The effect of network cementite dissolution on the nucleation and growth of prior austenite grains in high carbon low alloy steels

The state of austenite grains has an essential role in the microstructure transformation and mechanical properties of alloy steel during heat treatment or subsequent hot working. The initial microstructure of alloy steel is inseparable from the nucleation and growth of austenite grains. Hence, in this work, high carbon low alloy steel with the initial microstructure of lamellar pearlite and grain boundary cementite was selected, and the effect of cementite dissolution on austenite grain growth was analyzed from the perspective of the phase transition dilatometer curve. Three nucleation sites in high carbon low alloy steel were found by multi-perspective characterization, forming two types of austenite grains: pearlite-austenite grain and cementite-austenite grain. Under cementite pinning and solute drag effect, the growth of the prior austenite grains was retarded during the isothermal temperatures process. The average size of prior austenite grains increased only from 65.1 μm (1050 °C) to 69.8 μm (1150 °C). This work provides a foundation for optimizing the prior austenite grains state by utilizing grain boundary cementite dissolution.