A CRITERION FOR INTERGRANULAR BRITTLE-FRACTURE OF A LOW-ALLOY STEEL

The intergranular brittle fracture behaviour of a A533 B Cl 1 steel wa s investigated by applying a temper embrittlement heat treatment to si mulate the presence of local brittle zones (ghost lines) in the as-rec eived material. This heat treatment produced an embrittled material th at failed by an intergranular mode at low temperature. An increase in the Charpy transition temperature and a significant decrease in fractu re toughness were observed in the embrittled steel as compared to the as-received material. Tensile tests on smooth specimens and on notched bars were carried out to determine the critical stress corresponding to brittle intergranular fracture and to investigate the scatter in th e results. It is shown that the mean value of the critical stress seem s to be an increasing function of temperature. A statistical model, th e Beremin model, initially proposed to describe brittle cleavage fract ure was applied to intergranular fracture. Modifications are introduce d in this model to take into account the temperature dependence of the critical stress. It is shown that this modified model is able to pred ict the temperature dependence of fracture toughness and the scatter i n the experimental results.