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).
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