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Ultra high strength steels have contributed to weight reduction in automobiles. However, due to the poor formability of these materials, it is difficult to manufacture automotive parts with complex shapes using conventional sheet metal forming techniques such as deep drawing, bulging, and stretch flange forming. In this study, a bend-forming technology which enables forming of complex shapes with ultra high strength steel sheets is investigated. The target part was a front side member extension (FSM EXT) of a white body. The part has a dogleg shape and must provide adequate crashworthiness. The basic structure of the FSM EXT produced by this bend-forming technology was proposed. A bend-forming process consisting of three stages was proposed from the standpoint of commercial production. FSM EXT prototypes showed excellent crashworthiness in FEM simulations and crash tests.

New type of IF high strength steel (HSS) has been developed by hybridizing the grain refinement and the supplemental solid-solution hardening. Grain refinement was achieved by the fine distribution of carbide under the appropriate combination of the higher carbon content near 60ppm and niobium. Although the grain refinement is an effective method to improve the toughness of steel, this method has not been taken into consideration in view of formability. While this steel has the fine grain structure, yield ratio is decreased due to the unique carbide distribution, and r-value is improved by the favorable texture formation. As the result, it has been clarified that a new type of 440MPa grade grain-refined IF-HSS improved the press-formability and exhibited a superior secondary work-embrittlement to the conventional IF-HSS.