Multiphase field modeling of austenite to pearlite–ferrite transformation in hypoeutectoid steel

Hypoeutectoid steel, a crucial metal structural material, is characterized by the coexisting microstructure of ferrite and pearlite. Driven by multiphase competition and multicomponent characteristics, the intricate interplay among its composition, processing conditions, and microstructure substantially complicates the understanding of austenite decomposition kinetics and elemental diffusion mechanisms during phase transformations. The present study explores the effects of cooling rate, prior austenite grain size, and C content on the component distribution and microstructure evolution during the austenite decomposition of hypoeutectoid steels to address the aforementioned complexities. Results of a multiphase field model reveal that an increase in the cooling rate from 1.0 to 7.0°C/s leads to a reduction in the ferrite proportion and fine pearlite lamellae spacing from 52vol% to 22vol% at 400°C and from 1.01 to 0.67 μm at 660°C, respectively. Concurrently, a decreased prior austenite grain size from 25.23 to 8.92 μm enhances the phase transformation driving force, resulting in small average grain sizes of pearlite clusters and proeutectoid ferrite. Moreover, increasing the C content from 0.22wt% to 0.37wt% decreases the phase transition temperature from 795 to 750°C and enhances the proportion of pearlite phases from 27vol% to 61vol% at 500°C, concurrently refining the spacing of pearlite layers from 1.25 to 0.87 μm at 600°C. Overall, this work aims to elucidate the complex dynamics governing the microstructural transformations of hypoeutectoid steels, thereby facilitating their wide application across different industrial scenes.