Claims:We Claim:
1. CRNO(cold rolled non oriented) steel comprising of steel composition having
C (0.001 to 0.01%) by wt;
Si (1.0 to 1.65%) by wt;
Mn (0.2 to 0.25%) by wt;
S (up to 0.12%) by wt;
P (up to 0.15%) by wt;
Al (0.1 to 1.5) by wt. and balance being Fe, having a core loss of watt loss/Kg at 1.5 Tesla of < 5.3 watt preferably from 4.7 to 5.3.
2. CRNO steel as claimed in claim 1 having magnetic induction at 10,000 A T/M of 1.82 which is in the form of 0.5 mm thick coils.
3. CRNO steel as claimed in anyone of claims 1 or 2 in the form of 0.5mmthick coils having a core loss of watt loss/Kg at 1.5 Tesla of < 5.3 watt preferably from 4.7 to 5.3.
4. CRNO steel as claimed in anyone of claims 1 to 3 in the form of 0.5 mm thick coils having better stacking factor of about 97 to 98%.
5. A process for producing CRNO steel as claimed in anyone of claims 1 to 4 comprising the steps of
a. providing a steel composition comprising C (0.001 to 0.01%), Si (1.0 to 1.65%), Mn (0.2 to 0.25%), S (up to 0.12%), P (0.8 to 0.15%), Al (0.1 to 1.5) and balance being Fe, and obtaining CRNO slabs;
b. reheating said steels slabs and soaking in a reheating furnace to 1200-1300°C for 3 to 4.5 hours;
c. hot rolling said slabs in to 2.6 to 3.0 mm coils with finishing rolling temperature 860 to 950 ?C and coiling temperature 690 to 730 ?C;
d. said hot rolled coils are then cold rolled to 0.5mm thickness;
e. subjecting the cold rolled coils to annealing with annealing temperature maintained around 900 to 1000 ?C;and
f. carrying out decarb annealing between 800 to 850 ?C temperatures.
6. The process as claimed in claim 5 wherein said slabs are reduced in roughing stand with following passing sequence:
Reductions at Roughing Stands (mm):
R0 (3 Pass): 210-176-136-100,
R1(5 Pass): 100-85-70-55-44-32,
R2 (1 Pass): 32-23.
7. The process as claimed in claim 5 or 6, wherein said hot rolled coils of thickness 2.5 to 3.0 preferably about 3 mm are rolled to 0.5mm thick coils involving reverse passes preferably in 5 reversing passes.
8. The process as claimed in claim 5 wherein cold rolled coils are processed in tandem annealing and decarb line with line speed of about 18-21 mpm.
9. The process as claimed in claim 5 wherein said annealing comprising modified annealing cycle with annealing temperature increasing to 970 C in last 3 zone of the annealing furnace leading to lower core loss value and also better stacking factor > 98 % with the processed high P CRNO coils having better quality and higher electrical resistivity.

Dated this the 25th day of February, 2022
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
STEEL COMPOSITION AND A PROCESS FOR PRODUCTION OF COLD ROLLED NON ORIENTED(CRNO) STEEL COILS WITH IMPROVED CORE LOSS PROPERTIES.



2 APPLICANT (S)

Name : STEEL AUTHORITY OF INDIA LIMITED.

Nationality : Indian.

Address : Research & Development Centre for Iron & Steel,
Doranda, Ranchi, Jharkhand, India. PIN-834002.






3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
Present invention relates to cold rolled non oriented(CRNO) steel coils with improved core loss properties and a process for its production. More particularly, the present invention is directed to provide process technology for production of CRNO steel with a leaner chemistry with addition of P and achieving the lowest core loss properties <5.3 watt loss/Kg at 1.5 Tesla.

BACKGROUND OF THE INVENTION
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. Non-oriented electrical steels are widely used as the magnetic core material in a variety of electrical machinery and devices, particularly in motors where low core loss and high magnetic permeability in all directions of the strip are desired.The required electromagnetic properties of electrical steels are: high magnetic induction, high magnetic permeability and low core loss. The core loss consists of hysteresis loss and eddy current loss. Generally, the hysteresis loss decreases with increasing grain size, decreasing inclusion and impurities contents (C, S, O and N) while the eddy current loss increases with increasing grain size. These properties are achieved by increasing Mn content, addition of Sn, Sb, La, and Cu etc. Increase in alloying will result in increase in cost of steel production.

Some prior arts in the related field are summarized as follows:

US20040016530A1 discloseda method for producing a non-oriented electrical steel with low core loss and high magnetic permeability whereby the steel is produced from a steel melt which is cast as a thin strip or sheet, cooled, hot rolled and/or cold rolled into a finished strip. The finished strip is further subjected to at least one annealing treatment wherein the magnetic properties are developed, making the steel strip of the present invention suitable for use in electrical machinery such as motors or transformers.

CA2484738C discloseda method for producing a non-oriented electrical steel comprises a) preparing a non-oriented electrical steel melt having a composition in weight % comprising up to about 6.5% silicon, up to about 5% chromium, up to about 0.05% carbon, up to about 3% aluminum, up to about 3% manganese, and balance essentially iron and residuals; b) casting a steel strip by rapid solidification of the steel melt into a strip and developing an as-cast grain structure; c) rapidly cooling the strip to suppress one or both of a phase change in the strip or recrystallization of the as-cast grain structure: and (d) rolling the strip to reduce the thickness of the cast strip and minimize the recrystallization of the as-cast grain structure, wherein the act of rolling comprises at least one act of hot rolling.

1274/KOL/2014 relates to designing the alloy chemistry (1), hot rolling (5) parameters and optimize decarb-annealing (8) conditions to achieve low core loss value and high magnetic permeability in all directions of the Cold rolled non-oriented (CRNO) electrical steels strip. The alloy chemistry (1) of the steel melt is comprised of C: 0.025 max, Mn: 0.25 max, P: 0.02 max, S: 0.005 max, Si: 2.3-2.7 and Al: 0.15-0.20. Further the slab reheating and hot rolling (5) parameters are set wherein the slab soaking temperature is 1180-1200 C, slab retention time is 4 hrs, roughing temperature 1120-980 C, finish rolling temperature is 860-880 C and coiling temperature is maintained at around 680-700 C. Further in decarb-annealing (8) process maximum decarb temperature is maintained at around 840 C, annealing temperature in Zone#8 is varied from 950-970 C, maximum annealing temperature of 990 C is maintained in Zone#9 to Zone#11, and minimum decarb line speed is maintained at around 15 to 16 m/min.

EP 3 388 537 B1 disclosed a method for producing a non-oriented electrical steel sheet by hot rolling a steel slab having a chemical composition comprising C: not more than 0.0050 mass%, Si: not more than 5.0 mass%, Mn: not more than 3.0 mass%, P: not more than 0.2 mass%, S: not more than 0.005 mass%, Al: not more than 3.0 mass%, N: not more than 0.005 mass%, Ni: not more than 3.0 mass%, Cr: not more than 5.0 mass%, Ti: not more than 0.005 mass%, Nb: not more than 0.005 mass%, B: not more than 0.005 mass%, O: not more than 0.005 mass%, optionally one or two selected from Sn: 0.005-0.20 mass% and Sb: 0.005-0.20 mass%, optionally one or two or more selected from Ca: 0.0001-0.010 mass%, Mg: 0.0001-0.010 mass% and REM: 0.0001-0.010 mass%, and the remainder being Fe and inevitable impurities and subjecting the sheet to a cold rolling after a hot band annealing or without a hot band annealing and further to a finish annealing, characterized in that PH20/PH2 of an atmosphere in the finish annealing is not more than 0.1, and the heating in the finish annealing is conducted in two stages of performing an induction heating and subsequently a radiation heating, and the induction heating is conducted up to not lower than 720°C at an average heating rate of not less than 50°C/sec between 600°C and 700°C, and the heating rate by the radiation heating up to a soaking temperature is not less than 5°C/sec, and a time from the end of the induction heating to the start of the radiation heating is set to not more than 3 seconds. 2. The method for producing a non-oriented electrical steel sheet according to claim 1, wherein a ferrite grain size of a steel sheet structure before a final cold rolling in the cold rolling is set to not more than 70 mm.

RU2527827C2relates to production of electric steel. Proposed process comprises melting the steel of the following chemical composition, wt %: Si 0.1-1, Al 0.005-1.0, C=0.004, Mn 0.10-1.50, P=0.2, S=0.005, N=0.002, Nb+V+Ti=0.006, Fe and unavoidable impurities making the rest. Steel bar ingot is produced and heated to 1150-1200°C. It is kept at said temperature for definite time and subjected to hot rolling at 830-900°C to steel strip. The latter is cooled to =570°C and coiled. Hot-rolled strip is straightened by cold rolling at reduction factor of 2-5%. Cold-rolled strip is continuously normalised at, at least 950°C and held thereat for 30-180 s. Normalised strip is etched and cold rolled with total reduction factor of 70-80% to get the sheet of target depth. Said sheet is annealed by heating at the rate of 100°C/s to 800-1000°C. It is held at this temperature for 5-60 s and slowly cooled down to 600-750°C at the rate of 3-15°C/s.

KR101591222B1 disclosed a method of producing non-oriented electrical steel sheet comprising C: 0.005 mass% or less, Si: 4 mass% or less, Mn: 0.03 to 3 mass%, Al: 3 mass% or less, P: 0.03 to 0.2 mass%, S: 0.005 mass% or less and N: (Ca (mass%) / 40) / (S (mass%) / 32) in the range of 0.5 to 3.5, and the balance of Fe And annealing the steel slab made of inevitable impurities, hot-rolled sheet annealing, cold-rolling, and then carrying out recrystallization annealing which heats the steel sheet to at least 740 ?C at an average heating rate of 100 ?C / sec or more. Thereby producing a low-loss, non-oriented electrical steel sheet.

US9595376B2 disclosed a non-oriented electrical steel sheet comprising, Si: not less than 1.0 mass % nor more than 3.5 mass %, Al: not less than 0.1 mass % nor more than 3.0 mass %, Ti: not less than 0.001 mass % nor more than 0.01 mass %, Bi: not less than 0.001 mass % nor more than 0.01 mass %, wherein Expression (1) is satisfied when a Ti content (mass %) is represented as [Ti] and a Bi content (mass %) is represented as [Bi]: [Ti]?0.8×[Bi]+0.002.

US9574249B2 disclosed a method includes preparing a steel slab in which contents of inhibitor components have been reduced, i.e. content of Al: 100 ppm or less, and contents of N, S and Se: 50 ppm, respectively; subjecting the steel slab to hot rolling and then either a single cold rolling process or two or more cold rolling processes interposing intermediate annealing(s) therebetween to obtain a steel sheet having the final sheet thickness; and subjecting the steel sheet to primary recrystallization annealing and then secondary recrystallization annealing. The primary recrystallization annealing includes heating the steel sheet to temperature equal to or higher than 700° C. at a heating rate of at least 150° C./s, cooling the steel sheet to a temperature range of 700° C. or lower, and then heating the steel sheet to soaking temperature at the average heating rate not exceeding 40° C./s in a subsequent heating zone.

US8157928B2 is directed to provide a non-oriented electrical steel sheet being excellent in surface characteristics and having both excellent mechanical characteristics and magnetic characteristics necessary for a rotor of rotating machines such as motors and generators which rotate at a high speed, and a method for producing the same. To achieve the object, the present invention provides a non-oriented electrical steel sheet comprising in % by mass: 0.06% or less of C; 3.5% or less of Si; from 0.05% or more to 3.0% or less of Mn; 2.5% or less of Al; 0.30% or less of P; 0.04% or less of S; 0.02% or less of N; at least one element selected from the group consisting of Nb, Ti, Zr and V in the predetermined range; and a balance consisting of Fe and impurities; and having a recrystallized fraction being less than 90%.

US7942982B2 disclosed Grain-oriented electrical steel sheet excellent in coating adhesion. The steel sheet contains Si: 2 to 7% mass % and has a primary coating composed mainly of forsterite on its surface. A compound (A) containing one or more elements selected from among Ca, Sr and Ba, at least one rare earth metal, and sulfur is incorporated in the primary coating so as to reside in the interface layer between the primary coating and the steel sheet. As a result, occurrence of primary coating exfoliation at regions that are strongly worked during manufacture of a wound core transformer or the like is prevented.

The salient features of prior art and their differentiation with the present invention is highlighted below:

(a) Core loss properties was achieved with 3% Si and other alloying like Cr, Ti, and Ni etc.
(b) Magnetic properties was achieved with 6% Si, 5 % Cr and 3% Mn and 3% Al.
(c) Properties were achieved modifying hot rolling and cold rolling parameters.
(d) Properties were achieved thin strip casting.
(e) Properties was achieved by adding Nb, B, Mg, Ca and Sb.
(f) Properties was achieved by adding Nb+V+Ti=0.006.
(g) Properties was achieved by adding higher Si, Ca N and controlling heating rate of recrystallation parameters.
(h) Properties was achieved by adding Ti and Bi in ratio [Bi]: [Ti]?0.8×[Bi]+0.002.
(i) Properties was achieved by controlling N, S and Se: 50 and controlling primary recrystallization annealing and then secondary recrystallization annealing.
(j) Properties was achieved by adding Nb, Ti, Zr and V.
(k) Properties was achieved by adding Ca, Sr and Ba.
(l) Properties was achieved by controlling Copper sulphate precipitates.

The prior arts thus contained costly alloying elements and/or complex processing steps to achieve desired properties in CRNO steel sheets. Hence, the present patent aimed to formulate a lean chemistry with addition of P and achieving the required electrical properties.

OBJECT OF THE INVENTION
The basic object of the present invention is directed to providecold rolled non oriented(CRNO) steel coils with improved core loss properties and a process for its production.

A further object of the present invention is directed to development of process technology for production of CRNO steel with a leaner chemistry with addition of P and achieving the lowest core loss properties <5.3 watt loss/Kg at 1.5 Tesla.

A still further object of the present invention is directed to formulation of a comprehensive methodology for manufacturing CRNO steel with high phosphorous content and a modified annealing cycle leading to better stacking factor of about 97 to 98%.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to cold rolled non oriented(CRNO) steel comprising of steel composition having
C (0.001 to 0.01%) by wt;
Si (1.0 to 1.65%) by wt;
Mn (0.2 to 0.25%) by wt;
S (up to 0.12%) by wt;
P (up to 0.15%) by wt;
Al (0.1 to 1.5) by wt. and balance being Fe, having a core loss of watt loss/Kg at 1.5 Tesla of < 5.3 watt preferably from 4.7 to 5.3.

A further aspect of the present invention is directed to said CRNO steel having magnetic induction at 10,000 A T/M of 1.82 with 0.5 mm thickness of the cold rolled coils.

A still further aspect of the present invention is directed to said CRNO steel having a core loss of watt loss/Kg at 1.5 Tesla of < 5.3 watt preferably from 4.7 to 5.3.

A still further aspect of the present invention is directed to said CRNO steel in the form of 0.5mm thick coils having better stacking factor of about 97 to 98%.

Another aspect of the present invention is directed to said a process for producing CRNO steel as stated above comprising the steps of
a. providing a steel composition comprising C (0.001 to 0.01%), Si (1.0 to 1.65%), Mn (0.2 to 0.25%), S (up to 0.12%), P (up to 0.15%), Al (0.1 to 1.5) and balance being Fe, and obtaining CRNO slabs;
b. reheating said steels slabs and soaking in a reheating furnace to 1200-1300°C for 3 to 4.5 hours;
c. hot rolling said slabs in to 2.6 to 3.0 mm coils with finishing rolling temperature 860 to 950 ?C and coiling temperature 690 to 730 ?C;
d. said hot rolled coils are then cold rolled to 0.5 mm thickness;
e. subjecting the cold rolled coils to annealing with annealing temperature maintained around 900 to 1000 ?C;and
f. carrying out decarb annealing between 800 to 850 ?C temperatures.

Yet another aspect of the present invention is directed to said process wherein said slabs are reduced in roughing stand with following passing sequence:
Reductions at Roughing Stands (mm):
R0 (3 Pass): 210-176-136-100,
R1(5 Pass): 100-85-70-55-44-32,
R2 (1 Pass): 32-23.

A further aspect of the present invention is directed to said process wherein said hot rolled coils of thickness 2.5 to 3.0 preferably about 3 mm were rolled 0.5mm thick coils involving reverse passes preferably in 5 reversing passes.

A still further aspect of the present invention is directed to said process wherein cold rolled coils are processed in tandem annealing and decarb line with line speed of about 18-21 mpm.

A still further aspect of the present invention is directed to said process wherein said annealing comprising modified annealing cycle with annealing temperature increasing to 970 Cto 1000 C in last 3 zone of the annealing furnace leading to lower core loss value and also better stacking factor > 98 % with the processed high P CRNO coils having better quality and higher electrical resistivity.

The above and other aspects and advantages of the present invention are described hereunder in greater details with reference to accompanying non limiting illustrative drawing and example.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: shows comparison of conventional annealing cycle with modified annealing cycle with respect to core loss.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to providecold rolled non oriented(CRNO) steel coils with improved core loss properties and to development of process technology for production of CRNO steel with a leaner chemistry with addition of P and achieving the lowest core loss properties <5.3 watt loss/Kg at 1.5 Tesla.

As already described herein before that 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 core loss consists of hysteresis loss and eddy current loss. Generally, the hysteresis loss decreases with increasing grain size, decreasing inclusion and impurities contents (C, S, O and N) while the eddy current loss increases with increasing grain size.

The other factors which influence the magnetic properties of CRNO steels are annealing prior to cold rolling, heating rate during final annealing, finish rolling and coiling temperature, final annealing temperature etc. In addition to this, alloy chemistries, viz., lowering S and increasing Mn content, addition of Sn, Sb, La, Cu and P etc., decreases core loss and increases magnetic permeability of CRNO steels.

A ‘‘Lean Grade Policy’’ has been introduced by some electrical steel producers for non-oriented fully processed electrical steels. It means that lower alloyed steels are used as far as possible to fulfil the requirements according to customer specifications or international standards by improved processing of the steel. Therefore, production of high permeability material grades through process optimization is easiest way of cost saving and energy conservation.

The process according to present invention is described hereunder with reference to the following example:

EXAMPLE:

One heat made (Table 1) through BOF-VOR-LHF-CCM route. The trimmed chemistry has been concast into 5 slabs of dimensions 210 x 1090 x 700 mm by having Liquids Temperature: 1520 ?C, Tundish Temperature: 1540 ?C (max.) and casting speed of 0.3 m/min. to start with and then slowly to be increased to 0.7 m / min. after casting for 10 minutes. Casting speed may be increased to 0.8 m/min.

Table 1 Chemical composition of high phosphorous CRNO heats in wt%

Coil No C Mn P S Si Al ASTM Grain Size No
Aim Chemistry 0.020-0.025 0.20-0.25 0.12 0.12 1.5-1.6 0.10-0.15 3.0 to 5.0
1 0.003 0.22 0.080 0.012 1.64 0.119 5.5-6.0
2 0.003 0.23 0.116 0.013 1.64 0.143 4.5-5.0
3 0.006 0.22 0.103 0.020 1.61 0.118 5.0-6.0
4 0.003 0.21 0.102 0.023 1.65 0.119 6.0-6.5
5 0.004 0.22 0.116 0.018 1.65 0.071 5.0-6.0

Total 5 of the above heats have been hot charged in reheating furnace with slab temperature of 280 ?C and following parameters were maintained in the furnace (Table 2). The CRNO slabs of dimensions 210 x 1090 x 700 mm was reduced in roughing stand with following passing sequence

? Reductions at Roughing Stands (mm)
• R0 (3 Pass): 210-176-136-100
• R1(5 Pass): 100-85-70-55-44-32
• R2 (1 Pass): 32-23

Final hot Rolling CRNO slabs were rolled to 2.9 mm thickness with finishing rolling temperature 870 to 900 ?C and coiling temperature 690 ?C (Table 3).

Coils were processed through BUST Line earlier where side trimming of the HRNO coils was done from width of 1055mm to 1028mm. After that the coils were pickled in AP line (HCL, 7-10% & at 70 0C). Thereafter the coils were processed in Reversing Mill. Coils of thickness 3.1 mm were rolled to 0.5mm thick coils in 5 reversing passes (as the load was well within limit). The values of load, current and tension were comparable to normal CRNO rolling. 5 coils were processed in tandem annealing and decarb line with line speed of about 18-21 mpm. Decarburization temp kept at 805-843 °C annealing temp kept at 930-970 °C. The material was tested for its magnetic properties. All the coils were qualifying the 50 C 530 grade as per IS 684:2006 standard

Table 2 Reheating Furnace Parameters
Zone Paramters
PH zone 1150 ?C
Heating zone 1260-1280 ?C
Soaking zone 1250-1260 ?C
Residence time 3.5-4 hrs

Table 3 Hot rolling Parameters

Coil No. R0 Temp (?C) R2 Temp (?C) Finishing Temp (?C) Coiling Temp (?C) Thickness (Avg, mm)
1 1235 1075 878 691 3.12
2 1229 1073 881 688 2.98
3 1223 1073 881 693 2.96
4 1217 1052 857 693 2.99
5 1240 1072 897 698 2.93

Table 4 Mechanical and Magnetic properties of high phosphorus CRNO coils
Coil No. Annealing
Temp ?C Line speed
mpm ASTM
Grain size no Watt
loss/kg at 1.5T
Anisotropy
Stacking factor
Magnetic induction at 10000AT/m Hardness
1 Modified Annealing cycle 970 19 4.5-5 4.72 6.4 98 1.82 71
2 970 21 5.5-6 4.78 6.6 98 1.82 71
3 Conventional annealing cycle 930 21 5-6 5.14 6.6 96.5 1.82 70
4 930 19 6-6.5 5.12 6.4 96 1.82 72
5 930 18 5-6 5.15 6.6 96 1.82 72

It is clear from the Table 4 and accompanying Fig. 1 that modified annealing cycle (i.e increasing to 970 C) in last 3 zone of the annealing furnace given lower core loss value and also better stacking factor > 98 % which means the processed high P CRNO coils has better quality and higher electrical resistivity.

The above described steel composition and manufacturing process for lean chemistry high Phosphorous-based cold rolled non oriented steel coils with reduced core loss property is very different from the existing prior arts.

The present invention thus provide a process for manufacturing of leaner chemistry of Phosphorous-based CRNO steel.The innovation presents viable prospect of being utilized/commercialized manufacturing of leaner chemistry of Phosphorous-based CRNO steel with reduced watt loss <5.3 watt loss/Kg at 1.5 Tesla. This innovation will lead to the reduction in price of higher grade CRNO steel (reduced watt loss <5.3 watt loss/Kg at 1.5 Tesla).