JP2549039B2 - Carbonitriding heat treatment method for high strength gears with small strain - Google Patents

Carbonitriding heat treatment method for high strength gears with small strain

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Publication number
JP2549039B2
JP2549039B2 JP3236604A JP23660491A JP2549039B2 JP 2549039 B2 JP2549039 B2 JP 2549039B2 JP 3236604 A JP3236604 A JP 3236604A JP 23660491 A JP23660491 A JP 23660491A JP 2549039 B2 JP2549039 B2 JP 2549039B2
Authority
JP
Japan
Prior art keywords
tooth
less
carbonitriding
transformation point
tooth surface
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
JP3236604A
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Japanese (ja)
Other versions
JPH0570925A (en
Inventor
秀雄 蟹澤
俊道 森
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
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Priority to JP3236604A priority Critical patent/JP2549039B2/en
Publication of JPH0570925A publication Critical patent/JPH0570925A/en
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Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Description

【発明の詳細な説明】Detailed Description of the Invention

【0001】[0001]

【産業上の利用分野】本発明は、浸炭窒化熱処理方法、
特に焼入れ時の歪が少なく、騒音の少ない自動車トラン
スミッション用ギアを製造することのできる肌焼鋼の浸
炭窒化熱処理方法に関するものである。
The present invention relates to a carbonitriding heat treatment method,
In particular, the present invention relates to a carbonitriding heat treatment method for case-hardening steel capable of producing a gear for an automobile transmission with less distortion during quenching and less noise.

【0002】[0002]

【従来の技術】一般に、自動車用歯車には、耐疲労強度
および表面の耐摩耗性を高めるために、肌焼鋼が使用さ
れている。この場合、肌焼鋼は歯車等の所定形状に機械
加工された後、表面硬化のために浸炭窒化処理を施され
る。すなわち、炭素含有量の比較的低い低合金鋼の表面
に炭素と窒素を浸透させ、次に焼入れ、焼戻しを施し
て、歯表面をマルテンサイトにすることで硬化させ、か
つ歯車の靱性を確保する意味から、歯車芯部を一部マル
テンサイトあるいはベイナイトを含んだフェライト・パ
ーライト組織にする。ただし、歯車芯部とは図1(B)
の網掛で示す歯車の中央部である。このように歯表面と
歯車芯部の組織差を利用することは、耐疲労強度および
靱性を得るための基本原理であり、また浸炭窒化焼入れ
法において、冷却速度の質量効果を利用することにより
十分達成されていることは周知の事実である。
2. Description of the Related Art Generally, case hardening steel is used for automobile gears in order to improve fatigue resistance and surface wear resistance. In this case, the case-hardening steel is machined into a predetermined shape such as a gear and then carbonitrided for surface hardening. That is, carbon and nitrogen are infiltrated into the surface of a low alloy steel having a relatively low carbon content, and then quenching and tempering are performed to harden the tooth surface by making it martensite and to secure the toughness of the gear. From the point of view, the core of the gear has a ferrite-pearlite structure that partially contains martensite or bainite. However, the gear core is shown in Fig. 1 (B).
It is the central part of the gear shown by the mesh. Utilizing the difference in texture between the tooth surface and the gear core is a basic principle for obtaining fatigue strength and toughness, and in the carbonitriding and quenching method, it is sufficient to utilize the mass effect of the cooling rate. What has been achieved is a well-known fact.

【0003】しかしながら、歯車芯部は質量効果により
一部マルテンサイトあるいはベイナイトを含んだフェラ
イト・パーライト組織になるものの、歯内部(図1
(A)の斜線部で示される歯の浸炭層より内側の部分)
は芯部より冷速が速いため、焼入れ組織であるマルテン
サイトと一部ベイナイトの混在組織になる。この時、マ
ルテンサイト生成による変態応力(オーステナイトから
マルテンサイト組織に変化するときに生じる体積膨張に
起因する応力)が発生するため、熱処理変形の発生が避
けられず、歯車精度を維持することができない。特に、
自動車トランスミッション用ギアは、騒音に対して最も
厳しい制限があるにも拘らず、小さくかつ肉厚が薄いた
め、歯内部の組織はマルテンサイトとベイナイト組織に
なり、このことが歯車騒音の最大の原因になっている。
However, although the gear core part has a ferrite-pearlite structure containing a part of martensite or bainite due to the mass effect, the inside of the tooth (see FIG. 1).
(A portion inside the carburized layer of the tooth shown by the hatched portion in (A))
Has a faster cooling rate than the core, and therefore has a mixed structure of martensite, which is a quenched structure, and part of bainite. At this time, transformation stress due to martensite formation (stress due to volume expansion that occurs when changing from austenite to martensite structure) occurs, so heat treatment deformation cannot be avoided and gear precision cannot be maintained. . In particular,
Despite the strictest restrictions on noise, automotive transmission gears are small and thin, resulting in martensite and bainite microstructures inside the teeth, which is the largest contributor to gear noise. It has become.

【0004】そこで従来は、焼入れ歪に対して歯車研削
を追加することにより、精度を向上させる方法が用いら
れている。また、イオン窒化、ガス軟窒化やタフトライ
ドなどの低温で行う窒化処理等も検討されている。さら
に、特開昭55−6456号公報では、等温焼きなまし
処理によりフェライト・パーライト組織にした後、軟窒
化処理により表面のみ硬化する方法が開示されており、
また一旦フェライト・パーライト組織にした後、窒化処
理により表面層のA1 変態点を下げてオーステナイト化
を促進させ、急冷によって表面層のみマルテンサイト組
織を得る方法(金属臨時増刊号、1990年,Vo1
8,P25)が開示されている。
Therefore, conventionally, a method of improving accuracy by adding gear grinding to quenching distortion has been used. In addition, nitriding treatments performed at low temperatures such as ion nitriding, gas soft nitriding, and tuftride are being studied. Further, Japanese Patent Application Laid-Open No. 55-6456 discloses a method of forming a ferrite-pearlite structure by an isothermal annealing process and then hardening only the surface by a soft nitriding process.
In addition, a method in which after the ferrite / pearlite structure is once formed, the A 1 transformation point of the surface layer is lowered by nitriding treatment to promote austenitization and a martensite structure is obtained only in the surface layer by quenching (Metal Temporary Special Issue, 1990, Vo1
8, P25) is disclosed.

【0005】[0005]

【発明が解決しようとする課題】しかし、歯車機械研削
では浸炭窒化層を部分的に削り取ることから、製造工程
数が増加するほか、複雑な形状部品には適用しがたく、
また表面硬さや残留応力にムラを生ずることとなり、品
質上の問題があった。一方、イオン窒化、ガス軟窒化や
タフトライドおよび特開昭55−6456号公報の方法
では、焼入れ硬化層が薄く、また内部硬度が低いため、
十分な疲労強度が得られない。また、窒化処理により表
面層のA1 変態点を下げてオーステナイト化を促進さ
せ、急冷によって表面層のみマルテンサイト組織を得る
方法は、浸炭窒化部に異常化合物層の形成による硬度低
下が生じ、また内部硬度が低いため十分な疲労強度が得
られない、という問題を有してした。
However, in the mechanical grinding of gears, the carbonitriding layer is partially shaved off, which increases the number of manufacturing steps and makes it difficult to apply to parts having complicated shapes.
Further, the surface hardness and the residual stress are uneven, which is a quality problem. On the other hand, in the methods of ion nitriding, gas soft nitriding, tuftride and JP-A-55-6456, since the quench hardened layer is thin and the internal hardness is low,
Sufficient fatigue strength cannot be obtained. Further, in the method of lowering the A 1 transformation point of the surface layer by nitriding treatment to promote austenitization and obtaining the martensite structure only in the surface layer by rapid cooling, hardness is reduced due to formation of an abnormal compound layer in the carbonitrided portion, and There was a problem that sufficient fatigue strength could not be obtained due to the low internal hardness.

【0006】すなわち、従来の機械加工法では経済性と
歯車自身の品質を犠牲にしたものであり、材料側からの
取組みも、歯内部のマルテンサイト防止により歪は軽減
できるものの、歯車本来の特性である高疲労強度を犠牲
にしたものであり、高強度化を維持しつつ歯内部を完全
なフェライトとパーライト組織にする有効な方法が望ま
れている。
That is, the conventional machining method sacrifices economy and the quality of the gear itself, and even when the material is used, distortion can be reduced by preventing martensite inside the tooth, but the original characteristics of the gear are obtained. This is a sacrifice of high fatigue strength, and an effective method for forming a complete ferrite and pearlite structure inside the tooth while maintaining high strength is desired.

【0007】[0007]

【課題を解決するための手段】本発明者らは、このよう
な実情に対処して、浸炭窒化焼入れ処理による歪の発生
が少なく、かつ優れた硬化特性が得られる浸炭窒化歯車
用の素材を開発するために多くの研究を行ってきた。す
なわち、浸炭窒化処理は、表面層のみA1 変態点を下げ
るため、歯内部をフェライト・パーライト組織にしつつ
表面層のみオーステナイトにする極めて有効な方法であ
り、該処理における表層化合物層の生成挙動および歯内
部強度は主に鋼材組成に依存する。従って、高強度化を
維持しつつ歯内部を完全なフェライトとパーライト組織
にする有効な方法の開発を目的に、浸炭窒化条件および
鋼材組成の両面から詳細な検討を加えた結果、以下の知
見を得た。
Means for Solving the Problems The inventors of the present invention have dealt with such a situation, and have developed a material for carbonitrided gears in which distortion due to carbonitriding and quenching treatment is small and excellent hardening characteristics are obtained. Much research has been done to develop it. That is, the carbonitriding treatment is an extremely effective method for reducing the A 1 transformation point only in the surface layer and thus making only the surface layer austenite while forming the ferrite / pearlite structure inside the tooth. The internal strength of the tooth mainly depends on the steel composition. Therefore, for the purpose of developing an effective method for forming a complete ferrite and pearlite structure inside the tooth while maintaining high strength, as a result of conducting a detailed study from both aspects of carbonitriding conditions and steel composition, the following findings were obtained. Obtained.

【0008】浸炭窒化処理において,表層化合物層、
内部酸化層および不完全焼入れ層の生成が表層の硬度低
下をもたらす。これらの生成防止にはCrおよびSiを
低減しつつ、表層が十分に硬化するように焼入れ性を高
めておくことが有効である。 硬化層深さの増大には、浸炭窒化処理により表面層か
ら深くまでオーステナイト化することが必要であり、こ
れには表層の化合物層の生成を抑制することが有効であ
る。
In the carbonitriding treatment, the surface compound layer,
The formation of the internal oxide layer and the incompletely hardened layer causes a decrease in the hardness of the surface layer. To prevent the formation of these, it is effective to increase the hardenability so that the surface layer is sufficiently hardened while reducing Cr and Si. In order to increase the depth of the hardened layer, it is necessary to deepen the austenite from the surface layer by carbonitriding, and it is effective to suppress the formation of the surface compound layer.

【0009】歯内部がフェライト・パーライト組織に
なることによる硬度低下は、炭窒化物の析出硬化および
微細化効果により抑制できる。さらに、化合物層の生成
抑制の観点より、特定量のV添加が有効である。そこ
で、こうした知見に基づいて、具体的な達成手段を明ら
かにするため、さらに研究検討を重ね、特定の化学組成
の肌焼鋼より製造された歯車に、浸炭窒化処理を施した
直後に、特定の温度範囲に所定時間保持し、その後焼入
れ、焼戻しを行うことにより、表面硬さを低下させず
に、歯内部の組織をフェライトと微細パーライト組織と
し、かくして騒音の発生源となる歯の焼入れ時の歪を大
幅に低減し、かつ静粛性を著しく向上させ得る新しい歯
車の浸炭窒化熱処理方法を完成させた。
The decrease in hardness due to the ferrite / pearlite structure inside the tooth can be suppressed by the precipitation hardening and miniaturization effects of carbonitride. Further, addition of a specific amount of V is effective from the viewpoint of suppressing the formation of the compound layer. Therefore, based on these findings, in order to clarify the concrete means of achievement, further research and studies were carried out, and immediately after the carbonitriding treatment was applied to the gear manufactured from case hardening steel of a specific chemical composition, During the quenching of the tooth, which is a source of noise, the structure inside the tooth is made to be a ferrite and fine pearlite structure without lowering the surface hardness by holding in the temperature range for a specified time and then quenching and tempering. We have completed a new carbonitriding heat treatment method for gears that can significantly reduce the strain and significantly improve quietness.

【0010】すなわち、本発明の要旨とするところは下
記のとおりである。 (1)重量%で、C:0.1%以上0.3%未満、S
i:0.15%未満、Mn:0.30%以上1.50%
未満、Cr:0.30%以上1.00%未満、Mo:
0.10%以上1.00%未満、V:0.05%以上
1.00%未満を含有し、残部Feおよび不純物よりな
る鋼を素材とした歯車に、浸炭窒化処理を施し、その後
直ちに、あるいはいったん歯表面部(浸炭窒化部)のA
1 変態点以下の温度域まで冷却し、再度歯表面部(浸
炭窒化部)のAc3 変態点以上に加熱した後、歯表面部
(浸炭窒化部)のAr3 変態点以上で歯内部(非浸炭窒
化部)のAr1 変態点以下の温度域に5分以上2時間未
満保持して、歯表面をオーステナイト状態に保ちつつ歯
内部を微細なフェライト・パーライトにし、しかる後に
焼入れ、焼戻しを行うことにより、歯内部を微細なフェ
ライト・パーライト組織とすることを特徴とする歪の小
さい高強度歯車の浸炭窒化熱処理方法。
That is, the gist of the present invention is as follows. (1)% by weight, C: 0.1% or more and less than 0.3%, S
i: less than 0.15%, Mn: 0.30% or more and 1.50%
Less than, Cr: 0.30% or more and less than 1.00%, Mo:
Gears made of steel containing 0.10% or more and less than 1.00% and V: 0.05% or more and less than 1.00% with the balance Fe and impurities are carbonitrided, and immediately thereafter, Or once A of the tooth surface part (carbonitriding part)
r 1 is cooled to a temperature range below the transformation point, after heating to above Ac 3 transformation point of the tooth surface portion again (carbonitriding unit), the teeth inside the above Ar 3 transformation point of the tooth surface portion (carbonitriding unit) ( Hold the temperature in the temperature range below the Ar 1 transformation point of the (non-carbonitriding part) for 5 minutes or more and less than 2 hours to form a fine ferrite pearlite inside the tooth while keeping the tooth surface in the austenite state, and then quench and temper. Thus, a carbonitriding heat treatment method for a high-strength gear with small strain, characterized in that the inside of the tooth has a fine ferrite-pearlite structure.

【0011】ただし、歯内部とは図1(A)の斜線部で
示される歯の浸炭層より内側である。 (2)重量%で、C:0.1%以上0.3%未満、S
i:0.15%未満、Mn:0.30%以上1.50%
未満、Cr:0.30%以上1.00%未満、Mo:
0.10%以上1.00%未満、V:0.05%以上
1.00%未満を含むとともに、Nb:0.02%以上
0.20%以下、Ti:0.01%以上0.20%以下
の1種以上を含有し、残部Feおよび不純物よりなる鋼
を素材とした歯車に、浸炭窒化処理を施し、その後直ち
に、あるいはいったん歯表面部(浸炭窒化部)のAr1
変態点以下の温度域まで冷却し、再度歯表面部(浸炭窒
化部)のAc3 変態点以上に加熱した後、歯表面部(浸
炭窒化部)のAr3 変態点以上で歯内部(非浸炭窒化
部)のAr1 変態点以下の温度域に5分以上2時間未満
保持して、歯表面をオーステナイト状態に保ちつつ歯内
部を微細なフェライト・パーライトにし、しかる後に焼
入れ、焼戻しを行うことにより、歯内部を微細なフェラ
イト・パーライトとすることを特徴とする歪の小さい高
強度歯車の浸炭窒化熱処理方法。
However, the inside of the tooth is the inside of the carburized layer of the tooth shown by the shaded portion in FIG. 1 (A). (2) In% by weight, C: 0.1% or more and less than 0.3%, S
i: less than 0.15%, Mn: 0.30% or more and 1.50%
Less than, Cr: 0.30% or more and less than 1.00%, Mo:
0.10% or more and less than 1.00%, V: 0.05% or more and less than 1.00%, and Nb: 0.02% or more and 0.20% or less, Ti: 0.01% or more and 0.20. %, One or more of the steel containing the balance Fe and impurities is carbonitrided and then immediately or once Ar 1 of the tooth surface (carbonitrided part)
After cooling to a temperature range below the transformation point and heating again to the Ac 3 transformation point of the tooth surface portion (carbonitriding portion) or higher, inside the tooth (non-carburized) above the Ar 3 transformation point of the tooth surface portion (carbonitriding portion) By maintaining the temperature range below the Ar 1 transformation point of the nitrided part) for 5 minutes or more but less than 2 hours to make the tooth surface fine ferrite pearlite while keeping the tooth surface in an austenite state, and then quenching and tempering , A method for carbonitriding heat treatment of a high-strength gear with small strain, characterized in that the inside of the tooth is made of fine ferrite pearlite.

【0012】ただし、歯内部とは図1(A)の斜線部で
示される歯の浸炭層より内側である。以下に本発明の各
構成要件について説明する。最初に、本発明の浸炭窒化
熱処理方法が適用できる合金鋼の化学成分について述べ
る。
However, the inside of the tooth is the inside of the carburized layer of the tooth shown by the shaded portion in FIG. 1 (A). Each constituent element of the present invention will be described below. First, the chemical composition of the alloy steel to which the carbonitriding heat treatment method of the present invention can be applied will be described.

【0013】本発明における合金鋼は、浸炭窒化処理を
行う炉中の冷却で、歯内部の組織をフェライト・パーラ
イトにでき、しかも歯車としての剛性や靱性等を維持す
るのに十分な内部硬さでなければならない。一方、この
合金鋼は浸炭窒化されるため、浸炭窒化処理により悪影
響を受けない化学成分でなければならない。Cは自動車
用歯車として必要な強度、特に芯部強度を確保するため
に添加する元素であるが、0.1%未満ではこのような
効果を十分に得ることができず、0.3%以上では靱性
が低下して脆くなり、浸炭用鋼として使用が困難となる
ので、その含有量を0.1%以上0.3%未満とした。
The alloy steel of the present invention can be made into a ferrite / pearlite structure inside the tooth by cooling in a furnace for carbonitriding, and has an internal hardness sufficient to maintain rigidity and toughness as a gear. Must. On the other hand, since this alloy steel is carbonitrided, it must have a chemical composition that is not adversely affected by carbonitriding. C is an element added to secure the strength required for automobile gears, especially the core strength, but if it is less than 0.1%, such an effect cannot be sufficiently obtained, and 0.3% or more. In that case, the toughness is reduced and the steel becomes brittle, which makes it difficult to use as a carburizing steel, so the content thereof is set to 0.1% or more and less than 0.3%.

【0014】Siは浸炭用鋼の粒界酸化に著しく悪影響
を及ぼす元素であり、含有量は0.15%以上では浸炭
層に顕著な粒界酸化が形成され、浸炭用鋼の材質特性が
劣化するため、その含有量を0.15%未満とした。M
nは鋼に強度、靱性、焼入れ性を与えるのに必要な元素
であるが、1.50%以上では熱間圧延後の冷却におい
てベイナイトやマルテンサイトの硬質な組織になり、そ
の後の切削等の二次加工には適さなくなるために1.5
0%未満とする。しかし、Mnの添加量が0.30%未
満では焼入れ性向上の効果が十分でなく、その含有量は
0.30%以上とする。
Si is an element that has a significant adverse effect on the grain boundary oxidation of carburizing steel, and when the content is 0.15% or more, remarkable grain boundary oxidation is formed in the carburized layer, and the material properties of the carburizing steel deteriorate. Therefore, the content is set to less than 0.15%. M
n is an element necessary for imparting strength, toughness, and hardenability to steel, but when it is 1.50% or more, it becomes a hard structure of bainite or martensite in cooling after hot rolling, and after cutting etc. 1.5 because it is not suitable for secondary processing
Less than 0%. However, if the addition amount of Mn is less than 0.30%, the effect of improving the hardenability is not sufficient, and the content thereof is 0.30% or more.

【0015】Crは鋼の浸炭窒化層に化合物層を形成
し、表面硬度を低下し、併せてNの鉄中への固溶を阻害
し、また浸炭窒化層のオーステナイト化温度を上げ、オ
ーステナイト化を阻害する。1.00%以上では顕著に
化合物層を形成し、窒化処理を阻害するため1.00%
未満とする。しかし、Crの添加量が0.30%未満で
は焼入れ性向上の効果が十分でなく、その含有量は0.
30%以上とする。
Cr forms a compound layer in the carbonitrided layer of steel, lowers the surface hardness and, at the same time, inhibits the solid solution of N in iron, and raises the austenitizing temperature of the carbonitrided layer to austenite. Inhibit. At 1.00% or more, a compound layer is formed remarkably and nitriding treatment is hindered, so 1.00%
Less than However, if the added amount of Cr is less than 0.30%, the effect of improving the hardenability is not sufficient, and the content of Cr is 0.1.
30% or more.

【0016】Moは粒界酸化層を形成することなしに鋼
の耐摩耗性、焼入れ性、機械的特性を向上し、特に歯内
部の硬度上昇に有用な元素であり、0.10%未満では
その効果が十分でなく、1.00%以上では靱性を劣化
させるため、0.10%以上1.00%未満とする。V
は炭窒化物の析出硬化により、歯内部のフェライト・パ
ーライトの硬度上昇をもたらす元素であるが、0.05
%未満ではその効果が十分でなく、1.00%以上を含
有しても効果は飽和するため、0.05%以上1.00
%未満とする。
Mo is an element which improves the wear resistance, hardenability and mechanical properties of steel without forming an intergranular oxide layer, and is particularly useful for increasing the hardness inside the tooth. The effect is not sufficient, and if it is 1.00% or more, the toughness is deteriorated, so the content is made 0.10% or more and less than 1.00%. V
Is an element that increases the hardness of ferrite / pearlite inside the tooth due to the precipitation hardening of carbonitride.
%, The effect is not sufficient, and even if 1.00% or more is contained, the effect is saturated, so 0.05% or more and 1.00
Less than%.

【0017】TiおよびNbは炭窒化物を生成し、浸炭
結晶粒の微細化に効果のある元素であり、その効果を得
るには1種以上の元素をNbで0.02%以上およびT
iで0.01%以上の含有が必要である。しかし、Nb
で0.20%を超えて、Tiで0.20%を超えて含有
しても効果は飽和するため、上限をNbで0.20%、
Tiで0.20%とする。
Ti and Nb are elements that generate carbonitrides and are effective in refining carburized crystal grains. To obtain the effect, at least one element of Nb is 0.02% or more and T is T.
It is necessary that the content of i is 0.01% or more. However, Nb
If the content of Ti exceeds 0.20% and the content of Ti exceeds 0.20%, the effect is saturated, so the upper limit is 0.20% for Nb,
Ti is set to 0.20%.

【0018】上記成分のほか、以下に示す元素を添加す
ることにより、よりいっそう特性の向上が可能である。
CaはMnSの延伸抑制のために必要な元素であり、歯
車の疲労における異方性を軽減する。MnSの延伸抑制
効果を与えるために、Caを0.0010%以上含有さ
せる。しかし、0.010%を超えて含有させても、そ
の効果は飽和して経済性を損うため上限を0.010%
とする。
The characteristics can be further improved by adding the following elements in addition to the above components.
Ca is an element necessary for suppressing the stretching of MnS and reduces anisotropy in fatigue of gears. To give the effect of suppressing the stretching of MnS, Ca is contained in an amount of 0.0010% or more. However, even if the content exceeds 0.010%, the effect is saturated and the economy is impaired, so the upper limit is 0.010%.
And

【0019】次に、浸炭窒化法としては、ガス浸炭窒化
法または液体浸炭窒化法が好ましく、また浸炭窒化深さ
は表層硬さおよび残留応力の観点から0.5mm以上であ
ることが好ましい。表面炭素量が共析以上、Acm以下の
カーボンポテンシャルにて850〜980℃の温度で浸
炭窒化処理することにより、非浸炭窒化部に比べ浸炭窒
化部のAr 3 変態点が約50℃下がる(浸炭窒化温度:
930℃、カーボンポテンシャル:0.9%、Nポテン
シャル:2%、JIS SCM420での、本発明者ら
の実験例)。
Next, the carbonitriding method is gas carbonitriding.
Method or liquid carbonitriding method is preferable, and carbonitriding depth
Is 0.5 mm or more from the viewpoint of surface hardness and residual stress.
Preferably. Surface carbon content is more than eutectoid and less than Acm
Immerse at a temperature of 850-980 ° C with carbon potential
By carbonitriding, carbonitriding compared to non-carbonitriding parts
Ar of the chemical department 3The transformation point drops by about 50 ° C (carbonitriding temperature:
930 ° C, carbon potential: 0.9%, N potene
Shall: 2%, the present inventors at JIS SCM420
Experimental example).

【0020】浸炭窒化後炉冷等により660〜700℃
(歯表面部のAr3変態点以上で歯内部のAr1 変態点
以下)に冷却した後、一定時間保持することにより、非
浸炭窒化部の歯内部をフェライトと微細パーライトに変
態させつつ、歯表面の浸炭窒化部をオーステナイト状態
に維持する。保持時間は温度の均一性および熱処理コス
トより、5分以上2時間未満が好ましい(これ以上保持
時間を長くしても品質上での利点はなく、また不経済で
ある)。
After carbonitriding, the temperature is 660 to 700 ° C. by cooling the furnace.
After cooling to a temperature above the Ar 3 transformation point on the tooth surface and below the Ar 1 transformation point inside the tooth, and holding for a certain period of time, the tooth inside the non-carbonitrided portion is transformed into ferrite and fine pearlite, The carbonitrided portion of the surface is maintained in an austenite state. The holding time is preferably 5 minutes or more and less than 2 hours from the viewpoint of temperature uniformity and heat treatment cost (longer holding time does not have an advantage in quality and is uneconomical).

【0021】浸炭窒化部の結晶粒を細粒化する、より好
ましい条件としては、浸炭窒化後、歯表面部のAr1
態点以下まで徐冷し、次に歯表面部のAc3 変態点以上
に再加熱する。この時、浸炭窒化部のオーステナイト粒
の細粒化が図られる。次に歯表面部のAr3 変態点以上
で歯内部のAr1 変態点以下にした後、一定時間保持す
ることにより、非浸炭窒化部の歯内部は、微細なフェラ
イト・パーライトままで歯表面の浸炭窒化部のみ細粒の
オーステナイトに変態する。保持時間は温度の均一性お
よび熱処理コストより、5分以上2時間未満が好まし
い。
More preferable conditions for refining the crystal grains in the carbonitrided portion are as follows: after carbonitriding, the tooth surface is gradually cooled to the Ar 1 transformation point or lower, and then the tooth surface portion is Ac 3 transformation point or higher. Reheat to. At this time, the austenite grains in the carbonitrided portion are refined. Next, after the Ar 3 transformation point of the tooth surface portion is set to be equal to or lower than the Ar 1 transformation point of the inside of the tooth and held for a certain period of time, the inside of the tooth of the non-carbonitrided portion remains as fine ferrite / pearlite and is Only the carbonitrided part transforms into fine-grained austenite. The holding time is preferably 5 minutes or more and less than 2 hours in view of temperature uniformity and heat treatment cost.

【0022】以上のように、表面をオーステナイト化
し、歯内部をフェライトと微細パーライトにし、しかる
後に油あるいは塩浴中で焼入れすることにより、歯表面
の浸炭窒化部は全てマルテンサイトにでき、既に変態を
終了している歯内部は焼きの入っていないフェライトと
微細パーライトに維持できる。その後、浸炭窒化部の内
部応力の除去および強さ、ねばさを増すために、150
〜200℃の焼戻し処理を行う。
As described above, by austenitizing the surface, making ferrite and fine pearlite inside the tooth, and then quenching in an oil or salt bath, all the carbonitrided parts of the tooth surface can be made into martensite and already transformed. The inside of the finished tooth can be maintained with unhardened ferrite and fine pearlite. After that, in order to remove internal stress of the carbonitriding part and increase strength and tenacity, 150
A tempering process at ~ 200 ° C is performed.

【0023】以下に実施例を挙げてさらに説明する。The present invention will be further described below with reference to examples.

【0024】[0024]

【実施例】表1に示す化学成分の鋼を溶製し、162mm
角ビレットに分塊圧延した後、熱間圧延にて50mmφ棒
鋼に仕上げた。次に、得られた棒鋼を熱間鍛造および焼
ならしし、その後機械加工により、外径87mm、モジュ
ール3、歯数27、歯幅20mmの歯車を製作し、これら
を試料として浸炭窒化処理を施した。まず、試料をカー
ボンポテンシャル:0.9%、Nポテンシャル:2%、
温度:930℃で浸炭窒化した後、No. 1は歯表面部お
よび歯内部のAr3 変態点超の840℃、No. 2は歯内
部のAr1 変態点超で表面部のAr3 変態点以上の75
0℃、No. 3は歯表面部のAr3 変態点未満の630℃
まで炉冷し、30分保持後、それぞれを130℃の油浴
中で冷却した。No. 4〜No. 11は表1に示す歯表面部
(浸炭窒化部)のAr3 変態点以上で歯内部(非浸炭窒
化部)のAr1 変態点以下の温度に、No. 12〜No.1
6は歯表面部のAr1 変態点以下の600℃まで徐冷
し、次に歯表面部のAc3 変態点以上の850℃に再加
熱し、その後歯内部(非浸炭窒化部)のAr1 変態点以
下で歯表面部(浸炭窒化部)のAr3 変態点以上の温度
に、各々30分保持して、その後130℃の油浴中で冷
却した。次いで、全ての試料とも180℃、1時間の焼
戻しを行った。また歪量はJIS B1702により歯
形誤差を測定し、併せて表1および表2に示した。
Example: Steel having the chemical composition shown in Table 1 was melted to 162 mm.
After slab-rolling into a square billet, 50 mmφ steel bar was finished by hot rolling. Next, the steel bar thus obtained is hot forged and normalized, and then machined to produce a gear having an outer diameter of 87 mm, a module 3, 27 teeth and a tooth width of 20 mm, and carbonitriding these samples. gave. First, the sample is carbon potential: 0.9%, N potential: 2%,
After carbonitriding at a temperature of 930 ° C, No. 1 is 840 ° C above the Ar 3 transformation point on the tooth surface and inside the tooth, and No. 2 is above the Ar 1 transformation point inside the tooth and above the Ar 3 transformation point on the surface. More than 75
0 ℃, No. 3 is 630 ℃, which is lower than the Ar 3 transformation point of the tooth surface.
After furnace cooling to 30 minutes and holding for 30 minutes, each was cooled in an oil bath at 130 ° C. No. 4 to No. 11 are shown in Table 1 at temperatures above the Ar 3 transformation point of the tooth surface (carbonitriding portion) and below the Ar 1 transformation point of the inside of the tooth (non-carbonitriding portion), and No. 12 to No. .1
No. 6 was gradually cooled to 600 ° C. below the Ar 1 transformation point of the tooth surface, then reheated to 850 ° C. above the Ac 3 transformation point of the tooth surface, and then Ar 1 inside the tooth (non-carbonitrided portion). The tooth surface portion (carbonitrided portion) was kept at a temperature not lower than the Ar 3 transformation point below the transformation point for 30 minutes, and then cooled in an oil bath at 130 ° C. Then, all samples were tempered at 180 ° C. for 1 hour. For the amount of strain, the tooth profile error was measured according to JIS B1702, and is also shown in Table 1 and Table 2.

【0025】歯内部のAr3 変態点超で焼入れしたNo.
1は歯内部がマルテンサイトとなり、歯形歪量も多く、
また歯内部のAr1 変態点超で表面部のAr3 変態点以
上で焼入れしたNo. 2では歯内部は一部マルテンサイト
を含んだフェライト・パーライト組織になるため、歯形
歪量の低減も十分ではない。また、歯表面部のAr3
満で焼入れしたNo. 3は、表面部もベイナイトとパーラ
イト組織となり、歯車として必要な表面硬さを得ること
ができない。
[0025] No. hardened above the Ar 3 transformation point inside the tooth
In No. 1, the inside of the tooth becomes martensite and the amount of tooth profile distortion is large,
Further, in No. 2 which is hardened above the Ar 1 transformation point inside the tooth and above the Ar 3 transformation point in the surface, the tooth interior has a ferrite-pearlite structure that contains some martensite, so the reduction of the tooth profile distortion is sufficient. is not. Further, in No. 3 hardened with less than Ar 3 of the tooth surface portion, the surface portion also has a bainite and pearlite structure, and the surface hardness required as a gear cannot be obtained.

【0026】さらに、歯表面部のAr3 変態点以上で、
かつ歯内部のAr1 変態点以下の温度で焼入れしている
ものの、本発明範囲よりMnが高いNo. 4は、歯形歪量
は少ないにもかかわらず、歯内部硬度が高すぎ、靱性が
低く、実用には適さない。さらに、本発明範囲よりVが
少なすぎるNo. 5は、歯形歪量は少ないものの、歯内部
硬度が不十分で、実用には適さない。
Further, above the Ar 3 transformation point of the tooth surface,
Moreover, although quenching is performed at a temperature below the Ar 1 transformation point inside the tooth, No. 4 having a higher Mn than the range of the present invention has a low tooth profile distortion amount, but the tooth internal hardness is too high and the toughness is low. , Not suitable for practical use. Further, No. 5 in which V is too small compared to the range of the present invention has a small amount of tooth profile distortion, but the tooth internal hardness is insufficient and is not suitable for practical use.

【0027】これに対して本発明の範囲内にあるNo. 6
〜16では何れも歯内部はフェライト・パーライト組織
になり、歯内部の硬度も十分であり、歯形歪量も著しく
低減でき、また内部酸化層と不完全焼入れ層の抑制によ
り、疲労強度も高いことが明らかである。
On the other hand, No. 6 within the scope of the present invention
In all of ~ 16, the inside of the tooth has a ferrite-pearlite structure, the hardness inside the tooth is sufficient, the tooth profile distortion amount can be significantly reduced, and the fatigue strength is high due to the suppression of the internal oxide layer and the incompletely hardened layer. Is clear.

【0028】[0028]

【表1】 [Table 1]

【0029】[0029]

【表2】 [Table 2]

【0030】[0030]

【発明の効果】以上説明してきたように、本発明は浸炭
窒化焼入れにより製造される自動車用歯車の歯内部をフ
ェライト・パーライト組織にすることにより熱処理歪の
低減を図り、同時に表層の組織制御により疲労強度の向
上を図った、騒音の少ない高強度の自動車トランスミッ
ション用ギアを提供するものであり、工業上の効果は極
めて顕著なものがある。
As described above, according to the present invention, the heat treatment strain is reduced by forming the ferrite / pearlite structure inside the tooth of the automobile gear manufactured by carbonitriding and quenching, and at the same time, by controlling the structure of the surface layer. The present invention provides a high-strength automotive transmission gear with less noise and improved fatigue strength, and has an extremely remarkable industrial effect.

【図面の簡単な説明】[Brief description of drawings]

【図1】(A)は歯車の歯内部および(B)は歯車芯部
の説明図である。
FIG. 1A is an explanatory diagram of a tooth inside of a gear and FIG. 1B is an explanatory diagram of a gear core portion.

Claims (2)

(57)【特許請求の範囲】(57) [Claims] 【請求項1】 重量%で、C:0.1%以上0.3%未
満、Si:0.15%未満、Mn:0.30%以上1.
50%未満、Cr:0.30%以上1.00%未満、M
o:0.10%以上1.00%未満、V:0.05%以
上1.00%未満を含有し、残部Feおよび不純物より
なる鋼を素材とした歯車に、浸炭窒化処理を施し、その
後直ちに、あるいはいったん歯表面部(浸炭窒化部)の
Ar1変態点以下の温度域まで冷却し、再度歯表面部
(浸炭窒化部)のAc3変態点以上に加熱した後、歯表
面部(浸炭窒化部)のAr3 変態点以上で歯内部(非浸
炭窒化部)のAr1 変態点以下の温度域に5分以上2時
間未満保持して、歯表面をオーステナイト状態に保ちつ
つ歯内部を微細なフェライト・パーライトにし、しかる
後に焼入れ、焼戻しを行うことにより、歯内部を微細な
フェライト・パーライト組織とすることを特徴とする歪
の小さい高強度歯車の浸炭窒化熱処理方法。ただし、歯
内部とは図1(A)の斜線部で示される歯の浸炭層より
内側である。
1. By weight%, C: 0.1% or more and less than 0.3%, Si: less than 0.15%, Mn: 0.30% or more 1.
Less than 50%, Cr: 0.30% or more and less than 1.00%, M
O: 0.10% or more and less than 1.00%, V: 0.05% or more and less than 1.00%, gears made of steel with the balance Fe and impurities were carbonitrided, and then Immediately or after cooling to a temperature range below the Ar 1 transformation point of the tooth surface portion (carbonitriding portion) and heating again to above the Ac 3 transformation point of the tooth surface portion (carbonitriding portion), the tooth surface portion (carburizing portion) The temperature inside the tooth above the Ar 3 transformation point of the nitrided portion) (below the non-carbonitriding portion) below the Ar 1 transformation point is maintained for 5 minutes or more and less than 2 hours to keep the tooth surface in an austenitic state and A carbonitriding heat treatment method for high-strength gears with small strains, characterized in that a fine ferrite-pearlite structure is formed inside the tooth by making a proper ferrite-pearlite, and then quenching and tempering. However, the inside of the tooth is the inside of the carburized layer of the tooth shown by the hatched portion in FIG.
【請求項2】 重量%で、C:0.1%以上0.3%未
満、Si:0.15%未満、Mn:0.30%以上1.
50%未満、Cr:0.30%以上1.00%未満、M
o:0.10%以上1.00%未満、V:0.05%以
上1.00%未満を含むとともに、Nb:0.02%以
上0.20%以下、Ti:0.01%以上0.20%以
下の1種以上を含有し、残部Feおよび不純物よりなる
鋼を素材とした歯車に、浸炭窒化処理を施し、その後直
ちに、あるいはいったん歯表面部(浸炭窒化部)のAr
1 変態点以下の温度域まで冷却し、再度歯表面部(浸炭
窒化部)のAc3 変態点以上に加熱した後、歯表面部
(浸炭窒化部)のAr3 変態点以上で歯内部(非浸炭窒
化部)のAr1 変態点以下の温度域に5分以上2時間未
満保持して、歯表面をオーステナイト状態に保ちつつ歯
内部を微細なフェライト・パーライトにし、しかる後に
焼入れ、焼戻しを行うことにより、歯内部を微細なフェ
ライト・パーライトとすることを特徴とする歪の小さい
高強度歯車の浸炭窒化熱処理方法。ただし、歯内部とは
図1(A)の斜線部で示される歯の浸炭層より内側であ
る。
2. In% by weight, C: 0.1% or more and less than 0.3%, Si: less than 0.15%, Mn: 0.30% or more 1.
Less than 50%, Cr: 0.30% or more and less than 1.00%, M
O: 0.10% or more and less than 1.00%, V: 0.05% or more and less than 1.00%, Nb: 0.02% or more and 0.20% or less, Ti: 0.01% or more and 0 Gears made of steel containing 20% or less of one or more and the balance of Fe and impurities are carbonitrided, and then immediately or once after the tooth surface (carbonitrided) Ar
After cooling to a temperature range of 1 transformation point or lower and heating again to the Ac 3 transformation point of the tooth surface portion (carbonitriding portion) or higher, after the Ar 3 transformation point of the tooth surface portion (carbonitriding portion) or higher, the inside of the tooth (non- (Carbonitriding part) Hold the temperature in the temperature range below the Ar 1 transformation point for 5 minutes or more and less than 2 hours to form a fine ferrite pearlite inside the tooth while keeping the tooth surface in an austenite state, and then quench and temper. By this, a carbonitriding heat treatment method for a high-strength gear with small strain, characterized in that the inside of the tooth is made of fine ferrite pearlite. However, the inside of the tooth is the inside of the carburized layer of the tooth shown by the hatched portion in FIG.
JP3236604A 1991-09-17 1991-09-17 Carbonitriding heat treatment method for high strength gears with small strain Expired - Fee Related JP2549039B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP3236604A JP2549039B2 (en) 1991-09-17 1991-09-17 Carbonitriding heat treatment method for high strength gears with small strain

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP3236604A JP2549039B2 (en) 1991-09-17 1991-09-17 Carbonitriding heat treatment method for high strength gears with small strain

Publications (2)

Publication Number Publication Date
JPH0570925A JPH0570925A (en) 1993-03-23
JP2549039B2 true JP2549039B2 (en) 1996-10-30

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5746842A (en) 1995-09-29 1998-05-05 Toa Steel Co., Ltd. Steel gear
JP3909902B2 (en) 1996-12-17 2007-04-25 株式会社小松製作所 Steel parts for high surface pressure resistance and method for producing the same
JP4100751B2 (en) * 1998-01-30 2008-06-11 株式会社小松製作所 Rolling member and manufacturing method thereof
WO2011122651A1 (en) * 2010-03-30 2011-10-06 アイシン・エィ・ダブリュ株式会社 Carburized steel member and method for producing same
EP2679701B1 (en) 2011-02-23 2017-07-12 Dowa Thermotech Co., Ltd. Manufacturing method of a nitrided steel member
CN104053808B (en) 2012-01-26 2016-01-20 新日铁住金株式会社 The surface hardening steel that thermal treatment should diminish
JP5656908B2 (en) 2012-04-18 2015-01-21 Dowaサーモテック株式会社 Nitride steel member and manufacturing method thereof
JP6647792B2 (en) 2015-03-31 2020-02-14 Dowaサーモテック株式会社 Method of nitriding steel members

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