Prediction of embrittlement during aging of nuclear grade AISI 304 stainless steel TIG welds

Abstract

Simulated weldments of AISI grade 304 stainless steel having a ferrite content of 4-6% with three levels of nitrogen (0.03, 0.08, and 0.11 wt-%) were prepared using a modified elemental implant technique. From these weldments, subsize Charpy impact specimens were prepared and subjected to aging treatment at different temperatures, 623-748 K, and for different times, 10005000 h. Impact toughness curves for these aged samples were generated by testing at various temperatures from 77 K to 300 K. From the impact curves the upper shelf energy (USE) and lower shelf energy (LSE) were determined. It was observed that both USE and LSE decreased with aging time at all temperatures. Nitrogen seems to offer a beneficial effect as far as impact toughness is concerned, as both USE and LSE values increased with increasing nitrogen content. The worst aging conditions were identified as 748 K, 2000 h at the lowest nitrogen level of 0.03 wt-%. An empirical relation connecting the aging temperature, aging time, and nitrogen content to the LSE was developed, which can be used to predict the time for embrittlement at a given nitrogen level and aging temperature.