Advanced Characterization Of Haz Softening Of Ahss For Crash Modeling

Advanced characterization of the mechanical properties in the softened HAZ is vital for designing welded AHSS components, as it is needed to predict post-weld performance, such as during crash. The weld heat affected zone (HAZ) of advanced high strength steels (AHSS) containing significant volume fractions of martensite exhibit considerable softening because of tempering effects. HAZ softening of two AHSS; Usibor 1500 (press hardening steel) and M1500 with nominal ultimate tensile strength (UTS) of 1 500 MPa has been characterized in this study. Samples were subjected to various rapid tempering cycles using the Gleeble to simulate the microstructures found in different locations of the sub-critical HAZ. Mechanical properties of simulated weld areas have been measured with different geometries, representing different levels of stress triaxiality. Furthermore, Digital Image Correlation (DIC), to determine fracture strain of HAZ, measured the fracture strain of a spot weld and base metal for Usibor 1500. Uniaxial tensile and notch sample geometries were used to investigate the influence of different strain path. The results show fracture strain is a weak function of strain path for samples that fail in the HAZ, whereas fracture strain of the base material considerably depends on strain path.