Weldability Comparison of Tritium-charged-and-aged 304 and 316ln Stainless Steels

Measurement of the effects of helium (from tritium decay) on the weldability of Types 304 and ITER Grade 316LN stainless steel demonstrated the inherent complexities in designing and conducting an experimental program using tritium-charged-and-aged materials to simulate the effects of irradiation-induced helium on weld behavior. Differences in microstructure, surface condition and alloy chemistry are known to play key roles in tritium absorption and distribution and thus have direct effects on the subsequent He production and distribution. The helium embrittlement cracking produced in 0.5 in. (12.7 mm) thick 304 and 316LN plates that were tritium-charged in the same container and subsequently welded with gas metal arc, low heat input weld overlays and gas tungsten arc stringer beads, varied markedly. For example, the porosity in the weld beads was much higher in the 304 plate than in the 316LN plate. Additionally, crack measurements from weld cross-sections revealed more extensive intergranular cracking in the heat-affected zones of welds on the 304 plate when compared to the 316LN plate. However, the differences between the two types of stainless steel may not be a result of differences in the resistance to helium embrittlement cracking, but may be due to initial tritium concentration differences developed in the ascharged plates. Further work is necessary to identify the reasons for the apparent plate to plate variation in tritium/helium content and to demonstrate the similarities (or differences) between Types 304 and ITER grade 316LN stainless steel. WSRC-TR-2003-00077 ITER/US/02/INV-VV-01