SCC Behaviour of Sensitized Stainless Steels in Boiling Saturated Magnesium Chloride Solutions

The stress corrosion cracking (SCC) of three sensitized stainless steels was investigated as a function of test temperature in boiling saturated magnesium chloride solutions (MgCl₂) using a constant load method. Both of type 304 and type 316 exhibited similar corrosion elongation curves, while the corrosion elongation curve of type 310 was different. The relationship between the time to failure and applied stress fell in two straight lines on a semi-logarithmic scale as well as the relationship between the steady-state elongation rate and applied stress. These regions were considered to correspond to a SCC-dominated region and corrosion-dominated region. The results were compared to the results obtained for solution annealed stainless steels.

The relationship between the time to failure vs. steady state elongation rate on a logarithmic scale became a straight line, whereas the slope of the line for the stainless steels was similar the slope obtained for solution annealed stainless steels. 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. From the results obtained, it may be suggested that the cracking mechanism for sensitized stainless steels is similar to the cracking mechanism in solution annealed stainless steels in boiling saturated magnesium chloride solutions.