High Temperature Corrosion of Fe-25Cr and Fe-17Cr-1.5Si-0.5Al Alloys in Oxidizing and Sulfidizing Enviornments

The simultaneous oxidation and sulfidation of Fe 25Cr and Fe-17Cr-l.5Si-0.5Al alloys was studied at 1023K and 1223K in H₂-H₂O-H₂S gas mixtures. The kinetic boundary which indicates the transition from oxide to sulfide has heen found in these two alloys. The critical oxygen partial pressures of Fel7Crl.5SiO.5Al alloys were systematically lower than those of Fe-25Cr alloy. The reaction kinetics were measured by the stainless steel spring balance, and the reaction products were characterized by X-ray diffraction and scanning electron microscopy. The reaction rate usually decreased with the increase of the oxygen partial pressure at the constant sulfur partial pressure. The exista-nce of silicon plays an important role to suppress the sulfidation of Fel7Cr alloy.