Continuous galvanizing of ultrahigh-strength martensitic and complex phase steel sheet

Martensitic and complex phase ultrahigh-strength steels (UHSS) are amongst the most suitable materials for automotive anti-intrusion components such as side impact door reinforcement beams, bumper beams and roof reinforcements for anti-rollover applications. In order to process the above steels in the continuous galvanizing line (CGL), several challenges have to be overcome such as maintaining target strengths (> 1250 MPa) while maintaining a surface with sufficient reactive wetting surface suitable for galvanizing. In the present study the hot dip galvanizability of a candidate UHSS has been systematically analyzed to determine a suitable process window in the CGL. In order to accomplish this goal, microstructural characterization along with mechanical properties as a function of thermal cycles based on their continuous cooling transformation behavior will be discussed. The development of surface chemistry during intercritical or austenitic annealing and its subsequent effect on reactive wetting during galvanizing has also been characterized.