Cracking Process in Delayed Fracture of High-Strength Steel after Long Atmospheric Exposure

This paper is the first microscopic observation of entire cracking process in delayed fracture high-strength steel bolt after long-term atmospheric exposure. A sufficiently fresh surface exhibits initiation propagating crack a thin zone beneath screw groove, resulting from merging multiple cracks nucleated therein. The morphology initially intergranular, exhibiting three-dimensional shape prior austenite grains, but stress and strain states at nucleation sites are not uniquely specified. alters as extends intergranular to quasi-cleavage fine dimples, associated with increasing intensity under constant-displacement condition. change inter- trans-granular continuous, implying affinity among different morphologies increased density distribution potential front. propagation dimple regions step-wise about 50 µm per step. Recent studies function hydrogen embrittlement referred respect accumulation strain-induced damage. enhanced generation vacancies presumable compatible present findings.