Effects of constant load on corrosion cracking of 304 ASS at 600°C in molten salts

Abstract

The effects of constant load (CL) on corrosion cracking of 304 austenitic stainless steel (ASS) in molten salts (binary nitrate salts, 60 wt% NaNO 3 , and 40 wt% KNO 3 ) were investigated. A pair of novel clamping fixture was designed to fix the tensile sample, making the gauge section immersed in molten salts. The CL tensile tests were applied with the initial stress of 212 MPa and the temperature of 600°C. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize the deformation behavior and corrosion features. The results show that corrosion of 304 ASS in molten salts was aggravated by the continuous deformation due to the cracking of protective oxide scale. Grain boundaries were oxidized and weakened by the molten salt, leading to a crack propagating. Compared with the creep test result, a reduced rupture life of 304 ASS under constant loading in molten salts was observed.

Materials properties characterization in the most extreme environments

“…Similar responses have been observed in FLiNaK and FLiBe chemistries considered for molten salt cooled nuclear reactor designs, driving similar research efforts to identify and engineer new materials to withstand those related environments. [190][191][192] Surprisingly, after the seminal work of Atmani and Rameau in 1980, 191,193 who investigated stress-corrosion cracking (SCC) of stainless steel in molten NaCl-CaCl 2 at 840 K utilizing a uniquely designed tensile test apparatus, few groups have aimed at studying the combined impact of mechanical stress and chemical attack under CSP conditions. 194 This research gap, in part, is a result of expected low-stress conditions of CSP or molten salt reactor designs, but localized attack and grain-boundary embrittlement could well be anticipated in service.…”