Abstract
As the first report on the investigation of the bulk materials of iron used in hot-dip galvanizing, the loss of iron by dissolution and into Fe/Zn alloy layers were investigated with electrolytic iron and plain carbon steels which were immersed in molten zinc at 450° and also the loss by dissolution of some pure metals were investigated. And the results are as follows: (Furthermore, the loss of iron by dissolution (L) is shown by loss in weight (mg) of the specimen after the alloy layers were dissolved in SbCl3-HCl solution, divided by the surface area (cm2) of the specimen. (1) The loss by dissolution of pure metals i.e. Mo, W, Cr and Ni, immersed for 2 hours in molten zinc at 450°, amounted to 0, 0.14, 5.7 and 30.1 mg/cm2, respectively. (2) In the case of electrolytic iron, low carbon steel and 1.12% carbon steel, the relation between immersion time (t) and loss by dissolution (L) is of parabolic type i.e. L=k\sqrtt (k is a constant, showed in Fig. 1). The alloy layers formed on the iron surface consist of 3 kinds of compound layers i.e. Γ (21∼28% Fe), δ1 (7∼11.5% Fe) and ζ (6∼6.2% Fe) and the thickness of δ1 layer is substantially the same one another, but in the order of electrolytic iron →0.15→0.07→0.18% carbon steels, the thickness of Γ layer decreases and the thickness and the porosity of ζ layer increase. (3) In the case of hypo-eutectoid steels containing more than 0.4% carbon, 1.4% carbon steel and electrolytic iron (as melted, rolled and annealed), the relation between immersion time and loss by dissolution is of linear type i.e. L=kt (k is a constant, showed in Fig. 1) and loss by dissolution increases with the content of carbon. In their alloy layers there are no Γ layer and a very thin δ1 layer, and the ζ layer with much porosity increases remarkably with the loss by dissolution. (4) In view of the relation between C content and the thickness of the alloy layers (Fig. 4), it is characteristic that the alloy layers on the carbon steels showing little loss by dissolution have a thicker δ1 layer than the ζ layer and contain a Γ layer, and the more compact the alloy layers are, the more anti-attack is the specimen. In summary, it was concluded that the most suitable bulk material made of plain carbon steel was 0.07∼0.15% carbon steel.
