アークおよびレビテーション溶解における溶鉄および溶融鉄合金中への窒素溶解量について

抄録

The solubilities of nitrogen in arc-melted and levitation-melted iron and its alloys have been measured and the influence of Cr, Mo and V on the solubility has been determined. It is found that the nitrogen content of the arc-melted pure iron is proportional to the square root of the partial pressure of nitrogen up to 0.4% nitrogen-argon, while above 0.4% nitrogen-argon the content becomes nearly constant, and the arcmelted iron shows about 20 times higher solubility of nitrogen than the leviation-melted iron. This .anomalous solubility may be caused by the activation of atmosphere. The activation of nitrogen may be mainly attributed to the increased concentration of atomic nitrogen in the atmosphere. The dissolved nitrogen was assumed at first as being in equilibrium with the atomic nitrogen which originates from the arc-column by quenching. Then from the statistical-thermodynamical treatment of gas phase and molten iron the temperature of the arc-column was calculated as about 3000°K. This is quite lower than the actual temperature of arc-column, about 6000-10000°K. This and some other experimental facts suggest that the apparent solubility in arc melting may not be true equilibrium property but a steady state concentration between dissolution into and escape from the melt.
In arc-melting in the low nitrogen atmosphere (0.14% N₂-Ar), the influence of alloying element on the solubility of nitrogen was quite anomalous. At relatively high nitrogen atmosphere (3% or 5% N₂-Ar) it was influenced by the alloying elements in a manner similar to the equilibrium solubility. By levitation melting, the interaction parameters between nitrogen and Cr, Mo and V were obtained at 2140-2240°C as
eN(Cr)=-0.028 (Cr<10%)
eN(Mo)=-0.0051 (Mo<8%)
eN(V)=-0.062 (V<6%)
These values are reasonable in view of those at 1600°C and their temperature dependence.