Coating microstructure development during Zinquench galvanising of sheet steel

The influence of an elevated strip entry temperature on the kinetics of the galvanising reaction has been investigated for a titanium stabilised, inte rstitial free steel. Elevated strip entry temperatures (> 550 degrees C) ha ve been shown to accelerate greatly alloying between the substrate and the molten zinc, increasing the growth rate of the delta phase from 1 to simila r to 7 mu m s(-1) and preventing the formation of the zeta phase. The subst antial Fe-Zn phase layer seen at the coating/substrate interface at high st rip entry temperatures (> 550 degrees C) is attributed to the dissolution o f iron from the substrate into the molten zinc in the first second of immer sion, and the limited inhibition provided by the bath aluminium content(< 0 .15 wt-% effective). I&S/1455.