Wetting Characteristics of Aluminium-killed Steel with Molten Zinc

Abstract

Relations between Al-enrichment to the surface layer of Al-killed steel sheets during short-time heating in an H₂-N₂ atmosphere and its wetting characteristics with a molten zinc were studied in connection with the surface structures of the steel sheets.
1) The wettability of Al-killed steel sheets with the molten zinc after the reduction-heating for a short time varies depending on the Al concentration of the surface layer. It is degraded in accordance with the thickness of aluminosilicates which is formed on the surface layer.
2) While the degree of Al-enrichment is notably increased by heating at temperatures above 800°C, the wettability does not decrease. In this case, the film consists of a defect spinel type structure of <111> oriented γ-Al₂O₃ which is partially substituted with Fe at the vacancy site.
3) The degree of Al-enrichment to the surface layer varies depending on the quantity and the state of Al in the steel sheets. When Al is stabilized as AlN, the Al-enrichment by reduction-heating is significantly depressed.
4) The wettability does not decrease after the partial oxidizing treatment which forms visible oxide films on the steel surface, followed by the reduction-heating.