STUDIES ON THE DESULPHRIZATION OF MOLTEN PIG IRON BY MANGANESE (I)
Kokichi Sano, Michio Inouye
It is necessary to obtain the intimate knowledge of desulphurizing power of manganese, which always exists in molten iron during the iron and steelmaking processes. However, it should be pointed out that whilst many studies on the desulphurizing power of manganese had been established, there was no good agreement in their results perhaps because little attention was given to behaviour of sulphur in liquid iron.
Because recently the activity of sulphur in liquid iron containing various alloying elements had been determined, the authors tried to study the equilibrium between manganese and sulphur dissolved in liquid iron and to ascertain the desulphurizing power of manganese on the standpoint of sulphur potential. On this first report, the Mn-S equilibrium in carbon satuated iron was determined between 1200° and 1500°C.
The results obtained were in good agreement with those of W. Oelsen. It is noteworthy that the results suggested the possibility of decreasing sulphur content of pig iron containing more than 1% manganese to be useful for steelmaking by lowering the temperature to about 1200°C. Such effective desulphurizing power of manganese was ascribed to high sulphur potential in liquid iron. Assuming the activity coefficient of sulphur in these Fe-Csat-Mn-S melts was expressed thus, it was presumed that the values of fs were nearly constant at any temperature except in the higher manganese concentrations. The equilibrium of manganese and sulphur in molten iron was shown as follows: and from experimental data it was apparent that the product [S%][Mn%] was also approximately constant at comparatively lower temperatures. Although the activity coefficient of manganese in such solution had not yet been determined, it might be regarded as constant in lower sulphur concentrations and carbon saturation. On this assumption, in the above range aMnS might be also constant and the apparent equilibrium constant K"=[S%][Mn%] was conveniently substituted for the equilibrium constant K and written. and then the following thermodynamical data were obtained,
Compared the data of carbon solubility in these experiments with those of Fe-Mn-C melts, the effect of dissolved sulphur on carbon solubility in liquid iron were discussed. In lower sulphur concentrations, the following equation given by Turkdogan et al. might be applied, where ΔNSC was the atom fraction of carbon which was displaced from carbon saturated solution by dissolved sulphur and NS was the atom fraction of sulphur in Fe-C-S melts.