Fractography of Strengthened Low Alloy Steel Samples after Low-Cycle Tests

Abstract

The problems of fatigue failure of structural low-alloy steel subjected to severe plastic deformation are reviewed. Specimens of steel 09G2S in the delivery state and after hardening by equal channel angular pressing were subjected low-cycle tests with soft loading. Fractographic analysis of fatigue breaks was performed by scanning electron microscopy. We analyzed the influence of the volume hardening by equal channel angular pressing on the surfaces fracture micromorphology of low-alloy steel. It shows the difference in the mechanisms of fatigue fracture of the samples from the initial steel and hardened by equal channel angular pressing, depending on the parameters of cyclic loading. It was found that the character of the fracture of hardened 09G2S steel by equal channel angular pressing, at high numbers of cyclic loading is different from the initial state. At high stresses of cycle and a small number of loading cycles 09G2S steel in the initial and hardened condition is characterized by a quasi-static character of fracture. For hardened steel 09G2S it is significant the difference in the configuration of fatigue fracture zone against the initial sample break and brittle character of fracture at the final stage of a specimen fracture.