Scale levels of deformation and fracture and mechanical properties of 25CrlMolV steel before and after nonisothermal loading

In the work, the peculiarities of tensile deformation and fracture of 25CrlMolV steel subjected and not subjected to thermal cycling were studied on the basis of measured mechanical characteristics and data of optical and electron microscopy. It is shown that the deformation of the steel specimens in the initial state features very low strain hardening and considerable elongation at the stage of necking. After thermal cycling, the yield stress decreases, the plasticity grows markedly, and the strain hardening becomes more pronounced. The results of study are discussed with resort to metallographic data. Fractographic analysis suggests that the fracture pattern is governed by regularities of the nucleation of micropores, their coalescence, and formation of a central opening mode macrocrack. According to the experimental results, the specimen is fractured by a mixed “local shear - cleavage” mechanism and the character of fracture is strongly affected by secondary microcracking and severe intragranular plastic deformation. On the basis of the obtained results, a model of structural levels of deformation and fracture of the specimens under static tension is proposed.