CLIAMS:We Claim:

1. A method of producing low carbon not more than 0.03% non-oriented electrical steel sheets comprising:

treating steel composition from BOF converter comprising carbon 0.025-0.05%, manganese 0.01-0.04%, phosphorus 0.015-0.025%, sulphur 0.030-0.050%, silicon 0.003-0.009% in Vacuum Refining furnace (VOR) which includes oxygen blowing at a pressure of 10-14kg/cm2 along with lime addition with degassing for a period of at least 10 minutes under bath agitation maintaining variable argon flow rate of 10-15 nm3/hr during oxygen blowing for decarburization of steel by oxygen carbon reaction and Nitrogen level not more than 50 ppm. followed by addition of ferro alloys as per grade requirement maintaining silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements including carbon < 0.03%, sulphur < 0.025% and nitrogen and total oxygen <50 ppm.

2. A method as claimed in claim 1 where said blowing for decarburization comprises deep decarburization of liquid steel involving variable lance height during blowing with increased oxygen pressure of ~ 14kg/cm2, finally keeping a minimum lance height of 450-500 mm from liquid steel bath towards the end of blow and by bath agitation by way of variable argon flow rate of 10-15 nm3/hr during oxygen blowing.

3. A method as claimed in anyone of claims 1 or 2 wherein said addition of ferro-alloys is carried out following addition pattern which includes early slag formation involving addition of lime in said Vacuum Refining furnace (VOR) such as to achieve basicity of slag in the range 4-5 and initial heating with Silicon and subsequent addition of aluminium in batches.

4. A method as claimed in anyone of claims 1 to 3 wherein for non oriented electrical steel having composition silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements including carbon < 0.03%, sulphur < 0.025% following steps are followed:
i) addition of one fourth of total lime in VOR for early slag formation;
ii) addition of SiMn for initial de-oxidation during degassing;
iii) addition of remaining portion of lime keeping basicity of ladle top slag in the range of 4-5 & addition of FeSi for chemical heating;
iv) addition of FeSi and Al as per grade requirements and efficient purging for 2-3 minutes for bath homogenisation;
v) trimming addition Al & FeSi as per grade specification then soft purging @ 8-10 Nm3/hr for 6-8 minutes and then release of vacuum;

5. A method as claimed in anyone of claims 1 to 4 comprising
(i) obtaining steel tapped from BOF converter containing carbon 0.025-0.05%, manganese 0.01-0.04%, phosphorus 0.015-0.025%, sulphur 0.030-0.050%, silicon 0.003-0.009% and transferring to VOR;

(ii) treating the said steel in Vacuum Refining furnace (VOR) comprising
(a) oxygen blowing at a pressure of 10-14kg/cm2 along with lime addition with aim basicity of slag in the range 4-5;

(b) keeping degassing period for at least 10 minutes with vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing for efficient decarburization of steel by oxygen carbon reaction and maintaining Nitrogen level not more than 50 ppm;

(c) Addition of ferro alloys as per grade requirement maintaining silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements like carbon not more than 0.03%, sulphur not more than 0.025% and nitrogen and total oxygen not more than 50 ppm.

6. A method as claimed in anyone of claims 1 to 5 wherein said deep de-carburization of liquid steel in VOR comprises maintaining variable lance height during blowing with increased oxygen pressure of ~ 14kg/cm2, finally keeping a minimum lance height of 450-500 mm from liquid steel bath towards the end of blow and by vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing.

7. Low carbon (<0.03%) cold rolled non oriented(CRNO) silicon steels obtained through BOF-VOR-LHF-CC route as claimed in anyone of claims 1 to 6 comprising
C: upto 0.025wt%;
Mn: 0.2% to 0.3% preferably 0.25% wt%;
Si: 1.4% to 3.0% preferably 1.6 wt%;
Al: 0.08% to 0.2% preferably 0.1 wt%
S: upto 0.025 wt%
P: upto 0.025 wt%;
Nitrogen: upto 50 ppm;
and rest is iron and which is obtained as sheets for application in electric motors, generators, alternators etc. favouring low core loss values.

Dated this the 7th day of February, 2015
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

,TagSPECI:FIELD OF THE INVENTION

The present invention relates to providing an improved method for production of low carbon (<0.025%) cold rolled non oriented(CRNO) silicon steels and CRNO steel grade obtained thereof. More importantly, the present invention is directed to provide low carbon (<0.025%) cold rolled non oriented silicon steel for applications in electrical equipments like motors, generators, alternators etc. involving an improved steel manufacturing process comprising treating steel in vacuum oxygen refining unit with controlled decarburization ensuring achieving low carbon level of = 0.025% consistently and thereby the diversions/down gradation from CRNO grade due to high carbon level at steelmaking is almost eliminated.

BACKGROUND OF THE INVENTION

The Steel Melting Shop –I of Rourkela Steel Plant (RSP) of the applicant is pioneer in production of Cold Rolled Non-Grained Oriented (CRNO) electrical grades of steel in country. RSP is the only steel plant in India, producing variety of electrical grade CRNO Steel having Carbon percentage < 0.03%. This special steel CRNO is widely used in power sector basically in motors, generators and alternators. The conventional process route adopted for production of CRNO steel is as follows: BOF(Basic Oxygen Furnace) – VOR(Vacuum Oxygen Refining) – LHF(Ladle Heating Furnace) – CC(Continuous Casting).
Market demand of Cold Rolled Non-Oriented (CRNO) steels are in the form of sheets. These are used for the manufacture of efficient and powerful electrical devices which demand very high level of electrical and magnetic properties like core loss and permeability etc. These properties are achieved by using Si (1.4-3.0%) and Al (0.08-0.2%) for alloying and precise control of elements like C (<0.03%), S (<0.025%), N (<50 ppm) and total oxygen (<50 ppm). Besides, microstructure, inclusion morphology, cleanliness etc. are also the important parameters which control these properties. RSP produces different grades of CRNO steels like M47, M45, M43, M36, etc. Low carbon in liquid Steel for CRNO is a challenging task. High carbon content >0.03% in CRNO increases mill load in hot strip mill and also decarburization load in silicon steel mill. Carbon content >0.03% in liquid steel increases core loss and hence leads to high rejection of end product. The requirement of carbon in finished CRNO coils is < 0.003% and hence low carbon (< 0.03%) is a prerequisite for achieving the aimed carbon in finished CRNO coils. Production of these grades has been stabilised through process modification at several stages of steel making and BOF-VOR-LHF-CC is the normal production route.
The conventional process of steel making in vacuum oxygen refining unit for cold rolled non oriented silicon steel involved:
After tapping of steel from converter, the ladle was brought to Vacuum Oxygen Refining (VOR) chamber and 150-250 NM3 oxygen was blown for 5-7 minutes at a blowing pressure 8-10 Kg/cm2 and at a vacuum level of 750-850 mbar. For liquid steel purging from ladle bottom, argon flow rates were kept in the range of 6-10 Nm3/hr. After blowing of oxygen the evacuation process was again started till the lowest possible level of vacuum was attained depending on stream pressure.
Controlling High Carbon in liquid Steel for CRNO had been a challenging task. A high rate of CRNO heat rejection due to high Carbon > 0.03% were faced in the shop. Thorough investigations were done to find out the root cause of carbon pick up leading to final carbon of >0.03% was investigated under the present work. The broad areas which were explored as possible source of carbon pick up are as follows:
(a) Magnesia-Carbon refractory in ladle lining.
It was found that in the same Magnesia-Carbon lining ladle some heats were as per the specification. However, some heats were getting diverted due to high Carbon > 0.03%. So it was inferred that Magnesa- Carbon was not source of carbon pick up.
(b) Arcing by graphite electrode at Ladle Heating Furnace.
Some heats were processed bypassing Ladle Heating Furnace, though also high carbon problems were still experienced. So it was assumed that graphite electrode was not the cause of carbon pick up.
(c) Use of normal grade ferro-silicon during heat making.
Normal grade FeSi contains around 0.15% carbon and around 1500 kg of FeSi is added in CRNO heat. Some heats were in conformity to specification w.r.t carbon and some were not even after using normal grade Ferro-silicon from the same supply source. So it was concluded that Ferro- silicon was not the cause of carbon pick up.
(d) Poor and inconsistent vacuum.
The Vacuum Oxygen Refining unit was the oldest vacuum system in operation at Secondary Steel Making unit at Rourkela Steel Plant. It is difficult to achieve and maintain desired vacuum level for CRNO grade of steel. This affects the decarburization process in VOR.
There has been thus a need in the existing field of producing low carbon CRNO grade Cold Rolled Non-Grained Oriented (CRNO) electrical grades of silicon steel by limiting the carbon content in final steel positively below 0.025% and developing a process with control on selective parameters to ensure such limitation on carbon content to avoid rejections. Due to the innovative process modifications to get the desired carbon level in CRNO steel, not only carbon in liquid steel below 0.025% was achieved, but also rejection was minimize as number of heats above 0.025% C drastically reduced, particularly in treated liquid steel from secondary steel making units.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide an improved method for production of low carbon(<0.025%) cold rolled non grained oriented(CRNO) silicon steel for electrical applications through BOF-VOR-LHF-CC route and CRNO silicon steel obtained thereof.

A further object of the present invention is directed to provide low carbon(<0.025%) cold rolled non grained oriented(CRNO) silicon steel involving a standardised process with controlled parameters developed for consistently achieving carbon level of less than 0.025% during secondary refining suitable for use in electric motors, generators, alternators etc. resulting in low core loss values.
A further object of the present invention is directed to provide low carbon(<0.025%) cold rolled non grained oriented(CRNO) silicon steel involving a standardised process wherein effectively controlled decarburization is targeted during refining of steel in VOR to achieve Carbon level < 0.025% consistently to minimize the occurrence of high carbon in liquid steel and resultant degradation/rejection or diversion of steel grade produced in any batch.
A further object of the present invention is directed to provide an improved method of producing low carbon(<0.025%) cold rolled non grained oriented(CRNO) silicon steel wherein deep decarburization of liquid steel during refining treatment in VOR is achieved involving controlled argon purging, oxygen blowing with variable decreasing lance height from liquid steel bath, deoxidation and adopting selective ferro alloy addition pattern and controlled degassing.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a method of producing low carbon not more than 0.03% non-oriented electrical steel sheets comprising:
treating steel composition from BOF converter comprising carbon 0.025-0.05%, manganese 0.01-0.04%, phosphorus 0.015-0.025%, sulphur 0.030-0.050%, silicon 0.003-0.009% in Vacuum Refining furnace (VOR) which includes oxygen blowing at a pressure of 10-14kg/cm2 along with lime addition during degassing for a period of at least 10 minutes under bath agitation maintaining variable argon flow rate of 10-15 nm3/hr during oxygen blowing for decarburization of steel by oxygen carbon reaction and Nitrogen level not more than 50 ppm followed by addition of ferro alloys as per grade requirement maintaining silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements including carbon < 0.03%, sulphur < 0.025% and nitrogen and total oxygen <50 ppm.

A further aspect of the present invention is directed to said method where said blowing for decarburization comprises deep decarburization of liquid steel involving variable lance height during blowing with increased oxygen pressure of ~ 14kg/cm2, finally keeping a minimum lance height of 450-500 mm from liquid steel bath towards the end of blow and by bath agitation by way of variable argon flow rate of 10-15 nm3/hr during oxygen blowing.

A still further aspect of the present invention is directed to said method wherein said addition of ferro-alloys is carried out following addition pattern which includes early slag formation involving addition of lime in said Vacuum Refining furnace (VOR) such as to achieve basicity of slag in the range 4-5 and initial heating with Silicon and subsequent addition of aluminium in batches.
A still further aspect of the present invention is directed to said method wherein for non oriented electrical steel having composition silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements including carbon < 0.03%, sulphur < 0.025% following steps are followed:
i) addition of one fourth of total lime in VOR for early slag formation;
ii) addition of SiMn for initial de-oxidation during degassing;
iii) addition of remaining portion of lime keeping basicity of ladle top slag in the range of 4-5 & addition of FeSi for chemical heating
iv) addition of FeSi and Al as per grade requirements and efficient purging for 2-3 minutes for bath homogenisation;
v) trimming addition Al & FeSi as per grade specification then soft purging @ 8-10 Nm3/hr for 6-8 minutes and then release of vacuum.

Yet another aspect of the present invention is directed to said method comprising
(i) obtaining steel tapped from BOF converter containing carbon 0.025-0.05%, manganese 0.01-0.04%, phosphorus 0.015-0.025%, sulphur 0.030-0.050%, silicon 0.003-0.009% and transferring to VOR;
(ii) treating the said steel in Vacuum Refining furnace (VOR) comprising
(a) oxygen blowing at a pressure of 10-14kg/cm2 along with lime addition with aim basicity of slag in the range 4-5;
(b) keeping degassing period for at least 10 minutes with vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing for efficient decarburization of steel by oxygen carbon reaction and maintaining Nitrogen level not more than 50 ppm;
(c) Addition of ferro alloys as per grade requirement maintaining silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements like carbon not more than 0.03%, sulphur not more than 0.025% and nitrogen and total oxygen not more than 50 ppm.
A further aspect of the present invention is directed to said method wherein said deep de-carburization of liquid steel in VOR comprises maintaining variable lance height during blowing with increased oxygen pressure of ~ 14kg/cm2, finally keeping a minimum lance height of 450-500 mm from liquid steel bath towards the end of blow and by vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing.
A still further aspect of the present invention is directed to low carbon (<0.03%) cold rolled non oriented (CRNO) silicon steels obtained through BOF-VOR-LHF-CC route as described above comprising
C: upto 0.025wt%;
Mn: 0.2% to 0.3% preferably 0.25%wt%;
Si: 1.4 to 3.0% preferably 1.6wt%;
Al: 0.08 to 0.2% preferably 0.1wt%
S: upto 0.025 wt%
P: upto 0.025 wt%;
Nitrogen: upto 50ppm;
and rest is iron and which is obtained as sheets for application in electric motors, generators, alternators etc. favouring low core loss values.
The above and other objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1:is the graphical presentation showing Low carbon level = 0.025% consistently achieved by present process in resulting CRNO grade silicon steel with substantially higher percent of total number of heats.

Figure 2: is the graphical presentation showing low carbon CRNO silicon steel grade produced according to present process having carbon content higher than 0.025% is significantly reduced in number of heats.

Figure 3: is the graphical presentation showing that diversions of steel from CRNO grade is almost eliminated due to high carbon level at steelmaking stage.

Figure 4: is the flow chart showing the sequential steps of ferrosilicon addition pattern in VOR during refining stage for improved ferro alloys recovery.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
The present invention is directed to provide low carbon (<0.025%) cold rolled non oriented silicon steel for applications in electrical equipments like motors, generators, alternators etc. involving an improved steel manufacturing process ensuring achieving low carbon level of = 0.025% consistently and thereby the diversions/down gradation from CRNO grade steel due to high carbon level at steelmaking is almost eliminated.
It was observed that in the Vacuum Oxygen Refining(VOR) unit in operation at Secondary Steel Making unit at Rourkela Steel Plant, it is difficult to achieve and maintain desired vacuum level for CRNO grade of steel. This affects the decarburization process in VOR.
Hence, improvement in process parameters during refining of steel in VOR w.r.t decarburization was targeted so as to achieve Carbon level < 0.025%. The following process improvements were carried out to minimize the occurrence of high carbon in liquid steel:
a) Continued soft purging with argon during and after placement of steel ladle at VOR treatment station. This has helped in initial decarburization during purging.
b) Variable decreasing lance height was maintained and a minimum lance tip height from liquid steel bath of ladle was maintained by gradually lowering of lance. In conventional practice lance tip height was fixed during entire blow period. This was done to facilitate deep de-carburization of liquid steel.
c) Oxygen pressure during blowing in VOR was increased to 14 kg/cm2 from set norm of 10 kg/cm2. This helped in minimizing the lower stagnant zone in ladle, resulting in a high decarburization of steel.
d) Deoxidation and ferro alloy practice was modified. Practice of initial addition of around ~ 150 kg of SiMn was introduced during degassing in VOR. This helped in decarburization of extra carbon from SiMn.
e) Degassing period was increased from 7 to 10 minutes and gradual increase in argon flow rate from 10-15 nm3/hr during degassing was also introduced as compared to constant argon flow rate of ~10 nm3/hr in conventional method. These modifications enabled deep decarburization during refining in VOR.
Due to these innovative process modifications to get the desired carbon level in CRNO steel, not only carbon in liquid steel below 0.025% was achieved, but also rejection was minimized as number of heats above 0.025% C drastically reduced which is reflected in accompanying fig. 1, fig 2 & fig. 3 and table-1), particularly in treated liquid steel from secondary steel making.
Table I:

%C, Range Periods
%C, Range Period 1 Period 2 Period 3 Period 4 Period 5 Period 6
= 0.025 Heats 758 645 710 906 946 700
% 47.99 40.75 55.16 63.58 66.10 60.19
0.026-0.030 Heats 668 775 461 502 482 459
% 41.85 48.96 35.82 35.23 33.68 39.47
0.031-0.035 Heats 153 128 97 17 3 4
% 9.59 8.09 7.54 1.19 0.21 0.3
0.031 – 0.040 Heats 17 35 19 0 0 0
% 1.07 2.21 1.48 0.00 0.00 0.00
Improved process technology according to the present invention for production of low carbon (%c<0.025%) non oriented silicon steel with lower core loss values through BOF-VOR-LF-CC route are described below:

A standard practice has been developed for consistently achieving carbon level of less than 0.025% during secondary refining. Low carbon level in non oriented silicon steel, generally used in electric motors, generators, alternators etc. results in low core loss values. The developed practice was found very effective in controlling the carbon level below 0.025% in majority of heats resulting in less down gradation/rejection of steel.

A method of making non-oriented electrical steel sheets having excellent magnetic properties, comprising of steel tapped from BOF converter containing carbon 0.025-0.05%, manganese 0.01-0.04%, phosphorus 0.015-0.025 %, sulphur 0.030-0.050%, silicon 0.003-0.009% thereafter treating the steel in Vacuum Refining furnace (VOR). VOR treatment includes oxygen blowing at a pressure of 10-14kg/cm2 along with lime addition with aim basicity of slag in the range 4-5. The degassing period is kept for at least 10 minutes with vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing for efficient decarburization of steel by oxygen carbon reaction and Nitrogen level not more than 50 ppm. Addition of ferro alloys to be done as per grade requirement maintaining silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements like carbon not more than 0.03%, sulphur not more than 0.025% and nitrogen and total oxygen not more than 50 ppm.

The process according to the present invention also involved improved method of decarburizing liquid steel in VOR as follows:

The non oriented silicon steel was produced involving deep decarburization of liquid steel in VOR by an improved process of decarburization by adopting variable lance height during blowing with increased oxygen pressure of ~ 14kg/cm2, finally keeping a minimum lance height of 450-500 mm from liquid steel bath towards the end of blow and by vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing.

The process of producing low carbon(<0.025%) cold rolled non oriented (CRNO) silicon steel according to the present invention also involved addition pattern for improved ferro alloys recovery in VOR:
An improved addition pattern in VOR has been designed and implemented which helps in better recovery of ferro alloys and aluminium. The addition pattern includes early slag formation by addition of lime in VOR keeping aim basicity of around 4-5 and initial chemical heating with Silicon and subsequent addition of aluminium in batches. The standard addition practice developed for non oriented electrical steel having composition silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements like carbon not more than 0.03%, sulphur not more than 0.025% consists of the sequential steps as shown in accompanying Figure 4.
The above described modified process for making low carbon non oriented silicon steel involving process of deep decarburization of liquid steel in VOR can be successfully utilized in any steel melting shop with minor modifications in oxygen, argon flow rate and pressure. The stated modified process has been implemented in applicants’ Rourkela steel plant. The modified practice is fully incorporated in SOP of SMS-I, RSP. Adoption of modified practice results in better decarburization of steel, thus making it easier to achieve consistently low liquid steel carbon and consequently low diversion/rejection of heats due to off chemistry.

We Claim:

1. A method of producing low carbon not more than 0.03% non-oriented electrical steel sheets comprising:

treating steel composition from BOF converter comprising carbon 0.025-0.05%, manganese 0.01-0.04%, phosphorus 0.015-0.025%, sulphur 0.030-0.050%, silicon 0.003-0.009% in Vacuum Refining furnace (VOR) which includes oxygen blowing at a pressure of 10-14kg/cm2 along with lime addition with degassing for a period of at least 10 minutes under bath agitation maintaining variable argon flow rate of 10-15 nm3/hr during oxygen blowing for decarburization of steel by oxygen carbon reaction and Nitrogen level not more than 50 ppm. followed by addition of ferro alloys as per grade requirement maintaining silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements including carbon < 0.03%, sulphur < 0.025% and nitrogen and total oxygen <50 ppm.

2. A method as claimed in claim 1 where said blowing for decarburization comprises deep decarburization of liquid steel involving variable lance height during blowing with increased oxygen pressure of ~ 14kg/cm2, finally keeping a minimum lance height of 450-500 mm from liquid steel bath towards the end of blow and by bath agitation by way of variable argon flow rate of 10-15 nm3/hr during oxygen blowing.

3. A method as claimed in anyone of claims 1 or 2 wherein said addition of ferro-alloys is carried out following addition pattern which includes early slag formation involving addition of lime in said Vacuum Refining furnace (VOR) such as to achieve basicity of slag in the range 4-5 and initial heating with Silicon and subsequent addition of aluminium in batches.

4. A method as claimed in anyone of claims 1 to 3 wherein for non oriented electrical steel having composition silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements including carbon < 0.03%, sulphur < 0.025% following steps are followed:
i) addition of one fourth of total lime in VOR for early slag formation;
ii) addition of SiMn for initial de-oxidation during degassing;
iii) addition of remaining portion of lime keeping basicity of ladle top slag in the range of 4-5 & addition of FeSi for chemical heating;
iv) addition of FeSi and Al as per grade requirements and efficient purging for 2-3 minutes for bath homogenisation;
v) trimming addition Al & FeSi as per grade specification then soft purging @ 8-10 Nm3/hr for 6-8 minutes and then release of vacuum;

5. A method as claimed in anyone of claims 1 to 4 comprising
(i) obtaining steel tapped from BOF converter containing carbon 0.025-0.05%, manganese 0.01-0.04%, phosphorus 0.015-0.025%, sulphur 0.030-0.050%, silicon 0.003-0.009% and transferring to VOR;

(ii) treating the said steel in Vacuum Refining furnace (VOR) comprising
(a) oxygen blowing at a pressure of 10-14kg/cm2 along with lime addition with aim basicity of slag in the range 4-5;

(b) keeping degassing period for at least 10 minutes with vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing for efficient decarburization of steel by oxygen carbon reaction and maintaining Nitrogen level not more than 50 ppm;

(c) Addition of ferro alloys as per grade requirement maintaining silicon in the range of 1.4-3.0% and aluminium in the range of 0.08-0.2% and precise control of elements like carbon not more than 0.03%, sulphur not more than 0.025% and nitrogen and total oxygen not more than 50 ppm.

6. A method as claimed in anyone of claims 1 to 5 wherein said deep de-carburization of liquid steel in VOR comprises maintaining variable lance height during blowing with increased oxygen pressure of ~ 14kg/cm2, finally keeping a minimum lance height of 450-500 mm from liquid steel bath towards the end of blow and by vigorous bath agitation by keeping variable argon flow rate of 10-15 nm3/hr during oxygen blowing.

7. Low carbon (<0.03%) cold rolled non oriented(CRNO) silicon steels obtained through BOF-VOR-LHF-CC route as claimed in anyone of claims 1 to 6 comprising
C: upto 0.025wt%;
Mn: 0.2% to 0.3% preferably 0.25% wt%;
Si: 1.4% to 3.0% preferably 1.6 wt%;
Al: 0.08% to 0.2% preferably 0.1 wt%
S: upto 0.025 wt%
P: upto 0.025 wt%;
Nitrogen: upto 50 ppm;
and rest is iron and which is obtained as sheets for application in electric motors, generators, alternators etc. favouring low core loss values.

Dated this the 7th day of February, 2015
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT
TITLE: A METHOD FOR PRODUCTION OF LOW CARBON (<0.025%) COLD ROLLED NON ORIENTED(CRNO) SILICON STEELS THROUGH BOF-VOR-LHF-CC ROUTE .
The present invention is directed to providing an improved method for production of low carbon (<0.025%) cold rolled non oriented(CRNO) silicon steels and CRNO silicon steel grade obtained thereof for applications in electrical equipments like motors, generators, alternators etc. The manufacturing process of producing CRNO silicon steel grade according to the present invention comprising controlled argon purging, oxygen blowing with variable decreasing lance height from liquid steel bath, deoxidation and adopting selective ferro alloy addition pattern and controlled degassing while treating steel in vacuum oxygen refining unit for controlled deep decarburization ensuring achieving low carbon level of = 0.025% consistently and thereby the diversions/down gradation from CRNO grade due to high carbon level at steelmaking is almost eliminated.