Dynamic recrystallization and microstructure evolution of a Nb-V microalloyed forging steel during hot deformation

In this study, a forging steel alloyed with both Nb and V was used as experimental material and the hot deformation behavior has been studied for this steel by conducting the compressive deformation test at temperature of 900-1150s-1s-1 in a MMS-300 thermo-mechanical simulator. The microstructure evolution, particularly the dynamically recrystallized microstructure, of the experimental steel at elevated temperatures, strain rates and strain levels, was characterized by optical microstructural observation and the constitutive equation in association with the activation energy and Zener-Hollomon parameter. The curves of strain hardening rate versus stress were used to determine the critical strain and peak strain, and their relation was connected with Zener-Hollomon parameter. Under the conditions of processing temperature 900 ocand strain rate 0.01 s-1, the dynamic recrystallization took place and the austenite grain size was refined from 164.5 <i>&#181;</i>m to 28.9 <i>&#181;</i>m.