Application of 590/780MPa Grade TRIP Steel to Body-in-White

A highly ductile TRIP steel sheet has been developed and put into practical use to achieve weight savings in automotive Bodies-in-White. During deformation, TRIP steels experience a strain-induced transformation of retained austenite to hard martensite. This TRIP-effect increases the strength of the material and improves the formability by distributing strain over a larger area. In comparison to conventional high strength steel (HSS), TRIP steels have a superior balance between strength and ductility. The TRIP steels newly put into practical use at 590MPa and 780 MPa strength levels had equivalent formability to conventional HSS at the 440MPa and 590 MPa levels, respectively. Also it achieved equivalent coating quality, paintability and spot weldability to conventional HSS. Consequently, it was found that these TRIP steels can feasibly be applied to a wide variety of vehicle parts. The TRIP steels possessed an identical energy absorption characteristics to those of conventional steels in a 10% lighter structure, enabling a more than a 10 kg weight-per-vehicle reduction.