Effect of submicrocrystalline state on strength and impact toughness of low-carbon 12GBA steel

The effect of intense warm deformation on the structure and mechanical properties of low-carbon 12GBA steel was investigated. A submicrocrystalline (SMC) structure with an average element size of 0.3 μm was formed in the steel by isothermal overall forging. The formation of the SMC structure resulted in a sharp increase in strength by a factor of two to three in relation to the initial coarse-grained state while retaining a sufficient level of plasticity and impact toughness. After further annealing, steels exhibit an improved set of properties; i.e., as the strength decreases slightly, the plasticity increases sharply. Impact tests at low temperatures have shown the significant advantage of the SMC state of the steel over the coarse-grained state in the impact toughness. It is established that the cold resistance in the SMC state increases because the crack propagation prevails in the overall sample fracture.