The main function of controlled rolling would be to refine grain structure and, thereby, to boost the two strength and toughness of steel inside the as-hot-rol1ed condition. In case a survey is made of the introduction of controlled rolling, it may be seen that controlled rolling consists of three stages: (a) deformation in the recrystallization region at high temperatures; (b) deformation from the non-recrystallization region inside a low temperature range above Ar3; and (c) deformation within the austenite-ferrite region.
It is actually stressed that the value of deformation within the nonrecrystallization region is within dividing an austenite grain into several blocks by the creation of deformation bands inside it. Deformation in the austenite-ferrite region provides a mixed structure comprising equiaxed grains and subgrains after transformation and, thereby, it improves further the strength and toughness.
The primary difference between conventionally hot-rolled and controlled -rolled steels is in the point that the nucleation of ferrite occurs exclusively at austenite grain 34dexppky in the former, even though it occurs in the grain interior and also at grain boundaries from the latter, creating an even more refined grain structure. In Hot Rolled Steel Plate a crystallographic texture develops, that causes planar anisotropies in mechanical properties and embrittlement within the through -thickness direction.
The second is proven to function as the main cause of the delamination which appeared inside the fractured Charpy specimens. Fundamental facets of controlled rolling, like the recrystallization behaviour of austenite, the retardation mechanism of austenite recrystallization on account of 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.