The VIDP (Vacuum Induction Degassing and Pouring) is the most important melting plant in the production of high-purity steels for aircraft and aerospace industry. Those material grades are featured by a very low level of trace elements such as oxygen, nitrogen and in many cases carbon. During vacuum melting pressure dependent reactions like nitrogen removal, vacuumdecarburisation and vacuum-deoxidation can proceed and control the content of those trace elements. But thermodynamic equilibrium cannot be reached in VIDP operating range of a pressure of approximately 10-5 bar in economical reasonable time. Interface phenomenas inhibit the formation of reaction products and slow down the reduction of trace elements noticeably. These are amongst others the energy to form bubbles below the liquid metal surface or the interface allocation by surface active elements such as sulphur, which are reported in literature. The aim of this project is to evaluate the 'processequilibria of pressure depending reactions for different steel grades and to determine optimisation potential in lowering the content of trace elements. Investigations and experiments were carried out at alloys with different carbon levels and compared with literature and theory. The degradation of carbon, oxygen and nitrogen against time could be displayed by special sampling at the beginning of the melting and vacuum treatment. Thermodynamic calculations were worked out to evaluate the theoretical, pressure depending limits. In reality quasi-stationary conditions, which were not in thermodynamic equilibria, occurred for each alloy composition. Anyway, literature data showed that the VIDP can reach lower content of C, O and N in comparison to other vacuum plants by its characteristic melt agitation.
Vacuum induction melting - Optimisation of pressure dependent reactions
2007
6 Seiten, 11 Bilder, 2 Tabellen, 7 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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