Simulation of Hot-band Microstructure of C–Mn Steels during High Speed Cooling

The evolution of microstructure in a range of C–Mn steels during hot strip rolling and subsequent high speed cooling was simulated by quench dilatometry using cooling rates up to 600°C/s. The influence of coiling temperature on the microstructure and mechanical properties of the hot band was also investigated by interrupted cooling experiments. Continuous cooling transformation (CCT) diagrams for a range of cooling schedules were constructed for each steel where it was found that rapid cooling lowers significantly the Ar3 temperature, refines the ferrite to grain sizes in the range 3–6 μm and increases the hardness. An increase in Mn content (mass %) from 0.45 to 1.0% lowers the Ar3 temperature, retards the rate of γ→α transformation and promotes the formation of non-equilibrium phases. The role of alloying additions, in combination with cooling rate and coiling temperature is discussed in the context of microstructural development and strengthening of as-hot-rolled C–Mn strip.