The effect of test temperature on SCC behavior of austenitic stainless steels in boiling saturated magnesium chloride solution

The stress corrosion cracking (SCC) of the austenitic stainless steels of types 304, 310 and 316 was investigated as a function of test temperature in boiling saturated magnesium chloride solution (MgCl₂) using a constant load method. Both of types 304 and 316 exhibited similar corrosion elongation curves, while the corrosion elongation curve of type 310 was different from those of types 304 and 316, in terms of the three parameters such as time to failure (t_f), steady-state elongation rate (l_ss) and transition time to time to failure ratio (t_ss/t_f) obtained from the corrosion elongation curves for these stainless steels. The relationship between the time to failure and a reciprocal of test temperature fell in two straight lines on a semi-logarithmic scale as well as the relationship between the steady-state elongation rate and a reciprocal of test temperature. These regions were considered to correspond to a SCC-dominated region and a hydrogen embrittlement (HE)-dominated region from the value of (t_ss/t_f) and the fracture appearance. The relationship between the steady state elongation rates versus time to failure on a logarithmic scale became a straight line, whereas the slopes of the line for the stainless steels were different with the different fracture mechanism such as SCC and HE. It was found that the linearity of the relationship can be used to predict the time to failure for the stainless steels in the corrosive environment. In addition, type 310 did not suffer from HE, which means that type 310 showed only SCC. This would be explained by whether or not a formation of α′-martensite takes place.