EFFECTS OF THERMAL AGEING ON MICROSTRUCTURE AND HARDNESS OF NI CLADDING ON AUSTENITIC STAINLESS STEEL BY GTAW

As one of the most promising Generation IV nuclear reactors, thorium molten salt reactor (TMSR) possesses inherent safety, simplified fuel cycle and high power generation efficiency. However, the structure material of TMSR must encounter challenges of high-temperature environment and serious molten fluoride salts corrosion. Although the UNS N10003 alloy has excellent performance in TMSR, the high cost of this alloy reduces the economy of TMSR. Although the austenitic stainless steel possesses excellent high temperature strength and lower cost, it exhibits poor corrosion resistance in molten fluoride salts. Therefore, the purpose of this work is using Ni cladding on austenitic stainless steel by gas tungsten arc welding (GTAW) for corrosion protection and investigating the effects of thermal ageing on microstructure and hardness of cladding. The elements distribution and segregation, the precipitates behavior and the microstructure evolution of interface and cladding layer under as-welded and thermal ageing conditions were studied by a series of characterization methods respectively. The hardness evolution of claddings under as-welded and thermal ageing conditions were tested and discussed.