2018 Volume 58 Issue 9 Pages 1600-1607
The influence of the Si/Mn ratio on the galvannealing behavior of 1.5 wt% Si −1.5~2.5 wt% Mn-added steel in the Fe oxidation-reduction process was investigated. The Si/Mn ratio of the steel affected the formation of Si-containing oxides during the annealing process. The amount of SiO2 formed on the steel surface decreased with as the Si/Mn ratio decreased, while the amount of Mn2SiO4 increased. In addition, the internal oxide formed in a relatively narrow area near the surface in the lower Si/Mn ratio sample, which indicated that the content of solute Si near the surface was lower in the lower Si/Mn ratio sample. The galvannealing reaction was accelerated by decreasing the Si/Mn ratio of the steel. The species and morphology of the Si-containing oxides determined the galvannealing behavior of the Si-added steel. The Si-containing selective surface oxide affected the formation of the initial Fe–Zn intermetallic compounds (IMC) during hot-dipping in molten Zn. The formation of SiO2 was suppressed in the sample with the lower Si/Mn ratio, which resulted in accelerated Fe–Zn IMC formation. On the other hand, solute Si in the steel affected the growth of the Fe–Zn IMC during heating in the galvannealing process. The content of solute Si was assumed to be lower in the lower Si/Mn ratio sample, which resulted in acceleration of Fe–Zn IMC growth.
