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A number of experiments, including physical and numerical simulations, were performed in order to understand and model the origin of the PCG in indirect extrusion of 6xxx alloys.
GDRX grains form as a grain is heavily deformed to the point where its grain boundaries begin to "pinch off" and form new, equiaxed grains with high misorientation (>15).
Notice the fragmentation of the grains, especially in regions marked by arrows.
It can be seen that there is an intensive fragmentation of the grain, both at the grain boundaries and within the grains themselves.
Here, grains are loosely defined as regions of similar texture, due to the disappearance of a well - defined grain regions.

The tool stirring action generates the formation of fine, equiaxed, recrystallised grains.
In the weld nugget the original grain and subgrain boundaries appear to be replaced with fine, equiaxed, recrystallised grains characterised by a nominal size of a few m (Fig. 2).
The thermo-mechanical action of the tool pin determines grain demolition in the blank"s material up to a microstructure characterised by very fine, equiaxed grains.
It has to be emphasised that the topology of the utilized network has been defined on the basis of a optimization procedure aimed to improve the network performances: in particular the number of hidden layers and the number of neurons have been determined on the basis of the best performance of the neural network in the training stage following an analytical hierarchical procedure (AHP).
Fig. 5: The grain size measurement loci.

However, the machining processes involve unresolved problems concerning the safety of work environment and the cost of abrasive grains since a large quantity of abrasive grains is used.
The vitrified-bonded diamond wheel provides a high elastic modulus and high exhaust ability of the chips due to the presence of a great number of pores.
When grain size is large, surface roughness also increases.
Many clusters of abrasive grains and bond are formed.
The surface that was finished by 5-10Ǵm- and 2-4Ǵm-sized abrasive grains clearly retains the cutting marks left by the abrasive grains.

Research on the mechanical properties for medical stainless steel Ming WEN, Wei LI and Xiaoming CAO School of Material Science and Engineering, Hebei University of Technology,Tianjin, China e-mail: gd-wen@gadvanize.com.cn, shmily_lw@126.com,gd-sam@gadvanize.com.cn Keywords: Austenitic stainless steel; Grains; Crew; Torque; Torsion angle Abstract.
The original scan 400× 00Cr18Ni14Mo3 original austenite, from Fig.1 and Fig.2 we can see a large number of slip belt within the grain and black white spots, the initial suspect that these spots may be carbides, due to the presence of these spots on the hardness of the screw, plastic , has an impact toughness.
Carried out a number of experiments, we found that the bar is heated to 950 ° heat 1h water, torque and angle can meet well. 950 ℃ solution and water cooling.
Fig.5. 950 ℃ solution and water cooling scan 200 Fig.6. 950 ℃ solution and water cooling scan 400× Compared with the original sample, can be seen within the austenite grains slip bands disappeared completely, grain boundary is clear and grain grew up in different degrees.

a b Fig.4 Cast number 9#: a) Edges oxide skin, 500×; b) Inclusion at edge, 100×.
Fig.5 Inclusion at edge of cast number 13#, 100× Known from above microscopic analysis, the generation of strip surface defects has a direct relation with surface quality of cold rolled steel billet mainly.
Usually clear typical oxide layer is made up of outside, dense spread layer and along grain oxide layer.
Membrane particles thought as oxide and sulfide distribute near bulky grain, besides grains grow up strong when overheating and overburning, austenite grain boundaries are polluted by oxide and sulfide.
This is because after grain coarsening, total area of grain boundaries reduce greatly, oxygen and sulfur soluting in austenitic under high temperature enrich in grain boundary in subsequent cooling to near 1200ºC, they are just dense spread layer and along grain oxide layer.

Microcracks, micropores inside of grain or at the grain boundaries act as a crack initiators.
Nucleated microcracks inside grains tend to grain boundaries, at which can be arrested or can spread along the nearest grain boundary.
This is due to significantly less fracture toughness of this part of composite, or can pass through a grain boundary to the adjacent grain.
(8) In equations: (6) - (8) (k) c� is the number of kinks in RSE, whereas (k) c is the half length of the mesocrack, which creates the kink.
The crack propagation strongly depends on the grain boundary porosity spread along grain boundaries as well as thermal residual stresses.

The nucleation process in the grain begins when the dislocation density in the grain reaches the critical value rc.
The equation is of following form: (1) where – the maximal nucleation rate corresponding to the nucleation rate during the static recrystallization, NV – the current number of the grains, NVmd – the maximal number of the grains at the existing condition of deformation.
The differential equation (1) contains two elements: determines nucleation during the static recrystallization and NVmd, which determines number of new recrystallized grains during the dynamic recrystallization.
The grain boundary migration rate depends on driving force of recrystallization p and grain boundary mobility m: v = m p.
It gives the initial average grain size of about 52 μm.

This is different shape of grain boundary which shown as straight line in figure 1(b), where no grain boundary migration happened.
Dislocation loops of interstitial atoms type were formed in the early stage of irradiation, and their size and number density increased with irradiation time and then formed coarse and large size of dislocation loops [6].
Irradiation-induced grain boundary segregation.
(Measuring point : 5 point for grain boundary, 3 point for the nearest point from grain boundary and 1 point for near a grain boundary.)
The change of grain boundary segregation (Δ Cgb) was calculated from the difference between concentration at the grain boundary and concentration at the nearest position from the grain boundary.

A number of in-service failures of 12Cr-Ni stainless steel due to intergranular corrosion (IGC) in the HAZ have been reported in the past decades [15].
Fig.4 (a) shows that the microcracks are propagated along the prior austenite grain boundaries.
When the prior austenite grain boundaries were completely surrounded by cracks during exposed to boiling test solution, these grains would be etched off and then were instead by deposited copper.
Numbers of finely precipitated phases are observed along prior austenite grain boundaries or inside the martensite matrix in this picture.
However, large numbers of particles are also observed in LTHAZ of cover pass, but IGC does not occur in this location.

The 850℃ annealed alloy has visible fine recrystallized grains at the grain boundaries, and the 900~1,000℃ microstructure shows the original deformed grains and the new generation of grains.
The recrystallized grains are presented in a mixed state.
The results show that there are a large number of granular carbides, which is not exceed 1μm in diameter, and a lot of finer carbides at 900℃ and 1,000℃.The carbides of the annealed alloys at 1,240℃ are significantly reduced and their sizes are smaller.
Annealed at 850℃, fine recrystallized grains are already visible at grain boundaries.
The microstructure shows the original deformed grains mixed with newly formed recrystallized grains at 900~1,000℃.