Determination of Facet Plane and Cleavage Fracture Plane of the Top Dross Formed in a Molten Zinc Bath

Abstract

In a molten zinc bath of a continuous galvanizing line, top dross particles crystallize as Fe₂Al₅, an intermetallic compound containing Zn. These particles readily adhere to the steel sheets, causing surface defects. Therefore, controlling the top dross particles is a key issue. The present study focused on determining the facet plane of top dross particles via three-dimensional analysis of morphology by serial sectioning and electron back scattering diffraction (EBSD). Furthermore, the crystallographic plane of the cleavage fracture surface of the top dross was determined by EBSD, after a cleavage crack was introduced by Vickers hardness indentation. The facet planes of the top dross consist of two planes of (001), four planes of {110}, and eight planes of {111}. In addition, the top dross particles grow fastest in the [001] direction. Consequently, the top dross particle was concluded to possess a polyhedron structure with 14 facet planes. Finally, the cleavage fracture surface of the main crack in the top dross is the (100) plane.

(a) Trace analyses of a top dross particle with near ND//[001] showing four {110} facet planes and (b) their orientations in inverse pole figure. (c) Trace analyses of a top dross particle with normal direction perpendicular to (110) plane showing two (001) facet planes, two {110} facet planes and four {111} facet planes and (d) their orientations in inverse pole figure.