Stress Corrosion Cracking of Type 304 Stainless Steel Weldments in the Active State

Slow strain rate tests (SSRT) were conducted in solutions of hydrochloric acid (HCl) + sodium chloride (NaCl) at ambient temperature on type 304 (UNS S30400) stainless steel (SS) weldments that exhibited a duplex ferrite-austenite structure in the weld fusion zone. Results indicated the weld fusion zone corroded preferentially. Stress corrosion cracking (SCC) initiated and propagated along the ferrite-austenite interphase. Austenitic dendrite was observed by scanning electron microscopy (SEM) in the fracture surface morphology. This interfacial cracking was attributed to the formation of a complex cell structure consisting of weld fusion zone/parent metal with delta-ferrite/austenite in the weld zone. The delta-ferrite was microanodic phase. The proposed model of SCC for type 304 SS weldments in HCl + NaCl was film formation-slip (film rupture)-dissolution-crack propagation. Because of the presence of the complex cell structure, the surface film was nonuniform, which was favorable for crack initiation. SCC propagated faster through the active path of delta-ferrite than through the matrix.