ATTACK ON MAGNESIA CRUCIBLE BY MOLTEN IRON

The purpose of this research is to elucidate an interaction mechanism at an interface between molten iron and the magnesia crucible. Pure ir on used in the present study had less content of impurities except for oxygen, the content of which was classified into two groups (15 and 4 00 mass ppm). Magnesia crucibles were commercial dense products. Iron specimen was molten for 10 approximately 60 min at 1600-degrees-C unde r Ar atmosphere in a tungsten mesh-heater furnace. After cooling, the specimen was treated and observed with optical and scanning electron m icroscopes. And then the specimen interface was analyzed with an elect ron probe micro-analyzer, an analytical electron microscope and a surf ace roughness measuring instrument. It was also identified with an X-r ay 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 t he case of a low oxygen content (15 mass ppm) in molten iron, the inte rface of the magnesia crucible after melting was almost the same as th at before melting except for the very slight corrosion at the grain bo undary. On the contrary, the magnesia crucible was extraordinarily att acked 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 fo rmed at the interface of the magnesia crucible with molten iron lowers to about 2600-degrees-C. Although it is still solid at the experiment al temperature, the surface rearrangement among the relevant phases ma y occur. (3) Oxygen in molten iron is very interface-active. The disso lved oxygen atoms are concentrated on the interface between molten iro n and the crucible, and form FeO monolayer at the iron interface in th e case of 400 mass ppm O underbar. On the other hand, no FeO layer is formed in the case of 15 mass ppm O underbar. It is considered that su ch a monolayer may cause different types of attack on the magnesia cru cible by molten iron.