Abstract
In automobile manufacturing, application of laser welding to carbon steel thin plates is an important issue to achieve weight reduction for improved power efficiency. However, solidification cracking can occur near the edge of a carbon steel plate. In this study, effect of distance from an edge of the steel plate (offset) on solidification cracking during laser welding was investigated for high-carbon steel. Melt-run welding on the S45C thin plate was performed under five offsets varying from 1.5 mm to 5.5 mm with an intervals of 1.0 mm. A steel plate was fractured along a weld line for the four offsets except 5.5 mm. A liquid film was observed on most of the fracture surfaces, while a region without the liquid film was present at a bottom base of the fracture surface. Therefore, it was considered that the crack was initiated at the bottom base of the steel thin plate along the weld line. In addition, in a thermal-elastic-plastic simulation using the finite element method, a plastic strain increment became large both at the center and, front and back surfaces of the plate for the offsets of 1.5 and 2.5 mm. Contrary, that at the center of the plate almost disappeared for the offsets of 3.5 mm and more. Furthermore, the plastic strain increment decreased as offset increased. Consequently, it is concluded that increasing offset reduces plastic strain increment on the cross-sectional plane along a weld line, leading to prevent solidification cracking.
