Abstract: The formation of the grain-boundary structure of low-carbon steels occurs through the processes of heating, hot deformation, subsequent polygonization, recrystallization, phase transformations, temperature conditions of austenite decomposition, which determine the state of grain boundaries in products, their physical and service properties. Electron microscopy (transmission microscopy TEM) methods studied the effect of variable factors (ε, τ, t), as well as the relative amount of special low-energy boundaries in the ferritic and martensitic components of low-carbon steels in the concept of CSL (Coincidence Site Lattice). The optimal performances of thermoplastic deformation have been established, as a result of which the polygonization process takes place – a change in the configuration of grain boundaries, the formation of low-angle polygonal borders, interaction between themselves and high-angle, and special boundaries. The developed heat treatment performance provided an increase in impact hardness, both of the base metal and the heat-affected zone of lowcarbon steels such as steel 10ХФТБч (Standard of Ukraine). This is due to the appearance of special boundaries – twin, sigma 5 and others, as well as the occurrence of polygonization. It is shown that triple joints are more stable and play a large role in the formation of the final structure of low-perlitic steels, the border is 120 о.
Authors: Sergiy Shejko, Valerii Mishchenko, and George Sukhomlin
Keywords: low-alloyed steel, special grain boundaries, plastic deformation, grain boundary structure, polygonization, phase composition