The role of aluminium in chemical and phase segregation in a TRIP-assisted dual phase steel

In this work we have assessed the role of Al on the chemical segregation of Mn, Cr and Si during thermo-mechanical processing of a TRIP-assisted dual phase steel, based on microstructural observations backed by thermodynamic, numerical and analytical modelling. Chemical segregation in steels during casting leads to anisotropy in the microstructure (banding) and hence in mechanical properties. Although considerable attention has been paid to the effects of carbon and manganese, the segregation of other alloying elements and their influence on the resulting microstructure and properties remains largely unexplored. We demonstrate that the micro-segregation patterns of these elements established during casting remain present in the microstructure throughout the process and are not homogenised during industrial reheating cycles due to insufficient diffusion of solid solution elements. Aluminium exerts the largest individual effect of the substitutional elements on the formation of banding in these steels. Controlling micro-segregation during solidification is therefore critical for obtaining homogenous mechanical properties in the final product, as it controls the phase transformations occurring during thermo-mechanical processing and therefore the final microstructure.