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Abstract
Development of strong inter-particle necks requires successful removal of surface oxides, present on the powder particles, during the initial stages of sintering. In the case of water-atomised powder prealloyed with chromium, the surface oxide consists mainly of an iron oxide layer with some more stable fine particulate oxides. The formation of sufficiently strong inter-particle necks requires as a minimum full removal of the iron surface oxide layer. This can be achieved by gaseous reducing agents (e.g. H2, CO or a mixture of both) or by carbon, typically admixed in the form of graphite. The reducing power of various sintering atmospheres (active gas content ≤10 vol.-%) and their combined effect with graphite has been investigated by a thermal analysis technique. Results indicate that a combination of a dry hydrogen-containing atmosphere and fine graphite allows successful sintering of chromium alloyed PM steels.
Acknowledgements
Support from the Sustainable Production Initiative of Chalmers Area of Advance in Production is gratefully acknowledged. Further thanks are extended to Sigurd Berg and Professor Sven Bengtsson, Höganäs AB, for scientific cooperation and specimens supply. This work is based on a presentation at Euro PM 2013, organised by EPMA in Gothenburg, Sweden on 13–15 September 2013.