2.0% or less.
（Ｃａ：０．０１％以下、Ｍｇ：０．０１％以下、Ｔｅ：０．１％以下の内の１種または２種以上）
これらの元素は、鋼材中に残存するＭｎＳの延伸を抑制し、疲労強度を向上させる元素である。すなわち、ＭｎＳの延伸抑制効果を与えるために、Ｃａで０．０１％以下、Ｍｇで０．０１％以下及びＴｅで０．１％以下よりなる群から選択される、少なくとも１種以上を含有させることができる。
(Ca: 0.01% or less, Mg: 0.01% or less, Te: one or more of 0.1% or less)
These elements are elements that suppress the stretching of MnS remaining in the steel material and improve the fatigue strength. That is, in order to give the effect of suppressing the stretching of MnS, at least one selected from the group consisting of 0.01% or less of Ca, 0.01% or less of Mg and 0.1% or less of Te is contained. be able to.
各元素で上記量を超えて含有させてもその効果は飽和して経済性を損なうためＣａ：０．０１％、Ｍｇ：０．０１％、Ｔｅ：０．１％をそれぞれ上限とした。そして、ＭｎＳの延伸を抑制させる効果を確実に得るためには、Ｃａ：０．０００５％、Ｍｇ：０．０００５％、Ｔｅ：０．０００５％をそれぞれ下限とするのが好ましい。 Even if each element is contained in excess of the above-mentioned amount, the effect is saturated and the economy is impaired, so Ca: 0.01%, Mg: 0.01%, and Te: 0.1% were set as upper limits, respectively. And in order to acquire the effect which suppresses extending | stretching of MnS reliably, it is preferable to make Ca: 0.0005%, Mg: 0.0005%, Te: 0.0005% into a minimum, respectively.
本発明では、鋼材の特性向上のために、上述の選択元素を意図的に添加することができる。しかし、合金コスト低減などのために、これらの選択元素を何ら添加しなくても差し支えない。これらの元素は、意図的に添加しない場合であっても、不可避的不純物として、Ｂ：０．０００３％未満、Ｗ：０．００２５％未満、Ｍｏ：０．０５％未満、Ｃｒ：０．０１％未満、Ｖ：０．０５％未満、Ｎｂ：０．００５％未満、Ｃｕ：０．０１％未満、Ｃａ：０．０００５％未満、Ｍｇ：０．０００５％未満、Ｚｒ：０．０００５％未満、Ｔｅ：０．０００５％未満を、鋼中に含有することを許容し得る。これらの元素が、鋼中に不可避的不純物として、含有された場合であっても、本発明鋼には、何ら影響しない。 In the present invention, the above-mentioned selective elements can be intentionally added to improve the properties of the steel material. However, it is not necessary to add any of these selective elements in order to reduce alloy costs. Even when these elements are not intentionally added, B: less than 0.0003%, W: less than 0.0025%, Mo: less than 0.05%, Cr: 0.01 %, V: less than 0.05%, Nb: less than 0.005%, Cu: less than 0.01%, Ca: less than 0.0005%, Mg: less than 0.0005%, Zr: less than 0.0005% Te: Less than 0.0005% can be allowed to be contained in the steel. Even if these elements are contained as inevitable impurities in the steel, the steel of the present invention is not affected at all.
また、上記で規定した化学成分の他に本発明の効果を損なわない範囲で、Ｐｂ、Ｂｉ、Ｚｎ、Ｓｎ、Ｓｂ、ＲＥＭを含有させることができる。これらは、微量の添加でも鋼材製造時の製造性向上（ノズル詰まり防止）、部品製造時の製造性向上（切削加工性改善）、部品機能向上（耐食性改善）等に有効である。 Moreover, Pb, Bi, Zn, Sn, Sb, and REM can be contained in the range which does not impair the effect of this invention other than the chemical component prescribed | regulated above. These are effective to improve the manufacturability at the time of manufacturing steel materials (preventing nozzle clogging), improve the manufacturability at the time of manufacturing parts (improvement of cutting workability), improve the function of parts (improve corrosion resistance), etc.
（表面において、ＥＰＭＡ分析により、ＭｎとＳが１μｍ２以上のスポットで同時検出される点が、０．２５ｍｍ２あたり２５箇所以下）
上記の鋼材においてＭｎＳの生成が抑制されていることが望ましいが、実際には皆無とするまでではなく、ある一定の量よりも少なければ、耐食効果は充分に発揮できる。鋼材は熱間あるいは冷間の圧延あるいは鍛造により成形され、その加工に伴い硫化物等の非金属介在物も変形する。硫化物サイズが小さくなれば、局部電池反応は抑制され、耐食性がより有効になることが考えられる。種々の実験検討の結果、ＭｎＳの存在基準は対象鋼部品の表面においてＥＰＭＡにてＭｎとＳが１μｍ２以上のスポットで同時検出される点が０．２５ｍｍ２あたり２５箇所以下であれば耐食性が充分に確保できることを明らかにした。耐食性をさらに向上させる観点から、該検出点が０．２５ｍｍ２あたり１０箇所以下であればさらに好ましい。
(On the surface, by EPMA analysis, Mn and S are detected at spots of 1 μm 2 or more at the same time, 25 points or less per 0.25 mm 2 )
Although it is desirable that the production of MnS is suppressed in the steel material described above, the corrosion resistance effect can be sufficiently exhibited if the amount is less than a certain amount, not in practice. Steel materials are formed by hot or cold rolling or forging, and non-metallic inclusions such as sulfides are deformed along with the processing. If the sulfide size is reduced, the local battery reaction is suppressed, and it is considered that the corrosion resistance becomes more effective. As a result of various experimental studies, the presence criterion of MnS is that if the point where Mn and S are simultaneously detected by EPMA at the spot of 1 μm 2 or more on the surface of the target steel part is 25 or less per 0.25 mm 2, the corrosion resistance is good. It was clarified that it can be secured sufficiently. From the viewpoint of further improving the corrosion resistance, it is more preferable that the detection points are 10 or less per 0.25 mm 2 .
なお、発明では、ばね用鋼およびばね用鋼材を対象としており、鋳造から熱間圧延、伸線加工、調質(焼入れ焼戻し)、表面処理(窒化等)、までに至る工程を経て、ばねを製作するが、耐食性および微細硫化物分布の評価は熱間圧延後の状態で評価した。この理由は本発明の特性を活かすための化学成分Ｚｒ、Ｓ、Ｎおよび選択的に添加する場合のＮｂ、Ｖの濃度は、熱間圧延後と最終部品とで同一であること、微細硫化物分布についても同等であることが理由である。
また、本発明のばね用鋼およびばね用鋼材は、ばねに要求される強度特性等に関わらず、耐腐食特性の効果を発揮するものである。
The invention is intended for spring steel and spring steel, and the spring is subjected to processes ranging from casting to hot rolling, wire drawing, tempering (quenching and tempering), surface treatment (nitriding, etc.). Although manufactured, the corrosion resistance and fine sulfide distribution were evaluated in the state after hot rolling. This is because the chemical components Zr, S, N for making the best use of the characteristics of the present invention and the concentration of Nb, V when selectively added are the same after hot rolling and in the final part, The reason is that the distribution is also equivalent.
Moreover, the spring steel and spring steel material of the present invention exhibit the effect of corrosion resistance regardless of the strength characteristics required for the spring.
また、本発明の対象にはしていないが、ばね以外の調質部品、非調質部品、浸炭部品、窒化部品等の表面硬化処理を施した部品にも有効な技術である。 Although not the subject of the present invention, this technique is also effective for parts subjected to surface hardening treatment such as tempered parts other than springs, non-tempered parts, carburized parts, and nitrided parts.
以下に本発明を実施例によって具体的に説明する。なお、これらの実施例は本発明を説明するためのものであって、本発明の範囲を限定するものではない。 Hereinafter, the present invention will be specifically described by way of examples. These examples are for explaining the present invention, and do not limit the scope of the present invention.
表１−１〜表１−３、表２−１〜表２−３および表３−１〜表３−３に示す化学組成を有する鋼材を作成した。 Steel materials having chemical compositions shown in Tables 1-1 to 1-3, Tables 2-1 to 2-3, and Tables 3-1 to 3-3 were prepared.
最初に、これらの鋼材の熱間圧延性を評価するために、断面８０ｍｍ角の試験材に切削加工し、中心部に熱電対を取り付け、１０５０℃の電気炉に装入し、試験片中心部が１０４５℃に達してから３０分間後に炉から取り出し、表面温度が１０００℃となった時点で圧延加工した。圧延加工は３パス連続で行い、板厚８０ｍｍからを６４→５１→４１ｍｍとし、空冷で室温まで冷却した。もしくは同様の加熱条件で加熱した後に、熱間鍛造で丸棒に加工し、空冷で室温まで冷却した。 First, in order to evaluate the hot rollability of these steel materials, cutting was performed on a test material having a cross section of 80 mm square, a thermocouple was attached to the center portion, and the test piece was placed in an electric furnace at 1050 ° C. Was taken out of the furnace 30 minutes after reaching 1045 ° C., and rolled when the surface temperature reached 1000 ° C. The rolling process was performed continuously for 3 passes. The plate thickness was changed from 80 mm to 64 → 51 → 41 mm, and cooled to room temperature by air cooling. Or after heating on the same heating conditions, it processed into the round bar by hot forging, and cooled to room temperature by air cooling.
上記に示す圧延条件で製造した鋼材は、その後、圧延方向に垂直な断面を切断して温湿潤サイクル試験を施し、錆びの発生状況を評価した。なお、温湿潤サイクル試験はＪＩＳ Ｃ ６００６８−２−３８で指定される低温サイクルを除いた条件（附図２ｂ）で実施し、発錆状況の比較は２０サイクル後に行なった。なお、本発明に用いた温湿潤サイクル試験は、塩や酸と接触しない比較的穏やかな腐食環境を再現する試験である。 The steel materials manufactured under the rolling conditions described above were then cut in a cross section perpendicular to the rolling direction and subjected to a warm and wet cycle test to evaluate the occurrence of rust. The warm and wet cycle test was conducted under the conditions (Appendix Fig. 2b) excluding the low temperature cycle specified in JIS C 60068-2-38, and the rusting situation was compared after 20 cycles. The hot and humid cycle test used in the present invention is a test that reproduces a relatively mild corrosive environment that does not come into contact with salt or acid.
本発明鋼の孔食の程度は温湿潤サイクル試験２０サイクル後の○、△、×の３段階で評価した。２５０μｍ２の観察面あたり、○印は微少な孔食が試料全体で５個以下のもの、△印は、孔食が５〜２５個の軽微なものである。○あるいは△であれば発錆は軽微であり、耐食性にすぐれているとして判定し、発明鋼の要件とした。×印は２６個以上の錆発生があるものを表す。 The degree of pitting corrosion of the steel of the present invention was evaluated in three stages of ◯, Δ, and X after 20 cycles of the hot and wet cycle test. On the observation surface of 250 μm 2 , ◯ indicates a slight pitting corrosion of 5 or less in the entire sample, and Δ indicates a slight pitting corrosion of 5 to 25. If it was ○ or △, rusting was slight, and it was judged that it had excellent corrosion resistance, and it was set as a requirement for the invention steel. A cross indicates that there are 26 or more rusts.
なお、孔食は腐食でできたくぼみのことであり、明確に定義することは難しいが、ＳＥＭ等による表面観察において、明らかにくぼみが認められる点を孔食としてカウントした。発錆の初期段階ではくぼみ、および、その周辺に錆が観察されることも特徴のひとつである。 Pitting corrosion is a pit formed by corrosion, and it is difficult to define it clearly. However, in surface observation by SEM or the like, points where pits were clearly recognized were counted as pitting corrosion. One of the features is that dents are observed at the initial stage of rusting and rust is observed in the vicinity thereof.
その結果、本発明鋼１〜６０のいずれも発錆は軽微であり、錆抑制効果が確認された。その代表例として本発明鋼１の発錆状況を図１（ａ）に示す。本発明鋼２〜６０についても本発明鋼１と同様の発錆状況であった。比較鋼Ｃ０１〜Ｃ２０はＺｒ、Ｎ、Ｓのいずれかが本発明の成分範囲を逸脱する場合、あるいは本発明のＺｒ、Ｎ、Ｓ、Ｎｂ、Ｖから構成される条件式が本発明の請求項に示す範囲から逸脱し、ＭｎＳの抑制、硫化物の改質が不十分な場合、あるいはＺｒ、Ｎ、Ｓ、Ｎｂ、Ｖから構成される条件式が合致しても、個別の元素濃度範囲が本発明で規定した範囲を逸脱している。 As a result, rusting was minor in all of the inventive steels 1 to 60, and the effect of suppressing rust was confirmed. As a representative example, the rusting situation of the steel 1 of the present invention is shown in FIG. Inventive steels 2 to 60 also had the same rusting situation as invented steel 1. In the comparative steels C01 to C20, when any one of Zr, N, and S deviates from the component range of the present invention, or a conditional expression composed of Zr, N, S, Nb, and V of the present invention is claimed in the present invention. When the MnS suppression and the sulfide modification are insufficient, or even if the conditional expression composed of Zr, N, S, Nb, and V is met, the individual element concentration ranges are different. It deviates from the scope defined by the present invention.
図１（ｂ）はＺｒ添加が不十分な場合（比較鋼Ｃ０１）の発錆状況を示す。比較鋼Ｃ０３〜Ｃ２０についても図１（ｂ）と同様の発錆状況であった
図１（ａ）、（ｂ）を比較すると（ａ）で錆が抑制されていることは明らかであり、耐食性に優れていることが判る。
FIG. 1B shows the rusting situation when Zr addition is insufficient (comparative steel C01). The comparative steels C03 to C20 also had the same rusting situation as in FIG. 1B. When FIGS. 1A and 1B are compared, it is clear that rust is suppressed in FIG. It turns out that it is excellent in.
（ａ）と（ｂ）との比較において、Ｚｒの十分な添加により硫化物がＭｎＳからＺｒ系硫化物に改質させることにより耐食性が向上すること、十分な耐食性を発揮させるには硫化物および窒化物を充分に生成させる以上のＺｒの添加が必要であることを知見し、発明に至った。 In the comparison between (a) and (b), the sulfide is improved by improving the corrosion resistance from MnS to Zr-based sulfide by sufficient addition of Zr, and in order to exhibit sufficient corrosion resistance, sulfide and The inventors have found that it is necessary to add Zr more than sufficient to form nitrides, and have reached the invention.
硫化物分布が耐腐食特性へ及ぼす影響については、硫化物の特性／分布状況のみならず、評価基準が多様であること、例えば、腐食環境により差異が生じること、適用される部品の耐腐食要求度の異なること等、により明確に分類することは難しいが、本発明で評価した温湿潤サイクル試験条件での発錆状況の観察から、ＥＰＭＡ分析によりＭｎとＳが１μｍ２以上のスポットで同時検出される点が０．２５ｍｍ２あたり２５箇所以下であれば耐食性が充分に確保できるものである。 Regarding the influence of sulfide distribution on corrosion resistance, not only the characteristics / distribution status of sulfide, but also various evaluation criteria, such as differences due to corrosive environment, corrosion resistance requirements of applied parts Although it is difficult to classify clearly depending on the degree of difference, etc., from the observation of the rusting condition under the hot and humid cycle test conditions evaluated in the present invention, simultaneous detection at a spot where Mn and S are 1 μm 2 or more by EPMA analysis If the number of points is 25 or less per 0.25 mm 2, corrosion resistance can be sufficiently secured.
以上の通り、本発明の要件を満たすばね用鋼は、優れた耐腐食特性を有することが確認できた。
なお、この温湿潤サイクル試験、および、硫化物分布測定は圧延もしくは鍛造した鋼材の段階で評価を行なっているが、最終部品であるばねまで熱処理および加工を加えた場合でも、鋼の耐腐食特性、および、μｍオーダーの微細な球形硫化物の分布状態は同等である。したがって、化学成分、および、硫化物の分布が本発明の範囲に含まれば、最終製品であるばね自体の耐食性は鋼材と同等に確保されることは明らかである。
As described above, it was confirmed that the spring steel satisfying the requirements of the present invention has excellent corrosion resistance.
The temperature and humidity cycle test and the sulfide distribution measurement are evaluated at the stage of rolled or forged steel. Even when heat treatment and processing are applied to the spring, which is the final part, the corrosion resistance characteristics of the steel. , And the distribution of fine spherical sulfides on the order of μm are equivalent. Therefore, if the chemical composition and the distribution of sulfides are included in the scope of the present invention, it is clear that the corrosion resistance of the spring, which is the final product, is assured as steel.
Claims (4)
Ｃ：０．４〜１．２％、
Ｓｉ：０．０２〜３．０％、
Ｍｎ：０．３５〜２．５％、
Ａｌ：０．００１〜０．５％、
Ｎ：０．００３〜０．０１５％、
Ｚｒ：０．１〜０．５％
を含有し、
Ｓ：０．０３０％以下、
Ｐ：０．０３％以下、
Ｏ：０．００５０％以下
に制限し、
下記（１）式を満たし、
残部がＦｅ及び不可避的不純物よりなることを特徴とする耐腐食特性に優れたばね用鋼。
Ｚｒ／９１．２−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１ ・ ・ ・（１）
ここで、Ｚｒ、Ｓ、Ｎは、それぞれ鋼中質量％である。 Chemical composition is mass%,
C: 0.4 to 1.2%
Si: 0.02-3.0%,
Mn: 0.35 to 2.5%,
Al: 0.001 to 0.5%,
N: 0.003 to 0.015%,
Zr: 0.1 to 0.5%
Containing
S: 0.030% or less,
P: 0.03% or less,
O: limited to 0.0050% or less,
Satisfying the following formula (1)
A spring steel with excellent corrosion resistance characterized by the balance being Fe and inevitable impurities.
Zr / 91.2− (S / 32.1 + N / 14.0) ≧ 0.001 (1)
Here, Zr, S, and N are each mass% in steel.
Ｂ：０．００５％以下、
Ｗ：０．５％以下、
Ｍｏ：１．０％以下、
Ｃｒ：２．０％以下、
Ｖ：０．０５〜１．０％、
Ｎｂ：０．００５〜０．３％、
Ｃｕ：２．０％以下、
Ｎｉ：２．０％以下
の内の１種または２種以上を含有し、
下記（２）式を満たすことを特徴とする請求項１記載の耐腐食特性に優れたばね用鋼。
Ｚｒ／９１．２＋Ｎｂ／９２．９＋Ｖ／５０．９−（Ｓ／３２．１＋Ｎ／１４．０）≧０．００１ ・ ・ ・（２）
ここで、Ｚｒ、Ｎｂ、Ｖ、Ｓ、Ｎは、それぞれ鋼中質量％である。 Furthermore, the chemical component is mass%,
B: 0.005% or less,
W: 0.5% or less,
Mo: 1.0% or less,
Cr: 2.0% or less,
V: 0.05-1.0%
Nb: 0.005-0.3%
Cu: 2.0% or less,
Ni: containing one or more of 2.0% or less,
The spring steel excellent in corrosion resistance according to claim 1, wherein the following formula (2) is satisfied.
Zr / 91.2 + Nb / 92.9 + V / 50.9− (S / 32.1 + N / 14.0) ≧ 0.001 (2)
Here, Zr, Nb, V, S, and N are respectively mass% in steel.
Ｃａ：０．０１％以下、
Ｍｇ：０．０１％以下、
Ｔｅ：０．１％以下、
の内の１種または２種以上を含有することを特徴とする請求項１または２に記載の耐腐食特性に優れたばね用鋼。 Furthermore, the chemical component is mass%,
Ca: 0.01% or less,
Mg: 0.01% or less,
Te: 0.1% or less,
The spring steel having excellent corrosion resistance according to claim 1 or 2, characterized by containing one or more of them.
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| US10060014B2 (en) * | 2014-11-21 | 2018-08-28 | Hyundai Motor Company | Bearing steel having improved fatigue durability and method of manufacturing the same |
| CN113584265A (en) * | 2021-08-02 | 2021-11-02 | 江苏通工金属科技有限公司 | High-strength antirust alloy spring steel wire |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| US10060014B2 (en) * | 2014-11-21 | 2018-08-28 | Hyundai Motor Company | Bearing steel having improved fatigue durability and method of manufacturing the same |
| CN113584265A (en) * | 2021-08-02 | 2021-11-02 | 江苏通工金属科技有限公司 | High-strength antirust alloy spring steel wire |
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| JP6171473B2 (en) | 2017-08-02 |
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