Search results

Box: 15815-3538 Tehran Iran E.mail: m_esmailian@yahoo.com Keywords: Austenite grain size, Grain boundary and Intragranular ferrite growth Abstract.
Micrographs of different ferrite morphologies show that at high temperatures, where diffusion rates are higher, grain boundary ferrite nucleates both at the edge and corner of austenite grains and grows into both austenite grains.
A high number of oxide inclusions in weld metals and/or particles such as TiN, TiC, Nb(C, N) in plain carbon steels have strong influence on the austenite to ferrite transformation both by restricting the growth of the austenite grains as well as by providing favourable nucleation sites for microstructural constituents such as acicular ferrite [1,2,8].
Moreover results show that reaction time for completion of grain boundary ferrite decreases with increase of austenite grain size.
In the case of acicular ferrite, it seems that increase in austenite grain size causes decrease of transformation temperature and hence increases the number of particles which can be removed from solution.

Thus high strain and strain rate are directly related to the large number of turns and high rotation speed, respectively.
The SADP taken with the aperture of 740nm showed wholly completed rings confirming that a fine grain structure with 0 0 40 80 120160 200 240280 320400 Number Grain width , nm 12 8 4 16 360 12 8 4 0 Number 16 0 4080 120 160200 240 280320 400 360 Grain length , nm Grain length Grain width 500nm 500nm bcc α 500nm500nm 40 50 60 70 80 90 100 Intensity, cps 2 theta, deg.
It is generally considered that the α' nucleated at the shear bands intersections, which are in the forms of ε, mechanical twins and stacking-fault bundles, and the number of α' embryo increases with the number of intersections and the number of the intersections increases with imposed strain [13].
On the other hand, a large strain is beneficial to produce high 200nm200nm b cc α 200nm200nm Grain length Grain width 25 20 15 10 5 0 0 20 40 60 80 100120 140 160 180 Number Grain width , nm 25 20 15 10 5 0 0 2040 60 80 100 120 140 160 180 Number Grain length , nm densities of defects like deformation twins and stack faults.
These defects can produce a great number of intersections and hence the effective nucleation site for α' embryo.

Such rapid decrease of pinning force of grain growth can cause abnormal grain growth.
In addition, average grain diameters of all grains, {111}<112> grains and {100}<013> grains are analized from 20 merged areas in the initial sample.
Therefore, the grain growth is not inhibited and normal grain growth occurs in steel A.
Number and average grain diameter of all grains were 125392 and 16.8μm. {111}<112> and {100}<013> grains are selected within 5 degree of their ideal orientations from all the grains.
If large grains form partially in the matrix due to decrease of the pinning force, large grains around fine grains have higher migration speed of grain boundaries.

This difference is explained by variations in the dispersoid levels, grain structures (size and grain boundary misorientation) and the texture.
Alloy Fe Si Mg Mn Zn Zr 6063 0.19 0.44 0.45 - - - 6082 0.20 1.04 0.67 0.54 - - 7108+Zr 0.14 0.05 0.74 - 4.94 0.15 7108-Zr 0.12 0.05 0.85 - 5.63 - 6xxxA No dispersoids 6xxxB Medium number of dispersoids 6xxxC Highest number of dispersoids The alloys 6063, 6082, 7108 with and without Zr were DC-cast and homogenized according to standard industrial practice.
The alloy with the highest number of dispersoids (6xxxC), giving rise to an elongated grain structure and a relatively sharp cube texture, has significant higher Charpy values as compared to the other variants when tested normal to the extrusion direction, i.e. the machined crack is normal to the extrusion direction.
As seen from Figs. 1 and 2 the grain structures and the grain size are quite different, which are linked to differences in the dispersoid density.
This difference is explained by variations in grain structures (size and grain boundary misorientations) and the texture.

The scatter effect of grain behavior can be attributed to different grain sizes, shape and orientations which can be employed into each grain as a single element, functioning separately and mutually during the deformation process.
Instead of human input tediously, Python scripts can finish the setup with a large number of grains in GUI (ABAQUS/CAE) satisfactorily by typing given program statements.
In next section, grained heterogeneity will be implemented via Python scripting into each grain with a single plastic property in FE model.
Fig. 1 Voronoi tessellation in bending workpiece (a) 66 grains with grain size 24µm (b) 375 grains with grain size 10µm Grained heterogeneity.
The property of each grain will perform its role in the deformation process, especially the grains in deformed region.

The maximum grain size was 60cm.
Table 1 Representative graduation of three coarse grain soil fillers No.
LµS1/2µV1/3µF1/D (1) After confirming the concept of fractal dimension, Turcotte [2] raised the particle number-particle size fractal model according to the Mandelbrot’s fractal theory.
The coarse grained fillers were formed by the rock crushing.
Three different coarse grained fillers were chosen to find the result.

(a) Image Quality (IQ) map showing the columnar layer of grains and (b) boundary map showing the grain morphology on the normal plane.
A number of reasons may be hold responsible for the closing error problem.
Results and discussion Relative grain boundary energy.
Grain boundary character distribution.
An approximate number of 100 and 200 boundaries were analyzed in the electrolytic Fe and Fe-Si sample respectively.

Then, the number density of recrystallized grains can be expressed by a power law function of dislocation density evolved during cold rolling with an exponent of about 2.
An increase in the nucleation rate increases the number density of recrystallization nuclei and, therefore, results in a decrease in the recrystallized grain size.
Assuming that the size of recrystallized grains solely depends on the nucleation rate, it should be in inverse proportion to square root of the number of recrystallized nuclei per unit area, i.e., D ~ N-0.5.
Therefore, the number density of recrystallized grains in the cold rolled high-Mn steels can be expressed by a power law function of dislocation density evolved during cold rolling with an exponent of about 2, namely, N ~ r2.
In the case of site-saturated nucleation, the number density of recrystallized grains can be expressed by a power law function of dislocation density evolved during cold rolling with an exponent of about 2, i.e, N ~ r2.

ρ can be determined from the number of effective grains Nt divided by the evaluation area Ae.
When these values are determined, Nt can be calculate from the distribution Ng(h) as the number of grains existing within the range from the most periphery to the thickness of t (h=0～-t).
Here, assuming k as the supporting stiffness of grain, fh acts on the grain as shown in equation (2).
In order to calculate Fe , the grain supporting stiffness k is given as 3.13 N/μm according to the grain size and bond type.
On the other hand, Fig.5 shows the change in Nt, which means the number of grains within the peripheral layer with thickness of t.

peko@imm.rwth-aachen.de Keywords: Grain boundary motion, selective grain growth, magnetic annealing Abstract.
Result column denotes the series size (brackets) and the number of specimens that showed selective grain growth.
Typically a few new grains emerged.
On average new grains are tilted by 73±.
Grain boundary motion measurements A select number of non-notched samples allowed it to measure an actual boundary displacement.