Determination of inclusion characteristics in ‘low-carbon’ steel during up-hill teeming

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Abstract

Clean steel production requires good control of the size distribution and the composition of the inclusions at all stages of the steel making process. So far, there exists very little information on the behavior of the inclusion population during ingot casting of steel. Therefore, this study focus on providing information on the inclusion population before and during up-hill teeming of ‘low-carbon’ steel, based on plant trails carried out at Ovako Steel's facilities in Hofors, Sweden. Liquid steel samples were acquired from the casting ladle just before the start of the filling of the ingot molds and from the rising steel in the molds during the filling of the molds. Thereafter, the inclusion compositions for the different size classes were determined using a scanning electron microscope equipped with energy dispersive X-ray. It was found that the inclusion compositions were more complex in the samples taken in the mold in comparison to the ones taken in the ladle. In some cases large exogenous inclusions most likely formed due to a reaction with the mold flux were found. When a mold was filled without mold flux reoxidation of the steel due to reaction with the atmosphere took place. The inclusion size distributions were also determined using light optical microscopy and classified according to the Swedish standard SS111116 (JK chart II). The number of inclusions found in the sample taken in the mold were higher than in the sample taken in the ladle. The general conclusions are that more in-depth research is necessary to understand the reactions taking place during filling of an ingot.

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