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This can be simply explained by the significantly enhanced total grain boundary area in refined austenite leading to a larger number of nucleation sites for ferrite.
Particularly for case B a number of considerations have to be done.
During tempering a number of metallurgical effects take place as indicated in Figure 8.
There is evidence for the occurrence of this scenario in a number of alloy systems [17],[18].
In martensite a prior austenite grain contains a very large number of discrete laths of dislocated structure.

It should be noted that the ab-initio computations are currently limited to a relatively low number of atoms, on average less than 200.
Distribution function of the grain boundaries mis-orientation angle (a) and propensity of grain boundaries to grain boundary corrosion.
Change of grain boundary energy, in J/m2, due to alloying additions at the grain boundaries in aluminium.
A Molecular Dynamics Model of Curved Grain Boundaries Molecular dynamics is widely used in the modelling of engineering materials when a larger number of atoms need to be considered.
A model of the grain boundary geometry and their properties adopted in [24] - (a) Map of grain orientations and (b) grain rotation angles of boundaries for a structure with non-homogeneous grain size distribution.

The grains are the cutting tools during lapping.
In the first one, the grains roll in the working gap.
The number depends on the lap plate size.
It was verified if the plate temperature is influenced by the abrasive powder number.
For experiments three numbers of abrasive powder were taken: F400/17, F800/6.5, F1200/3.

Therefore, this study provides important theoretical basis for the ultra-fine grain of bar rolling development.
Although parameters of fabricating ultra-fine grain can be gotten in previous studies, the barrier to produce ultra-fine grain bar was strong plastic.
The flat-oval/ off-round groove system proposed in this paper has feature of so great elongation coefficient that can reduce the number of rolling passes.
In the process of refining grain, the grain size depends on strain, temperature and strain rate, and the quantitative relationship was set up by a lot of research.
The result of research indicated that the grain size depends on Z() factor, and the bigger Z leads smaller grain size.

For AZ61, the elongation increased with the increase of ECAE pass number and the decrease of grain size.
However, the elongation of AZ91 with more second phase particles decreased with the increase of ECAE pass number and the decrease of grain size.
Introduction Grain refinement is an important practice to improve the mechanical properties of magnesium alloy, where equal channel angular extrusion (ECAE) provides a technique for producing ultra-fine grain sizes in the submicrometer or nanometer range in bulk materials [1, 2].
For the AZ31 and AZ61 Mg alloy by ECAE, the elongation increased but the strength decreased with pass number increasing, which are similar with the study results in Jin's[6] and Kim's work [4], which were due to the grain refinement and texture evolution in these alloy.
However, for the AZ91 (a) (c) (b) (c) (b) (a) Mg alloy, the elongation decreased with the pass number increasing.

Larger effective strain gradients generated with compression pressure of 62 MPa and rotation number of 30 revolutions at the radius of 4 mm.
With the increase number of rotation, the effective strain is larger.
All of forming conditions, the effective strain distribution is obvious when number of rotation is 30 revolutions.
The effective strain increases when the number of rotation increase and strain gradient is more obvious.
In Fig.10, when the number of rotation increased to 30 revolutions, the grain size distribution of the contact plane will approach the value of 5 μm, but the simulated effective strain will continue to increase.

The grain abrasion resistance of the cladding layers is also discussed.
The grain abrasion resistance of the coating is also discussed.
While (b) and (c) show that the number of cracks and other defects are significantly reduced, the organization is relatively dense and the material uniformity is well improved.
Grain Abrasion.
The cladding layers consist of compact grains, little porosity and cracks.

Microstructure was quite homogeneous and polygonal grains were observed.
Mean grain size was 0.8 µm.
In this case mean grain size was 1.7 µm, while in Fig. 3b the microstructure of the sample annealed at 700°C x 3 min showed an inhomogeneous microstructure with some coarse grains, indicating that abnormal grain growth occurred.
Increasing the number of passes the non recrystallization temperature decreases and during heating and warm rolling some microstructural changes occur.
Inside the elongated grains there are a lot of small grains with low boundary angles.

The addition of Al–5Ti–1B master alloy to the aluminium melt introduces a large number of heterogeneous nucleating sites such as TiAl3, TiB2, and (Al,Ti)B2 particles into the melt for grain refinement [6–10].
Fig. 3 (a-c) depicts the effect of annealed grain refiner on the grain size of the cast Al-7Si-3Cu alloy.
It is observed that the annealed grain refiner produced more fine and equiaxed grains than as received grain refiner.
This is attributed to the fact that the number of TiAl3 particles increased.
This is due to the larger number of TiAl3 phase in annealed alloy.

In this study, the STSP is applied to grain refinement of an A5056 Al-Mg commercial alloy and the factors affecting the grain refinement are optimized.
The grain size tends to be smaller as the STSP temperature decreases: the average grain sizes are ~1.5 µm at 673 K, ~1.9 µm at 723 K and ~3.1 µm at 773 K.
The former leads to insufficient numbers of dislocations to create grain boundaries and the later makes it difficult to keep the grain size small.
Figure 6(a) shows that the microstructure at the slow cooling rate consists of fine grains and large grains with the average large grain size of ~5.5µm.
The SAED pattern indicates that the fine grains can be separated by high angle grain boundaries.