Development of 590MPa grade DP GA steel for automotive outer panel use

  • M. B. Moon
  • S. W. Lee
  • S. J. Park


Recently high strength steels with high formability for automotive parts have been being developed to meet the
demands of passenger safety and weight reduction of car body. Among these high strength steels, dual
phase(DP) steels are regarded as one of the attractive steels due to their excellent mechanical properties
including high strength and ductility. However, typical high strength steels contain strengthening elements that
forms surface oxide and thus deteriorate galvanizing property. Galvanizing of high strength steel is required to
satisfy corrosion resistance of automotive body. Typical outer panel parts requiring anti-dent property are
comprised of 340MPa grade bake hardened(BH) steel, but the trend of lightweight car body drives steels to
have higher strength for outer panel use. 490MPa grade DP steel is beginning to be applied into some
automobiles, and 590MPa grade DP steel is a good candidate for the future outer panel material. In this
study, several kinds of alloys for enhancing galvanizability were produced in the laboratory scale, and the
effects of continuous annealing conditions in CGL on the mechanical properties were investigated. The
microstructure and phase distribution were examined with SEM, EBSD, TEM and so on. Line trial production
was conducted with the selected chemical composition of steel. Formability, weldability and CAE analysis of
steel sheet was also performed. Through the study, the production of 590MPa grade dual phase galvannealed
steels with good formability and galvanizability was shown to be possible.