JP2007262506A - Method for producing machine parts - Google Patents
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- JP2007262506A JP2007262506A JP2006090038A JP2006090038A JP2007262506A JP 2007262506 A JP2007262506 A JP 2007262506A JP 2006090038 A JP2006090038 A JP 2006090038A JP 2006090038 A JP2006090038 A JP 2006090038A JP 2007262506 A JP2007262506 A JP 2007262506A
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Abstract
Description
本発明は、機械部品の製造方法に関し、特に本発明は、浸炭処理時に発生した不完全焼入れ層を抑制又は是正し、疲労強度を簡便に向上することができる機械部品の製造方法に関する。 The present invention relates to a method for manufacturing a machine part, and in particular, the present invention relates to a method for manufacturing a machine part that can suppress or correct an incompletely hardened layer generated during carburizing and can easily improve fatigue strength.
自動車や建設機械に含まれる機械部品は、歯車に代表される駆動系への負荷の増大に伴い、表面の耐磨耗性が要求されている。また、機械部品の破壊の原因となる疲労に対しては、表面が硬いほど亀裂発生に対する抵抗が高くなり安全性が向上する。そのため、機械部品の表面を硬化することは重要な技術となっている。 Mechanical parts included in automobiles and construction machines are required to have surface wear resistance as the load on a drive system represented by gears increases. In addition, with respect to fatigue that causes destruction of machine parts, the harder the surface, the higher the resistance to cracking and the greater the safety. Therefore, it is an important technique to harden the surface of the machine part.
表面硬化処理の１つとしてショットピーニング処理が実用化されている。ショットピーニング処理とは、大きさが一定の鋼球を噴射して材料の表面を冷間衝撃加工し、新たな圧縮残留応力を表面に付与させて硬化させる表面硬化処理である。また、機械部品の表面からの深さが１０〜３０μｍといった表面直下のごく浅い部分への圧縮残留応力の付与が、機械部品の疲労強度向上には効果が大きい。よって、非常に微細な鋼球でのショットピーニング処理（以下、小球ピーニング処理という）が有効である。 A shot peening process has been put to practical use as one of the surface hardening processes. The shot peening treatment is a surface hardening treatment in which a steel ball having a constant size is sprayed to cold impact the surface of the material, and a new compressive residual stress is applied to the surface to cure. Moreover, the application of compressive residual stress to a very shallow portion immediately below the surface, such as a depth of 10 to 30 μm from the surface of the machine component, is highly effective in improving the fatigue strength of the machine component. Therefore, shot peening treatment with very fine steel balls (hereinafter, referred to as small ball peening treatment) is effective.
また、歯車やシャフト類といった機械部品は、表面を硬化させるための熱処理として、大量生産が可能で品質が安定している、ガス浸炭焼入れ処理が広く行われている。しかし、図９に示すように、ガス浸炭処理時の雰囲気ガス中のＯ２と材料中のＣｒ、Ｍｎ、Ｓｉなどの合金元素が結晶粒界において偏析を起こし、粒界酸化物を形成する。これにより、表面の焼入れ性が劣化し、焼入れ不十分となり、硬度の低い層（ベイナイト、トルースタイト、又はソルバイトの混合組織層。以下、不完全焼入れ層という）が形成される。 In addition, mechanical parts such as gears and shafts are widely subjected to gas carburizing and quenching, which can be mass-produced and have stable quality as a heat treatment for hardening the surface. However, as shown in FIG. 9, O 2 in the atmospheric gas during the gas carburizing process and alloy elements such as Cr, Mn, Si, etc. in the material cause segregation at the grain boundaries to form grain boundary oxides. Thereby, the hardenability of the surface is deteriorated, the quenching becomes insufficient, and a layer having a low hardness (a mixed structure layer of bainite, troostite or sorbite, hereinafter referred to as an incompletely quenched layer) is formed.
そこで、従来の機械部品の製造方法では、浸炭焼入れ処理した機械部品の表面を研磨して不完全焼入れ層を除去し、その後小球ピーニング処理を施す方法がある。また、機械部品の表面に、不完全焼入れ層が発生しない真空浸炭処理を施し、その真空浸炭処理後の表面に、小球ピーニング処理を施す方法もある（例えば、特許文献１参照）。
上記浸炭焼入れ処理後に表面を研磨して不完全焼入れ層を除去する方法は、工程数の増加、及び完成品に至るまでのリードタイムの増加によるコストアップが問題である。また、特開２００２−３０３４４号公報の方法では、真空浸炭処理を行うための新規設備が必要となり、既存の設備を利用できないという問題点がある。 The method of removing the incompletely hardened layer by polishing the surface after the carburizing and quenching process has a problem in that the number of steps is increased and the cost is increased due to an increase in the lead time until a finished product is reached. In addition, the method disclosed in Japanese Patent Application Laid-Open No. 2002-30344 requires a new facility for performing vacuum carburization, and there is a problem that existing facilities cannot be used.
また、建設機械部品に含まれるような大物部品の浸炭焼入れ処理には長時間を要する。また、浸炭時間の１／２乗と硬化層深さは近似的に比例関係が成立することが知られている。そして、浸炭時間に比例して機械部品の表面に形成される不完全焼入れ層も厚くなる。よって、前記大物部品の浸炭処理後の表面には２０μｍを超える厚さの不完全焼入れ層が形成される。また、不完全焼入れ層の厚さが２０μｍを超えると小球ピーニング処理を行っても、機械部品の表面へ圧縮残留応力が付与できず、小球ピーニング処理の効果を十分に発揮させることができない。よって、疲労強度の向上においては不完全焼入れ層を２０μｍ以下に抑制、又は後処理により是正することが望ましい In addition, carburizing and quenching of large parts such as those contained in construction machine parts takes a long time. Further, it is known that a proportional relationship is established approximately between the carburizing time 1/2 power and the hardened layer depth. Further, the incompletely hardened layer formed on the surface of the machine part also increases in proportion to the carburizing time. Therefore, an incompletely hardened layer having a thickness exceeding 20 μm is formed on the surface of the large component after the carburizing treatment. In addition, if the thickness of the incompletely hardened layer exceeds 20 μm, even if the small sphere peening treatment is performed, the compressive residual stress cannot be imparted to the surface of the machine part, and the effect of the small sphere peening treatment cannot be exhibited sufficiently. . Therefore, in improving the fatigue strength, it is desirable to suppress the incompletely hardened layer to 20 μm or less or correct it by post-processing.
本発明は上記のような事情を考慮してなされたもので、その目的は、浸炭処理時に発生した不完全焼入れ層を抑制又は是正し、疲労強度を簡便に向上することができる機械部品の製造方法を提供することにある。 The present invention has been made in consideration of the above circumstances, and its purpose is to manufacture a machine part that can suppress or correct an incompletely hardened layer generated during carburizing treatment and can easily improve fatigue strength. It is to provide a method.
上記課題を解決すため、本発明に係る機械部品の製造方法は、機械部品に浸炭処理を行う工程と、
前記機械部品に窒化処理を行う工程と、
前記機械部品にショットピーニング処理を行う工程と、
を具備する。
In order to solve the above problems, a method of manufacturing a machine part according to the present invention includes a step of carburizing a machine part,
Nitriding the mechanical part; and
Performing a shot peening process on the mechanical parts;
It comprises.
また、前記浸炭処理を行う工程後の前記機械部品の表面は、粒界酸化物を有することが好ましい。また、前記浸炭処理を行う工程の直後に前記機械部品に第１の焼入れ処理を行う工程をさらに具備し、前記第１の焼入れ処理を行う工程後の前記機械部品の表面は、ベイナイト、トルースタイト及びソルバイトの少なくとも１つを備える混合組織層を有することが好ましい。 Moreover, it is preferable that the surface of the said machine component after the process of performing the said carburizing process has a grain boundary oxide. The method further includes a step of performing a first quenching process on the mechanical component immediately after the step of performing the carburizing process, and the surface of the mechanical component after the step of performing the first quenching process is bainite, troostite. And a mixed tissue layer comprising at least one of sorbite.
また、前記窒化処理を行う工程後の前記機械部品の表面は、粒界酸化物を有することが好ましい。また、前記窒化処理を行う工程後に前記機械部品に第２の焼入れ処理を行う工程をさらに具備し、前記第２の焼入れ処理を行う工程後の前記機械部品の表面は、ベイナイト、トルースタイト及びソルバイトの少なくとも１つを備える混合組織層を有することが好ましい。 Moreover, it is preferable that the surface of the mechanical component after the nitriding step has a grain boundary oxide. Further, the method further includes a step of performing a second quenching process on the mechanical component after the nitriding step, and the surface of the mechanical component after the second quenching process is formed of bainite, troostite, and sorbite. It is preferable to have a mixed tissue layer comprising at least one of the following.
前記ショットピーニング処理は２段行うことが好ましい。そして、２段目の鋼球の直径が１段目の鋼球の直径よりも小さく、２段目の鋼球の直径が０．１ｍｍ以下であることが好ましい。
また、前記ショットピーニング処理は、３段以上行ってもよい。そして、前記ショットピーニング処理の鋼球の直径は前段目の鋼球の直径よりも小さく、最後段の鋼球の直径が０．１ｍｍ以下であることが好ましい。
The shot peening process is preferably performed in two stages. The diameter of the second stage steel ball is smaller than the diameter of the first stage steel ball, and the diameter of the second stage steel ball is preferably 0.1 mm or less.
The shot peening process may be performed in three or more stages. And it is preferable that the diameter of the steel ball of the said shot peening process is smaller than the diameter of the steel ball of the front | former stage, and the diameter of the steel ball of the last stage is 0.1 mm or less.
以上説明したように本発明によれば、浸炭処理時に発生した不完全焼入れ層を抑制又は是正し、疲労強度を簡便に向上することができる機械部品の製造方法を提供することができる。 As described above, according to the present invention, it is possible to provide a method of manufacturing a machine component that can suppress or correct an incompletely hardened layer generated during carburizing treatment and easily improve fatigue strength.
以下、図面を参照して本発明に係る実施形態について説明する。本実施形態は、浸炭処理後に窒化処理を行うことにより機械部品の表面部の焼入れ性を改善し、不完全焼入れ層の抑制を図り、小球ピーニング処理によって機械部品の表面に圧縮残留応力を効率的に付与するものである。 Embodiments according to the present invention will be described below with reference to the drawings. This embodiment improves the hardenability of the surface part of the machine part by performing nitriding after the carburizing process, suppresses the incompletely hardened layer, and efficiently compresses the compressive residual stress on the surface of the machine part by the small ball peening process. Is given.
図１（ａ）は、本発明の実施形態に係る機械部品の製造方法の熱処理サイクルを示す図である。まず、機械部品に対して浸炭処理を行う（Ｓ１）。浸炭処理は、例えば処理室内に機械部品を配置し、処理室内に浸炭ガス（例えば、プロパン（Ｃ３Ｈ８）、ブタン（Ｃ４Ｈ１０）、炭酸ガス（ＣＯ２）など）を所定のガス圧に制御して供給すると共に処理室内を９３０℃まで加熱し、９．５時間浸炭を行う（Ｓ１ａ）。その後、ガス圧を制御して９３０℃で１時間拡散を行う（Ｓ１ｂ）。これにより、機械部品の表面に炭素が侵入し、表面が硬化される。また同時に、機械部品の表面に粒界酸化物が厚さ２０μｍ超で形成される。 Fig.1 (a) is a figure which shows the heat processing cycle of the manufacturing method of the machine component which concerns on embodiment of this invention. First, carburizing processing is performed on the machine part (S1). In the carburizing process, for example, mechanical parts are arranged in a processing chamber, and a carburizing gas (for example, propane (C 3 H 8 ), butane (C 4 H 10 ), carbon dioxide gas (CO 2 ), etc.) is used as a predetermined gas in the processing chamber. The pressure is controlled and supplied, and the processing chamber is heated to 930 ° C. and carburized for 9.5 hours (S1a). Thereafter, the gas pressure is controlled and diffusion is performed at 930 ° C. for 1 hour (S1b). As a result, carbon enters the surface of the machine part and the surface is cured. At the same time, a grain boundary oxide is formed on the surface of the machine component with a thickness exceeding 20 μm.
次いで、浸炭処理が行われた機械部品に対して窒化処理を行う（Ｓ２）。本実施形態に係る窒化処理の詳細は、処理室内に窒化ガス（例えば、アンモニア（ＮＨ３）など）を流量６リットル／分で供給しつつ、８７０℃で２０分間、浸炭処理が行われた機械部品に対して窒化処理を行う。前記窒化処理により、機械部品の表面の粒界酸化物の厚さを２０μｍ以下にする事ができる。次いで、窒化処理が行われた機械部品を６０℃から９０℃の温度域の油で急冷することにより、焼入れ処理を行う（Ｓ３）。このとき、前記のように窒化処理を行っているため、不完全焼入れ層の厚さを２０μｍ以下にする事ができる。 Next, nitriding is performed on the machined parts that have been carburized (S2). The details of the nitriding process according to the present embodiment are machines in which a carburizing process is performed at 870 ° C. for 20 minutes while supplying a nitriding gas (for example, ammonia (NH 3 )) at a flow rate of 6 liters / minute into the processing chamber. Nitriding is performed on the part. By the nitriding treatment, the thickness of the grain boundary oxide on the surface of the machine part can be reduced to 20 μm or less. Next, a quenching process is performed by quenching the machined part subjected to nitriding with oil in a temperature range of 60 ° C. to 90 ° C. (S3). At this time, since the nitriding treatment is performed as described above, the thickness of the incompletely quenched layer can be set to 20 μm or less.
次いで、窒化焼入れ処理を行った機械部品に対して、小球ピーニング処理を行う。図２は、小球ピーニング処理を説明するための概略図である。本発明に係る小球ピーニング処理の詳細は、φ０．８ｍｍ（ＨＲｃ６０±２）の鋼球２０で投射圧０．３５ＭＰａ、投射重量１５．０ｋｇ／分、カバレージ値４００％、アークハイト値０．７７ｍｍＡで第１段目の小球ピーニング処理を行う。次いで、φ０．１ｍｍ（ＨＲｃ６０〜６５）の鋼球２１で投射圧０．３５ＭＰａ、投射重量１５．０ｋｇ／分、カバレージ値４００％、アークハイト値０．３５ｍｍＡで第２段目の小球ピーニング処理を行う。これにより、機械部品に比べ、鋼球２０，２１は硬いので機械部品表面がへこまされ、表面に丸いくぼみを残すようになる。従って小球ピーニングを行った面は無数のくぼみ（痕）でおおわれるようになり梨子地模様となるが、表面の硬さが増し、また、繰り返し荷重に対しては表面層に付与された圧縮残留応力が相殺する形で作用し疲労強度が増す。また、２段目の小球ピーニング処理には、１段目より球径が小さい鋼球２１を投射することによって、１段目の小球ピーニング処理で生じた圧縮残留応力分布に、さらにごく表面近傍により大きな圧縮残留応力を付与させる効果がある。 Next, small ball peening is performed on the machine parts that have been subjected to nitriding and quenching. FIG. 2 is a schematic diagram for explaining the small ball peening process. The details of the small ball peening process according to the present invention are as follows: a steel ball 20 of φ0.8 mm (HRc 60 ± 2), a projection pressure of 0.35 MPa, a projection weight of 15.0 kg / min, a coverage value of 400%, and an arc height value of 0.77 mmA. The first stage small ball peening process is performed. Next, the second stage of small ball peening with a steel ball 21 of φ0.1 mm (HRc 60-65) at a projection pressure of 0.35 MPa, a projection weight of 15.0 kg / min, a coverage value of 400%, and an arc height value of 0.35 mmA I do. Thereby, since the steel balls 20 and 21 are harder than the machine part, the surface of the machine part is dented, and a round recess is left on the surface. Therefore, the surface subjected to small ball peening is covered with countless indentations (scratches), resulting in a pear-like pattern, but the surface hardness increases, and the compression applied to the surface layer for repeated loads Fatigue strength is increased by acting in the form that the residual stress cancels. Further, in the second stage small peening process, a steel ball 21 having a sphere diameter smaller than that in the first stage is projected to further reduce the surface of the compression residual stress distribution generated in the first stage small peening process. There is an effect of applying a larger compressive residual stress in the vicinity.
本発明の効果を調べるために、本方法により熱処理した機械部品（浸炭処理後に窒化処理、そして焼入れ処理を行い、その後小球ピーニング処理）と従来の方法で熱処理した機械部品（浸炭処理後に焼入れ処理を行い、小球ピーニング処理）とを用意し、以下の比較実験を行った。 In order to investigate the effect of the present invention, mechanical parts heat-treated by this method (nitriding and quenching after carburizing treatment, and then small ball peening) and mechanical parts heat-treated by conventional methods (quenching after carburizing treatment) Was prepared, and the following comparative experiment was conducted.
図３は、比較実験を行う機械部品の一例の歯車１を示す図である。図３（ａ）は、歯車１の正面図であり、図３（ｂ）は歯車１の歯元部の拡大図を示す。歯車１の詳細は、モジュール３．２５，圧力角２５°，歯数３６，ピッチ円径１１７．００ｍｍ、材質ＳＣＭ４２０Ｈ低合金製の平歯車である。 FIG. 3 is a diagram showing a gear 1 as an example of a machine part for performing a comparative experiment. FIG. 3A is a front view of the gear 1, and FIG. 3B is an enlarged view of a tooth root portion of the gear 1. The details of the gear 1 are a spur gear made of module 3.25, pressure angle 25 °, number of teeth 36, pitch circle diameter 117.00 mm, material SCM420H low alloy.
図４（ａ）は、浸炭処理を行った後に、窒化処理を行わず焼入れ処理を行った歯車の小球ピーニング処理を行う前の、歯元表面部の組織写真である。図４（ｂ）は、浸炭処理を行った後に、窒化処理を行った歯車の小球ピーニング処理を行う前の、歯元表面部の組織写真である。図４（ａ）に示すように、窒化処理を行わない熱処理では、表面部の不完全焼入れ層の厚さが２８μｍであるが、図４（ｂ）に示すように、浸炭処理後に窒化処理を行う熱処理では、表面部の不完全焼入れ層の厚さが１６μｍに減少している。 FIG. 4A is a structure photograph of the tooth root surface portion after the carburizing process and before the small ball peening process of the gear that has been subjected to the quenching process without performing the nitriding process. FIG. 4B is a structure photograph of the tooth root surface portion after the carburizing treatment and before the sphere peening treatment of the nitriding gear. As shown in FIG. 4A, in the heat treatment without nitriding, the thickness of the incompletely hardened layer on the surface is 28 μm, but as shown in FIG. 4B, the nitriding treatment is performed after the carburizing treatment. In the heat treatment to be performed, the thickness of the incompletely hardened layer on the surface portion is reduced to 16 μm.
図５は、上記各歯車に小球ピーニング処理を行ったときの表面の残留応力分布を示す。上記各熱処理方法を施した各歯車をＸ線解析装置を用いて表面の残留応力を測定した。ここで、マイナス成分は圧縮残留応力を示しており、圧縮残留応力値が高いほど疲労強度が高いとされている。これにより、浸炭処理後に窒化処理を行わない歯車より窒化処理を行った歯車のほうが、表面から２０μｍ領域の圧縮残留応力が高く、強度が高い。 FIG. 5 shows the residual stress distribution on the surface when the above-mentioned gears are subjected to small sphere peening. The residual stress on the surface of each gear subjected to each heat treatment method was measured using an X-ray analyzer. Here, the minus component indicates the compressive residual stress, and the higher the compressive residual stress value, the higher the fatigue strength. As a result, the gear subjected to nitriding after the carburizing treatment has higher compressive residual stress in the 20 μm region from the surface and higher strength.
図６は、油圧サーボパルサー繰り返し試験機１０（以下、試験機１０という）を用いた、測定装置の側面図である。測定方法の詳細は、歯車１を試験機１０の支持台１３に固定ボルト１４と留め具１５及びピン１６を用いて固定する。そして、歯車１の下部歯３のピッチ円直径部を試験機１０の下部治具１２に当て、上部歯２のピッチ円直径部を試験機１０の上部治具１１に当てる。次いで、試験機１０により上部治具１１から上部歯２に対して、周波数２０Ｈｚで繰り返し荷重を与える。そして、歯車１が破断するまでの繰り返し数を測定する。図７は、繰り返し負荷応力と、本方法と従来の方法で熱処理を施した歯車が破断するまでの繰り返し数の測定結果を示した図である。この測定結果によれば、疲労強度は浸炭処理後に窒化処理を行っていない歯車に比べて、窒化処理を施している歯車は、１．２倍程度向上している。 FIG. 6 is a side view of a measuring apparatus using a hydraulic servo pulsar repetitive testing machine 10 (hereinafter referred to as a testing machine 10). For details of the measuring method, the gear 1 is fixed to the support base 13 of the testing machine 10 using the fixing bolt 14, the fastener 15 and the pin 16. Then, the pitch circle diameter part of the lower teeth 3 of the gear 1 is applied to the lower jig 12 of the test machine 10, and the pitch circle diameter part of the upper teeth 2 is applied to the upper jig 11 of the test machine 10. Next, the test machine 10 repeatedly applies a load from the upper jig 11 to the upper teeth 2 at a frequency of 20 Hz. Then, the number of repetitions until the gear 1 is broken is measured. FIG. 7 is a diagram showing the measurement results of the repeated load stress and the number of repetitions until the gear subjected to the heat treatment by this method and the conventional method breaks. According to this measurement result, the fatigue strength of the gear subjected to the nitriding treatment is improved by about 1.2 times that of the gear not subjected to the nitriding treatment after the carburizing treatment.
図８は、歯元曲げ疲労強度と不完全焼入れ層の厚さとの関係を示した図である。これにより、不完全焼入れ層が厚いほど疲労強度が低下していることがわかる。つまり、不完全焼入れ層が厚い従来の方法では、小球ピーニング処理による疲労強度の向上の効果は小さい。しかし、本方法のように窒化処理を行い、不完全焼入れ層を減少させると、小球ピーニング処理による疲労強度の向上の効果は大きくなる。 FIG. 8 is a diagram showing the relationship between the root bending fatigue strength and the thickness of the incompletely hardened layer. Thereby, it turns out that fatigue strength is falling, so that the incomplete hardening layer is thick. That is, in the conventional method with a thick incompletely hardened layer, the effect of improving the fatigue strength by the small ball peening treatment is small. However, when nitriding is performed as in the present method to reduce the incompletely hardened layer, the effect of improving the fatigue strength by the small sphere peening increases.
以上、本実施形態によれば、浸炭処理を行った機械部品に対して、小球ピーニング処理を行う前に窒化処理を行っている。これにより、浸炭処理で形成された粒界酸化物の厚さが減少し、不完全焼入れ層の厚さが２０μｍ以下に抑制される。よって、小球ピーニング処理による疲労強度向上の効果を十分に発揮させることができ、機械部品の表面から２０μｍ以内に１００ｋｇｆ／ｍｍ２以上の高い圧縮残留応力を付与することが可能である。また、浸炭処理及び窒化処理を連続して同一の処理室で行うことが可能であるため、真空浸炭処理のように新規設備は不要であり、リードタイムを減少させコストダウンすることができる。また、長時間の浸炭時間を要し、不完全焼入れ層も深い大物部品に対して、簡便に疲労強度を向上させることができる。 As described above, according to the present embodiment, the nitriding treatment is performed on the machined parts subjected to the carburizing treatment before the small ball peening treatment. Thereby, the thickness of the grain boundary oxide formed by the carburizing process is reduced, and the thickness of the incompletely quenched layer is suppressed to 20 μm or less. Therefore, the effect of improving the fatigue strength by the small sphere peening treatment can be sufficiently exerted, and a high compressive residual stress of 100 kgf / mm 2 or more can be applied within 20 μm from the surface of the machine part. Further, since the carburizing process and the nitriding process can be performed continuously in the same processing chamber, no new equipment is required unlike the vacuum carburizing process, and the lead time can be reduced and the cost can be reduced. In addition, fatigue strength can be easily improved for large parts that require a long carburizing time and have a deep incompletely hardened layer.
また、窒化処理により、焼戻しによる軟化抵抗性も向上するため、摺動特性を要求される部品においては耐ピッチング強度の向上も合わせて期待できる。 In addition, the nitriding treatment also improves the resistance to softening by tempering, so that it is also expected to improve the pitting resistance in parts that require sliding characteristics.
尚、本発明は上述した実施形態に限定されるものではなく、本発明の主旨を逸脱しない範囲内で種々変更して実施することが可能である。例えば、上述した実施形態では、２段小球ピーニング処理を行っているが、これに限定されるものでなく、小球ピーニングを３段以上行ってもよい。この場合、鋼球の直径を前段よりも小さくする。そして、最後段での鋼球の直径をφ０．１ｍｍ以下にする。 Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the two-stage small sphere peening process is performed. However, the present invention is not limited to this, and three or more stages of small sphere peening may be performed. In this case, the diameter of the steel ball is made smaller than that in the previous stage. And the diameter of the steel ball in the last stage shall be 0.1 mm or less.
また、図１（ｂ）に示す熱処理サイクルのように、浸炭処理（Ｓ１）後の機械部品を油で急冷し焼入れ処理を行い（Ｓ４）、その後に再び加熱して窒化処理（Ｓ２）を行ってもよい。この時、焼入れ処理（Ｓ４）後の機械部品の表面に厚さ２０μｍ超で粒界酸化物及び不完全焼入れ層が形成される。しかし、窒化処理（Ｓ２）、焼入れ処理（Ｓ３）後において、機械部品の表面の粒界酸化物及び不完全焼入れ層の厚さを２０μｍ以下にすることができる。 Further, as in the heat treatment cycle shown in FIG. 1B, the machine parts after carburizing (S1) are quenched with oil and quenched (S4), and then heated again to perform nitriding (S2). May be. At this time, a grain boundary oxide and an incompletely hardened layer are formed with a thickness of more than 20 μm on the surface of the machine part after the quenching treatment (S4). However, after the nitriding treatment (S2) and the quenching treatment (S3), the thickness of the grain boundary oxide and the incompletely quenched layer on the surface of the machine part can be reduced to 20 μm or less.
１・・・歯車、２・・・上部歯、３・・・下部歯、１０・・・試験機、１１・・・上部治具、１２・・・下部治具、１３・・・支持台、１４・・・固定ボルト、１５・・・止め具、１６・・・ピン、２０，２１・・・鋼球
DESCRIPTION OF SYMBOLS 1 ... Gear, 2 ... Upper tooth, 3 ... Lower tooth, 10 ... Testing machine, 11 ... Upper jig, 12 ... Lower jig, 13 ... Support stand, 14 ... Fixing bolt, 15 ... Stopper, 16 ... Pin, 20, 21 ... Steel ball
Claims (10)
前記機械部品に窒化処理を行う工程と、
前記機械部品にショットピーニング処理を行う工程と、
を具備することを特徴とする機械部品の製造方法。 A process of carburizing machine parts;
Nitriding the mechanical part; and
Performing a shot peening process on the mechanical parts;
A method of manufacturing a machine part, comprising:
前記第１の焼入れ処理を行う工程後の前記機械部品の表面は、ベイナイト、トルースタイト及びソルバイトの少なくとも１つを備える混合組織層を有することを特徴とする請求項１又は２に記載の機械部品の製造方法。 Immediately after the step of performing the carburizing process, further comprising a step of performing a first quenching process on the machine part,
The machine part according to claim 1 or 2, wherein the surface of the machine part after the step of performing the first quenching process has a mixed structure layer including at least one of bainite, troostite, and sorbite. Manufacturing method.
前記第２の焼入れ処理を行う工程後の前記機械部品の表面は、厚さが２０μｍ以下のベイナイト、トルースタイト及びソルバイトの少なくとも１種備える混合組織層を有することを特徴とする請求項１から４のいずれかに記載の機械部品の製造方法。 A step of performing a second quenching process on the machine part after the nitriding process;
The surface of the machine part after the step of performing the second quenching process has a mixed structure layer having at least one of bainite, troostite, and sorbite having a thickness of 20 μm or less. The manufacturing method of the machine component in any one of.
The diameter of the steel ball of the shot peening process is smaller than the diameter of the steel ball of the previous stage, and the diameter of the steel ball of the last stage is 0.1 mm or less, Production method.
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