EXPERIMENTAL RESEARCH AND NUMERICAL SIMU- LATION OF SOLIDIFICATION CRACK DURING LASER WELDING OF RING STRUCTURE

The combined influence of metallurgical and mechanical factors on welding solidifica- tion cracking structure in laser welded ring was investigated by using both experiments and numerical simulation. It is found that solidification cracking is directly related with the overlap weld part. The microstructure was observed under OM, and the grain size was measured by EBSD observation. The grains in overlap weld part are much bigger than those in single weld part, which results in falling of ductility during solidification. The temperature and strain changes of weld metal in solidification temperature range were calculated out by using 3D finite element analysis. Compared with the single weld part, the strain rate with temperature drop is lower in overlap weld part, i.e., the mechanical driving force to solidification cracking is weaker in overlap weld part. Consequently, it is concluded that the low ductility caused by coarse grain results in the occurrence of solidification cracking in overlap weld part during laser welding of ring structure. This research not only helps to understand the mechanism of solidification cracking in more details, but also guides the study on prediction of solidification cracking occurrence.