through thickness cube texture

1. Development of Through-Thickness
Cube Recrystallization Texture in
Non- oriented Electrical Steels by
Optimizing Nucleation Environment
G. SUDHAKAR
PHD(MATERIAL ENGINEERING)

2. 1. NON-ORIENTED electrical steels (NOES)
are widely used in iron cores with
alternating magnetic flux, such as
generators and motors.
2. The various fabricating methods of NOES
have been reported, including con-ventional
rolling and annealing, powder metallurgy,
selective laser melting, CVD, PVD, rapid
solidification, spray forming, hot dipping, strip
casting.
3. Cube texture has won a high degree of
attention not only in NOES but in grain-
oriented electrical steels (GOES).
4.Actually, cube is difficult to develop as a
dominant recrystallization texture in virtue of
the disadvantages of the size or quantity in the
early stage of recrystallization produced by the
conven-tional rolling method.

3. 1. some special methods were adopted for
cube recrystallization texture, including
using columnar-grained polycrystals as
starting material, cross rolling, skew
rolling, surface annealing, strip casting,
andphasetransformation.
2. the complex- ity of these methods induces
high cost of production or equipment
investment and limits large-scale industrial
application.
3. warm rolling is proved to be an effective
way to control recrystallization texture of
NOES, and it has been found that the
recrystallization texture is closely related
to the content of interstitial atoms (C, N)
and the process parameters of warm
rolling.
4. the warm rolling temperature at which
dynamic strain aging (DSA) occurs was
beneficial to the formation of shear bands
and further promoting the preferential
development of Goss recrystallization
texture in NOES

4. 1. when warm rolling at higher temperatures,
strongly positive rate sensitivity effectively
eliminates the shear banding tendency,
thus the nucleation can be promoted at
the interface of deformation bands or
deformed grains.
2. There are two kinds of boundaries of
deformation bands: grain boundaries and
transition bands in the interior of grains.
3. Because of the large misorientation within
rather small regions, grain boundaries and
transition bands have higher strain-stored
energy than those in the interior of
deformation bands and the nucleation
would be enhanced at these sites.
4. cube grains obtain a prominent number
advantage at both SSS and SPS layers in
the partially recrystallized state, and finally
develop the dominant texture through
sheet thickness after primary
recrystallization.

5. Development of Through-Thickness Cube
Texture
1. cube grains obtain a prominent number
advantage at both SSS and SPS layers in
the partially recrystallized state, and finally
develop the dominant texture through
sheet thickness after primary
recrystallization. There- fore, the formation
of through-thickness cube texture is
derived from the quantitative advantage
of cube nuclei at both SPS and SSS layers
under the superiority of locally low density
of cube nuclei.
On the Nucleation Environment at Shear
Bands
1. opti-mization of nucleation environment at
deformation bands is a more stable way for
the control of through-thickness cube
texture in the process of NOES production.

6. Effect of Warm Rolling on the Nucleation Environment of Cube Grains
Three critical factors need to be satisfied to optimize the nucleation environment of
cube grains in warm rolled NOES sheets:
1. enough initial cube or near-cube grains in hot bands as the origins.
2. The high warm rolling temperature to prevent the occurrence of DSA (Dynamic Strain Aging)
which promotes the shear banding tendency favorable to the Goss texture evolution,
3.optimum warm rolling reductions to balance the quantity and strain-stored energy of
deformation bands for their effective nucleation at an early stage of recrystallization.
Because of low strain-stored energy, the sites of the cube nuclei need relatively large strain
to supply sufficient activation energy for recrystallization.
4. Meanwhile, the number of remained cube micro-regions originated from hot bands will
gradually decrease under the heavy strain due to the characteristics of metastability of cube
orientation under deformation conditions in BCC alloys.

7. Fig. 1—Warm rolling microstructure and texture of Fe-2.1 wt pct Si sheets: (a) microstructure under 70 pct rolling reduction, (b) constant u2 = 45 deg section of ODFs at different layers
under 70 pct rolling reduction, and (c) orientation densities of main texture components at different rolling reductions.
Fig. 2—(a) Constant u2 = 0 and 45 deg sections of ODFs at S = 0.5 layer under 70 pct rolling reduction, (b) orientation densities of main texture components at different thickness layers under
70 pct rolling reduction, and (c) orientation densities of main texture components under different rolling reductions in Fe-2.1 wt pct Si sheets after annealing at 1123 K (850 °C) for 10 min.

8. Fig. 3—(a) Orientation image maps, (b) constant u2 = 0 and 45 deg sections of ODFs, and (c) number fraction and average grain size of main texture components
at S = 0 layer in Fe-2.1 wt pct Si sheets after annealing at 1273 K (1000 °C) for 10 min.
Fig. 4—(a) Orientation image maps and (b) local enlarged maps in Fig. 4(a) and corresponding u2 = 45
deg section of ODFs of cube recrystallized grains and surrounded deformed matrices in 7 pct recrystallized Fe-2.1 wt pct Si sheets.

9. Fig. 5—(a) Orientation image maps and (b) constant u2 = 0 and 45 deg sections of ODFs of recrystallized grains within different thickness layers in 44 pct recrystallized Fe-2.1 wt pct Si sheets.
Fig. 6—(a) Orientation image maps and corresponding constant u2 = 45 deg section of ODFs of cube recrystallized grains and surrounded deformed matrices and (b) orientations of
deformed matrices in Fig. 6(a) marked in the u2 = 45 deg section in 44 pct recrystallized Fe-2.1 wt pct Si sheets.
Fig. 7—(a) Area fraction and (b) number fraction of main texture components of recrystallized grains in 44 pct recrystallized Fe-2.1 wt pct Si sheets.

10. Fig. 8—(a) Orientation image maps and (b, c, d) corresponding local enlarged maps in Fig. 8(a) and constant u2 = 45 deg section of ODFs of cube micro-regions retained at (b, c)
transition bands and (d) grain boundaries and surrounded deformation bands at S = 0 layer of warm rolled Fe-2.1 wt pct Si sheets under 70 pct reduction.

11. Fig. 9—Schematic representation of the formation of through-thickness cube texture during primary recrystallization:
(a) warm rolling microstructure,
(b) formation of cube grains at the boundaries of deformation bands with orientation in Regions I and II in the early stage of recrystallization, and
(c) formation of cube texture after primary recrystallization.

12. •In the present work, the facilitating role of warm rolling on the formation and development
of cube texture is mainly achieved by inhibiting the nucleation of c and Goss grains.
Compared with rolling at room temperature.
•nucleation of c grains is obviously inhibited during recrystallization in warm rolled sheets
due to the insufficient strain-stored energy at c deformed grain boundaries. Compared with
warm rolling in the tem- perature range where DSA phenomenon occurs,
• the shear bands are effectively inhibited during warm rolling at high temperature
•The optimizing nucleation environment of cube grains also requires a reasonable
warm rolling reduction.
•When rolling at 773 K (500 °C) under 60 pct rolling reduction, the nucleation of
cube deformed micro-regions is retarded by relatively low strain-stored energy,
which is further weakened by dynamic recovery during rolling.

13. As rolling reductions reach up to 70 pct, a
considerable number of {001} 230 -{001} 13
and {223} 362 -{114} 481 oriented deformation
bands form at different thickness layers in
warm rolled sheets. These deformation bands
obtain enough activation energy by
accumulated plastic strain, while the quantity
of remained cube micro-regions gradually
decreases. With increasing of rolling
reductions to 90 pct, the strain-stored energy
of deformation bands increases with the
further accumulated plastic strain, whereas
the quantity of remained cube micro-regions is
insufficient. Consequently, it can be deduced
that the applied processing parameters are
responsible for both the sufficientquantity of
remained cube micro-regions and enough
strain-stored energy of deformation bands at
different Thickness layers in warm rolled
sheets, which provide the favorable nucleation
environment for cube grains, and thus for the
development of through-thick- ness cube
recrystallization texture.

14. •CONCLUSIONS
h i h i
A through-thickness cube recrystallization texture is successfully obtained in 2.1 wt pct Si
NOES after final annealing by designing the initial texture and the applied processing
parameters.
Cube grains mainly nucleate at the boundaries of (mainly identified at the interfaces of)
{001} 230 -{001} 130 and {223} 362 -{114} 481 oriented deformation bands.
The formation of through-thickness cube recrystalliza-tion texture
is attributed to the optimization of nucle- ation environment, featuring quantitative
advantage of cube nucleiat both SPS and SSS layers under the superiority
of locally low density of cube nuclei.
No special requirements for the initial columnar grains or twin-roll casting, as well as the
simple processing route of rolling and annealing,
are expected to provide an efficient and significantly cheap way to optimize texture
of NOES for large-scale industrial applications.