Steam oxidation behaviour of plasma nitrided Fe-based alloys
Abstract
Purpose
It is well known that alloys, based on iron, were exposed to steam oxidation environment producing thick and non-protective oxide scale. More expensive stainless steels contain more Cr and are able to form more protective scales. The purpose of this research was to show ability to employ nitride coating on different alloys (T23, T91, E1250, 347HFG and HR3C) in order to enhance steam oxidation resistance.
Design/methodology/approach
The alloys were exposed to steam oxidation rig. Before the test, furnace was purged by nitrogen in order to remove moisture and oxygen. Di-ionised water was pumped from the reservoir using a peristaltic pump into the furnace. System was kept in the closed circle. To reduce solubility of oxygen, di-ionised water was constantly purged by nitrogen. The total exposure time was 2,000 h at 650°C under 1 bar pressure.
Findings
Due to the research, it was found that plasma nitriding process is detrimental for the protection of high-temperature structured materials; the high concentration and high activity of Cr produced a CrN phase. This phase is not stable in steam environment and underwent oxidation to Cr2O3 and further into volatile phase (CrO2(OH)2). Therefore, austenitic steels (E1250, 347HFG and HR3C) coated with nitride coating deposited by plasma nitriding process suffered similar degradation as the uncoated low Cr ferritic steel.
Research limitations/implications
The main limitation of the research conducted in this study was corrosion resistance of the exposed materials.
Originality/value
To the best of the authors' knowledge, this report is the first of its kind to present nitrided alloys (ferritic and austenitic) exposed in steam oxidation.
Keywords
Acknowledgements
The authors would like to acknowledge the support of The Energy Programme, which is a Research Councils UK cross council initiative led by EPSRC and contributed to by ESRC, NERC, BBSRC and STFC, and specifically the Supergen initiative (Grants GRyS86334y01 and EPyF029748) and the following companies; Alstom Power Ltd, Doosan Babcock, E.ON, National Physical Laboratory, Praxair Surface Technologies Ltd, QinetiQ, Rolls-Royce plc, RWE npower, Siemens Industrial Turbomachinery Ltd and Tata Steel, for their valuable contributions to the project.
Citation
Cockrem, J., Pawel Dudziak, T., Simms, N., Lukaszewicz, M. and Oakey, J. (2013), "Steam oxidation behaviour of plasma nitrided Fe-based alloys", Anti-Corrosion Methods and Materials, Vol. 60 No. 6, pp. 288-294. https://doi.org/10.1108/ACMM-01-2013-1239
Publisher
:Emerald Group Publishing Limited
Copyright © 2013, Emerald Group Publishing Limited