High-temperature sulphidation behaviour of Fe-Cr-Al and Fe-Cr-Al-Y alloys

摘要

High-Temperature corrosion of structural alloys in sulphur-bearing environments is many order of magnitude higher than in oxidizing environments. Efforts to increase the sulphidation resistance of these alloys include addition of alloying elements. Aluminum additions to iron-chromium alloys bring about increase in sulphidation resistance, and the increase in oxidation resistance of various alloys with addition of reactive elements such as yttrium is well known. However, the effect of yttrium on the sulphidation behaviour of Fe-Cr alloys is still inconclusive. This paper reports the effect of yttrium addition on the sulphidation behaviour of Fe-20 Cr-5 Al alloys in H_2 2 percent H_2S at 700 deg and 800 deg C. The FeCrAl and FeCrAlY alloys showed parabolic sulphidation kinetics at the two temperatures: on both alloys, the initial chromium sulphide (Cr_2S_3) formation at the grain boundaries and Al_2S_3 and FeCr_2S_4 formation over the grains is followed by formation of an outer Cr_2S_3 layer over a mixed sulphide layer. Yttrium segregated to the grain boundaries in the initial stages of sulphidation influenced sulphide formation, but had no significant effect on sulphidation kinetics, which was governed mainly by the Al in the alloys.