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Grain Boundary Engineering for Intergranular Corrosion Resistant Austenitic Stainless Steel H.
Recent studies on grain boundary structure have revealed that the sensitization depends strongly on grain boundary character and atomic structure, and that low energy grain boundaries such as CSL boundaries have strong resistance to intergranular corrosion [1-3].
The concept of ‘grain boundary design and control’ [4] has been developed as GBE [5].
In this study, grain boundaries with ��29 were regarded as low-� CSL boundaries, and Brandon’s criterion [8] was adopted for the critical deviation in the grain boundary characterization [3,9].
A number of twins formed in the growing grains compensate grain-coarsening.

A study has been carried out on the evolution of microstructure, grain boundary character and mechanical properties in a Twinning Induced Plasticity steel heavily cold rolled and subsequently annealed.The cold rolled mcrostructures showed fine lamellar boundaries with many shear bands.With progress of annealing, numerous numbers of recrystallized grains were generated.The fully recrystallized steel showed equi-axed nanocrystalline grains with a mean grain size of 400 nm that enhanced the yield strength significantly while retaining tensile ductility.
However, there is no information available about the effect of ultra grain refinement (grain size < 1 mm) on the tensile properties and their deformation behaviour.
Nanocrystalline grains are surrounded by high angle grain boundaries (HAGB) and many ∑3 annealing twin boundaries are involved in the microstructure.The mean grain size calculated including twin boundaries was 400 nm.
In summary, ultra grain refinement of the TWIP steel was examined.
In the fully recrystallized condition, equi-axed nanocrystalline grains with mean grain size of 400 nm was achieved by cold rolling and subsequent annealing.

Under these circumstances, there exists a competition between the decrease in grain size (grain refinement) due to the imposed plastic strain and an increase in grain size (grain coarsening) due to the increased temperature of the specimen subjected to deformation.
Since the evolution of ultrafine grains takes place by thermally activated processes, the role played by the interfaces such as grain boundaries in controlling the grain size is significant.
This assumes further significance due to the presence of large number of grain boundaries in ultrafine grained materials.
During large strain deformation, as the imposed strain increases, original grain boundaries are compressed and are elongated in the direction of grain flow resulting in high aspect ratio grains, with the thickness of grains decreasing with increasing strain.
Based on Fig.3(a), it may be noted that when the thickness of the deformed grain (grain size) is smaller than the grain boundary diffusion distance, atoms diffuse and ferrite structure is fully recrystallized consisting of new equiaxed ultrafine grains; On the other hand, when the thickness of deformed grain is larger than the grain boundary diffusion distance, atoms diffuse to a short distance leaving a mixture of elongated and newly generated grains.

But grains grew up obviously after normalizing annealing at 850°C for 1h because the mobility of grain boundary is so good at elevated temperature that pinning effect of precipitates can’t prevent the migration of grain boundary.
At least 100 grains were randomly measured in each case and the average grain sizes were estimated.
(a) (c) (b) (f) (e) (d) Fig. 1 Microstructures of the coiled bands (a) 550°C/1h, (b) 550°C/2h, (c) 550°C/3h, (d) 650°C/1h, (e) 650°C/2h, (f) 650°C/3h Table 1 Average grain sizes and the dates of precipitates in the coiled bands Process Average grain size [μm] Precipitate Average size [nm] Number density* Volume fraction [%] 550°C/1h 20 124 3.9 0.047 550°C/2h 23 134 5.0 0.065 550°C/3h 24 138 4.7 0.070 650°C/1h 21 148 4.5 0.067 650°C/2h 24 118 6.6 0.070 650°C/3h 29 110 9.1 0.084 * The number density of precipitates represents the average number of precipitates in a view field.
Hence, grains coarse obviously, which suggests normalizing annealing is necessary in order to gain large grains.
After normalizing annealing at 850°C for 1h, grains grew up obviously owing to the good mobility of grain boundary at elevated temperature and the average grain sizes are more than 100μm.

Both processing techniques, WP and CRA, leads to grain refinement and formation of the grain-subgrain structure of submicron scale in the steels.
Quasi-equiaxed grains with banded contrast are also observed in the structure of the WP-specimens because of formation of ε-phase plates in austenitic grains.
CRA-treatment produces the ultrafine-grained structure with a grain size of 210 nm in 321-type steel (Fig. 1d).
On the side-surfaces of hydrogen-precharged and broken samples, a large number of cracks formed in the fracture zone (Fig. 3f).
On the side surfaces of the samples, there is no large number of cracks (Fig. 4c), but on the fracture surfaces, a brittle 20 μm-zone with numerous secondary brittle cracks is observed (Fig. 4d).

In the pure Cu, the nano-sized grains were formed after third cycle with an average grain size of 200nm.
Once the 200 nm grains formed, further reduction in the grain size was not observed up to the 8 ARB process cycles.
This behavior is also reported in some Al and Ti alloys [6]. 0246810 0 100 200 300 400 500 Tensile Strength (MPa) Number of cycles OFC PMC-90 02468 0 10 20 30 40 50 Elongation (%) Number of cycles OFC PMC-90 Fig. 1.
A large number of dislocations began to be observed in both alloys after the first ARB cycle.
The increase in strength with increasing number of ARB cycle is attributed to the strain hardening in the initial stage.

There are a number of instances of ductile ultra fine-grained materials.
However, most of the limited number of studies of tensile ductility in nc elemental metals have revealed poor ductility.
Distributions of both number and volume fractions of grain sizes were presented.
The mode of the volume distribution was found to be much larger than that for the number distribution.
Ma, Ultrafine Grained Materials, ed.

Wheat grain has been irradiated by 200 keV and 305 keV of pulsed electron beams for changing of sowing parameters.
To solve a number of practical problems of the agroindustry, the use of ionizing radiation was widely used.
To determine the total microbial number (TMN), batches of 0.5 g were selected on the surface of wheat seeds.
To determine the germination and germination energy, the number of seeds was 150 pieces for each variant.
The mass of one grain was taken as 0.028 g.

The results revealed that the change of microstructure plays an important part in the toughness properties at different locations of the HAZ. the CGHAZ (coarsen grain HAZ) microstructure contains granular bainite with the large effective grain size and a number of rod-like M/A constituents, which provide the nucleation sites and linear propagation path for micro-crack, therefore, this location becomes a local brittle zone.
Granular bainite grains have large morphology domains and some prior austenite grain boundaries are retained due to accelerated cooling.
A number of rod-like or granular-like M/A (martensite/austenite) constituents are dispersive distribution in granular bainite.
Due to fine and irregular shaped grains, it is different to calculate average grain size of the FGHAZ according to the optical micrograph.
Each quasi-polygonal ferrite grain has its unique crystallographical orientation domain; therefore, the image quality map and corresponding grain color map exhibit that ferrite grains have very fine crystallographical size.

IN THIS WAY A SIGNIFICANT REFINEMENT OF GRAIN IS ACHIEVED BY SEVERE PLASTIC DEFORMATION.
Grain size reached the value G4 according to the ASTM.
Grain size reached the value from G5 to G6 according to the ASTM.
As it can be seen from Fig.7a (200°C/15 min) in this case no grain refinement took place, while grain refinement shown in Fig.7b (400°C/15 min) is bigger, than in the samples without heat treatment.
Grain size reached the value G8 according to the ASTM.