Rimmed steels are characterized by marked differences in chemical composition across the section and from top to bottom of the ingot. They have an outer rim that is lower in carbon, phosphorous and sulfur than the average composition of the whole ingot, and an inner portion, or core, that is higher than the average in those elements. The typical structure of the rimmed steel ingot results from a marked gas evolution during solidification of the outer rim. During the solidification of the rim, the concentration of certain element increase in the liquid portion of the ingot. During solidification of the core, there is some increase in segregation in the upper and central portions of the ingot. Normally, the carbon content of rimmed steels is less than 0.25% and the manganese content is less than 0.60%. Satisfactory rimmed steels do not retain any significant percentage of highly oxidizable elements such as aluminum, silicon, or titanium. The structural pattern of the ingot persists through the rolling process to the final product.
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