JP2007239068A - Machine parts and manufacturing method thereof - Google Patents

Machine parts and manufacturing method thereof Download PDF

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JP2007239068A
JP2007239068A JP2006065930A JP2006065930A JP2007239068A JP 2007239068 A JP2007239068 A JP 2007239068A JP 2006065930 A JP2006065930 A JP 2006065930A JP 2006065930 A JP2006065930 A JP 2006065930A JP 2007239068 A JP2007239068 A JP 2007239068A
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rolling
layer
groove
induction hardening
scale
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Kazuhiko Yoshida
和彦 吉田
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NTN Corp
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NTN Corp
NTN Toyo Bearing Co Ltd
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Priority to PCT/JP2007/054406 priority patent/WO2007102533A1/en
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Abstract

<P>PROBLEM TO BE SOLVED: To provide machine parts which unnecessitates scale removing processing after induction hardening and is capable of performing correspondence according to in-line processing, reducing the cost, moreover reducing a deformation after the induction hardening and prolonging the endurance life in a high-temperature environment, and to provide a manufacturing method of the machine parts. <P>SOLUTION: The machine parts comprises a rolling groove 4 through which a rolling body 6 rolls, wherein at least a groove surface layer of the rolling groove 4 is made to be a hardened layer by the induction hardening. A carburized layer in which a carbon concentration is made higher than that in the starting material is formed for the hardened layer of the rolling grooves 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、自動車、産業用の転動体（例えば、ボール）が転動する溝を有する機械部品及びその製造方法に関するものである。   The present invention relates to a machine part having a groove in which a rolling element (for example, a ball) for an automobile or industry rolls, and a manufacturing method thereof.

転動体が転動する溝を有する機械部品として、ボールねじがある。ボールねじは、一般的には、図５に示すように、外周面に螺旋状の転動溝１０２を有する軸部材１０１と、内周面に前記軸部材１０１の転動溝１０２に対応した螺旋状の転動溝１０３を有するナット部材１０４と、前記両転動溝１０２、１０３の間に転動自在に介装されている複数の転動体１０５とを備える。そして、軸部材１０１（またはナット部材１０４）の回転動力を、転動体１０５を介してナット部材１０４（または軸部材１０１）の推力に変換するものである。   There is a ball screw as a mechanical part having a groove on which a rolling element rolls. As shown in FIG. 5, the ball screw generally has a shaft member 101 having a spiral rolling groove 102 on the outer peripheral surface and a spiral corresponding to the rolling groove 102 of the shaft member 101 on the inner peripheral surface. A nut member 104 having a rolling groove 103 and a plurality of rolling elements 105 interposed between the rolling grooves 102 and 103 so as to be freely rollable. Then, the rotational power of the shaft member 101 (or the nut member 104) is converted into the thrust of the nut member 104 (or the shaft member 101) via the rolling element 105.

前記のようなボールねじには、転動溝の耐摩耗性を向上させるために、転動溝の溝表層に高周波焼入れしたものがある。   Some ball screws as described above are induction-hardened in the groove surface layer of the rolling groove in order to improve the wear resistance of the rolling groove.

しかしながら、高周波焼入れを行えば、高周波焼入れされた面には、酸化によりスケールが生成する。これにより、面粗さが低下して、寿命が低下する問題があった。更に、このスケールは剥がれ落ちたり、肉厚が一定でなかったりするので、寸法精度の低下と寸法ばらつきが増加する問題もあった。球状の転動体が作動する場合、点状の接触状態（純転がりに近い状態）で作動するため、焼入れ時に生じたスケール等の異物が接触面に噛み込んだり存在したりしていると、転動体の動きが急変し異音が発生しやすくなる。このため、スケールの除去は必須工程となる。   However, when induction hardening is performed, scale is generated by oxidation on the induction-quenched surface. As a result, there is a problem that the surface roughness is lowered and the life is shortened. Further, since this scale is peeled off and the thickness is not constant, there is a problem that the dimensional accuracy is lowered and the dimensional variation is increased. When a spherical rolling element is activated, it operates in a dot-like contact state (a state close to pure rolling). Therefore, if foreign matter such as scales generated during quenching is caught in the contact surface or is present, The movement of the moving object suddenly changes and noise is likely to occur. For this reason, removal of the scale is an essential process.

そこで、従来には、熱処理にて発生したスケールを除去するためにバフ処理を施すものがある（特許文献１）。すなわち、中炭素鋼を用いて転造加工を行い、その後、転動溝の溝表層を高周波焼入れによりＨＲＣ５５〜６２の範囲の硬化処理を行った後、バフ処理を行っていた。また、プレス機等で転造加工及び高周波焼入れ工程で生じた変形を矯正するため高周波焼入れ後に曲がり矯正をする必要があり、コスト増加を招く場合がある。   Therefore, conventionally, there is a technique that performs buffing in order to remove scale generated by heat treatment (Patent Document 1). That is, a rolling process was performed using medium carbon steel, and then a buffing process was performed after the groove surface layer of the rolling groove was hardened in the range of HRC55 to 62 by induction hardening. Further, it is necessary to correct the bending after the induction hardening in order to correct the deformation caused by the rolling process and the induction hardening process with a press machine or the like, which may increase the cost.

また、高周波焼入後に電解研磨によりスケール除去と仕上げを実施するものもある（特許文献２）。さらに、高周波焼入時の冷却水の圧力を高めてスケールを除去するものもある（特許文献３）。   In addition, there is a technique in which scale removal and finishing are performed by electrolytic polishing after induction hardening (Patent Document 2). Furthermore, there is also one that removes scale by increasing the pressure of cooling water during induction hardening (Patent Document 3).

さらに、非特許文献１には、真空油焼入れにより表層に残留オーステナイトを生成し、耐摩耗性を向上させることができる真空油焼入れにより生成した白層（残留オーステナイト）を有する高速度鋼についての記載がある。
特開２００３−１１９５１８号公報 特開２００３−２５１５２号公報 特開２００２−１２９２３１号公報 論文「真空油焼入れにより生成した白層を有する高速度鋼の耐摩耗性について」金属学会誌４１巻（１９７７）第６３９頁〜第６４６頁 Furthermore, Non-Patent Document 1 describes a high-speed steel having a white layer (residual austenite) generated by vacuum oil quenching that can generate retained austenite on the surface layer by vacuum oil quenching and improve wear resistance. There is.
JP 2003-119518 A JP 2003-25152 A JP 2002-129231 A The paper “Abrasion resistance of high-speed steel with white layer produced by vacuum oil quenching” Journal of the Japan Institute of Metals, Vol. 41 (1977), pages 639 to 646

しかしながら、引用文献１に記載されたバフ加工のみでは、完全にスケールを除去しきれない場合があり、しかも、加工時間が長いという問題があった。また、引用文献２に記載のものは、完全にスケールを除去できるものの、加工時間が大幅に長く、表面の面荒れ、化学反応熱による表層の軟化などの問題があった。さらに、引用文献３のものでは、スケールを均一に除去できず、微小な黒色のスケールが斑点状に残り、完全にスケール除去加工を廃止できないという問題があった。   However, there are cases where the scale cannot be completely removed only by the buffing described in the cited document 1, and there is a problem that the processing time is long. Moreover, although the thing of the cited reference 2 can remove scale completely, there existed problems, such as surface roughening and the softening of the surface layer by a chemical reaction heat, since processing time was significantly long. Furthermore, the thing of the cited reference 3 had the problem that a scale could not be removed uniformly, a fine black scale remained in the shape of a spot, and scale removal processing could not be abolished completely.

また、この様な高周波焼入されるボールねじにおいて、熱処理後の変形やスケールの発生を抑制すれば、振動の問題は解決する。しかし、高周波焼入部品を、高温の雰囲気（エンジン内または周辺やブレーキ付近など）で使用すると、軟化し転動寿命が低下する問題がある。すなわち、高周波焼入の表面硬度は、マルテンサイトの生成による組織的な硬さ圧縮残留応力による硬さからなるので、このような高周波焼入部品を高温雰囲気で使用すると、圧縮残留応力による硬さが急激に変化し、表面硬度が低下する。このため、この硬度低下により転動寿命が低下することになる。   In addition, in such an induction-hardened ball screw, the problem of vibration can be solved by suppressing deformation and scale generation after heat treatment. However, when an induction-hardened part is used in a high-temperature atmosphere (such as in the engine, around it, or near the brake), there is a problem that the rolling life is reduced. That is, the surface hardness of induction hardening is composed of hardness due to systematic hardness compressive residual stress due to the formation of martensite. When such an induction hardened component is used in a high temperature atmosphere, the hardness due to compressive residual stress. Changes rapidly and the surface hardness decreases. For this reason, the rolling life is reduced due to this decrease in hardness.

さらに、高温で長時間加熱し真空浸炭処理をすれば、高温での軟化抵抗を高めることができるが、長時間の処理でインライン化ができなく効率の悪い処理となっていた。また、もともと炭素を多く含む材料を使用し真空焼入れするとスケールが無く、軟化抵抗も増加するが、高炭素の材料となり、溝部の冷間加工性が著しく低下する問題がある。   Furthermore, if it is heated at a high temperature for a long time and subjected to a vacuum carburizing process, the softening resistance at a high temperature can be increased, but it cannot be inlined for a long time and has become an inefficient process. In addition, when a material containing a large amount of carbon is originally used and vacuum-quenched, there is no scale and the softening resistance increases. However, there is a problem that the material becomes a high-carbon material and the cold workability of the groove portion is significantly reduced.

なお、非特許文献１では、転動する溝を有する機械部品ではないが、真空油焼入れを行って、耐摩耗性の向上を図ることが記載されている。しかしながら、真空油焼入れでは、真空装置が必要であるが装置自体が高価で、インライン化に対応できない問題がある。   Non-Patent Document 1 describes that although it is not a mechanical part having a rolling groove, it is intended to improve wear resistance by performing vacuum oil quenching. However, the vacuum oil quenching requires a vacuum device, but the device itself is expensive, and there is a problem that it cannot cope with in-line.

本発明は、上記課題に鑑みて、高周波焼入れ後のスケール除去加工が不要でインライン化対応が可能となり、コストの低減を達成でき、しかも、高周波焼入れ後の変形を減少させることができ、高温雰囲気中での耐久寿命を延ばすことができる機械部品およびその製造方法を提供する。   In view of the above problems, the present invention eliminates the need for scale removal after induction hardening, enables in-line processing, achieves cost reduction, reduces deformation after induction hardening, and has a high temperature atmosphere. Provided are a mechanical component capable of extending the durability life thereof and a manufacturing method thereof.

本発明の機械部品は、転動体が転動する転動溝を有し、少なくとも転動溝の溝表層を高周波焼入れにより硬化層とした機械部品において、前記転動溝の溝表層を母材の炭素濃度よりも増加させて浸炭層を形成したものである。   The mechanical component of the present invention has a rolling groove in which a rolling element rolls, and at least a groove surface layer of the rolling groove is a hardened layer by induction hardening, and the groove surface layer of the rolling groove is a base material. The carburized layer is formed by increasing the carbon concentration.

本発明の機械部品では、浸炭層は、その組織が母材（硬化層以外の部位）より炭素濃度が増加している。これは、雰囲気の油から転動溝の表面に炭素が拡散（浸炭）したためである。この浸炭により酸化反応が抑制されてスケールの発生が抑制されている。炭素量の増加により、浸炭層（硬化層）は通常の高周波焼入れされた表面硬さより高くなる。   In the machine part of the present invention, the carburized layer has a carbon concentration higher than that of the base material (a portion other than the hardened layer). This is because carbon diffused (carburized) from the oil in the atmosphere to the surface of the rolling groove. Oxidation reaction is suppressed by this carburization and generation of scale is suppressed. Due to the increase in the amount of carbon, the carburized layer (hardened layer) becomes higher than the normal induction-hardened surface hardness.

浸炭層の表面には残留オーステナイトが生成されている。これにより、耐なじみ性向上と面圧の緩和硬化により寿命はさらに向上する。   Residual austenite is generated on the surface of the carburized layer. Thereby, the life is further improved by the improvement of the conformability and the relaxation hardening of the surface pressure.

本発明の機械部品の製造方法は、素形材に冷間加工にて転動溝を成形した後、油中にて高周波焼入れを行って、前記転動溝の溝表層に母材の炭素濃度よりも増加させて浸炭層を形成するものである。   The method of manufacturing a machine part according to the present invention includes forming a rolling groove on a base material by cold working, and then subjecting the surface of the rolling groove to a carbon concentration of a base material by induction hardening in oil. More than that, a carburized layer is formed.

本発明の機械部品の製造方法では、油中における高周波焼入れにて、形成される硬化層の浸炭層は、炭素が拡散（浸炭）して母材（硬化層以外の部位）より炭素濃度が増加する。このため、硬化層では酸化反応が抑制されてスケールの発生が抑制されている。また、この浸炭による炭素量の増加にて、硬化層は通常の高周波焼入れされた表面硬さより高くなる。   In the method of manufacturing a machine part according to the present invention, carbon is diffused (carburized) in the carburized layer of the hardened layer formed by induction hardening in oil, and the carbon concentration is increased from the base material (part other than the hardened layer). To do. For this reason, in the hardened layer, the oxidation reaction is suppressed and the generation of scale is suppressed. Moreover, the hardened layer becomes higher than the normal induction-hardened surface hardness due to the increase in the carbon amount due to the carburization.

本発明では、スケールの発生が抑制され、しかも、浸炭層は炭素量の増加により、表面硬さが高くなり、高温雰囲気での軟化抵抗が増加し、初期の硬さが維持され、耐摩耗性や耐剥離性が向上し、寿命（転動寿命）が増加する。また、材料（素形材）を低炭素鋼にしても、必要な表面硬度が得られる。このため、素材を低炭素化でき、変形能が向上し、浸炭と同様に冷間加工も可能となる。すなわち、本発明では、高周波焼入れ後のスケール除去加工が不要でインライン化対応が可能となり、コストの大幅低減を達成できる。しかも、高周波焼入れ後の変形を大幅に減少させることができ、高温雰囲気中での耐久寿命（転動寿命）を大幅に延ばすことができる。   In the present invention, the occurrence of scale is suppressed, and the carburized layer has a surface hardness that increases due to an increase in the carbon content, the softening resistance in a high temperature atmosphere increases, the initial hardness is maintained, and the wear resistance is increased. And the peel resistance is improved, and the life (rolling life) is increased. Moreover, even if the material (original material) is a low carbon steel, the necessary surface hardness can be obtained. For this reason, the carbon of the material can be reduced, the deformability is improved, and cold working can be performed in the same manner as carburizing. That is, according to the present invention, scale removal processing after induction hardening is not required, and in-line processing is possible, thereby achieving a significant cost reduction. In addition, deformation after induction hardening can be greatly reduced, and the durability life (rolling life) in a high-temperature atmosphere can be greatly extended.

本発明に係る機械部品の実施形態を図１〜図４に基づいて説明する。   An embodiment of a mechanical component according to the present invention will be described with reference to FIGS.

図１は、本発明に係る機械部品としてのボールねじを表示している。ボールねじは、外周面に螺旋状の転動溝５を有する軸部材１と、内周面に前記軸部材１の転動溝５に対応した螺旋状の転動溝４を有するナット部材３と、前記両転動溝４、５の間に転動自在に介装されている複数の転動体６と、前記ナット部材３に設けられた駒部材７とを備える。前記駒部材７は、ナット３に内外面に貫通して形成された嵌合用開口８に嵌合している。また、この駒部材７には連結溝９が設けられ、この連結溝９によって、ナット３に形成された螺旋状の転動溝５の隣合う部分同士を連結している。   FIG. 1 shows a ball screw as a machine part according to the present invention. The ball screw includes a shaft member 1 having a spiral rolling groove 5 on the outer peripheral surface, and a nut member 3 having a spiral rolling groove 4 corresponding to the rolling groove 5 of the shaft member 1 on the inner peripheral surface. A plurality of rolling elements 6 interposed between the rolling grooves 4 and 5 so as to freely roll, and a piece member 7 provided on the nut member 3. The piece member 7 is fitted in a fitting opening 8 formed in the nut 3 so as to penetrate the inner and outer surfaces. The piece member 7 is provided with a connecting groove 9, and the adjacent portions of the spiral rolling groove 5 formed in the nut 3 are connected by the connecting groove 9.

前記連結溝９により、ねじ軸２とナット３の転動溝４、５間で形成される螺旋状のボール転送路が周回経路を構成することができ、ボール６がこの周回経路を循環移動する。なお、ボール６は、連結溝９を通過するときは、ねじ軸２の転動溝（ねじ溝）４のねじ山を乗り越えることになる。   The connecting groove 9 allows a spiral ball transfer path formed between the screw shaft 2 and the rolling grooves 4 and 5 of the nut 3 to form a circular path, and the ball 6 circulates along the circular path. . When the ball 6 passes through the connecting groove 9, the ball 6 gets over the thread of the rolling groove (screw groove) 4 of the screw shaft 2.

この機械部品では、軸部材２の外周面及びナット部材３の内周面である転動体６の接触部位（転動溝４、５）の溝表層を硬化層としている。この硬化層は、油中で高周波焼入れを行うことになる。例えば、軸部材２やナット部材３を油中に浸漬した状態で高周波焼入れを行う。ここで、高周波焼入れとは、焼入れ用コイルに高周波電流を流すことによって、誘導体（被加工体）の表面部分に誘導電流を生じさせて発熱させ、この熱により被加工体の表面を急速に加熱して焼入れを行う方法である。この場合の高周波加熱の温度は、９００℃以上で１３５０℃以下が好ましい。   In this machine part, the groove surface layer of the contact portion (rolling grooves 4, 5) of the rolling element 6, which is the outer peripheral surface of the shaft member 2 and the inner peripheral surface of the nut member 3, is a hardened layer. This hardened layer is subjected to induction hardening in oil. For example, induction hardening is performed while the shaft member 2 and the nut member 3 are immersed in oil. Here, induction hardening means that an induction current is generated in the surface portion of the derivative (workpiece) by passing a high-frequency current through the quenching coil to generate heat, and this heat rapidly heats the surface of the workpiece. And quenching. In this case, the high-frequency heating temperature is preferably 900 ° C. or higher and 1350 ° C. or lower.

油中での高周波焼入れにより、形成された硬化層（浸炭層）は、その組織が母材（硬化層以外の部位）より炭素濃度が増加する。これは、雰囲気の油から転動体接触部位の表面に炭素が拡散（浸炭）したためである。この浸炭により酸化反応が抑制されてスケールの発生が抑制されている。   The hardened layer (carburized layer) formed by induction hardening in oil has a carbon concentration that is higher than that of the base material (a portion other than the hardened layer). This is because carbon diffuses (carburizes) from the oil in the atmosphere to the surface of the rolling element contact portion. Oxidation reaction is suppressed by this carburization and generation of scale is suppressed.

また、硬化層（浸炭層）の硬さは、図２に示すようになり、通常の高周波焼入れされた表面硬さより高くなっている。これは前記のように浸炭処理されたからであり、この硬さは、図４に示すように、炭素量の増加によるものである。このため、高温雰囲気での軟化抵抗が増加し、初期の硬さが維持され、耐摩耗性や耐剥離性が向上し、寿命（転動寿命）が増加する。   Further, the hardness of the hardened layer (carburized layer) is as shown in FIG. 2 and is higher than the surface hardness subjected to normal induction hardening. This is because the carburizing treatment was performed as described above, and this hardness is due to an increase in the amount of carbon as shown in FIG. For this reason, the softening resistance in a high temperature atmosphere increases, the initial hardness is maintained, the wear resistance and the peel resistance are improved, and the life (rolling life) is increased.

しかも、図３に示すように、硬化層（図３における浸炭層）の表面部には、残留オーステナイト（γ）が形成されている。ここで、残留オーステナイトとは、鋼を焼入れた場合、その鋼のマルテンサイト変態終了温度（Ｍｆ点）が室温以下になると、まだ変態を完了していないオーステナイトは、そのまま焼入れ後も残ることになり、この残ったものである。この残留オーステナイトは、じん性、転がり疲れ強さを向上させる。このため、硬化層は、耐なじみ性向上と面圧の緩和硬化により寿命はさらに向上することになる。   Moreover, as shown in FIG. 3, residual austenite (γ) is formed on the surface portion of the hardened layer (the carburized layer in FIG. 3). Here, retained austenite means that when a steel is quenched and the martensitic transformation end temperature (Mf point) of the steel is below room temperature, the austenite that has not yet undergone transformation remains as it is after quenching. This is what remains. This retained austenite improves toughness and rolling fatigue strength. For this reason, the life of the cured layer is further improved by improving the conformability and relaxing the surface pressure.

このように、本発明では、スケールの発生が抑制され、しかも、浸炭層は炭素量の増加により、表面硬さが高くなり、高温雰囲気での軟化抵抗が増加し、初期の硬さが維持され、耐摩耗性や耐剥離性が向上し、寿命（転動寿命）が増加する。また、材料（素形材）を低炭素鋼にしても、必要な表面硬度が得られる。このため、素材を低炭素化でき、変形能が向上し、浸炭と同様に冷間加工も可能となる。すなわち、本発明では、高周波焼入れ後のスケール除去加工が不要でインライン化対応が可能となり、コストの大幅低減を達成できる。しかも、高周波焼入れ後の変形を大幅に減少させることができ、高温雰囲気中での耐久寿命（転動寿命）を大幅に延ばすことができる。特に、高周波加熱の温度を９００℃以上で１３５０℃以下とすることよって、浸炭による酸化反応を安定して抑制できてスケールの発生を確実に抑制できる。なお、高周波加熱の温度が９００℃未満では、十分な硬さが得られず、酸化反応が促進されスケールの発生が増加し、浸炭量も少なくなり、高周波加熱の温度が１３５０℃を越えれば、浸炭層は増加するが結晶粒が粗大化し脆化する。   Thus, in the present invention, the occurrence of scale is suppressed, and the carburized layer is increased in surface hardness due to an increase in the carbon content, the softening resistance in a high temperature atmosphere is increased, and the initial hardness is maintained. , Wear resistance and peel resistance are improved, and the life (rolling life) is increased. Moreover, even if the material (original material) is a low carbon steel, the necessary surface hardness can be obtained. For this reason, the carbon of the material can be reduced, the deformability is improved, and cold working can be performed in the same manner as carburizing. That is, according to the present invention, scale removal processing after induction hardening is not required, and in-line processing is possible, thereby achieving a significant cost reduction. In addition, deformation after induction hardening can be greatly reduced, and the durability life (rolling life) in a high-temperature atmosphere can be greatly extended. In particular, by setting the temperature of the high frequency heating to 900 ° C. or more and 1350 ° C. or less, the oxidation reaction due to carburization can be stably suppressed, and the generation of scale can be reliably suppressed. In addition, when the temperature of the high frequency heating is less than 900 ° C., sufficient hardness cannot be obtained, the oxidation reaction is promoted, the generation of scale increases, the carburization amount decreases, and the temperature of the high frequency heating exceeds 1350 ° C. Although the carburized layer increases, the crystal grains become coarse and become brittle.

ところで、前記実施形態では、軸部材２の外周面及びナット部材３の内周面である転動体６の接触部位（転動溝４、５）の溝表層を硬化層としていたが、このどちらか一方であってもよい。すなわち、ナット部材３の内周面である転動溝４の溝表層のみを硬化層としたり、軸部材２の外周面である転動溝５の溝表層のみを硬化層としたりすることができる。また、機械部品として、ボールねじに限るものではなく、転動体が転動する転動溝を有するものであればよく、ボールねじとしては、図１に示すものに限るものではない。さらに、転動体としてボールではなく、ころやローラ等であってもよく、転動体が転動する転動溝としても螺旋状でなくてもよい。   By the way, in the said embodiment, although the groove | channel surface layer of the contact part (rolling grooves 4 and 5) of the rolling element 6 which is the outer peripheral surface of the shaft member 2 and the inner peripheral surface of the nut member 3 was made into the hardening layer, either One may be sufficient. That is, only the groove surface layer of the rolling groove 4 that is the inner peripheral surface of the nut member 3 can be a hardened layer, or only the groove surface layer of the rolling groove 5 that is the outer peripheral surface of the shaft member 2 can be a hardened layer. . Further, the mechanical part is not limited to the ball screw, but may be any one having a rolling groove on which the rolling element rolls, and the ball screw is not limited to that shown in FIG. Furthermore, the rolling element may be a roller or a roller instead of a ball, and the rolling groove on which the rolling element rolls may not be spiral.

図１に示す構造のボールねじについて、大気中で高周波焼入れを行った従来品Ａと、大気中で高周波焼入れを行った後バフ加工を施した従来品Ｂと、油中で高周波焼入れを行った発明品Ａ、Ｂとを製造して、これらの特性を比較し、その結果を次の表１に示した。いずれも、こま２列のボールねじを使用し、ねじ軸は、材質がＡＩＳＩ１０５０であり、軸径１６ｍｍで、リード３ｍｍのものを使用した。また、転動体の径（ボール径）３／３２”とした。耐久条件として、回転数を１５００ｒ／ｍとし、荷重を７００Ｎとして、試験雰囲気温度が８０℃として試験を行った。なお、焼入れ後の冷却は、従来品Ａ、Ｂでは水溶性の焼入液でスプレイ冷却を行い、発明品Ａ、Ｂでは、焼入れ油の油中冷却を行った。また、発明品Ａ、Ｂにおける油中高周波焼入れは、焼入れ油の雰囲気中で高周波加熱後加熱電源を切ると同時に冷却を開始し焼入れした。   The ball screw having the structure shown in FIG. 1 was subjected to induction hardening in the atmosphere, conventional product A subjected to induction hardening in the atmosphere, conventional product B subjected to buffing after induction hardening in the atmosphere, and induction hardening in oil. Inventions A and B were manufactured and their characteristics were compared. The results are shown in Table 1 below. In each case, two rows of ball screws were used, and the screw shaft was made of AISI1050, the shaft diameter was 16 mm, and the lead was 3 mm. Further, the rolling element diameter (ball diameter) was 3/32 ". As durability conditions, the rotation speed was 1500 r / m, the load was 700 N, and the test ambient temperature was 80 ° C. The test was performed after quenching. In the conventional products A and B, spray cooling was performed with a water-soluble quenching liquid, and in the invention products A and B, quenching oil was cooled in oil. Quenching was quenched by quenching at the same time as the heating power was turned off after induction heating in an atmosphere of quenching oil.

Figure 2007239068
Figure 2007239068

表１から分かるように、従来品Ａには黒色状でポーラスなスケールが大量に発生し、従来品Ｂには、濃灰色なスケールが大量に発生した。これに対して、発明品Ａ及び発明品Ｂは灰色のスケールが少し発生したが、黒色状のスケールはほとんど発生しなかった。   As can be seen from Table 1, a large amount of black and porous scale occurred in the conventional product A, and a large amount of dark gray scale occurred in the conventional product B. In contrast, Invention A and Invention B produced a little gray scale, but almost no black scale.

また、従来品Ａでは回転時において、異音が発生した。従来品Ｂでは、バフ加工前では回転時に異音があったが、バフ加工後回転時には異音は発生しなかった。これに対して、発明品Ａ、Ｂは、回転時の異音は発生しなかった。すなわち、発明品Ａ、Ｂは、バフ加工を施さなくても回転時の異音は発生しない。   Further, in the conventional product A, abnormal noise was generated during rotation. In the conventional product B, noise was generated during rotation before buffing, but no noise was generated during rotation after buffing. In contrast, the inventive products A and B did not generate abnormal noise during rotation. That is, the inventive products A and B do not generate any abnormal noise during rotation even if they are not buffed.

また、高周波焼入れ後の曲がり（振れ量）においては、従来品Ａは０．６８ｍｍであり、従来品Ｂが０．６５ｍｍであるのに対して、発明品Ａ、Ｂが０．１３０ｍｍである。また、耐久寿命は、従来品Ａは４００ｈｒであり、従来品Ｂは４６０ｈｒであるのに対して、発明品Ａは７５８ｈｒであり、発明品Ｂは９５０ｈｒである。このように、発明品Ａ、Ｂの曲がり（振れ量）が少なく、耐久寿命が長い。これは、従来品Ａ、Ｂでは残留オーステナイトが２％であったのに対し、発明品Ａは残留オーステナイトが１０％であり、発明品Ｂは残留オーステナイトが４５％生成したからである。   Further, in the bending (runout amount) after induction hardening, the conventional product A is 0.68 mm, the conventional product B is 0.65 mm, and the inventive products A and B are 0.130 mm. The durability life is 400 hr for the conventional product A and 460 hr for the conventional product B, whereas it is 758 hr for the inventive product A and 950 hr for the inventive product B. Thus, the products A and B have a small bend (amount of deflection) and a long durability life. This is because, in the conventional products A and B, the retained austenite was 2%, whereas in the invention product A, the retained austenite was 10%, and in the product B, the retained austenite was 45%.

このように、本発明では、黒色状のスケールの発生が抑制され、高周波焼入れ後の変形も大幅に減少でき、さらに耐久寿命が著しく増加している。   Thus, in this invention, generation | occurrence | production of a black scale is suppressed, the deformation | transformation after induction hardening can be reduced significantly, and also the durable life has increased remarkably.

本発明の実施形態を示す機械部品の要部断面図である。It is principal part sectional drawing of the machine component which shows embodiment of this invention. 前記機械部品の硬化層の硬さを示すグラフ図である。It is a graph which shows the hardness of the hardened layer of the said machine component. 前記機械部品の浸炭層の範囲を示す簡略図である。It is a simplified diagram showing the range of the carburized layer of the machine part. 前記機械部品の硬化層の炭素量を示すグラフである。It is a graph which shows the carbon content of the hardened layer of the said machine component. 従来の機械部品の要部断面図である。It is principal part sectional drawing of the conventional machine component.

符号の説明Explanation of symbols

４、５ 転動溝
６ 転動体 4, 5 Rolling groove 6 Rolling element

Claims (3)

転動体が転動する転動溝を有し、少なくとも転動溝の溝表層を高周波焼入れにより硬化層とした機械部品において、前記転動溝の硬化層に母材の炭素濃度よりも増加させて浸炭層を形成したことを特徴とする機械部品。   In a machine part having a rolling groove in which the rolling element rolls, and at least the groove surface layer of the rolling groove is hardened by induction hardening, the hardened layer of the rolling groove is made to increase above the carbon concentration of the base material. A machine part characterized by forming a carburized layer. 前記浸炭層の表面には残留オーステナイトが生成されていることを特徴とする請求項１の機械部品。   The machine part according to claim 1, wherein retained austenite is generated on a surface of the carburized layer. 素形材に冷間加工にて転動溝を成形した後、油中にて高周波焼入れを行って、前記転動溝の溝表層に母材の炭素濃度よりも増加させて浸炭層を形成すること特徴とする機械部品の製造方法。   After forming rolling grooves in the base material by cold working, induction hardening is performed in oil, and a carburized layer is formed on the groove surface layer of the rolling grooves by increasing the carbon concentration of the base material. A manufacturing method of a machine part characterized by the above.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010255702A (en) * 2009-04-23 2010-11-11 Nagato:Kk Shaft part with rolling groove
JP2020148299A (en) * 2019-03-15 2020-09-17 日立オートモティブシステムズ株式会社 Ball screw, method for manufacturing the same, power steering device, and method for manufacturing the same

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010255702A (en) * 2009-04-23 2010-11-11 Nagato:Kk Shaft part with rolling groove
US8573081B2 (en) 2009-04-23 2013-11-05 Ntn Corporation Shaft part formed with a rolling groove
JP2020148299A (en) * 2019-03-15 2020-09-17 日立オートモティブシステムズ株式会社 Ball screw, method for manufacturing the same, power steering device, and method for manufacturing the same
WO2020189253A1 (en) * 2019-03-15 2020-09-24 日立オートモティブシステムズ株式会社 Ball screw and method for manufacturing same, and power steering device and method for manufacturing same
JP7292067B2 (en) 2019-03-15 2023-06-16 日立Astemo株式会社 Ball screw and manufacturing method thereof, power steering device and manufacturing method thereof

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