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.