Strain-induced ferrite formation and its effect on mechanical properties of a dual phase steel produced using laboratory simulated strip casting

Thermo-mechanical processing of a strip cast dual phase (DP) steel was carried out using a Gleeble thermo-mechanical simulator. The effect of deformation temperatures in the range from 1050 to 700 °C on the microstructure evolution was investigated using optical, scanning and transmission electron microscopy along with electron backscattering diffraction (EBSD). Strain-induced ferrite (SIF) formation was observed following austenite deformation (∼0.41 reduction) in the 800–700 °C temperature range, leading to a ferrite grain refinement down to 3.1 ± 2.3 μm. A novel segmentation procedure was applied to separate selected EBSD maps into polygonal ferrite, SIF and second phase regions (bainite/martensite). Following this, the microtexture, misorientation angle distribution and the deviation from the Kurdjumov–Sachs and Nishiyama–Wasserman orientation relationships of each microstructure constituent were analysed. Based on iso-work modelling analysis of tensile stress-strain curves, the SIF was found to enhance strength with a slight decrease in ductility compared to polygonal ferrite. The tensile mechanical properties after deformation at 750 °C reached the level of DP 600 produced in industry, highlighting the potential to manufacture DP steels via the strip casting technique