Development of Nb Added Ferrite-Bainite Steels and their Automotive Application

The dual-phase steel was expected to have the potential to reduce wheel weight, but has not completely succeeded in doing so, in part, because of localized necking and fracture that occurs when the welded hoop is stretched during the initial flaring and the last rim rolling operation.

In order to solve these problems and to develop a new type of steel for wheel, especially for wheel rim, the effect of the nature of low temperature transformation products on the mechanical properties, stretch-flangeability, fatigue strength and flash butt weldability of multi-phase steels has been studied.

These studies show that Nb added ferrite-bainite sheet steel is preferred to dual-phase steel in fabrication of wheel rim and disc from the point of view of its lower production scrap rate and its lower cost.