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The microstructure of the wheel steel was composed of fine-grained ferrite and pearlite and carbides distributed along the ferrite grain boundaries.
In simple ferritic steels, D corresponds to the mean grain size of polygonal ferrite.
That is to say, when the effective grain size is smaller, impact toughness is better.
Fig. 4(b) shows the nano-scale precipitate of experimental steel, a large number of <10nm nano-scale precipitates were obtained.
Conclusions (1) The microstructure of hot-rolled 590MPa grade wheel steel was composed of fine-grained ferrite and pearlite, and carbides distributed along the ferrite grain boundaries.

The grain growth mechanism appears to relate to lattice or surface diffusion.
The production of HA with improved mechanical properties has led to a number of different studies with regard to HA composites with other ceramic [8], glass [9] or polymer additions [10].
Whilst there was a range of grain sizes observed in the microstructures after the various sintering times, no evidence of the exaggerated grain noted by Thangamani et al. [2] and Yeong et al. [13] was observed.
For the sake of interest, the grain growth exponent was extracted using the relationship (D-D0) = ktn, where D is the measured grain size after time t, D0 the average grain size after 0 minutes and k the rate constant.
A slow grain growth rate was observed but did not seem to have any significant effect on the microhardness.

The in-line transmission increases with a decrease in grain size.
Ceramics are polycrystalline materials composed of crystallized grains.
It is thought that the existence of grain boundaries has little relationship to light scattering or the scattering at grain boundaries can be neglected [10].
The scattering coefficient of birefringence is given as follows [11]: (13) Here, Ngr is the number of grains, rgr and Qgr are the radius and scattering efficiency factor of a grain.
Effect of grain size on in-line transmission at wavelength λ= 0.5μm.

For Si content ≥10.7%, grain sizes gradually reduced with annealing temperature increasing.
As Si content increased (CrAlSi3.7N, Fig. 1(b)), the size of and number of micro-hole reduced.
When the Si content ≥ 6.3%, the micro-hole basically disappeared and the grain distributed uniformly.
The effect of annealing temperature on grain size of CrAlSi8.6N and CrAlSi10.7N coatings are shown in Fig. 2.
The grain size of CrAl(Si)N coatings gradually decreased with Si content increasing.

Strip-shaped phase is observed at the austenitic grain boundary.
The severer plastic deformation in ferrite at the austenitic grain boundary can causes small voids form at austenitic grain boundary.
Fracture consists of large numbers of dimples.
Large numbers of deformation twins are observed, showing that the tensile specimen was deformed by twinning mode besides dislocation slip mode.
The second phase precipitation is observed along grain boundary.

. %) alloy was studied in the fine-grained state obtaining after equal channel angular pressing.
As a result, an equiaxed fine-grained structure with an average grain size of 1.1 μm was formed in the alloy.
(1a, 1b) SEM micrographs showing high magnifications of ductile fracture in area framed by number 1 in (a) and (b)
Sakai, K Tsuzaki, Ultrafine-grain structure formation in an Al-Mg-Sc alloy during warm ECAP, Metall.
Effect of grain refinement on jerky flow in an Al-Mg-Sc alloy, Metall.

Small-angle grain boundaries decrease or even disappear.
The Al3Ti grain size is approximately 500nm.
The lower-angle grain boundaries (<15 º) are about 3.12% , which showed characteristics of the high-angle grain boundaries.
This is because that a larger number of materials deforms during REA process.
The risen deformation temperature, the alloying formation and recrystallization occurred resulted in an increasing number of high-angle grain boundaries.

The plastic deformation is mainly dominated by the grain boundary atom slide.
The molecular dynamics (MD) model boxes are fixed as 8.58nm×8.58nm×8.58nm before relaxation, and the numbers of atoms contained in the samples are all about 50000.
The grain centers placed in the MD model boxes are 16, 27, 64, 125 respectively for four samples, and corresponding average grain sizes are 4.32nm, 3.55nm, 2.66nm and 2.13nm.
The abnormal mechanical properties are attributed to the high fraction of grain boundary atoms, and the plastic deformation is mostly carried out through atomic sliding on grain boundary and grain rotation.
The movement vectors of atoms on grain boundary are obviously different from that of atoms interior grain, the similar atomic vectors in a same grain end at grain boundary.

These grains develop specific features that can be attributed to grain competition and concomitant poisoning of growth caused by the rejection of aluminum in the melt.
Yet, their thermal behavior (high Prandtl number) is significantly different from metallic systems (low Prandtl number).
In all cases, the grains display facets all along growth.
The interface between the liquid and the two grains shows a cusp at the level of the grain boundary, and there are merely two facets on the left grain and three on right grain.
Nucleation and growth of new quasicrystal grains.

It can be seen that the grains are un-uniform where the bigger grains are surrounded by many small grains.
The microstructure is shown as Fig.1 (b) which has uniform grains with an average grain size of ~16.4μm.
The grain size was determined using a linear intercept method from a large number of non-overlapping measurements.
At room temperature, due to strengthening of grains, and grain boundaries by lots of fine precipitates and solute atoms, dislocations were difficult to glide in the interior of grains and grain boundaries were also difficult to move.
Summary Grains are refined significantly by ECAP.