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Four experiments with an increasing number of passes were conducted on the Gleeble MAXStrain system in order to obtain various effective strain levels.
Introduction The consequence of severe plastic deformation (SPD) is the crystal fragmentation of a large number of metallic alloys to an ultrafine or even nano-grained dimension.
Four different tests were conducted with different number of passes (4, 8, 16 and 32).
Estimated total values of the effective strain at the centers of compressed samples Number of passes 4 8 16 32 Total effective strain 2.1 3.8 6.2 9.1 STEM examinations.
A new local high-angle boundary grain appeared with the diameter of 300 nm (Fig. 4d).

ρ can be determined from the number of effective grains Nt divided by the evaluation area Ae.
When t is determined, Nt can be calculate from the distribution Ng(h) as the number of grains existing within the range from the most periphery to the depth of t (h=0～-t).
The highest points of the grains exist within the width of the average grain diameter d0 centered with the measuring line.
On the other hand, since the number of peaks is same as that of grains, the overall frequency is also same for both distributions.
(3) Since the estimated grain-height distribution agreed well to the distribution determined from the 3D-topography, the validity of the method has been confirmed. 0.3 0.2 0.1 0.48 0.24 0 -40 -30 -20 -10 0 10 20 30 Height μｍ Direction of wheel axis mm Direction of wheel circumference mm width -120 -100 -80 -60 -40 -20 0 20 0 100 200 300 400 500 600 Height μｍ Frequency Peak height distribution Grain height distribution Peak-height distribution Grain-height distribution Depth μm Frequency 0 1 2 3 4 5 6 7 8 9 10 11 12 0 5 10 15 20 25 Actual cutting-edge density Cutting-edge density Effective thicknee μm Density number/mm2 ρ　1/ｍｍ2 ｔ μm Acknowledgment A part of this study has been supported by a Grant in Aid for Scientific Research (Year: 2008, Science Research (C), Subject number: 20560112) from the Japan Society for the Promotion of Science.

Generally with the rise of temperature, stacking fault energy of ferrites increases and, dislocation climb and cross-slip occurs more easily, which produces a large number of sub-structures to increase the critical value Zc.
And the emergence of a large number of dislocations makes grains divide into more and tinier sub-grains and the strain-induced fine carbide particles precipitate inside grains and in grain boundaries.
Meanwhile, the carbide precipitation hinders the dislocation motion which makes a large number of dislocations accumulate here or in grain boundaries, and finally dynamic recrystallization occurs, obtaining uniform and tiny microstructures of which average size is less than 0.5μm.
Therefore, on this condition, recrystallization nucleation occurs rarely, the grain size that is about 1.5～2 μm is much larger than that of the above two conditions and there are a large number of dislocations in grain boundaries, as shown in Fig. 9.
As shown in Fig. 7, dynamic recrystallization occurs when the Z value is relatively high and it is a discontinuous process.9 After deformation, there are still considerable dense dislocations and a large number of fine carbides distributing inside grains and grain boundaries.

Box: 15815-3538 Tehran Iran E.mail: m_esmailian@yahoo.com Keywords: Austenite grain size, Grain boundary and Intragranular ferrite growth Abstract.
Micrographs of different ferrite morphologies show that at high temperatures, where diffusion rates are higher, grain boundary ferrite nucleates both at the edge and corner of austenite grains and grows into both austenite grains.
A high number of oxide inclusions in weld metals and/or particles such as TiN, TiC, Nb(C, N) in plain carbon steels have strong influence on the austenite to ferrite transformation both by restricting the growth of the austenite grains as well as by providing favourable nucleation sites for microstructural constituents such as acicular ferrite [1,2,8].
Moreover results show that reaction time for completion of grain boundary ferrite decreases with increase of austenite grain size.
In the case of acicular ferrite, it seems that increase in austenite grain size causes decrease of transformation temperature and hence increases the number of particles which can be removed from solution.

It was found through experiment that, the grain was very coarse in the cast ingot of 5N5 high pure aluminum, and the average grain size is about 50~60mm.
The grains are very coarse, and the average grain size is about 50~60mm.
We can see the presence of a large number of dislocations and the dislocation has occurred tangles, and has formed cellular sub-structures.
The dislocation inside the sub-grains significantly reduced.
(3) The large number of dislocations can be observed in the sample applied 1 pass extrusion.

Austenite grains were observed by optical microscope and grain size was measured by using the average linear intercept method.
As the temperature exceeds 1350℃, grains suddenly grow up and average grain size approaches to 40.3μm.
There are large number of nanometer particles in steel holding for 2s at 1200℃, however, these second-phase particles can hardly be seen in steel after holding for 2s at 1350℃.
So the number of TiN particles gradually decreases and average size of TiN gradually increases as temperature increment and time extension.
Summary (1) Austenite grains grow slowly as peak temperature is lower than 1250℃.As the temperature exceeds 1350℃, grains suddenly grow up and average grain size attains to 40.3μm

This difference is explained by variations in the dispersoid levels, grain structures (size and grain boundary misorientation) and the texture.
Alloy Fe Si Mg Mn Zn Zr 6063 0.19 0.44 0.45 - - - 6082 0.20 1.04 0.67 0.54 - - 7108+Zr 0.14 0.05 0.74 - 4.94 0.15 7108-Zr 0.12 0.05 0.85 - 5.63 - 6xxxA No dispersoids 6xxxB Medium number of dispersoids 6xxxC Highest number of dispersoids The alloys 6063, 6082, 7108 with and without Zr were DC-cast and homogenized according to standard industrial practice.
The alloy with the highest number of dispersoids (6xxxC), giving rise to an elongated grain structure and a relatively sharp cube texture, has significant higher Charpy values as compared to the other variants when tested normal to the extrusion direction, i.e. the machined crack is normal to the extrusion direction.
As seen from Figs. 1 and 2 the grain structures and the grain size are quite different, which are linked to differences in the dispersoid density.
This difference is explained by variations in grain structures (size and grain boundary misorientations) and the texture.

With increasing cyclic number, the mean stress max min( ) / 2 mσ σ σ= + decreases sharply from 50MPa to about 10MPa after 1000 cycles.
Grain boundaries with large angle have formed between grain A and grain D, as well as between grain B and grain C.
While in the case between grain C and grain D, coalescence of subgrain boundaries is proceeding.
At the same time, the dislocation boundaries of grain C and grain D is migrating outward.
Generally, the driving force for further grain growth decreases with recovery proceeding in grain interior.

peko@imm.rwth-aachen.de Keywords: Grain boundary motion, selective grain growth, magnetic annealing Abstract.
Result column denotes the series size (brackets) and the number of specimens that showed selective grain growth.
Typically a few new grains emerged.
On average new grains are tilted by 73±.
Grain boundary motion measurements A select number of non-notched samples allowed it to measure an actual boundary displacement.

Such rapid decrease of pinning force of grain growth can cause abnormal grain growth.
In addition, average grain diameters of all grains, {111}<112> grains and {100}<013> grains are analized from 20 merged areas in the initial sample.
Therefore, the grain growth is not inhibited and normal grain growth occurs in steel A.
Number and average grain diameter of all grains were 125392 and 16.8μm. {111}<112> and {100}<013> grains are selected within 5 degree of their ideal orientations from all the grains.
If large grains form partially in the matrix due to decrease of the pinning force, large grains around fine grains have higher migration speed of grain boundaries.