Evolution of the Microstructure and Mechanical Properties of the Ultrafine-Grained VT8M-1 during Isothermal Die Forging and Thermal Treatment

Abstract

The work addresses the microstructural evolution and mechanical properties of the ultrafine-grained (UFG) VT8M-1 subjected to isothermal die forging (IDF) and subsequent thermal treatment. An UFG microstructure with a mean size of secondary grains of about 0.3 μm was processed by a rotary swaging (RS) at Т=780°С. The ultimate tensile strength (UTS) of the alloy increased by 23% as compared to an initial state due to the formation of an UFG microstructure. It has been shown that isothermal die forging of the UFG alloy at Т=780°С leads to the growth of secondary phase grains by 0.7 μm. Subsequent heat treatment of the forged billets leads to hardening of 11%, which can be attributed both to the formation of additional interphase α/β boundaries at the precipitation of a tertiary α-phase and silicide dispersion.