High temperature attack by SO2 of laser boronized iron

H. Dao Duong; A. Galerie; M. Pons; M. Caillet

doi:doi:10.1051/jp4:1993963

Proceedings of the 3rd International Symposium on High Temperature Corrosion and Protection of Materials
Actes du 3ème Colloque International sur la Corrosion et la Protection des Matériaux à Haute Température

J. Phys. IV France 03 (1993) C9-599-C9-606
DOI: 10.1051/jp4:1993963

High temperature attack by SO₂ of laser boronized iron

H. Dao Duong, A. Galerie, M. Pons and M. Caillet

Laboratoire Science des Surfaces et Matériaux Carbonés, U.R.A. C.N.R.S. n° 413, E.N.S. d'Electrochimie et d'Electrométallurgie de Grenoble, Institut National Polytechnique de Grenoble, B.P. 75, Domaine Universitaire, 38402 Saint-Martin d'Hères, France

Abstract
Laser alloying of boron predeposited on iron samples led to Fe-Fe₂B alloys, with composition and microstructure depending on the irradiation conditions. Three different surface alloys were prepared corresponding to hypo-, hyper- and eutectic microstructures. This last kind of surface alloy exhibited the best behaviour in static SO₂ between 400 and 600 °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 SO₂ and S₂ transport, allowing the formation of a FeS-B₂O₃ internal sublayer. In this sublayer, slowly reacting Fe₂B transforms to B₂O₃ leading to an increased blocking during the course of the reaction.