Oxidic steel cleanness in high-carbon chromium-bearing steel

The total oxygen content in the finished material has been used as a measure of steel cleanness for high-carbon chromium-bearing steel for many years. The average value has decreased on a yearly basis from 11 ppm in 1985 to 5 ppm in 1996. Even the deviation from the mean total oxygen value has decreased from 1.88 ppm in 1985 to 0.67 ppm in 1996, which indicates that the process is becoming more stable with respect to the oxidic inclusion content. Instead of focusing on the finished material, this study's objective has been to determine the degree of oxidic steel cleanness of liquid steel under ladle treatment. Therefore, plant trials have been done where samples have been taken before and after vacuum degassing. The oxidic cleanness has been determined by analysing the total oxygen content using melt extraction, the inclusion composition using a scanning electron microscope, and the inclusion size distribution using an optical light microscope following the swedish standard SS111116.