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Introduction The application of magnesium alloy sheets are limited by their generally poor plasticity and stamping formability at ambient temperature due to a lack of sufficient number of slip systems associated with hexagonal close-packed (hcp) crystal structure and also a strong basal texture developed in rolled process [1, 2].
The average grain size is about 25 μm.
It can be clearly seen that grains are significant refined with a few of origin coarse grains embedded in new grained structure, the average size of fine grains is about 3 μm. q and Sq change discontinuously at the places correspond exactly to the grain boundaries, it is shown that new grains are mostly separated by high angle boundaries (> 20 degree).
New grains with high angle grain boundaries are developed.
Grain size is reduced to about 3 μm and the volume fraction of new grains reaches to about 0.8 after 8 passes

This can be explained by the formation of the necklace structure with small grains along the upper grain boundary of the elongated grain [see Fig. 2 (a)] that facilitates an easy grain boundary sliding (GBS).
The largest sliding takes place along the upper grain boundary of the elongated grain with the second largest - along the lower grain boundary of the same grain.
Considerable grain growth takes place in the stagnant zones and in contrast to this the formation of a number of small grains (necklace structure [20]) can be seen along the upper grain boundary of the elongated grain.
Elongated grain disappears at early stages of deformation being split into three grains, firstly, by low-angle grain boundaries that later transform into large-angle ones.
Small grains are mostly found along high-angle grain boundaries of larger grains.

To avoid this unwanted effect – since the cracks propagate mainly on high angle grain boundaries – our goal was to enhance the number of special coincident site lattice type grain boundaries with thermomechanical treatment.
The grain boundaries which have a given fraction of atoms in the grain boundary plane which are coincident to both lattices separated by the grain boundary are characterized by the Coincident Site Lattice (CSL) model [5].
By increasing the number of the CSL-boundaries better corrosion and fatigue properties can be obtained [2, 5-7].
Fig.6 Crack length and width into the surface versus the fraction of CSL/random high angle grain boundary Conclusions The relative fraction of CSL grain boundaries to the total amount of grain boundaries increased due to the thermomechanical treatments.
Watanabe, Correlation of grain boundary connectivity with grain boundary character distribution in austenitic stainless steel.

To this purpose a model is presented in which the grain size that appears in the Hall-Petch relation is substituted by an effective grain size that is dependent of the grain-shape morphology and the crystal orientation.
With the approximation of the grain shape as an ellipsoid, the grain size parameter Dθ was defined as the equivalent diameter of an ellipse which is the result of the intersection of the ellipsoid grain with the slip plane (cf.
The equivalent grain size for this slip plane and this grain ellipsoid is D0 ≈1.8 µm.
A spread of 15° from the ideal crystal orientation was allowed in order to include a representative number of grains in the statistics (cf.
Such a material is also very likely to produce a non-equi-axed grain shape, which also contributes to the grain shape anisotropy.

Images are stored in computers as matrix of number representing each pixels value.
In Fig.1 a) is shown a method according to which each grain is numbered by an operator and in Fig.2 b) is a model-image method where operator compares the samples with the models.
The aim of edge detection is to identify the grain boundary.
The SVM model provide as output contours of the grains in a vectorial information, as well as statistical analysis concerning different information such as grain surface and grain shape.
The automatic measurement method proposed in this paper based in SVM approach measure grain size via grain boundary reconstruction.

A remarkable decrease of the grain boundary effect was found at the tempering temperature of 673 K, which is due to a disappearance of film-like carbides on grain boundaries.
Although the block structure, which is smallest unit with high-angle boundary, is analogous to the effective grain, it is still hard to measure the grain size in µm scale and control the grain size experimentally to get a Hall-Petch plot.
As dislocations pile up on a slip plane against a grain boundary stress is transferred to the adjacent grain.
The shear stress τ at the dislocation source in the next grain is expressed as τ = ατs(L/r) 1/2, (1) where α is an orientation-dependent factor close to unity, τs is the average resolved shear stress on the slip plane, L is the distance along the slip plane between the head of the pile-up and the hindward dislocation source, which is directly proportional to the number of pile-up dislocations, and r is the distance from the head of the pile-up to the forward dislocation source in the adjacent grain [17,18].
In this way, a rocking parameter k can be semiquantitatively evaluated using data of nanohardness and grain size for just one sample without changing a grain size to have a Hall-Petch plot.

Some elements, especially microalloying elements, segregate at grain boundaries, and this significantly retards grain growth.
The concentration profile across a grain boundary during grain growth can be calculated by coupling Eq. 1 and Eq. 2
During grain growth with velocity, v, it is natural that grain size increases gradually.
The total number of grid points for a calculation was 601.
Using this model, the concentration profiles across grain boundaries and grain size evolution were calculated.

Model design and equilibration For the investigation of the deformation and heat treatment related dynamic behavior of an atomistic multiple grain structure, an MD program was developed that follows Parrinello-Rahman Lagrangian dynamics [8], i.e. with constant number of particles, pressure and temperature (NPT-system) as invariants of the system.
The bottom central grain as well as the top-right grain also shrunk in size, while the other grains kept or increased their size.
The former top-left and top-central grain form now one grain as the dislocation between them (see Fig. 1) moved through the top-left grain to its boundary.
The top-center grain did not rotate.
Comparing the crystal orientations between neighboring grains, the rotations seem to be forced by the grains which either try to align their {111} planes to a neighboring orientation (e.g. the top-left grain to the top-central grain or the center-left grain to the bottomleft grain) or to seek for a perpendicular orientation relative to the neighbor crystal (e.g. the top-right grain to the top-central grain or the bottom-central grain to the bottom-left grain).

The number of residual phases and grain size were also counted by Image Plus Pro (IPP) software to complement the validation of homogenization.
Meanwhile, in the high Mg alloy, it is mainly dark brown reticular and light gray phases, and the number of fine precipitated phases near the grain boundaries is significantly increased.
The reason for the high number of Ag-containing Al2CuMg phases in high Mg alloy may be related to the Mg-Ag clusters.
Grain Characteristics during Homogenization.
Furthermore, the grain boundaries become clear, indicating that the grain interior segregation is eliminated.

Inhomogeneity of grains in Fig. 1 (a) and (b) shows austenite grain growth trend that big grains swallow small ones.
a b c e d f Fig. 1 Variation AGS RE steel held at different austenitizing temperatures for 5min: (a) 1130 , (b) 1160 , (c) 1190 , (d) 1220 , (e) 1250 , and (f) 1280 Table 2 Experimental data of AGS of steel, isothermally treated for 5 min at different temperatures Temperature, D, μm ASTM grade, G steel A steel B steel A steel B 1130 62.7 60.4 4.7 4.8 1160 78.4 73.9 4.1 4.2 1190 88.5 82.9 3.7 3.9 1220 95.3 88.1 3.5 3.7 1250 105.1 102.2 3.2 3.3 1280 133.2 120.0 2.5 2.8 Fig. 2 Effect of soaking temperature on Fig. 3 Relationship between austenite austenite grain size grain size and soaking temperature AGS is smaller at lower temperature than high Niobium because there are a great number of second phase particles in the steel below 1250 .
These second-phase particles can pin austenite grain boundary and effectively prevent austenite grain growing in heating process.
Most grain boundaries intersect angle is (or close to) 120°, grain size more equalization and shape relatively steady.
Therefore, the effect soaking temperature on grain growth actually is atomic of grain boundary in steel across the grain boundary migration the impact of diffusion process.