Microstructure and Properties of Ti and Ti+Nb Ultra-Low-Carbon Bake Hardened Steels

Hot rolling, cold rolling and continuous annealing processes of Ti bearing and Ti+Nb stabilized ultra-low-carbon bake hardened steels were experimentally studied. The microstructure and texture evolution, as well as the morphology, size and distribution of second phase precipitates during hot rolling, cold rolling and continuous annealing were also analyzed. The results showed that the size of NbC precipitates in Ti+Nb stabilized ultra-low-carbon bake hardened steel was smaller than that of TiC precipitates in Ti bearing ultra-low-carbon bake hardened steel, which made the average grain size of Ti + Nb stabilized ultra-low-carbon bake hardened steel finer than that of Ti bearing ultra-low-carbon bake hardened steel: for the yield strength, the former was higher than the latter; but for the r value which reflects the deep-drawing performance, the former was lower than the latter.