Effect of Tool Temperature on Microstructure and Properties of Tailored Hot Stamping Components

Traditional boron steel hot stamping technology can achieve components with full martensite and tensile strength of 1500MPa. However, fully martensitic hot stamped components exhibit very low level of ductility and are rarely used in energy absorbing structures. Hot stamping with segmented heating and cooling tool can obtain multiphase quenched structures and the tailored mechanical properties. Hot stamping experiment of U-shape component was performed with segmented heating and cooling tool. Mechanical properties of the formed component were measured, and scanning electron microscope and color tint etching were used to quantify the quenched phases achieved under different tool temperatures. The results showed that hardness value decreased from 470 to 230HV and tensile strength reduced about 50% from 1406 to 730MPa and elongation increased from 4.19 to 10.20% as tool temperatures increased from 25 to 500 degrees C. Meanwhile, martensite decreased from 85 to 30% and bainite increased from 12 to 55%, and there was also a small increase in ferrite. In order to get the influence of quenched phases on the strength and hardness of tailored hot stamped component, linear fitting optimization was used to establish mathematical models for area fraction of quenched phases and strength and hardness.