Abstract
Tailored blanks are widely used for automobile bodies as a material, that achieves not only weight reduction but also maintains of strength and rigidity for an auto body. High-strength steel whose tensile strength is 590MPa or higher is usually strengthened by transformation hardening. When such occurring high-strength steel is welded, the weld metal becomes harder than the base metal owing to heat input and the subsequent rapid cooling occurring during the welding, while the heat-affected zone (HAZ) is possibly caused by temper softening. In this study, the relationship between a formability and HAZ hardness changes in laser welding was evaluated. As a result, the widths of the weld metal and HAZ became narrower and the Erichsen value was enhanced with an increase in the welding speed. In cases in which the width of the hardened weld metal is constant, when the softening degree and region width of HAZ are large, the Erichsen value deteriorates.
