Practical method for producing galvanised dual-phase steels with superior strength – ductility combination

Abstract

It is a challenge to produce galvanised dual-phase steels based on lean chemistries and with consistent mechanical properties over the entire coil length. A practical method was developed using hot band annealing (HBA) in the ferrite/austenite two-phase region before cold rolling and intercritical annealing. The HBA brings several benefits to the production of galvanised dual-phase steel sheets. First, a finer and more homogeneous microstructure can be obtained. Second, a higher tensile strength is yielded with a similar ductility to the sheets without HBA. The sensitivity of mechanical properties to the annealing parameters such as annealing temperature and cooling rate can also be reduced. Finally, the effect of the microstructure on the strain hardening behaviour was analysed.