Challenges in hot-dip galvanizing of high strength dual phase steel: Surface selective oxidation and mechanical property degradation

In this work, the two challenges in hot-dip galvanizing of high strength dual phase steel such as surface selective oxidation and mechanical property degradation were discussed. It was shown that the external selective oxidation occurred at low dew point − 30 °C caused the full coverage of oxides, which is a problem for reactive wetting by molten zinc. Although increase of dew point to + 10 °C decreased the surface coverage of oxides, the formation of internal oxides consumed the alloying element and accumulated in the subsurface area in a large scale. Furthermore, the heat treatment parameters of hot-dip galvanizing, i.e. cooling rate after inter-critical annealing and the 460 °C-isothermal soaking time influenced the mechanical properties.

► Low dew point − 30 °C annealing caused the surface fully covered by oxides.
► High dew point + 10 °C annealing caused internal oxide accumulated in subsurface area.
► The chemical composition also influenced the segregation and selective oxidation.
► Cr, Mo addition increased the stability of mechanical property after galvanizing.