Grain-Boundary Segregation and Temper-Brittle Fracture in a Low-Alloy Steel

AbstractConventional measurements of the degree of temperembrittlement suffered by a steel are made in terms of the shift of the notched-bar “fracture appearance” transition temperatures (FATT). Any fundamental explanation of temperembrittlement must be concerned with the lowering of grain-boundary cohesion by the segregation of impurity. elements to grain boundaries over a critical temperature range, typically 560–430° C. The use of transition shifts to estimate the kinetics of reduction of grain-boundary cohesion can be criticized on several counts. First, it is often the case that the unembrittled condition breaks by cleavage rather than by intergranular fracture at low temperatures, so that no measure of the unembrittled grain-boundary cohesion can be obtained. Secondly, even if both fractures are intergranular, the shift compares fracture events at different temperatures and there is no guarantee that the relative grain-boundary cohesive strengths do not change with temperature. Thirdly, the temper-b...