Multi-Phase Field Modeling of Austenite to Pearlite-Ferrite Transformation in Hypoeutectoid Steel

Hypoeutectoid steel is a crucial metal structural material, which is characterized by the coexisting microstructure of ferrite and pearlite. The intricate interplay among its composition, processing conditions, and resultant microstructure, driven by multi-phase competition and multi-component characteristics, significantly complicates the understanding of austenite decomposition kinetics and elemental diffusion mechanisms during phase transformations. In addressing these complexities, the current study delves into the effects of cooling rate, prior austenite grain size, and C content on the component distribution and microstructure evolution during the austenite decomposition process of hypoeutectoid steels. Using a multi-phase field model, it reveals that an increase in the cooling rate from 1.0 °C/s to 7.0 °C/s leads to a reduced ferrite proportion and finer pearlite lamellae spacing from 52% to 22%, and from 1.06 μm to 0.67 μm, respectively. Concurrently, a decreased PAGS from 25.23 μm to 8.92 μm enhances the phase transformation driving force, resulting in smaller average grain sizes of pearlite clusters and pro-eutectoid ferrite. Moreover, an increased C content from 0.22 wt.% to 0.37 wt.% decreases the phase transition temperature from 795 °C to 750 °C and enhances the pearlite phase proportion from 27% to 61%, concurrently refining the spacing of the pearlite layers from 1.25 μm to 0.87 μm. This work aims to shed light on the complex dynamics governing the microstructural transformations in hypoeutectoid steels, thereby facilitating their wider application across different industrial scenes.