Experimental and Numerical Investigations on Tailored Tempering Process of a U-channel Component with Tailored Mechanical Properties

Hot stamping of quenchenable ultra high strength steels currently represents a promising forming technology for the manufacturing of safety and crash relevant parts. For some applications, such as B-pillars and other structural components that may undergo impact loading, it may be desirable to create regions of the part with tailored mechanical properties. In the paper, a laboratory-scale hot stamped U-channel was manufactured by using a segmented die, which was heated by cartridge heaters and cooled by water channels independently. Local hardness values as low as 289 HV can be achieved using a heated die temperature of 400 degrees C while maintaining a hardness level of 490 HV in the fully cooled region. If the die temperature was increased to 450 degrees C, the Vickers hardness of elements in the heated region was 227 HV, with a reduction in hardness of more than 50%. Optical microscopy was used to verify the microstructure of the as-quenched phases with respect to the heated die temperatures. The FE model of the lab-scale process was developed to capture the overall hardness trends that were observed in the experiments.