Grain Growth Kinetics Model of High-Temperature Ferrite and Austenite in Ti Microalloyed Steel during Continuous Casting

The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence the thermoplasticity, thereby affecting the quality of the slab. In this work, a δ-γ phase transfer and growth model of Ti microalloyed steel was established, which considered the grain boundary inhibition effect of Ti carbonnitrides and driving force generated by grain curvature. The inhibition of grain boundary migration by Ti carbonitrides is strongest in the early stage of δ growth. The pinning effect of Ti carbonitrides weakens with the temperature decreasing, which resulted in a higher grain growth rate. During the δ-γ phase transition, the primary austenite is formed and its size is determined by introducing the δ-γ transformation coefficient. In this stage, Ti carbonnitrides have little effect on austenite formed. Rapid grain growth of γ phase occurs immediately after the completion of the transformation into a g single phase. In this stage, an entire cross-section austenite growth prediction model for slab continuous casting has been established based on the phase transformation model, with a prediction error of ≤5%. Under the influence of Ti carbonitrides and cooling rate, the grain sizes at the surface and center are 1524 μm and 5592 μm, respectively, differing by a factor of 3.67. As the Ti content increases from 0.02% to 0.04%, the grain refinement at the center is most significant, with an average grain size reduction of 27.14%.