2001 Volume 19 Issue 3 Pages 480-488
Heat conduction and the thermal elastic-plastic analyses were carried out by FEM to clarify the effects of thermal and strain cycles on liquation cracking in HAZ of laser welded joint. The thermal analysis has indicated that the necked zone of weld bead is held at higher temperatures for longer than other regions in HAZ during the weld thermal cycle. Thus, liquation temperature range of grain boundary in the necked zone is considered larger than in other regions. According to the result of the strain analysis during the cooling stage, plastic strain of HAZ in the necked zone showed bigger value compared with that in other regions. In addition, it has also been shown that as the curvature of the necked zone decreases, the principal plastic strain increases. On the basis of these results, the reason why liquation cracking preferentially occurs in the necked zone of HAZ has been considered as follows. When laser welding is carried out, grain boundary near fusion boundary is liquefied due to the eutectic melting of laves cluster during the heating stage. Furthermore, the liquation temperature range of grain boundary in the necked zone was wider than in other regions, and the necked zone is subjected to greater tensile strain during the cooling stage. As a result, liquation cracks preferentially occur in the necked zone of laser weld during welding.