Patent ID: 7416614

Claim:
A method of gas carburizing comprising the steps of: experimentally predetermining limiting carburizing conditions at which a surface layer of a sample of a steel treatment object present in a carburizing atmosphere is austenitized without melting at a carburizing temperature which is not higher than a peritectic point temperature at which δ iron and liquid phase are transformed into γ iron and is greater than a eutectic point temperature at which liquid phase is transformed into γ iron and cementite; and gas carburizing the treatment object under carburizing conditions which are set so as not to contradict the limiting carburizing conditions, at a carburizing temperature which is not higher than the peritectic point temperature and is greater than the eutectic point temperature, wherein the limiting carburizing conditions comprise: an upper limit value of a partial pressure of carburizing gas in the carburizing atmosphere at which the surface layer of the sample is austenitized without melting; and an upper limit value of carburizing temperature at which the surface layer of the sample is austenitized without melting and an upper limit value of carburizing time at which the surface layer of the sample is austenitized without melting; a relationship between the upper limit value of the partial pressure of carburizing gas, the upper limit value of carburizing temperature, and the upper limit value of carburizing time is predetermined; and a partial pressure of carburizing gas, a carburizing temperature, and a carburizing time are set as a set of carburizing conditions of the treatment object so as not to contradict the limiting carburizing conditions which satisfy the predetermined relationship.