Kinetic Description of (Cr, Fe)<sub>7</sub>C<sub>3</sub> Carbide Dissolution in Austenite of High-Carbon Fe-Cr-C Ternary Alloys

Abstract

The paper examines the available experimental data to produce a model for quantitative prediction of the change of M7C3 carbide fraction and austenite chemical composition during holding of ternary alloys Fe–Cr–C (used as wear-resistant white cast irons and tool steels) in austenite + carbide region. Carbide dissolution is well described by Avrami type equation with exponent n close to 1/2. Dependences of the coefficient of this equation on carbide fraction and of the activation energy of the temperature dependence of this coefficient on carbide composition are established. As a result, a model that permits to calculate the fraction and chemical composition of austenite and M7C3 carbide in an Fe–Cr–C alloy of arbitrary composition after isothermal holding at given temperature for given time is obtained; equilibrium phase composition is needed to be known from thermodynamic models. This allows predicting the results of hardening after different austenitization regimes.