Per: julio cezar de sousa zorzi (Usiminas), Henrique Lacerda Eleutério (Usiminas), Tairine Berbert Tavares (Usiminas)
Abstract:
Usiminas has been continuously working on the development and application of advanced high strength steels (AHSS) for automotive industry, aiming to combine the increase of safety requirements with the reduction of vehicle weight. In this context, the hot stamping process emerged as an alternative route for the production of auto parts with complex geometry and high mechanical strength. It is known that the 2 GPa tensile strength steel can result in a vehicle weight reduction from 15% to 20%, when compared to others hot stamped steels grades. Then, to reach this strength level, it was developed, in laboratory scale, two galvannealed steels with different conceptions, combining chemical composition and microstructure with processing parameters of hot stamping. It was obtained for both steels an excellent structural integrity, compatible with the one required for hot stamped materials. This result allows the application of the developed steels in the automotive industry, according to the VDA 238-100 standard requirements. Moreover, the application of a hot-dip galvannealed coating, suitable for the hot stamping process, enhanced the protection's efficiency against decarburization and oxidation during the stamping process. It also contributed to the increase of corrosion resistance during the auto part life cycle.