Critical stress for delamination fracture in HSLA steels

Abstract

Analysis of the behaviour of four classes of HSLA steels showing delaminations led to the conclusion that this type of fracture generally follows a critical tensile stress criterion, whose value has been accurately measured in all cases.

Plastic anisotropy and elongated non-metallic inclusions, while they appreciably increase the likelihood of delaminations occurring, do not seem to be the causes of the necessary lowering of the critical fracture stress along the through-thickness direction. Instead, it appears that an important source of delamination fracture might be the dimensional anisotropy of the microstructural unit which controls fracture: polygonal or acicular ferrite ‘grain’ (transgranular cleavage) or prior austenite grain (intergranular failure).