JP3541013B2

JP3541013B2 - Steel for power transmission components with excellent contact fatigue properties

Info

Publication number: JP3541013B2
Application number: JP2001009326A
Authority: JP
Inventors: 庸住田; 一衛野村; 哲己小川; 友章西川; 幸夫伊藤; 出山本; 秀雄相原; 昌澄大西; 修中野; 明彦篠原
Original assignee: Toyota Motor Corp; Aichi Steel Corp
Current assignee: Toyota Motor Corp; Aichi Steel Corp
Priority date: 2001-01-17
Filing date: 2001-01-17
Publication date: 2004-07-07
Anticipated expiration: 2021-01-17
Also published as: JP2002212668A

Description

【０００１】
【技術分野】
本発明は，摩擦係数の大きい潤滑油を介して，接触の摩擦力により動力を伝達する部品，例えばトロイダル式無段変速機等に使用される鋼，および部品に関し，特に優れた接触疲労特性を示す動力伝達部品用鋼，およびその鋼を用いた動力伝達部品に関する。
【０００２】
【従来技術】
一般に，自動車や産業機械等に用いられ，接触疲労を受ける部品としては歯車や軸受が代表される。歯車は動力伝達部品として，特に自動車用変速機に，また，軸受は回転体の支持部に使用されており，これらは動力損失の原因となる接触による摩擦力の低減が重要とされている。
【０００３】
近年，この歯車による変速機に代るものとして，トロイダル式無段変速機が採用され始めている。このトロイダル式無段変速機は，歯車の機械的かみ合いで動力を伝達するのではなく，駆動側回転体（円盤状部品，ディスクと呼ぶ）と従動側回転体（円盤状部品，ディスクと呼ぶ）との間に複数のローラを配置し，それぞれの接触部に発生する摩擦力によって回転し，動力を伝達するものである。従って，円盤状部品の上を円形軌道でローラが転がるため，その接触部においてスピンすべりが生じて発熱し，さらに，摩擦力によって動力を伝達するため接触部表面には通常の転がり接触にはない大きな摩擦力が発生する。このため，トロイダル式無段変速機は，構成部品に使用される鋼にとって，軸受等と比べて非常に苛酷な環境と考えられている。ここで，スピンすべりとは，円盤状部品の上を円形軌道でローラが転動する時，その接触面内における周速の差から生じるすべりを意味する。
【０００４】
従来から，接触疲労をともなう歯車や軸受等には，ＳＣＲ４２０やＳＣＭ４２０に代表される肌焼鋼や，ＳＵＪ２に代表される高炭素クロム軸受鋼が主に使用されている。しかし，これらの鋼をトロイダル式無段変速機等の用途に用いると，早期破損を起こす問題があった。そこで，このような特殊な使用環境下において，優れた接触疲労特性を有する鋼，およびその鋼を用いた部品が要望されている。
【０００５】
こうした状況のもとに提案された鋼は，これまでに，特開平８−３２６８６２，特開平９−７９３３７，特開平１０−１０３４４０などに開示されている。たとえば，特開平８−３２６８６２は表面硬化処理として高周波焼入を採用しており，また，特開平９−７９３３７は表面硬化処理として浸炭焼入と高周波焼入が併用しており，さらに特開平１０−１０３４４０は浸炭焼入を採用している。これらはいずれも，本用途に対して疲労寿命向上効果が十分ではなく，さらに浸炭については，その処理に膨大な時間とエネルギーを必要とし，同時にＣＯ２排出等の環境問題も生じる可能性があった。
【０００６】
【解決しようとする課題】
これらの問題を考慮し，本発明の目的は，軸受等とは異なり，高面圧で，かつ，大きな摩擦力と高温という非常に苛酷な環境下において，優れた接触疲労特性を示す動力伝達部品用鋼及び，その鋼を用いた動力伝達部品を提供することにある。
【０００７】
【課題の解決手段】
請求項１の発明は，Ｃ：０．５５〜０．６５重量％，Ｓｉ：０．５超〜２．０重量％，Ｍｎ：１．０重量％以下，Ｐ：０．０２５重量％以下，Ｓ：０．０３５重量％以下，Ｃｕ：０．３重量％以下，Ｃｒ：１．６〜３．０重量％，Ｍｏ：１．６〜２．５重量％，Ｖ：０．７５〜１．５重量％，Ａｌ：０．０５重量％以下，Ｏ：０．００１５重量％以下，Ｎ：０．０３０重量％以下，Ｔｉ：０．００５重量％以下を含有し，かつ，（Ｍｏ％＋Ｖ％）／Ｃ％：４．５〜６．０の関係を満足し，残部がＦｅおよび不可避的不純物よりなる鋼を球状化焼鈍した動力伝達部品用鋼であって，
該動力伝達部品用鋼に，焼入焼戻しをしたとき又は焼入焼戻しにサブゼロ処理を併用したとき，その硬さがＨｖ６８０以上になることを特徴とする優れた接触疲労特性を有する動力伝達部品用鋼である。
【０００８】
本発明によれば，潤滑油を介して接触し，その摩擦力を利用することで動力伝達を行う動力伝達部品用鋼に，溶製時の適正な化学成分と適切な硬化熱処理を施すことによって，一般的に用いられるＳＵＪ２，ＳＣＭ４２０および他の従来鋼に対して，優れた接触疲労特性向上効果を得ることができる。
このように本発明によれば，高面圧で，かつ，大きな摩擦力と高温という非常に苛酷な環境下において優れた接触疲労特性を示す動力伝達部品用鋼を提供することができる。
【０００９】
以下に各合金元素の限定理由について説明する。
Ｃ：０．５５〜０．６５重量％
Ｃは鋼の強度を保持するために必須であり，また，焼もどしによる２次硬化で高硬度を確保するためにも必要な元素である。そのためには，少なくとも０．５５重量％以上必要であるが，その含有量が多過ぎれば，Ｃとの結合力が特に強いＭｏやＶと結合することで，大型の共晶炭化物やネット状炭化物が析出し易くなり，熱間および冷間加工性を阻害し製造性を悪化させるばかりか，接触疲労特性をも劣化させるため，上限を０．６５重量％とした。
【００１０】
Ｓｉ：０．５超〜２．０重量％
Ｓｉは本発明にとって重要な元素の１つであり，発明者らは焼戻し軟化抵抗を与えるだけでなく，接触摩擦力によって動力伝達する部品において，その接触疲労特性の劣化を抑制する効果を見出した。その効果のためには０．５重量％を超えた含有量が必要である。しかし過剰に添加してもその効果は飽和するばかりでなく，鋼の変態点を高めるので熱処理温度を高温とする必要を生ずるほか，鍛造性および冷間加工性を損なうなどの弊害をもたらすので，Ｓｉ含有量の上限を２．０重量％とする。好ましくは０．６〜１．２重量％が望ましい。
【００１１】
Ｍｎ：１．０重量％以下
Ｍｎは鋼の焼入れ性を向上させる元素であるが，過剰に添加すると素材の軟化焼鈍を困難とし，また加工性および熱間加工性をも劣化させるため上限を１．０重量％とする。
【００１２】
Ｐ：０．０２５重量％以下
Ｐは鋼中に多量に存在すると結晶粒界に偏析し，粒界を脆化させる原因になる元素である。従って，可能な限り低いことが望ましく，上限を０．０２５重量％に規制する。
【００１３】
Ｓ：０．０３５重量％以下
Ｓは切削性を向上させる元素であるが，多量に添加すると大型のＭｎＳ等の非金属介在物を生成し，疲労特性を劣化させるため上限を０．０３５重量％とする。
【００１４】
Ｃｕ：０．３重量％以下
Ｃｕは鋼の焼入れ性，耐食性を向上させる元素である。本発明においては，その含有量が多すぎれば赤熱脆性等の不具合を起こし，製造性を悪化させるので上限を０．３重量％とする。
【００１５】
Ｃｒ：１．６〜３．０重量％
Ｃｒは本発明にとって必須の元素の１つで，焼戻し軟化抵抗性を与えるだけでなく，２次硬化にも寄与し，また，炭化物を生成することで耐摩耗性を付与するために必要な元素である。さらに，本発明において，Ｓｉ，Ｍｏ，Ｖと同時に添加することにより，接触摩擦力によって動力伝達する部品において，接触疲労特性の劣化を抑制する効果を見出した。その効果のためには１．６重量％以上添加する必要がある。しかし，過剰に添加してもその効果は飽和するばかりか，Ｍｏ，Ｖと複合した巨大な共晶炭化物を析出させることで疲労特性を劣化させる場合があり，さらにはいたずらにコストを高めるのみなので，その含有量上限を３．０重量％とする。
【００１６】
Ｍｏ：１．６〜２．５重量％
ＭｏはＣｒと同様に炭化物形成元素であり，２次硬化や耐摩耗性に影響を与え，さらに焼戻し軟化抵抗性も向上させる。さらに，本発明においては，Ｓｉ，Ｃｒ，Ｖと同時に添加することにより，接触疲労特性を向上できることを見出したことから必須の元素である。これらの効果のためには，少なくとも１．６重量％の添加が必要である。しかし，ＭｏはＣｒよりもより安定な炭化物を形成することから，その含有量が多くなると，疲労特性を劣化させる大型の共晶炭化物やネット状炭化物の生成を促進させ，さらに，２次硬化に必要な固溶Ｃ量を確保するための焼入れにおいて，その温度の高温化を招くことで熱処理コストを上昇させ，さらに熱間加工性等の鋼の生産性にも悪影響を及ぼすので，上限を２．５重量％以下とする。
【００１７】
Ｖ：０．７５〜１．５重量％
ＶはＭｏと同様に炭化物形成元素であり，２次硬化や耐摩耗性に影響を与える元素である。特に，２次硬化に関しては，その効果は大きいことに加え，本発明においては，Ｓｉ，Ｃｒ，Ｍｏと同時に添加することで，接触疲労特性を向上させることを見出した。これらの効果のためには，少なくとも，０．７５重量％以上が必要である。しかしながら，過剰に添加すると，ＣｒやＭｏに比べて非常に強い炭化物形成能を有することから，大型の共晶炭化物やネット状炭化物を生成しやすくなり，接触疲労特性を劣化させる場合があり，さらに加工性等をも劣化させるばかりか，いたずらにコストを上昇させてしまうため，上限を１．５重量％とする。
【００１８】
Ａｌ：０．０５重量％以下
Ａｌは鋼を製造する上で脱酸剤として使用するため不可避に存在するもので，Ｎと結合して，結晶粒の成長を抑制することが知られている一方，過剰に添加すると酸化物系介在物となりやすく，接触疲労特性に悪影響を及ぼすので，上限を０．０５重量％とする。
【００１９】
Ｏ：０．００１５重量％以下
ＯはＡｌと結合することで，接触疲労特性の低下を招く硬質な非金属介在物を形成する元素であるため，可能な限り低いことが望ましく，０．００１５重量％以下に規制する。
【００２０】
Ｎ：０．０３０重量％以下
ＮはＡｌと結合して結晶粒の成長を抑制することが知られており，その効果のために添加することが可能であるが，しかし過剰に添加すると，鋳造欠陥等の不具合を生じるので，その含有量上限を０．０３０重量％とする。
【００２１】
Ｔｉ：０．００５重量％以下
ＴｉはＮと結合して，大型で硬質な非金属介在物を生成しやすく接触疲労特性を劣化させるので，可能な限り低いことが望ましく，０．００５重量％以下に規制する。
【００２２】
（Ｍｏ％＋Ｖ％）／Ｃ％：４．５〜６．０
本発明の請求範囲内において，特に，Ｃ，Ｍｏ，Ｖの間に最適な範囲が存在することを見出した。すなわち，本発明の請求範囲において，接触疲労特性を向上させ，また，必要な２次硬化能を付与するためには，少なくとも，（Ｍｏ％＋Ｖ％）／Ｃ％が４．５以上必要である。しかし，Ｃとの結合力が強いＭｏ，ＶがＣ量に対して過多になると，凝固時に大型の共晶炭化物やネット状炭化物を生成し，接触疲労特性に悪影響を及ぼすばかりか，過剰な合金添加による鋼のコスト増になるため，（Ｍｏ％＋Ｖ％）／Ｃ％は６．０以下とする。
【００２３】
焼入焼もどし硬さ：Ｈｖ６８０以上
動力伝達部品用鋼は接触荷重を受けるため，材料の塑性変形を防止し，その面圧に耐える必要があることから下限をＨｖ６８０とした。
【００２４】
本発明において，２次硬化をより効果的にするために，熱処理として，サブゼロ処理を併用してもかまわない。
【００２５】
請求項２の発明のように，上記鋼は，更に，Ｎｉ：１．０重量％以下を含有していることが好ましい。
【００２６】
Ｎｉは鋼中マトリックスを強化して靭性を向上させる点で，疲労特性の向上に有効な元素である。しかし，含有量が多くなるとその効果が飽和するばかりか冷間加工性を阻害し，さらに材料コストの上昇を招くことからその含有量は上記のように１．０重量％以下とすることが好ましい。
【００２７】
次に，請求項３の発明は，Ｃ：０．５５〜０．６５重量％，Ｓｉ：０．５超〜２．０重量％，Ｍｎ：１．０重量％以下，Ｐ：０．０２５重量％以下，Ｓ：０．０３５重量％以下，Ｃｕ：０．３重量％以下，Ｃｒ：１．６〜３．０重量％，Ｍｏ：１．６〜２．５重量％，Ｖ：０．７５〜１．５重量％，Ａｌ：０．０５重量％以下，Ｏ：０．００１５重量％以下，Ｎ：０．０３０重量％以下，Ｔｉ：０．００５重量％以下を含有し，かつ，（Ｍｏ％＋Ｖ％）／Ｃ％：４．５〜６．０の関係を満足し，残部がＦｅおよび不可避的不純物よりなる鋼を球状化焼鈍した動力伝達部品用鋼からなる動力伝達部品であって，
該動力伝達部品には，焼入焼戻し又は焼入焼戻しにサブゼロ処理が併用されており，
上記動力伝達部品の硬さはＨｖ６８０以上であることを特徴とする優れた接触疲労特性を有する動力伝達部品である。
【００２８】
本発明の動力伝達部品は，摩擦力により動力を伝達するときに，優れた接触疲労特性を発揮することができる。また，高面圧で，かつ，大きな摩擦力と高温という非常に苛酷な環境下においても優れた接触疲労特性を発揮することができる。
【００２９】
請求項４の発明のように，上記鋼は，更に，Ｎｉ：１．０重量％以下を含有していることが好ましい。１．０重量％を超える場合には，冷間加工性を阻害し，材料コストの上昇を招くおそれがある。
本発明の動力伝達部品の具体例としては，たとえば，トロイダル式無段変速機などがある。
【００３０】
【発明の実施の形態】
発明者らは本発明を成すために，対象となる鋼あるいは部品が使用される環境を再現した試験を実施する必要があると考えた。すなわち，高面圧，摩擦力による動力伝達，高温，また接触面内におけるスピンすべり等が考慮された試験でなければならない。
【００３１】
図１は本発明に係わる試験で用いた接触疲労試験機を示す。本試験機は円盤状試験片（従動円盤）２上において，垂直荷重を受けた２ないし３つの駆動ローラ１が駆動モータ３にて転動し，十分な摩擦力を与えるために動力吸収機４によって制動している従動円盤２を，駆動ローラ１と接触させ，その接触面２１に発生する摩擦力を利用して駆動させるものである。
【００３２】
表１は，本試験機と，一般に歯車の代用評価として用いられるローラピッチング試験機と，軸受の代用評価として用いられるスラスト型転動寿命試験機の特徴を合わせて示す。表１より，本試験機は，スピンすべりを伴いながら，接触摩擦力により動力伝達をおこなう部品を評価するのに適している。
表２は本発明を成すために各種検討を実施した供試材の化学成分の一覧表を示す。これらの供試材は，ＶＩＭで溶製し，分塊圧延後，熱間で鍛伸および据込み鍛造して素形材とした。その後，鋼Ａ〜Ｖについては機械加工を容易にするために球状化焼鈍を施しており，特に鋼Ａ〜Ｕについては，その条件を８８０℃で５ｈｒ保持後，５５０℃まで１５℃／ｈｒの徐冷とした。これら素形材を所定の寸法に機械加工して，所定の硬化熱処理を施した。さらに表面を仕上加工することによりスケールや脱炭層を除去し，その状態で試験に供した。
【００３３】
なお，従来鋼Ｖ〜Ｚのなかで，硬化熱処理として浸炭や高周波焼入を施したものについては，当然のことながら，仕上加工代を０．１〜０．２ｍｍとして，有効硬化深さを加工によって浅くしないように配慮している。
【００３４】
表３は各供試材の熱処理，および仕上加工後のビッカース硬度計による表面硬さを示す。参考のため，Ｘ線回折法によって測定した，その表面の残留オーステナイト量も併記する。各供試材の熱処理のヒートパターンを図２〜図９に示す。図２は，試料Ａ〜Ｆ，Ｊ，Ｌ，Ｎ〜Ｑのヒートパターンを，図３は，試料Ｇ〜Ｉ，Ｋ，Ｍ，Ｒ〜Ｕのヒートパターンを示す。図４，図５，図６，図７，図８，図９は，順に，試料Ａ２，Ｖ，Ｗ，Ｘ，Ｙ，Ｚのヒートパターンを示す。なお，図６，図８および図９中のＣ．Ｐ．とは浸炭雰囲気中のカーボン・ポテンシャルを意味する。
【００３５】
これらの供試材を図１に示した接触疲労試験機において，表４に示す条件で試験を実施し，接触疲労特性は，接触面における剥離損傷の発生までの回転数として計測した。その結果を表５に示した。ここで，平均寿命比とは鋼Ｖ（ＪＩＳ−ＳＵＪ２）を１とした比で表わしている。
【００３６】
以下に本発明に係わる実施例について説明する。本発明鋼は表２における鋼Ａ〜Ｉであり，表３における鋼Ａ２は，鋼Ａに関して熱処理条件を変化させて，仕上加工後の表面硬さを変化させたため比較鋼である。これらの本発明鋼は，表５に示す平均寿命比がいずれも１０を超えており，優れた接触疲労特性を有することがわかる。
【００３７】
一方，比較鋼は表２における鋼Ｊ〜鋼Ｕであり，本発明鋼に対し，鋼Ｊ，鋼Ｋは（Ｍｏ％＋Ｖ％）／Ｃ％の値がそれぞれ下限未満，上限超過しており，表５に示すごとく，本発明鋼に比べて十分な寿命向上効果が得られていない。また，鋼Ｌ，鋼Ｎ，鋼Ｏ，鋼Ｐおよび鋼Ｑは，それぞれＳｉ，Ｃ，Ｃｒ，ＭｏおよびＶが本請求範囲より低くなっており，鋼Ｍ，鋼Ｒおよび鋼Ｓは，それぞれＣ，ＭｏおよびＶが本請求範囲より高くなっており，いずれの比較鋼も表５に示すごとく十分な寿命向上効果が得られていない。さらに，鋼ＴはＯが，また，鋼ＵはＴｉが本請求範囲を超えており，非金属介在物が増加していると考えられるため，表５に示すことく本発明鋼ほどの寿命向上効果を得るにいたっていない。
【００３８】
ここで，表３および表５の比較鋼として記載してある鋼Ａ２に関して説明する。この鋼Ａ２は本発明鋼Ａと同一成分であるが，焼入条件を鋼Ａとは変えることによって，表３に示すように，本請求範囲よりも表面硬さが低くなったものである。したがって，この鋼Ａ２においても，鋼Ａほどの寿命向上効果が得られていない。
【００３９】
さらに，表２における鋼Ｖ〜Ｚは従来鋼を示しており，表３にそれらの熱処理，硬さ，残留オーステナイト量などを示している。ここで，鋼ＶはＪＩＳ−ＳＵＪ２であり，鋼ＷはＪＩＳ−ＳＣＭ４２０であり，鋼Ｘは特開平８−３２６８６２に相当し，鋼Ｙは特開平９−７９３３７に相当し，鋼Ｚは特開平１０−１０３４４０に相当するものである。いずれの従来鋼も化学成分が本発明鋼の請求範囲を逸脱し，さらに，硬化熱処理手法が異なっており，表５に示すごとく本発明鋼より劣る寿命水準となっている。これらの本発明鋼，比較鋼および従来鋼の結果は，本発明の有効性および妥当性を示すものである。
【００４０】
以上に本発明の実施例を詳述したが，これは一例であり，本発明の意図を逸脱しない範囲で，摩擦力によって動力を伝達する動力伝達部品用鋼，および動力伝達部品に適用可能である。
【００４１】
【表１】

【００４２】
【表２】

【００４３】
【表３】

【００４４】
【表４】

【００４５】
【表５】

【００４６】
【発明の効果】
本発明によれば，高面圧で，かつ，大きな摩擦力と高温という非常に苛酷な環境下において，優れた接触疲労特性を示す動力伝達部品用鋼及び，その鋼を用いた動力伝達部品を提供することができる。
【図面の簡単な説明】
【図１】本発明の接触疲労特性を測定する接触疲労試験機の概要を示す説明図。
【図２】表３における熱処理のうち，一部の焼入焼もどしに関するヒートパターンを示す説明図。
【図３】表３における熱処理のうち，一部の焼入焼もどしに関するヒートパターンを示す説明図。
【図４】表３における熱処理のうち，一部の焼入焼もどしに関するヒートパターンを示す説明図。
【図５】表３における熱処理のうち，一部の焼入焼もどしに関するヒートパターンを示す説明図。
【図６】表３における熱処理のうち，一部の浸炭焼入に関するヒートパターンを示す説明図。
【図７】表３における熱処理のうち，高周波焼入に関するヒートパターンを示す説明図。
【図８】表３における熱処理のうち，浸炭および高周波焼入に関するヒートパターンを示す説明図。
【図９】表３における熱処理のうち，一部の浸炭焼入に関するヒートパターンを示す説明図。
【符号の説明】
１．．．駆動ローラ，
２．．．円盤状試験片（従動円盤），
２１．．．接触面，
３．．．駆動モータ，
４．．．動力吸収機，[0001]
【Technical field】
The present invention relates to a component for transmitting power by frictional force of contact through a lubricating oil having a large friction coefficient, for example, a steel used for a toroidal type continuously variable transmission and the like, and a component having particularly excellent contact fatigue characteristics. The present invention relates to a steel for a power transmission component and a power transmission component using the steel.
[0002]
[Prior art]
In general, gears and bearings are used as components used in automobiles and industrial machines and are subject to contact fatigue. Gears are used as power transmission parts, particularly in transmissions for automobiles, and bearings are used as supports for rotating bodies, and it is important to reduce frictional force due to contact that causes power loss.
[0003]
In recent years, a toroidal type continuously variable transmission has begun to be used as an alternative to the transmission using gears. This toroidal type continuously variable transmission does not transmit power by the mechanical engagement of gears, but uses a rotating body on the driving side (called a disk-shaped part or disk) and a rotating body on the driven side (called a disk-shaped part or disk). And a plurality of rollers are arranged between them, and are rotated by frictional force generated at respective contact portions to transmit power. Therefore, the roller rolls in a circular orbit on the disk-shaped part, causing a spin-slip at the contact part and generating heat. In addition, since the power is transmitted by frictional force, the surface of the contact part is not in normal rolling contact. Large friction force is generated. For this reason, the toroidal type continuously variable transmission is considered to be a very harsh environment for steel used as a component, compared to a bearing or the like. Here, the spin slip means a slip caused by a difference in peripheral speed in a contact surface when a roller rolls on a disk-shaped component in a circular orbit.
[0004]
Conventionally, case hardening steel represented by SCR420 and SCM420 and high carbon chromium bearing steel represented by SUJ2 have been mainly used for gears and bearings with contact fatigue. However, when these steels are used for applications such as toroidal-type continuously variable transmissions, there has been a problem of early breakage. Therefore, there is a demand for a steel having excellent contact fatigue properties under such a special use environment, and a part using the steel.
[0005]
The steel proposed in such a situation has been disclosed in Japanese Unexamined Patent Application Publication Nos. Hei 8-326862, Hei 9-79337, Hei 10-103440, and the like. For example, Japanese Unexamined Patent Publication No. Hei 8-326682 employs induction hardening as a surface hardening treatment, and Japanese Unexamined Patent Publication No. Hei 9-79337 employs both carburizing and induction hardening as a surface hardening treatment. -10440 adopts carburizing and quenching. All of these have insufficient fatigue life improvement effects for this application, and carburizing requires an enormous amount of time and energy to treat, and may also cause environmental problems such as CO2 emissions. .
[0006]
[Problem to be solved]
In view of these problems, an object of the present invention is to provide a power transmission component which exhibits excellent contact fatigue characteristics under a very harsh environment of high surface pressure, large frictional force and high temperature, unlike bearings and the like. And a power transmission component using the steel.
[0007]
[Means for solving the problem]
The invention of claim 1 is characterized in that: C: 0.55 to 0.65% by weight, Si: more than 0.5 to 2.0% by weight, Mn: 1.0% by weight or less, P: 0.025% by weight or less, S: 0.035% by weight or less, Cu: 0.3% by weight or less, Cr: 1.6 to 3.0% by weight, Mo: 1.6 to 2.5% by weight, V: 0.75 to 1. 5% by weight, Al: 0.05% by weight or less, O: 0.0015% by weight or less, N: 0.030% by weight or less, Ti: 0.005% by weight or less, and (Mo% + V% ) / C%: steel for power transmission parts, which spheroidized and spheroidized steel that satisfies the relationship of 4.5 to 6.0, with the balance being Fe and unavoidable impurities,
When the steel for power transmission parts is subjected to quenching and tempering or when sub-zero treatment is used in combination with quenching and tempering, the hardness of the steel becomes Hv680 or more. It is steel.
[0008]
According to the present invention, a steel for power transmission parts, which is in contact with the lubricating oil and transmits power by utilizing the frictional force, is subjected to an appropriate chemical component and an appropriate hardening heat treatment at the time of melting. As compared with SUJ2, SCM420 and other conventional steels which are generally used, an excellent contact fatigue property improving effect can be obtained.
As described above, according to the present invention, it is possible to provide a power transmission component steel exhibiting excellent contact fatigue characteristics under a very severe environment of a high surface pressure and a large frictional force and a high temperature.
[0009]
The reason for limiting each alloy element will be described below.
C: 0.55 to 0.65% by weight
C is an essential element for maintaining the strength of the steel, and is also an element necessary for securing high hardness by secondary hardening by tempering. For this purpose, at least 0.55% by weight or more is necessary, but if the content is too large, large eutectic carbides and net-like carbides are formed by bonding with Mo and V, which have a particularly strong bonding force with C. The upper limit is set to 0.65% by weight, since the precipitates are likely to precipitate, impairing the hot and cold workability and deteriorating the manufacturability as well as the contact fatigue characteristics.
[0010]
Si: more than 0.5 to 2.0% by weight
Si is one of the important elements for the present invention, and the inventors have found not only the effect of imparting the tempering softening resistance but also the effect of suppressing the deterioration of the contact fatigue characteristics in the parts that transmit power by the contact friction force. . A content exceeding 0.5% by weight is necessary for its effect. However, even if it is added excessively, the effect is not only saturated, but also raises the transformation point of the steel, so that it is necessary to increase the heat treatment temperature, and it also causes adverse effects such as impairing forgeability and cold workability. The upper limit of the Si content is set to 2.0% by weight. Preferably, it is 0.6 to 1.2% by weight.
[0011]
Mn: 1.0% by weight or less Mn is an element that improves the hardenability of steel. However, if added excessively, it becomes difficult to soften and soften the material, and the workability and hot workability are also deteriorated. 0.0% by weight.
[0012]
P: 0.025% by weight or less P is an element that, when present in a large amount in steel, segregates at crystal grain boundaries and causes embrittlement of the grain boundaries. Therefore, it is desirable to be as low as possible, and the upper limit is regulated to 0.025% by weight.
[0013]
S: 0.035% by weight or less S is an element that improves the machinability, but when added in a large amount, large non-metallic inclusions such as MnS are generated and the fatigue characteristics are deteriorated, so the upper limit is 0.035% by weight. And
[0014]
Cu: not more than 0.3% by weight Cu is an element that improves the hardenability and corrosion resistance of steel. In the present invention, if the content is too large, problems such as red-hot brittleness are caused and the productivity is deteriorated. Therefore, the upper limit is set to 0.3% by weight.
[0015]
Cr: 1.6 to 3.0% by weight
Cr is one of the essential elements for the present invention, and not only provides temper softening resistance, but also contributes to secondary hardening, and is an element necessary for imparting wear resistance by forming carbides. It is. Furthermore, in the present invention, it has been found that by adding simultaneously with Si, Mo, and V, an effect of suppressing the deterioration of the contact fatigue characteristics in a component that transmits power by contact frictional force. It is necessary to add 1.6% by weight or more for the effect. However, even if it is added excessively, the effect is not only saturated, but also the fatigue properties may be deteriorated by precipitating a huge eutectic carbide compounded with Mo and V. In addition, the cost is simply increased unnecessarily. The upper limit of the content is 3.0% by weight.
[0016]
Mo: 1.6 to 2.5% by weight
Mo is a carbide-forming element like Cr, and affects secondary hardening and wear resistance, and further improves tempering softening resistance. Furthermore, in the present invention, it has been found that by adding simultaneously with Si, Cr and V, it is possible to improve the contact fatigue properties, so that it is an essential element. For these effects, an addition of at least 1.6% by weight is necessary. However, Mo forms more stable carbides than Cr, so when its content increases, it promotes the formation of large eutectic carbides and net-like carbides that degrade fatigue properties, and further promotes secondary hardening. In the quenching to secure the required amount of solid solution C, the heat treatment cost is raised by inducing the temperature to be high, and the productivity of steel such as hot workability is adversely affected. 0.5% by weight or less.
[0017]
V: 0.75 to 1.5% by weight
V is a carbide forming element like Mo, and is an element that affects secondary hardening and wear resistance. In particular, it has been found that in addition to the effect of secondary hardening, the effect is great, and in the present invention, the simultaneous addition of Si, Cr and Mo improves the contact fatigue properties. For these effects, at least 0.75% by weight or more is required. However, if added excessively, it has a very strong carbide-forming ability as compared with Cr and Mo, so that large eutectic carbides and net-like carbides are easily formed, which may degrade the contact fatigue properties. The upper limit is set to 1.5% by weight because not only the workability is deteriorated, but also the cost is unnecessarily increased.
[0018]
Al: 0.05% by weight or less Al is inevitably present because it is used as a deoxidizing agent in the production of steel, and is known to combine with N to suppress the growth of crystal grains. , Excessive addition tends to form oxide inclusions, which adversely affects the contact fatigue properties. Therefore, the upper limit is set to 0.05% by weight.
[0019]
O: 0.0015% by weight or less O is an element which forms hard non-metallic inclusions which cause a decrease in contact fatigue characteristics when combined with Al. %.
[0020]
N: 0.030% by weight or less It is known that N bonds with Al and suppresses the growth of crystal grains, and it is possible to add N for its effect. Since defects such as defects occur, the upper limit of the content is set to 0.030% by weight.
[0021]
Ti: 0.005% by weight or less Ti is preferably as low as possible because it combines with N to form large hard nonmetallic inclusions and deteriorates contact fatigue characteristics. To be regulated.
[0022]
(Mo% + V%) / C%: 4.5-6.0
Within the scope of the claims of the present invention, it has been found that there is an optimal range among C, Mo and V. That is, in the claims of the present invention, at least (Mo% + V%) / C% is required to be 4.5 or more in order to improve the contact fatigue property and to provide the necessary secondary hardening ability. . However, when Mo and V, which have a strong bonding force with C, are excessive with respect to the C content, large eutectic carbides and net-like carbides are formed during solidification, which not only adversely affects contact fatigue properties but also causes excessive alloying. (Mo% + V%) / C% is set to 6.0 or less because the cost of steel increases due to the addition.
[0023]
Hardening and tempering hardness: Hv680 or higher Since steel for power transmission components receives a contact load, it is necessary to prevent plastic deformation of the material and to withstand the surface pressure, so the lower limit was set to Hv680.
[0024]
In the present invention, in order to make the secondary curing more effective, a sub-zero treatment may be used in combination as the heat treatment.
[0025]
Preferably, the steel further contains 1.0% by weight or less of Ni.
[0026]
Ni is an element effective in improving fatigue characteristics in that it strengthens the matrix in steel and improves toughness. However, when the content is increased, the effect is saturated, not only the cold workability is impaired, but also the material cost is increased. Therefore, the content is preferably set to 1.0% by weight or less as described above. .
[0027]
Next, the invention according to claim 3 is characterized in that: C: 0.55 to 0.65% by weight, Si: more than 0.5 to 2.0% by weight, Mn: 1.0% by weight or less, P: 0.025% by weight %, S: 0.035% by weight or less, Cu: 0.3% by weight or less, Cr: 1.6 to 3.0% by weight, Mo: 1.6 to 2.5% by weight, V: 0.75% 1.5% by weight, Al: 0.05% by weight or less, O: 0.0015% by weight or less, N: 0.030% by weight or less, Ti: 0.005% by weight or less, and (Mo % + V%) / C%: a power transmission component that satisfies the relationship of 4.5 to 6.0 and the balance is steel for a power transmission component obtained by spheroidizing and annealing steel including Fe and unavoidable impurities,
The power transmission component uses quenching and tempering or quenching and tempering together with sub-zero treatment.
The power transmission component has a hardness of Hv680 or more, and is a power transmission component having excellent contact fatigue characteristics.
[0028]
The power transmission component of the present invention can exhibit excellent contact fatigue characteristics when transmitting power by frictional force. In addition, excellent contact fatigue characteristics can be exhibited even under a very severe environment of high surface pressure, large frictional force and high temperature.
[0029]
It is preferable that the steel further contains Ni: 1.0% by weight or less. If the content exceeds 1.0% by weight, the cold workability may be impaired, leading to an increase in material cost.
Specific examples of the power transmission component of the present invention include, for example, a toroidal-type continuously variable transmission.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
The inventors thought that in order to carry out the present invention, it was necessary to carry out a test reproducing the environment in which the target steel or component was used. In other words, the test must take into account high surface pressure, power transmission by frictional force, high temperature, and spin slip in the contact surface.
[0031]
FIG. 1 shows a contact fatigue tester used in a test according to the present invention. In this tester, two or three drive rollers 1 which have been subjected to a vertical load are rolled by a drive motor 3 on a disk-shaped test piece (follower disk) 2 to apply a sufficient frictional force to a power absorber 4. The driven disk 2 which is being braked by this is brought into contact with the drive roller 1 and driven by utilizing the frictional force generated on the contact surface 21.
[0032]
Table 1 shows the features of the present test machine, a roller pitching test machine generally used as a substitute evaluation of gears, and a thrust rolling life test machine used as a substitute evaluation of bearings. From Table 1, this tester is suitable for evaluating components that transmit power by contact frictional force while involving spin slip.
Table 2 shows a list of the chemical components of the test materials that were subjected to various studies to implement the present invention. These test materials were melted by VIM, slab-rolled, and then hot forged and upset forged to obtain shaped materials. Thereafter, steels A to V are subjected to spheroidizing annealing in order to facilitate machining. Particularly, for steels A to U, the conditions are maintained at 880 ° C. for 5 hours, and then up to 550 ° C. at 15 ° C./hr. It was slowly cooled. These shaped members were machined to predetermined dimensions and subjected to predetermined hardening heat treatment. Furthermore, the scale and decarburized layer were removed by finishing the surface, and the specimen was subjected to the test in that state.
[0033]
Of the conventional steels V to Z, those that have been subjected to carburizing or induction hardening as the hardening heat treatment are, of course, finished with an allowance of 0.1 to 0.2 mm and an effective hardening depth. So that it is not shallow.
[0034]
Table 3 shows the surface hardness of each test material after heat treatment and finish processing by a Vickers hardness tester. For reference, the amount of retained austenite on the surface measured by the X-ray diffraction method is also shown. The heat pattern of the heat treatment of each test material is shown in FIGS. FIG. 2 shows heat patterns of samples A to F, J, L, N to Q, and FIG. 3 shows heat patterns of samples G to I, K, M, RU. 4, 5, 6, 7, 8, and 9 show heat patterns of samples A2, V, W, X, Y, and Z, respectively. Note that C.I. in FIG. 6, FIG. 8 and FIG. P. Means the carbon potential in a carburizing atmosphere.
[0035]
These test materials were tested on the contact fatigue tester shown in FIG. 1 under the conditions shown in Table 4, and the contact fatigue characteristics were measured as the number of rotations until the occurrence of peeling damage on the contact surface. Table 5 shows the results. Here, the average life ratio is expressed as a ratio of steel V (JIS-SUJ2) as 1.
[0036]
Hereinafter, embodiments according to the present invention will be described. The steels of the present invention are steels A to I in Table 2, and steel A2 in Table 3 is a comparative steel because the heat treatment conditions for steel A were changed to change the surface hardness after finishing. These steels of the present invention all have the average life ratios shown in Table 5 exceeding 10, indicating that they have excellent contact fatigue properties.
[0037]
On the other hand, the comparative steels are steel J to steel U in Table 2, and the steels J and K have (Mo% + V%) / C% values below the lower limit and the upper limit, respectively. As shown in Table 5, the effect of improving the life was not sufficiently obtained as compared with the steel of the present invention. Steel L, steel N, steel O, steel P and steel Q have Si, C, Cr, Mo and V respectively lower than the claimed range, and steel M, steel R and steel S have C respectively. , Mo and V are higher than the claimed range, and none of the comparative steels has a sufficient life improving effect as shown in Table 5. Further, since the steel T is O and the steel U is Ti in excess of the claimed range and the nonmetallic inclusions are considered to be increased, as shown in Table 5, the life is improved as much as the steel of the present invention. It has not been effective.
[0038]
Here, steel A2 described as a comparative steel in Tables 3 and 5 will be described. The steel A2 has the same composition as the steel A of the present invention, but has a lower surface hardness than the scope of the present invention as shown in Table 3 by changing the quenching conditions from the steel A. Therefore, even in steel A2, the effect of improving the life as steel A is not obtained.
[0039]
Further, steels V to Z in Table 2 show conventional steels, and Table 3 shows their heat treatment, hardness, residual austenite amount, and the like. Here, steel V is JIS-SUJ2, steel W is JIS-SCM420, steel X is equivalent to JP-A-8-326882, steel Y is equivalent to JP-A-9-79337, and steel Z is JP-A-9-79337. This corresponds to 10-103440. All of the conventional steels have chemical components outside the scope of the claimed invention, and further have different hardening heat treatment methods. As shown in Table 5, the life levels are inferior to those of the inventive steel. The results of the steel according to the present invention, the comparative steel and the conventional steel show the effectiveness and validity of the present invention.
[0040]
Although the embodiment of the present invention has been described in detail above, this is merely an example, and the present invention can be applied to a power transmission component steel and a power transmission component that transmit power by frictional force without departing from the intention of the present invention. is there.
[0041]
[Table 1]

[0042]
[Table 2]

[0043]
[Table 3]

[0044]
[Table 4]

[0045]
[Table 5]

[0046]
【The invention's effect】
According to the present invention, a steel for a power transmission component exhibiting excellent contact fatigue characteristics under a very harsh environment of high surface pressure, large frictional force and high temperature, and a power transmission component using the steel are provided. Can be provided.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an outline of a contact fatigue tester for measuring contact fatigue characteristics of the present invention.
FIG. 2 is an explanatory view showing a heat pattern relating to a part of quenching and tempering among the heat treatments in Table 3.
FIG. 3 is an explanatory diagram showing a heat pattern relating to a part of quenching and tempering among the heat treatments in Table 3.
FIG. 4 is an explanatory view showing a heat pattern relating to a part of quenching and tempering among the heat treatments in Table 3.
FIG. 5 is an explanatory view showing a heat pattern relating to a part of quenching and tempering among the heat treatments in Table 3.
FIG. 6 is an explanatory view showing a heat pattern relating to a part of carburizing and quenching among the heat treatments in Table 3.
FIG. 7 is an explanatory diagram showing a heat pattern related to induction hardening among the heat treatments in Table 3.
FIG. 8 is an explanatory view showing a heat pattern relating to carburizing and induction hardening in the heat treatments in Table 3.
FIG. 9 is an explanatory view showing a heat pattern relating to a part of carburizing and quenching among the heat treatments in Table 3.
[Explanation of symbols]
1. . . Drive roller,
2. . . Disc-shaped test piece (follower disc),
21. . . Contact surface,
3. . . Drive motor,
4. . . Power absorber,

Claims

C: 0.55 to 0.65 wt%, Si: more than 0.5 to 2.0 wt%, Mn: 1.0 wt% or less, P: 0.025 wt% or less, S: 0.035 wt% Hereinafter, Cu: 0.3% by weight or less, Cr: 1.6 to 3.0% by weight, Mo: 1.6 to 2.5% by weight, V: 0.75 to 1.5% by weight, Al: 0 0.05% by weight or less, O: 0.0015% by weight or less, N: 0.030% by weight or less, Ti: 0.005% by weight or less, and (Mo% + V%) / C%: 4. A steel for power transmission parts, which spheroidizes and spheroidizes a steel that satisfies the relationship of 5 to 6.0 and the balance is Fe and inevitable impurities;
When the steel for power transmission parts is subjected to quenching and tempering or when sub-zero treatment is used in combination with quenching and tempering, the hardness of the steel becomes Hv680 or more. steel.

The steel for a power transmission component having excellent contact fatigue characteristics according to claim 1, wherein the steel further contains 1.0% by weight or less of Ni.

C: 0.55 to 0.65 wt%, Si: more than 0.5 to 2.0 wt%, Mn: 1.0 wt% or less, P: 0.025 wt% or less, S: 0.035 wt% Hereinafter, Cu: 0.3% by weight or less, Cr: 1.6 to 3.0% by weight, Mo: 1.6 to 2.5% by weight, V: 0.75 to 1.5% by weight, Al: 0 0.05% by weight or less, O: 0.0015% by weight or less, N: 0.030% by weight or less, Ti: 0.005% by weight or less, and (Mo% + V%) / C%: 4. A power transmission component comprising a steel for a power transmission component which spheroidizes and spheroidizes a steel comprising Fe and inevitable impurities, the balance satisfying a relationship of 5 to 6.0.
The power transmission component uses quenching and tempering or quenching and tempering together with sub-zero treatment.
A power transmission component having excellent contact fatigue characteristics, wherein the hardness of the power transmission component is Hv680 or more.

4. The power transmission component according to claim 3, wherein the steel further contains Ni: 1.0% by weight or less.