Kinetics of Nitrogen Desorption of Liquid Iron, Liquid Fe-Mn and Fe-Cu Alloys under Reduced Pressures

Abstract

The rates of nitrogen desorption of inductively stirred liquid iron have been measured under reduced pressure at 1600°C and the effects of manganese and copper on the rates are discussed.
The rates of nitrogen desorption are apparently represented by the equation of 2nd order reaction in terms of nitrogen content in liquid iron as shown by the previous investigators under argon atmosphere. The values of the rate constant of nitrogen desorption, k_N, decrease with increasing oxygen-content in liquid iron and are nearly agreed with those obtained by other authors at higher concentration range than 0.02%. At low concentrations of oxygen in melts, however, the values of k_N obtained in the present work are higher than any of those by the others, though there are some discrepancies among them. These results are explained by the application of the mixed-control model including the mass transfer in both phases and the chemical reaction at the interface. Although the rate of nitrogen desorption has been regarded as the chemical reaction control, the mass transfer in liquid iron may play an important role on the nitrogen desorption at the lower oxygen range. It is also found that the vapourization of manganese or copper in liquid iron decreases the rate of nitrogen desorption, probably because of the local decrease of interfacial temperature due to the latent heat of vapourization and also because of the decrease of the effective reaction site for the nitrogen desorption.