Kabushiki Kaisha Fujikoshi

Takao Ishihara

Kaishu Yamazumi

Jun Takeuchi

A method of hardening steel so that it may have a surface layer with sufficient hardness to permit fabrication into machinery parts with a minimum of strain developed therein. The method comprises heating steel at a temperature in a range not lower than 100.degree. C. below its A.sub.1 transformation point (about 630.degree. C.) and not higher than 50.degree. C. thereabove (about 780.degree. C.) in an atmosphere consisting solely of ammonia gas, or composed of ammonia gas and at least one of organic liquids, petroleum gases, endothermic gases and neutral gases, while ammonia gas is being supplied continuously at a lower flow rate, or at a higher flow rate followed by a diffusion treatment to austenitize a surface layer of the steel by penetration of nitrogen thereinto, and quenching the steel to transform the austenitized surface layer into a martensite layer.

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Toyama, Japan

Takao Ishihara