Kinetics of Evaporation of Manganese, Copper and Sulfur from Iron Alloys in Vacuum Induction Melting (Metallurgy)

The evaporation-rate constant K_i (kg・m^・s^) for each of manganese, copper and sulfur in the vacuum induction melting of iron alloys has been determined. The rate constant K_v or K^s_v (kg・m^・s^) for the vaporization of these elements at the vacuum-melt interface is calculated. In each of the Fe-C-Mn. Fe-C-Cu and Fe-C-Si-S systems, the value of K_i at a lower stirring rate is about one half of that at a higher stirring rate ; hence mass transfer in the melt must be involved in the rate-determining step for their evaporation at the lower stirring rate. In the Fe-Cu and Fe-Mn systems, the value of K_ at 1973 K is obviously greater than that at 1873 K, but those of K K_ at both temperatures are close to each other. The rates of evaporation of manganese must be determined predominantly by the rate of its transfer in the melt in view of the values of ρK_m at both temperatures, which were calculated on the basis of the equation K_i=ρK_mK_v/(ρK_m+K_v), where ρ (kg・m^) is the density of the melt and K_m (m・s^) is the mass-transfer coefficient in the melt. In the Fe-Mn, Fe-Cu and Fe-Sn systems at 1873 K, most of the reported experimental values of K_ K_ and K_ agree well with their respective values calculated from the equation by taking ρK_m=6.8×10^(kg・m^・s^), but the present experimental values of K_ are smaller than the calculated value. The plots of K_s/f_s vs. a_ in the Fe-Si-S system are linear at two different stirring rates. The rate constants k_1 and k_2 given by this linear relation at a lower stirring rate are smaller than those at a higher stirring rate, respectively, and must involve K_m. In the desulfurization of Fe-S, Fe-C-S, Fe-Si-S and Fe-C-Si-S alloys at temperatures in the range 1688～1873 K, the relation between K_s and K^s_v is represented by a curve calculated from the equation by taking K_v=0.24 K^s_v and ρK_m=2.5 regardless of the temperatures and the alloy systems. This value of ρK_m is much greater than the value of ρK_m for Fe-Mn, Fe-Cu and Fe-Sn systems. Oxygen and sulfur hardly affect the rate of evaporation of copper from molten iron at 1873 K