Technical Note: Scanning Electron Microscopic Observation of Fracture Surface of Austenitic Stainless Steels in Stress Corrosion Cracking

Fracture surface of several austenitic stainless steels in stress corrosion cracking (SCC) in MgCl₂ and CaCl₂ solution was investigated fractographically by scanning electron microscopy. Effect of Mo, applied stress, and testing temperature on the fracture mode was studied. Type 304 steel and 310 steel fractured transgranularly in MgCl₂ solution boiling at 143 C (289 F). Transgranular fracture was characterized by a fine parallel pleat pattern. This pattern seemed to be traces of dissolution of metals. Intergranular SCC occurred in Type 316 steel and 16Cr-15Ni-2~4Mo steels, and it was also observed in Type 304 steel fractured at temperatures lower than 125 C (257 F). Intergranular fracture tended to occur with increasing Mo content, applied stress, and lowering testing temperature.