Behavior of weld defects in laser weldment of helium-doped stainless steel

Helium is generated within neutron-irradiated reactor components and entrapped in the stainless steel components. The repair of the components using conventional GTA welding practices is exceedingly difficult by entrapped helium, because of the initiation of helium bubbles and weld cracking. In this research, the behavior of helium bubble in the austenitic stainless steel weldment was investigated by utilizing stainless steels ion-implanted with helium and then welded by YAG laser apparatus. Helium ion implanting to the sample was carried out using 8MeV implantation apparatus, and the sample was doped with 2.45 x 1019 atoms/m2 dose at 6MeV and then doped with 1 x 1019 atoms/m2 dose at 5MeV. Helium bubbles are present at the bond region, heat-affected zone and weld metal. The increase of laser power causes the growth of helium bubble, toe cracks and cracks along the dendrite cell boundary in the weld metal. The helium bubble phenomena can be reproduced in the weld metal and in the heat-affected zone during repair welding using helium ion implanting technique. (author)