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The chemical definition of steel implies that steels. are solid products with uniform chemistry throughout sections of manufactured shapes. While liquid steel at the end of state-of-the-art steelmaking processes is essentially uniform in chemistry, 2 solidification produces macroscopic and microscopic partitioning of chemical elements between parent liquid and growing solid crystals, producing nonuniformity in the distribution of chemical elements inherited in fully solidified as-cast products. This partitioning or segregation of chemical elements occurs on a macroscopic level at the centerline of continuously cast steel products, and at the tops and bottoms as well as the centerlines of ingots. The effects of macroscopic segregation are outside the scope of this paper. On a microscopic scale, segregation occurs between dendrites throughout a solidified section. The latter segregation is aligned into longitudinal bands by hot rolling, and consequently is referred to as banding, especially when apparent as alternating bands of quite different microstructural constituents. Some degree of banding is found in all types of steel. 1 Reheating of as-cast products and hot rolling reduce chemical segregation, but further microstructural partitioning, often by design in parent austenite of uniform composition, occurs during diffusion-controlled solid-state phase transformations. 3-4 In view of the dependence of the kinetics of solid-state transformations on chemistry, residual solidification segregation may manifest itself as banding in the microstructure of finished steel products.

The purpose of this paper is to review the origins of chemical segregation and to describe the …