Mazda Motor Corporation

Kabushiki Kaisha Kobe Seiko Sho

Mikio Hirahara

Yukio Arimi

Yoshihiko Kojima

Yoshitake Matsushima

Akito Shiina

Morifumi Nakamura

Hisao Maeda

A manufacturing method of case-hardened parts whose chemical components comprising especially Fe, C, Si, Mn, S, Ni, Mo, Al, V and N including a step of the heat treatment 1 in which, after carburizing, carbonitriding or carburizing followed by carbonitriding steel is cooled gradually at a temperature less than 100.degree. C./minute, by another step of the heat treatment 2, in which steel is heated to a temperature higher than the Ac.sub.3 transformation point and less than 850.degree. C. and kept at the above temperature before quenching, or after keeping at the temperature, is cooled down to a level not below 600.degree. C. before quenching, or quenching is done after cooling down to and keeping the temperature not below 600.degree. C. is disclosed. This method makes the surface layer a mixture of martensite and retained austenite. Thus the case hardened steel products of high precision and high strength are obtainable.

Method of manufacturing case-hardened parts with little distortion in

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Hiroshima, Japan

Mikio Hirahara