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The influence of sulfur on initial high temperature corrosion of Fe-Cr model alloys

  • Ferritic steels with Cr-contents up to 13 wt. % are used as heat exchanger or boiler tube materials in combustion based power plants. These materials are subject to aggressive corrosion caused by the reaction of the steel with highly corrosive gases under high temperatures up to 650°C. The early stages of corrosion and sulfidation especially and the influence of the Cr-content in the alloy are thereby not understood but of fundamental interest. Our work shows corrosion mechanisms and presents corrosion models for Fe and different Fe-Cr-alloys under pure SO2 und SO2+O2 atmospheres for different time scales. Modell alloys of high purity are used to focus on the reaction of the intended elements: Fe, Cr, S, and O. Long-time experiments (≥12h) took place in tube furnaces and short-time experiments (≥5min) in a special designed light furnace. Heating and cooling took place under inert atmosphere. The reactive gases were added not until the experimental temperature was reached. SamplesFerritic steels with Cr-contents up to 13 wt. % are used as heat exchanger or boiler tube materials in combustion based power plants. These materials are subject to aggressive corrosion caused by the reaction of the steel with highly corrosive gases under high temperatures up to 650°C. The early stages of corrosion and sulfidation especially and the influence of the Cr-content in the alloy are thereby not understood but of fundamental interest. Our work shows corrosion mechanisms and presents corrosion models for Fe and different Fe-Cr-alloys under pure SO2 und SO2+O2 atmospheres for different time scales. Modell alloys of high purity are used to focus on the reaction of the intended elements: Fe, Cr, S, and O. Long-time experiments (≥12h) took place in tube furnaces and short-time experiments (≥5min) in a special designed light furnace. Heating and cooling took place under inert atmosphere. The reactive gases were added not until the experimental temperature was reached. Samples were analyzed using high resolution synchrotron X-ray diffraction using a micro focus setup and electron microscopy including FIB. Many earlier studies on corrosion and sulfidation on iron based alloys show a higher corrosion rate and material loss when sulfur was present in the atmosphere. In contrast, later studies propose an inhibiting effect of sulfur containing atmospheres. On the one side, most likely due to the formation of a protective layer of Mx(SO4)y -phases at the scale-gas interface. On the other side, a very recent study proposes the theory that MxSy-phases limit the further diffusion of elements. Up to now, no Mx(SO4)y –phases were detected in our samples, but sulfide phases nucleated within the oxide phases. For pure Fe our samples show FeS at the scale-metal interface working as a diffusion barrier for Fe-Cations from the base material in to the oxide scale. The above lying spalled off oxide-sulfide scale shows a wide area of small voids and accumulations of FeS-Crystals at the bottom. Under the main oxide scale a second generation of oxide-sulfide scale starts to form. For the Fe-Cr-alloys the inner oxide scale only shows FeS- and CrS-phases surrounded by hollow space. The here presented study will explain and discuss a new growth model for the shown phenomenon.zeige mehrzeige weniger

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Autor*innen:Kathrin Nützmann
Koautor*innen:Wencke Schulz, Romeo Saliwan Neumann, Nicole Wollschläger, Christiane Stephan, Axel Kranzmann
Dokumenttyp:Posterpräsentation
Veröffentlichungsform:Präsentation
Sprache:Englisch
Jahr der Erstveröffentlichung:2016
DDC-Klassifikation:Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten
Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Angewandte Physik
Freie Schlagwörter:Diffusion barrier; Fe-Cr alloys; Sulfidation
Veranstaltung:9th High Temperature Corrosion and Protection of Materials
Veranstaltungsort:Ile des Embiez, France
Beginndatum der Veranstaltung:15.05.2016
Enddatum der Veranstaltung:20.05.2015
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:15.11.2016
Referierte Publikation:Nein
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