Effects of deformation on stress-strain curve and microstructure of high strength IF steel

The stress-strain curves of high strength interstitial-free (IF) steel were worked out on Gleeble-3800 thermal mechanical simulator with 10 s-1 strain rate, the deformation temperature at 950, 850 °C, and deformation at 30%, 50% and 70% respectively. The results show that the stress-strain curve is a type of dynamic recovery when strain rate is 10 s-1 and deformation is 50%, the type of curve doesn't change with temperature. With the increase of deformation, the increment of flowing stress at 850 °C is far lower than that at 950 °C, the largest flowing stress in ferrite region at 850 °C is lower than the smallest flowing stress in single-phase pure austenite region at 950 °C. The ferrite grain is fine with higher deformation temperature and larger deformation. The deformation resistance increases with increment of reduction when temperature and strain rate are constant. With deformation at 850 °C and deformation at 70%, the static re-crystallization occurs, while dynamic recrystallization occurs when deformation is 70% and the temperature is 950 °C.