Developing High-Strength in a Deep Drawing Steel by a Post-Cold Rolling Nitriding Treatment

This study deals with the development of high strength in a Low-Carbon Deep Drawing Quality Special Killed - Fully Stabilized steel sheet [DDQSK-FS (Interstitial Free type)] by a novel internal nitriding process. The unique feature of this method is that strength is imparted to cold rolled steel by a nitriding treatment after annealing without affecting its texture, resulting in a high strength drawable sheet. Strength of the generic Interstitial Free type sheet (stabilized with M = Ti, Nb or V) is increased by the controlled precipitation of coherent MN in ferrite, and the level of the strengthening can be predicted based on alloy chemistry and the nitriding conditions. Results of both laboratory and plant nitriding trials at U. S. Steel's (USS) Irvin Plant Open Coil Annealing Facility are presented.