Effect of Alloying Elements On The Plastic Anisotropy in Super Formable if Hight Strength Steel Sheets

摘要

As a greater concern in global environmental problems has developed, considerable endeavors for reducing the weight of car-body have also steadily increased. To reduce the weight of a car-body, the use of materials with higher strength is desirable. However, it is very difficult to achieve the strength and formability at the same time because an increase of strength generally deteriorates formability. Therefore, the application of high strength sheet steels to the floor, fender and/or quarter panels, which is required much higher formability, is not easy due to the lack of formability. The purpose of this research is to develop a super-formable high strength cold rolled sheet steel with excellent drawability. The mechanical properties and precipitation behaviors of Interstitial Free(IF) steels with various contents of Ti, Nb, Mn and P were investigated. In addition, the effects of processing conditions such as the cold reduction ratio and the annealing temperature on the formability were investigated. The improved mean r-value was obtained in Ti content ranging from 0.015 percent to 0.025 percent in Ti-0.01 Nb steels. The r-value increased remarkably with an increase of Ti content up to 0.02 percent and then slowly decreased with Ti content above 0.02 percent. It was considered to be related to the non-scavenging in carbon and FeTiP precipitates. Furthermore, the mean r-value was increased with an increase of P content due to the refined grains in hot band.