The Phase Relations Of The Zn-Fe-B Ternary System

The hot-dip galvanizing has proven to be an effective anti-corrosion methodwhich has been used in industries. In a continuous galvanizing line （CGL）, thesubmersed hardware （e.g. bearings, sink roll, stabilizer, corrector rolls, support rollarms, and snout tip） is subject to corrosive attack by the molten zinc. Seriouscorrosion makes it rather challenging to select proper materials with longer servicelife. Boron is a known alloying element which is used to enhance the hardness ofsteels, even by a minor addition of a concentration up to10ppm. Experimental resultsshow that Fe₂B and FeB phases possess excellent corrosion resistance and exhibitnon-wetting with liquid zinc，a great deal of research interest has been attracted in thedevelopment of Fe-B alloys owing to the unique characteristic of boron in steel.Although many researchers have studied the corrosion resistance of the Fe-Balloys in molten zinc, there is no report about the phase equilibria in Zn-Fe-B ternarysystem. The information of the phase relationship of this system at the galvanizingtemperature is beneficial to optimize design of Fe-B alloys and understand thecorrosion mechanism in molten zinc. The purpose of the present paper is to determineexperimentally the Zn-Fe-B isothermal sections at600°C and450°C. The isothermalsections of Zn-Fe-B ternary system have been determined experimentally usingscanning electron microscopy, electron probe microanalysis and X-ray diffraction.Five three-phase regions, i.e., α-Fe+Γ+Fe₂B, Γ+δ+Fe₂B, δ+L-Zn+Fe₂B,L-Zn+Fe₂B+FeB and FeB+（B）+L-Zn; eight two-phase regions, i.e., α-Fe+Fe₂B，Γ+Fe₂B，δ+Fe₂B，L-Zn+Fe₂B，Fe₂B+FeB，FeB+（B），（B）+L-Zn，FeB+L-Zn existin the600°C isothermal section. Seven three-phase regions have been determinedexperimentally in the isothermal section at450°C, i.e., α-Fe+Γ+Fe₂B，Γ+Γ1+Fe₂B，Γ1+δ+Fe₂B， δ+ζ+Fe₂B， ζ+Fe₂B+FeB, ζ+L-Zn+FeB and FeB+（B）+L-Zn. Tentwo-phase regions, i.e., α-Fe+Fe₂B，Γ+Fe₂B，Γ1+Fe₂B，δ+Fe₂B，ζ+Fe₂B，ζ+FeB，Fe₂B+FeB，FeB+（B），（B）+L-Zn and FeB+L-Zn exist at450°C. B is almost insolublein the α-Fe phase and all Fe-Zn compounds. The solubility of Zn in Fe₂B and FeB at600°C is1.8at.%and2.5at.%, respectively, and that at450°C is1.7at.%and2.1at.%, respectively. The solubility of Zn in Fe₂B and FeB increases with temperature.All Fe-Zn compounds can be in equilibrium with Fe₂B at450°C. Both FeB and Fe₂Bare in equilibrium with the liquid phase at600°C. No ternary phase exists in thissystem.II...