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Its mean grain size was about 86µm.
The sample subjected to 4 ECAP passes consisted of equiaxed grains with a diameter of 0.3 ~ 0.5µm, as shown in Fig. 1(c).
Fig. 1(d) shows that the dislocations partly disappeared inside some of the grains after annealing, but no grain growth was observed.
It was found that the tensile strength of the Al 5052 alloy increased, while its elongation decreased, with increasing number of ECAP passes, due to grain refinement and the continuous increase in the dislocation density[3].
As shown in Fig. 3, the Vickers hardness increased as the number of passes increased.

The ferrite grain size number is 11.
The requirements of Nb microalloyed H beam are as fellow: yield strength is great than 365 MPa, ferrite grain size number is great than 9, charpy impact energy at -20°C is greater than 34 J.
Austenite grain size affects ferrite grain size of product.
When heating temperature are 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, the corresponding austenite grain size number is 4.5, 4, 3.5, 3, 2, 1, respectively.
The microstructure consists of ferrite and pearlite, and the ferrite grain size number is 11 (see Fig 4).

Recently, ultrafine grained microstructures with a grain size of less than one micrometer were obtained after annealing of severely deformed alloys [3-6].
Despite the large number of studies on continuous recrystallization operating in various metals and alloys processed by large strain deformations, some characteristics of this mechanism, e.g. texture evolution, are not known in detail.
In this case, the grain coarsening takes place homogeneously without preferential growth of any individual grains.
Number Fraction, Ni / N 0.0 0.1 0.2 0.3 0.4 0 10 20 30 40 50 60 0.0 0.1 0.2 0.3 0.4 Misorientation, θ (deg) 0 10 20 30 40 50 60 0 10 20 30 40 50 60 ε = 2.0 ε = 4.4 ε = 2.0 625o C, 30 min ε = 2.0 625 oC, 2 hours ε = 4.4 625o C, 30 min ε = 4.4 625 oC, 2 hours Fig. 6.
The development of primary recrystallization associated with grain boundary migration over long distances results in a decrease in the total number of low-angle subboundaries, while the fraction of high-angle grain boundaries increases.

The dependence of P1 and P2 on grain size indicates that the two peaks are originated from the grain boundary sliding, and P3 may be associated with the diffusion of Ce atoms or other impurities at grain boundaries.
It is well known that the solubility of solid solution of Ce element in Al is very low, and with annealing temperature or deformation rate increasing the segregation of Ce atoms may take place at grain boundaries.Based on the grain boundary sliding model, the grain boundary sliding is restricted by the triple grain boundary when the grain size is smaller than diameter of the sample.
Ke also discovered that the height of bamboo peak was proportional to the number of bamboo grains [6].
At a higher annealing temperature, more Ce atoms gathered to form participating particles at grain boundary, these participating particles may act as blockings to restrict the grain boundary sliding instead of the triple grain boundary.
Mori also found that participating particles at grain boundaries can act as triple grain boundaries to restrict the stress relaxation across the grain boundary when the bamboo peak appeares [7].

The number and the density of surface defect were increased.
CURM then produced a large number of sub-grains.
With the strain increasing, dislocation cells increased in the number and reduced in the size.
Finally there are many sub-grains within the grain, the size of grains on the metal surface is smaller.
It needed greater resistance to transform, which played the role of grain boundary strengthening, Smaller grain size in the same volume needs the larger number of grains in the same deformation.

The average grains size is 7-6 index, when welding without the TMF influence and the average grains size of the weld metal corresponds to 8 index, with separate inclusions of grains with 7 index when welding with the TMF influence.
These data are summarized in monographs [1, 2] and given in a significant number of publications [3-5].
Besides in a number of publications, it is shown that the transverse magnetic field (TMF) use also allows to obtain the above-mentioned positive effects.
Thus, the data on the TMF influence on the weld crystallization in arc welding are few in number.
Electromagnetic stirring and grain refinement in stainless steel GTA welds.

If it is assumed that nucleation only occurs at grain boundaries, then a given number of nuclei per length of grain boundary in a fine grained material will lead to more homogeneous recrystallisation than the same number in a coarse grained material.
Therefore, a large initial grain size provides fewer nucleation sites due to the reduction in grain boundary area per unit volume.
Note that after a reduction of 50%, the original fine-grained (A) material gave an appreciably finer grain size after recrystallisation than the original coarse-grained (C) material.
However, after a 70% reduction, the grain size after recrystallisation was similar regardless of different initial grain size.
The recrystallised grain size decreased markedly with increasing deformation and decreasing initial grain size.

The starting material had equiaxed austenite grains with mean grain size of 35 μm.
This is called grain subdivision which is the basic process of grain refinement by SPD process.
Fig. 4c shows the change in density of low angle boundaries versus number of the ARB cycles.
(b) (a) (c) Fig. 4 Relationship between the number of the ARB cycles and a) the martensite transformation starting temperature (Ms), b) the austenite grain size (boundary interval along ND), c) density of low angle boundaries (2°≤θ<15°) within the austenite.
(iii) The Ms temperature changed depending on the number of ARB cycles.

For smaller number of turns (N = 1), the Hv increased with distance from the disk center.
The ultimate tensile strength, UTS, and the total elongation, EL, were plotted in Fig. 8 as a function of number of turns.
Some continuous-recrystallized grains were observed.
Fig. 8 Mechanical properties of HPT-processed iron as a function of number of turns.
Langdon: Ultrafine Grained Materials III, TMS, ed. by Y.T.

Voronoin method[6,7] is a common method to construct nano-polycrystalline materials: First, a number of points whose Z coordinate are controlled to obey the linear probability density function are randomly generate as the center of the grains,and the distance between grain centers is adjusted to avoid the two grain centers being too close.Then, calling the Voronoin function of MATLAB to generate the grain boundary topology of GNG model.Finally, a C++ script from the literature[8] was developed to fill each grain with the face entered cubic (FCC) copper atom lattice.
The initial positions of crack tips in the three samples are in the grain, along the grain boundary, perpendicular to the grain boundary, respectively.
(4) Figure 2 Schematic diagram of relative crack calculation In the process of tensile deformation, as Fig. 3 shows, a large number of hexagonal close packed (HCP) structures occur in the interior of larger grains and near the crack tip, which reflects the intense dislocation activity and a large number of stacking faults in these two regions.
Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility, J.
Fracture behavior of precracked nano-grained materials with grain size gradients, J.