Stress Corrosion Cracking of 304 Austenitic Stainless Steel in H₂SO₄/NaCl Media at Room Temperature

The effects of Cl⁻ ion concentration, H₂SO₄ concentration, the applied potential, and the strain rate on the stress corrosion cracking (SCC) of 304 stainless steel were investigated. The postfracture scanning electron microscope micrographs of the fractured surfaces revealed that solutions of high H₂SO₄ concentration combined with low Cl⁻ ion concentration resulted in corrosion (active dissolution), while solutions of very low H₂SO₄ concentration combined with a relatively moderate Cl⁻ ion concentration resulted in ductile failure. Solutions with moderate concentrations of H₂SO₄ and Cl⁻ ions resulted in transgranular SCC. The susceptibility to SCC and the fracture surface morphology were found to depend on the [H₂SO₄]/[Cl⁻] ratio, the strain rate, and the applied potential. The average crack-growth rate (ACGR) was found to depend on the strain rate and the applied potential. For specimens undergoing SCC at the open-circuit potential, the ACGR increased with increasing the strain rate. For specimens undergoing SCC under applied potential in the active range, the ACGR increased with increasing the applied potential. The specimen eventually failed in a ductile manner when tested under an applied anodic potential in the passive range. The increase in the ACGR with increasing strain rate and the applied anodic potential is attributed to the enhanced dissolution at the crack tip. Moreover, secondary cracks formed when relatively high strain rates were used. The secondary cracks are believed to propagate mainly along the slip planes. The fracture surface morphology shows the {110} planes are the preferred fracture planes, with the fracture surface consisting of parallel facets separated by steps. Finally, the results indicate that hydrogen may play an indirect role in SCC.