Influence of the Thermal Deformation Treatment on the Structural State and Properties of Ti-Mo Microalloyed Steels of the Ferritic Class

Abstract

Abstract Investigation on influence of thermal deformation treatment on the special features of structural state, phase precipitates, strengthening mechanisms, and mechanical properties was carried out for low-carbon Ti-Mo microalloyed steel of ferritic class. The following parameters were analyzed: the finishing temperature of rolling and the cooling rate of the steel after rolling end to the coiling temperature. Methods of scanning and transmission electron microscopy, thermodynamic calculation, kinetic analysis, and testing of mechanical properties were used. It was shown that with an increase in the cooling rate from 3 to 22 °C/s, the type of carbide precipitates changes from interphase to ferritic. When fast cooling is applied, mainly mechanisms of dislocation and grain boundary strengthening are realized. When cooling is slowed down, the fraction of precipitation hardening increases. It was established that ferritic precipitates make a smaller contribution to precipitation hardening of steel than interphase ones. To create conditions favorable for the formation of interphase precipitates, the rates of γ → α phase transformation and cooling should be close.