Effect of heating parameters on laser welded tailored blanks of hot press forming steel

Al-Si coating on the hot press forming steel sheet is diluted and diffused into the weld metal during laser welding and successive hot press forming process. Even after the hot press forming process, Al was still not homogeneously distributed within the weld metal and partially ferritic structures in the weld metal were observed in the Al-rich zone. In this study, the effect of heating duration and temperature on microstructure was investigated utilizing two different laser beam diameters. When using the larger diameter laser beam during welding, a wider weld bead resulted in enhanced weld flow and mixing of Al within the welds and thereby increases the martensitic fraction in the weld metal. As the heating duration and temperature increase, the volumetric fraction of ferrite decreases and nearly full martensitic morphology could be achieved. The effect of Al and Si composition on phase transformation was also confirmed by the thermodynamic calculation.