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The grain refinement is achieved more effectively as the temperature for ECAP is lowered and the number of ECAP pass is increased.
Three important conclusions arise: first, the grain is more refined and distributed more homogeneously as the number of ECAP passes increases; second, the grain refinement is more effective as the ECAP temperature is lowered; and third, in order to lower the ECAP temperature without breaking the sample, it is necessary to obtain a homogeneous and equiaxed grain structure before ECAP.
Figure 2 plots the variation of ductility as a function of the number of ECAP passes.
Fig.2 Dependence of elongation on number of ECAP passes.
Fig.3 Dependence of elongation on number of ECAP passes showing effect of subsequent annealing. 0 1 2 3 4 0 0.1 0.2 0.3 0.4 NUMBER OF ECAP PASSES TRUE STRAIN T = R.T

At lower temperatures a number of electrically active twin boundaries increases but the most part of them remains inactive.
A width of these grains is varied from a few to 100 mm.
At liquid nitrogen temperature some additional twin boundaries give the EBIC contrast (Fig. 2b) but the relative number of electrically active twin boundaries still remains rather small.
Σ3 grain boundaries.
At liquid nitrogen temperature a number of electrically active twin boundaries increases but the most part of them still remains inactive.

Measurements of the Vickers microhardness showed improving hardness homogeneity with increasing numbers of HPT turns.
It is readily apparent that the structure before HPT processing contained nearly equiaxed grains with an average grain size of about 10.5 μm.
Thirdly, the samples processed by HPT under 6 GPa had relatively higher hardness compared with samples processed under 3 GPa for the same number of HPT revolutions.
The ω phase has been detected in HPT processed HP and CP Ti at various pressures and for various numbers of rotations of the HPT die [16,17].
The commercially pure Ti attained equiaxed grains with a grain size of ~105 nm after HPT under 6 GPa for 20 turns.

One way for enhancing the strength is decreasing the grains size and reach ultrafine grains.
In recrystallized samples at high temperatures, grain boundaries were moved toward out for decreasing the number of grains.
In uncommon growth few of the grains become course and other grains are covered by these grains.
The grain size was 21.5 μm but grains grew and the grain size became 31 μm at 620oC and 49 μm at 635oC.
Grain sizes were measured by the grain size Eq. (3): D=1N4A/πN (3) where D is the grain size , A is the area of grains measured by the UTHSCSA Image tool softwear and N is the number of grains.

The alloy had a grain size of ~80 µm.
For other orientations, recovered grains and (sub)grains could be observed within the original grains (Fig. 2d).
Grain aspect ratio (AR), is close to ~1.1.
The number and the average misorientation of DBs increase with further deformation by ECAE, leading to fragmentation of original coarse grains into different orientation regions and finally to the development of fine equiaxed grains at high strains.
The recrystallized grains replace subgrains evolved over a small number of passes through continuous transformation of their boundaries.

Ferrite Number The effect of sub-zero temperature on ferrite number is shown in Figure 1.
The yield strength increased significantly from 191 MPa for ferrite number 5 to 863 MPa for ferrite number 65.
The value of UTS increased from 1180 MPa for ferrite number 5 to 1418 MPa for ferrite number 65.
Effect of martensite reversion on the formation of nano/submicron grained AISI 301 stainless steel, Materials Characterization 63 (2009) 1220-1223
Formation of nano-grained structure in a 301 stainless steel using a repetitive thermo-mechanical treatment, Materials Letters 63(2009) 1442-1444 [5] Karpov LP.

The fracture was characterized by ductile fracture due to existence of a large number of dimples. 1 Introduction According to the Hall–Petch relationship, the average grain size of the material plays a significant role in determining the mechanical and physical properties of crystalline materials.
The spacing between each band is approximately 100-500nm.The smaller grains appear to be equiaxed whereas the larger grains are elongated.
The dimples in the fracture zone are mainly large and deep, and their number is high.
It is found that there are a large number of equiaxial dimple.
The average dimple size gradually decreases with increasing number of DECLE passes, which was beneficial to enhance the mechanical properties.

Diffusion rates are greatly enhanced on grain boundaries (GB).
Introduction Grain boundaries (GB) have excess free volume and energy.
The faster GB diffusion is responsible for changes at the length scale of the grain.
Eq. 4 is used in this work to distribute diffusion coefficients to GB as a function of a random number p.
Gust: Fundamentals of Grain and Interphase Boundary Diffusion (Wiley, Chichester, 1995)

The as-received hot-rolled U720Li alloy bar had been subjected to a large number of prior processing steps, so fully homogenous microstructures were got as shown in Fig. 1.
We can see that the alloy consists primarily of a fine mean grain size (20μm) gamma(γ) grains and primary gamma prime(γ’) with a size of 0.5-2.5μm between the γ grains or in the interior of grains.
The grain sizes were measured via two methods, linear intercept and determination of grain area, each of which gave similar results.
So grain growth rate increases when heating temperatures are higher than 1130°C, as well as the grain growth time exponent.
The primary γ’ phase pinned the grain boundary and hindered the γ grain growth.

The recrystallization grain sizes of the fibers annealed at different conditions were calculated by quantitative metallography using the equation (s is the sectional area of the fiber, and n is the number of the grains).
There are a large number of stripes on the surface of the fiber (Fig. 2(a)), which can be attributed to the bundle-drawing friction.
Grain coarsening accompanied by smoothing of the grain boundary takes place with the holding time increasing.
It has been reported [17] that a strong crystallographic texture can arise at least in part from a large number of grains of similar orientation leading to a greater number of low-angle boundaries.
After bundle drawn, a large number of stripes appear on the surface of the fiber.