The major reason for controlled rolling is to refine grain structure and, thereby, to enhance both the strength and toughness of steel inside the as-hot-rol1ed condition. In case a survey is constructed of the growth of controlled rolling, it might be seen that controlled rolling is made up of three stages: (a) deformation from the recrystallization region at high temperatures; (b) deformation within the non-recrystallization region in a low temperature range above Ar3; and (c) deformation in the austenite-ferrite region.
It really is stressed that the necessity of deformation inside the nonrecrystallization region is within dividing an austenite grain into several blocks by the introduction of deformation bands within it. Deformation within the austenite-ferrite region offers a mixed structure consisting of equiaxed grains and subgrains after transformation and, thereby, it improves further the strength and toughness.
The essential distinction between conventionally hot-rolled and controlled -rolled steels is based on the fact that the nucleation of ferrite occurs exclusively at austenite grain 34dexppky within the former, even though it happens in the grain interior and also at grain boundaries inside the latter, resulting in a more refined grain structure. In Galvanized Steel Coils/Hot Dip Galvanized Steel Coil a crystallographic texture develops, which in turn causes planar anisotropies in mechanical properties and embrittlement inside the through -thickness direction.
The latter is demonstrated to function as the main cause of the delamination which appeared inside the fractured Charpy specimens. Fundamental aspects of controlled rolling, including the recrystallization behaviour of austenite, the retardation mechanism of austenite recrystallization as a result of niobium, microstructural changes accompanying deformation, factors governing strength and toughness, etc., are reviewed. The concept of controlled rolling in plate and strip mills is outlined.