Analysis of Fracture Surface in Stress Corrosion Cracking of Austenitic Stainless Steel

Abstract

The crack morphology of the stress corrosion cracking of commercial 304-type austenitic stainless steel in boiling 42% magnesium chloride solution changes with the increase of the applied stress.In this paper it was intended to attest that this transformation depends upon the stress intensity factor at the crack tip, and to inspect whether the crack propagation proceeds along a particular crystallographic orientation. The ratio of intergranular cracking to transgranular one was measured on the single notched specimens fractured under various loads such as 2940, 3920 and 5880N.The relation between the crack morphology and the stress intensity factor at the crack tip was investigated, and the dependence of the crack propagation upon the crystallographic orientation was inspected by the etch pit method on the crack surface of the specimen fractured under the initial load, 2940N.The following conclusions were obtained from this experiment: The crack morphology transformed remarkably from transgranular cracking to intergranular cracking with increasing applied stress or the stress at the crack tip, and the degree of transformation was closely connected with the stress intensity factor at the crack tip.The transgranular cracking in the low stress region was likely to be formed by the crack growth following along direction on {110} planes, and the facets formed on the crack surface due to this dependence of crack propagation upon crystallographic orientation.These results indicate that this crack morphology was formed by the anodic dissolution of the sessile dislocation part and the tearing of the undissolved parts by stress.