Ca-Pb合金を用いたCa活量の制御による溶鉄のカルシウム脱酸および脱硫平衡の測定

抄録

It is essential to reduce the oxygen potential in steel to lower the sulfur content. The addition of calcium is considered the most effective. Therefore, many researchers have investigated the deoxidation and desulfurization equilibria of liquid iron by calcium; there is a scatter among previous studies because of the difficulties of the experiments due to the high vapor pressure and the limited solubility of calcium in the molten iron. This work reveals that the activity of calcium in molten iron can be controlled by equilibrating with Ca-Pb alloy, and the deoxidation and desulfurization equilibria of liquid iron by calcium are re-investigated. The following thermodynamic values have been derived from the experimental results in the present and previous studies.

　　　　　　　　CaS(s) = Ca_{(mass% in Fe)} + S_{(mass% in Fe)}

　　　　　　　　e_S^Ca= −23.7

　　　　　　　　e^S_Ca= −29.6

　　　　　　　　logK_CaS= −6.11 (1873 K)

Using the derived thermodynamic data, deoxidation and desulfurization equilibria of liquid iron by calcium are proposed. Deoxidation and desulfurization limits of liquid iron by calcium are calculated to be 2 mass ppm O at 20 mass ppm Ca and 4 mass ppm S at 40 mass ppm Ca under the condition of a_CaO = a_CaS = 1 at 1873 K.