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The microstructure of welding zone of welding metals with various heat treatments is grain boundary ferrite, Widmanstatten ferrite and acicular ferrite.
The hardness number of weld metals with quenching process have a highest number base metal, HAZ and weld metals.
On the other hand, base metal has a uniform fine grained microstructure of ferrite and pearlite with large grain sizes.
The hardness number of weld metals with quenching process have a highest number for all region.
The hardness number of weld metals with quenching process has a highest number for all regions.

At annealing temperatures between 700°C and 840°C, there was only a limited amount of grain growth due to grain boundary pinning by (Fe,Mn)3-carbides.
Above 840°C, the dissolution of these particles led to appreciably faster grain coarsening.
Grain growth was very limited because of direct impingement of growing grains.
A number of continuous annealing simulation cycles were performed on small samples under a protective atmosphere.
Once these particles had dissolved (above 800ºC), grain growth was more dominant.

Oswald ripening occurs for grains surrounded by recrystallized grains.
Giving the size distribution p(r), the total number of candidate subgrain is then can be given as: ∫ ∞ ⋅= acr s drrpNN )( (3) where Ns is the initial site number related to dislocation density and original austenite grain size.
The final grain size of recrystallized structure depends on both grain growth and coarsening.
In order to calculate them simultaneously, recrystallized grains are treated as two groups -- surface grains and interior grains.
The grain growing rate that combined growth and coarsening is: ) ( 3 2 3 2 dt dN NR dt dNr dt dR N dt dR NR dt dR rec rec rec rec c surf surf inte inte rec rec +⋅ ⋅+      ⋅+⋅⋅ = (5) where Nsurf and Ninte are number of surface grains and interior grains respectively.

The results show that the grain of the sample steel before pre-treatment (cold rolled then pre-annealed before leaving the factory) is coarser, and the microstructure of the steel plate after solution treatment has obvious refinement tendency and a large number of annealing twins are formed.
Moreover, the size of the grains is uniform.
It can be seen that the structure under water cooling conditions is very heterogeneous, part of the grain grows abnormally and undergoes secondary recrystallization (as shown in Fig. 4 (i)), the number of annealing twins is greatly reduced, also, it can be seen that the crystal grains obtained under air cooling conditions are also relatively large, and the dissolved carbide in the matrix precipitates again at the grain boundaries.
The grain increases the number of grain boundaries of the prior austenite, also, increases the number of nucleation in the subsequent cooling stage then achieves the purpose of refining the grain size; in the solution treatment at 1050 °C for 5 s, secondary recrystallization occurs, accompanied by the abnormal growth of some grains, which causes uneven grain of the structure, thus, the strength, hardness and the plasticity of the material decrease, which adversely affects the product property.
In the interval of 950 °C-1050 °C, the result shows that the number of annealing twins is significantly reduced and the carbides discontinuously precipitate along the grain boundaries, also this process is accompanied by abnormal growth of some grains, which seriously degrades the material properties.

Pipes with large grains and a broader grain size distribution had better corrosion resistance.
To date, a number of researches have been performed to investigate its corrosion and erosion-corrosion in seawater.
Utilizing unique grain color maps in the OIM system, the grains were colored to distinguish one grain from neighboring ones and to characterize grain size distribution.
Fig. 4 presents the grain size distributions in terms of area fraction corresponding to the grains in Fig. 3.
Pipe B have a broader grain size distribution, and the grain size of Pipe B are larger than that of Pipe A.

A distinguishing feature of the model is that all the relevant mechanical fields are represented in terms of grain-boundary variables only, which simplifies data preparation and re-meshing and reduces the overall number of DoFs with respect to other popular techniques.
Numerical tests In this section, the cracking behavior of a polycrystalline SiC 10-grain morphology with ASTM grain size G = 12 is tested.
(a) (b) Fig. 1: a) Grain boundary mesh of a 10-grain polycrystalline morphology with ASTM grain size G = 12; b) Volume stress average as a function of the load factor for the two considered values of the ratio between the inter- and trans-granular fracture toughness.
Future work will involve morphologies with larger numbers of grains and the coupling with other polycrystalline deformation mechanisms such as crystal plasticity [10].
Mallardo, A grain boundary formulation for crystal plasticity.

Consider first the movement of a grain boundary.
This is quite a small amount, only a few percent of that typical for recrystallisation or equivalent to the energy of grain boundaries in a metal with a grain size of about 200µm.
However, a number of caveats may apply.
This model was applied successfully to describe an observed phenomenon of grain rotation.
However, the number of systematic investigations are few, so many conclusions are tentative at present.

The values of strain rate sensitivity, m was determined, as a function of grain size, and it decreased from 0.45 to 0.33 to 0.18 with increasing the grain size.
FSP creates a region called the "stir zone" or "nugget", where the microstructural refinement occurs with equiaxed ultrafine grains with high angle grain boundaries.
This figure captures the abrupt change in the microstructure from elongated grains to ultra-fine equiaxed grains.
The Vickers hardness number of the base metal is about 80, whereas at the center of the nugget the hardness increases to about 95, for the 430-90 and 430-140 condition.
Table 1 presents a comparison about the grain boundary characteristics for all friction stir processed conditions in terms of grain size, average misorientation angle and percentage of high angle grain boundaries.

The sample surface to be treated was impacted by a large number of flying balls over a short period of time.
However, the surface became stronger and harder after HESP for a great number of dislocations and micro-strain were introduced into the surface layer, so the surface layer and matrix fracture were in different deforming mode. 2.2 X-ray diffraction (XRD) analysis Results of X-ray diffraction (XRD) for both two kinds of magnesium alloy before and after HESP were demonstrated in Fig.3.
The grain sizes for different crystallographic planes of α-Mg phase in the treated surface were slightly different but all of them were smaller than 100nm, and the average grain size of α-Mg phase for magnesium alloy AZ31B and AZ91D were about 49.46nm and 52.26nm respectively, which means surface nanocrystallization was realized by HESP.
It could be observed that lots of nanometer grains resembled into a big particle and the grain size for nanocrystalline by SEM was a little larger than that obtained by XRD, which maybe caused by the limit of the max resolution ability of SEM, the results of which were in accord with those of the literature[4].
Compared to original coarse grain, the nanocrystalline or super fine grain had much higher surface activation energy and percentage of grain boundary, which meant nanocrytalline were much more apt to be corroded.

Vickers Hardness Numbers (HV) calculated from a minimum of 240 indentations made across the SZ of each sample were presented as microhardness distribution contour maps.
Significant grain refinement can be observed in the SZ, as shown in Fig. 2b.
Table 3 Summary of the average grain sizes and mechanical testing results for AZ91 alloy.
Apart from that, the horizontal microhardness profiles plotted in Fig. 5 not only illustrate higher Vickers Hardness numbers within the SZ (dashed box region), but showed general uniformity in the microhardness across the SZ, as opposed to the high fluctuations observed in the outer, unstirred region.
Significant grain refinement from an average grain size of 123.1 μm to about 5.0 to 6.2 μm was achieved.