Studies of interface reactions between zinc and reduced red scale on a Mn/Si dual phase steel

- Interaction of reduced oxide scale with Zn (0.2%Al) on Mn/Si steel was investigated.
- The oxide scale with reduced annealing can be directly galvanized without pickling.
- Fe/Al phase exists on the reduced normal scale region after galvanization.
- Γ-Fe4Zn9 phase is strongly attached to FeO particles in reduced red scale region.

In the present study, the reduction behaviors of red scale and the galvanization behaviors on the reduced red scale region are investigated on the Si and Mn based dual phase steel. The experiments are conducted using an Iwatani simulator. After annealing in 30 vol% H2 at 800 °C for 120s, most of red scale can be reduced to iron but some residual FeO and SiO2 still exist at the scale/substrate interface. By microstructure analyses after they have been galvanized, Fe, Mn and Si oxides and pure iron are observed at the interface. Fe/Zn alloy is strongly attached to the FeO contained particles from the reduced oxide scale. It indicates that zinc can be selectively coated on the oxide which can be reduced more easily. A significant factor in the galvanizing of these steels has been determined to be the oxidation state of the alloying elements. The galvanization reactions taking place at the bath/substrate interface will be discussed.