The Solubility of Oxygen in δ-Iron
Akihiko KUSANO, Koin ITO, Kokichi SANO
Oxygen is one of the most important impurities present in iron or steel, mainly forming oxide inclusions. Therefore, it is often desirable to know the solubility of oxygen in solid iron with a reasonable accuracy, but investigations yield highly discordent results. As shown by many literatures, this is attributed to oxydizable impurities in solid iron, such as Si, Mn and Al, etc.
In the present work, we carried out the experiments in lowering the crucible very slowly under purified argon gas, using the Tammann furnace, and the equiliblium between solid iron and liquid was noted.
Then, chromium was added to liquid iron and the effect of it on the solubility of oxygen in δiron was also studied. These results were summarized as follows;
1. The measurement of the monotectic point in the Fe-O system showed that the concentration of oxygen was 0.16% and the temperature was 1528°C.
2. The liquidus line could be drawn by a straight line combining two points, i.e., the freezing point of purified iron (1538°C) and the monotectic point (1528°C, 0.16%0).
3. The distribution ratio of oxygen (Lo) is 0.076 in the temperature range between 1528°C and 1538°C, independent of the concentration of oxygen in liquid iron, and the solubility of oxygen is 0.012% at 1528°C.
4. The relation between the concentrations of chromium and oxygen was obtained in liquid iron at the temperature of solid-liquid interface. It has an approximately good agreement with the calculation using the values which were recommended by Japan Society of the Promotion of Science.
5. The distribution ratio of oxygen increased with increases in the concentration of chromium, and became 0.13 at 10% chromium.
6. The distribution ratio of oxygen in the Fe-O system has a good agreement with the ratio obtained in the Fe-O-Cr system by extraporation.