Abstract: A process for producing a galvanneal layer on a steel substrate, including forming a Zn-Fe coating having a predetermined Fe content F (wt. %) on the steel substrate; and heat treating the Zn-Fe coating on the substrate from a predetermined starting temperature T.sub.1 (.degree.C.) to a predetermined ending temperature T.sub.2 (.degree.C.) at a predetermined heating rate R (.degree.C./min.), wherein F, T.sub.1, T.sub.2, and R are selected so that the following condition is met,a.R.sup.2 +b.T.sup.2 +c.R.F.+d.R.T +e.R+f.T=gwhere a, b, c, d, e, f and g are predetermined constants, thereby to form a virtually 100% .delta..sub.1 phase galvanneal structure. Alternatively, the heat treatment can be preformed until the specimen temperature is just below a minimum temperature of the .delta..sub.1 phase stability range at at selected Fe content and heating rate, followed by an isothermal hold for a predetermined time period until transformation to the .delta..sub.1 phase occurs.