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ABSTRACT
Sintering of steels containing oxidation-sensitive elements such as Cr, Mn and Si is a big challenge for the powder metallurgy (PM) industry but also a chance that could open the door to a new variety of compositions, properties and prices. However, even when very small amounts of these elements are mixed with an iron base powder, the chemical reactions taking place during sintering can be changed significantly. Application of high purity sintering atmospheres is not sufficient to avoid the formation of stable oxides on the surface of the alloying particles, since the source of oxygen can be – and in general is – the base powder itself. This is because the gaseous reaction products from the reduction of the oxides covering the base powder particles act as oxidising agents for elements with higher oxygen affinity. In this study, thermoanalytical techniques have been applied in a systematic study about the influence of different alloying additions either as elemental powders (Cr, Mn, Si) or as master alloys. While Si shows to be relatively inert up to 900°C, Cr and especially Mn present high tendency to act as ‘oxygen-getters’ already at 400–500°C. When these elements are added in the form of a master alloy, their reactivity decreases, alleviating considerably the gettering effect. Moreover, reduction of the iron oxide layers with H2 at 400°C shows positive results, however, from 400°C Mn shows an important tendency to oxidation by reaction with the sintering atmosphere.
This paper is part of a special issue on the Advances in Materials and Processing Technologies (AMPT) 2015 and has subsequently been revised and extended before publication in Powder Metallurgy.
ORCID
Raquel de Oro Calderon http://orcid.org/0000-0001-7341-6267
Christian Gierl-Mayer http://orcid.org/0000-0001-8944-3534
Herbert Danninger http://orcid.org/0000-0002-7205-9058
Notes on contributors
Raquel de Oro Calderon has received Marie Sklodowska-Curie IEF post-doctoral fellowship at the Technical University of Vienna (Austria). She has a bachelor’s degree in Industrial Engineering, a master’s degree in Materials Engineering, and obtained her PhD in Materials Science and Engineering in 2012 at University Carlos III in Madrid (Spain), under the frame of the IV Höganäs Chair in Powder Metallurgy. Afterwards, she worked as a post-doctoral researcher at Chalmers University of Technology in Gothenburg (Sweden). Her main areas of research are related to sintering PM low alloy steels containing oxygen-sensitive alloying elements: master alloy approach, liquid phase design and evaluation, as well as application of thermal analysis techniques to study the chemical reactions during sintering. During her stay at Chalmers, she worked on the study of the interactions of different types or carbon sources with various combinations of atmospheres and metal/oxides. She is a member of the Editorial Board of the journal Powder Metallurgy, the author of more than 15 confidential scientific reports for industrial partners, 22 journal articles (5 of them invited), and 42 publications in Conference Proceedings. In 2015, she was awarded with a keynote paper at the EuroPM 2015 Conference. She has participated, as an invited speaker, in Special Interest Seminars at the EuroPM 2013 Conference in Gothenburg and at the PowderMet 2016 Conference in Boston (USA).
Dr Christian Gierl-Mayer is an assistant professor for Metallic Sintered Materials at Technische Universität Wien (Vienna University of Technology), Vienna, Austria. He obtained his PhD in Technical Chemistry in 2000 for his Dissertation ‘Manufacturing of PM-Parts by Optimized Sintering’, which fetched him the MIBA Award 2000 for the Promotion of Technical Sciences. He has been active in the field of Powder Metallurgy for more than 10 years, is the author of more than 100 publications in journals, conference proceeding and book chapters. His main research topics are the sintering behaviour of PM-materials and the thermal analysis of the sintering process. He is the author of five patents; chairman of the expert group ‘Sintering’ of ‘Gemeinschaftsausschuss Pulvermetallurgie’ (the Powder Metallurgy association of the German-speaking countries) and was the Head of Program Committee of the 31st Hagener Symposium Pulvermetallurgie. Since 2016, he has been the coordinator of the EPMA Powder Metallurgy Summer School where he also works as teacher, in charge of the topic ‘Atmosphere/Material Interaction’.
Herbert Danninger is a full professor at Chemical Technology of Inorganic Materials at Technische Universität Wien (Vienna University of Technology), Vienna, Austria, and currently the Dean of the Faculty of Technical Chemistry. He has been active in powder metallurgy for more than 35 years and is the author of more than 400 publications on powder metallurgy topics as well as several books and book chapters. He has worked mainly on high strength and high density sintered steels, with particular focus on sintering, microstructural characterisation and high cycle fatigue. He served as the co-chairman of the Powder Metallurgy World Congress 2004 in Vienna, Austria. Currently, he is the chairman of the ‘Gemeinschaftsausschuss Pulvermetallurgie’, the PM association of the German-speaking countries. Herbert Danninger received the ‘Skaupy lecture’ award of the ‘Gemeinschaftsausschuss Pulvermetallurgie’ in 2006 and was elected Fellow of APMI in 2010. He holds honorary doctoral degrees from Technical University Cluj-Napoca (Romania), of Universidad Carlos III de Madrid (Spain) and of University of Craiova (Romania).