Optimizing Cold Rolling and Mode of Annealing of Interstitial-Free High-Strength Steel Sheets

Abstract

Percentage of cold rolling and mode of annealing significantly influence the formation of structures and textures of steel sheets. The objective is to co-relate the micro-structures and textures at each step of processing and their effect on mechanical properties. In addition, an attempt has been made to distinguish the batch and continuous mode of annealing. In the present investigation, interstitial free high strength (IF-HS) steel was first hot rolled to 85-90%, followed by cold rolling (CR) and then annealed. Annealing was carried out in the batch as well as the continuous mode. It was found that a fine pancake type and strong hot band texture was developed after hot rolling. Its very strong orientations were (332)[(11) over bar3] and (112)[1 (1) over bar0]. An almost uniform alpha-fibre and gamma-fibre were developed at 80% cold reduction. After annealing, the new gamma-fibre was found to be developed replacing the old one for both modes of annealing i.e. batch and continuous. Further, it was observed that the intensity of the gamma-fibre was higher at 80% CR after continuous annealing than after batch annealing. The strain energy introduced during cold rolling could not be removed completely in batch annealing. Therefore, the drawability obtained through continuous annealing was higher than that after batch annealing. The process route of 80% CR and annealing, either in batch or in continuous mode, has developed optimum strength and drawability in steel sheets. Either batch or continuous mode can be used for annealing to cold rolled IF-HS steel sheets, but the latter one is found to be superior to the former one.