Effect of vanadium on galvanizing Si-containing steels

In the present study, the effect of V additions to the galvanizing bath on the microstructure and growth kinetics of the galvanized coating on Si-containing steels was experimentally investigated. Three different steels with effective Si contents of 0.158, 0.242 and 0.363 wt.%, were immersed for 0.5 to 8 min in Zn baths with four levels of V, ranging from 0 to 0.16 wt.%. The results indicated that V additions could adequately suppress the Si reactivity of all three steels. The potency of V increased with its increasing content in the bath. Crystallites of a ternary compound were found at the ζ/liquid interface.Based on the isotherms of Zn–Fe–V and Zn–Fe–Si–V systems at 450 °C, a diffusion path model was proposed to interpret the effect of V on galvanizing pure Fe or Si-containing steels. V in the bath introduced a new equilibrium state between the liquid and a ternary phase T and made the equilibrium state between the liquid-ζ phases metastable. Furthermore, the greater solubility of Si in T made the diffusion path more difficult to enter the (ζ + T + Liq. + FeSi) region and, thus, protected the integrity of a normal coating.