JP5969204B2 - Induction hardened gear having excellent wear resistance and surface fatigue characteristics and method for producing the same - Google Patents

Induction hardened gear having excellent wear resistance and surface fatigue characteristics and method for producing the same Download PDF

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JP5969204B2
JP5969204B2 JP2011257489A JP2011257489A JP5969204B2 JP 5969204 B2 JP5969204 B2 JP 5969204B2 JP 2011257489 A JP2011257489 A JP 2011257489A JP 2011257489 A JP2011257489 A JP 2011257489A JP 5969204 B2 JP5969204 B2 JP 5969204B2
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福岡 和明
和明 福岡
冨田 邦和
邦和 冨田
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JFE Steel Corp
JFE Bars and Shapes Corp
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本発明は自動車や各種産業機械に用いて好適な、耐摩耗性と面疲労特性を備えた歯車およびその製造方法に関する。   The present invention relates to a gear having wear resistance and surface fatigue characteristics suitable for use in automobiles and various industrial machines, and a method for manufacturing the same.

自動車等に用いられている歯車は、近年、省エネルギー化による車体重量の軽量化に伴うサイズの小型化が要求されているが、エンジンの高出力化により負荷は増大している。歯車の破損は、大きく分別して、歯の衝撃破壊、歯元の曲げ疲労破壊ならびに歯面の面圧疲労(面疲労とも言う)破壊が原因となる。   In recent years, gears used in automobiles and the like have been required to be reduced in size in accordance with the reduction in weight of the vehicle body due to energy saving, but the load has increased due to higher output of the engine. The gear breakage is largely classified, and is caused by tooth impact fracture, tooth root bending fatigue fracture and tooth surface pressure fatigue (also referred to as surface fatigue) fracture.

従来は、JISSCr420等の肌焼鋼を用いて歯車を成形し、浸炭等の表面処理を行って使用されてきた。しかし、浸炭では粒界酸化や浸炭異常層の影響による強度低下が大きく、それを避けるために素材を高合金添加系にするか、熱処理を真空雰囲気において実施することが必要となり、相当なコスト上昇が必要となる。   Conventionally, gears are formed using case-hardened steel such as JISSCr420, and surface treatment such as carburization is performed. However, in carburizing, there is a large drop in strength due to the effects of grain boundary oxidation and carburizing abnormal layers, and in order to avoid this, it is necessary to use a material with a high alloy addition system or to perform heat treatment in a vacuum atmosphere, resulting in considerable cost increase Is required.

そこで、近年、合金添加量の少ない素材に高周波焼入れによる表面硬化を施した歯車が提案されている。   Therefore, in recent years, gears obtained by subjecting a material with a small amount of alloy addition to surface hardening by induction hardening have been proposed.

たとえば、特許文献1には、高周波焼入れ部品を対象に、成分規定とともに材料内の介在物のサイズ・個数を規定することで、曲げ疲労強度および転動疲労強度を向上させることが記載されている。   For example, Patent Document 1 describes that for induction-hardened parts, the bending fatigue strength and rolling fatigue strength are improved by defining the size and number of inclusions in the material as well as the component definition. .

しかしながら、介在物のサイズ・個数の規定により曲げ疲労強度および転動疲労強度は向上するものの、介在物のサイズ・個数を制御する場合は成分組成に応じて鋳造、圧延の際の温度条件を制御することが必要となるため、製品を製造することは難しい。   However, although the bending fatigue strength and rolling fatigue strength are improved by defining the size and number of inclusions, when controlling the size and number of inclusions, the temperature conditions during casting and rolling are controlled according to the composition of the inclusions. It is difficult to manufacture a product because it is necessary to do so.

特許文献2では成分組成中のC、Si量を高めて、耐摩耗性、耐衝撃特性の向上を図っているが、C量が高いために内部の靭性が低く十分な衝撃特性の向上が得られない。   In Patent Document 2, the amount of C and Si in the component composition is increased to improve wear resistance and impact resistance characteristics. However, since the amount of C is high, internal toughness is low and sufficient impact characteristics can be improved. I can't.

また、特許文献3にはB添加によりC量を高めずに焼入性を向上させ、同時に内部の靭性向上を図った高周波焼入れ部品が記載されている。しかし、B添加だけでは衝撃特性が向上したとしても、歯車で必用な面圧疲労強度は向上しない。   Patent Document 3 describes an induction-hardened component that improves hardenability without increasing the amount of C by adding B and at the same time improves internal toughness. However, even if the addition of B alone improves the impact characteristics, the surface fatigue strength required for the gear does not improve.

特許文献4には、本発明者らが高周波焼入れにて作成される歯車について行った研究成果である、衝撃特性、曲げ疲労特性、面疲労特性の優れた歯車が記載されている。しかしながら、開発された歯車のこれらの特性は良好であったが、摩耗量が大きめで、潤滑油の交換の頻度が大きくなり、さらに摩耗により歯車装置の動力性能の損失量が大きくなり、伝達損失が増加した。   Patent Document 4 describes a gear excellent in impact characteristics, bending fatigue characteristics, and surface fatigue characteristics, which is a result of research conducted by the present inventors on gears created by induction hardening. However, these characteristics of the developed gear were good, but the amount of wear was large, the frequency of replacement of the lubricating oil increased, and the loss of power performance of the gear unit increased due to wear, resulting in transmission loss. increased.

特開平11−1749号公報Japanese Patent Laid-Open No. 11-1749 特公平04−8497号公報Japanese Patent Publication No. 04-8497 特許第3402562号Japanese Patent No. 3402562 特開2007−92107号公報JP 2007-92107 A

本発明は、上記特許文献1〜4における問題点を解決する、具体的には、現行の一般的な設備により製造可能な素材を用いた、衝撃強度、曲げ疲労強度は従来の歯車並を維持しつつ、耐摩耗性に優れ、且つ面疲労特性が従来の歯車より良好な歯車およびその製造方法を提供することを目的とする。   The present invention solves the problems in Patent Documents 1 to 4 above. Specifically, the impact strength and bending fatigue strength using the materials that can be manufactured by the current general equipment are maintained at the same level as conventional gears. However, it is an object of the present invention to provide a gear having excellent wear resistance and better surface fatigue characteristics than a conventional gear and a method for manufacturing the same.

本発明者らは、上記課題達成のため、鋭意研究を重ねて得た以下の(1)〜(5)の知見を基に、耐摩耗性、面疲労特性、すなわち面疲労強度を向上させる場合の素材の成分組成として、焼入性の管理により曲げ疲労性特性を確保した上で、焼戻軟化抵抗を高めて面疲労強度を向上させ、さらにAc変態点を高めた成分組成が有効であることを見出した。
(1)高周波焼入れ後において、現用の高周波焼入れ歯車と同等以上の優れた性能を得るためには、硬度分布を従来鋼と同等とすることが前提として必要で、焼入れ性指数:D値による調整が有効である。
(2)適量のSi、Cr量を含有することにより焼戻し軟化抵抗を高めると、歯車接触面での発熱による軟化が抑制され、歯車駆動時に歯面の亀裂発生が防止可能である。
(3)焼戻し軟化抵抗は10Si+Cr(但し、Si、Crは含有量(質量%))の値で整理される。
(4)高周波焼入れ前の焼入れ・焼戻し組織において炭化物の析出をコントロールし、高周波焼入れ後の硬化層に微細な炭化物を分散させる。それにより、高周波焼入れ部の硬さがさらに向上し、炭化物の存在により耐摩耗性が向上するとともに、焼戻しにおいて軟化が起こりにくくなる。
(5)曲げ疲労強度は、高周波焼入れ特有の結晶粒微細化効果で向上するが、さらにAc3変態点を高くして、高周波加熱後の結晶粒度を微細化すると、著しく向上する。
(5)Ac変態点の上昇による高周波焼入れ後の結晶粒微細化は、衝撃特性および面疲労強度も大きく増大させる。
In order to achieve the above-mentioned problems, the inventors have improved the wear resistance, surface fatigue characteristics, that is, surface fatigue strength, based on the following findings (1) to (5) obtained through repeated studies. As a component composition of this material, it is effective to secure a bending fatigue property by managing hardenability, to improve surface fatigue strength by increasing temper softening resistance, and to further increase the Ac 3 transformation point. I found out.
(1) In order to obtain excellent performance equal to or better than that of the current induction-hardened gear after induction hardening, it is necessary to make the hardness distribution equivalent to that of the conventional steel. Hardenability index: Adjustment by D value Is effective.
(2) If the temper softening resistance is increased by containing appropriate amounts of Si and Cr, softening due to heat generation on the gear contact surface is suppressed, and cracking of the tooth surface can be prevented when the gear is driven.
(3) The temper softening resistance is arranged by the value of 10Si + Cr (where Si and Cr are the contents (mass%)).
(4) The precipitation of carbides is controlled in the quenched and tempered structure before induction hardening, and fine carbides are dispersed in the hardened layer after induction hardening. Thereby, the hardness of the induction-hardened portion is further improved, the wear resistance is improved due to the presence of the carbide, and softening hardly occurs during tempering.
(5) The bending fatigue strength is improved by the crystal grain refinement effect peculiar to induction hardening. However, when the Ac3 transformation point is further increased and the crystal grain size after induction heating is refined, the bending fatigue strength is remarkably improved.
(5) The refinement of crystal grains after induction hardening by increasing the Ac 3 transformation point greatly increases impact characteristics and surface fatigue strength.

本発明は得られた知見をもとに更に検討を加えてなされたもので、すなわち、本発明は
1.質量%で、C:0.25〜0.65%、Si:0.70〜2.00%以上、Mn:0.30〜2.00%、Cr:1.50%以下を含有し、(1)式で計算されるZの値が15≦Z≦30で、残部がFeおよび不可避的不純物からなる成分組成を有し、高周波焼入れ部の組織が焼戻しマルテンサイト主体で内部に粒径300nm未満の炭化物が100μm2当り90個以上微細に分散していることを特徴とする耐摩耗性と面疲労特性に優れた高周波焼入れ歯車。
Z=10Si+Cr+50(D×Ceq)/A ・・・(1)
ここで、Si、Crはそれぞれの元素の含有する量(質量%)を示す。Dは焼入れ性指数、Ceqは炭素当量、AはAc変態点で、(2)、(3)、(4)式で計算された値とする。
D=8.76*√(C)*(1+0.64*Si)*(1+4.1*Mn)*(1+2.33*Cr)・・・(2)
但し、式において各合金元素は含有量(質量%)で、Bを添加した場合はD値はこの計算式による値の2倍とする。
Ceq=C+Si/7+Mn/5+Cr/9+0.023・・・(3)
但し、式において各合金元素は含有量(質量%)とする。
A=921−203√C+44.7*Si−30*Mn−11*Cr・・・(4)
但し、式において各合金元素は含有量(質量%)とする。
2.成分組成に、更に、質量%で、Nb:0.010〜0.060%、Ti:0.005〜0.050%、B:0.0005〜0.0100%の1種以上を含有することを特徴とする1記載の耐摩耗性と面疲労特性に優れた高周波焼入れ歯車。
3.1または2に記載の成分組成の鋼を、熱間鍛造を行った後に焼入れ・焼戻しを行い、その後歯車形状に加工し、表面硬化熱処理として高周波焼入れ・焼戻しを行い、高周波焼入れ部の組織を焼戻しマルテンサイト主体で内部に粒径300nm未満の炭化物が100μm2当り90個以上微細に分散しているものとすることを特徴とする、耐摩耗性と面疲労特性に優れた歯車の製造方法。
4.前記高周波焼入れ・焼戻し後、更に歯面にショットピーニングまたは研磨を行うことを特徴とする、3記載の耐摩耗性と面疲労特性に優れた歯車の製造方法。
The present invention has been made by further investigation based on the obtained knowledge. In mass%, C: 0.25 to 0.65%, Si: 0.70 to 2.00% or more, Mn: 0.30 to 2.00%, Cr: 1.50% or less, 1) The value of Z calculated by the formula is 15 ≦ Z ≦ 30, the remainder has a composition composed of Fe and inevitable impurities, the structure of the induction-hardened portion is mainly tempered martensite, and the particle size is less than 300 nm inside. An induction-hardened gear excellent in wear resistance and surface fatigue characteristics, characterized in that 90 or more carbides are finely dispersed per 100 μm 2 .
Z = 10Si + Cr + 50 (D × Ceq) / A (1)
Here, Si and Cr show the amount (mass%) which each element contains. D is a hardenability index, Ceq is a carbon equivalent, A is an Ac 3 transformation point, and is a value calculated by the equations (2), (3), and (4).
D = 8.76 * √ (C) * (1 + 0.64 * Si) * (1 + 4.1 * Mn) * (1 + 2.33 * Cr) (2)
However, in the formula, each alloy element is the content (% by mass), and when B is added, the D value is twice the value by this formula.
Ceq = C + Si / 7 + Mn / 5 + Cr / 9 + 0.023 (3)
However, the content of each alloy element in the formula (mass%).
A = 921-203√C + 44.7 * Si-30 * Mn-11 * Cr (4)
However, the content of each alloy element in the formula (mass%).
2. The component composition further contains one or more of Nb: 0.010 to 0.060%, Ti: 0.005 to 0.050%, and B: 0.0005 to 0.0100% by mass%. 2. An induction-hardened gear having excellent wear resistance and surface fatigue characteristics according to 1.
The steel having the composition described in 3.1 or 2 is quenched and tempered after hot forging, then processed into a gear shape, induction hardened and tempered as a surface hardening heat treatment, and the structure of the induction hardening portion A method for producing a gear excellent in wear resistance and surface fatigue characteristics, characterized in that 90 or more carbides having a particle size of less than 300 nm are finely dispersed in 100 μm 2 inside, mainly comprising tempered martensite .
4). 4. The method for producing a gear excellent in wear resistance and surface fatigue characteristics according to 3, wherein the tooth surface is further shot peened or polished after the induction hardening and tempering.

本発明によれば、コストの安い、設備と成分組成を用いて製造可能な耐摩耗性と面疲労特性に優れた歯車およびその製造条件が得られ、産業上極めて有用である。   According to the present invention, a gear having excellent wear resistance and surface fatigue characteristics that can be manufactured using equipment and a component composition at low cost and its manufacturing conditions can be obtained, which is extremely useful industrially.

実施例で使用した高周波熱処理のパターンを示す図で(a)は高周波焼入れ条件、(b)は焼戻し条件を示す。It is a figure which shows the pattern of the induction heat processing used in the Example, (a) shows induction hardening conditions, (b) shows tempering conditions. 実施例で使用した現行鋼No.38鋼の浸炭焼入れ・焼戻し処理のパターンを示す図。The current steel No. used in the examples. The figure which shows the pattern of the carburizing quenching and tempering process of 38 steel. ローラーピッチング試験片を説明する図。The figure explaining a roller pitching test piece.

本発明では1.素材となる鋼の成分組成、2.歯車の高周波焼入れ部のミクロ組織を規定する。以下に各限定理由について述べる。
[成分組成] 以下の説明において、%は質量%とする。
C:0.25〜0.65%
Cは強度確保のために必要であり、高周波焼入れ後の表面硬さを決定する。含有量が0.25%未満では表面硬さが500HV以下にまで低下するために歯車としての強度を確保できない。一方、0.65%を超えると歯車内部の靭性が低下して、疲労亀裂の進展が早くなるために、曲げ疲労特性が低下するため、0.25〜0.65%とする。
In the present invention, 1. 1. Component composition of steel used as material Defines the microstructure of the induction hardening part of the gear. Each limitation reason is described below.
[Component Composition] In the following description,% is mass%.
C: 0.25 to 0.65%
C is necessary for ensuring the strength, and determines the surface hardness after induction hardening. If the content is less than 0.25%, the surface hardness decreases to 500 HV or less, so that the strength as a gear cannot be ensured. On the other hand, if it exceeds 0.65%, the toughness inside the gear decreases and the fatigue crack progresses quickly, so that the bending fatigue characteristics deteriorate, so 0.25 to 0.65%.

Si:0.70〜2.00%
Siは焼戻し軟化抵抗を高め、それにより面疲労特性を向上させるのに有効な元素である。その効果を得るため0.70%以上とする。また、焼戻し軟化抵抗向上は炭化物の析出を遅らせる効果によるものであるため、高周波焼入れ前の焼入れ・焼戻し後において、炭化物を微細に析出させる事ができる。その結果、高周波焼入れの急速加熱においても、炭化物が固溶しやすくなり、高周波焼入れ後の表面硬度を高める事が出来る。更に、Ac変態点を上昇させて高周波焼入による結晶粒を微細化させる効果もある。上述した効果は2.00%を超えると飽和するので、含有量を0.70〜2.00%とする。
Si: 0.70 to 2.00%
Si is an element effective in increasing the temper softening resistance and thereby improving the surface fatigue characteristics. In order to obtain the effect, the content is made 0.70% or more. Further, since the improvement in resistance to temper softening is due to the effect of delaying the precipitation of carbides, the carbides can be finely precipitated after quenching and tempering before induction hardening. As a result, even in rapid heating by induction hardening, carbides are easily dissolved, and the surface hardness after induction hardening can be increased. Furthermore, there is an effect that the Ac 3 transformation point is raised and the crystal grains are refined by induction hardening. Since the effect mentioned above will be saturated if it exceeds 2.00%, content is made into 0.70 to 2.00%.

Mn:0.30〜2.00%
Mnは焼入れ性を高める元素であり、その効果を得るため0.30%以上とする。一方、2.00%を超えると過剰に焼入れ性が上がりすぎて靭性が劣化して曲げ疲労特性が低下する。また、加工性も劣化する、よって0.30〜2.00%とする。
Mn: 0.30 to 2.00%
Mn is an element that enhances hardenability, and is 0.30% or more in order to obtain the effect. On the other hand, if it exceeds 2.00%, the hardenability is excessively increased, the toughness is deteriorated, and the bending fatigue characteristics are lowered. Moreover, workability also deteriorates, so 0.30 to 2.00%.

Cr:1.50%以下
Crは焼入れ性と焼戻し軟化抵抗を高め、また、焼戻し時の炭化物析出にも大きく影響する元素であるため含有する。含有量が1.50%を超えると、焼入れ性が高くなりすぎるため歯車内部の靭性が劣化し、曲げ疲労強度が低下するため、1.50%以下とする。
Cr: 1.50% or less Cr is contained because it is an element that enhances hardenability and resistance to softening by tempering and greatly affects carbide precipitation during tempering. If the content exceeds 1.50%, the hardenability becomes too high, the toughness inside the gear is deteriorated, and the bending fatigue strength is lowered, so the content is made 1.50% or less.

15≦Z≦30
Zは焼戻し軟化抵抗、焼入れ性、Ac変態点を考慮したパラメータであり、Z=10Si+Cr+50(DxCeq)/A とする。ここで、Si、Crはそれぞれの元素の含有する量(質量%)を示す。Dは焼入れ性指数、Ceqは炭素当量、AはAc変態点で、以下の(2)〜(4)式で計算された値とする。
D=8.76*√(C)*(1+0.64*Si)*(1+4.1*Mn)*(1+2.33*Cr)・・・(2)
但し、式において各合金元素は含有量(質量%)で、Bを添加した場合はD値はこの計算式による値の2倍とする。
Ceq=C+Si/7+Mn/5+Cr/9+0.023・・・(3)
但し、式において各合金元素は含有量(質量%)とする。
A=921−203√C+44.7*Si−30*Mn−11*Cr・・・(4)
但し、式において各合金元素は含有量(質量%)とする。
15 ≦ Z ≦ 30
Z is a parameter in consideration of temper softening resistance, hardenability, and Ac 3 transformation point, and Z = 10Si + Cr + 50 (DxCeq) / A. Here, Si and Cr show the amount (mass%) which each element contains. D is a hardenability index, Ceq is a carbon equivalent, A is an Ac 3 transformation point, and is a value calculated by the following equations (2) to (4).
D = 8.76 * √ (C) * (1 + 0.64 * Si) * (1 + 4.1 * Mn) * (1 + 2.33 * Cr) (2)
However, in the formula, each alloy element is the content (% by mass), and when B is added, the D value is twice the value by this formula.
Ceq = C + Si / 7 + Mn / 5 + Cr / 9 + 0.023 (3)
However, the content of each alloy element in the formula (mass%).
A = 921-203√C + 44.7 * Si-30 * Mn-11 * Cr (4)
However, the content of each alloy element in the formula (mass%).

Zの値が15以上30以下の場合、面疲労強度を向上させ、且つ、衝撃強度、曲げ疲労強度を従来部品並に維持する事が可能である。Zの値が15未満では面疲労強度を向上させる効果が無く、30を超えると焼入れ性が高くなりすぎて焼き割れを起こしたり、硬さが高くなりすぎて機械加工性が低下する。   When the value of Z is 15 or more and 30 or less, the surface fatigue strength can be improved, and the impact strength and bending fatigue strength can be maintained at the same level as conventional parts. If the value of Z is less than 15, there is no effect of improving the surface fatigue strength, and if it exceeds 30, the hardenability becomes too high, causing cracking, or the hardness becomes too high and the machinability is lowered.

以上が本発明の基本成分組成で、残部Feおよび不可避的不純物とする。不可避的不純物としてのPおよび酸素含有量は、出来るだけ低いほうが望ましい。更に特性を向上させる場合、Nb、Ti、Bの1種以上を含有することができる。   The above is the basic component composition of the present invention, and the remainder is Fe and inevitable impurities. The contents of P and oxygen as unavoidable impurities are preferably as low as possible. Furthermore, when improving a characteristic, 1 or more types of Nb, Ti, and B can be contained.

Nb:0.010〜0.060%
Nbは炭窒化物形成により結晶粒を微細化させ、曲げ疲労強度を向上させる。結晶粒を微細化させるには0.010%以上必要であるが、0.060%を超えて含有してもその効果は飽和する。よってNbを含有する場合は0.010〜0.060%とする。
Nb: 0.010 to 0.060%
Nb refines crystal grains by forming carbonitride and improves bending fatigue strength. Although 0.010% or more is necessary for making the crystal grains finer, the effect is saturated even if the content exceeds 0.060%. Therefore, when it contains Nb, it is made into 0.010 to 0.060%.

Ti:0.005〜0.050%
Tiは炭窒化物形成により結晶粒を微細化させ、曲げ疲労強度を向上させる。結晶粒を微細化させるには0.005%以上必要であるが、0.050%を超えて含有してもその効果は飽和する。よって、Tiを含有する場合は0.005〜0.050%とする。
Ti: 0.005 to 0.050%
Ti refines crystal grains by forming carbonitride and improves bending fatigue strength. Although 0.005% or more is necessary to make the crystal grains fine, the effect is saturated even if the content exceeds 0.050%. Therefore, when it contains Ti, it is 0.005 to 0.050%.

B:0.0005〜0.0100%
Bは焼入れ性を上げるのに有効である。その効果は0.0005%以上で得られるが、0.0100%を超えて含有してもその効果は飽和する。よって、Bを含有する場合は0.0005〜0.0100%とする。
B: 0.0005 to 0.0100%
B is effective in increasing the hardenability. The effect is obtained at 0.0005% or more, but the effect is saturated even if the content exceeds 0.0100%. Therefore, when it contains B, it is made into 0.0005 to 0.0100%.

尚、本発明鋼において被削性を向上させる場合は、S、Pb、Se、Ca等の快削元素を添加する。   In order to improve machinability in the steel of the present invention, free cutting elements such as S, Pb, Se, and Ca are added.

[歯車の高周波焼入れ部のミクロ組織]
高周波焼入れ部のミクロ組織を、粒径300nm未満の炭化物が100μm2当り90個以上微細に分散した焼戻しマルテンサイトを主体とするミクロ組織に規定する。高周波焼入れ部のミクロ組織は歯車として必要な強度・靭性と耐摩耗性が得られるように焼戻しマルテンサイトを主体とする。主体とは少なくとも95%含む場合とする。焼戻しマルテンサイトに存在する炭化物は耐摩耗性に有効であるが粒径300nmを超えて大きくなると、介在物と同様に疲労破壊の起点となり、疲労強度が低下する。
[Microstructure of induction hardening part of gear]
The microstructure of the induction hardening portion is defined as a microstructure mainly composed of tempered martensite in which 90 or more carbides having a particle size of less than 300 nm are finely dispersed per 100 μm 2 . The microstructure of the induction-hardened part is mainly tempered martensite so that the strength, toughness and wear resistance required for gears can be obtained. It is assumed that the subject includes at least 95%. The carbides present in the tempered martensite are effective for wear resistance, but when the particle size exceeds 300 nm, the fatigue strength is reduced and the fatigue strength is reduced as in the case of inclusions.

一方、粒径が300nm未満と小さい場合であっても炭化物の密度が100μm2当り90個未満と少ない場合、耐摩耗性を向上させることができない。また、微細に分散していることも耐摩耗性を向上させるために必要である。よって上記のとおり限定した。ミクロ組織の観察方法は実施例において詳細に説明する。 On the other hand, even when the particle diameter is as small as less than 300 nm, the wear resistance cannot be improved when the density of the carbide is as small as less than 90 per 100 μm 2 . Further, the fine dispersion is necessary to improve the wear resistance. Therefore, it was limited as described above. The microstructure observation method will be described in detail in Examples.

本発明に係る歯車は上記成分組成の鋼を、熱間鍛造を行った後に焼入れ・焼戻しを行い、その後歯車形状に加工し、表面硬化熱処理として高周波焼入れ・焼戻しを行って製造する。高周波焼入れ・焼戻し後、更に歯面にショットピーニングまたは研磨を行っても良い。   The gear according to the present invention is manufactured by subjecting steel having the above component composition to hot forging, followed by quenching and tempering, then processing into a gear shape, and induction hardening and tempering as surface hardening heat treatment. After induction hardening and tempering, shot peening or polishing may be further performed on the tooth surface.

熱間鍛造は1000〜1300℃で行い、その後室温まで冷却し、850〜950℃まで再加熱した後、60〜130℃の油へ投入して焼入れするか、または鍛造後に780〜880℃まで空冷した後、同様に60〜130℃の油へ投入して焼入れする。その後、450〜700℃に再加熱して焼戻しを行い、歯車形状に加工することが望ましい。高周波焼入れ・焼戻し条件は、高周波焼入れ・焼戻し後における高周波焼入れ部のミクロ組織が上記ミクロ組織の規定を満足するように適宜選定する。本発明で高周波焼入れ部とは高周波焼入れ・焼戻しを受けて組織および硬さが変化した領域である。   Hot forging is performed at 1000 to 1300 ° C., then cooled to room temperature, reheated to 850 to 950 ° C., then poured into oil at 60 to 130 ° C. and quenched, or air cooled to 780 to 880 ° C. after forging. After that, similarly, it is put into oil at 60 to 130 ° C. and quenched. Then, it is desirable to reheat to 450-700 degreeC, temper, and process into a gear shape. The induction hardening and tempering conditions are appropriately selected so that the microstructure of the induction hardening portion after induction hardening and tempering satisfies the above-mentioned definition of the microstructure. In the present invention, the induction hardening portion is a region where the structure and hardness have been changed by induction hardening and tempering.

歯車の歯面にショットピーニングを行う場合は、(1)粒径が0.05〜0.1mmΦの硬さ700HV以上の粒を用いたショットピーニング、(2)粒径が0.4〜1.2mmΦの硬さ700HV以上の粒を用いて行った後、粒径が0.05〜0.1mmΦの硬さ700HV以上の粒を用いて再度行うショットピーニング、(3)粒径が0.4〜1.2mmΦの硬さ700HV以上の粒と、0.05〜0.1mmΦの硬さ700HV以上の粒を混合して行うショットピーニングのいずれかを行う。ショットピーニングとして(1)〜(3)の順で疲労特性は良好となるが、製造コストを考慮して適宜選定する。以下、本発明を実施例により比較例と対比し、さらに詳細に説明する。   When shot peening is performed on the tooth surface of the gear, (1) shot peening using particles having a particle size of 0.05 to 0.1 mmΦ and a hardness of 700 HV or more, and (2) particle size of 0.4 to 1. Shot peening performed using particles having a hardness of 700 HV or more having a particle size of 0.05 to 0.1 mmΦ after performing using particles having a hardness of 700 HV or more of 2 mmΦ, and (3) a particle size of 0.4 to 0.4 Either shot peening is performed by mixing grains having a hardness of 700 HV or more with a diameter of 1.2 mmΦ and grains having a hardness of 700 HV or more with a thickness of 0.05 to 0.1 mmΦ. As the shot peening, the fatigue characteristics are improved in the order of (1) to (3), but the proper selection is made in consideration of the manufacturing cost. Hereinafter, the present invention will be described in more detail in comparison with comparative examples by way of examples.

表1に示す化学成分を有する鋼を溶解し供試材とした。表に示すNo.1、3〜20は本発明範囲内の成分組成の鋼で、No.21〜37は本発明範囲外の成分組成の鋼である。No.22は従来鋼であるJIS SCr420鋼である。 Steels having chemical components shown in Table 1 were melted and used as test materials. No. shown in the table. Nos. 1 , 3 to 20 are steels having a composition within the range of the present invention. 21 to 37 are steels having a component composition outside the scope of the present invention. No. 22 is JIS SCr420 steel which is a conventional steel.

溶製された上記鋼のインゴットを熱間圧延により直径32〜70mmの丸棒鋼に調製し、得られた丸棒鋼に対し、No.1〜37の鋼は焼準処理後に焼入れ・焼戻しを、従来鋼には焼準処理を実施した。   The ingot made of the above-mentioned steel was prepared into a round bar steel having a diameter of 32 to 70 mm by hot rolling. Steels 1 to 37 were quenched and tempered after normalizing treatment, and normal steel was subjected to normalizing treatment.

No.1〜37の鋼は焼入れ・焼戻し後の棒鋼から、従来鋼には焼準処理後の棒鋼から20mmφの丸棒、JIS3号衝撃試験片、小野式回転曲げ疲労試験片、ローラーピッチング試験片を採取した。   No. Steels 1-37 are sampled from hardened and tempered steel bars, and conventional steels are taken from steel bars after normalizing treatment, 20 mmφ round bars, JIS No. 3 impact test pieces, Ono-type rotary bending fatigue test pieces, and roller pitching test pieces. did.

丸棒および各疲労試験片に対して、No.1〜37の鋼については、図1に示す高周波入れ・焼戻し処理(図1(a)は高周波焼入れ条件、図1(b)は焼戻し条件)を施した。No.38鋼については図2に示す浸炭焼入れ・焼戻し処理を施した後、表面硬度、内部硬度、有効硬化層深さの調査、および衝撃試験と回転曲げ疲労試験およびローラーピッチング試験を実施した。   No. for each round bar and each fatigue test piece. The steels 1 to 37 were subjected to induction hardening and tempering treatment shown in FIG. 1 (FIG. 1 (a) was induction hardening conditions and FIG. 1 (b) was tempering conditions). No. The 38 steel was subjected to carburizing quenching and tempering treatment shown in FIG. 2, and then the surface hardness, internal hardness and effective hardened layer depth were investigated, and the impact test, the rotating bending fatigue test and the roller pitching test were performed.

また、No.18の鋼材を用いて焼入れ焼戻し条件と高周波加熱条件について微調整を行い、高周波焼入れ部位に析出させる粒径300nm未満の炭化物の個数を変化させたものを作成し、同様の試験を実施した。以下にそれぞれの調査内容について説明する。   No. 18 steel materials were finely adjusted for quenching and tempering conditions and induction heating conditions, and the number of carbide particles having a particle size of less than 300 nm deposited at the induction hardening site was changed, and the same test was performed. The contents of each survey are described below.

[有効硬化層深さ、表面硬度、内部硬度調査、炭化物析出量]
20φ(mm)丸棒を切断し、No.1〜37の鋼については焼入れ・焼戻し後に高周波焼入れ・焼戻しを行い、従来鋼については浸炭焼入れ・焼戻しをした後、断面の硬度分布を測定し、ビッカース硬さで550HVの得られる深さを調査し有効硬化層深さとした。さらに表面から50μm深さ位置での硬度を表面硬度とし、内部(非硬化部)の硬度とともにビッカース硬度計を用いて測定した。また、No.1〜37の鋼については高周波焼入れ部位をFE−SEMで観察し、粒径300nm未満の炭化物について100μm2あたりの個数をカウントした。粒径は短径、長径の平均値とした。
[Effective hardened layer depth, surface hardness, internal hardness investigation, carbide precipitation amount]
A 20φ (mm) round bar is cut and For steel Nos. 1 to 37, induction quenching and tempering are performed after quenching and tempering, and for conventional steel, after carburizing quenching and tempering, the hardness distribution of the cross section is measured, and the depth at which 550 HV is obtained in terms of Vickers hardness is investigated. The effective hardened layer depth. Furthermore, the hardness at a depth of 50 μm from the surface was defined as the surface hardness, and was measured using a Vickers hardness meter together with the internal (non-hardened portion) hardness. No. For steels 1 to 37, the induction-quenched sites were observed by FE-SEM, and the number per 100 μm 2 of carbides having a particle size of less than 300 nm was counted. The particle size was the average value of the minor axis and the major axis.

[衝撃特性]
各鋼材を用いてJIS3号衝撃試験片を作製し、No.1〜37の鋼については高周波焼入れ・焼戻しを、従来材については浸炭焼入れ焼戻しを施した後、シャルピー試験機により試験温度20℃における衝撃値を調査した。
[Impact characteristics]
A JIS No. 3 impact test piece was prepared using each steel material. The steels 1 to 37 were subjected to induction quenching and tempering, and the conventional materials were subjected to carburizing quenching and tempering, and then the impact value at a test temperature of 20 ° C. was examined by a Charpy tester.

[回転曲げ疲労特性]
直径32mmの丸棒鋼から、平行部直径10mmの試験片を採取し、平行部に平行部と直角方向に深さ1.5mmの切り欠き(切り欠き係数:1.4)を全周にわたってつけた回転曲げ疲労試験片を調製した。No.1〜37の鋼については高周波焼入れ焼戻しを、従来鋼については浸炭焼入れ・焼戻し処理を行った。小野式回転曲げ疲労試験機を使用して10回を疲労限度として回転曲げ疲労試験を行い、回転曲げ疲労強度を測定した。
[Rotating bending fatigue characteristics]
A test piece having a parallel part diameter of 10 mm was taken from a round steel bar having a diameter of 32 mm, and a notch (notch coefficient: 1.4) having a depth of 1.5 mm was attached to the parallel part in the direction perpendicular to the parallel part. A rotating bending fatigue test piece was prepared. No. The steels 1 to 37 were induction-quenched and tempered, and the conventional steels were carburized and tempered. It performs rotation bending fatigue test as fatigue limit of 10 7 times using fatigue tester Ono-type rotating bending was measured rotating bending fatigue strength.

[面圧疲労特性]
面圧疲労特性をローラーピッチング試験により調査した。直径32mmの丸棒鋼から図3に示す試験面の直径が26mm、幅が28mmの円筒部を有する試験片を作製した。また、直径70mmの丸棒鋼を用いて、鍛造により直径135mmとした後、焼準処理を行い、直径130mm、幅18mmの大ローラーを作製した。
[Surface fatigue characteristics]
The surface pressure fatigue characteristics were investigated by a roller pitching test. A test piece having a cylindrical portion with a diameter of 26 mm and a width of 28 mm as shown in FIG. 3 was prepared from a round steel bar having a diameter of 32 mm. Further, using a round steel bar having a diameter of 70 mm, the diameter was set to 135 mm by forging, and then a normalizing process was performed to produce a large roller having a diameter of 130 mm and a width of 18 mm.

次いでローラー状試験片および大ローラーについて、No.1〜37の鋼については高周波焼入れ焼戻し処理を、従来鋼については浸炭焼入れ・焼戻し処理を行った。ローラーピッチング試験機を使用して10回を疲労限度として試験を行った。試験条件は回転数:1500r.p.m 、すべり率40%、潤滑剤:ミッションオイル、油温:120℃であった。 Subsequently, about a roller-shaped test piece and a large roller, it is No. The steels 1 to 37 were subjected to induction quenching and tempering, and the conventional steels were subjected to carburizing and tempering. Using a roller pitching tester, the test was conducted 10 7 times with a fatigue limit. The test condition is the number of revolutions: 1500 r. p. m, slip ratio 40%, lubricant: mission oil, oil temperature: 120 ° C.

また、面圧3000MPaにて1千万回試験を行い、その試験前後の試験片重量の差から、摩耗量を算出した。   Further, the test was conducted 10 million times at a surface pressure of 3000 MPa, and the amount of wear was calculated from the difference in the test piece weight before and after the test.

表2に調査結果を示す Table 2 shows the survey results .

比較例No.22はC含有量が本発明の範囲より低いために、焼入れ性が低すぎて表面硬度が低くなっている。また硬化層深さも浅すぎる。そのため、回転曲げ疲労強度および面疲労強度が低下した。   Comparative Example No. No. 22 has a C content lower than the range of the present invention, so the hardenability is too low and the surface hardness is low. Moreover, the hardened layer depth is too shallow. Therefore, rotational bending fatigue strength and surface fatigue strength were reduced.

比較例No.23はSi含有量が本発明の範囲よりも低い。そのために軟化抵抗が低すぎて面疲労強度が低下した。比較例No.24はSi含有量が本発明の範囲より高く、そのために靭性が低くなっており、衝撃値および回転曲げ疲労強度が低下した。   Comparative Example No. No. 23 has a Si content lower than the range of the present invention. Therefore, the softening resistance was too low and the surface fatigue strength was lowered. Comparative Example No. In No. 24, the Si content was higher than the range of the present invention, so that the toughness was low, and the impact value and the rotational bending fatigue strength were reduced.

比較例No.25はMn含有量が本発明範囲より低いために焼入性が低すぎて有効硬化層深さが浅すぎるために全体の強度が不足しており回転曲げ疲労強度が低下した。比較例No.26はMn含有量が本発明の範囲より高いために焼入れ性が高くなりすぎている。そのため、衝撃値および回転曲げ疲労強度が低下した。   Comparative Example No. In No. 25, since the Mn content was lower than the range of the present invention, the hardenability was too low and the effective hardened layer depth was too shallow, so the overall strength was insufficient and the rotary bending fatigue strength was lowered. Comparative Example No. No. 26 has too high hardenability because the Mn content is higher than the range of the present invention. Therefore, the impact value and the rotational bending fatigue strength decreased.

比較例No.27はCr含有量が本発明範囲より高い。そのために靭性が低下し、曲げ疲労強度が低下した。比較例No.28、29はNb含有量が本発明範囲よりも低いために結晶粒が大きめになって衝撃値および曲げ疲労強度が低下した。   Comparative Example No. 27 has a Cr content higher than the range of the present invention. As a result, the toughness decreased and the bending fatigue strength decreased. Comparative Example No. In Nos. 28 and 29, since the Nb content was lower than the range of the present invention, the crystal grains became larger and the impact value and the bending fatigue strength were lowered.

比較例No.30、31、35はTi含有量が本発明範囲よりも低いために結晶粒が大きくなって衝撃値および曲げ疲労強度が低下した。
比較例No.32、33、34はB含有量が本発明範囲よりも低いために焼入れ性が不足しており、硬化層深さが浅く、内部硬度も低めであるために全体の強度が不足して回転曲げ疲労強度が不足した。
Comparative Example No. In 30, 31, and 35, since the Ti content was lower than the range of the present invention, the crystal grains became large, and the impact value and the bending fatigue strength were lowered.
Comparative Example No. Nos. 32, 33, and 34 have a B content lower than the range of the present invention, so that the hardenability is insufficient, the hardened layer depth is shallow, and the internal hardness is low, so that the overall strength is insufficient and the rotational bending Fatigue strength was insufficient.

比較例No.36はZの値が本発明範囲より低くなっており、面疲労強度が低下した。比較例No.37はZの値が本発明範囲よりも高くなっており、焼入れ性が高く、硬化深さ、内部硬度が高くなりすぎて衝撃値が低下し、回転曲げ疲労強度も低下した。   Comparative Example No. In 36, the value of Z was lower than the range of the present invention, and the surface fatigue strength decreased. Comparative Example No. No. 37 has a Z value higher than the range of the present invention, and has high hardenability, the hardening depth and internal hardness are too high, the impact value decreases, and the rotary bending fatigue strength also decreases.

これに対して本発明鋼であるNo.1、3〜20は比較例No.21〜37および従来鋼No.38に比べて、衝撃特性、回転曲げ疲労特性、面疲労特性ともに良好な結果が得られた。 On the other hand, No. which is steel of the present invention. Nos. 1 , 3 to 20 are comparative example Nos. 21-37 and conventional steel No. Compared to 38, favorable results were obtained in impact characteristics, rotational bending fatigue characteristics, and surface fatigue characteristics.

表3に高周波焼入れ部位に析出させる粒径300nm未満の炭化物の個数を変化させて回転曲げ疲労特性、面疲労特性を調査した結果を示す。径が300nm以下の炭化物の個数が本発明範囲よりも少ない18−5、18−6、18−7は摩耗量が大きい。それに対して本発明範囲内である18−1、18−2、18−3、18−4は摩耗量が少なく耐耗性が良好である。 Table 3 shows the results of investigating the rotational bending fatigue characteristics and the surface fatigue characteristics by changing the number of carbide particles having a particle size of less than 300 nm to be precipitated at the induction-quenched site. 18-5, 18-6, 18-7 in which the number of carbides having a diameter of 300 nm or less is smaller than the range of the present invention has a large wear amount. 18-1,18-2,18-3,18-4 is within range of the present invention is good less resistance to friction耗性wear amount relative thereto.

Claims (4)

質量%で、C:0.25〜0.49%、Si:0.70〜2.00%、Mn:0.30〜2.00%、Cr:1.50%以下を含有し、(1)式で計算されるZの値が15≦Z≦30で、残部がFeおよび不可避的不純物からなる成分組成を有し、高周波焼入れ部の組織が焼戻しマルテンサイト主体で、前記高周波焼入れ部内部に粒径300nm未満の炭化物が100μm2当り90個以上微細に分散していることを特徴とする耐摩耗性と面疲労特性に優れた、耗量が24mg以下である高周波焼入れ歯車。
Z=10Si+Cr+50(D×Ceq)/A・・・(1)
ここで、Si、Crはそれぞれの元素の含有する量(質量%)を示す。Dは焼入れ性指数、Ceqは炭素当量、AはAc変態点で、(2)、(3)、(4)式で計算された値とする。
D=8.76*√(C)*(1+0.64*Si)*(1+4.1*Mn)*(1+2.33*Cr)・・・(2)
但し、式において各合金元素は含有量(質量%)で、Bを添加した場合はD値はこの計算式による値の2倍とする。
Ceq=C+Si/7+Mn/5+Cr/9+0.023・・・(3)
但し、式において各合金元素は含有量(質量%)とする。
A=921−203√C+44.7*Si−30*Mn−11*Cr・・・(4)
但し、式において各合金元素は含有量(質量%)とする。
C: 0.25 to 0.49%, Si: 0.70 to 2.00 %, Mn: 0.30 to 2.00%, Cr: 1.50% or less, ) The value of Z calculated by the formula is 15 ≦ Z ≦ 30, the remainder has a component composition consisting of Fe and inevitable impurities, and the structure of the induction-hardened part is mainly tempered martensite, inside the induction-hardened part. carbides having a particle size of less than 300nm and an excellent wear resistance and surface fatigue properties, characterized in that it is dispersed in 100 [mu] m 2 per 90 or more fine, induction hardening gears grinding耗量is less than 24 mg.
Z = 10Si + Cr + 50 (D × Ceq) / A (1)
Here, Si and Cr show the amount (mass%) which each element contains. D is a hardenability index, Ceq is a carbon equivalent, A is an Ac 3 transformation point, and is a value calculated by the equations (2), (3), and (4).
D = 8.76 * √ (C) * (1 + 0.64 * Si) * (1 + 4.1 * Mn) * (1 + 2.33 * Cr) (2)
However, in the formula, each alloy element is the content (% by mass), and when B is added, the D value is twice the value by this formula.
Ceq = C + Si / 7 + Mn / 5 + Cr / 9 + 0.023 (3)
However, the content of each alloy element in the formula (mass%).
A = 921-203√C + 44.7 * Si-30 * Mn-11 * Cr (4)
However, the content of each alloy element in the formula (mass%).
成分組成に、更に、質量%で、Nb:0.010〜0.060%、Ti:0.005〜0.050%、B:0.0005〜0.0100%の1種以上を含有することを特徴とする請求項1記載の耐摩耗性と面疲労特性に優れた高周波焼入れ歯車。   The component composition further contains one or more of Nb: 0.010 to 0.060%, Ti: 0.005 to 0.050%, and B: 0.0005 to 0.0100% by mass%. The induction-hardened gear excellent in wear resistance and surface fatigue characteristics according to claim 1. 請求項1または2に記載の成分組成の鋼を、熱間鍛造後、焼入れ・焼戻しを行い、その後歯車形状に加工し、表面硬化熱処理として高周波焼入れ・焼戻しを行い、高周波焼入れ部の組織を焼戻しマルテンサイト主体で内部に粒径300nm未満の炭化物が100μm2当り90個以上微細に分散したものとすることを特徴とする、耐摩耗性と面疲労特性に優れた耗量が24mg以下である高周波焼入れ歯車の製造方法。 The steel having the composition of claim 1 or 2 is hot forged, quenched and tempered, then processed into a gear shape, induction hardened and tempered as a surface hardening heat treatment, and the structure of the induction hardened portion is tempered. characterized in that it is assumed that the carbide particle size of less than 300nm therein was 2 per 90 or more 100μm finely dispersed martensite mainly, friction耗量is below 24mg having excellent abrasion resistance and surface fatigue properties Induction hardening gear manufacturing method. 前記高周波焼入れ・焼戻し後、更に歯面にショットピーニングまたは研磨を行うことを特徴とする、請求項3記載の耐摩耗性と面疲労特性に優れた高周波焼入れ歯車の製造方法。   4. The method of manufacturing an induction-hardened gear excellent in wear resistance and surface fatigue characteristics according to claim 3, further comprising performing shot peening or polishing on the tooth surface after the induction hardening and tempering.
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