Abstract
The structure of the galvannealed coating was studied by etching and measuring the potential time curve for the electro-chemical stripping.
The formation of Γ phase was found to have the following extreme cases :
(1) Γ layer is formed along the Zn/Fe boundary, which was typically shown in 1.6% Mn steel.
(2) Γ grains are scattered in the δ1(c) layer near the Zn/Fe boundary ((δ1+Γ) layer), which is typically shown in P-Nb bearing steel.
The behavior of cracks in the coating was observed after bending. The cracks were generated from the Γ layer or(δ1+Γ)layer.The cracks propagated most easily in the Γ layer, followed by the(δ1+Γ) layer. The length of crack propagating along the Zn/Fe boundary was mainly dependent upon the thickness of the Γ layer. Therefore, the form of Γ phase was found to affect the powdering behavior.
