Microstructure evolution model for hot strip rolling of Nb-Mo microalloyed complex phase steel

A microstructure model for hot strip rolling of an Nb-Mo microalloyed complex phase steel has been proposed. The constitutive behaviour of austenite is described by the Kocks-Mecking model. The static softening kinetics is simulated by a combined recovery recrystallisation model using the law of mixtures. Ferrite transformation start is modelled with an approach that considers the early growth of corner nucleated ferrite. Bainite start is related to a critical driving pressure. Both ferrite and bainite reactions are described using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach in combination with the additivity rule. The martensite fraction is empirically related to the carbon enrichment in austenite and is, thus, a function of the ferrite fraction formed in the final microstructure. Precipitation strengthening during coiling is simulated with a modified Shercliff-Ashby model. The microstructure models for these metallurgical phenomena have been validated with experimental studies of laboratory simulated hot strip rolling conditions and run-out table cooling strategies.