Effect of Boron on Mechanical Properties and Recrystallization Behavior of Ti-added Ultra-low Carbon Cold-rolled Steel Sheets

Effect of boron (B) on mechanical properties and recrystallization behavior of Ti-added IF steel sheets was studied. Recovery-, nucleation- and grain growth-rates were measured separately in order to clarify the effect of B on recovery and recrystallization process. Grain size of hot band was constant regardless of B addition. However, Lankford value (r-value) of annealed steel sheets was lowered with increasing B content. Recrystallization finishing temperature rose remarkably with increasing B content up to 5 ppm, and gradually over 5 ppm. Recovery rate was not varied with increasing B content up to 5 ppm, and decreased over 5 ppm. Nucleation rate of recrystallized grains decreased drastically with increasing B content up to 5 ppm, and slightly decreased with increasing B content over 5 ppm. Growth rate of recrystallized grains decreased progressively with increasing B content up to 16 ppm, and was not varied so much over 16 ppm. The suppression in nucleation and growth was thought to be due to the B segregation to the prior grain boundary of hot band and to the boundary of nuclei, respectively.