Table 2. Number of bubbles generated at various gas flow rates-converted based on the calculation of gas flow rate divided by the volume of bubble.
The nitrogen solubilities in liquid manganese, manganese-iron, manganese-carbon, and manganeseiron-carbon alloys have been measured by the gas-liquid metal equilibration technique in the temperature range of 1623 to 1823 K. The equilibrium nitrogen content in pure liquid manganese at an atmospheric nitrogen pressure is high, and it does not follow Sievert's law, i.e., f N is not unity. The reduced nitrogen partial pressures by dilution with argon enabled us to obtain more reliable information on the thermodynamics of nitrogen in liquid manganese. The nitrogen dissolution follows Sievert's law at nitrogen contents below 1 wt pct. The standard free-energy change for the dissolution of nitrogen in pure liquid manganese has been determined as Ϫ67,222 ϩ 30.32T J/g atom, with the standard state of nitrogen taken as a 1 wt pct solution. Carbon and iron in manganese-rich melts decrease the nitrogen solubility significantly. The first-and second-order interaction parameters between nitrogen and other elements in manganese alloy melts have been determined. The activity coefficient of nitrogen in a ferromanganese alloy melt can be expressed as log f N ϭ 0.005 (pct N) ϩ 0.029 (pct N) 2 ϩ 0.015 (pct Fe) ϩ 0.09 (pct C) ϩ 0.013 (pct C) 2 where the interaction parameters are independent of temperature in the temperature range of 1623 to 1823 K.
Decarburization tests of high-carbon ferromanganese melts by oxygen refining were successfully carried out in a model converter with 2-ton production capacity. During the oxygen refining, the manganese loss was inherently accompanied by oxidation and evaporation. The oxidation loss of manganese into slag was affected by slag composition, melt temperature and slag weight. The oxidation loss of manganese into slag was minimum at a slag basicity of about 1.5 and it increased with temperature and slag weight. The amount of manganese evaporation loss was comparable to that of oxidation loss. An empirical equation for the evaporation loss of manganese was derived as a function of process variables. The apparent vaporization coefficient, ~, was significantly affected by the oxygen mixing ratio in bottom blowing gas and the fraction of top blown oxygen.
The effect of oxygen/argon mixing ratio in the bottom blowing gas on the decarburization behaviour of high carbon ferromanganese melt was investigated in the temperature range of 1350 -1550°C. Thermodynamic analysis indicates that high melt temperature and low Pea are essential for an effective decarburization. An empirical equation for the utilization ratio of oxygen for decarburization was derived as functions of the melt temperature and the oxygen/argon mixing ratio in the refining gas. The utilization ratio of oxygen for decarburization sharply increases as the melt temperature increases and the oxygen ratio in blowing gas decreases. In oxygen refining of high carbon ferromanganese melt, it is not desirable to inject oxygen through bottom tuysres in an early stage of refining. When the melt temperature is low, the oxygen predominantly oxidizes the manganese in melt in spite of high carbon contents. The injection of oxygen/argon mixture gas is found to be an effective decarburization technique when the melt temperature is higher than 1500°C. Cas Entkohlungsverhalten von hochkohlenstoffhaltigenFerromanganschmelzen. Der EinfluB des Oz/Ar-Mischunqsverhaltnisses im Ruhrqas beim Bodenblasen auf das Entkohlungsverhalten einer hochkohlenstoffhaltigen Ferromanganschmelze wurde im Temperaturbereich 1350 -1550°C untersucht. Die thermodynamische Analyse zeigt, daB eine hohe Temperatur und ein niedriger Pea grundlegend fur eine wirksame Entkohlung mit Sauerstoff sind. In Abhiingigkeit von der Temperatur und dem O/2Ar-Mischungsverhiiltnis wurde eine empirische Gleichung, die den Sauerstoffnutzungsgrad fur die Entkohlung beschreibt, hergeleitet. Der Sauerstoffnutzungsgrad nimmt mit zunehmender Temperatur und abnehmendem 02/Ar-Verhaltnis deutlich zu. 1m ersten Blasabschnitt des Frischprozesses ist das Bodenblasen mit Sauerstoff im Faile hochkohlenstoffhaltiger Ferromanganschmelzen nicht erwunscht. Obwohl der Kohlenstoffgehalt hoch ist, oxidiert Mangan bei niedriger Badtemperatur bevorzugt in der Schmelze. Das Einblasen eines Oz/Ar-Gasqernisches in die Schmelze erweist sich als gunstig, sobald die Badtemperatur auf uber 1500°C ansteigt.
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