High strength steels for automobile use and the role of microalloying

There has been a steady increase in the amount of high strength steels used in automobile industries in order to meet the strong demands for the weight reduction and the improvement of the crashworthiness of auto-bodies. Various types of high or ultra-high strength steel sheets have been developed for this purpose. It is also well established that these high or ultra-high strength steel sheets should have good press formability, weldabilty and corrosion resistance etc. Phase transformations, precipitations and grain refinement hardenings are used together with solid solution hardening to strengthen the steel sheets with acceptable deteriorations of other properties than strength. Micro alloying is one of the key technologies in this field not only for the strengthening but also for the controlling of microstructures of steels. (AU)