Dynamic recrystallization behavior during hot deformation of as-cast 4Cr5MoSiV1 steel.

The dynamic recrystallization behavior of as-cast 4Cr5MoSiV1 steel was studied by hot compression tests conducted at various temperatures (900–1150 °C) and strain rates (0.01–10 s−1). Flow stress curves and microstructural observation were employed to experimentally identify the various flow mechanisms during deformation. A revised Sellars' constitutive equation was adopted to construct the thermal activation energy map, which considered the effects of deformation temperature and strain rate on the material variables. The Johnson–Mehl–Avrami-Kolmogorov (JMAK) type equation X D = 1 - exp [ - k (ε - ε c ε p) m ] , (ε ≥ ε c) was applied to characterize the evolution of dynamic recrystallization (DRX) volume fraction. The nucleation of DRX was performed by the bulging, sub-grain swallowing. The presence of dendrite segregation would affect the DRX to a large extent that the segregated alloying elements and carbide precipitates inhibited the migration of boundaries. The thermal activation energy varied from 4310 to 470 kJ/mol and the thermal activation energy increased sharply at temperature below 1000 °C due to the dendrite segregation. By further analysis of the true stress–strain curves, the material constant m in JMAK type equation was determined to be 1.29366, indicating the DRX was difficult. [ABSTRACT FROM AUTHOR]