Mazda Motor Corporation

Kabushiki Kaisha Kobe Seiko Sho

Yukio Arimi

Yoshihiko Kojima

Yoshihisa Miwa

Yoshitake Matsushima

Shinya Shibata

Hisao Maeda

Mikio Hirahara

Akito Shiina

Morifumi Nakamura

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

A method of manufacturing a steel member comprising the steps of: carburizing and quenching or carbo-nitriding and quenching a steel material; shot-peening the steel material quenched in the first step without tempering; and aging the steel material shot-peened in the second step. Preferably the steel material comprises 0.1 to 0.4 wt. % C, 0.06 to 0.15 wt. % Si, 0.3 to 1.0 wt. % Mn, 0.9 to 1.2 wt. % Cr, 0.3 to 0.5 wt. % Mo, and the remainder Fe. The steel member is preferably used in transmission gears for automobiles, which require superior strength.

Method of forming hard steels by case hardening, shot-peening and aging

A method of carburizing and quenching involves the following three steps of: pre-carburizing a steel member containing Cr with precipitating carbide by heating to achieve a surface carbon concentration of not less than 1%; spheroidizing the carbide obtained by alternately holding the steel member at a temperature slightly above and slightly below the A.sub.1 transformation temperature under a carbon potential of from 0.5 to 1.0%; and carburizing and quenching or carbo-nitriding and quenching the steel member followed by reheating at not more than the heating temperature of pre-carburizing.

Method of carburizing spheroidizing and quenching

Growing community of inventors

Hiroshima, Japan

Yukio Arimi