The most important function of controlled rolling is usually to refine grain structure and, thereby, to enhance both strength and toughness of steel from the as-hot-rol1ed condition. When a survey is made of the creation of controlled rolling, it may be seen that controlled rolling is made up of three stages: (a) deformation in the recrystallization region at high temperatures; (b) deformation in the non-recrystallization region in just a low temperature range above Ar3; and (c) deformation from the austenite-ferrite region.
It really is stressed that the necessity of deformation in the nonrecrystallization region is within dividing an austenite grain into several blocks by the introduction of deformation bands there. Deformation in the austenite-ferrite region offers a mixed structure made up of equiaxed grains and subgrains after transformation and, thereby, it increases further the strength and toughness.
The primary distinction between conventionally hot-rolled and controlled -rolled steels lies in the truth that the nucleation of ferrite occurs exclusively at austenite grain 34dexppky from the former, even though it occurs in the grain interior along with at grain boundaries inside the latter, resulting in an even 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 second is demonstrated to be the main source of the delamination which appeared in the fractured Charpy specimens. Fundamental aspects of controlled rolling, for example 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 technique of controlled rolling in plate and strip mills is outlined.