The most important intent behind controlled rolling is always to refine grain structure and, thereby, to improve the strength and toughness of steel in the as-hot-rol1ed condition. In case a survey consists of the creation of controlled rolling, it can be seen that controlled rolling contains three stages: (a) deformation from the recrystallization region at high temperatures; (b) deformation within the non-recrystallization region within a low temperature range above Ar3; and (c) deformation within the austenite-ferrite region.
It can be stressed that the necessity of deformation inside the nonrecrystallization region is in dividing an austenite grain into several blocks by the creation of deformation bands inside it. Deformation within the austenite-ferrite region provides a mixed structure made up of equiaxed grains and subgrains after transformation and, thereby, it improves further the strength and toughness.
The basic difference between conventionally hot-rolled and controlled -rolled steels is in the fact that the nucleation of ferrite occurs exclusively at austenite grain 34dexppky in the former, though it takes place in the grain interior and also at grain boundaries inside the latter, resulting in a much more refined grain structure. In Clad Plate a crystallographic texture develops, that causes planar anisotropies in mechanical properties and embrittlement from the through -thickness direction.
The latter is shown to be the main source of the delamination which appeared from the fractured Charpy specimens. Fundamental elements of controlled rolling, such as the recrystallization behaviour of austenite, the retardation mechanism of austenite recrystallization due to niobium, microstructural changes accompanying deformation, factors governing strength and toughness, etc., are reviewed. The practice of controlled rolling in plate and strip mills is outlined.