Effect of auto-tempering on the cold roll-ability of medium-Mn steel

ABSTRACTRecently, medium-Mn steels have attracted attention for high-strength automotive components. However, because they exhibit martensitic microstructure at room temperature, low cold roll-ability is concerned so that annealing or tempering is often performed before cold rolling. Therefore, we investigated whether cold roll-ability can be improved by adjusting coiling condition in the hot rolling process. For comparison, some specimens were water-quenched or air-cooled after hot rolling. While the water-quenched specimen revealed cracks at ∼30% cold reduction, air-cooled and coiling-simulated specimens at high reductions above ∼68%. This is because the latter had lower and wider ranged hardness values compared to the former due to partial auto-tempering occurring after coiling. The higher coiling temperature caused higher cold roll-ability probably due to the active recovery of austenite.