Transition between alloy–element partitioned and non-partitioned growth of austenite from a ferrite and cementite mixture in a high-carbon low-alloy steel

Abstract

The growth of austenite from a mixture of ferrite and cementite in low-alloy steels can be classified into three temperature ranges above the eutectoid temperature. In the first range, the austenite growth and cementite dissolution are controlled by alloy element diffusion from the beginning. In the second, they are controlled by carbon diffusion and switch to alloy element diffusion control at a later stage. In the third, the cementite dissolution, if the ferrite matrix has transformed to austenite upon heating, is controlled by carbon diffusion until completion. The transition temperatures between these ranges are evaluated in a quaternary alloy containing Mn and Cr by Thermo-calc and DICTRA simulation, and are in essential agreement with earlier experimental results. The proposed simple approach of calculating the transition temperatures may facilitate our understanding of austenitization kinetics and the design of heat treatment, for example, homogenization and soaking, of high-carbon steels.