Formability of the ultra high strength automotive steel docol 1500 bor by using hot processing maps and austenite reconstruction

In this study, the hot processing map was drawn to study the hot formability of high strength automotive steel Docol 1500 Bor. The quenching microstructure of the test steel was observed under optical microscope and EBSD and the deformed PA (parent austenite) was reconstructed under different conditions according to KS (Kurdjumov–Sachs) OR (orientation relationship). The results indicate that the optimal deformation conditions in the stable region are strain rates less than 1s⁻¹ and temperatures higher than 900 °C. Overall, the fine-grained martensite structure with a larger Schmid factor has a better deformation ability for subsequent service. The texture component {011} <100> appears in the PA at the strain rate of 5 s⁻¹ and the temperature of 1000 °C, while the dynamic recrystallization is significantly inhibited. The quenched martensite is found coarse. In the stable region, the recrystallized austenite grains with certain deformation transforms into the martensite grains with low cumulative misorientation values and higher Schmid factors. In the unstable region, the austenite grains are smaller in size, in which severe cumulative misorientation caused by higher strain rates leads to poor plasticity.