Evaluation of the thermal ageing of austenitic stainless steel welds with 10 % of δ-ferrites

Abstract

Three austenitic stainless steel welds (ASSW), such as E308, ER316L and ER347, with about 10% of δ-ferrite were thermally aged at 400 °C up to 10000 h to accelerate the thermal ageing expected in pressurized water reactor (PWR) environment. Fluctuation of Fe and Cr due to spinodal decomposition is observed with width of 5–12 nm within the ferrite phase. For all 3 welds, increase in strength and decrease in tensile elongation is observed after thermal aging at room temperature and 320 °C. The reduction in fracture resistance, measured as J-R curves, is most significant for ER316L weld with decrease by about 50%. However, it is quite small (about 10% decrease) for ER347 weld even after ageing at 400 °C for 10000 h despite the large reduction in tensile elongation. Finally, the double loop-electrochemical potentiodynamic reactivation (DL-EPR) tests show the degree of sensitization (DOS) values are negligible even after the accelerated thermal ageing at 400 °C for 10000 h.