In the automotive industry, structural components are often produced via press hardening, enabling rapid production and the use of ultra-high-strength steels. In this process, steels are heated to an austenitic state and are then formed and quenched in rapid succession. The initial steel that enters the press-hardening production line varies, where the microstructure is a result of previous production steps. This work was performed to investigate the possible effects of the initial microstructure on the final mechanical properties for rapidly quenched samples. Although the initial microstructure is transformed during austenitization, the steel can still be affected by its prior history. Steels with three different initial microstructures were evaluated, with only minor variations in chemical composition and thicknesses. The Lankford coefficients and the failure strains were dependent on the orientation of the samples. However, for a given orientation, there were only minor variations between the different steels with respect to anisotropy, strength, and ductility. The anisotropy could be correlated with the microstructure through the calculation of Taylor factors based on measurements using electron backscatter diffraction. The minor influence from the initial steel microstructure on the final mechanical properties indicates robustness suitable for mass production.

During production of components using press hardening, the steel will at one point be heated to an austenitic state. Grain growth can occur during this austenitization if the time and temperature are sufficient, where the microstructure becomes increasingly coarse. The final austenite grain size can affect both the phase transformations during quenching and the final mechanical properties of a fully martensitic microstructure. In this work, austenite grain growth was modeled using measurements of the mean grain diameters from isothermal experiments, while the model was validated using non-isothermal experiments. The temperature and time ranges used in the isothermal experiments were 900–960 C and 1-1200 seconds, respectively. Bending tests according to VDA 238-100 were performed, using samples previously austenitized at 900, 930, and 960 C and then rapidly quenched. The isothermal grain growth up to 930 C could be modeled using the average grain size, while at 960 C the microstructure displayed a more complex growth behavior. The grain growth during the non-isothermal validation experiments could be predicted with the exception of one thermal cycle. No effect of the austenitization temperature on the bending performance was observed when short austenitization times were utilized, and only a minor effect was observed for a longer austenitization time.