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

Abstract

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.