The effect of the grain size of the ferritic-pearlitic steel 45 on the parameters of its fracture under impact loading

The article investigates the influence of the grain size of the ferritic-pearlitic steel 45 with standard composition in the range 2–50 Μm on the parameters of the energy of crack nucleation and propagation in the process of impact loading in the temperature range from ?100 to +150?C. It is shown that reduction of the grain size from 50 to 2 Μm has no effect on the fracture energy and on the “true” specific values of impact toughness at temperatures inducing completely brittle or ductile fracture, and that it increases the fracture energy and KCV_tru solely in the region of temperatures of the viscobrittle transition. Dissipation of the fracture energy expanded on the nucleation of secondary cracks and microcracks has no significant effect on the KCV_tru of the steel in all the examined ranges of grain sizes and temperatures. The article notes the structural insensitivity of the process of crack and microcrack nucleation in steel 45 under dynamic loading.