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The discontinuous dynamic recrystallization (DDRX) mechanism is complex, it depends on the rheology of the material (strain hardening and dynamic recovery), and it involves the nucleation of new grains and the migration of grain boundaries as well.
This is partly because such alloys contain a large number of addition elements which may interact in a complicated way during hot deformation, thus requiring description of phenomena such as solute drag and Zener pinning, and their effect on grain-boundary migration [1].
A number of laws have been proposed for modeling this deformation range from dislocation concepts.
Piot et al., Modeling grain boundary mobility during dynamic recrystallization of metallic alloys, Mater.
Damamme, A grain scale approach for modeling steady-state discontinuous dynamic recrystallization, Acta Mater. 57 (2009) 1602-1612

Besides, the coarse grain causes low impact toughness of metal, especially at negative temperatures (steel cold brittleness threshold raises).
Several ways of grain refinement are known
• A steel microalloying with nitride- and carbide forming elements, such as vanadium, niobium, aluminum, titanium, boron, etc., that causes refinement of austenitic and real grain [2]
Simple analysis makes it possible to choose the 3rd way of steel grains refinement in view of its low cost and high performance.
Carried out researches were aimed to formation of fine grain structure of shape-rolled steel made of 09G2S low alloyed steels in the steel rolling conditions.

The destruction of propellers is affected by a number of technological factors (pores, inclusions, residual stresses, etc.) and operational ones: (corrosion, fatigue, mechanical damage and other factors).
The TiNiCo layer has a nanoscale structure with a grain size of 30-190 nm (Fig. 3b), the martensitic structure of the TiNiCo layer is shown in Fig. 3c.
The resulting B4C-Co layer has a nanoscale structure with a grain size of 30-95 nm (Fig. 3f).
Dependence of the average grain size and its percentage: TiNiCo - a); B4C-Co-b) The Ni3Ti, NiTi2 phases are mainly released during crystallization and are located along grain boundaries.
The highest value of the amplitude of variable stresses, up to which the samples did not break down, the basic number of cycles (endurance limit, σ-1) for uncoated steel 30HGSA is 495 MPa (heat treatment mode normalization), and after surface modification by TiNiCo-B4C-Co composite surface layers is 590 MPa (HVOF), i.e., it increased by ≈16.1%, TiNiCo-B4C-Co is 645 MPa (HVOF + annealing + surface plastic deformation), i.e. it increased by ≈23.3% .

Niobium, insoluble in solid solution, is squeezed out of αFe-Si and inhibits grain growth.
Thus, the drag effect of grain boundaries in the crystallization weakens when replacing Nb with W or Mo.
In an alloy with niobium, only a small number of Nb atoms dissolve in α-Fe and, accordingly, a smaller number of vacancies are formed, which stabilize the domain walls less.
Yamauchi, New Fe-based soft magnetic alloys composed of ultrafine grain structure, J.
Shvindlerman, Grain boundary migration in metals: thermodynamics, kinetics, applications, CRC Press, Boca Raton, London, New York, 2010

Fig. 1(a) shows that little deposited silver exists on the surface of Al powder after substitution plating, while a uniform thin silver layer existed on Al-Ag powder, some grain boundaries can be seen in certain areas in Fig.1(b).
Fig.2 shows many Al peaks and a small number of Ag2Al peaks,coinciding with alloy the equilibrium phase diagram of Al-Ag.
After electroless silver plating, we can see a large number of Ag peaks and different intensity diffraction peaks at 2θ-38. 12°,44. 31°,64. 45°and 77. 41°which correspond respectively to Ag (111),(200),(220) and (311).
Fig.3 Back-scattering SEM pattern of powder (a) Back-scattering SEM pattern of Al-Ag powder (b)Al-Ag powder’s profile after electroless plating Ag2Al distributed unevenly on the grain boundaries of the alloy powder.
Owning to the difference of potential between the grains and the Ag2Al-enriched grain boundaries, many microbatteries appeared as the alloy powder immersing in silver salt solution.

The averarge grain diameter is very large (>500 mm).
The Contour numbers represents the efficiency of power dissipation in percent.
The micostructure shown in Domain 1 (Fig. 6a) did not reveal fully dynamic recrystallized (DRX) grains,because the large number of hard CaMgSn particlespresent in the matrix generate considerable back stress and restricts the basal+prismatic slip.
iv) The microstructures obtained in the components forged under Domain 2 revealed fully DRX grains and is recommended for hot processing of this alloy.
v) The bifurcation region has to be avoided in processing this alloy since it leads to grain growth.

The results show that owing to the low cooling rate nearby the arc thick-walled department and the trasition region between the thick and thin-walled of the connection beam casting, leading to the morphology of the crystalline grains and silicon particles in this vicinity are thick.
The mechanical properties results of test samples Metallographic survey The test results of low and high magnification microstructure observations are shown in Fig.5 and Fig.6, by the yellow wireframes in Fig.5, it shows that the grain sizes of 4,5and 6 test patterns are significantly small than other test samples, equation 1 shows that the mechanical properties is inversely proportional to the grain size [2] [3] (σs and σ0 are ultimate strength and foundation strength separately, k is a constant coefficient, relating to the materials, d is the grain size).
Whereas, the silicon particles spheroidization process of other test specimens after T6 heat treatment is relatively perfect, small dense spherical silicon particles are evenly distributed nearby the grain boundary.
Aluminum and silicon accounts for 28.36% and 71.06% apiece, proving that the fracture of test specimens mostly take place in the binary Al-Si eutectic mixture within the grain boundary, also attesting that the intergranular fracture is the main failure mode.
The relationship of grain size and cooling rate is inverse, also the mechanical properties (such as tensile strength, yield strength and elongation) of casting and grain size are in inverse proportion, therefore result in the thin-wall, forward stud and square box region have higher mechanical properties than other places.

The solutionized and aged specimens were coarse-grained with an equiaxed grain size of 0.5 to 1 mm.
The cyclic-deformation curves of specimens OA and UA are shown in Figs. 1 (a) and (b), where the plastic strain amplitude εpl is plotted against the number of fatigue cycles (N).
The results of fatigue life tests (S-N curves) for specimens UA and OA are shown in Fig. 3, where σa is plotted as a function of the number of cycles to failure (Nf).
In the specimen OA, precipitate-free zones (PFZs) were formed near the grain boundaries, and the averaged PFZs width was about 200 nm.
These PFZs have a low yield stress in comparison with the grain interior, thus favoring dislocation movement, and eventually crack nucleation seems to occur within the PFZs.

However conventional analysis of XRD data suffers from a number of shortcomings.
Apart from these, overlapping of adjacent lines may pose serious problems in detecting the number of measurable lines, particularly in complex systems.
Microalloyed steel though only shows fine ferrite grains in its microstructure, a small amount of cementite phase was detected by XRD measurement.
The crystallite sizes thus obtained are quite small compared to the grain sizes for the samples.
This may have caused the evolution of large number of deformed grains and sub grains on the surface of the samples.

And the decrease of Ca(OH)2 accelerates the hydration of cement, then, makes the crystalline grain of Ca(OH)2 more small.
The results demonstrate that along with the process of concrete liquefaction, the number of CSH gel increases more and more due to reaction between SiO2 and Ca(OH)2.
At the same time, the number decrease of Ca(OH)2 accelerates the liquefaction of concrete.
The fineness of LSR grain and fly ash are quite close.
And the test proves that the strength of LSR grains is much weaker than fly ash.