Effect of Microstructure and Mechanical Properties on the Stress Corrosion Cracking Assessment of Type 304 Stainless Steel Using Slow Strain Rate Tests

Abstract

ABSTRACTThe stress corrosion cracking (SCC) of the commercial austenitic stainless steel type 304 was investigated as function of test temperature, microstructure and mechanical properties in acidic chloride solution (25 wt.%-MgCl2) using slow strain rate tests (SSRT). Susceptibility and mechanism of SCC was investigated using SSRT performed at strain rate of 1 x 10-6 in/s in a glass autoclave containing a magnesium chloride solution at 20, 50 and 80°C. The SCC assessment was carried out in function of the results of time to failure ratio (TFR), elongation ratio (ELR), ultimate tensile strength ratio (UTS-R), strain ratio(eR), yielding strength ratio (YS-R) and stress rupture ratio (SR-R). This assessment was complemented by some scanning electron microscopy (SEM) observations, in order to determine the type of fracture and its features. SSRT results indicate that 304 stainless steel was susceptible to SCC at 50 and 80°C. SCC susceptibility increases as the temperature increase. By the contrary, the mechanical properties decreases with temperature increase. SEM observations showed a ductile type of fracture, indicating that cracks appear to be originated from the pits, increasing the number of cracks as the temperature increases. Corrosion pits are one of the main potential sites for surface crack initiation. The stress concentration in the pits will be the nucleation site for cracks.