EFFECT OF OXIDE SPECIES AND BATH TEMPERATURE ON REACTIONS IN A GALVANIZING BATH OF SI-CONTAINING STEEL(58)

摘要

Reaction behavior was investigated in a galvanizing bath between Si-containing steel and moltenZn, in order to understand the influence of Si oxides and solute Si on galvanizing reactions. For the0.2Si steel, only MN_2SiO4 formed on the surface of the substrate after reduction annealing. Aftergalvanizing, the Fe amount in the coatings slightly increased with the rise of the bath temperature. Incontrast, the Al amount at the substrate/coating interface (interfacial Al) decreased. As suchbehavior is similar to 0.01Si steel, it was suggested that the influence of MN_2SiO4 on a galvanizingreaction is small. For the 1.2Si steel, on the other hand, SiO2 formed on the surface of the substratein addition to MN_2SiO4 after reduction annealing, and the galvanizing reaction was quite differentfrom other kinds of steel. Although both the Fe in the coatings and interfacial Al were much lowerbelow 450oC, the Fe in the coatings increased sharply with a rise in bath temperature to more than460oC. As SiO2 was detected on the coating/substrate interface, even after galvanizing at 470oC forthe 1.2Si steel, it was considered that SiO2 exhibits a barrier effect on the reaction in the bath.Furthermore, for the 1.2Si steel, the Fe-Zn compounds seemed to form easily compared to otherkinds of steel. It was implied that the balance of stability between the Fe-Zn compounds and Fe-Alcompounds was changed by the solute Si in the substrate in addition to Si oxides.