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 magnesia crucible. Pure iron used in the present study has less content of impurities except for oxygen, the content of which is classified into two groups (15 and 400 mass ppm). Magnesia crucible is commercial dense product. Iron specimen has been molten for 10 approximately 60 min at 1600-degrees-C under Ar atmosphere in a tungsten mesh-heater furnace. After cooling, the specimen is treated and observed with optical and scanning electron microscopes and a surface roughness detector. And then the specimen interface is analysed with an X-ray probe microanalyser and an analytical electron microscope and identified with an X-ray diffractometer. The results obtained are as follows: (1) Depending on the initial oxygen content in iron specimens, the appearance of the interface between the iron specimen and the magnesia crucible was very different. In the case of low oxygen content (15 mass ppm) in molten iron, the interface of magnesia crucible after melting was the almost 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) Oxygen in molten iron is very interface-active. The dissolved oxygen concentrates on the interface of molten iron and crucible, and forms a single molecular FeO layer at the interface in the case of 400 mass ppm 0. On the other hand, no layer is formed in the case of 15 mass ppm O. (3) Accordingly, in the former case there may be an oxide phase-oxide phase contact at the interface. The latter interface consists of metal and oxide phases. It is considered that such different combinations cause the different types of attack on the magnesia crucible by molten iron.