1993 Volume 34 Issue 5 Pages 460-466
The purpose of this research is to elucidate an interaction mechanism at an interface between molten iron and the magnesia crucible. Pure iron used in the present study had less content of impurities except for oxygen, the content of which was classified into two groups (15 and 400 mass ppm). Magnesia crucibles were commercial dense products. Iron specimen was molten for 10∼60 min at 1600°C under Ar atmosphere in a tungsten mesh-heater furnace. After cooling, the specimen was treated and observed with optical and scanning electron microscopes. And then the specimen interface was analyzed with an electron probe micro-analyzer, an analytical electron microscope and a surface roughness measuring instrument. It was also identified with an X-ray diffractometer.
The results obtained are as follows:
(1) Depending on the initial oxygen content in the iron specimen, the appearance of the iron specimen-magnesia crucible interface was very different. In the case of a low oxygen content (15 mass ppm) in molten iron, the interface of the magnesia crucible after melting was almost the same as that before melting except for the very slight corrosion at the grain boundary. On the contrary, the magnesia crucible was extraordinarily attacked by molten iron which had a high oxygen content (400 mass ppm).
(2) In the latter case, the solidus temperature of the MgO–FeO phase formed at the interface of the magnesia crucible with molten iron lowers to about 2600°C. Although it is still solid at the experimental temperature, the surface rearrangement among the relevant phases may occur.
(3) Oxygen in molten iron is very interface-active. The dissolved oxygen atoms are concentrated on the interface between molten iron and the crucible, and form FeO monolayer at the iron interface in the case of 400 mass ppm O. On the other hand, no FeO layer is formed in the case of 15 mass ppm O. It is considered that such a monolayer may cause different types of attack on the magnesia crucible by molten iron.