JP3687275B2

JP3687275B2 - Non-tempered steel for induction hardening

Info

Publication number: JP3687275B2
Application number: JP16318097A
Authority: JP
Inventors: 幸一郎井上; 貞行中村
Original assignee: Daido Steel Co Ltd
Current assignee: Daido Steel Co Ltd
Priority date: 1997-05-19
Filing date: 1997-05-19
Publication date: 2005-08-24
Anticipated expiration: 2017-05-19
Also published as: JPH10317095A

Description

【０００１】
【発明の属する技術分野】
本発明は，熱間鍛造で成形される機械構造用部品で機械加工後，高周波焼入により表面硬化処理を施す部品，例えば変速ギヤ，無段変速機用転動体，等速ジョイントアウターレース，ドライブシャフトその他で曲げ疲労強度，ねじり疲労強度および転がり接触疲労強度に優れた高強度高周波焼入用鋼に関する。
【０００２】
【従来の技術】
中炭素鋼に微量のＶを添加した非調質鋼は熱間鍛造後の焼入・焼戻し処理を省略しても目的とした強度が得られるため，広く機械構造用部品に適用されている。このような非調質鋼鍛造品において高い接触疲労強度や曲げ，ねじり疲労強度が要求される部品には熱間鍛造後，機械加工を施した後に高周波焼入を行うことが一般的である。しかし，中炭素鋼に微量のＶを添加した従来の非調質鋼は初析フェライト面積率が多く，均質な高周波焼入組織を得るためには十分に長い時間加熱する必要があった。
【０００３】
近年ではこれらの部品に対してさらなる高強度化が要求されており，０．１〜１．０ｓｅｃ．の超短時間の加熱で部品形状に沿った焼入を行う技術が開発されている。このような高周波輪郭焼入技術を用いた焼入材は高い圧縮残留応力が付与されるため，優れた強度を得られることが特徴である。従来の非調質鋼に加熱時間の短い高周波輪郭焼入技術を適用する場合には前にも述べた理由により均質な硬化層を得ることができず，かえって強度が低下する問題があった。
【０００４】
また，非調質鋼でない炭素鋼では，高周波輪郭焼入の場合には均質な硬化層組織を得るために熱間鍛造後に焼入・焼戻しなどの調質処理を行うことが行われているが，非調質鋼は調質処理を行わないのが特徴であり調質処理を行うことはその工程省略によるコストメリットを失うことになり好ましくない。
【０００５】
【発明が解決しようとする課題】
本発明は，上記のような事情を背景としてなされたもので，本発明の目的とするところは，熱間鍛造後に目的とする部品形状に加工し，調質処理を行うことなく，超短時間加熱の高周波輪郭焼入で均質な硬化層組織が得られ，高い曲げまたはねじり疲労強度および転がり接触疲労強度を有する高周波輪郭焼入用非調質鋼に関する。
【０００６】
【課題を解決するための手段】
本発明は，種々の合金元素の組み合わせについて検討した結果，曲げまたはねじり疲労強度および転がり接触疲労強度を向上させるためにはＣ含有量を通常のＳ４０Ｃ〜Ｓ４５Ｃの炭素鋼より高い０．４５％以上の添加とした。また，Ｃ，Ｍｎ，Ｃｒ含有量と初析フェライト面積率の関係を調査し各々の合金元素が下式で表わされる焼入性指数が０．３以下となる様に調整することにより超短時間でも均質な硬化層を得ることができることを見い出した。
焼入性指数：１．２−１．４×Ｃ（％）−０．２８×Ｍｎ（％）−０．４９×Ｃｒ（％）≦０．３
【０００７】
また，場合によってはＢを添加することにより焼入性を向上させるとともに硬化層組織の強度を改善した。これにより熱間鍛造後に目的とする部品形状に加工し，調質処理を行うことなく，超短時間加熱の高周波輪郭焼入で均質な硬化層組織が得られ，高い曲げまたはねじり疲労強度および転がり接触疲労強度を有する高周波輪郭焼入用非調質鋼を開発した。
【０００８】
すなわち、本発明の高強度高周波焼入用鋼は、基本的な合金組成としては、重量基準で、Ｃ：０．４５〜０．８０％、Ｓｉ：０．０１〜１．００％、Ｍｎ：０．６０〜１．５０％、Ｃｒ：０．１０〜１．００％、Ｖ：０．０５〜０．２５％、およびｓ−Ａｌ：０．０１５〜０．０５０％を含有し、残部Ｆｅおよび不純物からなり、かつ、下記の式により定義される焼入性指数が０．３以下である高周波輪郭焼入用非調質鋼である。
焼入性指数：１．２−１．４×Ｃ(％)−０．２８×Ｍｎ(％)−０．４９×Ｃｒ(％)
【０００９】
本発明の高周波輪郭焼入用非調質鋼は、変更態様として、上記の基本的な合金成分に加えて、重量基準で、Ｂ：０．０００５〜０．００５０％、およびＴｉ：０．００５〜０．０５０％を含有することができる。さらにこの非調質鋼は、上記の基本的な合金成分に加えて、または上記の変更態様に従う合金成分に加えて、重量基準で、Ｓ：０．２０％以下およびＴｅ：０．１０％以下の１種または２種を含有することができる。
【００１０】
以下に各合金成分の限定理由について説明する。
Ｃ：０．４５〜０．８０％
Ｃは高周波焼入後，鋼の強度を保持するための必須の元素であり，高周波焼入後の表面硬さを確保し，静的強度や曲げ疲労強度および転がり接触疲労強度を向上させるために０．４５％以上添加する必要がある。しかし，その含有量が０．８０％の共析点を超えて添加するとむしろ表面硬さが低下し，強度向上の劣化を招く。また，初析セメンタイトが生成して靭性を損なうなどの弊害をもたらすので，Ｃ含有量の上限を０．８０％にした。
【００１１】
Ｓｉ：０．０１〜１．００％
Ｓｉは溶製時の脱酸剤として作用する元素である。しかし多量に添加すると被削性や熱間加工性を低下させるので０．０１〜１．００％に規定した。
【００１２】
Ｍｎ：０．６０〜１．５０％
Ｍｎは溶製時の脱酸剤として作用する元素であり、また高周波焼入性を向上させる元素である。この効果は、０．１０％以上の添加により認められるが、０．６０％以上の添加で確実になる。過剰に添加すると、熱間鍛造後ベイナイトが発生して、被削性を低下させる。このため、Ｍｎ含有量の上限を１．５０％とする。
【００１３】
Ｃｒ：０．１０〜１．００％
ＣｒはＭｎと同様に高周波焼入性を向上させる元素であるが，多量の添加はベイナイトの生成により素材硬さを高め被削性および加工性を劣化させるので０．１０〜１．００％に規定した。
【００１４】
Ｖ：０．０５〜０．２５％
Ｖは熱間鍛造後、空冷時に炭窒化物として微細析出し強度を高める元素であり、調質処理を行うことなく目的とする強度を得ることができる、非調質鋼には必須の元素である。このような効果を得るためには０．０５％以上の添加が必要である。しかし、多量の添加は経済的に不利となるため、０．２５％以下とする必要がある。
【００１５】
ｓ−Ａｌ：０．０１５〜０．０５０％
ｓ−Ａｌは溶製時の脱酸剤として作用する元素であり，０．０１５％以上添加する必要がある．しかし，多量に添加すると靭性や疲労強度の低下をきたすので０．０５０％以下に限定した．
【００１６】
Ｂ：０．０００５〜０．００５０％
Ｂは焼入性を高め安定した硬化層深さを得るために役立つとともにＭｎ，Ｃｒ含有量の変化による焼入性の変動を効果的に抑制することができる。この効果を安定して得るためにも０．０００５％以上の添加を必要とする。しかし，過剰に添加してもその効果はかえって低下するので上限を０．００５０％以下にした。
【００１７】
Ｔｉ：０．００５〜０．０５０％
Ｔｉは鋼中のＮと結びつき，ＴｉＮ化合物の生成によりＢＮ化合物の生成を抑制し，Ｂによる焼入性向上効果を確保するために必要な元素である。このため，Ｂを添加する場合には必ず添加する必要がある。しかし，多量に添加すると靭性や疲労強度の低下をきたすので０．００５〜０．０５０％に限定した。また，Ｔｉ望ましい添加量はＴｉ／Ｎ≧３．４である。
【００１８】
Ｓ：０．２０％以下
Ｔｅ：０．１０％以下
Ｓ，Ｔｅは被削性を高める元素であって，それぞれ０．２０％以下，０．１０％以下の範囲で単独に，または複合添加しても良い。ただしこれ以上添加すると機械的性質が劣化するので上限を定めた。
【００１９】
焼入性指数：１．２−１．４×Ｃ（％）−０．２８×Ｍｎ（％）−０．４９×Ｃｒ（％）≦０．３
上述した式で示される焼入性指数が０．３を超えるとでは熱間鍛造後の初析フェライト量が多く超短時間の焼入では均質な硬化層が得られず，高周波焼入後も充分な強度を得ることができない。
【００２０】
【実施例】
表１に示す化学組成をもつ各鋼材を高周波誘導炉で溶解し１５０ｋｇの鋼塊に鋳造した。その後，１２００℃で熱間鍛造し直径３２ｍｍの丸棒にした。鍛造後は適当な間隔をおいて室温まで放冷した。たこれらの丸棒より下記の試験条件にて転動試験，回転曲げ疲労試験を下記の条件で行い評価した。その結果を表２に示す。また実施例に示される鋼には通常の鋼に含まれるＰ：０．０３０％以下，Ｃｕ：０．３０％以下，Ｎｉ：０．２０％以下，Ｎ：０．０３０％以下，Ｏ：０．００３％以下の不純物が含有されている．
【００２１】
転動試験は試験部直径１２．３ｍｍの疲労試験片を削りだし，周波数：１５０ｋＨｚ，方式：定置焼入，加熱時間：０．３ｓ，電力：６００ｋＷ，最高加熱温度：９８０℃，冷却水：水，焼戻し：なしの条件で高周波焼入焼戻し処理を施した。試験はラジアル型転動試験機により，ＳＵＪ２製ボールを用いて面圧５８８０ＭＰａにて試験を実施した。回転曲げ疲労試験は応力集中係数１．８の切欠きを有し，切欠き底半径８ｍｍの試験片を用い周波数：１５０ｋＨｚ，方式：定置焼入，加熱時間：０．２５ｓ，電力：６００ｋＷ，最高加熱温度：９８０℃，冷却水：水，焼戻し：なしの条件で高周波焼入焼戻し処理を施し小野式回転曲げ疲労試験を行った。
【００２２】
被削性は歯切り試験によって行った。１５０ｋｇ鋼塊を直径９０ｍｍの丸棒に鍛造し，これを１１００℃で１時間の焼ならし処理により非調質鍛造をシミュレーションした。その後，焼ならしままで直径８６．４ｍｍの試験片に加工し，表３に示した条件で試験に供した。表２に示す工具寿命はクレーター磨耗が５０μｍに達した時点とし，従来鋼Ｂの工具寿命を１としたときの相対値で示した。
【００２３】
【表１】

【００２４】
【表２】

【００２５】
【表３】

【００２６】
表１の実施例１〜１２は本発明にかかわる成分組成および焼入性指数の全ての条件を満足する実施例であり，回転曲げ疲労強度，転動疲労特性および歯切り被削性のすべてに優れている。また，快削元素を添加した９，８，１１，１２鋼は同じ硬さの発明鋼に比べて被削性が改善されていることがわかる。
【００２７】
これに対して比較鋼Ａ，ＢはＣ含有量が請求範囲外であり，Ａ鋼はＣ含有量が低すぎるために硬化層の焼入硬さが低く強度が低下している。また，Ｂ鋼はＣ含有量が多すぎるために初析セメンタイトが発生し強度を低下させている。
【００２８】
比較鋼Ｃ，Ｄ，Ｅ，ＦはそれぞれＳｉ，Ｍｎ，Ｃｒ，Ｖ含有量が高すぎるため熱間鍛造後の素材硬さが高くなりすぎて被削性を著しく低下させている。
【００２９】
比較鋼Ｇはｓ−Ａｌ含有量が低すぎるために熱間鍛造後の結晶粒が粗大化し，強度が低下している。また，比較鋼Ｈはｓ−Ａｌ含有量が高すぎるため，Ａｌの窒化物が過剰に生成し，強度を低下させている。
【００３０】
比較鋼ＪはＴｉ含有量が高すぎるためにＴｉの炭窒化物が介在物として多量に存在するため強度低下を招いている。また，比較鋼Ｌは化学成分は請求範囲内であるが，焼入性指数が大きすぎるために超短時間高周波加熱では均質な硬化層組織が得られず，強度が低下している。
【００３１】
比較鋼ｌ，ＫはＳ，Ｔｅを過剰に添加しているため被削性は大きく改善されるが強度は低下している。
【００３２】
【発明の効果】
以上説明してきたように，本発明の高周波輪郭焼入用非調質鋼は重量基準でＣ：０．４５〜０．８０％，Ｓｉ：０．０１〜１．００％，Ｍｎ：０．１０〜１．５０％，Ｃｒ：０．１０〜１．００％，Ｖ：０．０５〜０．３０％，ｓ−Ａｌ：０．０１５〜０．０５０％また，必要に応じて，Ｂ：０．０００５〜０．００５０％，Ｔｉ：０．００５〜０．０５０％を含有すことができ，同じく必要に応じてＳ：０．２０％以下，Ｔｅ：０．１０％以下のうちから選ばれる１種または２種以上を含み，残部Ｆｅおよび不純物よりなり，かつ下記の式を満たすことを特徴とし，熱間鍛造後に目的とする部品形状に加工したのち調質処理を行うことなく，超短時間加熱の高周波輪郭焼入で均質な硬化層組織が得られ，高い曲げまたはねじり疲労強度および転がり接触疲労強度を有する高強度高周波焼入用非調質鋼を得ることができる。
焼入性指数：１．２−１．４×Ｃ（％）−０．２８×Ｍｎ（％）−０．４９×Ｃｒ（％）≦０．３[0001]
BACKGROUND OF THE INVENTION
The present invention is a machine structural part formed by hot forging, and is subjected to surface hardening treatment by induction hardening, such as a transmission gear, a continuously variable transmission rolling element, a constant velocity joint outer race, a drive, etc. The present invention relates to a high strength induction hardening steel excellent in bending fatigue strength, torsional fatigue strength and rolling contact fatigue strength in shafts and others.
[0002]
[Prior art]
Non-tempered steel obtained by adding a small amount of V to medium carbon steel is widely applied to machine structural parts because the desired strength can be obtained even if the quenching and tempering treatment after hot forging is omitted. In such non-tempered steel forgings, parts that require high contact fatigue strength, bending and torsional fatigue strength are generally subjected to induction hardening after hot forging and machining. However, the conventional non-tempered steel in which a small amount of V is added to the medium carbon steel has a large proeutectoid ferrite area ratio, and it is necessary to heat it for a sufficiently long time in order to obtain a homogeneous induction hardened structure.
[0003]
In recent years, there has been a demand for higher strength for these parts, and 0.1 to 1.0 sec. Technology has been developed for quenching along the shape of the part by heating for a very short time. A hardened material using such a high-frequency contour quenching technique is characterized by being able to obtain an excellent strength because it is imparted with a high compressive residual stress. When applying high-frequency contour quenching technology with a short heating time to conventional non-tempered steel, a uniform hardened layer cannot be obtained for the reason described above, and there is a problem that the strength is lowered.
[0004]
In the case of carbon steel that is not non-tempered steel, tempering treatment such as quenching and tempering is performed after hot forging in order to obtain a homogeneous hardened layer structure in the case of induction hardening. , Non-tempered steel is characterized by not performing tempering treatment, and performing tempering treatment is not preferable because it loses the cost merit by omitting the process.
[0005]
[Problems to be solved by the invention]
The present invention has been made in the background as described above, and the object of the present invention is to process into an intended part shape after hot forging and perform a tempering process for a very short time. The present invention relates to a non-heat treated steel for high-frequency contour quenching that has a uniform hardened layer structure obtained by high-frequency contour quenching and has high bending or torsional fatigue strength and rolling contact fatigue strength.
[0006]
[Means for Solving the Problems]
As a result of studying combinations of various alloy elements, the present invention has a C content of 0.45% or more higher than that of ordinary S40C to S45C carbon steel in order to improve bending or torsional fatigue strength and rolling contact fatigue strength. Was added. In addition, by investigating the relationship between the C, Mn, Cr content and the pro-eutectoid ferrite area ratio, and adjusting each alloy element so that the hardenability index represented by the following formula is 0.3 or less, ultra-short time However, it has been found that a homogeneous hardened layer can be obtained.
Hardenability index: 1.2-1.4 × C (%) − 0.28 × Mn (%) − 0.49 × Cr (%) ≦ 0.3
[0007]
Further, in some cases, by adding B, the hardenability was improved and the strength of the hardened layer structure was improved. As a result, a uniform hardened layer structure can be obtained by high-frequency contour quenching with ultra-short heating without processing to the desired part shape after hot forging, and with high bending or torsional fatigue strength and rolling. A non-tempered steel for induction hardening with high contact fatigue strength was developed.
[0008]
That is, the high strength induction hardening steel of the present invention has a basic alloy composition of C: 0.45 to 0.80%, Si: 0.01 to 1.00%, Mn: Containing 0.60 to 1.50%, Cr: 0.10 to 1.00%, V: 0.05 to 0.25%, and s-Al: 0.015 to 0.050%, the balance being Fe And a non-tempered steel for high-frequency contour quenching that has a hardenability index defined by the following formula and is 0.3 or less.
Hardenability index: 1.2-1.4 × C (%) − 0.28 × Mn (%) − 0.49 × Cr (%)
[0009]
The non-heat treated steel for high-frequency contour quenching of the present invention has, as a modification, B: 0.0005 to 0.0050% and Ti: 0.005 on a weight basis in addition to the above basic alloy components. It can contain up to 0.050%. Further, the non-tempered steel has an S: 0.20% or less and a Te: 0.10% or less on a weight basis in addition to the above basic alloy components or in addition to the alloy components according to the above-described modification. 1 type or 2 types of can be contained.
[0010]
The reason for limiting each alloy component will be described below.
C: 0.45-0.80%
C is an indispensable element for maintaining the strength of steel after induction hardening, in order to ensure the surface hardness after induction hardening and to improve static strength, bending fatigue strength and rolling contact fatigue strength. It is necessary to add 0.45% or more. However, if its content exceeds the eutectoid point of 0.80%, the surface hardness is rather lowered, leading to deterioration of strength improvement. In addition, since the proeutectoid cementite is formed and the toughness is impaired, the upper limit of the C content is set to 0.80%.
[0011]
Si: 0.01-1.00%
Si is an element that acts as a deoxidizer during melting. However, if added in a large amount, the machinability and hot workability are lowered, so the content was specified to be 0.01 to 1.00%.
[0012]
Mn: 0.60 to 1.50%
Mn is an element that acts as a deoxidizer during melting, and is an element that improves induction hardenability. This effect is recognized by addition of 0.10% or more, but is ensured by addition of 0.60% or more. If excessively added, bainite is generated after hot forging, and machinability is lowered. For this reason, the upper limit of the Mn content is set to 1.50%.
[0013]
Cr: 0.10 to 1.00%
Cr, like Mn, is an element that improves induction hardenability, but adding a large amount increases the material hardness due to the formation of bainite and degrades machinability and workability, so 0.10 to 1.00% Stipulated.
[0014]
V: 0.05-0.25%
V is an element that, after hot forging, finely precipitates as carbonitride during air cooling and increases the strength, and is an essential element for non-tempered steel that can obtain the desired strength without tempering treatment. is there. In order to obtain such an effect, addition of 0.05% or more is necessary. However, since a large amount of addition becomes economically disadvantageous, it is necessary to make it 0.25% or less.
[0015]
s-Al: 0.015 to 0.050%
s-Al is an element that acts as a deoxidizer during melting, and it is necessary to add 0.015% or more. However, when added in a large amount, the toughness and fatigue strength are lowered, so it was limited to 0.050% or less.
[0016]
B: 0.0005 to 0.0050%
B is useful for increasing hardenability and obtaining a stable hardened layer depth, and can effectively suppress variation in hardenability due to changes in Mn and Cr contents. In order to stably obtain this effect, 0.0005% or more must be added. However, even if it is added excessively, the effect is reduced, so the upper limit was made 0.0050% or less.
[0017]
Ti: 0.005 to 0.050%
Ti is an element necessary for binding to N in steel, suppressing the formation of a BN compound by the formation of a TiN compound, and ensuring the effect of improving the hardenability by B. For this reason, it is necessary to add B whenever B is added. However, if added in a large amount, the toughness and fatigue strength are lowered, so the content is limited to 0.005 to 0.050%. Further, a desirable addition amount of Ti is Ti / N ≧ 3.4.
[0018]
S: 0.20% or less Te: 0.10% or less S and Te are elements for improving the machinability, and are added individually or in combination in the range of 0.20% or less and 0.10% or less, respectively. May be. However, since the mechanical properties deteriorate if added more than this, an upper limit was set.
[0019]
Hardenability index: 1.2-1.4 × C (%) − 0.28 × Mn (%) − 0.49 × Cr (%) ≦ 0.3
If the hardenability index expressed by the above formula exceeds 0.3, the amount of pro-eutectoid ferrite after hot forging is large, and a uniform hardened layer cannot be obtained by quenching for a very short time. Sufficient strength cannot be obtained.
[0020]
【Example】
Each steel material having the chemical composition shown in Table 1 was melted in a high frequency induction furnace and cast into a 150 kg steel ingot. Thereafter, it was hot forged at 1200 ° C. to obtain a round bar having a diameter of 32 mm. After forging, it was allowed to cool to room temperature at an appropriate interval. From these round bars, a rolling test and a rotating bending fatigue test were performed under the following conditions and evaluated. The results are shown in Table 2. Further, the steels shown in the examples include P: 0.030% or less, Cu: 0.30% or less, Ni: 0.20% or less, N: 0.030% or less, O: 0 contained in ordinary steel. .003% or less of impurities are contained.
[0021]
In the rolling test, a fatigue test piece having a diameter of 12.3 mm in the test part was cut out, frequency: 150 kHz, method: stationary quenching, heating time: 0.3 s, power: 600 kW, maximum heating temperature: 980 ° C., cooling water: water , Tempering: Induction quenching and tempering were performed under the conditions of none. The test was carried out with a radial rolling tester using SUJ2 balls at a surface pressure of 5880 MPa. The rotating bending fatigue test has a notch with a stress concentration factor of 1.8, uses a test piece with a notch bottom radius of 8 mm, frequency: 150 kHz, method: stationary quenching, heating time: 0.25 s, power: 600 kW, maximum An ono type rotary bending fatigue test was performed by induction hardening and tempering under the conditions of heating temperature: 980 ° C., cooling water: water, and tempering: none.
[0022]
Machinability was performed by a gear cutting test. A 150 kg steel ingot was forged into a round bar with a diameter of 90 mm, and a non-tempered forging was simulated by normalizing at 1100 ° C. for 1 hour. Then, it processed into the test piece of diameter 86.4mm until normalizing, and used for the test on the conditions shown in Table 3. The tool life shown in Table 2 is the relative value when the tool life of the conventional steel B is 1 when the crater wear reaches 50 μm.
[0023]
[Table 1]

[0024]
[Table 2]

[0025]
[Table 3]

[0026]
Examples 1 to 12 in Table 1 are examples that satisfy all the conditions of the component composition and the hardenability index according to the present invention, and all of the rotational bending fatigue strength, rolling fatigue characteristics, and gear cutting machinability. Are better. It can also be seen that the 9, 8, 11, and 12 steels to which free-cutting elements are added have improved machinability compared to the invention steels with the same hardness.
[0027]
On the other hand, the C contents of the comparative steels A and B are outside the claimed range, and the steel A has a low quenching hardness and a low strength because the C content is too low. Further, since the steel B has too much C content, pro-eutectoid cementite is generated and the strength is lowered.
[0028]
Since the comparative steels C, D, E, and F have too high contents of Si, Mn, Cr, and V, respectively, the material hardness after hot forging becomes too high and the machinability is remarkably lowered.
[0029]
Since the comparative steel G has a too low s-Al content, the crystal grains after hot forging are coarsened and the strength is reduced. In addition, since the comparative steel H has an excessively high s-Al content, an excessive amount of Al nitride is generated to reduce the strength.
[0030]
Since the comparative steel J has a too high Ti content, a large amount of Ti carbonitrides are present as inclusions, resulting in a decrease in strength. Further, although the chemical composition of the comparative steel L is within the claimed range, since the hardenability index is too large, a uniform hardened layer structure cannot be obtained by ultrashort high-frequency heating, and the strength is reduced.
[0031]
In comparison steels 1 and K, since S and Te are added excessively, the machinability is greatly improved, but the strength is lowered.
[0032]
【The invention's effect】
As described above, the non-heat treated steel for high-frequency contour quenching according to the present invention is C: 0.45-0.80%, Si: 0.01-1.00%, Mn: 0.10 on a weight basis. To 1.50%, Cr: 0.10 to 1.00%, V: 0.05 to 0.30%, s-Al: 0.015 to 0.050%, and, if necessary, B: 0 .0005 to 0.0050%, Ti: 0.005 to 0.050% can be contained, and if necessary, S is selected from 0.20% or less, Te: 0.10% or less. It is characterized by including one or more types, the balance Fe and impurities, and satisfying the following formula. A homogeneous hardened layer structure is obtained by high-frequency contour quenching with time heating, and high bending or torsional fatigue strength is achieved. Fine rolling contact fatigue strength can be obtained high strength induction hardening microalloyed steel having.
Hardenability index: 1.2-1.4 × C (%) − 0.28 × Mn (%) − 0.49 × Cr (%) ≦ 0.3

Claims

On a weight basis, C: 0.45-0.80%, Si: 0.01-1.00%, Mn: 0.00. 60 to 1.50%, Cr: 0.10 to 1.00%, V: 0.05 to 0. 25%, and s-Al: containing from 0.015 to 0.050%, having a Ru alloy composition Na balance being Fe and impurities, and the hardenability index defined by the following formula 0.3 frequency contour hardening microalloyed steels, characterized in that at most.
Hardenability index: 1.2-1.4 × C (%) − 0.28 × Mn (%) − 0.49 × Cr (%)

In addition to the alloy components defined in claim 1, further B: 0.0005 to 0.0050% and Ti: frequency contour hardening of claim 1 having the alloy composition you containing from 0.005 to 0.050 percent For non-tempered steel.

In addition to the alloy components defined in claim 1, further S: 0.20% or less and Te: frequency contour hardening of claim 1 having the alloy composition you contain one or 0.10% of For non-tempered steel.

In addition to the alloy components defined in claim 1, in addition to B: 0.0005 to 0.0050% and Ti: 0.005 to 0.050%, S: 0.20% or less and Te: 0.0. 10% or less of one or high frequency contour hardening microalloyed steel according to claim 1 having the alloy composition you containing two.