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Materials Performance of HRBF500 Grain Reinforcing Bar.
Fine grain steel, through the refinement of the grain boundary dislocation, refinement of blocked, the strength of steel enhanced.
Grain refinement with the most significant and effect in steel, increasing strength and toughness [4].
At present, our country has smelting, rolling weathering steel and 800MPa ultra-fine grained steel, and using Q235 steel make industrial experiment, producing 630MPa tensile strength and yield strength of 500 ~ 650MPa of fine grain steel successfully.
the role of the number usually only once, load value is particularly large, but uncertain.

The powder volume contained grains with a random texture and average grain size of 50 µm.
To this end, the ratio of the number of the cells in the powder domain belonging the grains originated from the substrate to the total number of the cells in the powder domain was calculated.
Fig. 2(d) shows a decrease of FEG by the substrate grain size.
It shows that the probability of the preferred grain orientations within the AM portion of the substrate decreases by the grain size, leading to the reduction of the FEG.
CAFD results for substrates with grain sizes of (a) 50, (b) 100, and (c) 200 µm, and (d) FEG as a function of the substrate grain size.

However, the addition of Ce increased the proportion of high-angle grain boundary from 33.2% to 40.2%.
A large number of studies[1-4] have shown that adding appropriate amount of rare earth in steel can improve the welding performance, mechanical processing performance and mechanical properties of the material by refining the grain, metamorphic inclusion and microalloying.
In the boundary maps of the 1# (Figure 3c) and 2# (Figure 3d) steels, the blue and red lines respectively denote the low-angle grain boundaries (5°＜θ＜15°) and high-angle grain boundaries (θ＞15°).
The HAGBs can change the crack propagation direction or interrupt the crack, hinder the crack propagation effectively, facilitate grain boundary sliding and enhanced grain rotation, which improve the ductility of the material [6].
(b) (a) Low-angle grain boundary (5°<θ<15°) High-angle grain boundary (θ>15°) (c) (d) (f) (e) Figure 3.

The studied sample contained large grains with grain size of approx. 0.5 to 3 mm.
A large number of indentation tests was carried out on the sample with a loading rate of 0.2 mN/s.
The average indentation hardness (5.0±0.4) GPa was similar as to the first grain, however the average elastic modulus (75±2) GPa was substantially different from the average value obtained in the first grain.
(Grain 2).
The average hardness (5.0±0.4) GPa in the second studied grain was almost the same as in case of the first grain.

Fig. 4 (c) shows that, in the central undeformed area (3#), the reversed austenite grains mainly locate in the original austenite grain boundaries, while some of them distribute within grains.
The reason is as follows: (1) Tensile deformation is good for reversed austenite transforming into martensite, because martensite transformation is a process with volume expansion [10, 11], the interface between the new generation of martensite and austenite is large angle boundaries which reduce the proportion of the small angle grain boundaries; compression deformation promotes martensitic transformation to a lesser extent relative to the tensile deformation, thus large angle grain boundaries are improved to a lesser extent; (2) When grain was stretched, the density of the dislocation in matrix will be decreased for that some of the dislocation in matrix disappeared by tangling and rearranging , which will reduce the number of small angle grain boundaries and improve the proportion of large angle grain boundaries; when grain was squeezed, the dislocation density of per unit area decreased and the number of small angle grain boundaries increased, so as to reduce the proportion of large
angle grain boundaries.
This is because of that the concentration of stress in the original austenitic grain boundary is larger, which will make it easier for reverse austenite to transform into martensite; and the stress concentration will be reduced for large size grains will coordinate mutually in the process of deformation, and at the same time the stability of reversed austenite in grains will become higher for boundary protection.
Besides, the retained austenite mainly locates within grains.

The mean grain size of each state is 33.65um, 24.53um, 32.04um and 32.98um.
Yield strengthvaries with the grain size.
The smaller the grains are, the greater the total grain boundary is, and the more difficult is for the dislocations to traverse, resulting in the stacking of the dislocations.
Therefore, the fine-grained material with 1h cryogenic treatment has the highest strength.
Acknowledgements This work was supported by the key scientific and technological project of Chongqing (Project Number: CSTC, 2009AB4005).

The microstructure of the steel consists of equiaxed ferritic grains which average grain intercept length at the principal directions of the sheet are 23.9 µm (RD), 21.4 µm (TD) and 15.9 µm (ND).
Various types of particles were found homogeneously distributed embedded in the ferritic matrix in either grain boundaries or inside grains although it was more common the first ones.
The fraction of titanium particles is predominant in the material with around 83% of the total number of particles and their shape is close to cubical with an equivalent length of 2.54 µm.
A concentration of these dislocation features were observed close to the grain boundaries.
Acknowledgements This research was carried out under project number MC5.05220 in the framework of the Strategic Research programme of the Netherlands Institute for Metals Research in the Netherlands (www.nimr.nl).

As the time change from t to t + δt, grains position will also change to , where it holds in general that
Function sign() in Eq. (5) is defined as (6) and the overlap between grains ξij is defined as in [11] , (7) where Di is diameter of grains i.
Experiment Two dimension grains are represented by small and thin disks, which are distributed artificially.
Each configuration is recorded and then analyzed using tailored software to get particles position and number of contacts on each particle.
Each particle position and contacts are obtained from tailored software, where illustration of the observed contacts between grains is given in Fig. 2.

Note that type K - damage refers to cases with little damage outside the main lines of damage; type C damage refers to cases with distributed cavity formations; - at low levels of orientated cavitation (class 3a lower limit) types K and C may be inseparable; - cavity chain = formation with several cavities on a grain boundary extending to adjacent grains - GB = grain boundary 3.
NORDTEST NT TR 302 thus specifies the number of cavities in more detail, especially in damage classes 3 and 4, which makes evaluation of creep cavitation damage more independent on the subjective visual observation and evaluation.
Cavities were found at grain boundaries and also at the inclusion-matrix interface, where it was not possible to exactly confirm or deny their presence by OM.
On the other hand, coarse grained part of heat affected zone (CG HAZ) was heated up to temperatures well above Ac3 and microstructure completely transformed during welding.
At the same time, significant inhomogeneity of cavitation damage was confirmed again, when the number of cavities decreases with increasing distance from the outer surface of the pipe.

SEM micrographs of the two sialon compositions (Fig.2) show a microstructure with a bright phase with an equiaxed grain morphology that corresponds to α-sialon and dark grains with elongated morphology corresponding to β-sialon.
The small bright spots are rich in Neodymium and represent the small fraction of amorphous grain boundary phase located at triple junctions.
Especially for materials with such a large crack growth exponent n the number of spontaneous failures during load application and survivals is larger than the number of tests with regular failure.
Before this stress level was reached, a number of 5 specimens failed spontaneously.
The large number of spontaneous failure and survivals made the development of a modified procedure necessary in order to obtain a significant database.