Temperature effect on impact fracture of 25CrlMolV ferrite-pearlite steel

The paper analyzes dynamic strain diagrams, deformation reliefs and fracture surfaces of 25CrlMolV steel specimens impact loaded at 293, 648 and 873 K. It is shown that the lower relaxation capacity of 25CrlMolV steel under impact loading at room temperature (T = 293 K) causes the specimen to bend with the formation of a compressive stress zone and local longitudinal delamination in brittle fracture ahead of the crack tip. At elevated temperatures (T = 648 K), the specimens feature maximum ductility and increasing fracture energy capacity during the crack nucleation and propagation. At high temperatures (T = 873 K), the maximum softening of the material leads to more intricate fracture mechanisms and to delamination microcracking of the specimen during the crack growth, and this decreases the crack nucleation energy at this test temperature. In view of the findings it is proposed to interpret the observed differences in the context of a leading scale of deformation and fracture and stage character of the developing processes. The temperature effect on the character of fracture is discussed in the context of stress stiffness and scale levels of rotational deformation modes.