BEHAVIOR OF TYPE-316 AUSTENITIC STAINLESS-STEEL UNDER SLOW STRAIN-RATE TECHNIQUE CONDITIONS IN LITHIUM BROMIDE HEAVY BRINE ENVIRONMENTS

The corrosion and stress corrosion cracking (SCC) behavior of type 316 (UNS S31600) austenitic stainless steel (SS) in a 55% lithium bromide (LiBr) environment was investigated using slow strain rate testing (S SRT) and potentiodynamic polarization measurements. The experiments we re performed at temperatures from 80 degrees C to 140 degrees C and fr om pH 4 to 11.6. The effect of 1 wt% potassium iodide (KI) and potassi um chromate (K2CrO4) addition was evaluated. The ultimate tensile stre ss (UTS) and the elongation were decreased by raising the temperature from 80 degrees C to 140 degrees C in the LiBr environments. Scanning electron microscopy (SEM) revealed environmental embrittlement feature s on the lateral surface, the free surface of the specimen, in all the tested environments. Addition of 1 wt% KI to 55% LiBr brine of pH = 4 acted as an inhibitor to SCC and improved mechanical properties. In t his case, fracture occurred by microvoid coalescence. In the presence of 1 wt% K2CrO4 high cathodic overpotential was recorded potentiodynam ically and evaluated. Inhibition of the passivation process because of high cathodic activation energy resulted in a low cathodic exchange c urrent density. This resulted in a corrosion potential located in the active zone of the anodic polarization curves. SEM showed intergranula r and transgranular modes of fracture in this case, instead of microvo id coalescence. Addition of 1 wt% K2CrO4 enhanced the SCC sensitivity of type 316 SS in 55% LiBr environments, resulting in reduced mechanic al properties and formation of a typical brittle fracture surface.