Claims:WE CLAIM:

1. Non-oriented electrical Si steels of improved magnetic properties, favourable texture and low core loss having the composition ( in wt.%) comprising
C: 0.002 – 0.01; Si: 1.20 –2.50; Mn: 0.20 – 0.45; S: 0.002 –0.01; Al: 0.03 –0.20; P: 0.004 – 0.16; or Sn: 0.001 -0.15; or Sb: 0.001 –0.10.

2. Non-oriented electrical Si steels as claimed in claim 1, wherein the Si content is 2.27%.

3. Non-oriented electrical Si steels as claimed in claim 1, wherein the Si content is 1.52% and the P content is 0.11%.

4. Non-oriented electrical Si steels as claimed in claim 1, wherein the Si content is ~1.5 % Si and Sn content is 0.11% and Sb content is 0.05%.

5. Non-oriented electrical Si steels as claimed in claims 1 to 4, which have high hot band grain size, high low angle boundaries and high fraction of sub-grains.

6. Non-oriented electrical steels as claimed in claims 1 to 4 which have a favourable (100)[0vw] texture where Si content is increased to 2.27% and also for low Si (~ 1.50%) steel containing 0.11% P or 0.05 % Sb after final annealing at 950o C.

7. Non-oriented electrical steels as claimed in claims 1 to 4, which have a favourable isotropic (100) [0vw] texture and the same is predominant when Si content is increased to 2.27 % and in the presence of 0.11% Sn or 0.05% Sb in low Si (~1.5 % Si) steels after final annealing at 950o C for 2 min, which were previously hot band annealed at 950o C.

8. Non-oriented electrical steels as claimed in claims 1 to 7, which have a good strength and ductility with YS: 200 – 300 MPa; UTS : 420 – 360 MPa and % EL 20 – 30 MPa after final annealing at 950o C which were with and without band annealing at 950o C.

9. A process for the production of non-oriented electrical Si steel characterized in that
the non-oriented Si steels are processed to final cold rolled annealed sheets after firstly, soaking the pencil ingots at 1050 to 1150o C followed by hot rolling into the final thickness of 2.0 – 2.5 mm with finishing temperature in the range of 780 to 1050o C followed by cold rolling into 0.49 – 0.54 mm thickness and a two stages annealing process where the first stage annealing being carried out at 830 to 860o C and the second stage final annealing being carried out at 900 to 950o C.

10. A process for the production of non-oriented Si steels characterized in that the non-oriented Si steels are processed to final cold rolled annealed sheets after firstly, soaking the pencil ingots at 1050 to 1150o C followed by hot rolling into final thickness of 2.0 – 2.5 mm with finishing temperature in the range of 780 to 1050o C and a hot band annealing at 930 to 1000o C followed by cold rolling into 0.49 – 0.54 mm thickness and a two stages annealing process where the first stage annealing being carried out at 830 to 850o C and the second stage final annealing being carried out at 900 to 950o C.

Dated: this 19th day of March, 2018

, Description:
NON-ORIENTED SILICON STEEL COMPOSITIONS CONTAINING PHOSPHORUS OR TIN OR ANTIMONY AND A PROCESS FOR PRODUCING THE SAME

FIELD OF THE INVENTION

This invention relates to non-oriented electrical Si steels. The invention more particularly relates to non-oriented electrical Si steels which are CRNO steels with high magnetic properties, favourable texture and low core loss.

BACKGROUND OF THE INVENTION AND PRIOR ART

Electrical steels, popularly known as silicon steels, are one of the most important material used in lamination form to carry magnetic flux in a variety of energy- efficient alternating current, electrical machinery such as generators, motors, lamp ballast, small and medium size transformers .These steels are further categorized into CRGO and CRNO.CRNO steels of various grades contain silicon in the range of 1.0 - 2.5 %Si and Al in some higher grades. The required electromagnetic properties of electrical steels are: high magnetic induction, high magnetic permeability and low core loss. The decrease in core loss is achieved with increasing grain size, decreasing inclusion and impurities contents (C,S,O and N).Furthermore, the presence of magnetically favourable texture components, i.e., {100}<0vw>,also decreases core loss of CRNO steel.

In the conventional art a good number of patents exist on the field. Some of the said closely related art is mentioned here for reference. See for instance, CN102127702A, CN106756522A, KR2030010232A, KR20130010229A, KR100779579B1, KR20040089481A, KR20040055906A, KR20030053146A, KR20010028403A, KR100270392B1, JPH0657332A, EP3214195A1, EP0567612A1, CA2507970C, JP2006241554, JP2006279859, JP2006192731, JP2006057332, JP2005140648, US4204890A, US20150013844A156, US20170241002A1.

Though the aforesaid prior arts show good magnetic properties, texture and low core loss there is scope for further improving the said properties and also to obtain more economical products.

OBJECT OF THE INVENTION

The main object of the invention is to provide for non-oriented electrical Si steels with high magnetic properties, favourable texture and low core loss value.

Another object of the invention is to provide for non-oriented electrical Si steel which is economical with respect to the conventional Si steels.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig. 1 shows stress-strain curve corresponding to 10 pass hydra wedge mode in Gleeble 3500 C for the experimental steels (a) SN1, (b) SN2, (c) SN3, (d) SN4 and (e) SN5

Fig. 2 shows light optical photomicrographs of (a) SN2 and (b) SN5 showing coarse elongated ferrite grains while sub-surface region showing fine equiaxed grains

Fig. 3 shows optical photomicrographs of (a) SN1, (b) SN2, (c) SN4 showing elongated ferrite grains much smaller than that shown in Fig. 2

Fig. 4 shows correlated misorientation in digrees of rolled steels of (a) SN1, (b) SN2, (c) SN3, (d) SN4, and (e) SN5

Fig. 5 shows standard phi2=45o according to Bunge notation

Fig. 6 shows ODF of phi2 45o section of (a) SN1, (b) SN2, (c) SN3, (d) SN4 and (e) SN5 after annealing at 950o C for 5 min.

Fig. 7 shows ODF of phi2 45o section of (a) SN1, (b) SN2, (c) SN3, (d) SN4, and (e) SN5 after annealing at 950o C for 2 min. which were previously hot band annealed.

DESCRIPTION OF THE INVENTION

In the present invention it has surprisingly been found that addition of very small amount of phosphorus or tin or antimony to low silicon steels, the resultant steels display high magnetic properties, favourable texture and low core loss. The developed steels are also more economical than the conventional products.

According to the invention there is provided non-oriented electrical Si steels with improved magnetic properties, favourable texture and low core loss and having the composition ( in wt. %) comprising C: 0.002 – 0. 01; Si: 1.20 –2.50; Mn: 0.20 – 0.45; S: 0.002 – 0.01; Al: 0.03–0.20; P: 0.004 –0.16; or Sn: 0.001 – 0.15 or Sb: 0.001 – 0.010.

The invention includes a process for producing the said steels.

Following details describe the invention with the help of accompanying drawings along with experimental data:

EXPERIMENTAL:

Five nos. of laboratory heats of 50 kg each were made in laboratory as given in the Table 1 below:

Table-1: Chemical composition of experimental steels (in wt. %)

Steel C Si Mn P S Al Sn Sb
SN1 0.009 1.35 0.38 0.005 0.006 0.14 trace trace
SN2 0.006 2.27 0.35 0.004 0.006 0.13 trace trace
SN3 0.006 1.48 0.33 0.004 0.005 0.10 0.109 trace
SN4 0.006 1.44 0.32 0.004 0.006 0.10 trace 0.05
SN5 0.005 1.52 0.36 0.110 0.006 0.12 trace trace

After casting, the 100mm × 100 mm square pencil ingots were hot rolled to 2.0-2.5 mm. In the first stage, ingots were rolled into 18 - 20 mm thick plates through five passes after soaking at 11000 C for 2.5 hours. In the second stage, once again these plates were soaked for 1 hour at 11000 C and hot rolled into 4-5 mm thick plates. In the third stage of rolling, 4-5 mm thick plates were hot rolled to 2-2.5 mm thick sheets after soaking at 11000C for 10 min. The finishing temperature was in the range of 780 to 8500 C. However, the studied sheets were selected with finishing temperature at 8000 C. The metallography was carried out for these hot bands. Subsequently, cold rolling was carried out into 0.49-0.54 mm thickness after pickling of hot bands. These cold rolled sheets were annealed initially at 8400 C for 4 min simulating decarb annealing process and finally annealing was carried out at 9000 C and 9500 C for 2 min and 5 min respectively. The metallography, electron back scattered diffraction study (EBSD) and core loss tests were carried out for these sheets. In another set of experiment, before cold rolling, the hot bands were annealed at 9500 C for 5 min. Cold rolling and annealing were carried out like above.

In one embodiment of the invention, the non oriented Si steels are processed to final cold rolled annealed sheets after firstly, soaking the pencil ingots at 10500 C to 11500 C followed by hot rolling into the final thickness was 2.0-2.5 mm with finishing temperature in the range of 780 to 10500 C. This followed cold rolling into 0.49-0.54 mm thickness and a two stages annealing process. The first stage annealing was carried out at 8300 to 8600 C and the second stage final annealing was carried out at 9000 C to 950 0C.

In another embodiment, the non oriented Si steels are processed to final cold rolled annealed sheets after firstly, soaking the pencil ingots at 10500 C to 11500 C followed by hot rolling into the final thickness was 2.0-2.5 mm with finishing temperature in the range of 780 to 10500 C and hot band annealing at 9300 C to 10000 C. It followed by cold rolling into 0.49-0.54 mm thickness and a two stages annealing process. The first stage annealing was carried out at 8300 to 8500 C and the second stage final annealing was carried out at 9000 C to 9500 C.

Still in another embodiment of the invention, the Si content in the non-oriented Si steels is increased to 2.27 % and also for low Si (1.52%) steel containing 0.11% P which resulted in high hot band grain size, high low angle boundaries and high fraction of sub grains, which are beneficial for obtaining favourable texture and low core loss of final cold rolled and annealed steel. This was confirmed from the multi pass compression test in Gleeble, which showed the existence of the no-recrystallization temperature (Tnr) when finish rolling will be carried out near to or above 10000 C. Tnr is the temperature at which recrystallization starts to be inhibited during hot rolling.

Fig. 1 of the accompanying drawings shows the stress-strain curve corresponding to 10 pass hydra wedge mode in Gleeble 3500 C for the experimental steels: (a) SN1, (b) SN2, (c) SN3, (d) SN4 and (e) SN5. The first pass was carried out at 11500 C and last pass at 9250 C with 250 C intervals. Figure 1(b) and (e) clearly indicate that recrystallization is inhibited at 10000 C and below corresponding to 7th pass to 10th pass. This is attributed to the effect of high Si, i.e., when Si content is increased to 2.27% (SN2 in Fig. 1(b)) or due to the presence of 0.11% P (SN5 in Fig. 1 (e)) in low Si (1.52%) steel. Therefore, firstly these two steels will be beneficial with respect to improve magnetic properties of the final steel as Tnr temperature exists in these two steels. Further, the processing methods, especially hot rolling with finish rolling temperature of these two steels can be defined to be above 1000 0 C.

Further, large hot band grains have been observed in these two cases only as shown in Fig. 2 of the accompanying drawings. In contrast to the observed grain size of SN2 and SN5, the hot band of SN1, SN3 and SN4 show much smaller grains in Fig. 3 of the accompanying drawings.

In addition to the grain size, the low angle grain boundaries (LAGBs) and high angle grain boundaries (HAGBs) were also measured through EBSD for understanding the degree of recrystallization. The results in Fig. 4 of the accompanying drawings indicate that only high angle boundaries of recrystallised microstructure are found in the case of SN1 steels. In the case of SN2 steel, the fraction of LAGBs is maximum followed by that of SN5. The fraction of LAGBs is much lower than that of HAGBs in SN3 and SN4. This indicated that both SN2 and SN5 steels are partially recrystallized while SN3 and SN4 steels are sufficiently recrystallized. On the other hand SN1 steel is fully recrystallized. As discussed above rolling in the temperature zone which will prevent recrystallization will be beneficial for magnetic properties in final steel. In view of this, the SN2 and SN5 steels are more suitable followed by SN3 and SN4.

In a further embodiment of the invention the non-oriented Si steels have favourable (100)[0vw] texture with no anisotropy, i.e., isotropic texture is predominant of the non oriented electrical steels when Si content is increased to 2.27% and also for low Si (~1.50%) steel containing 0.11% P as well as 0.05% Sb after final annealing at 9500 C.

Before explaining above, let us understand (100)[0vw] texture from the standard (phi2)q2 = 450 shown in Fig. 5 of the accompanying drawings. In this figure, the encircled region is called as q fiber which has plane component (001) while direction component varies as [0vw]. It has been reported that the magnetic properties improves with the presence of q fiber component.

Therefore, the q fiber component with isotropic texture (100)[0vw] is only found in Fig. 6(b) in SN2 steel and also in Fig. 6(d) and (e) of the accompanying drawings containing Sb and P, respectively.

Still in another embodiment of the invention the non-oriented Si steels have favourable isotropic (100)[0vw] texture predominant of the non oriented electrical steels when Si content is increased to 2.27 % and in low Si (~1.5 % Si) steel containing 0.11% Sn or 0.05% Sb after final annealing at 9500 C for 2 min, which were previously hot band annealed at 9500 C. This is shown in Fig. 7 of the accompanying drawings.

In another embodiment of the invention the non oriented Si steels according to the invention, final annealed at 9500 C, possess low core loss when measured at 50 Hz and 2500 A/m field strength. The core loss (Watt/Kg) at flux density of 1.5 Tesla in longitudinal direction for the steel composition according to the invention is 3.70 to 4.82. The highest core loss (4.82 Watt/Kg) is found for only low Si (1.35) steel without any alloying addition (SN1 steel). In the case of previously hot band annealed case, the core loss is also highest in low Si (1.35) steel without any alloying addition, which is named as H-1. This is presented in Table 2.

Table 2: Core loss and permeability at 50 Hz and 2500 A/m Field Strength of cold rolled strips final annealed at 9500C along with hot band annealed steels prior to cold rolling

Samples Core loss (Watt/Kg) at different flux density ‘B’
1T 1.5T
SN1 2.25 4.82
SN2 1.71 3.95
SN3 1.67 3.70
SN4 2.01 4.64
SN5 1.94 4.42
H-1 2.17 4.70
H-2 1.79 3.97
H-3 1.92 4.24
H-4 2.05 4.48
H-5 1.81 4.11

The non oriented electrical steels according to the invention show good strength and ductility with YS: 200-300MPa, UTS: 420-360 MPa and %EL 20-30 MPa after final annealing at 9500 C, which were with and without hot band annealing at 9500 C cases are shown in Table 3.

Table 3 Tensile properties of cold rolled strips final annealed at 9500C along with hot band annealed steels prior to cold rolling

Steels YS (MPa) UTS (MPa) %EL n
SN1 208 343 24 0.23
SN2 300 428 22 0.18
SN3 216 345 27 0.22
SN4 234 355 26 0.21
SN5 223 348 28 0.22
H1 242 388 32 0.25
H2 295 434 30 0.22
H3 222 376 31 0.24
H4 147 351 28 0.24
H5 162 397 28 0.24

Although the invention described herein mentions a few embodiments, it could be possible for a person skilled in the art to develop other similar embodiments as well beyond those disclosed herein with little modifications. However, all such modifications are deemed to be within the scope of the invention claimed herein.

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