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Crack length and number of cracks on the punched surface were measured and counted by an optical microscope.
Standard tensile specimens (number 5 test piece of JIS) were prepared by machining the steel sheets.
Results and discussion 3.1.Crack length and the number of cracks Fig. 6 Relationship between the number of cracks and crack length.
Moreover, Mn segregates at the grain boundary, and Mn weakens grain boundary cohesion.
Moreover, Mn segregates at the grain boundary, and Mn weakens grain boundary cohesion.

As discussed above, because a large number of t-ZrO2 nano-micron fibers are embedded in the rod-shaped sapphire, there are a large number of fine heterophase interfaces in the rod-shaped sapphire.
According to the analyses of Sayir [5], a large number of fine low energy heterophase interfaces established during eutectic solidification cause the rod-shaped sapphire to be reinforced.
In addition, as the crack bypasses the rod-shaped sapphires, it is inevitably met by the nearby large plate-like α-Al2O3 grains.
Subsequently, as the crack becomes trapped the nearby rod-shaped sapphires, secondary microfractures develop along the boundaries of the bridging grains and the frictionally interlocked grains are formed, and frictionally interlocked toughening effect by the large plate-like α-Al2O3 grains is initiated.
A large number of fine low energy heterophase interfaces and the strong compressive residual stresses in the rod-shaped sapphires make the sapphires reinforced, and major toughening mechanisms are the fracture energy consumed in creating the debonded interfaces and the stored strain energy in the rod-shaped sapphires, followed by the frictionally interlocked effect of the plate-like α-Al2O3 grains.

With the increase of cycle number, the closed hysteresis loops become gradually obvious.
Obviously, the ratcheting strain increases sharply with the increase of cycle numbers at the initial stage, and tends to be a constant after certain cycles.
It can be seen that zone A is relatively flat, with a great number of lamellar structures.
It can be found that the twins bands are located in some larage grains , while there is no twins in very small grains.
This is atrribtuded to the critial resolved shear stress (CRSS) for twinning is not achieved in those small grains.

Some austenite also nucleated on the ferrite grain boundaries or the carbide particles within the ferrite grain.
A small amount of recrystal grains emerged within the ferrite grain, and the nucleation site is near the grain boundaries of deformed ferrites, as shown in Fig. 1(b).The recrystallized grains were equiaxed and very fine and small.
When the temperature was heated to 690℃{TTP}8451 , a large number of recrystallized grains had been formed.
Here the recrystallized ferrite grains were equaxed, and the size of the grains was uniform.
The recrystallized grains were equiaxed and very fine and small. 2）When the temperature heated to 690℃{TTP}8451 , a large number of recrystallized grains had been formed.

As the number of ARB cycles increased to 3, the cell structure was well defined and the dislocation density increased (Fig. 2b).
However, it exhibited an ultrafine grained structure in which the grains hardly contain the dislocations in the interior and were surrounded by sharply defined and straight boundaries.
The SAD pattern clearly indicates that the misorientation between the grains is very large.
However, the grain boundaries were sharply defined.
The mean grain size of ultrafine grains formed by LDR-ARB was smaller than that by HDR-ARB.

After straining to 4 the (sub)grain size attains 0.65 µm.
The mechanism of cDRX includes the appearance of a number of strain-induced low-angle subboundaries (LABs) at relatively small deformation and then the significant increase in the misorientations among the subgrains leading to the formation of UFGs surrounded by high-angle boundaries (HABs) at large strains.
The pressing leads to large number of low-angle strain-induced subboundaries (θ<15°) crossing initial grains and DMBs.
The number of UFG increases significantly in the strain range of 2<ε<4.
The effect of ECAP pass number on the strength and the elongation is shown in Fig. 3.

Two different precipitations are observed in pipeline steel X80, a class of TiN precipitations is mainly and a small number of (Nb, V)(C, N) complex precipitations in the TiN around, and the other for large number of NbC precipitations and a small amount of TiC, VC and simultaneous deposition of the complex formed precipitations.
Remarkable strengthening and grain refinement can ne caused by these precipitations.
Introduction Distance, a large number of transportation of natural gas, oil produce large pressure to the pipeline.
Fine grain strengthening is obvious, which contributed greatly to the strength and toughness of pipeline steel.
The formation of the crystal contains a large number of dislocation and subgrain, which strengthen the wrong place and sub-grain.

A majority of the orientations scatter around the main texture component in ODF, which indicates that a number of grains keep similar crystal orientations to the main texture component in grain subdivision during ECAE processing.
Many low angle grain boundaries are produced in the course of grain refinement.
In the meantime, orientation distribution becomes more scattered around main texture component with increasing number of ECAE passes.
The ODF results show that the orientation of a number of grains deviates farther from the main texture component after more ECAE passes.
Ultrafine-grained materials III.

With an increase in the substrate temperature, tight grain boundaries are formed between the growing columnar grains.
Finally, zone III (0.5 grains and a bright smooth surface due to the grain growth driven by bulk diffusion.
The void between grain columns decreased and the width of the grain columnar increased slightly.
The result was attributed to the zone II structure of the SZM (tight grain boundaries and faceted grains).
Acknowledgments This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (grant number: 2019R1H1A2101121).

The average grain size and the number of grains are 50 μm and twenty, respectively.
Comparing Fig. 4 (a) with (c), the number of grains in which the plastic strain is spreading in (a) than that in (c).
When the number of slip systems is limited, the number of grains with low Schmid factor increase compared with the case with the large number of slip systems.
Even though the number of the activated slip systems is different, plastic strains are observed in all grains, which is different from those with the high CRSS as seen in Fig. 5 (d).
Although the little amount of stress concentration is observed at the grain boundaries in Fig.5 (d) because of the large plastic anisotropy in the limited number of active slip systems, stress distribution which increases the proof stress is not seen across the grains.