JP3607583B2 - Steel for power transmission parts and power transmission parts - Google Patents
Steel for power transmission parts and power transmission parts Download PDFInfo
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- JP3607583B2 JP3607583B2 JP2000234770A JP2000234770A JP3607583B2 JP 3607583 B2 JP3607583 B2 JP 3607583B2 JP 2000234770 A JP2000234770 A JP 2000234770A JP 2000234770 A JP2000234770 A JP 2000234770A JP 3607583 B2 JP3607583 B2 JP 3607583B2
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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,および部品に関して,良好な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ついて提案する。
【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,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,ド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,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,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,円盤状部品の上をローラが転動する時,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,良好な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】
【解決しようとする課題】
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いるが,本用途に対して疲労寿命向上効果が十分ではない。また,特開平10−103440は表面硬化処理として浸炭を採用しているが,浸炭や浸炭窒化含めた方法は,十分な疲労寿命向上効果が得られておらず,また,これらの処理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問題があった。
【0006】
これらの問題点を考慮し,本発明の目的は,熱処理として通常の焼入焼もどし,または高周波焼入において,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となる動力伝達部品,たとえばトロイダル式無段変速機等に関して,良好な接触疲労特性を示す動力伝達部品用鋼,および動力伝達部品を提供することにある。
【0007】
【課題の解決手段】
発明者らは鋭意検討を実施した結果,上記の課題を解決するために,C:0.65超〜0.90wt%,Si:0.5超〜2.0wt%,Mn:1.0wt%以下,P:0.025wt%以下,S:0.035wt%以下,Cu:0.3wt%以下,Cr:4.0超〜6.0wt%,Al:0.05wt%以下,O:0.0015wt%以下,N:0.030wt%以下,Ti:0.005wt%以下を含有し,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鋼であって,この鋼からなる部品を焼入焼もどしした時に,その部品の未固溶炭化物を除くマトリックス中の固溶C量が0.40超〜0.65wt%を有し,その部品の硬さがHv700以上になることを特徴とし,更に,Ni:1.0%以下,Mo:1.0%以下の1種および2種を含有することができ,更に,焼入および焼もどしに関して,高周波誘導加熱を用いることができる,良好な接触疲労特性を有する摩擦力により動力を伝達する動力伝達部品用鋼を提供する。
【0008】
また,更に,C:0.65超〜0.90wt%,Si:0.5超〜2.0wt%,Mn:1.0wt%以下,P:0.025wt%以下,S:0.035wt%以下,Cu:0.3wt%以下,Cr:4.0超〜6.0wt%,Al:0.05wt%以下,O:0.0015wt%以下,N:0.030wt%以下,Ti:0.005wt%以下を含有し,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鋼からなる部品を焼入焼もどしした後に,その部品の未固溶炭化物を除くマトリックス中の固溶C量が0.40超〜0.65wt%を有し,その部品の硬さがHv700以上であることを特徴とし,更に,Ni:1.0%以下,Mo:1.0%以下の1種および2種を含有することができ,更に,焼入および焼もどしに関して,高周波誘導加熱を用いることができる,良好な接触疲労特性を有する摩擦力により動力を伝達する動力伝達部品を提供する。
【0009】
以下に各合金元素の限定理由について説明する。
C:0.65超〜0.90wt%
Cは鋼の強度を保持するために必須の元素であり,焼入焼もどし処理の後に未固溶炭化物を残留させた上で所要の硬さを得るためには,0.65wt%超の含有量が必要である。しかし,その含有量が多過ぎれば,大型の共晶炭化物や粒界にネット状の炭化物を析出し易くなり,冷間および熱間加工性を阻害し製造性を悪化させるため上限を0.90wt%とした。好ましくは0.70〜0.80wt%が望ましい。
【0010】
Si:0.5超〜2.0wt%
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0.5wt%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2.0wt%とする。好ましくは1.1〜1.7wt%が望ましい。
【0011】
Mn:1.0wt%以下
Mnは鋼の焼入れ性を向上することにより基地マルテンサイトの靭性,硬度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1.0wt%とする。
P:0.025wt%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0.025wt%に規制する。
S:0.035wt%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0.035wt%とする。
【0012】
Cu:0.3wt%以下
Cuは鋼の焼入れ性,耐食性を向上させる元素であるが,しかし本発明においては,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0.3wt%とする。
Ni:1.0wt%以下
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,また焼入れ時に残留オーステナイト量が増加し,硬さが低下して疲労特性を劣化させ,さらに材料コストの上昇を招くことからその含有量は1.0wt%以下とする。
【0013】
Cr:4.0〜6.0wt%
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,炭化物を生成することで耐摩耗性を付与し,さらに,本発明において,Si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4.0wt%を超えて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し,むしろ巨大な炭化物を析出させることで返って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6.0wt%とする。
【0014】
Mo:1.0wt%以下
MoはCrと同様に炭化物形成元素であり,硬度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。本発明においては,その添加により接触疲労特性をさらに改善できることを見出したことから添加することができる。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の生成を促進させ,さらに固溶C量を確保するために焼入れ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,1.0wt%以下とする。
【0015】
Al:0.05wt%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0.05wt%とする。
O:0.0015wt%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,0.0015wt%以下に規制した。
【0016】
N:0.030wt%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0.030wt%とする。
Ti:0.005wt%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,0.005wt%以下に規制した。
焼入後のマトリックス中の固溶C量:0.40超〜0.65wt%
本発明において,部品を焼入焼もどしした時のマトリックス中の固溶C量が,摩擦力によって動力伝達する際の接触疲労特性に影響することを見出した。その向上のためにはその固溶C量を0.40超〜0.65wt%の範囲にする必要がある。0.40wt%以下になると焼入焼もどし硬さが低下して接触疲労特性の劣化を招き,また,0.65wt%を超える固溶C量になると,たとえば,必要な硬さは維持できていても接触疲労特性を劣化させることを見出したので上限を0.65wt%とした。好ましくは0.45〜0.60wt%が望ましい。
【0017】
焼入焼もどし硬さ:Hv700以上
本発明に係わる対象部品は接触荷重を受けるため,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Hv700とした。
【0018】
【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。
【0019】
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,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。
【0020】
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た素形材を用い,硬さを低減して機械加工を容易にするため,球状化焼鈍として,850℃で5hr保持後,550℃まで15℃/hrの徐冷を施した後に,所定の寸法に機械加工して,所定の焼入熱処理を施した。さらに表面を仕上加工することでスケールや脱炭層を除去して試験に供した。
【0021】
表3は各供試材の熱処理(熱処理の詳細は,表4,図2,図3及び図4に記載),および仕上加工後の表面のマトリックス中の固溶C量と表面硬さを示す。なお,図3および図4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。ここで,固溶C量はX線回折によるγ(220)の格子定数測定から求めており,表面硬さは10kgのビッカース硬度計で測定した。測定は,円盤状試験片(従動円盤)2における駆動ローラ1との接触面21において行った。
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5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6に示し,ここで,平均寿命比は鋼R(JIS−SUJ2)を1とした比で表わしている。
【0022】
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〜Jであり,表3における鋼E2および鋼E3は,鋼Eに関して熱処理条件を変化させて,マトリックス中の固溶C量および硬さを変化させたものである。また表3における鋼H2は,鋼Hの熱処理に高周波焼入を用いたものである。これらの本発明鋼は,表6に示す平均寿命比が4.1〜6.2の良好な接触疲労特性を有することがわかる。
【0023】
一方,比較鋼は表2における鋼K〜鋼Pであり,本発明鋼に対し,鋼KはC量が多く,また,鋼NはC量が低くなっており,表6に示すごとく十分な寿命向上が得られず,また,鋼LはSi量が,鋼MはCr量が本発明鋼より低く,同様に十分な寿命向上が得られていない。さらに,鋼OはTi量が本発明鋼より高く,非金属介在物が多くなっていると考えられるため十分な効果がえられていない。
ここで,鋼Pは化学成分は本発明の範囲内であるが,表3中の鋼P,P2およびP3として,それぞれ表4中の▲4▼,▲5▼および▲6▼の熱処理条件としたものであり,鋼Pは焼入温度が高く,マトリックス中の固溶C量が多くなっており,また,鋼P2は焼入温度が低く,マトリックス中の固溶C量が少なくなっており,また,鋼P3はマトリックス中の固溶C量は本発明の範囲内であるが,焼もどし温度が高く,硬さが本発明の範囲よりも低いものである。従って,これら鋼P〜P3に関して,表6に示すごとく,本発明鋼に比べて十分な寿命向上が得られていない。
【0024】
さらに,表2における鋼Q〜Tは従来鋼を示しており,表3にその熱処理とマトリックス中の固溶C量および硬さを示している。ここで,鋼QはJIS−SUJ2であり,鋼RはJIS−SCM420であり,鋼Sは特開平8−326862に相当し,鋼Tは特開平10−103440に相当するものである。いずれの従来鋼も本発明鋼に対して合金量が低く,さらに浸炭する鋼Rと鋼Tはマトリックス中の固溶C量が高く,表6に示すごとく十分な寿命向上が得られていない。これらの比較鋼および従来鋼の結果は発明の妥当性を示すものである。
【0025】
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。
【0026】
【表1】
【0027】
【表2】
【0028】
【表3】
【0029】
【表4】
【0030】
【表5】
【0031】
【表6】
【0032】
【発明の効果】
本発明は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および動力伝達部品に関して,溶製時の適正な化学成分と熱処理後の固溶C量と硬さを制御することにより,摩擦力により動力を伝達する部品に関して,一般的に用いられるSUJ2,SCM420および他の従来鋼に対して,十分な接触疲労特性向上効果を確保するものである。
【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。
【図2】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。
【図3】表3における熱処理のうち,一部の浸炭に関するヒートパターンを示す。
【図4】表3における熱処理のうち,一部の浸炭に関するヒートパターンを示す。
【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 exhibits good contact fatigue characteristics with respect to parts that transmit power by contact frictional force, such as steel and parts used in toroidal continuously variable transmissions, etc., through lubricating oil having a large friction coefficient. We propose steel for power transmission parts and power transmission parts using the steel.
[0002]
[Prior art]
Generally, gears and bearings are used as parts used in automobiles, industrial machines, etc. and subjected to contact fatigue. Gears are used as power transmission parts, especially in automobile transmissions, and bearings are used in support parts of rotating bodies, and it is important to reduce frictional force due to contact that causes power loss.
[0003]
In recent years, as an alternative to this gear-type transmission, a droidal continuously variable transmission has begun to be adopted. This toroidal continuously variable transmission does not transmit power by mechanical meshing of gears, but a driving side rotating body (referred to as a disk-shaped part or disk) and a driven side rotating body (referred to as a disk-shaped part or disk). A plurality of rollers are arranged between the two and rotated by the frictional force generated at each contact portion to transmit power. Therefore, since the roller rolls on the disk-shaped part, a spin slip occurs at the contact portion, and heat is generated. Further, a large frictional force is generated on the contact portion surface that is not in a normal rolling contact to transmit power. . For this reason, it is considered that the steel used for component parts is a very harsh environment compared to bearings. Here, the spin slip means a slip generated from a difference in peripheral speed in the contact surface when the roller rolls on the disk-shaped part.
[0004]
Conventionally, case-hardened steel represented by SCR420 and SCM420 and high carbon chromium bearing steel represented by SUJ2 are mainly used for gears and bearings with contact fatigue. However, when these steels are used in applications such as toroidal-type continuously variable transmissions, there is a problem of causing early breakage. Thus, there is a demand for steel having good contact fatigue characteristics and parts using the steel under such a special use environment.
[0005]
[Problems to be solved]
To date, steels proposed under such circumstances have been disclosed in JP-A-8-326862, JP-A-10-103440, and the like. For example, Japanese Patent Laid-Open No. 8-326862 uses induction hardening as a surface hardening treatment, but the fatigue life improving effect is not sufficient for this application. Japanese Patent Laid-Open No. 10-103440 employs carburizing as the surface hardening treatment, but the methods including carburizing and carbonitriding have not been able to obtain a sufficient fatigue life improving effect. However, there is a problem that enormous amount of time and energy are required, and environmental problems such as CO2 emission occur at the same time.
[0006]
In view of these problems, the object of the present invention is to achieve a high surface pressure, a high frictional force, a high frictional force and a high temperature in the ordinary quenching tempering or induction quenching as a heat treatment. An object of the present invention is to provide a power transmission component steel and a power transmission component that exhibit good contact fatigue characteristics with respect to a power transmission component that becomes a harsh environment, such as a toroidal continuously variable transmission.
[0007]
[Means for solving problems]
As a result of intensive studies, the inventors have found that C: more than 0.65 to 0.90 wt%, Si: more than 0.5 to 2.0 wt%, and Mn: 1.0 wt% in order to solve the above problems. Hereinafter, P: 0.025 wt% or less, S: 0.035 wt% or less, Cu: 0.3 wt% or less, Cr: more than 4.0 to 6.0 wt%, Al: 0.05 wt% or less, O: 0.0. A steel which is formed by spheroidizing a steel containing Fe and unavoidable impurities, and containing a part containing this steel. When tempering is performed, the solid solution C content in the matrix excluding the undissolved carbide of the part is more than 0.40 to 0.65 wt%, and the hardness of the part is Hv 700 or more. Furthermore, Ni: 1.0% or less, Mo: 1.0% or less Providing steel for power transmission components that can contain seeds and two types, and that can use high-frequency induction heating for quenching and tempering and that transmits power by frictional force with good contact fatigue characteristics To do.
[0008]
Furthermore, C: more than 0.65 to 0.90 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 wt% or less, Cr: more than 4.0 to 6.0 wt%, Al: 0.05 wt% or less, O: 0.0015 wt% or less, N: 0.030 wt% or less, Ti: 0.0. After quenching and tempering a part made of spheroidized steel containing 005 wt% or less, the balance being Fe and unavoidable impurities, the amount of solute C in the matrix excluding undissolved carbide of the part Is more than 0.40 to 0.65 wt%, and the hardness of the component is Hv 700 or more, and further, one of Ni: 1.0% or less, Mo: 1.0% or less, and It can contain two types, and further relates to quenching and tempering It can be used a high-frequency induction heating, to provide a power transmission part for transmitting power by frictional force with good contact fatigue properties.
[0009]
The reason for limitation of each alloy element is demonstrated below.
C: Over 0.65 to 0.90 wt%
C is an indispensable element for maintaining the strength of steel, and in order to obtain the required hardness after leaving undissolved carbide after quenching and tempering treatment, the content of C exceeds 0.65 wt%. A quantity is needed. However, if the content is too large, large eutectic carbides and net-like carbides are likely to precipitate at grain boundaries, and the upper limit is set to 0.90 wt. %. Preferably 0.70 to 0.80 wt% is desirable.
[0010]
Si: more than 0.5 to 2.0 wt%
Si is one of the important elements for the present invention, and the inventors found not only the resistance to tempering and softening but also the effect of suppressing the deterioration of the contact fatigue characteristics in the parts that transmit power by the contact friction force. . For that effect, a content exceeding 0.5 wt% is required. However, adding excessive amounts not only saturates the effect, but also raises the transformation point of the steel, so that the heat treatment temperature must be increased, and the forging and cold workability are impaired. The upper limit of Si content is 2.0 wt%. Preferably 1.1 to 1.7 wt% is desirable.
[0011]
Mn: 1.0 wt% or less Mn is an element that improves the toughness and hardness of the base martensite by improving the hardenability of the steel. However, if added excessively, softening annealing of the material becomes difficult, and workability and heat The upper limit is made 1.0 wt% in order to deteriorate the inter-workability.
P: 0.025 wt% or less P is an element that segregates at the grain boundaries and causes embrittlement of the grain boundaries when present in a large amount in steel. Therefore, it is desirable that it is as low as possible, and the upper limit is regulated to 0.025 wt%.
S: 0.035 wt% or less S is an element that improves machinability, but if added in a large amount, large metal non-inclusions such as MnS are generated, and the upper limit is set to 0.035 wt% to deteriorate fatigue characteristics. .
[0012]
Cu: 0.3 wt% or less Cu is an element that improves the hardenability and corrosion resistance of steel. However, in the present invention, if its content is too large, problems such as red heat embrittlement occur and the productivity deteriorates. The upper limit is 0.3 wt%.
Ni: 1.0 wt% or less Ni is an element effective in improving fatigue characteristics in that it strengthens the matrix in steel and improves toughness. However, if the content is increased, the effect is saturated and cold workability is inhibited, the amount of retained austenite increases during quenching, the hardness decreases to deteriorate the fatigue characteristics, and further increases the material cost. Therefore, the content is 1.0 wt% or less.
[0013]
Cr: 4.0-6.0 wt%
Cr is one of the elements essential for the present invention, and not only provides resistance to temper softening, but also provides wear resistance by forming carbides. In the present invention, Cr is added simultaneously with Si, We found an effect to suppress deterioration of contact fatigue characteristics in parts that transmit power by contact friction force. For that effect, it is necessary to add over 4.0 wt%. However, even if added excessively, the effect is saturated. Rather, precipitation may result in the precipitation of huge carbides, which may deteriorate the fatigue characteristics. 0 wt%.
[0014]
Mo: 1.0 wt% or less Mo is a carbide forming element like Cr, affects hardness and wear resistance, and further improves temper softening resistance. In the present invention, it can be added because it has been found that the contact fatigue characteristics can be further improved by the addition. However, since Mo forms a more stable carbide than Cr, increasing its content promotes the formation of large eutectic carbides that degrade fatigue properties, and further secures a solid solution C content. By increasing the quenching temperature, the heat treatment cost is increased and the steel productivity such as hot workability is adversely affected.
[0015]
Al: 0.05 wt% or less Al is unavoidable because it is used as a deoxidizer in the production of steel, and is known to bind to N and suppress the growth of crystal grains, If added excessively, it tends to be oxide inclusions and adversely affects contact fatigue characteristics, so the upper limit is made 0.05 wt%.
O: 0.0015 wt% or less O is an element that forms hard non-metallic inclusions that cause a decrease in contact fatigue characteristics by bonding with Al. Therefore, it is desirable that O be as low as possible. 0.0015 wt% or less Regulated.
[0016]
N: 0.030 wt% or less N is known to bind to Al and suppress the growth of crystal grains, and can be added for its effect, but if added excessively, casting defects Therefore, the upper limit of the content is set to 0.030 wt%.
Ti: 0.005 wt% or less Ti binds to N and easily forms large and hard non-metallic inclusions and degrades contact fatigue characteristics. did.
Solid solution C amount in matrix after quenching: more than 0.40 to 0.65 wt%
In the present invention, it has been found that the amount of dissolved C in the matrix when quenching and tempering a part affects the contact fatigue characteristics when power is transmitted by frictional force. In order to improve this, the amount of dissolved C needs to be in the range of more than 0.40 to 0.65 wt%. If it becomes 0.40 wt% or less, the quenching and tempering hardness decreases and the contact fatigue characteristics are deteriorated. If the amount of solute C exceeds 0.65 wt%, for example, the necessary hardness can be maintained. However, since it was found that the contact fatigue characteristics were deteriorated, the upper limit was set to 0.65 wt%. Preferably 0.45 to 0.60 wt% is desirable.
[0017]
Quenching and tempering hardness: Hv700 or higher Since the target part according to the present invention receives a contact load, it is necessary to prevent plastic deformation and withstand the surface pressure, so the lower limit is set to Hv700.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The inventors considered that it was necessary to carry out a test that reproduced the environment in which the target steel or part was used in order to achieve the present invention. That is, the test must take into account high surface pressure, power transmission by frictional force, high temperature, and spin slip in the contact surface.
[0019]
FIG. 1 shows a contact fatigue tester used in a test according to the present invention. In this testing machine, a
[0020]
Table 1 shows the characteristics of this testing machine, a roller pitching testing machine generally used as a substitute evaluation of gears, and a thrust type rolling life testing machine used as a substitute evaluation of bearings. From Table 1, this testing machine is suitable for evaluating parts that transmit power by contact friction force with spin slip.
Table 2 shows a list of chemical components of the test materials that have been subjected to various studies in order to achieve the present invention. These specimens are melted with VIM, and after batch rolling, they are shaped by hot forging and upsetting forging, and spheroidized to reduce hardness and facilitate machining. As annealing, after holding at 850 ° C. for 5 hours, and then gradually cooling to 550 ° C. at 15 ° C./hr, it was machined to a predetermined size and subjected to a predetermined quenching heat treatment. Furthermore, the surface and the decarburized layer were removed by finishing the surface and used for the test.
[0021]
Table 3 shows the amount of solute C and surface hardness in the matrix of the surface after heat treatment (details of heat treatment are described in Table 4, FIG. 2, FIG. 3 and FIG. 4), and finish processing. . In FIG. 3 and FIG. P. Means the carbon potential in a carburizing atmosphere. Here, the amount of dissolved C was determined from the measurement of the lattice constant of γ (220) by X-ray diffraction, and the surface hardness was measured with a 10 kg Vickers hardness tester. The measurement was performed on the
These specimens were tested in the contact fatigue tester shown in FIG. 1 under the conditions shown in Table 5, and the contact fatigue characteristics were measured as the number of revolutions until the occurrence of peeling damage on the contact surface. The results are shown in Table 6, where the average life ratio is expressed as a ratio where steel R (JIS-SUJ2) is 1.
[0022]
Examples according to the present invention will be described below. The steels of the present invention are steels A to J in Table 2. Steels E2 and E3 in Table 3 are obtained by changing the heat treatment conditions for steel E and changing the amount of solid solution C and hardness in the matrix. is there. Steel H2 in Table 3 uses induction hardening for the heat treatment of steel H. It can be seen that these steels of the present invention have good contact fatigue characteristics with an average life ratio shown in Table 6 of 4.1 to 6.2.
[0023]
On the other hand, the comparative steels are steel K to steel P in Table 2, and steel K has a larger C content and steel N has a lower C content than the steel of the present invention, and is sufficient as shown in Table 6. The life cannot be improved, and the steel L has a lower Si content and the steel M has a lower Cr content than the steel according to the present invention. Furthermore, steel O has a higher Ti content than the steel of the present invention, and is considered to have more non-metallic inclusions, so a sufficient effect is not obtained.
Here, the chemical composition of the steel P is within the scope of the present invention, but the steel P, P2, and P3 in Table 3 are the heat treatment conditions of (4), (5), and (6) in Table 4, respectively. Steel P has a high quenching temperature and a large amount of solute C in the matrix, and Steel P2 has a low quenching temperature and a small amount of solute C in the matrix. Steel P3 has a solute C content in the matrix within the range of the present invention, but has a high tempering temperature and a hardness lower than the range of the present invention. Therefore, regarding these steels P to P3, as shown in Table 6, a sufficient life improvement is not obtained as compared with the steel of the present invention.
[0024]
Further, steels Q to T in Table 2 show conventional steels, and Table 3 shows the heat treatment, the amount of dissolved C in the matrix, and hardness. Here, the steel Q is JIS-SUJ2, the steel R is JIS-SCM420, the steel S corresponds to JP-A-8-326862, and the steel T corresponds to JP-A-10-103440. None of the conventional steels has a lower alloy amount than the steel of the present invention, and the carburized steel R and steel T have a high amount of solute C in the matrix, and as shown in Table 6, a sufficient improvement in life has not been obtained. The results of these comparative steels and conventional steels show the validity of the invention.
[0025]
Although the embodiment of the present invention has been described in detail above, this is merely an example, and can be applied to steel for power transmission parts and power transmission parts that transmit power by frictional force without departing from the intention of the present invention. is there.
[0026]
[Table 1]
[0027]
[Table 2]
[0028]
[Table 3]
[0029]
[Table 4]
[0030]
[Table 5]
[0031]
[Table 6]
[0032]
【The invention's effect】
The present invention relates to steel for power transmission parts and power transmission parts that contact with each other via lubricating oil and transmit power by utilizing the frictional force, and appropriate chemical components at the time of melting and the amount of solute C after heat treatment. By controlling the hardness, it is possible to secure a sufficient effect of improving contact fatigue characteristics with respect to parts that transmit power by frictional force as compared to SUJ2, SCM420 and other conventional steels that are generally used.
[Brief description of the drawings]
FIG. 1 shows an outline of a contact fatigue testing machine for measuring contact fatigue characteristics of the present invention.
FIG. 2 shows a heat pattern related to induction hardening among the heat treatments in Table 3.
FIG. 3 shows a heat pattern related to partial carburization in the heat treatment in Table 3.
FIG. 4 shows a heat pattern related to partial carburization in the heat treatment in Table 3.
[Explanation of symbols]
1. . . Driving roller,
2. . . Disk-shaped specimen (driven disk),
21. . . Contact surface,
3. . . Drive motor,
4). . . Power absorber,
Claims (6)
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US9890446B2 (en) | 2010-03-30 | 2018-02-13 | Nippon Steel & Sumitomo Metal Corporation | Steel for induction hardening roughly shaped material for induction hardening |
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