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  • Design of cast stainless steels with controlled delta ferrite content
    Šuštaršič, Borivoj ...
    Cast Fe-Cr-Ni-Mo based stainless steels (ASTM CF3, CF8 and CF8M) are commonly used in thermo-energetic objects for moderate thermally exposed components such as pipes, elbows, valvec, flanges etc. ... The choice of these materials was driven from the possibility of centrifugal or sand casting of large complex shapes and their relatively good mechanical properties and resistance to corrosion. These materials have a duplex microstructure composed of ferrite and austenite. It is quite unstable non-equilibrium microstructure formed during cooling of castings. Ferrite represents typically 5 to 25 vol. % of the total. Actually, it is unstable delta ferrite because it is formed at high temperatures during alloy solidification and generally can not be transformed into the low temperature alpha ferrite (except with very long low temperature ageing). Delta ferrite spinodally decomposes with time at elevated working temperatures (above 300 [compositum]C). The result of this spinodal decomposition is thermal degradation of material; i.e. increase of hardness and strength but significant decrease of ductility and toughness. It is controlled primarily with delta ferrite content. Experimentally determined limit value is somewhere between 10 and 15 vol. % at working temperature 320 [compositum]C. At higher temperatures this value is significantly decreased. There fore, it is necessary to know the ways of design and synthesis of cast stainless steels, which enable to produce the castings with suitable delta ferrite content. In the frame of the conference new Calphad based computer tools for the prediction of phase composition will be presented, as well as practical approach for the synthesis of cast stainless steels. Some comparisons between really determined delta ferrite contents and predicted with computer tools will also be presented.
    Vir: Program in knjiga povzetkov = Program and book of abstracts (Str. 219)
    Vrsta gradiva - prispevek na konferenci
    Leto - 2012
    Jezik - angleški
    COBISS.SI-ID - 963242

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