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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.

Since galvannealed steel sheets (GA) are widely used for automobile body parts, they require excellent features such as press formability, resistant spot weldability and phosphatability. We have focused on improving the press formability of GA since the late 1990s, and have developed a new type of surface modified GA which has a lower friction coefficient than conventional GA. The developed surface modified GA based on mild steel is now used by all automakers in Japan, especially for those parts such as side panels that are difficult to form. This paper describes the features of the surface modified GA.

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.

A galvannealed steel sheet (GA) with a Ni-base inorganic lubricant film has been developed to meet the needs of the automotive industry, especially for improved press formability. This paper describes the results of tests performed to evaluate formability, spot weldability, phosphatability, paintability and corrosion resistance of the GA with the Ni-base lubricant film. The coefficient of friction as measured by flat sliding test decreases with increasing Ni content in the lubricant film. The spot weldability evaluated by electrode tip life test is slightly improved after the application of the lubricant film. Phosphatability, paintability and corrosion resistance of the GA with the lubricant film are equivalent to those of GA without the lubricant film.