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But the surface roughness of the specimens with large grains are 1.4 to 4 times higher than that of the specimens with small grains.
The averaged grain size is about 30ìm and 150ìm.
Grain morphology change with the applied strain.
For the crystal C as the increase of strain the twin numbers are increased.
As the roughness increases there are two mutational points in the large grain whereas it is continuously change in the small grain.

Szekeres [8] referred to these abnormally large prior austenite grains, larger than 1 mm, as "blown-grains" and contended that the existence of abnormally large prior austenite grains is the key factor and mandatory prerequisite for transverse cracking [8,9].
In the limit of powder diffraction when the gage volume contains an infinite number of randomly oriented crystallites, full Debye-Scherrer rings are recorded.
Preliminary neutron diffraction studies confirmed that large delta-ferrite grains transform to large austenite grains.
Large austenite grains seem to originate from large delta-ferrite grains.
Delta grains are typically greater than a millimeter in diameter and very large austenite grains are likely to develop from the large delta-ferrite grains in the thin solidifying shell close to the meniscus although the surface grains that initially form on solidification may be small.

The research shows that the number of twinning crystal decreases, the number of the core of dynamically recrystallized grain increases, and the grain size become fine and isotropy by differential speed rolling with the increase of the reduction and the improving of the rolling temperature to some extent.
A great deal of fine grain are distributed at the converged place of big grain bound, which is the result of dynamical recrystallization as shown in Fig.4.
With the increase of the rolling temperature farther, when rolled at the temperature of 350˚C, the proportion of fine dynamically recrystallized grain increase evidently, but some twinning grain and coarse grain still exist as shown in Fig.6.
As a result, the orientation which produce compressing twinning grain decrease, and the inclination which produce compressing twinning grain decrease [4].
With the increase of the speed ratio, the number of compressing twinning grain decreases, and the number of short elongating twinning grain increases.

As the number of MAF pass increases the average grain size was reduced because of plastic deformation by plane strain condition.
The strength was also increased as the number of passes increased [13].
As the number of passes increases the silicon particle reduced their size from dendrite structure [10].
More number of grain boundaries interact with the external force which restricts the movements of dislocations by entanglement with other dislocations and grain boundaries this may be the other reason for the increase in hardness value.
Number of MDF Pass Grain size (μm) UTS Hardness (VHN) Compression Strength(MPa) (MPa) 1 As-received 90 120 55 315 2 1 46 150 69 390 3 2 22 159 76 435 4 3 9 171 81 495 Fractography Figure 5 shows the fracture surface as (a), (b), (c) and (d).

Grains Ultra-refinement of Materials Imposed by Pulse Laser M.
Accordingly, the mechanisms of grains refinement are explored.
Fig.1 Experimental schematic of grains ultra-refinement induced by pulse laser.
Results Grains ultra-refinement had happened on the sample top layer after LSP.
(a) Elongated subgrains perpendicular (b) Equiaxed subgrains to the direction of τ1 Fig.3 SEM micrographs of treated zones after LSP (a) Original grains about 20~30µm in size; (b) Parallel streak-like grains; (c) Parallel dislocation walls in a streak-like subgrain; (d) Numbers from 1 to 6 denote subgrains with high misorientation angles.

In practice, non-neighboring grains in the initial microstructure (separated by a certain number of grains) can be grouped to form global LS (GLS) functions.
This approach allows to use a small number of functions Np compared to the total number of grains constituting the microstructure Ng and thus limits the numerical cost.
The number of possible values for the energy jump ej − ei is then rather limited because Np << Ng.
We are currently interested in an improvement of this formalism which would both enables to use a small number of LS functions and to define an independent stored energy for each grain in the same time.
It is obvious that the complexity of such a brutal algorithm is linear (i.e. in O(e)), where e is the number of elements contained in the collection.

It is well known that Ca addition is effective to obtain homogeneous microstructure of fine grains and highly resistive grain boundaries.
When the sintering temperature was lower than the critical temperature, Ca content greatly affected the grain boundary mobility and dominated the grain growth.
G=π×L/n, where L is the length of the diagonal line of the image to be analyzed, n is the grain boundary intersection count (the number of times the diagonal line cuts across).
It is noticed that the changing trend in number and size of the porosity at different temperature ranges was almost the same as shown in Fig. 5.
Thus, Ca segregated at grain boundary plays a dominate role for the grain growth when temperature is lower than the critical temperature.

Impurity segregation at grain boundaries in polycrystalline alloys is known to have a tremendous impact on the material properties such as grain boundary mobility, cohesion...
Impurity segregation depends on the misorientation of the grain boundary [1] but unfortunately, there are no direct techniques that allow to conveniently measure both segregation level and misorientation on a large number of GBs.
In spite off the relatively low number of boundaries, the population is reasonably close to a random one.
The samples were quenched before completion of recrystallization in order to observe the interfaces between recrystallized grains and non-recrystallized grains.
Because of the high dislocation density in deformed grains it is not possible to get the misorientation information between new grains and deformed ones using EBSD.

Additional rolling after ECAE also enhances grain refinement [6-8].
Mean intercept length of recrystallized grains was evaluated as grain size.
The starting material had equiaxed recrystallized grains, with a mean grain size of 16µm.
In the specimen s1, deformed grains remained.
The change in deformation route may increase the stored energy and produces finer recrystallized grains. 500 520 540 560 580 600 620 640 8 10 12 14 16 18 20 22 s1 s0.8 s0.6 s0.3 s0 Annealing temperature, T/K Recrystallized grain size, d/ m µ Fraction of shear strain Fig.5 Effect of annealing temperature on recrystallized grain size. 0 0.2 0.4 0.6 0.8 1 8 10 12 14 16 18 20 22 Recrystallized grain size, d/ mµ Fraction of shear strain 533K 543K 553K 573K 623K Annealing temperature Fig.6 Effcet of deformation route on recrystallized grain size. 0 100 200 300 400 500 600 s1(1.28) s0.8(1.28) s0.6(1.28) s0.3(1.28) s0(1.28) Sample name Number of high angle boundaries /mm-1 15-30° 30-40° >40° Fig.7 Effect of deformation route on number of high angle boundaries.

Martensite nucleation events may take place in a number of grains leading to a certain number of clusters or spreads.The fill-in and the spread are illustrated in Fig. 1.
This quantity is important because is a measure of spread event that is independent of impingement.The number of grains in a spherical cluster containing tetrakaidecahedral grains the number of grains located within the cluster, γS, γS = 243π 1024 (λEG λγ )3 (2) where λγ is the mean intercept length of the parent austenite grains.
There are a high number of clusters with a small number os grains.
At the end of the simulation the number of grains per cluster is recorded.
Fig. 5 shows the mean number of grains per cluster as a function transformation probability.