Special aspects of thermal treatment of steel for hot forming dies production

Abstract

Abstract It was found the influence of heat treatment parameters on the structure and properties of perspective die steel for hot working 70Cr3Mn2WTiB. It was specified the optimal mode of heat hardening for hot working hammer die from offered steel including spheroidizing annealing by the temperature of 780 °C with furnace cool up to 550 °C and then in a smooth air to the normal temperature; hardening by 1000 °C with cooling in oil; high-temperature tempering by 550–600 °C with cooling in a smooth air. During the hardening the formation of lath martensite with the high density of dislocation and the hardness HRC 57–62 occurs however it stays 0, 5–0,6% insoluble carbide phase. It’s shown that at the stage of high-temperature tempering by 550–600 °C in steel 70Cr3Mn2WTiB can be seen the process of hardness stabilization through the formation of special complex carbide intermetallic inclusions. The analysis of carbide phase by the temper showed that the combinations of type Me7C3 and Me3C are carbides the composition of which is changing during thermal influence. Thus, some atoms Fe and Cr are changed by titanium and vanadium atoms at different ratio. The simulation of temperature stressed condition of hammer die by thermal treatment was made. It’s shown that the offered mode of thermal treatment of steel 70Cr3Mn2WTiB leads to dispersed ferrite cementite structure with dispersed in it special carbides, high level of mechanical characteristics, provides homogeneous spreading of heat isotherms in extent of the hot deformation stamp and as a consequence insignificant inner residual strength. At the stage of high-temperature soak the temperature difference reduces to 25–30 °C.