ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Phase Evolution in Galvanneal Coatings on Steel Sheets
C. S. LinM. MeshiiC. C. Cheng
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1995 Volume 35 Issue 5 Pages 503-511

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Abstract

The evolution of the phases in galvanneal coatings on IF and IFP steel sheets is studied by combining optical microscopy (OM), scanning electron microscopy (SEM) with X-ray microanalysis (EDS) and transmission electron microscopy (TEM). The early stage of galvannealing is dominated by the formation of intermetallic compounds, particularly δ phase by constitutional supercooling except the region near the steel substrate where rapid formation of a thin alloy layer, the nature of which depends strongly on surface segregation of minor elements such as phophorus in a steel substrate. The Γ phase, which shows a well-defined columnar structure, grows at the expense of the Γ1 phase. The thickness of the Γ1 phase decreases, while maintaining the total thickness of (Γ+Γ1) constant, 2 μm, during galvannealing, Three different grain morphologies of δ phase have been observed. The surface segregation of phosphorus in steel was found to promote the nucleation of the Γ1 phase at the solid-liquid interface in the very beginning of galvannealing. The formation of the Γ phase was retarded accordingly. The hot-dip simulator was found to reproduce the microstructures of galvanneal coatings obtained by the in-line production and to facilitate the investigation of the phase evolution during hot-dip galvanizing and galvannealing.

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© The Iron and Steel Institute of Japan
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