Designing and optimizing the galvanized quenching and partitioning process: Evolution of microstructure and transformation behavior

This work explores key aspects of designing and optimizing the quenching and partitioning process integrated with galvanizing (GI Q&P) for developing next-generation automotive steels. A conventional CMnSi steel was quenched below the martensite-start temperature, followed by partitioning at 460 °C for time durations (t P ) between 3 and 60 s, to simulate the GI Q&P process using a dilatometer. Carbon redistribution between martensite and remaining austenite was observed during initial quenching, which continued during isothermal holding at the quenching temperature (T Q ) and subsequent partitioning at 460 °C, leading to the stabilization of austenite. Transition carbides and/or cementite and bainite formation were observed during different stages of Q&P. Transition carbides formed during initial quenching and holding at T Q , and then dissolved during partitioning at 460 °C after 30 s, followed by precipitation of cementite. The amount of retained austenite increased with increasing T Q , while its carbon content was not affected much. With increasing t P , both the amount and carbon content of retained austenite first increased, attained a maximum value (∼15 vol pct after t P of 10 s and ∼0.82 wt pct carbon after t P of 30 s), and then decreased, due to austenite decomposition into bainite, and ferrite and cementite.