Effect of Aluminum Content on Solidification Process and Microsegregation of δ-TRIP Steel

As a third-generation advanced high-strength steel (AHSS), δ-TRIP steel exhibits the characteristics of high strength, high plasticity, and low density. However, the addition of Al to steel will affect solidification and segregation, which may impact the final microstructure and mechanical properties of the product. In this study, thermodynamic calculations and microsegregation model analysis were employed to investigate the effects of Al addition on the solidification path, peritectic reaction range, equilibrium partition coefficients, and microsegregation behavior of δ-TRIP steel. The results show that with an increase in the Al content, the carbon content range in which δ ferrite is retained without complete transformation during the solid-state phase transition becomes broader. Simultaneously, the carbon concentration range of the peritectic zone expands. The segregation of the C, Si, Mn, P, and S elements increases with increasing Al content, whereas the segregation of Al decreases as the Al content increases. Under non-equilibrium solidification conditions, unlike equilibrium solidification, the temperature difference between the solid and liquid phases initially increases, then decreases, and subsequently levels off with further Al addition. This study provides information for the composition design and production process optimization of δ-TRIP steel, and the research results can provide a reference for similar high-aluminum, low-density steels.