Laboratory investigations on copper-alloyed interstitial free steel part II: Effect of coiling temperature

The effect of coiling temperature on the annealing behaviour of copper-alloyed interstitial free steel has been studied during batch and continuous annealing. The batch annealing kinetics undergoes a severe sluggishness in the so-called industrial low temperature coiling condition, while retardation is less with high temperature coiling. The mechanism is believed to be the particle pinning effect exerted by peak-aged or over-aged copper precipitates. Room and high temperature coiled materials show similar strength and ductility after batch annealing. However, the texture development is different in the two cases, which leads to a variation in deep drawability. Copper precipitation has been observed to give rise to an unusual trend in strain hardening with the progress of batch annealing. The strength and formability parameters of the continuous annealed copper-alloyed interstitial free steel do not depend on the coiling temperature due to dissolution of copper precipitates of the hot rolled material during continuous annealing. Irrespective of the coiling temperature continuous annealed copper-alloyed interstitial free steels are as good as conventional interstitial free steels particularly in formability parameters.