Effects of Prior Cold Rolling and Post Temper Rolling on the Properties of Continuously Annealed Low Carbon Dual Phase Steel

Abstract

The effects of two processing variables, prior cold reduction and temper rolling, on the mechanical properties of a continuously annealed 0.05 pct C low alloy dual phase steel were studied. It was found that cold rolling affected the strength of the dual phase steel through its influence on the recrystallized ferrite grain size. The correlation between yield strength and mean free path in ferrite was shown to follow a Hall-Petch type relationship. Similarly, temper rolling also had a pronounced effect on the yield strength of the steel. The effect was strongly dependent upon the previous overaging treatment; the lower the overaging temperature, the stronger the effect. Basically, the effect of temper rolling on dual phase steel was not much different from that on mild steel and HSLA in terms of the change in yield strength and yield point elongation. Another interesting observation was the influence of quenching rate on the strength of the dual phase steel. A slower quenching rate in the heavier gauge dual phase steel caused pearlite rims to form around martensite colonies and thus decreased the strength of the steel.