Honda Motor Co., Ltd.

Nippon Steel Corporation

Seiji Kobayashi

Makoto Okonogi

Hideki Matsuda

Takashi Tanaka

Kenichiro Naito

Hiroki Masuda

Kohki Mizuno

Yasushi Kawahito

The present invention provides a method of production of a steel soft nitrided machine part comprising: preparing a steel material containing, by mass %, C: 0.15-0.30%, Si: 0.03-1.00%, Mn: 0.20-1.5%, S: 0.04-0.06%, Cr: 0.01-0.5%, Mo: 0.40-1.5%, Nb: 0.005-0.05%, Ti: 0.005-0.03%, V: 0.2-0.4%, Ni: 0.05-1.5%, N: 0.002-0.0048%, a balance of Fe and unavoidable impurities, limiting P to 0.02% or less, limiting Ceq. (equation (1)) to 0.65-0.85, controlling DI (equation (2)) to 80-155, log Kp (equation (3)) to 2.5-8, and Si and Mn contents according to equation (4), heating the steel material to 1150-1280&#xb0; C., hot forging the steel material to the shape of the part, cooling the steel material at a 0.5-1.5&#xb0; C/sec cooling rate to obtain a hot forged part having a micrometallic structure with more than 50% of bainite, machining the hot forged part, and soft nitriding the machined hot forged part at 550-650&#xb0; C. for 30 minutes or more.

Method of production of steel soft nitrided machine part

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Wako, Japan

Seiji Kobayashi