Development of 780MPA Grade Galvannealed Dual Phase Steels for Automotive Structural Parts

by K.C.Yang, H.C. Cheng

Publisher - China Steel Corporation, Kaohsiung, Taiwan

Category - General Novel

Recently, light-weight and energy-saving requirements for the automobile industry are extremely important in order to protect the environment by a reduction of the emission of CO2. One of this ways to attain the aim is the reduction of steel thickness, but maintaining safety must be the prerequisite. In order to simultaneously satisfy these requirements, high strength steels are used. Among these, dual phase (DP) steels have attracted much attention due to their superior properties. Hot-dip galvannealed steels, moreover, have been widely used for corrosion resistance. In this study, the annealing simulations were first performed to investigate the effect of alloying elements. After comparing simulated steels, several mill trials were carried out with an appropriate composition. The developed 780MPa grade galvannealed DP steel with the good bendability, hole expansion ratio and powdering resistance can be stably produced. After performing the mold trial of the front rail, the part showed no fracture and small springback which had been overcome. The result confirms that the developed 780MPa grade galvannealed DP steel can meet the requirement of automotive structure parts.

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