Influence of surface oxide on mechanical properties of laser-welded hot-press-forming steel with strength of 1.8 GPa

The hot-press-forming (HPF) steel has been proposed to overcome the insufficient formability of the GPa-grade high-strength steel. During the HPF process, a steel sheet is heated over a full austenitization (Ac3) temperature and thick oxidation scales are formed on the surface unless it is protected with an appropriate coating layer. In this study, the laser weldability of 1.8-GPa-grade HPF steel was investigated, and the effect of oxidation scales on the sheets was examined. Bead-on-plate welding and overlap welding were conducted on the 1.8-GPa HPF steel sheets with the oxidized surface layer. The oxide was diluted into the weld metal, which changed the microstructure of the weld metal and had a detrimental effect on the mechanical properties. The oxide layer on the sheet should be removed prior to welding so as to improve the weld strength. (C) 2018 Laser Institute of America.