Phase Evolution in Galvanneal Coatings on Steel Sheets
Journal
ISIJ International
Journal Volume
35
Journal Issue
5
Pages
503-511
Date Issued
1995
Author(s)
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 microanalyses (EDS) and transmission electron microscopy (TEM). The early stage of galvannealing is dominated by the formation of intermetallic compounds, particularly 5 phase by constitutional supercooling except the region near the steel substrate where rapid formation of a thin alloy layer, the nature of which dependsstrongly on surface segregation of minor elements such as phosphorus in a steel substrate. The F phase, which shows a well- defined colunlnar structure, grows at the expense of the F* phase. The thickness of the r* phase decreases, while maintaining the total thickness of (F + F,) constant, -2,tm, during galvannealing. Three different grain morphologies of 8 phase have been observed. The surface segregation of phosphorus in steel was found to promote the nucleation of the F, phaseat the solid-liquid interface in the very beginning of galvannealing.
Type
journal article