Slow Strain Rate Stress Corrosion Cracking of Type 304 Stainless Steels

Slow strain rate experiments have been performed on Type 304L and 304 stainless steel sheet material in boiling MgCl2 as a function of solution temperature and strain rate. Additionally, some experiments were performed on specimens containing a single transverse weldment with a duplex δ-γ structure and on all-weld specimens. Results indicate that intergranular stress corrosion cracking (SCC) is observed at temperatures below 135 C and transgranular cracking is observed at 154 C. Corrosion potential measurements showed a shift in the active direction upon yielding indicating a film rupture process, exposing active metal to the corrosive environment. The crack path appears to be determined by the Cl− concentration with higher concentrations resulting in preferential reactions at emerging slip bands and lower concentrations reacting in the vicinity of grain boundaries. Specimens containing a single transverse weld showed cracking in the δ-γ interface at both 135 and 154 C, apparently due to non-equilibrium solute segregation. All welded specimens showed interphase cracking at all solution temperatures.