The most important intent behind controlled rolling is always to refine grain structure and, thereby, to further improve the two strength and toughness of steel inside the as-hot-rol1ed condition. In case a survey is constructed of the development of controlled rolling, it can be seen that controlled rolling is made up of three stages: (a) deformation within the recrystallization region at high temperatures; (b) deformation inside the non-recrystallization region inside a low temperature range above Ar3; and (c) deformation from the austenite-ferrite region.
It really is stressed that the importance of deformation inside the nonrecrystallization region is dividing an austenite grain into several blocks by the development of deformation bands there. Deformation inside the austenite-ferrite region offers a mixed structure composed of equiaxed grains and subgrains after transformation and, thereby, it increases further the strength and toughness.
The primary difference between conventionally hot-rolled and controlled -rolled steels is in the fact that the nucleation of ferrite occurs exclusively at austenite grain 34dexppky from the former, though it occurs in the grain interior along with at grain boundaries within the latter, leading to a far more refined grain structure. In Clad Steel Plate a crystallographic texture develops, which causes planar anisotropies in mechanical properties and embrittlement within the through -thickness direction.
The latter is shown to function as the main cause of the delamination which appeared within the fractured Charpy specimens. Fundamental aspects of controlled rolling, including the recrystallization behaviour of austenite, the retardation mechanism of austenite recrystallization because of niobium, microstructural changes accompanying deformation, factors governing strength and toughness, etc., are reviewed. The technique of controlled rolling in plate and strip mills is outlined.