JP5548920B2 - Method for carburizing a workpiece having an edge - Google Patents
Method for carburizing a workpiece having an edge Download PDFInfo
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Description
本発明は、エッジ部を有するワーク（例えば、歯車など）の表面部に浸炭層を形成する浸炭方法、特に改良されたプラズマ浸炭方法に関する。 The present invention relates to a carburizing method for forming a carburized layer on a surface portion of a workpiece having an edge portion (for example, a gear), and more particularly to an improved plasma carburizing method.
各種鋼材（ワーク）のプラズマ浸炭は、真空炉内にワークを収容して８５０℃〜１１００℃に加熱し、炉内に反応ガスとしてメタンなどの炭化水素ガスを導入し、グロー放電を生起させて陰極としたワークの表面を浸炭する方法であって、ガス浸炭による場合に比べて高い浸炭能率を得ることができ、一般的に高い炭素濃度でもワーク表面全域に均一な濃度分布を得ることができるという利点がある。プラズマ浸炭後は、取り込まれた炭素をワーク内部に拡散させ、所定厚の浸炭層を形成するため、必要に応じて引き続き拡散処理が施される。 Plasma carburization of various steel materials (workpieces) is carried out by placing the work in a vacuum furnace and heating it to 850 ° C to 1100 ° C, introducing hydrocarbon gas such as methane as a reaction gas into the furnace, and causing glow discharge. This is a method of carburizing the surface of a work piece as a cathode, which can obtain a higher carburizing efficiency than the case of gas carburizing, and can obtain a uniform concentration distribution over the entire work surface even in general with a high carbon concentration. There is an advantage. After the plasma carburizing, the captured carbon is diffused into the workpiece and a carburized layer having a predetermined thickness is formed, so that a diffusion treatment is continuously performed as necessary.
プラズマ浸炭によりワーク表面に取り込まれた炭素は、浸炭処理中および続く拡散処理中にワーク内部に次第に拡散し、所定厚の浸炭層を形成する。しかしながら、このようなプラズマ浸炭を歯車のようにエッジを有するワークに適用した場合、該ワークのエッジ部の浸炭層は、ワークの平坦部に比べて相対的に炭素濃度が高くなっている。これは、エッジ部と平坦部の形状の相違に基づくもので、エッジ部は平坦部に比べて表面積が大きい割りに内部の拡散可能な領域が少なく、取り込まれた炭素が内部に拡散しにくく、表面炭素濃度が下がりにくいためである。 Carbon taken into the workpiece surface by plasma carburizing gradually diffuses into the workpiece during the carburizing treatment and the subsequent diffusion treatment, thereby forming a carburized layer having a predetermined thickness. However, when such plasma carburizing is applied to a workpiece having an edge like a gear, the carburized layer at the edge portion of the workpiece has a relatively high carbon concentration as compared with the flat portion of the workpiece. This is based on the difference in shape between the edge part and the flat part, and the edge part has a smaller surface area than the flat part, but the inner diffusible region is small, and the incorporated carbon is difficult to diffuse inside, This is because the surface carbon concentration is difficult to decrease.
エッジ部と平坦部の表面炭素濃度の不均一は、プラズマ浸炭において顕著であり、ガス浸炭であまり問題にはならない。つまり、ガス浸炭であれば平衡状態下の浸炭であるため、ワーク表面の炭素濃度は雰囲気のカーボンポテンシャルに平衡する濃度以上には上昇せず、また、ワーク表面の炭素濃度が上昇すると浸炭速度が落ちるので、浸炭処理中にエッジ部と平坦部の表面炭素濃度は大きく違わないで推移する。しかし、プラズマ浸炭は、元々非平衡状態下の浸炭であり、浸炭処理中にエッジ部の表面炭素濃度が上昇しても炭素が取りこまれる速度は、平坦部と変わらないため、浸炭処理後の表面炭素濃度の相違は大きくなり易い。そして炭素濃度の不均一は、通常の拡散処理を施しても解消しない。 The unevenness of the surface carbon concentration at the edge portion and the flat portion is conspicuous in plasma carburizing and does not cause much problem in gas carburizing. In other words, since gas carburizing is carburizing under equilibrium conditions, the carbon concentration on the workpiece surface does not rise above the concentration that balances the carbon potential of the atmosphere, and the carburizing rate increases as the carbon concentration on the workpiece surface increases. Since it falls, the surface carbon concentration of the edge part and the flat part does not change greatly during the carburizing process. However, plasma carburizing is originally a carburizing under a non-equilibrium state, and even if the surface carbon concentration of the edge portion increases during the carburizing process, the rate of carbon incorporation is not different from that of the flat part. The difference in surface carbon concentration tends to be large. And the nonuniformity of the carbon concentration is not eliminated even if a normal diffusion treatment is performed.
従って拡散処理を終えた段階で、平坦部の浸炭層において共析点を越える炭素濃度の個所がなくなった場合でも、エッジ部の浸炭層においては炭素濃度が下がりにくいため、共析点を超える炭素濃度の部分が残る場合があり、その場合には冷却後のワークのエッジ部に粒界に沿って網状の炭化物が生成する。粒界に沿って生成した網状の炭化物は脆く割れの起点となり、一旦生成したものはその後の熱処理によっても容易には消滅しない。このような炭素濃度の不均一性を是正する方法としてプラズマ浸炭処理後、引き続き脱炭処理する方法が提案されている（特許文献１）。 Therefore, at the stage where the diffusion treatment has been completed, even if there are no carbon concentration points exceeding the eutectoid point in the carburized layer in the flat part, the carbon concentration in the carburized layer at the edge part is less likely to decrease. In some cases, a concentration portion may remain, and in this case, a net-like carbide is formed along the grain boundary at the edge portion of the workpiece after cooling. The net-like carbide produced along the grain boundary is brittle and becomes the starting point of cracking, and once produced, it does not disappear easily even by the subsequent heat treatment. As a method for correcting such non-uniformity of carbon concentration, a method of continuously decarburizing after plasma carburizing has been proposed (Patent Document 1).
上記特許文献１に記載の方法による浸炭処理後の拡散処理（特許文献１では脱炭処理と記載されている）では、浸炭処理によって供給された炭素が試料内部に熱拡散すると同時に、その一部が炉雰囲気に放出される。これは、平坦部についても生じる現象であり、効率的に炭素供給を行えるプラズマ浸炭の特長を阻害している。 In the diffusion treatment after the carburizing process by the method described in Patent Document 1 (described as decarburizing process in Patent Document 1), the carbon supplied by the carburizing process is thermally diffused inside the sample and a part thereof. Is released into the furnace atmosphere. This is a phenomenon that occurs also in the flat portion, and hinders the feature of plasma carburizing that can efficiently supply carbon.
従って本発明の目的は、エッジ部を有する各種ワークをプラズマ浸炭方法で浸炭を行う際、エッジ部と平坦部との炭素濃度の差が小さく、冷却時にエッジ部に生じる網状の炭化物の生成を抑制し、さらに特許文献１に記載の方法における課題も同時に解決することである。 Therefore, the object of the present invention is to reduce the difference in carbon concentration between the edge part and the flat part when carburizing various workpieces with edge parts by the plasma carburizing method, and suppress the formation of net-like carbides generated at the edge part during cooling. Furthermore, the problem in the method described in Patent Document 1 is to be solved at the same time.
上記目的は以下の本発明によって達成される。すなわち、本発明は、真空炉内に、エッジ部を有するワークを収容し、該真空炉内に浸炭性ガスを供給してグロー放電するプラズマ浸炭処理（浸炭処理工程）を施した後、引き続きアルゴンに代表される不活性ガスを含む中性あるいは還元性のガスプラズマ処理によりワーク表面層の炭素をワーク内部に拡散させる工程（拡散工程）を有することを特徴とする、エッジ部を有するワークの浸炭方法を提供する。 The above object is achieved by the present invention described below. That is, according to the present invention, a workpiece having an edge portion is accommodated in a vacuum furnace, and after performing a plasma carburizing process (carburizing process) in which a carburizing gas is supplied and glow discharge is performed in the vacuum furnace, Carburizing a workpiece having an edge, characterized by having a step (diffusion step) of diffusing carbon in the workpiece surface layer into the workpiece by neutral or reducing gas plasma treatment containing an inert gas typified by Provide a method.
また、上記浸炭処理工程または拡散工程の後で、不活性ガス雰囲気中での拡散工程を施すことを付加することができる。
また、上記浸炭処理工程または拡散工程の後で、窒化性ガス雰囲気中での窒化工程を施すことを付加することができる。
Moreover, after the said carburizing process or a diffusion process, performing the diffusion process in inert gas atmosphere can be added.
Moreover, after the said carburizing process or a diffusion process, performing the nitriding process in nitriding gas atmosphere can be added.
上記本発明の方法においては、前記浸炭処理工程と前記拡散工程とを２回または３回繰り返すことが好ましく、また、最後の拡散工程の後に、ワーク表面の炭化物を酸化除去する工程を付加することもできる。 In the method of the present invention, the carburizing treatment step and the diffusion step are preferably repeated twice or three times, and a step of oxidizing and removing carbides on the workpiece surface is added after the last diffusion step. You can also.
上記本発明の方法においては、前記浸炭方法の後に、成膜温度１００〜３００℃である硬質皮膜を被覆する工程を付加することもできる。 In the method of the present invention, a step of coating a hard film having a film forming temperature of 100 to 300 ° C. may be added after the carburizing method.
本発明によれば、エッジ部を有する各種ワークをプラズマ浸炭方法で浸炭を行う際、エッジ部と平坦部との炭素濃度の差が小さく、冷却時にエッジ部に生じる網状の炭化物の生成を抑制し、さらに特許文献１に記載の方法における課題も同時に解決することができる。 According to the present invention, when various workpieces having an edge portion are carburized by the plasma carburizing method, the difference in carbon concentration between the edge portion and the flat portion is small, and the generation of net-like carbides generated at the edge portion during cooling is suppressed. Furthermore, the problem in the method described in Patent Document 1 can be solved at the same time.
次に発明を実施するための形態を挙げて本発明をさらに詳しく説明する。
本発明の方法で、浸炭処理されるワークは、主に機械構造用鋼材である肌焼鋼であり、エッジ部を有するものである。エッジ部を有するワークとしては、例えば、パワートレイン部品のディファレンシャルギア、プラネタリーギア、ファイナルドライブ装置などが挙げられる。このようなワークは、従来のプラズマ浸炭処理において、そのエッジ部（コーナー部）の炭素濃度が他の部分（平坦部）よりも高濃度になり易い。
Next, the present invention will be described in more detail with reference to modes for carrying out the invention.
The workpiece to be carburized by the method of the present invention is case-hardened steel which is a steel material for machine structure, and has an edge portion. Examples of the workpiece having an edge portion include a differential gear, a planetary gear, and a final drive device that are power train components. In such a workpiece, the carbon concentration of the edge portion (corner portion) tends to be higher than that of the other portion (flat portion) in the conventional plasma carburizing process.
本発明で使用するプラズマ浸炭装置は、従来公知であり、例えば、減圧下で加熱、プラズマ印加および浸炭ができ、かつ加圧ガス冷却が可能な設備であり、該設備は、真空チャンバーと冷却室を有している。真空チャンバーには、外周壁に加熱ヒーターが設置され、内部にはプラズマ電源に接続された電極がワーク（被浸炭処理物）のトレーを兼用して設置されている。装置下部は、排気管を経由して真空ポンプに接続され、減圧雰囲気を可能とする。そしてアルゴン、窒素、酸素、水素、炭化水素系ガスが上部のガス導入ノズルを介して真空チャンバーに供給できる装置となっている。冷却室には、最大１ＭＰａのヘリウムガスを供給でき、冷却ファンと配管によってヘリウムガスが循環できる装置となっている。 The plasma carburizing apparatus used in the present invention is conventionally known. For example, the apparatus is capable of heating, applying plasma and carburizing under reduced pressure, and capable of cooling with pressurized gas. The equipment includes a vacuum chamber and a cooling chamber. have. In the vacuum chamber, a heater is installed on the outer peripheral wall, and an electrode connected to a plasma power source is installed inside the vacuum chamber also serving as a tray for workpieces (carburized products). The lower part of the apparatus is connected to a vacuum pump via an exhaust pipe to enable a reduced pressure atmosphere. And it is an apparatus which can supply argon, nitrogen, oxygen, hydrogen, and a hydrocarbon type gas to a vacuum chamber via an upper gas introduction nozzle. The cooling chamber can supply a maximum of 1 MPa of helium gas, and the helium gas can be circulated by a cooling fan and piping.
本発明の方法におけるプラズマ浸炭処理自体は、従来公知の方法でよく、前記ワークを上記装置の真空炉内に収容し、該真空炉内に浸炭性ガスを供給してグロー放電するプラズマ浸炭処理する。本発明の特徴は、上記プラズマ浸炭に引き続きアルゴンに代表される不活性ガスを含む中性あるいは還元性のガスプラズマ処理することが特徴である。さらに、浸炭処理後に窒化性ガスを供給してプラズマ浸炭窒化処理することもできる。 The plasma carburizing process itself in the method of the present invention may be a conventionally known method, and the workpiece is housed in a vacuum furnace of the above apparatus, and a carburizing gas is supplied into the vacuum furnace to perform a plasma carburizing process for glow discharge. . A feature of the present invention is that the plasma carburization is followed by neutral or reducing gas plasma treatment containing an inert gas typified by argon. Further, a plasma carbonitriding process can be performed by supplying a nitriding gas after the carburizing process.
図１に示す実施形態を参照して本発明の方法を説明する。前記ワークを上記装置の真空炉内に収容し、炉内を１０-3〜１０3Ｐａ程度の減圧にしつつ、約１〜２時間で８５０〜１０３０℃に昇温する。まず、最初にワークの表面をクリーニングするために、炉内に水素を０〜８０容量％含むアルゴンガスを供給し、上記の温度で圧力５０〜２００Ｐａで、電圧５００〜７００Ｖで、電流密度０．３〜１．２ｍＡ／ｃｍ2の条件で１５〜６０分間プラズマ処理を行う。 The method of the present invention will be described with reference to the embodiment shown in FIG. The workpiece is housed in the vacuum furnace of the above apparatus, and the temperature is raised to 850 to 1030 ° C. in about 1 to 2 hours while reducing the pressure in the furnace to about 10 −3 to 10 3 Pa. First, in order to first clean the surface of the workpiece, an argon gas containing 0 to 80% by volume of hydrogen is supplied into the furnace, the pressure is 50 to 200 Pa at the above temperature, the voltage is 500 to 700 V, and the current density is 0.00. Plasma treatment is performed for 15 to 60 minutes under conditions of 3 to 1.2 mA / cm 2 .
上記クリーニング処理後にプラズマ浸炭を行う。浸炭条件は従来公知の条件でよく、例えば、炉内温度８５０〜１０３０℃でメタンガスなどの炭化水素系ガスを炉内に導入し、炭化水素系ガス分圧を１５０〜９００Ｐａとし、電圧２８０〜３５０Ｖで、電流密度０．１〜０．４ｍＡ／ｃｍ2の条件で５〜６０分間プラズマ浸炭処理を行う。この浸炭処理においては、ワークのエッジ部の炭素濃度は、平坦部の炭素濃度よりも絶対値で０．１〜０．８％程度高濃度となる。 Plasma carburization is performed after the cleaning process. The carburizing condition may be a conventionally known condition. For example, a hydrocarbon gas such as methane gas is introduced into the furnace at a furnace temperature of 850 to 1030 ° C., the hydrocarbon gas partial pressure is 150 to 900 Pa, and the voltage is 280 to 350 V. Then, plasma carburizing treatment is performed for 5 to 60 minutes under the condition of current density of 0.1 to 0.4 mA / cm 2 . In this carburizing process, the carbon concentration at the edge portion of the workpiece is about 0.1 to 0.8% higher in absolute value than the carbon concentration in the flat portion.
上記浸炭処理完了後、炭化水素系ガスの供給を中断し、アルゴンに代表される不活性ガスを含む中性あるいは還元性のガスを炉内に供給し、前記クリーニング工程と同様な条件でワークの表面層の炭素をワーク内部に拡散させる。この拡散工程によって浸炭層の表面の炭素はワークの内部方向に拡散する。このとき、浸炭処理または拡散工程の後に、真空雰囲気またはアルゴンなどの不活性ガス雰囲気で表面の炭素をワーク内部に拡散させる工程を適宜施すこともできる。また、これらの拡散処理によってワークの表面へのさらなる浸炭（２次、３次浸炭）が可能になる。拡散処理が終了した後、冷却室内で装置の上部から冷却用のヘリウムガスを供給し、試料表面温度をＡ１変態点以下である７００℃〜室温とする。以上の浸炭処理および拡散処理を１次工程とする（クリーニング工程を含まない）（図１参照）。 After the carburizing process is completed, the supply of hydrocarbon gas is interrupted, and a neutral or reducing gas containing an inert gas typified by argon is supplied into the furnace. The carbon of the surface layer is diffused inside the workpiece. By this diffusion process, carbon on the surface of the carburized layer diffuses in the internal direction of the workpiece. At this time, after the carburizing treatment or the diffusion step, a step of diffusing carbon on the surface into the workpiece in a vacuum atmosphere or an inert gas atmosphere such as argon can be appropriately performed. Further, these diffusion treatments enable further carburization (secondary and tertiary carburization) on the surface of the workpiece. After the diffusion treatment is completed, helium gas for cooling is supplied from the upper part of the apparatus in the cooling chamber, and the sample surface temperature is set to 700 ° C. to room temperature, which is lower than the A1 transformation point. The above carburizing process and diffusion process are defined as the primary process (not including the cleaning process) (see FIG. 1).
本発明の特徴は、上記１次工程の拡散処理にあるが、本発明では、球状炭化物を析出させる高濃度浸炭を達成するために、図１に示すように１次工程に引き続き２次工程および３次工程を行うことが好ましい。２次工程は、浸炭および拡散の温度が１次工程に比べて約０〜１００℃低い以外は１次工程と同じである。３次工程は最後に行う保持工程を除き２次工程と同様である。保持工程は、炉内へのアルゴンガスの供給を中止し、炉内を１０-3〜１０3Ｐａ程度に維持しつつ、約１５〜３０分で試料の適正な焼入れ温度である７５０〜９３０℃に維持し、その後に２次工程と同様に冷却してワークを取り出す。この保持工程によって焼入れが行われる。 The feature of the present invention resides in the diffusion treatment of the primary process described above. In the present invention, in order to achieve high-concentration carburization for precipitating spherical carbides, the secondary process and the primary process as shown in FIG. It is preferable to perform a tertiary process. The secondary process is the same as the primary process except that the carburization and diffusion temperatures are lower by about 0-100 ° C. than the primary process. The tertiary process is the same as the secondary process except for the last holding process. In the holding step, the supply of argon gas to the furnace is stopped and the inside of the furnace is maintained at about 10 −3 to 10 3 Pa, and the proper quenching temperature of the sample is about 750 to 930 ° C. in about 15 to 30 minutes. Then, the workpiece is cooled and taken out in the same manner as in the secondary process. Quenching is performed by this holding step.
本発明の特徴は、上記１次工程の拡散処理にあるが、本発明では、図５に示すように浸炭の焼入れ性改善並びに焼戻し軟化抵抗の改善を達成するための工程を行うことができる。上記処理は、拡散処理におけるアルゴンなどに代表される不活性ガスを含む中性あるいは還元性のガスの供給を停止し、７５０〜９３０℃の温度で窒素などの窒化性ガスを供給し、上記の温度で圧力１００〜４００Ｐａで、電圧２５０〜５５０Ｖで、電流密度０．２〜０．４ｍＡ／ｃｍ2の条件で１０〜３０分間プラズマ窒化処理を行うことで実施される（実施例６参照）。
なお、図１では、１次工程〜３次工程の全ての拡散工程においてアルゴンに代表される不活性ガスを含む中性あるいは還元性のガスプラズマ処理を行っているが、１次工程と２次工程の拡散工程をアルゴンに代表される不活性ガスを含む中性あるいは還元性のガスプラズマ処理で行い、３次工程の拡散処理は真空拡散処理としても本発明の効果が得られる（実施例２参照）。
The feature of the present invention resides in the diffusion process of the primary process described above. In the present invention, as shown in FIG. 5, a process for achieving an improvement in carburizing hardenability and an improvement in temper softening resistance can be performed. In the above process, the supply of a neutral or reducing gas containing an inert gas typified by argon or the like in the diffusion process is stopped, and a nitriding gas such as nitrogen is supplied at a temperature of 750 to 930 ° C. This is carried out by performing plasma nitriding for 10 to 30 minutes under the conditions of a temperature of 100 to 400 Pa, a voltage of 250 to 550 V, and a current density of 0.2 to 0.4 mA / cm 2 (see Example 6).
In FIG. 1, neutral or reducing gas plasma treatment including an inert gas typified by argon is performed in all diffusion steps of the primary step to the tertiary step. However, the primary step and the secondary step are performed. The diffusion step of the step is performed by neutral or reducing gas plasma treatment containing an inert gas typified by argon, and the effect of the present invention can be obtained even when the diffusion treatment of the tertiary step is a vacuum diffusion treatment (Example 2). reference).
図２には、本発明の他の実施形態を示す。この実施形態は、図１に示す実施形態の３次工程における拡散処理工程と保持工程との間に酸化工程を設けた以外は図１の実施形態と同じである。図１に示す実施形態において得られた浸炭処理されたワークの表面には微細な炭化物の微粒子が無数に残っており、上記微粒子を除去することが要求される場合（慴動性など）がある。上記の酸化工程は、拡散処理におけるアルゴンに代表される不活性ガスを含む中性あるいは還元性のガスの供給を停止し、７５０〜９３０℃の温度で、酸素、二酸化炭素などの酸化性ガスを供給し、上記の温度で圧力１００〜４００Ｐａで、電圧２５０〜３５０Ｖで、電流密度０．２〜０．４ｍＡ／ｃｍ2の条件で１０〜３０分間プラズマ酸化処理を行うことで実施される。 FIG. 2 shows another embodiment of the present invention. This embodiment is the same as the embodiment of FIG. 1 except that an oxidation step is provided between the diffusion treatment step and the holding step in the tertiary step of the embodiment shown in FIG. An infinite number of fine carbide fine particles remain on the surface of the carburized workpiece obtained in the embodiment shown in FIG. 1, and it may be required to remove the fine particles (such as peristaltic properties). . In the above oxidation step, the supply of neutral or reducing gas containing an inert gas typified by argon in the diffusion treatment is stopped, and an oxidizing gas such as oxygen or carbon dioxide is supplied at a temperature of 750 to 930 ° C. This is carried out by performing plasma oxidation treatment for 10 to 30 minutes under the conditions of the above-mentioned temperature, pressure of 100 to 400 Pa, voltage of 250 to 350 V, and current density of 0.2 to 0.4 mA / cm 2 .
図６には、本発明の他の実施形態を示す。この実施形態は、図１に示す実施形態の３次工程における拡散処理工程と保持工程との間に窒化工程を設けた以外は図１の実施形態と同じである。図１に示す実施形態において得られた浸炭処理されたワークの焼入れ性改善並びに焼戻し軟化抵抗の改善を要求される場合がある。上記の窒化工程は、拡散処理におけるアルゴンに代表される不活性ガスを含む中性あるいは還元性のガスの供給を停止し、７５０〜９３０℃の温度で窒素などの窒化性ガスを供給し、上記の温度で圧力１００〜４００Ｐａで、電圧２５０〜５５０Ｖで、電流密度０．２〜０．４ｍＡ／ｃｍ2の条件で１０〜３０分間プラズマ窒化処理を行うことで実施される。 FIG. 6 shows another embodiment of the present invention. This embodiment is the same as the embodiment of FIG. 1 except that a nitriding step is provided between the diffusion treatment step and the holding step in the tertiary step of the embodiment shown in FIG. In some cases, it is required to improve the hardenability and temper softening resistance of the carburized workpiece obtained in the embodiment shown in FIG. In the nitriding step, the supply of a neutral or reducing gas containing an inert gas typified by argon in the diffusion treatment is stopped, and a nitriding gas such as nitrogen is supplied at a temperature of 750 to 930 ° C. This is performed by performing plasma nitriding for 10 to 30 minutes under the conditions of a pressure of 100 to 400 Pa, a voltage of 250 to 550 V, and a current density of 0.2 to 0.4 mA / cm 2 .
上記した実施形態の焼入れ処理を施した後に、前記ワークを上記装置の真空炉内に収容し、炉内を１０-3〜１０3Ｐａ程度の減圧にしつつ、約１〜２時間で１００〜３００℃に昇温する。まず、最初にワークの表面をクリーニングするために、炉内に水素を０〜８０容量％含むアルゴンガスを供給し、上記の温度で、圧力５〜５０Ｐａで、電圧４００〜７００Ｖの条件で１５〜６０分間プラズマ処理を行う。
上記クリーニング処理後にコーティングを行う。浸炭条件は従来公知の条件でよく、例えば、炉内温度１００〜３００℃でメタンガスなどの炭化水素系ガスを炉内に導入し、炭化水素系ガス分圧を５〜５０Ｐａとし、電圧４００〜７００Ｖの条件６０〜２４０分間プラズマ浸炭処理を行う。
After performing the quenching process of the above-described embodiment, the workpiece is accommodated in the vacuum furnace of the apparatus, and the pressure in the furnace is reduced to about 10 −3 to 10 3 Pa, and about 100 to 300 in about 1 to 2 hours. The temperature is raised to ° C. First, in order to first clean the surface of the workpiece, argon gas containing 0 to 80% by volume of hydrogen is supplied into the furnace, and the pressure is 5 to 50 Pa and the voltage is 400 to 700 V at the above temperature. Plasma treatment is performed for 60 minutes.
Coating is performed after the cleaning process. The carburizing condition may be a conventionally known condition. For example, a hydrocarbon gas such as methane gas is introduced into the furnace at a furnace temperature of 100 to 300 ° C., the hydrocarbon gas partial pressure is 5 to 50 Pa, and the voltage is 400 to 700 V. Plasma carburizing treatment is performed for 60 to 240 minutes.
次に実施例および比較例を挙げて本発明をさらに具体的に説明する。
［供試材料］
下記表１に示す機械構造用鋼材である肌焼鋼を用い、機械加工にてφ２５×１０ｍｍのコイン型試験片を作成した。
Next, the present invention will be described more specifically with reference to examples and comparative examples.
[Sample material]
Using a case-hardened steel, which is a steel for machine structure shown in Table 1 below, a coin-shaped test piece of φ25 × 10 mm was created by machining.
［プラズマ浸炭装置］
上記試験片の浸炭拡散は、減圧下で加熱、プラズマ印加および浸炭ができ、かつ加圧ガス冷却が可能な設備を用い、本発明の浸炭処理を行った。
設備は、真空チャンバーと冷却室を有している。真空チャンバーには、外周壁に加熱ヒーターが設置され、内部にはプラズマ電源に接続された電極が試験片トレーを兼用して設置されている。下部は排気管を経由して真空ポンプに接続され減圧雰囲気を可能とする。アルゴン、窒素、酸素、水素、炭化水素系ガスが上部のガス導入ノズルを介して真空チャンバーに供給できる装置となっている。冷却室は、最大１ＭＰａのヘリウムガスを供給でき、冷却ファンと配管とによってヘリウムガスが循環できる装置となっている。
[Plasma carburizing equipment]
The carburizing diffusion of the test piece was performed by carburizing treatment of the present invention using equipment capable of heating, applying plasma and carburizing under reduced pressure and capable of cooling with pressurized gas.
The facility has a vacuum chamber and a cooling chamber. In the vacuum chamber, a heater is installed on the outer peripheral wall, and an electrode connected to a plasma power source is installed inside the vacuum chamber also as a test piece tray. The lower part is connected to a vacuum pump via an exhaust pipe to enable a reduced pressure atmosphere. Argon, nitrogen, oxygen, hydrogen, and hydrocarbon gas can be supplied to the vacuum chamber via the upper gas introduction nozzle. The cooling chamber can supply a maximum of 1 MPa of helium gas, and the helium gas can be circulated by a cooling fan and piping.
［評価方法］
実施例および比較例で得られた浸炭試験片につき、表面炭素濃度、組織観察、断面硬度および摩擦摩耗特性を調べて評価した。評価方法は以下の通りである。
［表面炭素濃度］
浸炭処理後に、表面から５μｍ位置をグロー放電発光分光分析にて測定した。
[Evaluation method]
The carburized specimens obtained in the examples and comparative examples were evaluated by examining the surface carbon concentration, the structure observation, the cross-sectional hardness and the frictional wear characteristics. The evaluation method is as follows.
[Surface carbon concentration]
After carburizing treatment, the position of 5 μm from the surface was measured by glow discharge emission spectroscopic analysis.
［組織観察］
浸炭・拡散・焼入れ・焼戻しを行ったコイン型試験片を切断・研磨後、３％ナイタールで腐食後、最表面から５０μｍまでを光学顕微鏡写真撮影（観察倍率１，０００倍）を行い、画像解析して面積率および粒径の測定を行った。
網目状炭化物は、上記と同様の条件で網目状炭化物の有無を観察した。ここで網目状炭化物は粗大な炭化物が結晶粒界に沿って網目状をなすように析出したものである。
[Tissue observation]
Coin-shaped specimens that have been carburized, diffused, quenched, and tempered are cut and polished, corroded with 3% nital, and then optical micrographs (observation magnification 1,000 times) are taken from the outermost surface to 50 μm for image analysis Then, the area ratio and the particle size were measured.
With respect to the network carbide, the presence or absence of the network carbide was observed under the same conditions as described above. Here, the net-like carbide is a precipitate in which coarse carbides form a net-like shape along the crystal grain boundary.
［断面硬度］
ＪＩＳ Ｚ ２２４４に準拠し、表面から内部に向かって測定を行った。
［摩擦摩耗特性］
ボールオンディスク摩擦摩耗試験機を用いて、摺動相手材はφ６ｍｍのＳＵＪ２であり、無潤滑条件下、負荷荷重２Ｎ、周速３００ｒｐｍ、摺動半径１０ｍｍの条件で試験した。
[Cross section hardness]
Based on JIS Z 2244, the measurement was performed from the surface toward the inside.
[Friction and wear characteristics]
Using a ball-on-disk friction and wear tester, the sliding mating member was SUJ2 with a diameter of 6 mm, and was tested under non-lubricating conditions under a load of 2 N, a peripheral speed of 300 rpm, and a sliding radius of 10 mm.
［実施例１］
治具に試験片を平置きし、前記装置の処理室に搬入した。加熱パターンを図１に示す。１次工程として、１×１０-3Ｐａの減圧雰囲気で処理室内雰囲気温度を９８０℃まで９０分かけて加熱した。２０％Ａｒ／８０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによるクリーニング処理を３０分行った。
[Example 1]
The test piece was placed flat on a jig and carried into the processing chamber of the apparatus. A heating pattern is shown in FIG. As a primary process, the processing chamber atmosphere temperature was heated to 980 ° C. in a reduced pressure atmosphere of 1 × 10 −3 Pa over 90 minutes. A gas mixture of 1 L / min of 20% Ar / 80% H 2 was introduced at an in-furnace pressure of 50 Pa, and cleaning treatment with glow discharge plasma of 0.6 mA / cm 2 · 500 V was performed for 30 minutes.
クリーニング処理終了後、続いて１００％ＣＨ4ガス１０Ｌ／ｍｉｎを炉内圧力３００Ｐａで導入し、０．４ｍＡ／ｃｍ2・３３０Ｖのグロー放電プラズマによる浸炭処理を２０分行った。続いて、真空排気を行い、真空雰囲気にて５分保持し、続いて、２０％Ａｒ／８０％Ｈ2の混合ガス計１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによる拡散処理を４０分行い、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。 After completion of the cleaning process, 100% CH 4 gas 10 L / min was subsequently introduced at a furnace pressure of 300 Pa, and carburizing process with glow discharge plasma of 0.4 mA / cm 2 · 330 V was performed for 20 minutes. Subsequently, evacuation is performed, and the mixture is held in a vacuum atmosphere for 5 minutes. Subsequently, a gas mixture meter of 1% / min of 20% Ar / 80% H 2 is introduced at a furnace pressure of 50 Pa, and 0.6 mA / cm 2 is introduced. -Diffusion treatment with 500 V glow discharge plasma was performed for 40 minutes, and it was transported to a cooling chamber and cooled with pressurized He gas.
続いて２次工程として、１×１０-3Ｐａの減圧雰囲気で処理室内雰囲気温度を９００℃まで９０分かけて再加熱を行い、１００％ＣＨ4ガス１０Ｌ／ｍｉｎを炉内圧力３００Ｐａで導入し、０．４ｍＡ／ｃｍ2・３３０Ｖのグロー放電プラズマによる浸炭処理を２０分行った。続いて、真空排気を行い、真空雰囲気にて５分保持し、続いて、２０％Ａｒ／８０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによる拡散処理を４０分行い、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。 Subsequently, as a secondary process, reheating is performed in a reduced pressure atmosphere of 1 × 10 −3 Pa for 90 minutes up to 900 ° C., and 100% CH 4 gas 10 L / min is introduced at a furnace pressure of 300 Pa. Carburizing treatment with glow discharge plasma of 0.4 mA / cm 2 · 330 V was performed for 20 minutes. Subsequently, evacuation is performed, and the mixture is kept in a vacuum atmosphere for 5 minutes. Subsequently, a mixed gas of 1% / min of 20% Ar / 80% H 2 is introduced at a furnace pressure of 50 Pa, and 0.6 mA / cm 2 · Diffusion treatment with glow discharge plasma of 500 V was performed for 40 minutes, and it was transported to a cooling chamber and cooled with pressurized He gas.
さらに３次工程として、１×１０-3Ｐａの減圧雰囲気で処理室内雰囲気温度を９００℃まで９０分かけて再加熱を行い、１００％ＣＨ4ガス１０Ｌ／ｍｉｎを炉内圧力３００Ｐａで導入し、０．４ｍＡ／ｃｍ2・３３０Ｖのグロー放電プラズマによる浸炭処理を２０分行った。続いて、真空排気を行い、真空雰囲気にて５分保持し、続いて、２０％Ａｒ／８０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによる拡散処理を４０分行った。真空排気をして、焼入れ温度８７０℃まで降温して３０分保持した後、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。 Further, as a third step, the processing chamber atmosphere temperature is reheated to 900 ° C. over 90 minutes in a reduced pressure atmosphere of 1 × 10 −3 Pa, and 100 L CH 4 gas 10 L / min is introduced at a furnace pressure of 300 Pa. Carburizing treatment with glow discharge plasma of 0.4 mA / cm 2 · 330 V was performed for 20 minutes. Subsequently, evacuation is performed, and the mixture is kept in a vacuum atmosphere for 5 minutes. Subsequently, a mixed gas of 1% / min of 20% Ar / 80% H 2 is introduced at a furnace pressure of 50 Pa, and 0.6 mA / cm 2 · Diffusion treatment with 500 V glow discharge plasma was performed for 40 minutes. After evacuation, the temperature was lowered to a quenching temperature of 870 ° C. and held for 30 minutes, and then transferred to a cooling chamber and cooled with pressurized He gas.
この試験片の組織観察を行った結果、試験片端部（エッジ部）に析出する炭化物の形状は球状となり、浸炭の懸案課題であった試験片端部の析出炭化物形状が改善された。すなわち、イオン化したアルゴンがスパッタリングを行い、試験片端部を中心に加熱されて炭素の拡散が促進された。さらに、加熱によって炭素の固溶限界が高まることで、網目状炭化物の析出を抑制していた。 As a result of observing the structure of this test piece, the shape of the carbide precipitated at the end (edge) of the test piece became spherical, and the shape of the precipitated carbide at the end of the test piece, which was a concern for carburization, was improved. That is, ionized argon was sputtered and heated around the end of the test piece to promote carbon diffusion. Furthermore, the precipitation of reticulated carbide was suppressed by increasing the solid solubility limit of carbon by heating.
［比較例１］
１次工程から３次工程において、拡散処理を全て真空雰囲気で行い、それ以外は実施例１と同様の処理を行った。この試験片の組織観察を行った結果、平坦部においては球状炭化物の析出が全体を占めていたが、試験片端部においては炭素成分が固溶し切れず、粒界に沿って網目状炭化物が析出した。
[Comparative Example 1]
In the primary process to the tertiary process, all diffusion processes were performed in a vacuum atmosphere, and the same processes as in Example 1 were performed except that. As a result of observing the structure of this test piece, the precipitation of spherical carbides occupied the whole in the flat part, but the carbon component was not completely dissolved in the end part of the test piece, and the reticulated carbide was found along the grain boundaries. Precipitated.
［実施例２］
３次工程のみにおいて、拡散処理を全て真空雰囲気で行い、それ以外は実施例１と同様の処理を行った。この試験片の組織観察を行った結果、試験片端部に析出する炭化物の形状は球状となり、さらに平面部においては球状炭化物が微細かつ多量に析出する組織が得られた。すなわち、１次工程と２次工程で炭素の拡散促進と炭素固溶限界の向上により、網目状炭化物の析出を抑制した。続いて、３次工程において真空雰囲気中で拡散させることによって、２次工程まで固溶していた炭素を粒内に炭化物として析出させたことで、試験片端部は球状炭化物が析出し、平面部は炭化物の核が多量にできた組織が得られた。
[Example 2]
In the third step only, all diffusion processes were performed in a vacuum atmosphere, and the other processes were performed in the same manner as in Example 1. As a result of observing the structure of the test piece, the shape of the carbide precipitated at the end of the test piece was spherical, and a structure in which the spherical carbide was finely precipitated in a large amount at the plane part was obtained. That is, in the primary process and the secondary process, the precipitation of mesh carbide was suppressed by promoting the diffusion of carbon and improving the carbon solid solution limit. Subsequently, by diffusing in a vacuum atmosphere in the third step, carbon that had been dissolved until the second step was precipitated as carbides in the grains, so that spherical carbide was precipitated at the end of the test piece, and the plane portion A structure with a large amount of carbide nuclei was obtained.
［比較例２］
３次工程のみにおいて、拡散処理は２０％Ａｒ／８０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマ雰囲気で行い、それ以外は比較例１と同様の処理を行った。
[Comparative Example 2]
In the third step only, diffusion treatment is performed in a glow discharge plasma atmosphere of 0.6 mA / cm 2 · 500 V by introducing 1 L / min of a mixed gas of 20% Ar / 80% H 2 at a furnace pressure of 50 Pa. The same treatment as in Comparative Example 1 was performed.
この試験片の組織観察を行った結果、平坦部においては球状炭化物の析出が全体を占めていたが、試験片端部においては炭素成分が固溶し切れず、粒界に沿って網目状炭化物が析出した。１次工程または２次工程ですでに網目状炭化物が析出しており、３次工程のプラズマ雰囲気で網目状炭化物は再固溶しなかった。 As a result of observing the structure of this test piece, the precipitation of spherical carbides occupied the whole in the flat part, but the carbon component was not completely dissolved in the end part of the test piece, and the reticulated carbide was found along the grain boundaries. Precipitated. In the primary process or the secondary process, the reticulated carbide had already precipitated, and the reticulated carbide did not re-dissolve in the plasma atmosphere of the tertiary process.
上記したこれら試験結果の、表面炭素濃度、端部の炭化物面積率、端部の炭化物平均粒径、端部の網目状炭化物の有無、表面から５０μｍ位置の断面硬度をまとめたものを表２に示す。 Table 2 shows a summary of the surface carbon concentration, the carbide area ratio at the end, the average carbide particle size at the end, the presence or absence of mesh carbide at the end, and the cross-sectional hardness at a position of 50 μm from the surface of these test results described above. Show.
［実施例３］
３次工程において、真空排気をして焼入れ温度８７０℃まで降温し、８０％Ｏ2／２０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力１００Ｐａで導入し、０．３ｍＡ／ｃｍ2・２６０Ｖのグロー放電プラズマ雰囲気で１０分行い、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。それ以外は実施例１と同様の処理を行った。ヒートパターンを図２に示す。この試験片の表面を電子顕微鏡で観察した結果、浸炭によって析出する球状炭化物は消失していた。図３に倍率２０００倍の電子顕微鏡観察写真を示す。
[Example 3]
In the third step, vacuum evacuation is performed to lower the quenching temperature to 870 ° C., and 1 L / min of a mixed gas of 80% O 2 /20% H 2 is introduced at a furnace pressure of 100 Pa, and 0.3 mA / cm 2 · 260 V For 10 minutes in a glow discharge plasma atmosphere and conveyed to a cooling chamber for cooling with pressurized He gas. Otherwise, the same processing as in Example 1 was performed. A heat pattern is shown in FIG. As a result of observing the surface of this test piece with an electron microscope, the spherical carbide precipitated by carburization was lost. FIG. 3 shows an electron microscope observation photograph at a magnification of 2000 times.
［実施例４］
３次工程において、真空排気をして焼入れ温度８７０℃まで降温し、８０％Ｏ2／２０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力１００Ｐａで導入し、０．３ｍＡ／ｃｍ2・２６０Ｖのグロー放電プラズマ雰囲気で３０分行い、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。それ以外は実施例１と同様の処理を行った。上記処理の後、プラズマＣＶＤ法によって硬質皮膜（ＤＬＣ）を表面に形成した。成膜開始時の雰囲気温度は２００℃であった。この試験片の摩擦摩耗特性をボールオンディスク摩擦摩耗試験機で評価したところ、摺動距離は３００ｍであった。
[Example 4]
In the third step, vacuum evacuation is performed to lower the quenching temperature to 870 ° C., and 1 L / min of a mixed gas of 80% O 2 /20% H 2 is introduced at a furnace pressure of 100 Pa, and 0.3 mA / cm 2 · 260 V For 30 minutes in a glow discharge plasma atmosphere and conveyed to a cooling chamber for cooling with pressurized He gas. Otherwise, the same processing as in Example 1 was performed. After the above treatment, a hard coating (DLC) was formed on the surface by plasma CVD. The ambient temperature at the start of film formation was 200 ° C. When the frictional wear characteristics of this test piece were evaluated using a ball-on-disk frictional wear tester, the sliding distance was 300 m.
［実施例５］
治具に試験片を平置きし、処理室に搬入した。ヒートパターンを図４に示す。処理工程として、１×１０-3Ｐａの減圧雰囲気で処理室内雰囲気温度を９８０℃まで９０分かけて加熱した。２０％Ａｒ／８０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによるクリーニング処理を３０分行った。クリーニング処理終了後、続いて１００％ＣＨ4ガス１０Ｌ／ｍｉｎを炉内圧力３００Ｐａで導入し、０．４ｍＡ／ｃｍ2・３３０Ｖのグロー放電プラズマによる浸炭処理を２０分行った。続いて、真空排気を行い、真空雰囲気にて５分保持し、続いて、２０％Ａｒ／８０％Ｈ2の混合ガス計１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによる拡散処理を４０分行い、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。
[Example 5]
The test piece was placed flat on the jig and carried into the processing chamber. A heat pattern is shown in FIG. As a treatment step, the atmosphere in the treatment room was heated to 980 ° C. over 90 minutes in a reduced pressure atmosphere of 1 × 10 −3 Pa. A gas mixture of 1 L / min of 20% Ar / 80% H 2 was introduced at an in-furnace pressure of 50 Pa, and cleaning treatment with glow discharge plasma of 0.6 mA / cm 2 · 500 V was performed for 30 minutes. After completion of the cleaning process, 100% CH 4 gas 10 L / min was subsequently introduced at a furnace pressure of 300 Pa, and carburizing process with glow discharge plasma of 0.4 mA / cm 2 · 330 V was performed for 20 minutes. Subsequently, evacuation is performed, and the mixture is held in a vacuum atmosphere for 5 minutes. Subsequently, a gas mixture meter of 1% / min of 20% Ar / 80% H 2 is introduced at a furnace pressure of 50 Pa, and 0.6 mA / cm 2 is introduced. -Diffusion treatment with 500 V glow discharge plasma was performed for 40 minutes, and it was transported to a cooling chamber and cooled with pressurized He gas.
この試験片の組織観察を行った結果、試験片端部には網状の炭化物が析出せず、プラズマ浸炭の懸案課題であった試験片端部の炭化物析出が改善された。すなわち、イオン化したアルゴンがスパッタリングを行い、試験片端部を中心に加熱されて炭素の拡散が促進された。さらに、加熱によって炭素の固溶限界が高まることで、網目状炭化物の析出を抑制していた。 As a result of observing the structure of the test piece, no reticulated carbide was deposited at the end of the test piece, and the carbide precipitation at the end of the test piece, which was a concern for plasma carburization, was improved. That is, ionized argon was sputtered and heated around the end of the test piece to promote carbon diffusion. Furthermore, the precipitation of reticulated carbide was suppressed by increasing the solid solubility limit of carbon by heating.
［比較例３］
処理工程において、拡散処理を全て真空雰囲気で行い、それ以外は実施例５と同様の処理を行った。この試験片の組織観察を行った結果、平坦部においてはマルテンサイト組織と残留オーステナイト組織が全体を占めていたが、試験片端部においては炭素成分が固溶し切れず、粒界に沿って網目状炭化物が析出した。
[Comparative Example 3]
In the treatment process, all the diffusion treatment was performed in a vacuum atmosphere, and the other treatments were performed in the same manner as in Example 5. As a result of observing the structure of this test piece, the martensite structure and the retained austenite structure occupied the whole in the flat part, but the carbon component did not completely dissolve at the end part of the test piece, and the mesh along the grain boundary. A carbide was deposited.
［実施例６］
治具に試験片を平置きし、処理室に搬入した。ヒートパターンを図５に示す。処理工程として、１×１０-3Ｐａの減圧雰囲気で処理室内雰囲気温度を９８０℃まで９０分かけて加熱した。２０％Ａｒ／８０％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによるクリーニング処理を３０分行った。クリーニング処理終了後、続いて１００％ＣＨ4ガス１０Ｌ／ｍｉｎを炉内圧力３００Ｐａで導入し、０．４ｍＡ／ｃｍ2・３３０Ｖのグロー放電プラズマによる浸炭処理を２０分行った。
[Example 6]
The test piece was placed flat on the jig and carried into the processing chamber. A heat pattern is shown in FIG. As a treatment step, the atmosphere in the treatment room was heated to 980 ° C. over 90 minutes in a reduced pressure atmosphere of 1 × 10 −3 Pa. A gas mixture of 1 L / min of 20% Ar / 80% H 2 was introduced at an in-furnace pressure of 50 Pa, and cleaning treatment with glow discharge plasma of 0.6 mA / cm 2 · 500 V was performed for 30 minutes. After completion of the cleaning process, 100% CH 4 gas 10 L / min was subsequently introduced at a furnace pressure of 300 Pa, and carburizing process with glow discharge plasma of 0.4 mA / cm 2 · 330 V was performed for 20 minutes.
続いて、真空排気を行い、真空雰囲気にて５分保持し、続いて、２０％Ａｒ／８０％Ｈ2の混合ガス計１Ｌ／ｍｉｎを炉内圧力５０Ｐａで導入し、０．６ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマによる拡散処理を４０分行った。続いて、焼入れ温度８７０℃まで降温し、３３％Ｎ2／６７％Ｈ2の混合ガス１Ｌ／ｍｉｎを炉内圧力３００Ｐａで導入し、０．３ｍＡ／ｃｍ2・５００Ｖのグロー放電プラズマ雰囲気で３０分行い、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。
この試験片の組織観察を行った結果、試験片端部には網状の炭化物が析出せず、プラズマ浸炭の懸案課題であった試験片端部の炭化物析出が改善された。すなわち、イオン化したアルゴンがスパッタリングを行い、試験片端部を中心に加熱されて炭素の拡散が促進された。
Subsequently, evacuation is performed, and the mixture is held in a vacuum atmosphere for 5 minutes. Subsequently, a gas mixture meter of 1% / min of 20% Ar / 80% H 2 is introduced at a furnace pressure of 50 Pa, and 0.6 mA / cm 2 is introduced. -Diffusion treatment with 500 V glow discharge plasma was performed for 40 minutes. Subsequently, the quenching temperature is lowered to 870 ° C., 1 L / min of a mixed gas of 33% N 2 /67% H 2 is introduced at a furnace pressure of 300 Pa, and the glow discharge plasma atmosphere is 0.3 mA / cm 2 · 500 V. The sample was divided and conveyed to a cooling chamber, and cooled with pressurized He gas.
As a result of observing the structure of the test piece, no reticulated carbide was deposited at the end of the test piece, and the carbide precipitation at the end of the test piece, which was a concern for plasma carburization, was improved. That is, ionized argon was sputtered and heated around the end of the test piece to promote carbon diffusion.
［比較例４］
処理工程において、拡散処理を真空雰囲気で行い、それ以外は実施例６と同様の処理を行った。この試験片の組織観察を行った結果、平坦部においてはマルテンサイト組織と残留オーステナイト組織が全体を占めていたが、試験片端部においては炭素成分が固溶し切れず、粒界に沿って網目状炭化物が析出した。
[Comparative Example 4]
In the treatment process, the diffusion treatment was performed in a vacuum atmosphere, and the same treatment as in Example 6 was performed except that. As a result of observing the structure of this test piece, the martensite structure and the retained austenite structure occupied the whole in the flat part, but the carbon component did not completely dissolve at the end part of the test piece, and the mesh along the grain boundary. A carbide was deposited.
［参考例］
３次工程において、真空排気をして焼入れ温度８７０℃まで降温し、真空雰囲気で、３０分保持を行い、冷却室に搬送して加圧Ｈｅガスによる冷却を行った。それ以外は実施例１と同様の処理を行った。上記処理の後、プラズマＣＶＤ法によって硬質皮膜（ＤＬＣ）を表面に形成した。成膜開始時の雰囲気温度は２００℃であった。この試験片の摩擦摩耗特性をボールオンディスク試験機で測定したところ、摺動距離は１００ｍであった。
[Reference example]
In the third step, vacuum evacuation was performed and the temperature was lowered to a quenching temperature of 870 ° C., held in a vacuum atmosphere for 30 minutes, conveyed to a cooling chamber, and cooled with pressurized He gas. Otherwise, the same processing as in Example 1 was performed. After the above treatment, a hard coating (DLC) was formed on the surface by plasma CVD. The ambient temperature at the start of film formation was 200 ° C. When the frictional wear characteristics of this test piece were measured with a ball-on-disk tester, the sliding distance was 100 m.
本発明によれば、エッジ部を有する各種ワークをプラズマ浸炭方法で浸炭を行う際、エッジ部と平坦部との炭素濃度の差が小さく、冷却時にエッジ部に生じる網状の炭化物の生成を抑制し、さらに特許文献１に記載の方法における課題も同時に解決することができる。 According to the present invention, when various workpieces having an edge portion are carburized by the plasma carburizing method, the difference in carbon concentration between the edge portion and the flat portion is small, and the generation of net-like carbides generated at the edge portion during cooling is suppressed. Furthermore, the problem in the method described in Patent Document 1 can be solved at the same time.
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