Thermal conductivity of the CaO-Al 2 O 3 -SiO 2 system, which is one of the most important silicate melts in iron-and steelmaking processes, was measured using non-stationary hot wire method in the range from liquidus temperature to 1 873 K. Measurements were carried out at various compositions, and iso-thermal conductivity line of the CaO-Al 2 O 3 -SiO 2 system was drawn in iso-thermal sections at 1 673 K, 1 773 K, and 1 873 K. Thermal conductivity decreased with basicity increase, when CaO/SiO 2 ratio is smaller than unity, whereas it showed constant value when CaO/SiO 2 ratio is larger. In case Al 2 O 3 content was varied at constant CaO/SiO 2 ratio of 0.39 and 0.90, thermal conductivity showed maximum at 15-20 mass% Al 2 O 3 , suggesting that Al 2 O 3 behaves as an amphoteric oxide. In the temperature range of interest, the thermal conductivity of each composition decreased as temperature rises. Temperature dependence showed deviation from linearity with the reciprocal of absolute temperature, which was considered to be due to the thermallyinduced depolymerisation of the silicate structure at higher temperature. Also, thermal conductivity was found to conform to an exponential function of 1/T during deploymerization with the apparent activation energy.KEY WORDS: thermal conductivity; slag; non-stationary hot wire method; silicate melt; IR.

Due to its superior features compared to plain steel products, stainless steel has been widely used for various applications, since it is commercialized in the beginning of the 1900's. Since stainless steel is characterized by high chromium (and nickel) content, stainless steelmaking processes have been developed differently to those of ordinary steelmaking. However, like plain carbon steels, non-metallic inclusions significantly influence the quality of stainless steel products. In order to gain a better understanding of the impact of inclusions on the characteristics of stainless steel products, information from a large amount of previous research on non-metallic inclusions in stainless steel is reviewed. As expected, non-metallic inclusions are a probable cause of pitting corrosion, as well as crack initiation and growth. The formation and origin of inclusions during the steelmaking and continuous casting processes are also discussed based on a number of relevant studies.[ Ã ] Prof.

The behaviors of several types of inclusions at a high temperature were examined using a confocal scanning laser microscope (CSLM, 1LM21H/SVF17SP). Although alumina inclusions tended to impact on each other, agglomerate, and grow quickly, no other inclusion type, such as spinel as well as solid and liquid calcium aluminate, was observed to attract each other. The results of confocal microscope study were compared with the industrial investigation. For this purpose, many steel samples were taken at different stages of ladle treatment. The samples were analyzed by scanning and light optical microscopes. Approximately 50,000 inclusions of several types were examined. Only alumina inclusions were attracted to each other and agglomerate. No agglomeration by attractive behavior was observed in the other types of inclusions, including liquid inclusions. Both the industrial data and the in situ observation by CSLM indicate that, although the attraction force and the agglomeration play a significant role in the growth of alumina inclusions, the agglomeration of spinel and calcium aluminate inclusions does not need special consideration in ladle treatment. The agglomeration of liquid calcium aluminate inclusions took place only when they occasionally met as a result of external force, which led to low collision probability. However, the agglomeration of the liquid calcium aluminate inclusions along with alumina particles could be detrimental in the casting process.

Al-O equilibria in molten Fe-Al alloys were experimentally investigated. Molten steel with varying Al content (0.01-10 mass%) was equilibrated with a pure Al 2 O 3 (s) crucible at 1 873 K in an Ar atmosphere with 3 vol% H 2 . The oxygen content of steel with Al content higher than 1.0 mass% was found to be much lower than that found in previous works, while the oxygen content for Al content less than 1 mass% was found to be slightly higher, resulting in a smaller equilibrium constant. The interaction parameters as well as the equilibrium constant of the Al-O equilibria in molten steel at 1 873 K were reevaluated in the present study. The equilibrium for the Al deoxidation of molten steel was well represented up to 10.0 mass% Al using the reevaluated parameters.KEY WORDS: deoxidation; aluminum; equilibrium constant; interaction parameters. 1483© 2009 ISIJ (and a few equilibria at other temperatures) measured in previous studies.

A study on the formation mechanism of liquid calcium aluminate inclusions from MgO·A1203 spinel was carried out. It was found that spinel reacted with dissolved Ca in liquid steel forming liquid calcium aluminate phase. Stability calculations showed good agreement with the experimental result. According to the thermodynamic calculation, liquid calcium aluminate inclusions would form from spinel even at very low level of dissolved Ca content at 1873 K. At lower temperatures, the compound CaO·2AI 20 3 was found to be the stable phase at the spinelmetal interlace. Potential sources of dissolved Ca during ladle processes were also discussed.

In the present study, the inclusion removal mechanism by rising bubbles around the open eye in a gas stirred ladle was investigated using a cold model. Water and silicone oils were employed to simulate liquid metal and slag respectively. Both fine silicone oil droplets and charcoal particles were used to simulate inclusions. Around the open eye, the oil layer exhibited a sphere bed structure when a critical gas flowrate was reached. The sphere bed was composed of many oil droplets, each of which was coated with a thin water film. The injected inclusions mostly followed the stream of water flow and were brought up to the open eye by the gas-water plume. A fraction of the inclusions were captured by the sphere bed when passing through the openings between the oil droplets, while the rest of the inclusions came back to the water bath and joined the stream of the flow again. The sphere bed was found to function as a filter to the tiny particles or oil droplets. On the basis of this mechanism, a preliminary comparison of the contribution of inclusion removal by metal-gas plume in the open eye region with the contribution of buoyancy was made.

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