Deoxidation Equilibria of Manganese, Silicon, and Aluminum in Iron-Nickel-Chromium Melts
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TRODUCTION
OXYGEN is a reactant in all steelmaking processes. For this reason, the study of properties of oxygen solutions in liquid metals and alloys is an important problem of modern theoretical and experimental metallurgy. Oxygen in steel and alloys worsens their operation characteristics. Production of metal with the minimum oxygen concentration is the main aim of deoxidation. Other conditions being equal, the degree of a decrease in the content of dissolved oxygen is due to the deoxidation ability of element deoxidizer. The deoxidation ability of this element can be determined as the concentration of oxygen dissolved in melt that is in equilibrium with a certain amount of this deoxidizer at a given temperature. The stronger the deoxidation ability of element at the same temperature and concentration, the lower the oxygen concentration in melt. Upon production of iron-nickel-chromium alloys, the most frequently used deoxidizing elements are manganese, silicon, and aluminum. In these alloys, the chromium content can exceed 30 to 40 pct. Chromium is an VIKTOR DASHEVSKII, Professor, Head of Laboratory, ALEKSANDR ALEKSANDROV and AKIM KANEVSKII, Senior Researchers, and LEOPOLD LEONT’EV, Professor, Chief Researcher, Academician of RAS, are with Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences (IMET RAS), Leninskii prosp., 49, Moscow, 119991, Russia. Contact e-mail: [email protected] Manuscript submitted March 18, 2015. Article published online March 3, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
inefficient deoxidizer in comparison with the above elements. In the iron-nickel melts, minimum oxygen concentrations are reached at a chromium content of above 2 to 5 pct (depending on the nickel content); further increase in the chromium concentration causes a rise in the oxygen solubility.[1] In commercial practice, when deoxidizers are selected and their amounts are determined, it is necessary to take into account the effect of chromium on the activity and solubility of oxygen and also on the activity of the deoxidizer. The study of physicochemical characteristics of oxygen solutions in the Fe-Ni-Cr melts and of their deoxidation is of not only theoretical but also commercial importance, since it allows one to optimize the production of these alloys. In practice, the complex deoxidation is frequently used upon production of these alloys, i.e., the deoxidation with two or more deoxidizers together. This deoxidation technique has to be studied too. The reaction of oxygen in Fe-Ni melts containing manganese, silicon, and aluminum was previously thermodynamically analyzed and experimentally studied.[2,3] The present paper describes a similar investigation for Fe-Ni-Cr alloys.
II.
THERMODYNAMIC CONSIDERATIONS
In Fe-Ni-Cr melts, at chromium contents above 0.5 to 1.5 pct (depending on the nickel content), Cr2O3 is the product of interaction of chromium with oxygen in the melt[1]: Cr2 O3 ðsÞ ¼ 2½Cr þ 3½O;
½1
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KCr
ð½PctCr fCr Þ2 ð ½PctO fO Þ3 ¼ :
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