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 beh avior of Ti-added IF steel sheets was studied. Recovery-, nucleation- and grain growth-rates were measured separately in order to clarify th e effect of B on recovery and recrystallization process. Grain size of hot band was constant regardless of B addition. However, Lankford val ue (r-value) of annealed steel sheets was lowered with increasing B co ntent. Recrystallization finishing temperature rose remarkably with in creasing B content up to 5 ppm, and gradually over 5 ppm. Recovery rat e was not varied with increasing B content up to 5 ppm, and decreased over 5 ppm. Nucleation rate of recrystallized grains decreased drastic ally with increasing B content up to 5 ppm, and slightly decreased wit h increasing B content over 5 ppm. Growth rate of recrystallized grain s 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 b oundary of hot band and to the boundary of nuclei, respectively.