Stress Corrosion Cracking of 304L Austenitic Steel and the Martensite Transformation

Studies have been conducted on the failure of notched and annealed rods of 304L austenitic steel stressed in tension in an aqueous solution of MgCl2 boiling at 154 C (309 F). The phases present on the actual fracture surfaces were studied by electron diffraction techniques. Martensite etching techniques were used to detect the presence of martensite phases adjacent to stress corrosion cracks and to relate stress corrosion crack topography with the morphology of martensite formation. The observations were consistent with a mechanism of stress corrosion cracking involving formation of b.c.c. α′ -phase adjacent to the crack tip and subsequent propagation of the crack through this phase. The possible mechanism by which α′-phase is formed and the possible mechanism of crack propagation through the α′-phase are both discussed.