1994 Volume 34 Issue 1 Pages 123-131
For the weight reduction of automotive body, an ultra-low C Ti-added cold-rolled sheet steel with a tensile strength of 450 N/mm2 has been developed by means of adding P and Mn together. In order to develop the sheet steels of higher tensile strength, the effect of Si on the mechanical property of the ultra-low C Ti-added sheet steel has been studied by using steels containing 0.05-1.5 mass%Mn or 0.07 mass%P and coiled at 500°C in the hot rolling process. As a result it has been found, that ultra-low C Ti-added IF sheet steels with Mn ranging from 0.05 to 1.5 mass% exhibits maximal mean r-value at a medium Si content, which increases with the Mn content. This change in the r-value with the Si and Mn is illustrated in terms of the Mn-C dipole formed at 600°C during heating stage of continuous-annealing. With decrease in the Mn-C dipole the r-value increases. Then it is concluded that the Ar3 transformation temperature should be controlled to be about 900°C and the Mn content should be as low as possible for the improvement of deep drawability.