Effects of Roughing on Finish Rolling Simulations in Microalloyed Strip Steels

The effects of a roughing pass in hot rolling simulations were assessed in VN and Nb-Ti steels. Continuous cooling phase transformation temperatures, flow curves, softening mechanisms (dynamic transformation DT and dynamic recrystallization DRX), and deformed microstructure morphologies were analyzed. The application of one or more roughing passes eliminates the effects of prior microstructural history and ensures that all stock material experiences equivalent hot working conditions and state of the microalloying elements. It has been shown that roughing in hot simulation has the following positive influences: (1) provide more reliable flow stress data; (2) give greater consistencies and accuracy in analysis of softening mechanisms giving three distinct regimes (DT regime at temperatures below 800 °C, DT/DRX inter-mode regime between 800 and 950 °C and DRX regime for temperatures above 950 °C for VN steel); (3) promotion of softening mechanisms as evidence by low critical strains (${\epsilon }_{\text{c}\text{DT}}$ was within the range 0.08-0.12, while for finishing-only pass, the ${\epsilon }_{\text{c}\text{DT}}$ was in the range of 0.11-0.14 at $\dot{\epsilon }=0.1$ s⁻¹); (4) for roughing and finishing schedules, DT was verified to occur at temperatures 117 and 133 °C above $A{e}_3$ for VN steel and Nb-Ti steel, respectively, compared to the F-only schedules which showed that DT can only occur at temperatures below the $A{e}_3$; (5) RF schedules promoted uniform microstructural morphologies compared to inhomogeneous microstructures realized in F-only schedules.