Stress Corrosion of Type 304 Steel in H2SO4/NaCl Environments at Room Temperature

The stress corrosion cracking of Type 304 stainless steel in 5N H2SO4 + 0.5N NaCl at room temperature has been studied by scanning electron microscopy. Specimens in the form of thin sheet with two grain sizes were subjected to simple U-bend tests. Cracking was initiated mainly as a consequence of grain boundary corrosion but below the outer layer of grains cracking was mainly transgranular. Crack propagation occurred as a result of the formation of parallel tunnels across a grain. The width of tunnels was greater in the larger grain size material. The subsequent formation of the crack surface occurred partly as a result of tearing of tunnel walls because of the stress component acting normal to the fracture plane and partly as a result of lateral dissolution. Crack propagation occurred across {111} planes in the large grain material quenched from 1300 C (2372 F). Cracking results from the interaction of dislocation pile ups with the environment as a result of which transgranular dissolution occurs more rapidly than grain boundary corrosion. The relative rates of corrosion of these metallographic features are a function of alloy constitution and environment composition.