*1.1.1 Reheating of slabs*

The first step involves heating up of slabs to remove dendritic segregation and facilitate solutionizing of microalloying element which is intended to precipitate during hot rolling, contributing to the strength of the material.

In general, in hot rolling method of conventional controlled rolling (CCR), methods of achieving strength would largely be dependent upon the grain size control of austenitic phase and eventually the phase transformation which is controlled by means of addition of microalloying elements in steel chemistry alongside or singly with application thermomechanical treatment practices during rolling. The basic underlying principle of CCR is obtaining steel which possess both high

toughness and strength through grain refinement. The successive methods to

2.Finish rolling which induces the successive heavy reduction in the nonrecrystallization zone, i.e., rolling just above the non-recrystallization

Here, the austenitic grains are refined due to recrystallization.

nucleation sites for alpha grains, its size is restricted.

size and restricts formation of pearlite.

restricting transformation of gamma phase.

**2. Recrystallization phenomenon during rolling**

strains, and strain rates.

**223**

**Figure 2.**

1.Repeated deformation in roughing mill at recrystallization temperature range.

temperature TNR. During finish rolling gamma (austenite) grains are forced to elongate in rolling direction, creating annealing twin deformation bands to cause alpha (ferrite) to form with a very fine size. Thus, by inducing numerous

3.Accelerated cooling that additionally promotes refinement of the ferrite grain

Static recrystallization is likely favored phenomenon in steels during roughing passes and for plain carbon steels it continues between finishing passes as well. The static recrystallization is favored by low alloying levels and high temperatures,

The recovery is suppressed during finish interpasses, but as dislocation density is increasing on account of work hardening at finish rolling, dynamic recrystallization (**Figure 3**) is initiated after surpassing a critical strain value εC. Dynamic recrystallization is markedly identified by necklace-type grain structure. After dynamic

4.Addition of microalloying elements also helps in enhancing strength by restricting movement of grain boundaries by formation of precipitates and

achieve finer grains are carried out as explained below:

*Recrystallization controlled rolling and conventional controlled rolling.*

*Grain Boundary Effects on Mechanical Properties: Design Approaches in Steel*

*DOI: http://dx.doi.org/10.5772/intechopen.88564*
