JP4297705B2

JP4297705B2 - High Cr steel for current-carrying parts with improved conductivity

Info

Publication number: JP4297705B2
Application number: JP2003070429A
Authority: JP
Inventors: 聡鈴木; 定幸中村; 佳幸藤村
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2003-03-14
Filing date: 2003-03-14
Publication date: 2009-07-15
Anticipated expiration: 2023-03-14
Also published as: JP2004277807A

Description

【０００１】
【発明の属する技術分野】
本発明は、電気接点材料などの通電部品に使用する導電性を向上させた高Ｃr鋼材に関する。
【０００２】
【従来の技術】
従来、電気接点材料には電気伝導性（導電性）の観点から主として銅合金が使用されている。しかし、同時に耐食性や強度（ばね性）が良好であることも望まれ、そのような銅合金としては必然的に高コストな材料を選択せざるを得ない。
【０００３】
耐食性が良好で比較的安価な材料としてフェライト系ステンレス鋼等の高Ｃr鋼がある。強度面でも銅合金よりコストメリットが大きい。しかし、鉄合金である以上、導電性においては銅合金にかなわない。このため、高Ｃr鋼を電気接点等の通電部品に使用して銅合金部品と代替可能な導電性を確保するには、部品の断面積を大きくすることで対処せざるを得ない。これは部品や装置の小型・軽量化に反し設計自由度を狭める結果になるので、高Ｃr鋼を用いた通電部品はあまり普及していない。
【０００４】
電気接点材料としては接触相手との間に生じる「接触抵抗」を小さくすることもトータルの導電性を向上させるうえで有効である。そのような観点から、下記特許文献１には接触抵抗を低減したステンレス鋼板が開示されている。これは、Ｃuを1.0％以上含有するステンレス鋼板にＣuリッチ相を析出させた後、「光輝焼鈍」または「大気焼鈍＋電解酸洗」を行って不動態皮膜または最表層にＣuを濃化させるものである。
【０００５】
一方、抗菌性を付与する目的でステンレス鋼にＣuを添加し、Ｃuリッチ相を析出させたものが下記特許文献２〜４に記載されている。しかし、導電性を改善する手段については教示がない。
【０００６】
【特許文献１】
特開2001−89865号公報
【特許文献２】
特開平9−170053号公報
【特許文献３】
特開平10−273758号公報
【特許文献４】
特開平11−279744号公報
【０００７】
【発明が解決しようとする課題】
特許文献１の技術によれば、ステンレス鋼部品の接触抵抗を低減する効果は大きい。しかし、基材自体の導電性はあまり大きく変化しない。このため、銅合金部品の代替材として使用するには依然として部品の断面積をかなり大きくする必要があり、小型・軽量化という観点からは従来のステンレス鋼を使用した場合と比べあまり大きなメリットは得られない。
【０００８】
本発明は、ステンレス鋼のなかでも安価なフェライト系ステンレス鋼をベースとした高Ｃr鋼において、基材自体の導電性を大幅に向上させ、上記問題を克服する技術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】
本発明者らは耐食性の良好な高Ｃr鋼材の導電性を向上させるために種々検討を重ねてきた。その結果、Ｃuを含有したものにおいて、Ｃuを主体とする析出物の粒径をある特定範囲にコントロールしたとき、導電性が顕著に向上することを発見した。本発明はこの知見に基づき完成した。
【００１０】
すなわち、上記目的は、質量％でＣr：9.0〜20.0％，Ｃu：1.0〜15.0％，Ｃ＋Ｎ：0.10％以下，Ｍn：2.0％以下，Ｓi：2.0％以下，Ｔi：0（無添加）〜0.5％，Ｎb：0（無添加）〜0.5％、残部がＦeおよび不可避的不純物であり、粒径１〜500nmの時効析出したＣuリッチ相がフェライト相マトリクスに分散している導電性を改善した通電部品用高Ｃr鋼材によって達成される。なかでもその時効析出物の粒径が５〜20nmであるとき導電性の改善効果は非常に大きい。
「Ｃuリッチ相」とはＣuを主体とする（すなわち、Ｃuを80原子％以上含む）第２相をいう。
【００１１】
Ｃu含有量が多い場合の好ましい態様として、質量％でＣr：9.0〜20.0％，Ｃu：6.0〜15.0％，Ｃ＋Ｎ：0.10％以下，Ｍn：2.0％以下，Ｓi：2.0％以下，Ｔi：0（無添加）〜0.5％，Ｎb：0（無添加）〜0.5％、残部がＦeおよび不可避的不純物であり、粒径５〜20nmの時効析出したＣuリッチ相と粒径2000nm以上のＣuリッチ相とがフェライト相マトリクスに共存して分散している導電性を改善した通電部品用高Ｃr鋼材が提供される。
ここで、「粒径2000nm以上のＣuリッチ相」は時効処理前に未固溶のまま残存していたＣuの富化した第２相であり、時効処理で初めて生成する「時効析出物」とは異なる。Ｃuリッチ相が時効析出物であるかどうかは、例えば当該材料を1000℃以上に均熱１分以上加熱したときそのＣuリッチ相が消失するかどうかで判別できる。消失すればそれは時効析出物である。
【００１２】
また、電気抵抗率の向上効果に着目し、Ｃu含有量の範囲に応じて以下の２通りの鋼材が提供される。
[1] 質量％でＣr：9.0〜20.0％，Ｃu：1.0〜3.0％未満，Ｃ＋Ｎ：0.10％以下，Ｍn：2.0％以下，Ｓi：2.0％以下，Ｔi：0（無添加）〜0.5％，Ｎb：0（無添加）〜0.5％、残部がＦeおよび不可避的不純物であり、時効析出したＣuリッチ相がフェライト相マトリクスに分散しており、下記(1)式を満たす電気抵抗率ρを有する導電性を改善した通電部品用高Ｃr鋼材。
ρ／ρ₀≦0.85 ……(1)
[2] 質量％でＣr：9.0〜20.0％，Ｃu：3.0〜15.0％，Ｃ＋Ｎ：0.10％以下，Ｍn：2.0％以下，Ｓi：2.0％以下，Ｔi：0（無添加）〜0.5％，Ｎb：0（無添加）〜0.5％、残部がＦeおよび不可避的不純物であり、時効析出したＣuリッチ相がフェライト相マトリクスに分散しており、下記(2)式を満たす電気抵抗率ρを有する導電性を改善した通電部品用高Ｃr鋼材。
ρ／ρ₀≦0.75 ……(2)
ここで、ρは当該鋼材の電気抵抗率（μΩ・cm）、ρ₀は当該鋼材の時効析出したＣuリッチ相を消失させた状態での電気抵抗率（μΩ・cm）である。
これら[1] [2] の鋼材は時効析出したＣuリッチ相の粒径が５〜20nmであるものに概ね対応する。
【００１４】
また、以上の発明鋼材において、特に、質量％でＴi：0.5％以下，Ｎb：0.5％以下の１種または２種を含有し、かつ下記(4)式を満たすものが提供される。
７(Ｃ＋Ｎ)≦Ｔi＋Ｎb≦７(Ｃ＋Ｎ)＋0.3 ……(4)
ここで、(4)式の元素記号の箇所には質量％で表されたそれぞれの元素含有量が代入される。
【００１５】
【発明の実施の形態】
本発明ではＣr：9.0〜20.0質量％，Ｃu：1.0〜15.0質量％を含有する高Ｃr鋼を対象とする。特にフェライト系ステンレス鋼の組成を基本としてＣuを含有させたものが好適である。
Ｃrは鋼の耐食性を改善するために必須の元素である。ただし、過剰の添加は導電性を低下させ、製造性を劣化させるので20質量％以下に制限される。
【００１６】
Ｃuは鋼材の導電性向上のために添加する。1.0質量％未満では後述の時効析出による導電性向上効果が十分に発揮されない。一方、Ｃu含有量が増すと熱間加工性および耐食性が低下してくる。本明細書では、以下、Ｃuを主体とする時効析出物が生成する前の組織状態を有する材料を「ベース材」と呼ぶ。ベース材の具体例としては900〜1100℃で均熱30秒以上加熱したのち急冷した組織状態を有するものが挙げられる。Ｃu含有量が多くなってベース材に第２相であるＣuリッチ相が未固溶のまま存在するようになると、ベース材の導電性レベルが一段と向上する。しかも、時効処理による導電性向上効果も一層大きくなる傾向がある。このため、導電性の向上を重視する場合はＣu含有量を高めることが有利となる。種々検討の結果、Ｃu含有量が15.0質量％以下であれば工業的に鋼材の製造は可能であり、耐食性劣化も一般的な電気接点材料としては良好であることがわかった。ただし、鋼板を製造する場合など、熱間加工性劣化によるコスト増が顕著になる場合には8.0質量％以下の範囲でＣuを含有させることが望ましい。
【００１７】
Ｃuを含有させた高Ｃr鋼においてＣuリッチ相がマトリクス中に分散した材料は既に存在する（特許文献１〜４）。しかしながら、析出物の量ではなく、粒径に着目し、時効析出したＣuリッチ相を粒径１〜500nmあるいは５〜20nmの範囲で分散させた通電部品用鋼材は知られていない。個々の粒子の粒径は最大径によって表される。最近の透過型電子顕微鏡観察手段を用いると粒径１nm程度の極めて微細な析出物の存在を確かめることができる。個々の極微粒子の粒径を定量的に表示することは難しいが、平均粒径が１〜500nmあるいは５〜20nmの範囲にあることを判別することは十分可能である。
【００１８】
発明者らの研究の結果、Ｃuを主体とする粒径１〜500nmの時効析出物をフェライト相マトリクスに分散させたとき、ベース材（前述）の状態に比べ導電性が明らかに向上することが判明した。特にその析出物の粒径を５〜20nmにコントロールしたとき、導電性はピーク的に顕著に向上するのである。また、Ｃu含有量が概ね６質量％以上と多い場合、ベース材中に未固溶のＣuリッチ相が存在すると、時効処理でＣuを主体とする上記粒径の時効析出物をフェライト相マトリクス中に分散させることにより、時効析出した極微細なＣuリッチ相と時効処理前から存在した粗大なＣuリッチ相とが共存した組織状態を作ることができる。この場合、より一層顕著な導電性向上が図れる。特に、粒径５〜20nmの時効析出したＣuリッチ相と粒径2000nm以上のＣuリッチ相とをフェライト相マトリクスに共存分散させたとき導電性向上効果が最も大きくなる。これらの現象が生じる理由は現時点で明らかではない。
【００１９】
下記(3)式で定義されるＡ値が13.0〜21.2となる条件でベース材を時効処理すると粒径１〜500nmのＣuリッチ相をフェライト相マトリクス中にほぼ均一に分散析出させることができる。特にＡ値が15.0〜19.0となる条件で時効処理するとその粒径を５〜20nmの非常に好ましいサイズにコントロールできる。
Ａ＝Ｔ(20＋logｔ)×10^-3 ……(3)
ここで、Ｔは絶対温度で表した時効温度（Ｋ）、ｔは時効時間（ｈ）である。ただし、時効時間を長くしすぎても効果は飽和し不経済であるから、ｔ≦30とすることが好ましい。
【００２０】
ベース材に対する時効処理後の導電性向上効果は、Ｃu含有量レベルによって多少変わってくる。Ｃu含有量が1.0〜3.0質量％未満の場合と3.0〜15.0％の場合に大きく分けて整理することができる。析出物の粒径を５〜20nmにコントロールしたものにおいて、Ｃu含有量レベルが1.0〜3.0質量％未満の場合は下記(1)式、同3.0〜15.0％の場合は下記(2)式を満たす鋼材を得ることができる。
ρ／ρ₀≦0.85 ……(1)
ρ／ρ₀≦0.75 ……(2)
ここで、ρは時効処理後の電気抵抗率（μΩ・cm）である。ρ₀はベース材の電気抵抗率（μΩ・cm）であるが、時効処理後の鋼材についてρ₀を事後的に知りたい場合は、当該鋼材のサンプルを実験的に900〜1100℃に均熱30秒以上加熱したのち急冷して時効析出したＣuリッチ相を消失させた状態とし、これをベース材とみなして電気抵抗率（μΩ・cm）を測定すればよい。もし、Ｃu含有量が多いために未固溶のＣuリッチ相が第２相として残存しても、この第２相は時効析出物と共存していたものであるから、時効析出物が消失している限りこれをベース材とみなしてよい。
【００２１】
Ｃr，Ｃu以外の合金元素については、質量％でＣ＋Ｎ：0.10％以下，Ｍn：2.0％以下，Ｓi：2.0％以下とし、必要に応じてＴi：0.5％以下，Ｎb：0.5％以下のうち１種または２種を含有させ、残部Ｆeおよび不可避的不純物とする。
【００２２】
Ｔi：0.5％以下，Ｎb：0.5％以下の１種または２種を含有させる場合、下記(4)式を満たすようにすることが望ましい。
７(Ｃ＋Ｎ)≦Ｔi＋Ｎb≦７(Ｃ＋Ｎ)＋0.3 ……(4)
Ｔi，Ｎbの添加量が少なすぎるとＣ，Ｎを固定して耐食性や製造性を改善する効果が薄れ、逆に多すぎると製造性が悪化するからである。
【００２３】
本発明の鋼材は、板，棒，線など種々の形態において優れた導電性向上効果を発揮する。
【００２４】
【実施例】
表１に示すフェライト系鋼を真空溶解炉で溶製し、熱間圧延にて板厚3mmの熱延板とし、これを1000℃で10分焼鈍したのち、冷間圧延にて板厚1.0mmの冷延板とした。各冷延板を1000℃で均熱１分加熱して急冷する仕上焼鈍を施した。これらの仕上焼鈍鋼板を「ベース材」として350〜900℃の種々の温度で時効処理を施した。なお、SUS430とF1鋼はＣu含有量が本発明規定範囲に満たない比較鋼である。
【００２５】
【表１】

【００２６】
時効処理後の鋼板について、透過型電子顕微鏡観察を行い、フェライト相マトリクスに分散しているＣuリッチ相のサイズを調べた。一部の鋼種ではベース材（時効処理なし）についても調べた。時効処理条件および時効析出したＣuリッチ相の粒径を表２，表３に示した。粒子は極めて微細であるため、個々の粒子の粒径を正確に決定することは困難であるが、粒径の分布が少なくともどの範囲内にあるかを表示することは可能である。そこで、表２，表３には各試料について粒径が属する範囲を「時効析出したＣuリッチ相の粒径」として表示した。例えば、粒径が５〜20nmと表示したものは、観察された時効析出物（Ｃuリッチ相）の粒径が５〜20nmの範囲内にあることを意味する。
【００２７】
Ｃuリッチ相の粒径を求めた材料について、厚さ１mm×幅３mm×長さ100mmの試験片を用いて４端子法（JIS C 2525）にて電気抵抗率ρを測定した。時効析出したＣuリッチ相の粒径が１〜500nmの材料（本発明例）の大部分のものについて、当該材料の電気抵抗率ρとベース材相当材の電気抵抗率ρ₀の比ρ／ρ₀を求めた。その結果を表２，表３に示した。時効処理を行ってもＣuリッチ相の生成が認められなかった試料は時効処理前のベース材とほぼ同等の電気抵抗率を示すので、ここでは時効処理の有無にかかわらず時効析出物の生成が認められなかった試料の電気抵抗率をρ₀ としてρ／ρ₀を求めた。表２に示したρ値のうち[ ]を付したものは、その鋼種のρ₀値として表３のρ／ρ₀の算出に用いた値である。
【００２８】
【表２】

【００２９】
【表３】

【００３０】
本発明例の鋼板はＣuを主体とする時効析出物の粒径が１〜500nmの範囲にあり、導電性が改善された。これらはＡ値が13.0〜21.2となる条件で時効処理したものである。なかでもＡ値が15.0〜19.0となる条件で時効処理したものは時効析出したＣuリッチ相の粒径が５〜20nmとなり、ρ／ρ₀値は、Ｃuが1.0〜3.0質量％未満のもので0.85以下（F2，F3参照）、Ｃuが3.0〜15.0質量％のものでは0.75以下（F5〜F8参照）と、特に優れた導電性改善効果を示した。ここで、No.26〜28のF5，F6は時効析出したＣuリッチ相と時効処理前から存在していたＣuリッチ相（粒径2000nm以上）とが共存するものであるが、他の発明例と比べても電気抵抗率の絶対値が低く、ρ／ρ₀は0.70以下と導電性改善効果も非常に大きかった。
【００３１】
これに対し、比較例No.1〜3はＣu含有量が1.0質量％未満と少ないため、時効処理してもＣuリッチ相は認められなかった。No.4，6は時効条件のＡ値が低すぎたためＣuリッチ相が生成しなかった。No.5，7，8は逆にＡ値が高すぎたため時効析出したＣuリッチ相の粒径が粗大化してしまい、それぞれ同一鋼種の本発明例（表３）と比べ電気抵抗率が高かった。No.9，10はＣu含有量が多いため時効処理前（ベース材）において粒径2000nm以上のＣuリッチ相が存在した。これらはベース材の電気抵抗率が他のものより低レベル（良好）であるが、時効処理した同一鋼種の本発明例（表３）よりかなり高い。No.11，12は時効処理しなかったためＣuリッチ相が生成していない。
【００３２】
図１に、本発明例の試料（表３のNo.21）における透過型電子顕微鏡写真を示す。微細な析出物が分散していることがわかる。図２に、比較例の試料（表２のNo.５）における透過型電子顕微鏡写真を示す。棒状に粗大化した析出粒子が見られる。
【００３３】
【発明の効果】
本発明によれば、高Ｃr鋼材において基材の導電性を大幅に向上させることが可能になった。このため、電気接点等の通電部品に適用した場合、従来の高Ｃr鋼材と比べ電気・電子部品や装置の小型・軽量化をもたらす。広く使用されている銅合金部品の代替においても比較的軽微な設計変更で対応できる。また、この材料はフェライト系ステンレス鋼をベースとした組成を有するため、電気接点等の用途において優れた耐食性を呈する。このため、汎用の銅合金部品と代替すると耐食性向上による信頼性向上をもたらし、高価な高耐食性銅合金部品と代替すると優れたコストメリットを生じる。
【図面の簡単な説明】
【図１】本発明例の試料（表３のNo.21）における透過型電子顕微鏡写真である。
【図２】比較例の試料（表２のNo.５）における透過型電子顕微鏡写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high Cr steel material with improved conductivity used for current-carrying parts such as electrical contact materials.
[0002]
[Prior art]
Conventionally, a copper alloy is mainly used as an electrical contact material from the viewpoint of electrical conductivity (conductivity). However, at the same time, it is also desired that the corrosion resistance and strength (spring property) are good, and as such a copper alloy, a high-cost material is inevitably selected.
[0003]
High Cr steels such as ferritic stainless steel are examples of materials that have good corrosion resistance and are relatively inexpensive. In terms of strength, the cost advantage is greater than that of copper alloys. However, as long as it is an iron alloy, it does not match a copper alloy in terms of conductivity. For this reason, in order to use high Cr steel for current-carrying parts such as electrical contacts to ensure conductivity that can be substituted for copper alloy parts, it is necessary to cope with the problem by increasing the cross-sectional area of the parts. This is contrary to the reduction in size and weight of parts and devices, and results in narrowing the degree of design freedom. Therefore, current-carrying parts using high Cr steel are not very popular.
[0004]
As an electrical contact material, reducing the “contact resistance” generated with the contact partner is also effective in improving the total conductivity. From such a viewpoint, the following Patent Document 1 discloses a stainless steel plate with reduced contact resistance. This is because a Cu-rich phase is precipitated on a stainless steel plate containing 1.0% or more of Cu, and then "bright annealing" or "atmospheric annealing + electrolytic pickling" is performed to concentrate Cu on the passive film or the outermost layer. Is.
[0005]
On the other hand, the following Patent Documents 2 to 4 describe that Cu is added to stainless steel for the purpose of imparting antibacterial properties, and a Cu rich phase is precipitated. However, there is no teaching on means for improving conductivity.
[0006]
[Patent Document 1]
JP 2001-89865 A [Patent Document 2]
Japanese Patent Laid-Open No. 9-170053 [Patent Document 3]
JP 10-273758 A [Patent Document 4]
Japanese Patent Laid-Open No. 11-279744 [0007]
[Problems to be solved by the invention]
According to the technique of Patent Document 1, the effect of reducing the contact resistance of stainless steel parts is great. However, the conductivity of the substrate itself does not change much. For this reason, it is still necessary to significantly increase the cross-sectional area of the parts to be used as an alternative material for copper alloy parts. From the standpoint of miniaturization and weight reduction, there are significant advantages compared to using conventional stainless steel. I can't.
[0008]
An object of the present invention is to provide a technique for overcoming the above problems by significantly improving the conductivity of a base material itself in a high Cr steel based on an inexpensive ferritic stainless steel among stainless steels. .
[0009]
[Means for Solving the Problems]
The present inventors have made various studies in order to improve the conductivity of the high Cr steel material having good corrosion resistance. As a result, it has been found that in the case of containing Cu, the conductivity is remarkably improved when the particle size of the precipitate mainly composed of Cu is controlled within a specific range. The present invention has been completed based on this finding.
[0010]
That is, the above-mentioned purpose is, in mass%, Cr: 9.0 to 20.0%, Cu: 1.0 to 15.0% , C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 (no addition) to 0.5 %, Nb: 0 (no addition) to 0.5%, the balance is Fe and inevitable impurities, and the Cu-rich phase with an aging particle size of 1 to 500 nm is dispersed in the ferrite phase matrix. Achieved by high Cr steel for parts. In particular, when the particle size of the aging precipitate is 5 to 20 nm, the effect of improving the conductivity is very large.
The “Cu rich phase” refers to a second phase mainly composed of Cu (that is, containing 80 atomic% or more of Cu).
[0011]
As a preferable embodiment when the Cu content is high, Cr: 9.0 to 20.0%, Cu: 6.0 to 15.0% , C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 ( % by mass ) No addition) to 0.5%, Nb: 0 (no addition) to 0.5%, the balance being Fe and unavoidable impurities, an aged Cu-rich phase having a particle size of 5 to 20 nm, and a Cu-rich phase having a particle size of 2000 nm or more There is provided a high Cr steel material for current-carrying parts having improved conductivity in which the coexistence is dispersed in the ferrite phase matrix.
Here, the “Cu rich phase with a particle size of 2000 nm or more” is a second phase enriched with Cu that remained undissolved before the aging treatment, and is the first “aging precipitate” that is formed by the aging treatment. Is different. Whether or not the Cu-rich phase is an aging precipitate can be determined, for example, by whether or not the Cu-rich phase disappears when the material is heated to 1000 ° C. or higher for 1 minute or more. If it disappears, it is an aging precipitate.
[0012]
Moreover, paying attention to the improvement effect of electrical resistivity, the following two steel materials are provided according to the range of Cu content.
[1] Cr: 9.0 to 20.0%, Cu: 1.0 to less than 3.0% , C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 (no addition) to 0.5% by mass% Nb: 0 (no additive) to 0.5%, the balance is Fe and inevitable impurities, the Cu-rich phase that is aged is dispersed in the ferrite phase matrix, and has an electrical resistivity ρ that satisfies the following formula (1) High Cr steel material for current-carrying parts with improved conductivity.
ρ / ρ ₀ ≦ 0.85 (1)
[2] In mass%, Cr: 9.0 to 20.0%, Cu: 3.0 to 15.0% , C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 (no addition) to 0.5%, Nb : 0 (no additive) to 0.5%, the balance is Fe and inevitable impurities, the Cu-rich phase that has been aged is dispersed in the ferrite phase matrix, and has an electrical resistivity ρ that satisfies the following formula (2) High Cr steel material for current-carrying parts with improved performance.
ρ / ρ ₀ ≦ 0.75 (2)
Here, ρ is the electrical resistivity (μΩ · cm) of the steel material, and ρ ₀ is the electrical resistivity (μΩ · cm) in a state where the Cu-rich phase that has aged out from the steel material has disappeared.
These [1] and [2] steel materials generally correspond to those in which the grain size of the aging-deposited Cu-rich phase is 5 to 20 nm.
[0014]
Further, in the above invention steel, especially in Ti weight%: 0.5% or less, Nb: it contains one or two or more than 0.5%, and is provided to satisfy the following equation (4).
7 (C + N) ≤Ti + Nb≤7 (C + N) +0.3 (4)
Here, the content of each element expressed in mass% is assigned to the element symbol in the formula (4).
[0015]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a high Cr steel containing Cr: 9.0 to 20.0 mass% and Cu: 1.0 to 15.0 mass% is an object. In particular, those containing Cu based on the composition of ferritic stainless steel are suitable.
Cr is an essential element for improving the corrosion resistance of steel. However, excessive addition reduces conductivity and deteriorates manufacturability, so it is limited to 20% by mass or less.
[0016]
Cu is added to improve the electrical conductivity of the steel material. If it is less than 1.0% by mass, the effect of improving conductivity by aging precipitation described later is not sufficiently exhibited. On the other hand, when the Cu content is increased, hot workability and corrosion resistance are lowered. In the present specification, hereinafter, a material having a texture state before an aging precipitate mainly composed of Cu is generated is referred to as a “base material”. Specific examples of the base material include those having a textured state of being rapidly cooled after heating at 900 to 1100 ° C. for 30 seconds or more. When the Cu content is increased and the Cu rich phase as the second phase is present in the base material in an undissolved state, the conductivity level of the base material is further improved. In addition, the effect of improving the conductivity by the aging treatment tends to be further increased. For this reason, when importance is attached to the improvement of conductivity, it is advantageous to increase the Cu content. As a result of various studies, it has been found that if the Cu content is 15.0% by mass or less, it is possible to manufacture steel materials industrially, and corrosion resistance deterioration is good as a general electric contact material. However, when the increase in cost due to deterioration of hot workability becomes significant, such as in the case of manufacturing a steel plate, it is desirable to contain Cu in the range of 8.0% by mass or less.
[0017]
There is already a material in which a Cu rich phase is dispersed in a matrix in a high Cr steel containing Cu (Patent Documents 1 to 4). However, a steel material for current-carrying parts in which the Cu-rich phase that has been aged is dispersed in a particle size range of 1 to 500 nm or 5 to 20 nm is known, focusing on the particle size, not the amount of precipitates. The particle size of individual particles is represented by the maximum diameter. By using a recent transmission electron microscope observation means, it is possible to confirm the presence of extremely fine precipitates having a particle size of about 1 nm. Although it is difficult to quantitatively display the particle size of individual ultrafine particles, it is sufficiently possible to determine that the average particle size is in the range of 1 to 500 nm or 5 to 20 nm.
[0018]
As a result of research by the inventors, when aging precipitates having a particle size of 1 to 500 nm mainly composed of Cu are dispersed in a ferrite phase matrix, the conductivity is clearly improved compared to the state of the base material (described above). found. In particular, when the particle size of the precipitate is controlled to 5 to 20 nm, the conductivity is remarkably improved in a peak. In addition, when the Cu content is as large as approximately 6% by mass or more, and there is an insoluble Cu-rich phase in the base material, an aging precipitate having the above particle size mainly composed of Cu in the aging treatment is contained in the ferrite phase matrix. By disperse | distributing to, the structure | tissue state in which the very fine Cu rich phase which age-deposited and the coarse Cu rich phase which existed before aging treatment coexisted can be made. In this case, a further remarkable improvement in conductivity can be achieved. In particular, when the aging-precipitated Cu-rich phase having a particle size of 5 to 20 nm and the Cu-rich phase having a particle size of 2000 nm or more are coexistingly dispersed in a ferrite phase matrix, the effect of improving conductivity is maximized. The reason why these phenomena occur is not clear at this time.
[0019]
When the base material is aged under the condition that the A value defined by the following formula (3) is 13.0 to 21.2, a Cu-rich phase having a particle size of 1 to 500 nm can be dispersed and precipitated almost uniformly in the ferrite phase matrix. In particular, when an aging treatment is performed under conditions where the A value is 15.0 to 19.0, the particle size can be controlled to a very preferable size of 5 to 20 nm.
A = T (20 + logt) × 10 ^-3 (3)
Here, T is an aging temperature (K) expressed in absolute temperature, and t is an aging time (h). However, if the aging time is too long, the effect is saturated and uneconomical, so it is preferable to satisfy t ≦ 30.
[0020]
The conductivity improving effect after aging treatment on the base material varies somewhat depending on the Cu content level. The Cu content can be roughly divided into cases where the Cu content is less than 1.0 to 3.0% by mass and cases where the Cu content is 3.0 to 15.0%. In the case where the particle size of the precipitate is controlled to 5 to 20 nm, the following formula (1) is satisfied when the Cu content level is less than 1.0 to 3.0% by mass, and the following formula (2) is satisfied when the Cu content level is 3.0 to 15.0%. Steel material can be obtained.
ρ / ρ ₀ ≦ 0.85 (1)
ρ / ρ ₀ ≦ 0.75 (2)
Here, ρ is the electrical resistivity (μΩ · cm) after aging treatment. ρ ₀ is the electrical resistivity (μΩ · cm) of the base material, but if you want to know ρ ₀ afterwards for steel after aging treatment, the steel sample is experimentally soaked at 900-1100 ° C. After heating for 30 seconds or more, it is cooled rapidly, and the Cu rich phase that has been aged is eliminated, and this is regarded as a base material and the electrical resistivity (μΩ · cm) may be measured. Even if an undissolved Cu-rich phase remains as the second phase due to the high Cu content, the second phase coexists with the aging precipitate, so the aging precipitate disappears. As long as this is the case, this may be regarded as the base material.
[0021]
For alloy elements other than Cr and Cu, C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, and Ti: 0.5% or less, Nb: 0.5% or less as required. A seed or two kinds are contained, and the balance is Fe and inevitable impurities .
[0022]
When one or two of Ti: 0.5% or less and Nb: 0.5% or less are contained, it is desirable to satisfy the following formula (4).
7 (C + N) ≤Ti + Nb≤7 (C + N) +0.3 (4)
This is because if the amount of Ti and Nb added is too small, the effect of fixing C and N and improving the corrosion resistance and manufacturability will be diminished, and conversely if too large, the manufacturability will deteriorate.
[0023]
The steel material of the present invention exhibits an excellent conductivity improving effect in various forms such as a plate, a rod, and a wire.
[0024]
【Example】
Ferritic steel shown in Table 1 is melted in a vacuum melting furnace, hot rolled into a hot rolled sheet with a thickness of 3 mm, annealed at 1000 ° C. for 10 minutes, and then cold rolled to a thickness of 1.0 mm. The cold-rolled sheet was used. Each cold-rolled sheet was subjected to finish annealing, which was rapidly cooled by heating at 1000 ° C. for 1 minute. These finish-annealed steel sheets were subjected to aging treatment at various temperatures of 350 to 900 ° C. as “base materials”. Note that SUS430 and F1 steel are comparative steels whose Cu content is less than the specified range of the present invention.
[0025]
[Table 1]

[0026]
The steel plate after the aging treatment was observed with a transmission electron microscope, and the size of the Cu rich phase dispersed in the ferrite phase matrix was examined. For some steel types, the base material (without aging treatment) was also examined. Tables 2 and 3 show the aging treatment conditions and the grain size of the Cu-rich phase subjected to aging precipitation. Since the particles are very fine, it is difficult to accurately determine the particle size of each particle, but it is possible to indicate at least in what range the particle size distribution is. Therefore, in Tables 2 and 3, the range to which the particle size belongs for each sample is displayed as “particle size of the Cu-rich phase that has been aged”. For example, what is indicated as a particle size of 5 to 20 nm means that the particle size of the observed aging precipitate (Cu rich phase) is in the range of 5 to 20 nm.
[0027]
About the material which calculated | required the particle size of Cu rich phase, the electrical resistivity (rho) was measured by the 4 terminal method (JIS C 2525) using the test piece of thickness 1mm * width 3mm * length 100mm. For most of materials (examples of the present invention) in which the grain size of the Cu-rich phase that has been aged is 1 to 500 nm, the ratio ρ / ρ between the electrical resistivity ρ of the material and the electrical resistivity ρ ₀ of the base material equivalent material ₀ was determined. The results are shown in Tables 2 and 3. Samples that did not show the formation of a Cu-rich phase even after aging treatment show almost the same electrical resistivity as the base material before aging treatment, so here aging precipitates are produced regardless of the presence or absence of aging treatment. the electrical resistivity of the observed sample was determined the ρ / ρ ₀ as ρ _0. Of the ρ values shown in Table 2, those with [] are the values used for the calculation of ρ / ρ _{0 in} Table 3 as the ρ ₀ value of the steel type.
[0028]
[Table 2]

[0029]
[Table 3]

[0030]
In the steel sheet of the present invention, the grain size of aging precipitates mainly composed of Cu was in the range of 1 to 500 nm, and the conductivity was improved. These are aging-treated under conditions where the A value is 13.0 to 21.2. Among them, those subjected to an aging treatment under conditions where the A value is 15.0 to 19.0 has a particle size of the Cu-rich phase which has been aged to be 5 to 20 nm, and the ρ / ρ ₀ value is such that the Cu is less than 1.0 to 3.0% by mass. In the case of 0.85 or less (see F2, F3) and Cu of 3.0 to 15.0% by mass, 0.75 or less (see F5 to F8), particularly excellent conductivity improvement effects were shown. Here, F5 and F6 of Nos. 26 to 28 coexist with the Cu-rich phase subjected to aging precipitation and the Cu-rich phase (particle size of 2000 nm or more) that existed before the aging treatment. The absolute value of electrical resistivity was low, and ρ / ρ ₀ was 0.70 or less, and the conductivity improvement effect was very large.
[0031]
On the other hand, Comparative Examples No. 1 to No. 3 had a low Cu content of less than 1.0% by mass, so that no Cu-rich phase was observed even after aging treatment. In Nos. 4 and 6, since the A value of the aging condition was too low, a Cu rich phase was not generated. On the other hand, Nos. 5, 7, and 8 had an A value that was too high, and the grain size of the Cu-rich phase that had been aged was coarsened, and each had a higher electrical resistivity than the present invention example (Table 3) of the same steel type. . Since Nos. 9 and 10 had a high Cu content, a Cu-rich phase having a particle size of 2000 nm or more was present before the aging treatment (base material). These have a lower level (good) of electrical resistivity of the base material than the others, but are considerably higher than the present invention example (Table 3) of the same steel grade that has been aged. Since No. 11 and 12 were not subjected to aging treatment, a Cu rich phase was not generated.
[0032]
FIG. 1 shows a transmission electron micrograph of the sample of the present invention (No. 21 in Table 3). It can be seen that fine precipitates are dispersed. FIG. 2 shows a transmission electron micrograph of the comparative sample (No. 5 in Table 2). Precipitated particles coarsened in a rod shape can be seen.
[0033]
【The invention's effect】
According to the present invention, it has become possible to greatly improve the conductivity of a base material in a high Cr steel material. For this reason, when applied to current-carrying parts such as electrical contacts, the electrical and electronic parts and devices are made smaller and lighter than conventional high-Cr steel materials. Even in the replacement of widely used copper alloy parts, it can be handled with relatively minor design changes. Moreover, since this material has a composition based on ferritic stainless steel, it exhibits excellent corrosion resistance in applications such as electrical contacts. For this reason, if it replaces with a general purpose copper alloy part, it will bring about the reliability improvement by corrosion resistance improvement, and if it replaces with an expensive high corrosion resistance copper alloy part, the outstanding cost merit will arise.
[Brief description of the drawings]
FIG. 1 is a transmission electron micrograph of a sample of the present invention (No. 21 in Table 3).
FIG. 2 is a transmission electron micrograph of a comparative sample (No. 5 in Table 2).

Claims

Cr: 9.0-20.0%, Cu: 1.0-15.0%, C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 (no addition) to 0.5%, Nb: 0 (% by mass) High Cr steel material for current-carrying parts with improved conductivity, in which the additive-free) to 0.5%, the balance being Fe and inevitable impurities, and the Cu-rich phase with an aging particle size of 1 to 500 nm is dispersed in the ferrite phase matrix.

Cr: 9.0-20.0%, Cu: 1.0-15.0%, C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 (no addition) to 0.5%, Nb: 0 (% by mass) High Cr steel material for current-carrying parts with improved conductivity, in which the additive-free) to 0.5%, the balance being Fe and unavoidable impurities, and the Cu-rich phase having an aging particle size of 5 to 20 nm is dispersed in the ferrite phase matrix.

In the mass%, Cr: 9.0 to 20.0%, Cu: 6.0 to 15.0% are contained, and the Cu-rich phase having an aging particle size of 5 to 20 nm and the Cu-rich phase having a particle size of 2000 nm or more coexist in the ferrite phase matrix. High Cr steel for energized parts with improved electrical conductivity.

Cr: 9.0 to 20.0%, Cu: 1.0 to less than 3.0%, C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 (no addition) to 0.5%, Nb: 0% by mass (No additive) -0.5%, the balance is Fe and unavoidable impurities, Cu-rich phase aged is dispersed in the ferrite phase matrix, and has electrical resistivity ρ satisfying the following formula (1) Improved high-Cr steel for current-carrying parts.
ρ / ρ ₀ ≦ 0.85 (1)
Here, ρ is the electrical resistivity (μΩ · cm) of the steel material, and ρ ₀ is the electrical resistivity (μΩ · cm) in a state where the Cu-rich phase that has aged out from the steel material has disappeared.

Cr: 9.0-20.0%, Cu: 3.0-15.0%, C + N: 0.10% or less, Mn: 2.0% or less, Si: 2.0% or less, Ti: 0 (no addition) to 0.5%, Nb: 0 (% by mass) Additive) ~ 0.5%, the balance is Fe and inevitable impurities, Cu-rich phase aged is dispersed in the ferrite phase matrix, improving conductivity with electrical resistivity ρ satisfying the following formula (2) High Cr steel for energized parts.
ρ / ρ ₀ ≦ 0.75 (2)
Here, ρ is the electrical resistivity (μΩ · cm) of the steel material, and ρ ₀ is the electrical resistivity (μΩ · cm) in a state where the Cu-rich phase that has aged out from the steel material has disappeared.

The steel material according to any one of claims 1 to 5 , which contains one or two of mass%, Ti: 0.5% or less, Nb: 0.5% or less, and satisfies the following formula (4).
7 (C + N) ≤Ti + Nb≤7 (C + N) +0.3 (4)