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In the oxidation at temperatures of more than the solid solution temperature, the grain size before the oxidation changed to coarse grain size.
It was confirmed that the steel with ASTM grain size finer than number 8 forms a uniform and protective Cr rich oxide layer at the metal–oxide interface, but the steel with coarser grains forms the Cr2O3 oxide scale only locally, in the steam oxidation of 18Cr-10Ni austenitic steels used in the superheater tubes of actual boiler for 15,000 hours [3].
However, when the fine grains changed to coarse grains in the temperature range of 1,000º to 1,100ºC, the steel with fine grain size showed abnormal oxidation because the oxide scale fractured due to the shift of grain boundaries [7].
Fig. 7 Effect of grain size on the flux ratio of Cr from grain boundary diffusion and internal diffusion during oxidation.
At every temperature, when grain size was less than 10 μm, the ratio of Cr from grain boundary diffusion is extremely large.

On the other hand, it is reported that grain refinements cause improvement of ductility and appearance of super plasticity.
However, the tensile strength of AC4CH declined along with the increase in the number of passes.
During the pressing, the billet undergoes severe shear deformation but retains the same cross-sectional geometry so that it is possible to repeat the pressings for a number of passes, each one refining grain size.
Moreover, ECAP-Back Pressure (ECAP-BP) method was reported to be more effective for grain refinements than ECAP method [9].
Fig.4 shows the relationship between number of passes and Charpy impact strength.

However, a good number are believed to originate from dislocation accumulation processes, during which the misorientation angle across certain strain-induced low angle boundaries (LAB) rises with increasing strain.
The grains of the pure Fe grade were even coarser.
Grain aspect ratio (AR).
Equiaxed grains were considered to have AR < 2. 4.
Secondly, the correlated distributions indicate a large number of LAB (practically 50 % of all detected boundaries) that are virtually absent in the uncorrelated plots; this clearly shows that the LAB are an important feature of the deformed microstructures and not merely the result of texture development.

Three different tendencies for the development of the volume fraction with increasing number of cycles were distinguished.
Cycling of one specimen was periodically interrupted at different number of cycles.
Then the fraction of grains containing PSBs (open triangles) grows continuously with increasing number of cycles.
Each line corresponds to the development of the volume fraction of cumulated PSBs with increasing number of cycles for an individual grain.
Therefore, the volume fraction of these grains is very low, even with increasing the number of cycles.

The large grains appeared with at least 4 - 5 sharp edges.
Each three or four grains are meeting together in one point.
The patches of the new Mo rich phase might be surrounded by large number of V"Zn.
The decrease of E0 with Mo content is attributed to the decrease in the number of active grain boundaries connected in series [15].
Fig. 6, (1/C - 1/2C0)2 vis the applied voltage V per grain boundary Table 1; Properties of the grain׳s boundary of Zinc Molybdenum ceramic; Sample number, Mo content, non linearity coefficient α, height of the interface potential barrier Ф (eV), donor density Nd, density Ns of the interface states, the width W (10 -6) cm of the depletion layer and The threshold electric field Eo(V/cm).

The grain selection behavior in grain selector directly determines the casting's final microstructure and properties.
The grain selection process in the grain selector and final microstructure of casting were simulated.
Based on simulated results, a newly designed grain selector with optimized geometry was proposed to avoid stray grains.
Usually it's difficult to calculate the heat radiation in directional solidification, because of the huge number of memories required to store the view factors for each surface cell against others.
Fig. 8 shows the grain evolution with optimized geometry grain selector during solidification.

The first region provides the lattice diffusivity whilst the second or tail region provides (for self-diffusion) the product of the grain boundary width and the grain boundary diffusivity, i.e. δ Dgb.
The rest of the lattice represents the grains.
To simulate a thin-film (instantaneous) tracer source, 10 6-108 particles are created and released from the surface and allowed to diffuse for a time t (proportional to the number of jump attempts per particle).
These concentration profiles are built up simply by determining the number of particles that have reached a given distance from the tracer source plane after the diffusion time t [12].
Again, remarkably, this value seems to be independent on the grain size and ∆.

The use of calculated parameters of grain size distributions is proposed to identify groups of grains by their origin.
However, detailed analysis with the possibility of grains division into groups according to their characteristics is of great interest since a number of competing processes may take place in a material under deformation, for example, by HPT, including various relaxation processes directly under deformation, after it or at following annealing [18-21].
Histograms of grain size distributions with approximation results: 1, 2 – groups of grains.
However, this approach requires more qualitative experimental data containing larger number of measurements.
Plasticity and grain boundary diffusion at small grain sizes, Adv.

Grain-Workpiece Interaction Study of Grinding Process through Single Grain Cutting Simulation Lan Yan1, Zhixiong Zhou1, Feng Jiang 2 , X.K.
From this point of view, a number of grinding experiments with a single abrasive grain were performed [1-3].
Single Grain Cutting Model The shape of abrasive grain is irregular because the grains are made from breaking of crystal, and they are very difficult to classify geometrically.
The single grain cutting parameters are shown in Table 1. 46 # alumina grain is selected, as the 46# grinding wheel is widely used in the coarse grinding.
Grinding process A r Cutting speed V Workpiece Single grain cutting TO 2θ Grain Depth of cut Single grain Fig.1 Optical image of a wheel surface Fig.2 Single grain cutting Table 1 Cutting parameters of single grain cutting simulation Grain material Al2O3 (10~15% ZrO2) Grain shape[9] 46# grain; 2θ = 110°; r=0.028mm Workpiece material D2 steel Cutting speed (m/min) 1200, 1800, 4200, 5400 Depth of cut (mm) 0.006, 0.008, 0.01, 0.012, 0.032, 0.08, 0.12 Grinding condition Dry Results and Discussion Cutting Force.

The more the bend numbers in the channel are, the better the slurry is, i.e. the primary a-Al grains are more spherical and finer.
The subsequently turbulent melt continuously washes against the primary α-Al grains on the channel inner surface, so this phenomenon impels a great number of the primary α-Al grains to gradually separate away from the inner surface.
This condition means that a great number of the separated primary α-Al grains can be survived and the spheroidization of the primary α-Al grains can be more perfect.
This condition means that a great number of the separated primary α-Al grains can be difficult to be survived and the spheroidization of the primary α-Al grains can be not perfect or not possible. 3.2 Effect of bend number on the slurry microstructure The bend number in the channel has also an important effect on the slurry microstructure.
(2)The more the bend numbers in the channel are, the better the slurry microstructure is, i.e. the primary a-Al grains are more spherical and finer