Modelling effect of hot rolling process variables on microstructure and mechanical properties of low carbon strip steels

The microstructure and mechanical properties of hot rolled strip are determined by the chemical composition and the hot rolling process. Slab reheating temperature and time, roughing delivery temperature, finishing delivery temperature and coiling temperature are the four main variables to be controlled during hot rolling. In the present work a computer aided model has been developed, combining metallurgical phenomena and the thermal evolution process, which can be used to simulate the microstructural evolution and predict the mechanical properties of low carbon steel strip with 0.05-0-25 wt-% C. The developed model has been employed to analyse the effect of the hot rolling process on the microstructure and mechanical properties of the final product. It is shown that slab reheating temperature and time has little influence on the above. Roughing delivery temperature has a small influence on recrystallisation and grain evolution during roughing passes, but no influence on the microstructure and mechanical properties of the final product. Finishing delivery temperature has a larger influence, not only on recrystallisation between finishing passes, but also on subsequent phase transformation after rolling. Coiling temperature has the strongest influence on the microstructure and mechanical properties of the final product, through changing the cooling rate during phase transformation. The present work is helpful for both prediction of mechanical properties and optimisation of the hot strip rolling process.