Dependence of the Carburization Occurring during Vacuum Oil-Quenching of Steels upon Quenching Temperature

Abstract

A diffusion equation which describes carburizing of steels during oil-quenching has been developed on the assumption that the diffusion of carbon into the steels is a rate-controlling step as,
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\ oindentwhere C is the concentration of carbon at a distance x below the surface, C₀ the initial concentration within the steels, C_s the concentration at the surface, T_cs and T_cf are respectively the starting and the finishing temperatures of carburizing, D(T) the diffusion coefficient, which is assumed to be a function of temperature T only, and t=f⁻¹(T) is an inverse function of the cooling curve T=f(t) at a vapor cooling stage. Measurements of the case depth have been made on iron specimens quenched from various temperatures in two kinds of oils. A comparison between the measured and the calculated depths has shown that the above equation expresses the dependence of the case depth upon quenching temperature fairly well. Effects of T_cs, T_cf, and T=F(t) on the case depth have been discussed based on this equation.