JP5258458B2 - Gears with excellent surface pressure resistance - Google Patents

Gears with excellent surface pressure resistance Download PDF

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JP5258458B2
JP5258458B2 JP2008222341A JP2008222341A JP5258458B2 JP 5258458 B2 JP5258458 B2 JP 5258458B2 JP 2008222341 A JP2008222341 A JP 2008222341A JP 2008222341 A JP2008222341 A JP 2008222341A JP 5258458 B2 JP5258458 B2 JP 5258458B2
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shot peening
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JP2010053429A (en
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学 藤田
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Kobe Steel Ltd
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本発明は、自動車などの輸送機器や建設機械、その他の各種産業機械などにおいて、高面圧下で使用される歯車およびその製造方法に関するものである。   The present invention relates to a gear used under high surface pressure in a transport device such as an automobile, a construction machine, and other various industrial machines, and a manufacturing method thereof.

近年、環境保全の観点から、歯車は小型・軽量化することが要望されている。歯車を小型化すると歯への負荷が増大し、歯の曲げ強度や剥離強度を高める必要がある。歯の曲げ強度については工法技術の向上等により実用上問題にならない程度にまで向上している。一方、剥離強度については、歯の耐熱性を向上させる試みがなされている。すなわち、歯は摺動時の発熱によって軟化し剥離を起こすことから、歯の初期硬さや軟化抵抗性を高めることによって剥離寿命を向上させるというものである。具体的には、セメンタイトを析出させる高濃度浸炭処理や、窒化物を析出させる浸炭窒化処理があり、炭化物や窒化物の硬い性質や、熱分解し難い性質を利用している。   In recent years, from the viewpoint of environmental conservation, gears are desired to be reduced in size and weight. If the gear is downsized, the load on the teeth increases, and it is necessary to increase the bending strength and peel strength of the teeth. The bending strength of the teeth has been improved to such an extent that it does not cause any practical problems by improving the construction technique. On the other hand, as for the peel strength, attempts have been made to improve the heat resistance of teeth. That is, since teeth soften and peel due to heat generated during sliding, the initial life and softening resistance of the teeth are increased to improve the peel life. Specifically, there are high-concentration carburizing treatment for precipitating cementite and carbonitriding treatment for precipitating nitrides, which utilize the hard properties of carbides and nitrides and the properties that are difficult to thermally decompose.

また特許文献1では、曲げ疲労特性を向上するとの目的でカーボンポテンシャルが0.9〜1.5%で高濃度浸炭し、所定の温度域で保持することによりセメンタイトを生成させ、浸炭部品の硬さを一定範囲内に確保している。   Further, in Patent Document 1, for the purpose of improving bending fatigue characteristics, high concentration carburization is performed at a carbon potential of 0.9 to 1.5%, and the cementite is generated by maintaining in a predetermined temperature range. This is ensured within a certain range.

しかし、高濃度浸炭処理は処理時間が長く生産性に劣り、また浸炭窒化処理は専用の炉が必要でありコストアップを招くため、いずれも汎用性に欠けるものである。また特許文献1の方法による初期硬さの向上効果は、剥離寿命を向上させるためには十分とは言えない。
特開2007−308772号公報
However, the high-concentration carburizing process has a long processing time and is inferior in productivity, and the carbonitriding process requires a dedicated furnace and causes an increase in cost. Further, the effect of improving the initial hardness by the method of Patent Document 1 cannot be said to be sufficient for improving the peeling life.
JP 2007-308772 A

本発明は上記事情に鑑みてなされたものであって、その目的は通常の浸炭処理によって剥離寿命の長い歯車を製造する方法を提供することにある。   This invention is made | formed in view of the said situation, The objective is to provide the method of manufacturing a gear with a long peeling life by normal carburizing process.

上記課題を解決することのできた本発明に係る歯車の製造方法とは、C:0.15〜0.25%(質量%の意味。以下、化学成分組成について同じ。)、Si:0.50〜1.6%、Mn:0.3〜2%、P:0.02%以下(0%を含まない)、S:0.03%以下(0%を含まない)、Cr:0.5〜2%、Al:0.1%以下(0%を含まない)、N:0.03%以下(0%を含まない)を含有し、残部は鉄および不可避不純物である鋼で形成された歯車を、炭化物を生じることなく浸炭して表面C濃度を0.80%以上とし、焼入れ・焼戻しした後、アークハイト値が0.5mmA以上のショットピーニングをし、前記ショットピーニングにより、表面組織に占める割合で10面積%以上の残留オーステナイトを加工誘起マルテンサイト変態させたことを特徴とするものである。   The manufacturing method of the gear according to the present invention that has solved the above-mentioned problems is: C: 0.15 to 0.25% (meaning mass%; hereinafter, the same as the chemical component composition), Si: 0.50 -1.6%, Mn: 0.3-2%, P: 0.02% or less (not including 0%), S: 0.03% or less (not including 0%), Cr: 0.5 -2%, Al: 0.1% or less (not including 0%), N: 0.03% or less (not including 0%), the balance being made of iron and steel which is an inevitable impurity The gear is carburized without generating carbides, and the surface C concentration is set to 0.80% or more. After quenching and tempering, shot peening with an arc height value of 0.5 mmA or more is performed. Work-induced martenser with 10% by area or more of retained austenite It is characterized in that by preparative transformation.

本発明の製造方法に用いる鋼は、必要に応じてさらに(a)Mo:0.08〜0.8%、(b)B:0.0005〜0.005%、Nb:0.01〜0.1%、Ti:0.01〜0.1%よりなる群から選ばれる少なくとも一種以上、を含有していてもよい。   The steel used in the production method of the present invention may further include (a) Mo: 0.08 to 0.8%, (b) B: 0.0005 to 0.005%, Nb: 0.01 to 0 as necessary. 1%, Ti: at least one selected from the group consisting of 0.01 to 0.1% may be contained.

本発明には、上記成分組成を満たす鋼からなり、浸炭されている歯車であって、表面C濃度が0.80%以上であり、表面の炭化物が0面積%であるとともに、表面のビッカース硬さが880Hv以上である耐高面圧性に優れた歯車も包含される。   The present invention includes a carburized gear made of steel satisfying the above component composition, having a surface C concentration of 0.80% or more, a surface carbide content of 0 area%, and a surface Vickers hardness. A gear excellent in high surface pressure resistance having a thickness of 880 Hv or more is also included.

本発明に係る歯車の製造方法によれば、母材としてSi量の多い鋼を用い、炭化物の生成を避けつつ表面C濃度を0.80%以上となる様に浸炭し、増大する残留オーステナイトをアークハイト量が0.5mmA以上のショットピーニングで加工誘起変態させているため、歯車表面の荒れを防ぎながらそのビッカース硬さを880Hv以上とすることができ、従来よりも剥離寿命の長い歯車を提供することが可能である。   According to the gear manufacturing method of the present invention, steel with a large amount of Si is used as a base material, and carburization is performed so that the surface C concentration becomes 0.80% or more while avoiding the formation of carbides. Work-induced transformation is performed by shot peening with an arc height of 0.5 mmA or more, so the Vickers hardness can be increased to 880 Hv or more while preventing the surface of the gear from being roughed, and a gear having a longer peeling life than conventional ones is provided. Is possible.

本発明者は、高濃度浸炭処理や浸炭窒化処理などの特別な熱処理を行うことなく、通常の浸炭処理の条件を最適化するだけで歯車の初期硬さを確保し、剥離寿命を向上させるべく鋭意研究を重ねた。その結果、炭化物を生じることなく浸炭して表面C濃度を0.80%以上に高くし、焼入れ・焼戻しした後、アークハイト値が0.5mmA以上のショットピーニングをすれば、C濃度の高い残留オーステナイトが所定量以上変態し、C濃度の高い加工誘起変態マルテンサイトとなるので、初期硬さが飛躍的に上昇することを見出した。また前記の所定以上のアークハイト量のショットピーニングは、一般鋼であるSCr420H等では歯先のダレ、歯面の粗さ上昇の原因となり、歯車の静粛性が欠如してしまう。そこで、本発明ではSi量が所定以上の鋼を用い、歯車の強度および0.2%耐力を高めることによって、歯車の静粛性を損なうことなく所定以上のアークハイト量のショットピーニングを適用することが可能となった。   The present inventor aims to ensure the initial hardness of the gear and improve the stripping life only by optimizing the conditions of normal carburizing treatment without performing special heat treatment such as high-concentration carburizing treatment or carbonitriding treatment. Researched earnestly. As a result, after carburizing without generating carbides, increasing the surface C concentration to 0.80% or more, quenching and tempering, and then performing shot peening with an arc height value of 0.5 mmA or more, a high C concentration remains. It has been found that since the austenite is transformed by a predetermined amount or more and becomes a work-induced transformation martensite having a high C concentration, the initial hardness is dramatically increased. In addition, the above-mentioned shot peening with an arc height greater than a predetermined amount causes the sagging of the tooth tip and the increase in the roughness of the tooth surface in the case of general steel such as SCr420H, and the silence of the gear is lacking. Therefore, in the present invention, a steel having a predetermined amount of Si or more is used, and by increasing the strength and 0.2% proof stress of the gear, shot peening having a predetermined amount of arc height is applied without impairing the quietness of the gear. Became possible.

まず、本発明の歯車に用いる鋼の成分組成について以下に説明する。   First, the component composition of steel used for the gear of the present invention will be described below.

C:0.15〜0.25%
Cは歯車として必要な芯部硬さを確保する上で重要な元素である。C量が0.15%未満であると、芯部硬さが不足することにより、歯車としての静的強度が不足する。そこでC量を0.15%以上と定めた。C量は好ましくは0.17%以上であり、より好ましくは0.18%以上である。一方、C量が過剰になると、硬さが過度に高くなって鍛造性や被削性が低下する。そこでC量を0.25%以下と定めた。C量は好ましくは、0.22%以下であり、より好ましくは0.20%以下である。
C: 0.15-0.25%
C is an important element in securing the core hardness necessary for the gear. If the C amount is less than 0.15%, the core portion hardness is insufficient, and the static strength as a gear is insufficient. Therefore, the C amount is set to 0.15% or more. The amount of C is preferably 0.17% or more, more preferably 0.18% or more. On the other hand, when the amount of C becomes excessive, the hardness becomes excessively high, and forgeability and machinability deteriorate. Therefore, the C amount is set to 0.25% or less. The amount of C is preferably 0.22% or less, more preferably 0.20% or less.

Si:0.50〜1.6%
Siは固溶強化元素として強度向上に寄与し、0.2%耐力も向上させる。強度を向上させ、0.2%耐力を向上させることにより、所定以上のアークハイト量のショットピーニングを行った場合でも歯先のダレや歯面の荒れを抑制することができる。このような効果を発揮させるためSi量を0.50%以上と定めた。Si量は好ましくは0.6%以上である。一方、Si量が過剰になると被削性、冷間加工性および熱間加工性に悪影響を与える。そこでSi量を1.6%以下と定めた。Si量は好ましくは1.5%以下である。
Si: 0.50 to 1.6%
Si contributes to strength improvement as a solid solution strengthening element and also improves 0.2% proof stress. By improving the strength and improving the 0.2% proof stress, sagging of the tip of the tooth and roughening of the tooth surface can be suppressed even when shot peening is performed with a predetermined arc height or more. In order to exert such an effect, the Si amount is determined to be 0.50% or more. The amount of Si is preferably 0.6% or more. On the other hand, if the amount of Si is excessive, it adversely affects machinability, cold workability, and hot workability. Therefore, the Si amount is set to 1.6% or less. The amount of Si is preferably 1.5% or less.

Mn:0.3〜2%
Mnは脱酸剤として作用し、酸化物系介在物量を低減して鋼材の品質を高める作用を有する。また、焼入れ性を向上させ歯車の芯部硬さや硬化層深さを高め、歯車の強度を確保するのに有効な元素である。そこでMn量を0.3%以上と定めた。Mn量は好ましくは0.35%以上である。一方、Mn量が過剰になると縞状の偏析が顕著となり、材質のバラツキが大きくなる結果、冷間加工性に悪影響を与える。従ってMn量を2%以下と定めた。Mn量は好ましくは1.6%以下であり、より好ましくは1.0%以下(特に0.7%以下)である。
Mn: 0.3-2%
Mn acts as a deoxidizer and has the effect of reducing the amount of oxide inclusions and improving the quality of the steel material. Further, it is an element effective for improving the hardenability, increasing the hardness of the gear core and the depth of the hardened layer, and ensuring the strength of the gear. Therefore, the amount of Mn is set to 0.3% or more. The amount of Mn is preferably 0.35% or more. On the other hand, when the amount of Mn is excessive, stripe-like segregation becomes remarkable, and as a result, the variation of the material becomes large, which adversely affects cold workability. Therefore, the amount of Mn is set to 2% or less. The amount of Mn is preferably 1.6% or less, more preferably 1.0% or less (particularly 0.7% or less).

P:0.02%以下(0%を含まない)
Pは鋼材中に不可避的に含まれる元素であり、結晶粒界に偏析して歯車の衝撃特性を低下させる元素である。そこでP量を0.02%以下と定めた。P量は好ましくは0.018%以下、より好ましくは0.015%以下(特に0.01%以下)である。
P: 0.02% or less (excluding 0%)
P is an element inevitably contained in the steel material, and is an element that segregates at the grain boundaries and lowers the impact characteristics of the gear. Therefore, the P content is set to 0.02% or less. The amount of P is preferably 0.018% or less, more preferably 0.015% or less (particularly 0.01% or less).

S:0.03%以下(0%を含まない)
Sは、Mnと結合してMnS系介在物を形成し、歯車の疲労強度、衝撃強度を低下させる元素であるため、できるだけ低減することが好ましい。従ってS量を0.03%以下と定めた。S量は好ましくは0.02%以下、より好ましくは0.015%以下である。一方、Sは切削性を向上させる作用を有するため、積極的に0.005%程度含有させることも好ましい。
S: 0.03% or less (excluding 0%)
Since S is an element that combines with Mn to form MnS inclusions and lowers the fatigue strength and impact strength of the gear, it is preferably reduced as much as possible. Therefore, the S content is set to 0.03% or less. The amount of S is preferably 0.02% or less, more preferably 0.015% or less. On the other hand, since S has the effect | action which improves machinability, it is also preferable to contain actively about 0.005%.

Cr:0.5〜2%
Crは焼入性を高め、歯車の芯部硬さや硬化層深さを高め、歯車の静的強度および疲労強度を確保する上で重要な元素である。こうした作用を発揮させるため、Cr量を0.5%以上と定めた。Cr量は好ましくは0.7%以上、より好ましくは1%以上である。一方、Cr量が過剰になると被削性および鍛造性の劣化を招く。そこでCr量を2%以下と定めた。Cr量は好ましくは1.5%以下であり、より好ましくは1.2%以下である。
Cr: 0.5-2%
Cr is an important element for enhancing the hardenability, increasing the hardness of the gear core and the depth of the hardened layer, and ensuring the static strength and fatigue strength of the gear. In order to exert such an effect, the Cr content is set to 0.5% or more. The amount of Cr is preferably 0.7% or more, more preferably 1% or more. On the other hand, when the amount of Cr is excessive, machinability and forgeability are deteriorated. Therefore, the Cr content is set to 2% or less. The amount of Cr is preferably 1.5% or less, and more preferably 1.2% or less.

Al:0.1%以下(0%を含まない)
Alは脱酸剤として作用し、酸化物系介在物を低減して鋼材の内部品質を高める作用を有するため、0.01%程度(より好ましくは0.02%程度)含有させることが好ましい。一方、Al量が過剰になると粗大で硬いAl23が生成し、疲労特性を低下させる。そこでAl量を0.1%以下と定めた。Al量は好ましくは0.07%以下であり、より好ましくは0.05%以下である。
Al: 0.1% or less (excluding 0%)
Since Al acts as a deoxidizer and has the effect of reducing the oxide inclusions and improving the internal quality of the steel material, it is preferably contained in an amount of about 0.01% (more preferably about 0.02%). On the other hand, when the amount of Al becomes excessive, coarse and hard Al 2 O 3 is generated, and the fatigue characteristics are lowered. Therefore, the Al content is set to 0.1% or less. The amount of Al is preferably 0.07% or less, and more preferably 0.05% or less.

N:0.03%以下(0%を含まない)
Nは鋼材に不可避的に含まれる元素であるが、NはTi等と結合してTiN介在物等を生成し、切削性や転動疲労強度を低下させるとともに、鋼材の硬さ、変形抵抗を増大させ鍛造性を低下させる。そこでN量を0.03%以下と定めた。N量は好ましくは0.02%以下であり、より好ましくは0.015%以下である。
N: 0.03% or less (excluding 0%)
N is an element inevitably contained in the steel material, but N combines with Ti or the like to produce TiN inclusions and the like, which reduces the machinability and rolling fatigue strength, and reduces the hardness and deformation resistance of the steel material. Increase and decrease forgeability. Therefore, the N amount is set to 0.03% or less. The amount of N is preferably 0.02% or less, and more preferably 0.015% or less.

本発明に用いる鋼の基本成分は上記の通りであり、残部は実質的に鉄である。但し、原料、資材、製造設備等の状況によって持ち込まれる不可避不純物(例えば、O、Cu、Ni、Sn、As、Sb、Ca、Mg等)が鋼中に含まれることは、当然に許容される。さらに本発明に用いる鋼は、必要に応じて、以下の任意元素を含有していても良い。   The basic components of the steel used in the present invention are as described above, and the balance is substantially iron. However, it is naturally allowed that unavoidable impurities (for example, O, Cu, Ni, Sn, As, Sb, Ca, Mg, etc.) brought into the steel depending on the situation of raw materials, materials, manufacturing equipment, etc. are contained in the steel. . Furthermore, the steel used for this invention may contain the following arbitrary elements as needed.

Mo:0.08〜0.8%
Moは鋼材の焼入れ性を向上させる作用を有し、さらに耐衝撃強度の向上に有効な元素である。こうした作用を発揮させるため、Mo量を0.08%以上と定めた。Mo量は好ましくは0.1%以上であり、より好ましくは0.15%以上である。一方、Mo量が過剰になると母材の硬さが硬くなり被削性が低下する。また、Moは高価な元素であるためコストアップの原因ともなる。そこでMo量を0.8%以下と定めた。Mo量は好ましくは0.5%以下であり、より好ましくは0.3%以下(特に0.25%以下)である。
Mo: 0.08 to 0.8%
Mo has an effect of improving the hardenability of the steel material, and is an element effective for improving the impact strength. In order to exert such an effect, the Mo amount is determined to be 0.08% or more. The amount of Mo is preferably 0.1% or more, and more preferably 0.15% or more. On the other hand, when the amount of Mo becomes excessive, the hardness of the base material becomes hard and the machinability deteriorates. Moreover, since Mo is an expensive element, it causes a cost increase. Therefore, the Mo amount is set to 0.8% or less. The amount of Mo is preferably 0.5% or less, more preferably 0.3% or less (particularly 0.25% or less).

B:0.0005〜0.005%、Nb:0.01〜0.1%、Ti:0.01〜0.1%よりなる群から選ばれる少なくとも一種以上
Bは微量で鋼材の焼入れ性を著しく向上させる作用を有し、さらに結晶粒界を強化して衝撃強度を高める作用を有する元素である。そこでB量を0.0005%以上と定めた。B量は好ましくは0.001%以上である。一方、B量が過剰になるとBN等のほう化物が析出し、疲労破壊の起点となって寿命を低下させる。そこでB量を0.005%以下と定めた。B量は好ましくは0.003%以下である。
B: at least one selected from the group consisting of 0.0005-0.005%, Nb: 0.01-0.1%, Ti: 0.01-0.1% B is a small amount of hardenability of the steel material It is an element that has the effect of remarkably improving, and further has the effect of enhancing the impact strength by strengthening the grain boundaries. Therefore, the B amount is set to 0.0005% or more. The amount of B is preferably 0.001% or more. On the other hand, when the amount of B becomes excessive, BN and other borides precipitate, which becomes a starting point of fatigue failure and shortens the life. Therefore, the B amount is set to 0.005% or less. The amount of B is preferably 0.003% or less.

NbおよびTiは窒化物や炭化物を形成し結晶粒の微細化に寄与する元素である。従ってNb量を0.01%以上、Ti量を0.01%以上とした。Nb量は好ましくは0.03%以上であり、Ti量は好ましくは0.03%以上である。一方、Nb量およびTiが過剰となると窒化物、炭化物等の介在物が増加し介在物が起点となって剥離し寿命を低下させる。そこでNb量を0.1%以下、Ti量を0.1%以下とした。Nb量は好ましくは0.09%以下、Ti量は好ましくは0.09%以下である。   Nb and Ti are elements that form nitrides and carbides and contribute to the refinement of crystal grains. Therefore, the Nb content is 0.01% or more and the Ti content is 0.01% or more. The amount of Nb is preferably 0.03% or more, and the amount of Ti is preferably 0.03% or more. On the other hand, when the amount of Nb and Ti are excessive, inclusions such as nitrides and carbides increase, and the inclusions start as a starting point and reduce the life. Therefore, the Nb content is 0.1% or less and the Ti content is 0.1% or less. The Nb amount is preferably 0.09% or less, and the Ti amount is preferably 0.09% or less.

本発明の歯車は、上記成分の鋼を必要に応じて調質など適宜熱処理した後、所定の歯車形状に加工し、炭化物を生成させることなく高C濃度で浸炭焼入れ・焼戻しし、所定以上のアークハイト量でショットピーニングすることによって製造する。この製造工程は、高C濃度浸炭と所定以上のアークハイト量のショットピーニングを組み合わせた点に第1の特徴を有し、高C濃度浸炭時に炭化物を生成させない条件を選択する点に第2の特徴を有する。炭化物の生成を防止しながら浸炭濃度を高くすることで、C濃度の高い残留オーステナイトを多量に生成できる。このC濃度の高い残留オーステナイトを所定以上のアークハイト量のショットピーニングで多量に加工誘起変態させることで、硬さの極めて高いマルテンサイトを多量に生成でき、歯面の初期硬さを著しく向上でき、耐高面圧性を高めることができる。以下、順を追ってより詳細に説明する。   The gear of the present invention is appropriately heat treated, such as tempering the steel of the above components, then processed into a predetermined gear shape, carburized and tempered at a high C concentration without generating carbide, Manufactured by shot peening with arc height. This manufacturing process has a first feature in that high-C concentration carburization is combined with shot peening of an arc height amount greater than or equal to a predetermined value, and a second feature is that a condition that does not generate carbides during high-C concentration carburization is selected. Has characteristics. By increasing the carburization concentration while preventing the formation of carbides, a large amount of retained austenite having a high C concentration can be generated. By processing and transforming a large amount of retained austenite with a high C concentration by shot peening with an arc height of a predetermined amount or more, a large amount of martensite with extremely high hardness can be generated, and the initial hardness of the tooth surface can be significantly improved. High surface pressure resistance can be improved. Hereinafter, it demonstrates in detail later on in order.

(1)浸炭
浸炭では、炭化物を生じない範囲で、表面C濃度を0.80%以上にする。
(1) Carburizing In carburizing, the surface C concentration is set to 0.80% or more as long as no carbide is generated.

炭化物が生成すると、炭化物が起点となって剥離が生じ、剥離寿命が低下するため、本発明では炭化物が生じないように浸炭することとした。浸炭時の炭化物の生成を防止するためには、表面C濃度を高くし過ぎないことが重要である。すなわち表面C濃度の上限は、事実上、炭化物の生成防止の観点から制限され、その値は鋼の成分組成により異なるが、状態図のAcm線を参照しつつ適宜設定できる。なお、前記炭化物とはセメンタイトを意味する。   When the carbide is generated, the carbide becomes a starting point and peeling occurs, and the peeling life is reduced. Therefore, in the present invention, carburization is performed so that the carbide is not generated. In order to prevent the formation of carbides during carburizing, it is important not to make the surface C concentration too high. That is, the upper limit of the surface C concentration is practically limited from the viewpoint of preventing the formation of carbides, and the value varies depending on the component composition of the steel, but can be appropriately set with reference to the Acm line of the phase diagram. The carbide means cementite.

表面C濃度を0.80%以上としたのは、第一にショットピーニングにより加工誘起マルテンサイト変態する残留オーステナイト量(以下、「変態残留オーステナイト量」と呼ぶ場合がある)を一定以上確保するためであり、第二に加工誘起変態マルテンサイト中のC濃度を高くして、マルテンサイト組織自体の硬さを向上させるためである。   The reason why the surface C concentration is 0.80% or more is to secure a certain amount or more of retained austenite that undergoes work-induced martensite transformation by shot peening (hereinafter sometimes referred to as “transformed retained austenite amount”). Secondly, the C concentration in the processing-induced transformation martensite is increased to improve the hardness of the martensite structure itself.

表面C濃度が0.80%未満になって、焼入れ・焼戻し後の残留オーステナイト量が不足すると、ショットピーニングを行っても、途中まで加工誘起マルテンサイト変態が進行したところで残留オーステナイトが安定化してしまい、それ以上はマルテンサイト変態しない。したがって加工誘起マルテンサイト量が不足し、初期硬さを十分に上昇させることができない。表面C濃度を0.80%以上とすることで、加工誘起マルテンサイト量を確保できる。   If the surface C concentration is less than 0.80% and the amount of retained austenite after quenching and tempering is insufficient, even if shot peening is performed, the retained austenite is stabilized when the processing-induced martensite transformation proceeds partway. No more martensitic transformation. Accordingly, the amount of work-induced martensite is insufficient and the initial hardness cannot be sufficiently increased. By setting the surface C concentration to 0.80% or more, the amount of processing-induced martensite can be secured.

また、表面C濃度が0.80%未満であると、所定量以上の残留オーステナイトを加工誘起マルテンサイト変態させたとしても、該マルテンサイト自体の硬さが低いため、十分な硬さを確保することができない。表面C濃度を0.80%以上にすることで、残留オーステナイト中のC濃度を高くでき、その結果、上述した様に、加工誘起マルテンサイト中のC濃度を高くすることができる。そして、加工誘起マルテンサイトの硬さは、該マルテンサイトのC濃度に比例して硬くなる。従って浸炭後の表面硬さを飛躍的に向上できる。   In addition, when the surface C concentration is less than 0.80%, even if a predetermined amount or more of retained austenite is transformed into work-induced martensite, the hardness of the martensite itself is low, so that sufficient hardness is ensured. I can't. By setting the surface C concentration to 0.80% or more, the C concentration in the retained austenite can be increased. As a result, as described above, the C concentration in the processing-induced martensite can be increased. And the hardness of a process induction martensite becomes hard in proportion to C density | concentration of this martensite. Therefore, the surface hardness after carburizing can be dramatically improved.

表面C濃度はより好ましくは0.88%以上、特に0.93%以上である。   The surface C concentration is more preferably 0.88% or more, particularly 0.93% or more.

本発明における浸炭は、ガス浸炭や真空浸炭などによって表面C濃度を適宜調整して行えばよい。本発明において、有効硬化層深さは、浸炭による効果を有効に発揮させるために、例えば0.7mm以上、好ましくは0.8mm以上、より好ましくは0.9mm以上にすることが推奨される。一方、有効硬化層深さが、2.0mmを超えると、長時間の浸炭が必要となりコストアップを招く。従って、有効硬化層深さの上限は2.0mm程度とするのが好ましい。なお、有効硬化層深さとは、JIS G0557で定義されるものを意味し、歯車の表面のビッカース硬さを測定したときに、硬さが550Hv以上となる領域の厚みを指す。   Carburization in the present invention may be performed by appropriately adjusting the surface C concentration by gas carburization, vacuum carburization, or the like. In the present invention, it is recommended that the effective hardened layer depth is, for example, 0.7 mm or more, preferably 0.8 mm or more, more preferably 0.9 mm or more in order to effectively exhibit the effect of carburization. On the other hand, when the effective hardened layer depth exceeds 2.0 mm, carburizing for a long time is required, resulting in an increase in cost. Therefore, the upper limit of the effective hardened layer depth is preferably about 2.0 mm. In addition, the effective hardened layer depth means what is defined by JIS G0557, and when the Vickers hardness of the surface of a gear is measured, it points out the thickness of the area | region where hardness becomes 550 Hv or more.

浸炭焼入れ・焼戻しのヒートパターンは特に限定されず、通常の条件が採用できる。例えば上記浸炭焼入れの後、焼戻ししても良いし、浸炭の後歪みを考慮して所定温度まで降温してから直接焼入れ・焼戻ししてもよい。   The heat pattern for carburizing and tempering is not particularly limited, and normal conditions can be adopted. For example, after carburizing and quenching, the steel may be tempered, or may be directly quenched and tempered after being cooled to a predetermined temperature in consideration of the distortion after carburizing.

(2)ショットピーニング
ショットピーニングは、アークハイト値が0.5mmA以上となるようにする。所定以上のアークハイト量のショットピーニングを行うことによって変態残留オーステナイト量を十分に確保することができ、その結果加工誘起変態マルテンサイト量が多量に生成し、歯車の初期硬さを向上させることができる。好ましいアークハイト値は0.50mmA以上である。アークハイト値の上限は特に限定されないが1.0mmA程度であってもよい。
(2) Shot peening In shot peening, the arc height value is set to 0.5 mmA or more. By performing shot peening with an arc height greater than a predetermined amount, a sufficient amount of transformation residual austenite can be secured, resulting in a large amount of work-induced transformation martensite and an improvement in the initial hardness of the gear. it can. A preferable arc height value is 0.50 mmA or more. The upper limit of the arc height value is not particularly limited, but may be about 1.0 mmA.

加工誘起マルテンサイト量は、ショットピーニング前後の残留オーステナイト量(変態残留オーステナイト量)によって評価できる。変態残留オーステナイト量は、例えば10面積%以上、好ましくは12面積%以上、さらに好ましくは13面積%以上である。変態残留オーステナイト量の上限は、特に限定されないが、例えば25面積%以下、特に20面積%以下程度であってもよい。   The amount of work-induced martensite can be evaluated by the amount of retained austenite before and after shot peening (the amount of transformation retained austenite). The amount of transformation residual austenite is, for example, 10 area% or more, preferably 12 area% or more, and more preferably 13 area% or more. The upper limit of the amount of transformation retained austenite is not particularly limited, but may be, for example, about 25 area% or less, particularly about 20 area% or less.

上記のようにして製造される本発明の歯車は、上述したように表面C濃度が0.80%以上(より好ましくは0.88%以上、特に0.93%以上)であり、表面に炭化物が生じていない(具体的には表面の炭化物が0面積%)ものである。さらに、焼入れ・焼戻し後の残留オーステナイトを所定量以上加工誘起マルテンサイト変態させているため、表面のビッカース硬さが880HV以上(好ましくは890HV以上、特に900〜940HV)となっている。なお本発明において「表面」とは厳密には表層から深さ50μmの位置のことをいう。   As described above, the gear of the present invention manufactured as described above has a surface C concentration of 0.80% or more (more preferably 0.88% or more, particularly 0.93% or more), and a carbide on the surface. (Specifically, the surface carbide is 0 area%). Further, since the retained austenite after quenching and tempering is transformed into a work-induced martensite by a predetermined amount or more, the surface Vickers hardness is 880 HV or more (preferably 890 HV or more, particularly 900 to 940 HV). In the present invention, the “surface” means a position at a depth of 50 μm from the surface layer.

以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に包含される。   EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

表1に示す化学組成の鋼を通常の溶製方法に従って溶解し、鋳造、分塊した後、熱間圧延し、その後φ32mmに熱間鍛造した。得られた棒状材を所定の形状に加工し、表2、3に示す表面C濃度となるように浸炭した(以下、浸炭後の試験片を「試験片a」と呼ぶ。)。浸炭温度は930℃、浸炭時間は240分である。その後、図1に示すように、油冷し(油温:50℃)、続いて170℃で120分の焼戻しを行った。   Steel having the chemical composition shown in Table 1 was melted in accordance with a normal melting method, cast, divided, hot rolled, and then hot forged to 32 mm. The obtained rod-shaped material was processed into a predetermined shape and carburized so as to have a surface C concentration shown in Tables 2 and 3 (hereinafter, the test piece after carburizing is referred to as “test piece a”). The carburizing temperature is 930 ° C. and the carburizing time is 240 minutes. Thereafter, as shown in FIG. 1, oil cooling was performed (oil temperature: 50 ° C.), followed by tempering at 170 ° C. for 120 minutes.

次いで、表2、3に示すアークハイト値でショットピーニングを行い(以下、ショットピーニング後の試験片を「試験片b」と呼ぶ。)、図2において「試験面」と表した部分の表層を10μm研磨、その他の部分を150μm研磨する仕上げ加工を施し、図2に示す形状および寸法の試験片(以下、「試験片c」と呼ぶ)を作成した。   Next, shot peening is performed at the arc height values shown in Tables 2 and 3 (hereinafter, the test piece after shot peening is referred to as “test piece b”), and the surface layer of the portion indicated as “test surface” in FIG. Finishing was performed by polishing 10 μm and polishing other parts by 150 μm, and a test piece having the shape and dimensions shown in FIG. 2 (hereinafter referred to as “test piece c”) was produced.

(1)ショットピーニング条件
ショット方式:空気式
ショット粒:直径:0.6〜0.8mm、硬さ:600〜800HV
(1) Shot peening conditions Shot method: Pneumatic shot grain: Diameter: 0.6 to 0.8 mm, Hardness: 600 to 800 HV

(2)表面C濃度の測定
表面C濃度の測定は、前記熱間鍛造後の棒状材を、φ26.02mm×130mmの形状に加工した後、上記同様に浸炭焼入れ・焼戻しし、表面を10μm研磨した試験片を用いた。前記試験片の、表面〜深さ50μmと、表面からの深さが50〜100μmからそれぞれ切粉サンプルを採取し、CS600型炭素硫黄分析装置(LECO社製)によってC濃度を測定した。表面〜深さ50μmのC濃度と、表面からの深さが50〜100μmのC濃度の平均値を、表面C濃度とした。
(2) Measurement of surface C concentration The surface C concentration was measured by processing the rod-shaped material after hot forging into a shape of φ26.02 mm × 130 mm, carburizing and tempering in the same manner as above, and polishing the surface by 10 μm. The test piece was used. Chip samples were collected from the surface to a depth of 50 μm and a depth from the surface of 50 to 100 μm, respectively, and the C concentration was measured by a CS600 type carbon sulfur analyzer (manufactured by LECO). The average value of the C concentration from the surface to the depth of 50 μm and the C concentration from the surface to the depth of 50 to 100 μm was defined as the surface C concentration.

(3)炭化物面積率の測定
炭化物面積率は、前記試験片cの長手方向の中央部を横断で切断し、表面から深さ50μmの位置を走査型電子顕微鏡(SEM)を用いて測定した。任意の9μm×12μmの視野を、倍率8000倍で観察し、画像解析ソフトで炭化物の部分を識別し面積率を求めた。測定は3視野行い、それら3視野の算術平均を炭化物の面積率とした。
(3) Measurement of carbide area ratio The carbide area ratio was measured by cutting the longitudinal central portion of the test piece c across the surface and using a scanning electron microscope (SEM) at a position 50 μm deep from the surface. An arbitrary visual field of 9 μm × 12 μm was observed at a magnification of 8000 times, and the carbide portion was identified by image analysis software to determine the area ratio. The measurement was performed for 3 fields of view, and the arithmetic average of these 3 fields of view was defined as the area ratio of carbide.

(4)残留オーステナイト量の測定
残留オーステナイト量の面積率は、ショットピーニング前(浸炭焼入れ焼き戻し後)と、ショットピーニング後の試験片についてそれぞれ測定した。ショットピーニング前の試験片については、前記試験片aの中央部を電解研磨によって表面から60μm研磨し、微小部X線測定装置(リガク製)を用いて、残留オーステナイトの面積率を測定した。ショットピーニング後の試験片の残留オーステナイト面積率については、前記試験片bの中央部を電解研磨によって表面から60μm研磨し、前記微小部X線測定装置を用いて測定した。ショットピーニング前、後ともに、測定は3箇所について行った。ショットピーニング前、後それぞれについて前記3箇所の測定値の算術平均を求め、それぞれショットピーニング前、後の残留オーステナイト量(面積率)とした。
(4) Measurement of amount of retained austenite The area ratio of the amount of retained austenite was measured for each test piece before shot peening (after carburizing, quenching and tempering) and after shot peening. About the test piece before shot peening, the center part of the said test piece a was grind | polished 60 micrometers from the surface by electropolishing, and the area ratio of the retained austenite was measured using the micro part X-ray measuring apparatus (product made from Rigaku). About the retained austenite area ratio of the test piece after shot peening, the center part of the said test piece b was grind | polished 60 micrometers from the surface by electrolytic polishing, and it measured using the said micro part X-ray measuring apparatus. Measurement was performed at three locations both before and after shot peening. Before and after shot peening, the arithmetic average of the measured values at the three locations was determined, and the amount of retained austenite (area ratio) before and after shot peening was obtained.

(5)表面粗さの測定
表面粗さは、表面粗さ測定機(小坂研究所製、SE3300)を用い、前記試験片bの長手方向中央部を、軸芯に対して90°毎に4ヶ所測定し、それぞれ算術平均粗さを求めた。それら4箇所の算術平均粗さの平均値を表面平均粗さとした。表面平均粗さが2.0μm以下を合格とした。
(5) Measurement of surface roughness Using a surface roughness measuring machine (SE3300, manufactured by Kosaka Laboratories), the surface roughness is 4 for each 90 ° with respect to the central portion in the longitudinal direction of the test piece b. Measurements were made at various points, and the arithmetic average roughness was obtained. The average value of the arithmetic average roughness at these four locations was defined as the surface average roughness. A surface average roughness of 2.0 μm or less was accepted.

(6)剥離寿命の測定
剥離寿命の測定は、前記試験片cを用い、二円筒試験機(コマツエンジニアリング製、RP201型)によって行った。試験条件は、面圧:3.0GPa、回転速度:1500rpm、相対すべり率:60%、油温:90℃で行った。寿命は、一般的な肌焼鋼であるSCr420Hの0.75%浸炭品(ショットピーニング無し)の寿命を1とした場合の寿命比で評価した。
(6) Measurement of peeling life The peeling life was measured by a two-cylinder testing machine (manufactured by Komatsu Engineering, RP201 type) using the test piece c. The test conditions were as follows: surface pressure: 3.0 GPa, rotation speed: 1500 rpm, relative slip ratio: 60%, oil temperature: 90 ° C. The life was evaluated by the life ratio when the life of a 0.75% carburized product (no shot peening) of SCr420H, which is a general case-hardened steel, was 1.

結果を表2、3に示す。   The results are shown in Tables 2 and 3.

No.1〜22は成分組成、表面C濃度、アークハイト値の全てにおいて本発明要件を満たしているため、残留オーステナイトの変態量を10面積%以上とすることができ、また炭化物面積率も本発明要件を満たすため、剥離寿命がSCr420Hの0.75%浸炭品(ショットピーニング無し)に対する寿命比(以下、単に「寿命比」と呼ぶ)で10倍以上となった例である。一方、No.23〜34は前記のいずれかの要件を満足しなかったため、寿命比の向上がNo.1〜22に比較して不十分だった例である。   No. 1 to 22 satisfy the requirements of the present invention in all of the component composition, surface C concentration, and arc height value, so that the transformation amount of retained austenite can be made 10 area% or more, and the carbide area ratio is also a requirement of the present invention. In order to satisfy the above, the peeling life is an example in which the life ratio (hereinafter simply referred to as “lifetime ratio”) with respect to the 0.75% carburized product of SCr420H (hereinafter simply referred to as “lifetime ratio”) is 10 times or more. On the other hand, no. No. 23 to 34 did not satisfy any of the above requirements. This is an example that was insufficient as compared with 1-22.

No.23は、表面C濃度が少なかったため、浸炭焼入れ・焼戻し後の残留オーステナイト量(表2、3中、「ショットピーニング前の残留γ量」で表す)が少なく、残留オーステナイトの変態量を10面積%以上確保することができず、硬さが低かった例である。硬さが低いことによってショットピーニングによる凹凸を生じ、表面平均粗さが上昇したため、二円筒試験が行わなかった例である。   No. No. 23 had a small surface C concentration, so the amount of retained austenite after carburizing and tempering was small (in Tables 2 and 3, "Residual γ amount before shot peening"), and the transformation amount of retained austenite was 10% by area. This is an example in which the above cannot be ensured and the hardness is low. This is an example in which the two-cylinder test was not performed because unevenness due to shot peening was generated due to low hardness and the surface average roughness was increased.

No.24、25は、表面C濃度が低かったため焼入れ・焼戻し後の残留オーステナイト量が少なく、変態残留オーステナイト量が確保できず、硬さが低いものとなり、寿命比の向上が不十分だった例である。   No. Nos. 24 and 25 are examples in which the amount of retained austenite after quenching and tempering was small because the surface C concentration was low, the amount of transformation retained austenite could not be secured, the hardness was low, and the life ratio was insufficiently improved. .

No.26、27は表面C濃度が高く、炭化物が生成してしまい炭化物を起点として剥離が発生したため、変態残留オーステナイト量、硬さ、および表面粗さを全て満足するにも関わらず、寿命比の向上が不十分だった例である。   No. Nos. 26 and 27 have high surface C concentrations, and carbides are generated and peeling occurs from the carbides. Therefore, the life ratio is improved despite satisfying all of the transformation residual austenite amount, hardness, and surface roughness. Is an example of insufficient.

No.28、29は、Si量が少なかったため表面粗さが上昇したため、二円筒試験を行わなかった例である。   No. Nos. 28 and 29 are examples in which the two-cylinder test was not performed because the surface roughness increased because the amount of Si was small.

No.30、31は、ショットピーニングのアークハイト値が低かったため、変態残留オーステナイト量が少なく、硬さが低いものとなり、寿命比の向上が不十分だった例である。   No. Nos. 30 and 31 are examples in which the arc height value of shot peening was low, the transformation retained austenite amount was small, the hardness was low, and the life ratio was insufficiently improved.

No.32、33はそれぞれ、JISのSCr420H、SCM420Hに相当する成分組成であるが、Si量が少ないため、ショットピーニングにより表面粗さが上昇し、二円筒試験が行わなかった例である。   No. 32 and 33 are component compositions corresponding to JIS SCr420H and SCM420H, respectively. However, since the amount of Si is small, the surface roughness is increased by shot peening and the two-cylinder test is not performed.

No.34はJISのSCr420Hに相当する成分組成であるが、Si量が少なかったためショットピーニングによる表面粗さが上昇したとともに、表面C濃度が低かったため焼入れ・焼戻し後の残留オーステナイト量が少なく、変態残留オーステナイト量が確保できず、寿命比の向上が不十分だった例である。   No. 34 is a component composition corresponding to JIS SCr420H, but since the amount of Si was small, the surface roughness due to shot peening increased, and since the surface C concentration was low, the amount of retained austenite after quenching and tempering was small, and transformed retained austenite. This is an example where the amount could not be secured and the improvement in the life ratio was insufficient.

実施例の欄の浸炭焼入れ・焼戻しのヒートパターンを示す概略図である。It is the schematic which shows the heat pattern of carburizing quenching and tempering of the column of an Example. 二円筒試験に用いた試験片の形状を示す概略図である。It is the schematic which shows the shape of the test piece used for the two-cylinder test.

Claims (4)

C :0.15〜0.25%(質量%の意味。以下、化学成分組成について同じ。)、
Si:0.50〜1.6%、
Mn:0.3〜2%、
P :0.02%以下(0%を含まない)、
S :0.03%以下(0%を含まない)、
Cr:0.5〜2%、
Al:0.1%以下(0%を含まない)、
N :0.03%以下(0%を含まない)
を含有し、残部は鉄および不可避不純物である鋼で形成された歯車を、
炭化物を生じることなく浸炭して表面C濃度を0.80%以上とし、焼入れ・焼戻しした後、
アークハイト値が0.5mmA以上のショットピーニングをし、
前記ショットピーニングにより、表面組織に占める割合で10面積%以上の残留オーステナイトを加工誘起マルテンサイト変態させたことを特徴とする耐高面圧性に優れた歯車の製造方法。
C: 0.15 to 0.25% (meaning mass%, hereinafter the same for chemical composition)
Si: 0.50 to 1.6%,
Mn: 0.3-2%,
P: 0.02% or less (excluding 0%),
S: 0.03% or less (excluding 0%),
Cr: 0.5-2%
Al: 0.1% or less (excluding 0%),
N: 0.03% or less (excluding 0%)
Containing the gears formed of steel, the balance of which is iron and inevitable impurities,
After carburizing without producing carbides and making the surface C concentration 0.80% or more, quenching and tempering,
Shot peening with an arc height value of 0.5 mmA or more,
A method for producing a gear excellent in high surface pressure resistance, characterized in that, by shot peening, 10% by area or more of retained austenite as a percentage of the surface structure is transformed into work-induced martensite.
前記鋼は、更に
Mo:0.08〜0.8%を含有する請求項1に記載の製造方法。
The manufacturing method according to claim 1, wherein the steel further contains Mo: 0.08 to 0.8%.
前記鋼は、更に
B :0.0005〜0.005%、
Nb:0.01〜0.1%、
Ti:0.01〜0.1%
よりなる群から選ばれる少なくとも一種以上を含有する請求項1または2に記載の製造方法。
The steel further contains B: 0.0005 to 0.005%,
Nb: 0.01 to 0.1%,
Ti: 0.01 to 0.1%
The manufacturing method of Claim 1 or 2 containing at least 1 or more types chosen from the group which consists of.
請求項1〜3のいずれかに記載の成分の鋼からなり、浸炭されている歯車であって、
表面C濃度が0.80%以上であり、
表面の炭化物が0面積%であるとともに、
表面のビッカース硬さが880Hv以上であることを特徴とする耐高面圧性に優れた歯車。
A gear made of steel of the component according to any one of claims 1 to 3 and carburized,
The surface C concentration is 0.80% or more,
The surface carbide is 0 area%,
A gear having excellent high surface pressure resistance, wherein the surface has a Vickers hardness of 880 Hv or more.
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