METHOD FOR PREDICTING AMOUNT OF Г PHASE TO BE FORMED IN GALVANNEALED STEEL SHEET AND PROCESS FOR PRODUCING GALVANNEALED STEEL SHEET

摘要

[Problem] To easily and precisely predict the amount of a Г phase to be formed in a galvannealed steel sheet. [Solution] A method for predicting the amount of a Г (capital gamma) phase to be formed in the coating layer when producing a galvannealed steel sheet through a hot-dip plating line that includes a hot-dip galvanizing bath immersion zone, a temperature-rising zone, a soaking zone, and a cooling zone in this order, the method comprising using the following equation (1) to predict the total average thickness, Г_TOTAL (μm), of the Г phase formed by passing the steel sheet through all the zones. Г_TOTAL=V(T₀)×(t₀-Δt)^1/2 (1) In equation (1), V(T₀) is the rate of increase in the thickness of the Г phase (μm/sec^1/2), t₀ is the converted soaking time (sec), and Δt is the retardation time (sec) attributable to a delay in Г-phase formation in the beginning of immersion in the plating bath.