JP5077814B2 - Shaft and manufacturing method thereof - Google Patents

Shaft and manufacturing method thereof Download PDF

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JP5077814B2
JP5077814B2 JP2007249028A JP2007249028A JP5077814B2 JP 5077814 B2 JP5077814 B2 JP 5077814B2 JP 2007249028 A JP2007249028 A JP 2007249028A JP 2007249028 A JP2007249028 A JP 2007249028A JP 5077814 B2 JP5077814 B2 JP 5077814B2
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shaft
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soft nitriding
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JP2009079253A (en
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貢士 小▲柳▼
尚美 三浦
孝雄 林
義夫 岡田
新一 荒木
貴大 宮崎
英利 稲垣
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Nissan Motor Co Ltd
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本発明は、例えば、自動車のトランスミッション、差動装置など駆動伝達部品を始めとする各種の機械装置に用いられるシャフト部品に係わり、特に高い耐摩耗性、耐焼付き性と共に、繰返し衝撃曲げ強度が要求される部位に好適に用いられるシャフトと、その製造方法に関するものである。   The present invention relates to a shaft component used in various mechanical devices such as a drive transmission component such as an automobile transmission and a differential gear, and particularly requires high impact resistance and seizure resistance, and repeated impact bending strength. The present invention relates to a shaft suitably used for a portion to be manufactured and a manufacturing method thereof.

高い耐摩耗性、焼付き性に加えて、衝撃入力を繰返し受ける際の曲げ強度を要求されるシャフト部品としては、従来、JIS G 4052に規定されるSCr420H、SCM420H、SCM440H等を母材として、浸炭焼入れ焼戻し後、550〜650℃にて塩浴軟窒化処理を施したものが使用されている。
また、従来の差動ピニオン及びメートシャフトとしては、例えば上記JIS規格に規定される構造用鋼鋼材を材料としており、互いの摺動接触部分の耐摩耗性等を高めるために、差動ピニオンの内周面に摺動接触するメートシャフトの外径面に、軟窒化処理又はニッケル−リンめっきを施したものがあった(例えば、特許文献1参照)。
特開2002−30338号公報
In addition to high wear resistance and seizure properties, shaft parts that require bending strength when repeatedly receiving impact inputs are conventionally based on SCr420H, SCM420H, SCM440H, etc. defined in JIS G 4052, After carburizing, quenching and tempering, a salt bath nitrocarburized treatment at 550 to 650 ° C. is used.
In addition, as a conventional differential pinion and mate shaft, for example, a structural steel material defined in the JIS standard is used as a material, and in order to improve the wear resistance and the like of the sliding contact portions of the differential pinion, Some mate shafts that are in sliding contact with the inner peripheral surface are subjected to soft nitriding treatment or nickel-phosphorous plating (see, for example, Patent Document 1).
JP 2002-30338 A

一方、窒化用鋼としては、Cr、Mo、Vと共に、Alを適量添加することによって、焼入れ焼戻し処理を行うことなくフェライト+ベイナイト組織とし、もって優れた被削性と素材強度を両立させることが開示されている(特許文献2参照)。
特開平8−176732号公報
On the other hand, as a steel for nitriding, by adding an appropriate amount of Al together with Cr, Mo, V, a ferrite + bainite structure can be obtained without performing quenching and tempering treatment, thereby achieving both excellent machinability and material strength. It is disclosed (see Patent Document 2).
JP-A-8-176732

しかしながら、上記特許文献1に記載の技術では、浸炭焼入れ後の焼戻し温度130〜200℃に対して、塩浴軟窒化処理温度が550〜650℃と高いため、浸炭材が本来有している衝撃曲げ強度が低下するという問題がある。
また、特許文献2に記載の窒化用鋼は、フェライト+べイナイトの金属組織であるため、マルテンサイト金属組織からなる素材よりは強度が劣ることになる。
However, in the technique described in Patent Document 1, since the salt bath soft nitriding temperature is as high as 550 to 650 ° C. with respect to the tempering temperature 130 to 200 ° C. after carburizing and quenching, the impact that the carburized material originally has. There is a problem that the bending strength decreases.
Moreover, since the nitriding steel described in Patent Document 2 has a ferrite + bainite metal structure, the strength is inferior to that of a material made of a martensite metal structure.

本発明は、このような従来技術の問題点に着目してなされたものであって、その目的とするところは、良好な耐衝撃曲げ性を有し、しかも良好な耐摩耗と耐焼付き性を備えたシャフト部品を実現することにある。   The present invention has been made paying attention to such problems of the prior art, and its object is to have good impact bend resistance and good wear resistance and seizure resistance. It is to realize the provided shaft parts.

本発明者らは、上記課題を解決すべく、シャフトに用いる鋼の成分組成や、熱処理条件等について鋭意検討を重ねた。その結果、MoとVを含有させることによって、これらの炭窒化物の析出による二次硬化が生じ、550〜650℃の条件下で軟窒化処理を施してもシャフトの耐衝撃曲げ性が低下せず、上記目的が達成されることを見出し、本発明を完成するに到った。   In order to solve the above-mentioned problems, the present inventors have made extensive studies on the component composition of steel used for the shaft, heat treatment conditions, and the like. As a result, the inclusion of Mo and V causes secondary hardening due to precipitation of these carbonitrides, and the impact bend resistance of the shaft is reduced even when soft nitriding is performed at 550 to 650 ° C. However, the inventors have found that the above object can be achieved and have completed the present invention.

本発明は上記知見に基づくものであって、本発明のシャフトは、質量比で、0.15〜0.60%のC、0.2%以下のSi、0.10〜0.70%のMn、0.03%以下のP、0.03%以下のS、0.1〜1.6%のCr、0.6〜1.5%のMo、0.05〜0.40%のVに加えて、0.01〜0.20%のTi及び0.01〜0.20%のNbの少なくとも一方を含有し、残部がFe及び不可避的不純物である鋼から成り、内部のビッカース硬さが400Hv以上、表面から0.05mmの深さ位置におけるビッカース硬さが600Hv以上であると共に、表面に25μm以下の厚さの窒化物層を備えていることを特徴とする。
また、本発明のシャフトは、上記範囲のC、Si、Mn、P、S、Cr、Mo、Vに加えて、0.3%以下のPb、0.1%以下のBi及び0.1%以下のCaから成る群から選ばれた少なくとも1種の元素を含有すると共に、上記した内部硬さ、表面硬さを有し、上記厚さの窒化層を備えていることを特徴とする。さらに、上記範囲のC、Si、Mn、P、S、Cr、Mo、V、Pb、Bi、Caに加えて、0.01〜0.20%のTi及び0.01〜0.20%のNbの少なくとも一方の元素を含有すると共に、上記した内部硬さ、表面硬さを有し、上記厚さの窒化層を備えていることを特徴としている。
The present invention is based on the above knowledge, and the shaft of the present invention is 0.15 to 0.60% C, 0.2% or less Si, 0.10 to 0.70% in mass ratio. Mn, 0.03% or less P, 0.03% or less S, 0.1 to 1.6% Cr, 0.6 to 1.5% Mo, 0.05 to 0.40% V In addition to the above, it contains at least one of 0.01 to 0.20% Ti and 0.01 to 0.20% Nb, and the balance is made of steel containing Fe and inevitable impurities, and has an internal Vickers hardness. 400 Vv or more, Vickers hardness at a depth of 0.05 mm from the surface is 600 Hv or more, and a nitride layer having a thickness of 25 μm or less is provided on the surface.
Moreover, in addition to C, Si, Mn, P, S, Cr, Mo, V in the above range, the shaft of the present invention has 0.3% or less of Pb, 0.1% or less of Bi, and 0.1%. It contains at least one element selected from the group consisting of the following Ca, has the above-mentioned internal hardness and surface hardness, and has a nitride layer with the above thickness. Further, in addition to C, Si, Mn, P, S, Cr, Mo, V, Pb, Bi, and Ca in the above ranges, 0.01 to 0.20% Ti and 0.01 to 0.20% It contains at least one element of Nb, has the above-mentioned internal hardness and surface hardness, and has a nitride layer having the above thickness.

また、本発明のシャフトの製造方法においては、上記成分組成の鋼材に、880℃以上の温度で焼入れ処理を施した後、550〜650℃の温度で塩浴軟窒化あるいはガス軟窒化処理を施すことを特徴としている。
In the shaft manufacturing method of the present invention, the steel material having the above composition is subjected to quenching treatment at a temperature of 880 ° C. or higher, and then subjected to salt bath soft nitriding or gas soft nitriding treatment at a temperature of 550 to 650 ° C. It is characterized by that.

本発明によれば、質量比で、0.15〜0.60%のC、0.2%以下のSi、0.10〜0.70%のMn、0.03%以下のP、0.03%以下のS、0.1〜1.6%のCr、0.6〜1.5%のMo、0.05〜0.40%のVに加えて、0.01〜0.20%のTi及び0.01〜0.20%のNbの少なくとも一方の元素及び/又は0.3%以下のPb、0.1%以下のBi及び0.1%以下のCaから成る群から選ばれた少なくとも1種の元素を含有し、残部がFe及び不可避的不純物である鋼から成るものであり、内部のビッカース硬さが400Hv以上、表面から0.05mmの深さ位置におけるビッカース硬さが600Hv以上、さらに表面に25μm以下の厚さの窒化物層を備えているため、耐衝撃曲げ性、耐摩耗、耐焼付き性に優れたシャフトとすることができる。
また、このようなシャフトは、上記成分の鋼材に、880℃以上の温度で焼入れ処理を施した後、550〜650℃の温度で塩浴軟窒化又はガス軟窒化処理を施すことにより得ることができる。
According to the present invention, by mass ratio, 0.15 to 0.60% C, 0.2% or less Si, 0.10 to 0.70% Mn, 0.03% or less P, 0.0. In addition to S of 03% or less, 0.1 to 1.6% Cr, 0.6 to 1.5% Mo, 0.05 to 0.40% V , 0.01 to 0.20% Selected from the group consisting of at least one element of Ti and 0.01 to 0.20% Nb and / or Pb of 0.3% or less, Bi of 0.1% or less and Ca of 0.1% or less. Further, it is made of steel containing at least one element and the balance being Fe and inevitable impurities, the internal Vickers hardness is 400 Hv or more, and the Vickers hardness at a depth of 0.05 mm from the surface is 600 Hv. As described above, since a nitride layer having a thickness of 25 μm or less is further provided on the surface, impact bending resistance, wear resistance, It can be an excellent shaft in seizure resistance.
Further, such a shaft can be obtained by subjecting the steel material having the above components to quenching treatment at a temperature of 880 ° C. or higher and then subjecting the steel material to salt bath soft nitriding or gas soft nitriding treatment at a temperature of 550 to 650 ° C. it can.

以下、本発明のシャフトとその製造方法について、各合金成分の作用及びその数値限定理由と共に、さらに詳細に説明する。なお、本明細書において「%」は、特記しない限り、質量百分率を意味するものとする。   Hereinafter, the shaft of the present invention and the manufacturing method thereof will be described in more detail together with the action of each alloy component and the reasons for limiting the numerical values thereof. In the present specification, “%” means mass percentage unless otherwise specified.

本発明は、上記したように、MoとVを含有させると、これら元素の炭窒化物が析出して二次硬化をするため、550〜650℃という高温度の条件下で軟窒化処理を施してもシャフトの耐衝撃曲げ性が低下しないという知見に基づくものである。
そして、本発明によれば、良好な耐衝撃曲げ性と共に、良好な耐摩耗、耐焼付き性を備えたシャフト部品を実現することができ、例えばディファレンシャル機構用ピニオンメートシャフトなどに適用することができる。
In the present invention, as described above, when Mo and V are contained, carbonitrides of these elements are precipitated and secondarily hardened. Therefore, soft nitriding treatment is performed under a high temperature condition of 550 to 650 ° C. However, this is based on the knowledge that the impact bending resistance of the shaft does not decrease.
According to the present invention, a shaft component having good wear resistance and seizure resistance as well as good impact bending resistance can be realized, and can be applied to, for example, a pinion mate shaft for a differential mechanism. .

本発明においては、上記成分に加えて、後述するような所定量のTi及び/又はNbを添加することができ、これによって高温焼入れによる結晶粒の粗大化を防止して、基地の靭性強化を図ることができる。
また、素材鋼の被削性を向上させる観点からは、Pb、Bi及びCaのうちの少なくとも1種を後述する範囲内で添加することが望ましい。
In the present invention, in addition to the above components, a predetermined amount of Ti and / or Nb as described later can be added, thereby preventing coarsening of the crystal grains due to high-temperature quenching and strengthening the toughness of the base. Can be planned.
Further, from the viewpoint of improving the machinability of the raw steel, it is desirable to add at least one of Pb, Bi and Ca within the range described below.

以下に、本発明における各成分元素の作用と共に、その数値限定理由について説明する。   The reasons for limiting the numerical values are described below together with the action of each component element in the present invention.

C:0.15〜0.60%
Cは、熱処理によって所要の強度を得るために有効であるので、そのために含有させる元素である。
しかし、Cの含有量が0.15%未満では効果に乏しい。一方、0.60%を超えると靭性低下による衝撃曲げ強度の低下をもたらすと共に、素材の硬さの上昇を招き、加工コストの増大を招くことがある。したがって、C含有量については、0.15〜0.60%の範囲内とすることが必要となる。
C: 0.15-0.60%
Since C is effective for obtaining a required strength by heat treatment, it is an element to be contained for that purpose.
However, if the C content is less than 0.15%, the effect is poor. On the other hand, if it exceeds 0.60%, the impact bending strength is reduced due to a decrease in toughness, the hardness of the material is increased, and the processing cost may be increased. Accordingly, the C content needs to be in the range of 0.15 to 0.60%.

Si:0.2%以下
Siは、オーステナイト化時の高温加熱による粒界酸化を助長する元素であり、粒界強度低下により衝撃曲げ強度を劣化させる。また、PやSなどの不純物元素の粒界への偏析を助長する作用があり、これも衝撃曲げ強度を劣化させる要因となる。さらに、素材の硬さの上昇を招くことがある。
これらのことから、Si含有量は低い方が望ましく、0.2%以下に限定することが必要となる。
Si: 0.2% or less Si is an element that promotes grain boundary oxidation by high-temperature heating during austenitization, and deteriorates impact bending strength due to a decrease in grain boundary strength. Moreover, it has the effect | action which promotes the segregation to the grain boundary of impurity elements, such as P and S, and this also becomes a factor which degrades impact bending strength. Furthermore, the hardness of the material may be increased.
For these reasons, it is desirable that the Si content is low, and it is necessary to limit the Si content to 0.2% or less.

Mn:0.10〜0.70%
Mnは、鋼溶製時の脱酸剤として有効であると共に、焼入性の向上に寄与する元素であるが、Siと共に焼入れ時の粒界酸化を助長し、衝撃曲げ強度を劣化させる。また、Siと同様にPやSなどの不純物元素の粒界への偏析を助長し、衝撃曲げ強度を劣化させる要因になる元素である。さらに、素材の硬さの上昇を招くことがある。
したがって、Mn含有量は、脱酸剤としての有効量以上に添加することは望ましくなく、0.10〜0.70%とする必要がある。
Mn: 0.10 to 0.70%
Mn is an element that is effective as a deoxidizer during steel melting and contributes to improvement of hardenability, but together with Si, promotes grain boundary oxidation during quenching and degrades impact bending strength. Further, like Si, it is an element that promotes the segregation of impurity elements such as P and S to the grain boundaries and causes the impact bending strength to deteriorate. Furthermore, the hardness of the material may be increased.
Therefore, it is not desirable to add the Mn content beyond the effective amount as a deoxidizer, and it is necessary to set the content to 0.10 to 0.70%.

P:0.03%以下
Pは、オーステナイト域に加熱するとオーステナイト粒界に偏析し、粒界を脆化させて耐衝撃特性を劣化させるので、低い方が望ましく、その含有量を0.03%以下とする必要がある。
P: 0.03% or less P is segregated at the austenite grain boundary when heated in the austenite region, embrittles the grain boundary and degrades the impact resistance, so a lower content is desirable, and its content is 0.03%. It is necessary to do the following.

S:0.03%以下
Sは、Pと同様にオーステナイト域に加熱するとオーステナイト粒界に偏析し、粒界を脆化させて耐衝撃特性を劣化させるので、低いことが望ましく、その含有量を0.03%以下とすることが必要である。
S: 0.03% or less S, like P, is segregated at the austenite grain boundary when heated to the austenite region, embrittles the grain boundary and degrades the impact resistance, so the content is desirably low. It is necessary to make it 0.03% or less.

Cr:0.1〜1.6%
Crは、焼入性を向上させる作用があるので、そのために含有させる元素である。このような効果を得るためには、0.1%以上含有させる必要があるが、1.6%を超えて過剰に添加すると、SiやMnと同様に粒界酸化を助長して、オーステナイト粒界の脆化を招いて耐衝撃特性を却って低下させることになる。
したがって、Cr含有量は、0.1〜1.6%の範囲内とする。
Cr: 0.1 to 1.6%
Since Cr has an effect of improving hardenability, it is an element to be contained for that purpose. In order to acquire such an effect, it is necessary to make it contain 0.1% or more, but when it adds exceeding 1.6% excessively, it promotes grain boundary oxidation like Si and Mn, and austenite grain This leads to embrittlement of the boundary, and lowers the impact resistance.
Therefore, the Cr content is within the range of 0.1 to 1.6%.

Mo:0.6〜1.5%
Moは、鋼の焼入れ性を向上させるとともに、結晶粒の微細化及びオーステナイト粒界の強度向上に寄与すると共に、焼戻し時に十分な二次硬化をもたらし、良好な母材強度を得るのに効果的な元素である。すなわち、550℃を超える条件の軟窒化処理温度においても、ビッカース硬さ400Hv以上の高い硬さを得るために添加する元素である。
しかし、含有量が0.6%未満では効果に乏しい一方、多くなると効果が飽和するばかりでなく、巨大な一次炭化物が析出して靭性低下による衝撃曲げ強度の低下をもたらすので、その上限を1.5%とする。
Mo: 0.6 to 1.5%
Mo improves the hardenability of steel, contributes to refinement of crystal grains and the strength of austenite grain boundaries, and provides sufficient secondary hardening during tempering, and is effective in obtaining good base material strength. Element. That is, it is an element added to obtain a high hardness of Vickers hardness of 400 Hv or higher even at a soft nitriding temperature exceeding 550 ° C.
However, if the content is less than 0.6%, the effect is poor. On the other hand, if the content is large, not only the effect is saturated, but also the huge primary carbide precipitates and the impact bending strength is reduced due to the decrease in toughness. .5%.

V:0.05〜0.40%
Vは、Moと同様に、焼戻し時にバナジウム炭化物を形成させて、十分な二次硬化及び母材強度を得るために含有させる元素である。
このような効果を得るためには、0.05%以上含有させる必要があるが、過剰に添加すると巨大な一次炭化物が晶出し、焼入れ時に残存して二次硬化に寄与するV固溶量が飽和するばかりでなく、靭性低下による衝撃曲げ強度の低下をもたらすので、その上限を0.40%とする。
V: 0.05 to 0.40%
V, like Mo, is an element that is contained to form a vanadium carbide during tempering to obtain sufficient secondary hardening and base material strength.
In order to obtain such an effect, it is necessary to contain 0.05% or more. However, if added excessively, a huge primary carbide crystallizes out, and the amount of V solid solution remaining at the time of quenching and contributing to the secondary hardening is small. In addition to saturation, the impact bending strength is reduced due to a decrease in toughness, so the upper limit is made 0.40%.

Ti:0.01〜0.20%、Nb:0.01〜0.20%
Ti及びNbは、いずれも結晶粒の微細化に寄与し、強靱化に有効な元素であるため、必要に応じて、これらの一方又は両方を上記範囲内で添加することができる。
Ti: 0.01-0.20%, Nb: 0.01-0.20%
Since Ti and Nb are both elements that contribute to refinement of crystal grains and are effective for toughening, one or both of them can be added within the above range as necessary.

Tiは、焼戻し時の二次硬化に寄与するMo及びVを焼入れ時に十分溶け込ますためには880℃以上の高温焼入れが必要であるが、一方において結晶粒の粗大化を招くので、これを抑えるために添加する元素である。すなわち、Tiは、微細な炭化物を形成し、結晶粒の微細化に寄与する。このような効果を得るには、0.01%以上含有させる必要があるが、多くなり過ぎても効果が飽和するばかりでなく、素材硬さの上昇を招くので、その上限を0.10%とする。
一方、Nbは、微細な炭・窒化物を形成し、結晶粒の微細化に寄与し、基地の靭性強化に有効な元素であるが、含有量が0.01%未満では効果に乏しい。また、0.20%を超えて添加しても、効果が飽和するので、その上限を0.20%とする。すなわち、Nbは、TiCによる結晶粒微細化効果が不十分な場合、Nb(C,N)を析出させ、その析出物を利用するために含有させる。
Ti requires high-temperature quenching at 880 ° C. or higher in order to sufficiently dissolve Mo and V, which contribute to secondary hardening during tempering, during quenching. It is an element to be added. That is, Ti forms fine carbides and contributes to refinement of crystal grains. In order to obtain such an effect, it is necessary to contain 0.01% or more, but even if it is too much, not only the effect is saturated, but also the hardness of the material is increased, so the upper limit is 0.10% And
On the other hand, Nb is an element that forms fine carbon / nitride and contributes to refinement of crystal grains and is effective for strengthening the toughness of the matrix, but its effect is poor when the content is less than 0.01%. Moreover, even if added over 0.20%, the effect is saturated, so the upper limit is made 0.20%. That is, Nb is contained in order to precipitate Nb (C, N) and utilize the precipitate when the effect of crystal grain refinement by TiC is insufficient.

Pb:0.3%以下、Bi:0.1%以下、Ca:0.1%以下
Pb、Bi、Caは、いずれも被削性を向上させるのに有効な元素であり、さらに良好な被削性が要求される場合に、必要に応じてこれらのうちから選ばれる1種又は2種以上を適量添加することができる。
Pb: 0.3% or less, Bi: 0.1% or less, Ca: 0.1% or less Pb, Bi, and Ca are all effective elements for improving the machinability, and have better coverage. When machinability is required, an appropriate amount of one or more selected from these can be added as necessary.

すなわち、Pb及びBiは、金属粒として鋼中に分散し、切欠き効果により切削抵抗を減らすと共に、切削熱により溶融することによって工具と切屑の摩擦を減らし、被削性のさらなる改善効果を発揮する。しかし、過剰に添加すると、その鋼の靭性を低下させるため、Pbの上限を0.3%、Biの上限値については0.1%とすることが望ましい。
また、Caは、鋼中でアノールサイト,ゲーレナイトといったCaを含有した酸化物系介在物を形成し、切削時に工具すくい面にベラーグと呼ばれる皮膜を形成することによって、特に旋削工具寿命を改善する機能を有する。しかし、0.1%を超えると鋼の靭性を低下させるため、その含有量を0.1%以下に限定する。
In other words, Pb and Bi are dispersed in steel as metal grains, reducing cutting resistance by the notch effect, and reducing friction between the tool and chips by melting by cutting heat, thereby further improving the machinability. To do. However, if added excessively, the toughness of the steel is lowered, so it is desirable to set the upper limit of Pb to 0.3% and the upper limit of Bi to 0.1%.
In addition, Ca forms oxide inclusions such as anolsite and gehlenite in steel and forms a coating called belag on the rake face of the tool during cutting, thereby improving the life of the turning tool in particular. Have However, if it exceeds 0.1%, the toughness of the steel is reduced, so the content is limited to 0.1% or less.

次に、本発明の高強度シャフトの製造方法において、焼入れ温度を880℃以上に、軟窒化処理温度を550〜650℃に限定する理由について説明する。
本発明の高強度シャフトの製造方法においては、MoやV系炭化物の析出による二次硬化を利用するようにしており、この二次硬化を十分に得るためには焼入れ前のMoやV系炭化物を十分に固溶させる必要があるため、焼入れ温度を880℃以上とする。880℃に満たない温度で焼入れを行うと、衝撃曲げ強度の劣化を招く。
Next, the reason for limiting the quenching temperature to 880 ° C. or higher and the soft nitriding temperature to 550 to 650 ° C. in the method for producing a high-strength shaft of the present invention will be described.
In the method for producing a high-strength shaft according to the present invention, secondary curing by precipitation of Mo or V-based carbides is used. In order to sufficiently obtain this secondary curing, Mo or V-based carbides before quenching are used. Therefore, the quenching temperature is set to 880 ° C. or higher. When quenching is performed at a temperature lower than 880 ° C., the impact bending strength is deteriorated.

一方、軟窒化処理については、この処理の間に、焼入れ組織が焼戻しされるため、これらの炭化物を析出させて十分な二次硬化を得るためには、当該軟窒化処理温度を550℃以上とする必要がある。また、軟窒化処理温度が650℃を超えると焼戻しによる軟化が始まり、鋼母材で400Hv以上のビッカース硬さが得られなくなるので、その上限温度を650℃とする必要がある。   On the other hand, for the soft nitriding treatment, the quenched structure is tempered during this treatment. Therefore, in order to precipitate these carbides and obtain sufficient secondary hardening, the soft nitriding treatment temperature is set to 550 ° C. or higher. There is a need to. Further, when the soft nitriding temperature exceeds 650 ° C., softening by tempering starts and Vickers hardness of 400 Hv or more cannot be obtained with the steel base material, so the upper limit temperature needs to be 650 ° C.

本発明においては、衝撃曲げ強度を確保するために、2つの破損形態に対する強度向上方策を講じている。
すなわち、シャフトの内部硬さを400Hv以上とすることにより耐変形性を確保し、さらに、シャフト外形表面からの深さが0.05mmの位置におけるビッカース硬さを600Hv以上とすることによって、衝撃入力があった際にシャフト表層で破壊が生じる限界を向上させている。
In the present invention, in order to secure the impact bending strength, measures for improving the strength with respect to two damaged forms are taken.
That is, deformation resistance is ensured by setting the internal hardness of the shaft to 400 Hv or higher, and impact input is provided by setting the Vickers hardness at a position where the depth from the outer surface of the shaft is 0.05 mm to 600 Hv or higher. This improves the limit at which breakage occurs on the surface of the shaft when there is a problem.

また、軟窒化処理を施すことにより、シャフト外形面に厚さ25μm以下の窒化物層、すなわち鉄と窒素の化合物からなる窒化物層が形成される。
なお、本発明において「窒化物層」とは、鋼母材の表層付近に炭素や窒素などが拡散して強化される層を含まない。すなわち、母材の表面上に形成される化合物層を意味するものとする。
Further, by performing soft nitriding, a nitride layer having a thickness of 25 μm or less, that is, a nitride layer made of a compound of iron and nitrogen is formed on the outer surface of the shaft.
In the present invention, the “nitride layer” does not include a layer in which carbon, nitrogen, or the like is diffused and strengthened in the vicinity of the surface layer of the steel base material. That is, it means a compound layer formed on the surface of the base material.

この窒化物層は、ビッカース硬さで約1000〜1200Hv程度であり、良好な耐摩耗性、耐焼き付き性を有している一方、硬くて脆いという性質があるため、窒化物層が厚すぎると、摺動時の振動や衝撃入力によって、割れが発生する恐れがある。このような理由によって、窒化物層の厚さ上限を25μmとする必要がある。   This nitride layer has a Vickers hardness of about 1000 to 1200 Hv, and has good wear resistance and seizure resistance, while it is hard and brittle, so if the nitride layer is too thick Cracks may occur due to vibration or impact input during sliding. For this reason, the upper limit of the thickness of the nitride layer needs to be 25 μm.

以下、本発明を実施例及び比較例に基づいて、さらに詳述するが、本発明はこれらの実施例に限定されるものではない。   EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example and a comparative example, this invention is not limited to these Examples.

〔試験片の準備〕
表1に示す化学組成を有する鋼を溶製し、続いて、常法に基づいて圧延、焼きならした後、図1に示すように、径15mm、長さ107mmの棒状をなし、機械加工仕上げにより一端側に5mm径の貫通孔を備えた耐衝撃特性試験片に加工した。そして、各試験片について、表2に示すそれぞれの条件のもとに、熱処理と、軟窒化や被膜処理などの表面処理を行った。これら処理後の試験片の硬さや硬質表面処理膜の厚さの測定結果を表2に併せて示す。
[Preparation of specimen]
A steel having the chemical composition shown in Table 1 was melted and subsequently rolled and normalized according to a conventional method, and then, as shown in FIG. 1, a rod shape having a diameter of 15 mm and a length of 107 mm was formed and machined. Was processed into an impact resistance test piece having a 5 mm diameter through hole on one end side. Each test piece was subjected to a heat treatment and a surface treatment such as soft nitriding or coating under the conditions shown in Table 2. Table 2 also shows the measurement results of the hardness of the test pieces after the treatment and the thickness of the hard surface treatment film.

また、焼付き試験に供するために、径5mm、長さ30mmのシャフト状試験片に加工し、同様の熱処理及び表面処理を行ったのち、その表面粗さをRaで0.2μm程度に仕上げた。
なお、鋼を電炉溶製する場合には、Cu、Niが不純物として混入することがあるが、これらの成分量がそれぞれ0.30%以下であれば、何ら問題ないことを確認している。
Moreover, in order to use for a seizure test, after processing into the shaft-shaped test piece of diameter 5mm and length 30mm and performing the same heat processing and surface treatment, the surface roughness was finished to about 0.2 micrometer by Ra. .
In addition, when steel is melted in an electric furnace, Cu and Ni may be mixed as impurities, but it has been confirmed that there is no problem if these component amounts are each 0.30% or less.

〔耐衝撃特性試験〕
上記によって得られた耐衝撃特性試験片(図1)を図2に示すように4点で支持し、そのうちの2点に480Nの衝撃入力を繰返し加える試験を行い、破断に到るまでの回数、及び100回の繰返し入力時の変形量を測定した。その結果を表3に示す。
なお、試験結果については、比較例2の結果を「1」とする相対比で表記した。また、破断回数については、比較例2に対する破断回数比が5.0を超えるものを「○」、100回入力時の変形量については、比較例2に対する変形量比が3.0を超えないものを「○」と評価した。
[Impact resistance test]
The impact resistance test piece (FIG. 1) obtained as described above is supported at four points as shown in FIG. 2, and a test in which an impact input of 480 N is repeatedly applied to two points is performed, and the number of times until fracture occurs. , And the deformation at the time of repeated input 100 times. The results are shown in Table 3.
In addition, about the test result, it represented with the relative ratio which sets the result of the comparative example 2 to "1". As for the number of breaks, “◯” indicates that the ratio of the number of breaks with respect to Comparative Example 2 exceeds 5.0, and the amount of deformation at the time of 100 times input does not exceed 3.0 with respect to Comparative Example 2. The thing was evaluated as “◯”.

その結果、比較例1〜3、5、7、9に較べて、A鋼、B鋼、C鋼、D鋼を用いた実施例1〜4の破断に到るまでの回数が多く、また、繰返し入力に対する塑性変形量については、実施例1〜4のものが、比較例1、3、5〜7、8よりも少ないことから、耐衝撃性が必要なシャフト部品として、実施例1〜4によるものが有利であることを示している。   As a result, compared to Comparative Examples 1 to 3, 5, 7, and 9, the number of times until the breakage of Examples 1 to 4 using Steel A, Steel B, Steel C, and Steel D was increased, As for the amount of plastic deformation with respect to repeated input, since Examples 1 to 4 are less than Comparative Examples 1, 3, 5 to 7 and 8, Examples 1 to 4 are used as shaft parts that require impact resistance. Is advantageous.

また、550〜650℃の温度条件下でガス軟窒化又は塩浴軟窒化処理を施した実施例1〜4、及び比較例4においては、シャフト内部がビッカース硬さ400Hv以上、かつシャフト外形表面からの深さ0.05mm位置でのビッカース硬さが600Hv以上であった。これに対して、同様の温度条件下で塩浴軟窒化を施した比較例1では、Mo,V成分の添加量が不足しており、シャフト内部のビッカース硬さが400Hvに達していないために、耐衝撃性が劣る結果となった。
また、比較例2では、浸炭焼入れ焼戻しの後、95℃で燐酸マンガン皮膜処理を実施しており、シャフト内部硬さ400Hv以上、シャフト外形表面からの深さ0.05mm位置でのビッカース硬さ600Hv以上が得られているものの、炭素濃度の高い浸炭層を有していることから、シャフト表層付近の靭性が不足しており、耐衝撃特性に劣る結果となった。
In Examples 1 to 4 and Comparative Example 4 subjected to gas soft nitriding or salt bath soft nitriding under a temperature condition of 550 to 650 ° C., the inside of the shaft has a Vickers hardness of 400 Hv or more, and from the outer surface of the shaft. The Vickers hardness at a depth of 0.05 mm was 600 Hv or more. On the other hand, in Comparative Example 1 in which the salt bath soft nitriding was performed under the same temperature condition, the addition amount of the Mo and V components was insufficient, and the Vickers hardness inside the shaft did not reach 400 Hv. The impact resistance was inferior.
In Comparative Example 2, after carburizing, quenching, and tempering, the manganese phosphate coating was performed at 95 ° C., the shaft internal hardness was 400 Hv or more, and the Vickers hardness was 600 Hv at a depth of 0.05 mm from the shaft outer surface. Although the above was obtained, since it has a carburized layer with a high carbon concentration, the toughness in the vicinity of the shaft surface layer was insufficient, resulting in poor impact resistance.

比較例3では、焼入れ処理の後、550℃以上での焼戻し処理を施すことにより、シャフトの靭性は比較例2によりも向上するものの、シャフト内部及びシャフト外形表面からの深さ0.05mm位置でのビッカース硬さが309Hvと不足しているために、実施例よりも耐衝撃性に劣ることが確認された。
さらに、比較例5、6、7の化学成分組成では、Mo,V成分の添加量が不足しており、熱処理によってシャフト内部硬さ400Hv以上を確保できず、耐衝撃特性に劣る結果であった。また、比較例9では、焼入れ焼戻しの熱処理を行っていないために、シャフト内部の硬さについて400Hv以上を確保することができず、耐衝撃特性に劣る結果となった。
In Comparative Example 3, the toughness of the shaft is improved by tempering at 550 ° C. or higher after the quenching treatment, but the shaft toughness is improved as compared with Comparative Example 2, but at a depth of 0.05 mm from the inside of the shaft and the outer surface of the shaft. Since the Vickers hardness of 309Hv was insufficient, it was confirmed that the impact resistance was inferior to that of the examples.
Furthermore, in the chemical component compositions of Comparative Examples 5, 6, and 7, the addition amounts of Mo and V components were insufficient, and the shaft internal hardness of 400 Hv or more could not be secured by heat treatment, resulting in poor impact resistance characteristics. . In Comparative Example 9, since heat treatment for quenching and tempering was not performed, the hardness inside the shaft could not be ensured to be 400 Hv or more, resulting in poor impact resistance.

〔焼付き試験〕
図3に示すように、上記によって得られたシャフト状試験片Sを周速0.4m/sで回転させ、これにブロック状試験片B(10×10×30mm)を押し付け、焼付きが発生するときの荷重を測定した。
このとき、両試験片A,Bの摺接面には、潤滑油を毎分3cc滴下し、ブロック状試験片Bのシャフト状試験片Sとの摺接面の表面粗さについては、Raで1.5μm程度とした。
[Seizure test]
As shown in FIG. 3, the shaft-shaped test piece S obtained as described above is rotated at a peripheral speed of 0.4 m / s, and a block-shaped test piece B (10 × 10 × 30 mm) is pressed against the test piece to cause seizure. The load when measuring was measured.
At this time, 3 cc of lubricating oil is dropped on the sliding contact surfaces of both test pieces A and B per minute, and the surface roughness of the sliding contact surface of the block-like test piece B with the shaft-like test piece S is expressed as Ra. About 1.5 μm.

その結果を表3に併せて示す。
なお、試験結果については、比較例2の結果を「1」とする相対比で表記した。また、比較例2に対する焼付き荷重比が1.8以上のものを「○」評価した。
The results are also shown in Table 3.
In addition, about the test result, it represented with the relative ratio which sets the result of the comparative example 2 to "1". Further, “◯” was evaluated when the seizure load ratio with respect to Comparative Example 2 was 1.8 or more.

表3に示すように、窒化物層を有する実施例1〜4、及び比較例1、9では、窒化処理無しの比較例2、3、5、6、8に対して、耐焼付き性が向上していることが判明した。 また、比較例4では、窒化処理によって形成される窒化物層の厚さが27μmと厚すぎるために、試験時に割れが発生した。   As shown in Table 3, in Examples 1 to 4 having a nitride layer and Comparative Examples 1 and 9, the seizure resistance is improved compared to Comparative Examples 2, 3, 5, 6, and 8 without nitriding treatment. Turned out to be. Further, in Comparative Example 4, the nitride layer formed by the nitriding treatment was too thick as 27 μm, so that cracks occurred during the test.

耐衝撃特性試験に用いる試験片の形状を示す平面図及び側面図である。It is the top view and side view which show the shape of the test piece used for an impact-resistant characteristic test. 耐衝撃特性試験の実施要領を示す説明図である。It is explanatory drawing which shows the implementation point of an impact-resistant characteristic test. 焼付き試験の実施要領を示す説明図である。It is explanatory drawing which shows the implementation point of a seizure test.

Claims (7)

質量比で、C:0.15〜0.60%、Si:0.2%以下、Mn:0.10〜0.70%、P:0.03%以下、S:0.03%以下、Cr:0.1〜1.6%、Mo:0.6〜1.5%、V:0.05〜0.40%に加えて、Ti:0.01〜0.20%及びNb:0.01〜0.20%の少なくとも一方を含有し、残部がFe及び不可避的不純物である鋼から成り、内部のビッカース硬さが400Hv以上、表面から0.05mmの深さ位置におけるビッカース硬さが600Hv以上であると共に、表面に25μm以下の厚さの窒化物層を備えていることを特徴とするシャフト。 By mass ratio, C: 0.15 to 0.60%, Si: 0.2% or less, Mn: 0.10 to 0.70%, P: 0.03% or less, S: 0.03% or less, In addition to Cr: 0.1 to 1.6%, Mo: 0.6 to 1.5%, V: 0.05 to 0.40%, Ti: 0.01 to 0.20% and Nb: 0 contains at least one of .01~0.20%, balance Ri consists of steel is Fe and unavoidable impurities, the interior of the Vickers hardness of not less than 400 Hv, Vickers hardness at a depth position of 0.05mm from the surface shaft but which is characterized with at least 600 Hv, that you have provided a nitride layer of a thickness of less than 25μm on the surface. 質量比で、C:0.15〜0.60%、Si:0.2%以下、Mn:0.10〜0.70%、P:0.03%以下、S:0.03%以下、Cr:0.1〜1.6%、Mo:0.6〜1.5%、V:0.05〜0.40%に加えて、Pb:0.3%以下、Bi:0.1%以下及びCa:0.1%以下から成る群から選ばれた少なくとも1種の元素を含有し、残部がFe及び不可避的不純物である鋼から成り、内部のビッカース硬さが400Hv以上、表面から0.05mmの深さ位置におけるビッカース硬さが600Hv以上であると共に、表面に25μm以下の厚さの窒化物層を備えていることを特徴とするシャフト。 By mass ratio, C: 0.15 to 0.60%, Si: 0.2% or less, Mn: 0.10 to 0.70%, P: 0.03% or less, S: 0.03% or less, Cr: 0.1 to 1.6%, Mo: 0.6 to 1.5%, V: 0.05 to 0.40%, Pb: 0.3% or less, Bi: 0.1% following and Ca: contains at least one element selected from the group consisting of 0.1% or less, and the balance Ri consists of steel is Fe and unavoidable impurities, the interior of the Vickers hardness of not less than 400 Hv, the surface Vickers hardness at a depth position of 0.05mm along with at least 600 Hv, the shaft characterized that you have provided a nitride layer of a thickness of less than 25μm on the surface. 質量比で、C:0.15〜0.60%、Si:0.2%以下、Mn:0.10〜0.70%、P:0.03%以下、S:0.03%以下、Cr:0.1〜1.6%、Mo:0.6〜1.5%、V:0.05〜0.40%に加えて、Ti:0.01〜0.20%及びNb:0.01〜0.20%の少なくとも一方と、Pb:0.3%以下、Bi:0.1%以下及びCa:0.1%以下から成る群から選ばれた少なくとも1種の元素を含有し、残部がFe及び不可避的不純物である鋼から成り、内部のビッカース硬さが400Hv以上、表面から0.05mmの深さ位置におけるビッカース硬さが600Hv以上であると共に、表面に25μm以下の厚さの窒化物層を備えていることを特徴とするシャフト。 By mass ratio, C: 0.15 to 0.60%, Si: 0.2% or less, Mn: 0.10 to 0.70%, P: 0.03% or less, S: 0.03% or less, In addition to Cr: 0.1 to 1.6%, Mo: 0.6 to 1.5%, V: 0.05 to 0.40%, Ti: 0.01 to 0.20% and Nb: 0 0.01% to 0.20% and at least one element selected from the group consisting of Pb: 0.3% or less, Bi: 0.1% or less, and Ca: 0.1% or less. the balance Ri consists of steel is Fe and unavoidable impurities, the interior of the Vickers hardness of not less than 400 Hv, with Vickers hardness is not less than 600Hv at a depth position of 0.05mm from the surface, a thickness of less than 25μm on the surface shaft characterized that you have provided a a nitride layer. ディファレンシャル機構用ピニオンメートシャフトであることを特徴とする請求項1〜のいずれか1つの項に記載のシャフト。 It is a pinion mate shaft for differential mechanisms, The shaft as described in any one of Claims 1-3 characterized by the above-mentioned. 質量比で、C:0.15〜0.60%、Si:0.2%以下、Mn:0.10〜0.70%、P:0.03%以下、S:0.03%以下、Cr:0.1〜1.6%、Mo:0.6〜1.5%、V:0.05〜0.40%に加えて、Ti:0.01〜0.20%及びNb:0.01〜0.20%の少なくとも一方を含有し、残部がFe及び不可避的不純物である鋼材に、880℃以上の温度で焼入れ処理を施した後、550〜650℃の温度で塩浴軟窒化又はガス軟窒化処理を施すことを特徴とするシャフトの製造方法。 By mass ratio, C: 0.15 to 0.60%, Si: 0.2% or less, Mn: 0.10 to 0.70%, P: 0.03% or less, S: 0.03% or less, In addition to Cr: 0.1 to 1.6%, Mo: 0.6 to 1.5%, V: 0.05 to 0.40%, Ti: 0.01 to 0.20% and Nb: 0 Steel material containing at least one of 0.01 to 0.20% , the balance being Fe and inevitable impurities, after quenching at a temperature of 880 ° C. or higher, and then salt bath soft nitriding at a temperature of 550 to 650 ° C. Or the manufacturing method of the shaft characterized by performing gas soft nitriding treatment. 質量比で、C:0.15〜0.60%、Si:0.2%以下、Mn:0.10〜0.70%、P:0.03%以下、S:0.03%以下、Cr:0.1〜1.6%、Mo:0.6〜1.5%、V:0.05〜0.40%に加えて、Pb:0.3%以下、Bi:0.1%以下及びCa:0.1%以下から成る群から選ばれた少なくとも1種の元素を含有し、残部Fe及び不可避的不純物から成る鋼材に、880℃以上の温度で焼入れ処理を施した後、550〜650℃の温度で塩浴軟窒化又はガス軟窒化処理を施すことを特徴とするシャフトの製造方法。By mass ratio, C: 0.15 to 0.60%, Si: 0.2% or less, Mn: 0.10 to 0.70%, P: 0.03% or less, S: 0.03% or less, Cr: 0.1 to 1.6%, Mo: 0.6 to 1.5%, V: 0.05 to 0.40%, Pb: 0.3% or less, Bi: 0.1% The steel material containing at least one element selected from the group consisting of the following and Ca: 0.1% or less, and the balance Fe and inevitable impurities is subjected to a quenching treatment at a temperature of 880 ° C. or more, and then 550 A method for producing a shaft, wherein salt bath soft nitriding or gas soft nitriding is performed at a temperature of ˜650 ° C. 質量比で、C:0.15〜0.60%、Si:0.2%以下、Mn:0.10〜0.70%、P:0.03%以下、S:0.03%以下、Cr:0.1〜1.6%、Mo:0.6〜1.5%、V:0.05〜0.40%に加えて、Ti:0.01〜0.20%及びNb:0.01〜0.20%の少なくとも一方と、Pb:0.3%以下、Bi:0.1%以下及びCa:0.1%以下から成る群から選ばれた少なくとも1種の元素を含有し、残部がFe及び不可避的不純物である鋼材に、880℃以上の温度で焼入れ処理を施した後、550〜650℃の温度で塩浴軟窒化又はガス軟窒化処理を施すことを特徴とするシャフトの製造方法。By mass ratio, C: 0.15 to 0.60%, Si: 0.2% or less, Mn: 0.10 to 0.70%, P: 0.03% or less, S: 0.03% or less, In addition to Cr: 0.1 to 1.6%, Mo: 0.6 to 1.5%, V: 0.05 to 0.40%, Ti: 0.01 to 0.20% and Nb: 0 0.01% to 0.20% and at least one element selected from the group consisting of Pb: 0.3% or less, Bi: 0.1% or less, and Ca: 0.1% or less. The shaft is characterized in that the steel material, the balance of which is Fe and inevitable impurities, is subjected to quenching treatment at a temperature of 880 ° C. or higher, and then subjected to salt bath soft nitriding or gas soft nitriding treatment at a temperature of 550-650 ° C. Manufacturing method.
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