Welding of Helium-Doped Austenitic and Ferritic Stainless Steels

摘要

Helium was uniformly implanted into type 316 stainless steel and Sandvik HT-9 (12Cr-1MoVW) to levels of 0.18 to 256 appm and 0.3 to 1 appm, respectively, using the ''tritium trick'' technique. Bead-on-plate welds were then produced under fully constrained conditions using the gas tungsten arc (GTA) process. For 316 stainless steel, catastrophic intergranular fracture occurred in the heat-affected zone (HAZ) of welds with helium levels equal to or greater than 2.5 appm. Brittle cracking along the central line of the fusion zone was also observed for the welds containing 105 and 256 appm He. For HT-9, intergranular cracking occurred in the HAZ along prior-austenite grain boundaries of welds containing 1 appm He. Electron microscopy observations showed that the cracking in the HAZ originated from the growth and coalescence of grain boundary helium bubbles and that the fusion zone cracking resulted from the growth of helium at dendrite interfaces. Results of this study indicate that the use of conventional fusion welding techniques to repair irradiation-degraded materials containing even small amounts of helium may be difficult. 8 refs., 3 figs. (ERA citation 14:028734)