Laser alloying of boron predeposited on iron samples led to Fe-Fe2B al
loys, with composition and microstructure depending on the irradiation
conditions. Three different surface alloys were prepared correspondin
g to hypo-, hyper- and eutectic microstructures. This last kind of sur
face alloy exhibited the best behaviour in static SO2 between 400 and
600-degrees-C. The parabolic rate law, tending to a 3rd and 4th power
law at the highest temperatures was explained as the result of outward
iron diffusion leading to a magnetite external sublayer and inward SO
2 and S2 transport, allowing the formation of a FeS-B2O3 internal subl
ayer. In this sublayer, slowly reacting Fe2B transforms to B2O3 leadin
g to an increased blocking during the course of the reaction.