JP2004231996A

JP2004231996A - Cu-PLATED STEEL SHEET FOR SPRING SUPERIOR IN CONDUCTIVITY AND SPRING MATERIAL FOR ELECTRICAL CONTACT

Info

Publication number: JP2004231996A
Application number: JP2003019332A
Authority: JP
Inventors: Noriyuki Nakahara; 敬之中原; Satoshi Tagashira; 聡田頭; Terushi Hiramatsu; 昭史平松
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2003-01-28
Filing date: 2003-01-28
Publication date: 2004-08-19
Anticipated expiration: 2023-01-28
Also published as: JP4097535B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Cu-plated steel sheet having adequate conductivity and superior spring properties both equal to those of phosphor bronze for a spring for an electric contact. <P>SOLUTION: The Cu-plated steel sheet for a spring comprises a substrate steel sheet and a Cu-plating layer and has a spring limit value of 250 MPa or higher and a conductivity of 12% IACS or higher. The substrate steel sheet has a chemical composition satisfying expression (1): C≥0.1 and expression (2): 17.53C+13.75Si+6.25Mn<24, has a processed metal structure consisting of any of a ferrite + spherical cementite structure, a ferrite + pearlite structure, and a pearlite structure, and has a spring limit value of 300 MPa or higher. The Cu-plating layer has a thickness satisfying expression (3): 0.19-0.016×Aw≤tc/tw<0.093×ln(Kbw)-0.27 [wherein Aw is the conductivity (%IACS) of the substrate steel sheet; tw is the thickness (mm) of the substrate steel sheet; Kbw is the spring deflection limit (MPa) of the substrate steel sheet; and tc is the total thickness (mm) of the Cu-plated layers on both sides of the substrate steel sheet]. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、導電性に優れたばね用Ｃｕめっき鋼板および電気接点ばね材料に関する。
【０００２】
【従来の技術】
電気・電子機器に使用される電気接点ばねには、それ自体が導電体となって通電を担う機能とともに、通電状態において接触相手部材と容易に外れないよう接触点において自らを相手部材に強固に押しつける機能が要求される。したがって、その材料には良好な導電性とばね特性が求められる。
【０００３】
従来より、電気接点ばね材料には導電性とばね特性のバランスに優れる「りん青銅」が多く使用されている。りん青銅は、例えばＳｎ：３．５〜９．０質量％，Ｐ：０．０３〜０．３５質量％を含む銅合金であり、導電率は概ね１２〜１８％ＩＡＣＳを呈する。素材形状としては、電気接点においては平面同士が接触する仕組みである方が接触不良が少ない上に接触抵抗も小さいので、板材が多用されている。この板材は、通常、ばね限界値２５０ＭＰａ以上のばね特性を有するものが使用される。
【０００４】
一方、線材用途として、下記特許文献１には、高炭素鋼線の表面にＣｕめっきとＮｉめっきを施した電池押さえばね用鋼線が示されている。これは、Ｃｕめっきによって従来の電池押さえばね用鋼線の導電性を改善したものである。
【０００５】
【特許文献１】特開平６−１５８３５３号公報
【０００６】
【発明が解決しようとする課題】
電気・電子機器部品には材料を含む低コスト化，小型化，軽量化が求められている。
従来から使用されているりん青銅は、特性バランスに優れている反面、高価な材料である。りん青銅を、これと同等の性能を有する安価な材料で代替することができれば、電気・電子機器部品のコスト低減に貢献できる。
【０００７】
しかし、特許文献１の材料は線材であるため接触抵抗の観点から上記の板材接点用途に適用することはできない。一方、従来のばね用鋼板にＣｕめっきを施して導電率を改善する手法も考えられるが、この場合、鋼板自体が導電性に劣るため、全体として十分な導電率を得るにはかなり厚目付のＣｕめっき層を形成する必要がある。このため、めっきによるコスト増およびばね特性劣化を考慮するとりん青銅の代替として使用することは困難である。
【０００８】
本発明は、上記の電気接点用りん青銅の板材に匹敵する「ばね特性」と「導電率」を具備する低廉な材料を提供することを目的とする。
【０００９】
【課題を解決するための手段】
発明者らは上記目的を達成すべく種々検討を重ねた結果、りん青銅に匹敵するばね特性と導電性を有する低廉な材料を実現するには、素材自体にそのような優れた特性を持たせた「単独材料」を開発するよりも、高いばね特性を有する基材の表面に、Ｃｕ，Ａｌ，Ａｇ，Ａｕといった高導電性の金属を被覆した「複合材料」を開発する方が合理的であるとの見解を得た。
【００１０】
この場合、基材としては「ばね特性」と「低廉さ」を重視すると鋼材が有利になる。しかし、既存のばね用鋼板は導電性が低いため、これを補うためにはＣｕ等の被覆を厚く形成する必要があり、その結果、基材の特長である「ばね特性」および「低廉さ」は没却されてしまう。このため、鋼板を基材に用いるのであれば、「ばね性」を維持したまま鋼材の「導電性」を向上させる技術の確立が望まれる。ところが、そのような積極的な研究は未だ十分になされていないのが現状である。
【００１１】
そこで発明者らは、鋭意研究を行った結果、化学組成と金属組織を厳しく限定したうえ、冷間圧延と時効処理を組み合わせた適切な組織制御を行えば鋼材に良好な導電性と優れたばね特性を同時に付与できることを見出した。そして、そのような鋼板を基材とした場合に、個々の基材鋼板の特性に応じてＣｕめっき層の厚さを適切に制御すれば、ばね特性の劣化やコスト高騰を避けながら更なる導電性の向上が実現できることを見出した。本発明はこれらの知見に基づいて完成したものである。
【００１２】
すなわち、上記目的は、Ｃ，Ｓｉ，Ｍｎの含有量が質量％で下記（１）式および（２）式を満たし残部がＦｅおよび不可避的不純物からなる化学組成を有し、フェライト＋球状セメンタイト組織，フェライト＋パーライト組織，パーライト組織のいずれかの冷間加工された金属組織を呈し、ばね限界値が３００ＭＰａ以上である基材鋼板の表面に、下記（３）式を満たす厚さのＣｕめっき層を形成したばね限界値が２５０ＭＰａ以上、導電率が１２％ＩＡＣＳ以上である導電性に優れたばね用Ｃｕめっき鋼板によって達成される。
Ｃ≧０．１ ……（１）
１７．５３Ｃ＋１３．７５Ｓｉ＋６．２５Ｍｎ＜２４ ……（２）
０．１９−０．０１６×Ａｗ≦ｔｃ／ｔｗ＜０．０９３×ｌｎ（Ｋｂｗ）−０．２７ ……（３）
ただし、Ａｗ：基材鋼板の導電率（％ＩＡＣＳ）
ｔｗ：基材鋼板の板厚（ｍｍ）
Ｋｂｗ：基材鋼板のばね限界値（ＭＰａ）
ｔｃ：基材鋼板両面のＣｕめっき層合計厚さ（ｍｍ）
【００１３】
ここで、（１）式および（２）式の元素記号の箇所には質量％で表された各元素の含有量が代入される。ばね限界値は、ＪＩＳＨ３１３０に規定されるばね限界値試験法により求まるものである。導電率％ＩＡＣＳは、材料の導電性を、国際標準軟銅線（ＩｎｔｅｒｎａｔｉｏｎａｌＡｎｎｅａｌｅｄＣｏｐｐｅｒＳｔａｎｄａｒｄ）の電気抵抗率（１．７２４１×１０^−８Ω・ｍ）に相当する導電率を１００とした相対比（％）で表示したものである。（３）式中の「ｌｎ」は自然対数を表す。
【００１４】
また本発明では、Ｃ，Ｓｉ，Ｍｎの含有量が質量％で上記（１）式および（２）式を満たし残部がＦｅおよび不可避的不純物からなる化学組成を有し、フェライト＋球状セメンタイト組織，フェライト＋パーライト組織，パーライト組織のいずれかの金属組織に調整された鋼板に、冷延率１５％以上好ましくは１５〜９０％の冷間圧延と、次いで６００℃以下の時効処理好ましくは３００〜５００℃で１〜３０時間保持する時効処理を施して得られる組織状態を有し、ばね限界値が３００ＭＰａ以上である基材鋼板の表面に、上記（３）式を満たす厚さのＣｕめっき層を形成したばね限界値が２５０ＭＰａ以上、導電率が１２％ＩＡＣＳ以上である導電性に優れたばね用Ｃｕめっき鋼板を提供する。このうち、特にＣｕめっきを施す基材鋼板の導電率が７％ＩＡＣＳ以上であるものを提供する。
【００１５】
さらに、上記の導電性に優れたばね用Ｃｕめっき鋼板のうち板厚が０．１〜０．６ｍｍに調整されたものを用いた電気接点ばね材料を提供する。
【００１６】
【発明の実施の形態】
本発明では、りん青銅と同等あるいはそれ以上のばね特性と導電性を両立するＣｕめっき鋼板を得るために、めっき基材となる鋼板の化学組成を厳しく限定する必要がある。
Ｃは、本来鋼の強度を確保する上で必須の元素であるが、本発明では後述する「冷間圧延＋時効処理」によりばね特性を大幅に向上させるため、０．１質量％以上の含有量を確保する。Ｃが０．１質量％を下回ると、マルテンサイトが存在しないように調整された金属組織（後述）においては、基材鋼板自体に必要な最小限のばね限界値３００ＭＰａ（後述）をクリアすることが困難になる。そこで、（１）式による規制を設けた。
Ｃ≧０．１ ……（１）
なお、Ｃの上限については後述の（２）式により制限される。
【００１７】
基材鋼板に高い導電率を付与するためには、Ｃ，Ｓｉ，Ｍｎの含有量をいずれも低減することが重要である。本発明ではＣｕめっき後の導電率を１２％ＩＡＣＳ以上に向上させることを狙いとしているが、そのためにはＣｕめっきを施す基材鋼板自体の導電率を７％ＩＡＣＳ以上に改善しておくことが望ましい。しかし、上述のようにＣは０．１質量％以上を確保しなければならない。種々検討の結果、後述の適正な金属組織においては、Ｃ，Ｓｉ，Ｍｎの含有量を（２）式に従って厳しく制限することによって、０．１質量％以上のＣ量を維持しながら７％ＩＡＣＳ以上の導電率が実現できることが明らかになった。
１７．５３Ｃ＋１３．７５Ｓｉ＋６．２５Ｍｎ＜２４ ……（２）
【００１８】
（２）式によると、Ｃ，Ｓｉ，Ｍｎの含有量範囲の上限は以下のように制限される。
・Ｃの上限；（２）式にＳｉ＝０％とＭｎ＝０％を代入することにより、Ｃ＜１．３７％に制限される。
・Ｓｉの上限；（２）式にＣの下限値０．１％とＭｎ＝０％を代入すると、Ｓｉ＜１．６２％に制限される。
・Ｍｎの上限；（２）式にＣの下限値０．１％とＳｉ＝０％を代入すると、Ｍｎ＜３．５６％に制限される。
したがって、Ｃ，Ｓｉ，Ｍｎの含有量上限については、個々に規定しなくても（２）式による制限で十分である。
【００１９】
Ｃ，Ｓｉ，Ｍｎの残部はＦｅおよび不可避的不純物で占められる。鋼の代表的な不純物であるＰは０．０３０質量％まで、Ｓも０．０３０質量％まで許容できる。
【００２０】
次に、金属組織については、導電性確保の観点からマルテンサイトを含まない組織に限定される。マルテンサイトが存在すると、同じ化学組成でも導電率は大幅に低下するのである。この現象は、例えば次のような実験で確かめられた。
すなわち、発明者らは、（１）式および（２）式を満たす化学組成の鋼を種々溶製し、焼入れ処理を行ってマルテンサイトを含む金属組織とした鋼板と、焼きが入らない処理を行ってフェライト＋球状セメンタイト組織，フェライト＋パーライト組織，パーライト組織のいずれかの金属組織とした鋼板を作った。これらを用いて板厚０．２５ｍｍで、ばね限界値が概ね３００ＭＰａと一定になるようにサンプルを用意した。ばね限界値の調整は、マルテンサイトを含むもの（焼入れ材）では焼戻し温度のコントロールにより行い、マルテンサイトを含まないものでは冷延率と時効温度を適切に組み合わせることにより行った。各サンプルの導電率を測定したところ、同じ組成の鋼ではいずれの場合も、マルテンサイトを含むものは、含まないものより大幅に導電率が低下した。
【００２１】
本発明で規定する化学組成の鋼においてマルテンサイトを含まない金属組織を得るには、例えば、熱延鋼板または冷延鋼板に焼鈍処理を施すときＡ_１点を超えない温度に加熱するようにすればよい。Ａ_１点を超える温度に加熱する焼鈍を施す場合でも、Ａ_１点から６００℃までの冷却速度を１℃／秒以下にすればマルテンサイトが生成することはない。Ｃ含有量，冷却速度などにより、フェライト＋球状セメンタイト組織，フェライト＋パーライト組織，パーライト組織のいずれかの組織が得られる。これらいずれの組織に調整した場合においても、基材鋼板の段階でばね限界値３００ＭＰａ以上、かつ導電率７％ＩＡＣＳ以上の特性を得ることが可能である。したがって、本発明では、金属組織をフェライト＋球状セメンタイト組織，フェライト＋パーライト組織，パーライト組織のいずれかに調整することを要件とした。
【００２２】
以上の化学組成および金属組織に調整した鋼板をベースに、冷間圧延および時効処理を施して、基材鋼板に優れたばね特性を付与する。「冷間圧延＋時効処理」の組み合わせにより歪み時効の現象が発現し、これがばね限界値の大幅な向上をもたらすものと考えられる。すなわち、冷間圧延により多数の可動転位が導入され、続く時効処理でＣ原子が転位を固着する位置に入り込む（コットレル効果）。その結果、変形するのに大きな力が必要となり、ばね限界値は上昇する。
冷間圧延率を増加すること、および、ある温度範囲で時効温度を高めることは、いずれもばね限界値を向上させる方向に働く。
【００２３】
Ｃｕめっきを施す基材鋼板は、３００ＭＰａ以上のばね限界値を有することが必要である。これは、後述の（３）式に従う厚さでＣｕめっき層を形成させた場合に、りん青銅と同レベルの２５０ＭＰａ以上のばね限界値が安定的に得られるようにするためである。すなわち、Ｃｕめっき層の形成はばね限界値の低下を伴うので、基材鋼板には少なくとも３００ＭＰａ以上の高いばね限界値が要求される。
【００２４】
発明者らの検討の結果、冷間圧延率を１５％以上にすると、時効温度を最適化することで３００ＭＰａ以上のばね限界値を基材鋼板に付与することが可能であった。冷間圧延率の上限は特に制限する必要はないが、あまり高いと製造性が低下するので９０％程度以下の範囲で行うのが実用的である。
【００２５】
時効処理については、１５０℃以上に加熱しないと積極的に歪み時効を起こさせることが難しく、冷間圧延率を高めても基材鋼板のばね限界値を安定的に３００ＭＰａ以上にコントロールすることができない。２００℃以上にすると種々の冷間圧延率のものに適応できるようになり好ましい。３００℃以上とすることにより、一層高いばね限界値が得られる。ただし、５００℃を超えるとばね限界値の上昇傾向はほとんど飽和し、さらに６００℃を超えると冷間圧延組織が再結晶するためにばね限界値の急激な低下が生じるようになる。このため、６００℃以下の温度で時効処理を行う必要がある。時効時間は０．５〜５０時間とすることができる。
特に、１５〜９０％の冷間圧延を行い、次いで３００〜５００℃で１〜３０時間保持する時効処理を施すことが望ましい。
【００２６】
次に、Ｃｕめっき層について説明する。
基材鋼板表面へのＣｕめっき層の形成は導電率の向上を目的として行う。基本的にＡｌ，Ａｇ，Ａｕ等、Ｃｕ以外の高導電性金属めっきを採用することも可能であるが、本発明では製造コストと性能を考慮してＣｕめっきを採用する。ただし、前記基材鋼板表面に単にＣｕめっきを施せば本発明の目的が達成されるわけではない。すなわち、Ｃｕめっき層の形成はばね特性を低下させる。これは、Ｃｕめっき層がばね特性の低い純銅に近い組成で構成されていることに大きく影響されているものと考えられる。また、基材鋼板の導電率やばね限界値は化学組成や製造履歴によって個々に変化する。板厚も製品仕様によって様々である。したがって、一律にＣｕめっき層の厚さを規定するだけでは、最終的にりん青銅に匹敵するばね限界値２５０ＭＰａ以上，導電率１２％ＩＡＣＳ以上の特性を安定して得ることはできない。
【００２７】
発明者らは詳細な研究を重ねた結果、使用する基材鋼板の導電率，ばね限界値および板厚をパラメータにして、ばね限界値２５０ＭＰａ以上，導電率１２％ＩＡＣＳ以上の特性を安定して得るために必要なＣｕめっき層厚さを（３）式を用いて特定することに成功した。
０．１９−０．０１６×Ａｗ≦ｔｃ／ｔｗ＜０．０９３×ｌｎ（Ｋｂｗ）−０．２７ ……（３）
ただし、Ａｗ：基材鋼板の導電率（％ＩＡＣＳ）
ｔｗ：基材鋼板の板厚（ｍｍ）
Ｋｂｗ：基材鋼板のばね限界値（ＭＰａ）
ｔｃ：基材鋼板両面のＣｕめっき層合計厚さ（ｍｍ）
ここで、Ｃｕめっき層は高導電性（好ましくは導電率６０％ＩＡＣＳ以上）を有する被覆層であることが必要である。そのようなＣｕめっき層は公知の電気めっき法によって形成可能である。ｔｃは鋼板片面当たりのＣｕめっき層厚さではなく、一方の面のＣｕめっき層厚さと他方の面のＣｕめっき層厚さを合計したものである。一方の面と他方の面でＣｕめっき層厚さが異なっていても構わない。
【００２８】
（３）式のうち０．１９−０．０１６×Ａｗ≦ｔｃ／ｔｗの部分は、１２％ＩＡＣＳ以上の導電率を得るためには基材鋼板の導電率に応じてＣｕめっき層厚さと基材鋼板厚さの比率を一定以上に大きくする必要があることを表したものである。また（３）式のうちｔｃ／ｔｗ＜０．０９３×ｌｎ（Ｋｂｗ）−０．２７の部分は、２５０ＭＰａ以上のばね限界値を得るためには基材鋼板のばね限界値に応じてＣｕめっき層厚さと基材鋼板厚さの比率を一定未満の値にする必要があることを表したものである。
【００２９】
以上のようにして得られる導電性に優れたばね用鋼板は、所定の寸法に切断し、所定の形状に加工して、各種電気接点ばね材料に好適に使用できる。特に板厚を０．１〜０．６ｍｍに調整したものは、りん青銅を用いた従来の電気接点ばね材料の代替として多くの用途を有し汎用性が高い。
なお、電気接点ばね材料の用途によっては、特にその表面において低い接触抵抗などの特性を求められることがあるが、本発明の導電性に優れたばね用めっき鋼板はＮｉめっきやＳｎめっき等の表面処理を施してから用いても良い。
【００３０】
【実施例】
〔実施例１〕
質量％で、Ｃ：０．０５〜１．０６％，Ｓｉ：０．０２〜１．６７％，Ｍｎ：０．２４〜０．８８％の範囲でこれらの元素を含み残部がＦｅおよび不可避的不純物からなる鋼（不純物のＰ，Ｓはともに０．０３％以下）を溶製し、板厚２〜３ｍｍの熱延板を得た。これを用いて下記の３通りの工程にて板厚０．２５ｍｍの薄板サンプルを合計２４種類作製した。
〔工程Ａ〕焼鈍→「冷間圧延→焼鈍」→最終冷延（１０〜９０％）→時効処理（３００〜５００℃×１〜３０時間）
〔工程Ｂ〕研削による薄肉化→最終冷延（１５〜９０％）→時効処理（３００〜５００℃×１〜３０時間）
〔工程Ｃ〕焼鈍→「冷間圧延→焼鈍」→最終冷延（１０〜９０％）→焼入れ→焼戻し
ここで、工程ＡおよびＣの「冷間圧延→焼鈍」は１回または必要に応じて２回以上行った。
【００３１】
その後、これらの鋼板サンプルを基材にして、その表面に電気めっき法によりＣｕめっき層を形成した。めっき層厚さは一方の面と他方の面の合計厚さが２０μｍとなるようにした。この場合、前記（３）式中のｔｃ／ｔｗの値は０．０８０となる。なお、Ｃｕめっきは、前処理として酸洗・脱脂を行った後、浴組成：ＣｕＳＯ_４；２００ｇ／Ｌ，Ｈ_２ＳＯ_４；５０ｇ／Ｌの電解浴を用いて浴温４０℃，電流密度５Ａ／ｄｍ^２の条件下で行った。めっき後、ベンゾトリアゾールを用いてめっき層表面の変色防止処理を行った。
【００３２】
各サンプルの化学組成，工程，金属組織，および後述の各種試験結果を表１にまとめてある。表１中の「Ｋ値」は前記（２）式の左辺「１７．５３Ｃ＋１３．７５Ｓｉ＋６．２５Ｍｎ」の値、「Ｌ値」は前記（３）式左辺「０．１９−０．０１６×Ａｗ」の値である。なお、工程Ａ〜Ｃの最終冷延前には、いずれもフェライト＋球状セメンタイト組織，フェライト＋パーライト組織，パーライト組織のいずれかを呈していた。また、工程ＡおよびＢの時効処理は高いばね限界値が得られる好ましい条件で実施した。
【００３３】
各サンプルについて、Ｃｕめっき前および後のばね限界値と導電率を求めた。ばね限界値は、ＪＩＳＨ３１３０で規定されるばね限界値試験法により求め、その値が２５０ＭＰａ以上のものを○印、それ未満を×印で示した。導電率はＪＩＳＨ０５０５で規定される導電率測定法に基づいて求め、その値が１２％ＩＡＣＳ以上を○印、それ未満を×印で示した。
【００３４】
【表１】

【００３５】
化学組成（Ｃ，Ｓｉ，Ｍｎ含有量およびＫ値）が本発明の規定を満たし、金属組織がフェライト＋球状セメンタイト組織，フェライト＋パーライト組織，パーライト組織のいずれかを呈し、「冷間圧延＋時効処理」を上述の適正条件として作製したばね限界値が３００ＭＰａ以上の基材鋼板の表面に、Ｌ値≦ｔｃ／ｔｗの条件（（３）式）を満たした膜厚でＣｕめっき層を形成した本発明例は、いずれも２５０ＭＰａ以上の優れたばね限界値と、１２％ＩＡＣＳ以上の高い導電率を呈し、電気接点ばね材料に適したものであった。
【００３６】
これに対し、比較例Ｎｏ．１はＣ含有量が低く（１）式を満たさないためばね特性が悪かった。Ｎｏ．２，６は時効処理前の冷間圧延率が低すぎたため基材鋼板のばね限界値が３００ＭＰａに未達であり、Ｃｕめっき後に２５０ＭＰａ以上のばね限界値が得られなかった。Ｎｏ．１３〜１６はＫ値が高く（２）式を外れるため、またＮｏ．２３，２４はマルテンサイト組織であるため、これらはいずれも基材鋼板の導電率が低くなり、その結果、Ｌ値≦ｔｃ／ｔｗの条件を満たさなかったため、Ｃｕめっき後に１２％ＩＡＣＳ以上の導電率が得られなかった。なお、Ｎｏ．１３〜１６，２３，２４は、Ｃｕめっき厚をさらに増大すれば導電率についても満足できる特性を付与することが可能であると考えられる。しかしその場合、表１に示した本発明例のものよりめっきコストが高騰し、不利となる。
【００３７】
〔実施例２〕
表１に示したＮｏ．３，７，９，１０，１２，１７，１９，２０，２２の基材鋼板（いずれも本発明で規定する化学組成，金属組織，ばね限界値を満たす）を用いて、その表面に実施例１と同様の方法でＣｕめっきを施し、両面のＣｕめっき層合計厚さが１０〜８０μｍの範囲になるように調整した。各サンプルについてばね限界値と導電率を測定した。これらの測定法および評価基準は実施例１と同様とした。表２に結果を示す。表２中、「Ｋ値」は前記（２）式の左辺「１７．５３Ｃ＋１３．７５Ｓｉ＋６．２５Ｍｎ」の値、「Ｕ値」は（３）式の右辺「０．０９３×ｌｎ（Ｋｂｗ）−０．２７」の値を意味する。
【００３８】
【表２】

【００３９】
表２より、Ｃｕめっき層厚さが増すに伴い導電率が向上し、ばね限界値が低下する傾向がわかる。ｔｃ／ｔｗ＜Ｕ値の条件（（３）式）を満たした膜厚でＣｕめっき層を形成した本発明例のものは、２５０ＭＰａ以上のばね限界値を呈した。これに対し、ｔｃ／ｔｗ＜Ｕ値の条件（（３）式）を満たさなかった比較例のものはばね限界値が２５０ＭＰａを下回った。
【００４０】
〔実施例３〕
質量％で、Ｃ：０．５７〜０．８８％，Ｓｉ：０．１８〜０．２２％，Ｍｎ：０．３１〜０．６５％の範囲でこれらの元素を含み残部がＦｅおよび不可避的不純物からなる鋼（不純物のＰ，Ｓはともに０．０３％以下）を溶製し、板厚２〜３ｍｍの熱延板を得た。これを用いて基材Ｎｏ．２５〜２７は下記工程Ａ、基材Ｎｏ．２８，２９は下記工程Ｂにて板厚０．１〜０．６ｍｍの薄板サンプルを作製した。
〔工程Ａ〕焼鈍→「冷間圧延→焼鈍」→最終冷延（５０〜８０％）→時効処理（３５０〜６５０℃×５〜１０時間）
〔工程Ｂ〕研削による薄肉化→最終冷延（２０〜６０％）→時効処理（２５０〜４００℃×１〜３０時間）
ここで、工程Ａの「冷間圧延→焼鈍」は１回または必要に応じて２回以上行った。
その後、これらの鋼板を基材にして、その表面に実施例１と同様の方法でＣｕめっきを施し、両面のＣｕめっき層合計厚さが４〜９０μｍの範囲になるように調整した。各サンプルについてばね限界値と導電率を測定した。これらの測定法および評価基準は実施例１と同様とした。表３に結果を示す。表３中の「Ｋ値」「Ｌ値」「Ｕ値」は実施例１，２と同様のものである。
【００４１】
【表３】

【００４２】
基材鋼板の化学組成，金属組織，ばね限界値が本発明の規定を満たし、かつめっき層厚さが前記（３）式で規定される「Ｌ値≦ｔｃ／ｔｗ＜Ｕ値」を満たす本発明例のものは、いずれもりん青銅に匹敵する２５０ＭＰａ以上のばね限界値と１２％ＩＡＣＳ以上の導電率を呈し、電気接点ばね材料に適したものであった。
これに対し、比較例Ｎｏ．２６−１は時効温度が高すぎたため基材鋼板のばね限界値が３００ＭＰａに到達せず、またＣｕめっき層厚さがＬ値≦ｔｃ／ｔｗを満たさなかったことから、ばね特性，導電性ともに不十分であった。Ｎｏ．２５−１，２７−１，２８−１はばね特性は良好であるものの、Ｌ値≦ｔｃ／ｔｗを満たさなかったため導電性が劣化した。Ｎｏ．２５−３，２８−４はばね特性は良好であるものの、ｔｃ／ｔｗ＜Ｕ値を満たさなかったため導電性が不十分であった。
【００４３】
【発明の効果】
以上のように、本発明では銅合金に比べて安価な「鋼」という素材を基材として、従来から広く使用されているりん青銅に匹敵する「ばね特性」と「導電性」とを同時に付与することを可能にした。本発明のＣｕめっき鋼板は、高価なりん青銅の代替として使用することができる。また、基材は鋼板であるためりん青銅よりも強度が高く、部品の薄肉化が可能になる。したがって本発明は、電気・電子機器の小型化・低コスト化に寄与するものである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a Cu-plated steel sheet for a spring having excellent conductivity and an electrical contact spring material.
[0002]
[Prior art]
Electric contact springs used in electric and electronic devices have the function of conducting electricity by themselves as conductors, and firmly attach themselves to the mating member at the contact point so that they do not easily come off the mating member in the energized state. A pressing function is required. Therefore, the material is required to have good conductivity and spring characteristics.
[0003]
Conventionally, “phosphor bronze”, which has an excellent balance between conductivity and spring characteristics, is often used as an electric contact spring material. Phosphor bronze is a copper alloy containing, for example, Sn: 3.5 to 9.0% by mass and P: 0.03 to 0.35% by mass, and has a conductivity of approximately 12 to 18% IACS. As for the material shape, a plate material is frequently used because a structure in which planes are in contact with each other has less contact failure and lower contact resistance in an electrical contact. As this plate material, one having a spring characteristic of a spring limit value of 250 MPa or more is usually used.
[0004]
On the other hand, as a wire rod application, Patent Literature 1 listed below discloses a steel wire for a battery pressing spring in which Cu plating and Ni plating are applied to the surface of a high carbon steel wire. This is an improvement in conductivity of a conventional steel wire for a battery holding spring by Cu plating.
[0005]
[Patent Document 1] JP-A-6-158353
[Problems to be solved by the invention]
Electrical and electronic equipment parts are required to be low cost, small in size and light in weight, including materials.
Conventionally used phosphor bronze has an excellent property balance, but is an expensive material. If phosphor bronze can be replaced with an inexpensive material having the same performance, it can contribute to cost reduction of electric and electronic equipment parts.
[0007]
However, since the material of Patent Document 1 is a wire, it cannot be applied to the above-mentioned plate contact from the viewpoint of contact resistance. On the other hand, a method of improving the electrical conductivity by applying a Cu plating to a conventional steel plate for a spring can be considered, but in this case, since the steel plate itself has poor electrical conductivity, it is quite thick to obtain a sufficient electrical conductivity as a whole. It is necessary to form a Cu plating layer. For this reason, it is difficult to use as a substitute for phosphor bronze in consideration of cost increase and deterioration of spring characteristics due to plating.
[0008]
An object of the present invention is to provide an inexpensive material having “spring characteristics” and “conductivity” comparable to the above-mentioned phosphor bronze plate material for electric contacts.
[0009]
[Means for Solving the Problems]
The present inventors have conducted various studies to achieve the above object, and as a result, in order to realize an inexpensive material having spring properties and conductivity comparable to phosphor bronze, the material itself must have such excellent properties. It is more reasonable to develop a “composite material” in which a highly conductive metal such as Cu, Al, Ag, or Au is coated on the surface of a base material having high spring characteristics, rather than developing a “single material”. I got the view that there was.
[0010]
In this case, as a base material, a steel material is advantageous when importance is placed on “spring characteristics” and “low cost”. However, since existing spring steel sheets have low conductivity, it is necessary to form a thick coating of Cu or the like to compensate for this, and as a result, the characteristics of the base material, "spring characteristics" and "low cost" Will be buried. Therefore, if a steel sheet is used as the base material, it is desired to establish a technique for improving the “conductivity” of the steel material while maintaining the “spring property”. However, such aggressive research has not yet been sufficiently conducted.
[0011]
Therefore, the inventors conducted intensive research and found that if the chemical composition and metallographic structure were strictly limited and the appropriate microstructure control combining cold rolling and aging treatment was performed, the steel material would have good conductivity and excellent spring properties. Can be provided simultaneously. When such a steel sheet is used as a base material, if the thickness of the Cu plating layer is appropriately controlled in accordance with the characteristics of each base steel sheet, further conductivity can be achieved while avoiding deterioration of the spring characteristics and a rise in cost. It has been found that the improvement of the performance can be realized. The present invention has been completed based on these findings.
[0012]
That is, the above object is to provide a ferrite + spherical cementite structure having a chemical composition in which the content of C, Si, and Mn satisfies the following formulas (1) and (2) and the balance is Fe and unavoidable impurities. , Ferrite + pearlite structure, or a pearlite structure, and a Cu plating layer having a thickness satisfying the following formula (3) on the surface of a base steel plate having a spring limit value of 300 MPa or more. Is formed by a Cu-plated steel sheet for spring having excellent conductivity, having a spring limit value of 250 MPa or more and a conductivity of 12% IACS or more.
C ≧ 0.1 (1)
17.53C + 13.75Si + 6.25Mn <24 (2)
0.19−0.016 × Aw ≦ tc / tw <0.093 × ln (Kbw) −0.27 (3)
Here, Aw: conductivity of base steel sheet (% IACS)
tw: thickness of base steel sheet (mm)
Kbw: spring limit value (MPa) of the base steel sheet
tc: Total thickness of Cu plating layers on both sides of base steel sheet (mm)
[0013]
Here, the content of each element expressed in mass% is substituted for the element symbol in the formulas (1) and (2). The spring limit value is determined by a spring limit value test method specified in JIS H 3130. The electrical conductivity% IACS is a relative ratio of the electrical conductivity of the material to the electrical conductivity (1.7241 × 10 ⁻⁸ Ω · m) corresponding to the electrical resistivity (1.7241 × 10 ⁻⁸ Ω · m) of the International Annealed Copper Standard. %). “3” in the expression (3) represents a natural logarithm.
[0014]
Further, in the present invention, the content of C, Si, and Mn in mass% satisfies the above formulas (1) and (2), and the balance has a chemical composition consisting of Fe and unavoidable impurities. A steel sheet adjusted to any one of a ferrite + pearlite structure and a pearlite structure is subjected to cold rolling at a cold rolling rate of 15% or more, preferably 15 to 90%, and then to an aging treatment at 600 ° C. or less, preferably 300 to 500%. A Cu plating layer having a thickness that satisfies the above formula (3) is formed on the surface of a base steel sheet having a structural state obtained by performing an aging treatment at 1 ° C. for 1 to 30 hours and having a spring limit value of 300 MPa or more. Provided is a Cu-plated steel sheet for spring having excellent conductivity, having a formed spring limit value of 250 MPa or more and a conductivity of 12% IACS or more. Among them, the one in which the conductivity of the base steel sheet to be plated with Cu in particular is 7% IACS or more is provided.
[0015]
Further, there is provided an electric contact spring material using a Cu-plated steel sheet for spring having excellent conductivity as described above, whose thickness is adjusted to 0.1 to 0.6 mm.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, it is necessary to severely limit the chemical composition of a steel plate as a plating base material in order to obtain a Cu-plated steel plate having both the same or higher spring characteristics and conductivity as phosphor bronze.
C is an essentially essential element for ensuring the strength of steel, but in the present invention, the content of 0.1% by mass or more is used in order to greatly improve the spring characteristics by "cold rolling + aging treatment" described later. Secure quantity. When C is less than 0.1% by mass, in a metal structure (described later) adjusted so that martensite does not exist, the minimum spring limit value 300 MPa (described later) necessary for the base steel sheet itself must be cleared. Becomes difficult. Therefore, a regulation based on equation (1) is provided.
C ≧ 0.1 (1)
Note that the upper limit of C is limited by the following equation (2).
[0017]
In order to impart high conductivity to the base steel sheet, it is important to reduce the contents of C, Si, and Mn. Although the present invention aims to improve the conductivity after Cu plating to 12% IACS or more, it is necessary to improve the conductivity of the base steel sheet itself to be Cu-plated to 7% IACS or more. desirable. However, as described above, C must secure 0.1% by mass or more. As a result of various investigations, in an appropriate metal structure described later, the content of C, Si, and Mn is strictly limited according to the formula (2), thereby maintaining a C content of 0.1% by mass or more while maintaining a 7% IACS. It became clear that the above conductivity can be realized.
17.53C + 13.75Si + 6.25Mn <24 (2)
[0018]
According to the equation (2), the upper limit of the content range of C, Si, and Mn is limited as follows.
-Upper limit of C; By substituting Si = 0% and Mn = 0% into the equation (2), C is limited to less than 1.37%.
-Upper limit of Si; Substituting the lower limit value of C of 0.1% and Mn = 0% into the equation (2) limits Si to 1.62%.
-Upper limit of Mn; Substituting the lower limit of C of 0.1% and Si = 0% into equation (2) limits Mn to less than 3.56%.
Accordingly, the upper limit of the content of C, Si, and Mn is sufficient to be limited by the expression (2) without individually defining the upper limit.
[0019]
The balance of C, Si, and Mn is occupied by Fe and inevitable impurities. P, which is a typical impurity of steel, is allowable up to 0.030% by mass, and S is also allowable up to 0.030% by mass.
[0020]
Next, the metal structure is limited to a structure that does not contain martensite from the viewpoint of ensuring conductivity. The presence of martensite significantly reduces the electrical conductivity for the same chemical composition. This phenomenon was confirmed by the following experiment, for example.
That is, the inventors melted various steels having a chemical composition satisfying the formulas (1) and (2) and quenched the steel plates to obtain a metal structure containing martensite, and a process for preventing quenching. A steel sheet having any one of a ferrite + spherical cementite structure, a ferrite + pearlite structure, and a pearlite structure was produced. Using these, a sample was prepared such that the plate thickness was 0.25 mm and the spring limit value was approximately constant at 300 MPa. Adjustment of the spring limit value was performed by controlling the tempering temperature for those containing martensite (quenched material), and for those not containing martensite, by appropriately combining the cold rolling ratio and the aging temperature. When the electrical conductivity of each sample was measured, the electrical conductivity of steel having the same composition was significantly lower in those containing martensite than those not containing it.
[0021]
To obtain a metal structure without the martensite in the steel of the chemical composition defined in the present invention, for example, suffices to heat to a temperature not exceeding ₁ point A when subjected to annealing treatment in hot-rolled steel sheet or cold-rolled steel sheet Just fine. Even when subjected to annealing by heating to a temperature above the A ₁ point, martensite will not be generated if the cooling rate from the A ₁ point to 600 ° C. below 1 ° C. / sec. Any of ferrite + spherical cementite structure, ferrite + pearlite structure, and pearlite structure can be obtained depending on the C content, the cooling rate, and the like. In the case of adjusting to any of these structures, it is possible to obtain a characteristic having a spring limit value of 300 MPa or more and a conductivity of 7% IACS or more at the stage of the base steel sheet. Therefore, in the present invention, it is required that the metal structure be adjusted to any one of a ferrite + spherical cementite structure, a ferrite + pearlite structure, and a pearlite structure.
[0022]
Cold rolling and aging treatment are performed on the steel sheet adjusted to the above chemical composition and metal structure to impart excellent spring properties to the base steel sheet. It is considered that the phenomenon of strain aging appears due to the combination of "cold rolling + aging treatment", and this leads to a significant improvement in the spring limit value. That is, a large number of movable dislocations are introduced by cold rolling, and C atoms enter the positions where the dislocations are fixed by the subsequent aging treatment (Cottrell effect). As a result, a large force is required to deform, and the spring limit increases.
Increasing the cold rolling reduction and increasing the aging temperature in a certain temperature range both work to improve the spring limit.
[0023]
The base steel sheet to be subjected to Cu plating needs to have a spring limit value of 300 MPa or more. This is to ensure that a spring limit value of 250 MPa or more, which is the same level as that of phosphor bronze, can be stably obtained when a Cu plating layer is formed with a thickness according to the expression (3) described later. That is, since the formation of the Cu plating layer involves a decrease in the spring limit value, the base steel sheet is required to have a high spring limit value of at least 300 MPa or more.
[0024]
As a result of the study by the inventors, when the cold rolling reduction is 15% or more, it is possible to give a spring limit value of 300 MPa or more to the base steel sheet by optimizing the aging temperature. The upper limit of the cold rolling reduction does not need to be particularly limited, but if it is too high, the productivity is reduced.
[0025]
Regarding the aging treatment, it is difficult to cause strain aging positively unless heated to 150 ° C. or more, and it is possible to stably control the spring limit value of the base steel sheet to 300 MPa or more even when the cold rolling reduction is increased. Can not. A temperature of 200 ° C. or higher is preferable because it can be adapted to various cold rolling reductions. By setting the temperature to 300 ° C. or higher, a higher spring limit value can be obtained. However, when the temperature exceeds 500 ° C., the increasing tendency of the spring limit value is almost saturated, and when the temperature exceeds 600 ° C., the cold-rolled structure recrystallizes, so that the spring limit value sharply decreases. Therefore, it is necessary to perform the aging treatment at a temperature of 600 ° C. or less. The aging time can be 0.5 to 50 hours.
In particular, it is preferable to perform cold rolling of 15 to 90% and then perform aging treatment at 300 to 500 ° C. for 1 to 30 hours.
[0026]
Next, the Cu plating layer will be described.
The formation of the Cu plating layer on the surface of the base steel sheet is performed for the purpose of improving the electrical conductivity. Basically, it is possible to employ a highly conductive metal plating other than Cu, such as Al, Ag, and Au. However, in the present invention, Cu plating is employed in consideration of manufacturing cost and performance. However, the object of the present invention is not necessarily achieved by simply performing Cu plating on the surface of the base steel sheet. That is, the formation of the Cu plating layer lowers the spring characteristics. This is considered to be largely affected by the fact that the Cu plating layer has a composition close to pure copper having low spring characteristics. Further, the electrical conductivity and the spring limit value of the base steel sheet change individually depending on the chemical composition and the manufacturing history. The plate thickness also varies depending on the product specifications. Therefore, by simply defining the thickness of the Cu plating layer uniformly, it is not possible to stably obtain a characteristic having a spring limit value of 250 MPa or more comparable to that of phosphor bronze and a conductivity of 12% IACS or more.
[0027]
As a result of detailed studies, the inventors have found that the conductivity, spring limit, and plate thickness of the base steel sheet to be used are used as parameters to stably maintain the characteristics of a spring limit of 250 MPa or more and a conductivity of 12% IACS or more. The thickness of the Cu plating layer required for obtaining was successfully specified by using the equation (3).
0.19−0.016 × Aw ≦ tc / tw <0.093 × ln (Kbw) −0.27 (3)
Here, Aw: conductivity of base steel sheet (% IACS)
tw: thickness of base steel sheet (mm)
Kbw: spring limit value (MPa) of the base steel sheet
tc: Total thickness of Cu plating layers on both sides of base steel sheet (mm)
Here, the Cu plating layer needs to be a coating layer having high conductivity (preferably, conductivity of 60% IACS or more). Such a Cu plating layer can be formed by a known electroplating method. tc is not the thickness of the Cu plating layer per one side of the steel sheet, but the sum of the thickness of the Cu plating layer on one side and the thickness of the Cu plating layer on the other side. The thickness of the Cu plating layer may be different between one surface and the other surface.
[0028]
In the formula (3), the portion of 0.19-0.016 × Aw ≦ tc / tw is used to obtain a conductivity of 12% IACS or more, in order to obtain a conductivity of 12% IACS or more, in accordance with the conductivity of the base steel sheet. It indicates that it is necessary to increase the ratio of the thickness of the steel sheet to a certain value or more. In the expression (3), the portion of tc / tw <0.093 × ln (Kbw) −0.27 is used for Cu plating in accordance with the spring limit of the base steel sheet in order to obtain a spring limit of 250 MPa or more. It indicates that the ratio between the layer thickness and the thickness of the base steel plate needs to be less than a certain value.
[0029]
The spring steel sheet having excellent conductivity obtained as described above can be cut into a predetermined size, processed into a predetermined shape, and suitably used for various electric contact spring materials. In particular, a sheet whose thickness is adjusted to 0.1 to 0.6 mm has many uses as a substitute for a conventional electric contact spring material using phosphor bronze and has high versatility.
Depending on the use of the electrical contact spring material, characteristics such as low contact resistance may be required particularly on the surface thereof. However, the plated steel sheet having excellent conductivity according to the present invention may be subjected to surface treatment such as Ni plating or Sn plating. May be used.
[0030]
【Example】
[Example 1]
In mass%, C: 0.05 to 1.06%, Si: 0.02 to 1.67%, Mn: 0.24 to 0.88%, these elements are contained and the balance is Fe and inevitable. Steel made of impurities (both P and S of impurities are 0.03% or less) was melted to obtain a hot-rolled sheet having a thickness of 2 to 3 mm. Using this, a total of 24 types of thin plate samples having a plate thickness of 0.25 mm were produced in the following three steps.
[Step A] annealing → “cold rolling → annealing” → final cold rolling (10 to 90%) → aging treatment (300 to 500 ° C x 1 to 30 hours)
[Step B] Thinning by grinding → Final cold rolling (15 to 90%) → Aging treatment (300 to 500 ° C × 1 to 30 hours)
[Step C] Annealing → “Cold rolling → Annealing” → Final cold rolling (10 to 90%) → Quenching → Tempering Here, “Cold rolling → Annealing” in Steps A and C is performed once or as necessary. Performed more than once.
[0031]
Then, using these steel sheet samples as a substrate, a Cu plating layer was formed on the surface thereof by an electroplating method. The thickness of the plating layer was such that the total thickness of one surface and the other surface was 20 μm. In this case, the value of tc / tw in the equation (3) is 0.080. In the Cu plating, after performing pickling and degreasing as a pretreatment, a bath composition of CuSO ₄ ; 200 g / L, H ₂ SO ₄ ; an electrolytic bath of 50 g / L, a bath temperature of 40 ° C., and a current density of 5 A / Dm ² . After plating, the surface of the plating layer was treated to prevent discoloration using benzotriazole.
[0032]
Table 1 summarizes the chemical composition, process, metal structure, and various test results described below for each sample. In Table 1, “K value” is the value of “17.53C + 13.75Si + 6.25Mn” on the left side of the above equation (2), and “L value” is “0.19−0.016 × Aw” on the left side of the above equation (3). Is the value of Before the final cold rolling in Steps A to C, any one of ferrite + spherical cementite structure, ferrite + pearlite structure, and pearlite structure was exhibited. In addition, the aging treatments in Steps A and B were performed under preferable conditions capable of obtaining a high spring limit value.
[0033]
For each sample, the spring limit value and conductivity before and after Cu plating were determined. The spring limit value was determined by a spring limit value test method specified in JIS H 3130, and those having a value of 250 MPa or more were indicated by ○, and those less than that were indicated by x. The electric conductivity was determined based on the electric conductivity measurement method specified in JIS H 0505. The value of 12% IACS or more was indicated by ○, and the value less than 12% IACS was indicated by ×.
[0034]
[Table 1]

[0035]
The chemical composition (C, Si, Mn content and K value) satisfies the requirements of the present invention, and the metal structure shows any of ferrite + spherical cementite structure, ferrite + pearlite structure, and pearlite structure. A Cu plating layer having a thickness satisfying the condition of L value ≦ tc / tw (formula (3)) was formed on the surface of a base steel plate having a spring limit value of 300 MPa or more prepared using the “treatment” as the above appropriate condition. Each of the examples of the present invention exhibited an excellent spring limit value of 250 MPa or more and a high conductivity of 12% IACS or more, and was suitable for an electric contact spring material.
[0036]
On the other hand, in Comparative Example No. No. 1 had a low C content and did not satisfy the expression (1), so the spring characteristics were poor. No. In Nos. 2 and 6, since the cold rolling reduction before the aging treatment was too low, the spring limit value of the base steel sheet did not reach 300 MPa, and a spring limit value of 250 MPa or more was not obtained after Cu plating. No. Nos. 13 to 16 have high K values and deviate from equation (2). 23 and 24 each have a martensitic structure, so that the conductivity of the base steel sheet is low, and as a result, the condition of L value ≦ tc / tw was not satisfied. No rate was obtained. In addition, No. It is considered that 13 to 16, 23, and 24 can impart satisfactory characteristics with respect to the conductivity by further increasing the Cu plating thickness. However, in that case, the plating cost is higher than that of the example of the present invention shown in Table 1, which is disadvantageous.
[0037]
[Example 2]
No. shown in Table 1. Using the base steel sheets of 3, 7, 9, 10, 12, 17, 19, 20, and 22 (all satisfy the chemical composition, metal structure, and spring limit value specified in the present invention), the surface of each of the examples was used. Cu plating was performed in the same manner as in Example 1, and the total thickness of the Cu plating layers on both surfaces was adjusted to be in the range of 10 to 80 μm. The spring limit and conductivity were measured for each sample. These measurement methods and evaluation criteria were the same as in Example 1. Table 2 shows the results. In Table 2, “K value” is the value of “17.53C + 13.75Si + 6.25Mn” on the left side of the above equation (2), and “U value” is “0.093 × ln (Kbw) -0” on the right side of the equation (3). .27 ".
[0038]
[Table 2]

[0039]
From Table 2, it can be seen that as the thickness of the Cu plating layer increases, the conductivity increases, and the spring limit value tends to decrease. The example of the present invention in which the Cu plating layer was formed with a film thickness satisfying the condition of tc / tw <U value (formula (3)) exhibited a spring limit value of 250 MPa or more. On the other hand, in the case of the comparative example which did not satisfy the condition of tc / tw <U value (formula (3)), the spring limit value was less than 250 MPa.
[0040]
[Example 3]
In mass%, C: 0.57 to 0.88%, Si: 0.18 to 0.22%, Mn: 0.31 to 0.65%, these elements are contained, and the balance is Fe and inevitable. Steel made of impurities (both P and S of impurities are 0.03% or less) was melted to obtain a hot-rolled sheet having a thickness of 2 to 3 mm. The base material No. 25 to 27 are processes A, base material Nos. 28 and 29 produced thin plate samples having a plate thickness of 0.1 to 0.6 mm in the following step B.
[Step A] annealing → “cold rolling → annealing” → final cold rolling (50 to 80%) → aging treatment (350 to 650 ° C × 5 to 10 hours)
[Step B] Thinning by grinding → Final cold rolling (20 to 60%) → Aging treatment (250 to 400 ° C × 1 to 30 hours)
Here, the “cold rolling → annealing” in the process A was performed once or as required twice or more.
Then, using these steel sheets as a base material, Cu plating was performed on the surface by the same method as in Example 1 so that the total thickness of the Cu plating layers on both surfaces was adjusted to be in the range of 4 to 90 μm. The spring limit and conductivity were measured for each sample. These measurement methods and evaluation criteria were the same as in Example 1. Table 3 shows the results. “K value”, “L value”, and “U value” in Table 3 are the same as those in the first and second embodiments.
[0041]
[Table 3]

[0042]
The chemical composition, metal structure, and spring limit value of the base steel sheet satisfy the requirements of the present invention, and the plating layer thickness satisfies “L value ≦ tc / tw <U value” defined by the above formula (3). All of the examples of the invention exhibited a spring limit value of 250 MPa or more comparable to phosphor bronze and a conductivity of 12% IACS or more, and were suitable for electric contact spring materials.
On the other hand, in Comparative Example No. In No. 26-1, the spring limit value of the base steel sheet did not reach 300 MPa because the aging temperature was too high, and the Cu plating layer thickness did not satisfy L value ≦ tc / tw. Was not enough. No. 25-1, 27-1, and 28-1 had good spring characteristics, but did not satisfy L value ≦ tc / tw, so that the conductivity was deteriorated. No. 25-3 and 28-4 had good spring characteristics, but did not satisfy tc / tw <U value, and thus had insufficient conductivity.
[0043]
【The invention's effect】
As described above, in the present invention, a material called "steel", which is inexpensive compared to a copper alloy, is used as a base material, and at the same time, "spring properties" and "conductivity" comparable to phosphor bronze which has been widely used conventionally are simultaneously provided. Made it possible to do so. The Cu-plated steel sheet of the present invention can be used as a substitute for expensive bronze. Further, since the base material is a steel plate, the strength is higher than that of phosphor bronze, and the thickness of the part can be reduced. Therefore, the present invention contributes to miniaturization and cost reduction of electric and electronic devices.

Claims

The content of C, Si, and Mn is in mass%, and the following formulas (1) and (2) are satisfied and the balance is a chemical composition consisting of Fe and unavoidable impurities. A spring limit value in which a Cu plated layer having a thickness satisfying the following formula (3) is formed on the surface of a base steel sheet having a cold-worked metal structure of a pearlite structure and a spring limit value of 300 MPa or more. A Cu-plated steel sheet for spring having excellent conductivity of 250 MPa or more and conductivity of 12% IACS or more.
C ≧ 0.1 (1)
17.53C + 13.75Si + 6.25Mn <24 (2)
0.19−0.016 × Aw ≦ tc / tw <0.093 × ln (Kbw) −0.27 (3)
Here, Aw: conductivity of base steel sheet (% IACS)
tw: thickness of base steel sheet (mm)
Kbw: spring limit value (MPa) of the base steel sheet
tc: Total thickness of Cu plating layers on both sides of base steel sheet (mm)

The content of C, Si, and Mn is in mass%, and the following formulas (1) and (2) are satisfied and the balance is a chemical composition consisting of Fe and unavoidable impurities. Ferrite + spherical cementite structure, ferrite + pearlite structure, A steel sheet adjusted to any metal structure of pearlite structure has a structure state obtained by performing cold rolling at a cold rolling rate of 15% or more and then aging treatment at 600 ° C. or less, and has a spring limit value of 300 MPa. A Cu plating layer having excellent conductivity having a spring limit value of 250 MPa or more and a conductivity of 12% IACS or more formed by forming a Cu plating layer having a thickness satisfying the following formula (3) on the surface of the base steel sheet. steel sheet.
C ≧ 0.1 (1)
17.53C + 13.75Si + 6.25Mn <24 (2)
0.19−0.016 × Aw ≦ tc / tw <0.093 × ln (Kbw) −0.27 (3)
Here, Aw: conductivity of base steel sheet (% IACS)
tw: thickness of base steel sheet (mm)
Kbw: spring limit value (MPa) of the base steel sheet
tc: Total thickness of Cu plating layers on both sides of base steel sheet (mm)

The content of C, Si, and Mn is in mass%, and the following formulas (1) and (2) are satisfied and the balance is a chemical composition consisting of Fe and unavoidable impurities. A steel sheet adjusted to any metal structure of pearlite structure is subjected to cold rolling at a cold rolling rate of 15 to 90% and then to aging treatment at 300 to 500 ° C. for 1 to 30 hours to obtain a structure state obtained. A Cu plating layer having a thickness satisfying the following formula (3) is formed on the surface of a base steel plate having a spring limit of 300 MPa or more, and has a spring limit of 250 MPa or more and a conductivity of 12% IACS or more. Cu-plated steel sheet for spring with excellent conductivity.
C ≧ 0.1 (1)
17.53C + 13.75Si + 6.25Mn <24 (2)
0.19−0.016 × Aw ≦ tc / tw <0.093 × ln (Kbw) −0.27 (3)
Here, Aw: conductivity of base steel sheet (% IACS)
tw: thickness of base steel sheet (mm)
Kbw: spring limit value (MPa) of the base steel sheet
tc: Total thickness of Cu plating layers on both sides of base steel sheet (mm)

The Cu-plated steel sheet for a spring according to any one of claims 1 to 3, wherein the conductivity of the base steel sheet to be Cu-plated is 7% IACS or more.

The electrical contact spring material using the Cu-plated steel sheet according to any one of claims 1 to 4, the thickness of which is adjusted to 0.1 to 0.6 mm.