Investigation of the occurrence of hot cracking in pulsed Nd-YAG laser welding of Hastelloy-X by numerical and microstructure studies

Abstract

The hot cracking characteristic of the welded Hastelloy X is studied through the metallographic investigation of the weld zone and the thermo-mechanical modeling of the pulsed Nd-YAG laser process in SYSWELD™. The location of liquation cracking is determined by the incorporation of precipitation and the microstructure evolution of Hastelloy X and the temperature and stress profiles of the weld regions. The results reveal that increasing the speed of welding, with the maintenance of the penetration depth of the weld, leads to a decrease in liquation cracking in the heat affected zone. Microstructural evaluation indicates that solidification cracks are initiated from liquation cracks in the base metal and are propagated intergranular along the grain boundaries of the weld metal. It is also shown that the healing of liquated grain boundaries through backfilling can have a significant role in the resistance to liquation cracking in the heat affected zone and that, in turn, can affect tendency for solidification cracking in the weld metal. The analysis of the simulation identifies for dε/dT higher than 0.007 (10-3/°K), the hot cracking is initiated in the middle zone of weld pool vicinity, where the strain rate was maximum.