Alloying Behavior of Galvannealed Steel Sheets

Abstract

For galvannealed steel sheets, the properties such as adherence of coated layer depend upon the degree of alloying with base steel.
It is necessary to know the moment of alloying of zinc surface in order to control the degree of alloying.
That moment was detected in the laboratory by measuring the irregular reflection intensity and the emittance during galvannealing of the specimen.
The behavior of irregular reflection intensity generally corresponds to the change of the surface roughness (R_max) during the course of alloying. On the other hand, the emittance increases mainly when the liquid of zinc on the very surface of the coating changes to the crystalline solid such as ζ or δ₁ phase. The change of the former precedes the latter.