Influence of Accumulated Strain on the Fracture Behavior of Low‐ and Medium‐Carbon Steels Processed by Equal‐Channel Angular Pressing

Herein, commercial ferritic–pearlitic unalloyed low‐carbon and medium‐carbon steel samples containing a machined U‐shaped notch are subjected to equal‐channel angular pressing (ECAP) under varying total strains. The impact toughnesses and fracture surface structures of these samples are assessed through Charpy impact testing and scanning electron microscopy. The given results show that during the first pass of ECAP, the impact toughness decreases sharply. However, as the total strain in the ECAP process increases, the impact strength increases to ≈60% of that in the initial coarse‐grained (hot‐rolled) state. In low‐carbon steel, the fracture mechanism changes from ductile to ductile–brittle and then to predominantly ductile. In medium‐carbon steel, the fracture mechanism varies from brittle to ductile–brittle. Moreover, the strength characteristics in the low‐carbon steel increase by 90%, whereas those in the medium‐carbon steel increase by 50%. The observed effect is explained by the intense structural refinement of the ferrite component due to the formation of shear bands and ultrafine grains, for which the volume percent increases with increasing strain.