FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A method for the production of semi-processed grade of electrical steel.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Dumbre Jayshri and Ingle Asha; both of Advanced Materials and Process Technology Center, CG Global R&D Centre, Kanjur Marg (E), Mumbai, Maharashtra, India and Pendse Ganesh of Stamping Division, Crompton Greaves Limited, Kanjur Marg (E), Mumbai, Maharashtra, India; all Indian Nationals.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

Technical field:
The present invention relates to a method for the production of electrical steel.
Particularly, the present invention relates to a method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T from single grade of semi-processed electrical steel.
Background of the invention:
Electrical steel is a special type of steel used in the construction of the cores of transformers and the stator of motors and generators. This steel is also known as silicon steel. It is an alloy of iron with silicon. The silicon content can be upto 3.5 weight %. The silicon increases resistivity of steel; minimizing eddy currents and the resulting heat loss. Electrical steel also has a small hysteresis curve, reducing iron losses. Heat treatment is done which increases grain size of the steel and reduces hysteresis loss.
In electric machines such as transformers and motors, etc., the steel is made in the form of thin sheets which are coated on both sides by the steel manufacturer. This is done in order to prevent eddy currents from circulating in the core. Electrical steel should be handled carefully. Wrong bending or rough handling can adversely affect the magnetic properties of the steel.

Electrical steel, also called lamination steel, silicon electrical steel, silicon steel or transformer steel, is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (small energy dissipation per cycle, or low core loss) and high permeability.
The material is usually manufactured in the form of cold-rolled strips less than 2 mm thick. These strips are called laminations when stacked together to form a core. Once assembled, they form the laminated cores of transformers or the stator and rotor parts of electric motors.
Cold rolled non oriented (CRNO) electrical steel has two basic types depending on their condition of heat treatment, (1) fully processed and (2) semi processed electrical steels. Fully processed steels are those for which decarburizing annealing is done at supplier's end. Fully processed steels are further coated with organic or inorganic coating and hence, there is no need of any further heat treatment at stamping manufacturer's end. Semi processed steels are those for which the last operation carried out is normally a skin pass rolling and further heat treatment is carried out at stamping manufacturer's end. Generally, after punching electrical steel sheet coil, the punched laminations undergo stress relieving treatment to eliminate stress generated during punching operation. The heat treatment to the semi processed electrical steel sheet in order to develop a magnetite layer on the sheet surface is called 'bluing treatment'. Another type of heat treatment, a 'grain growth annealing' is carried out at higher temperature at around 800°C under reducing atmosphere and is essential to get desired magnetic properties.

Nearly all semi processed grades of electrical steel are required to do grain growth annealing treatment in order to get the magnetic properties similar to commercially available CRNO grades like M43 or M45 or M47 grades. The stamping manufacturer deals with various motor manufacturers requiring different magnetic properties. To fulfill the wide range of customer requirements a stamping manufacturer needs to have various grades of fully processed as well as semi processed electrical steels. This leads to very high inventory cost. The grain growth annealing is an expensive process as it requires high temperature and controlled atmosphere.
The grain growth annealing is the most widely used heat treatment for the semi processed grade of electrical steels. This heat treatment results in grain growth, decarburization and formation of thin magnetite layer on the sheet surface of motor lamination. The temperature required for grain growth and decarburization mechanisms is quite high and therefore the motor laminations are normally treated at the temperatures up to 850°C for a sufficient period of time in a controlled atmosphere followed by furnace cooling. After grain growth annealing, the magnetic properties improve to a large extent, however are lower than that of fully processed grades.
The heat treatment process of magnetite layer formation (bluing process) is developed in order to get improved magnetic properties of motor laminations. However the improvement in properties is very marginal and not suitable for the motor manufacturing and there always remains a need to go for the grain growth annealing in order to get improved magnetic properties which are acceptable to motor manufacturer.

Thus, there is need to develop the method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T, from the single grade semi-processed electrical steel which will be cost-effective and gets magnetic properties equivalent to that of commercially available CRNO grades like M43 or M45 or M47 grades.
Objects of the invention:
An object of the invention is to provide a method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T equivalents to that of commercially available CRNO grades like M43 or M45 or M47 grades.
Another object of the invention is to provide the method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T equivalents to that of commercially available CRNO grades like M43 or M45 or M47 grades from the single grade semi-processed electrical steel thereby lowering the inventory cost.
Another object of the invention is to provide the method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T which involves heat treatments of motor laminations punched from single grade in particular manner to get range of magnetic properties which will fulfill the wide range of motor manufacturer requirements and are comparable to the magnetic properties of the fully processed electrical steel grades.

Another object of the invention is to provide the method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T which involves heat treatments of motor laminations punched from single grade in particular manner where the oxide layer formation mechanism occurs at much lower temperature than the grain growth annealing temperature, thus resulting in low energy consumption and making the method cost-effective.
Another object of the invention is to provide the method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T which involves hot air oxidation and substantially eliminates the use of reduced atmosphere, thus making the method cost-effective.
Detailed Description:
According to one of the embodiment of the invention there is provided, a method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz, 1.5T; said method comprises
a punching of laminations of semi-processed electrical steel by using a machine press or stamping press;
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 400° C for 30 to 120 minutes; and/or
c. subjecting punched laminations to heat treatment at temperature in the
range of 500° C to 600° C for 30 to 120 minutes; and/or

d. subjecting punched laminations to heat treatment at temperature in the range of 700° C to 850° C under reduced atmosphere for 30 to 120 minutes.
The semi processed electrical steel used in the invention has Si and Al content in the range of 0.4 to 1.5 weight %. Particularly, the semi processed electrical steel has Si content is in the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %. The steps (b), (c), and (d) is used in combinations to achieve wide range of magnetic properties.
According to another embodiment of the invention there is provided, a
method for the production of electrical steel having wide range of magnetic
properties from 7.0 W/Kg to 12.0 W/Kg at 50Hz 1.5T;
said method comprises
a punching of laminations of semi-processed electrical steel by using a
machine press or stamping press; and
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 600° C for 30 to 120 minutes.
Particularly, the semi processed electrical steel used in the production of electrical steel having wide range of magnetic properties from 7.0 W/Kg to 12.0 W/Kg at 50Hz 1.5T; has Si content is in the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %.
According to another embodiment of the invention there is provided, a method for the production of electrical steel having wide range of magnetic properties from 5.0 W/Kg to 7.0 W/Kg at 50Hz 1.5T;

said method comprises
a punching of laminations of semi-processed electrical steel by using a machine press or stamping press;
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 400° C for 30 to 120 minutes; and
c. subjecting punched laminations to heat treatment at temperature in the
range of 500° C to 700° C for 30 to 120 minutes.
Particularly, the semi processed electrical steel used in the production of electrical steel having wide range of magnetic properties from 5.0 W/Kg to 7.0 W/Kg at 50Hz 1.5T; has Si and A1 content is in the range of 0.4 to 1.5 weight % and Si content is in the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %.
According to another embodiment of the invention there is provided, a method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 5.0 W/Kg at 50Hz 1.5T; said method comprises
a punching of laminations of semi-processed electrical steel by using a machine press or stamping press;
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 400° C for 30 to 120 minutes;
c. subjecting punched laminations to heat treatment at temperature in the
range of 500° C to 600° C for 30 to 120 minutes; and
d. subjecting punched laminations to heat treatment at temperature in the
range of 700° C to 850° C under reduced atmosphere for 30 to 120
minutes.

Particularly, the semi processed electrical steel used in the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 5.0 W/Kg at 50Hz 1.5T; has Si and Al content is in the range of 0.4 to 1.5 weight % and Si content is in the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %.
According to the invention, the set of heat treatments can be selected to achieve the magnetic properties equivalent to the commercially available CRNO grades of M47, M45 and M43. The core loss values achieved are 8.0W/kg, 6.0 W/kg and 4.0 W/kg respectively at 50Hz 1.5T.
Thus the present invention provides three different sets of heat treatments of motor laminations punched from single grade to get a range of magnetic properties which will fulfill the wide range of motor manufacturer requirements and are comparable to the magnetic properties of the fully processed electrical steel grades. The present invention provides electrical steel having wide range of magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz 1.5T equivalents to that of commercially available CRNO grades like M43 or M45 or M47 grades from the single grade semi-processed electrical steel thereby lowering the inventory cost. In the present invention, the electrically insulating oxide layer formation mechanism occurs at much lower temperature than the grain growth annealing temperature, thus resulting in low energy consumption making the method cost effective. Further heat treatments are carried out in the presence of air, thus substantially eliminating the use of reduced atmosphere and hence making the method cost-effective. The electrically insulating oxide film formed in

the present invention eliminates necessity of annealing. The resulting magnetic properties of the electrical steel after processing according to the invention is apparently due to the reduction of the quantity of impurities in the metal.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof:
Examples 1 to 7 (i.e. ES1 to ES7)
Semi-processed electrical steel containing 0.2 to 1.2 weight % of Si and 0.2 to 0.3 weight % A1 sheets were punched in the desired dimensions of the stator frame. The punched laminations were subjected to heat treatment as per the conditions provided in table 1. The core loss was measured and compared with the standard CRNO grades at 50Hz at 1.5T (W/kg). The results of the same are illustrated in Table 2.
Table 1: Heat treatment conditions in examples 1 to 7 to punch laminations

SrNo Heat treatments used Electrical steel
Wt. % Si Wt. % Al
ESI 1.Heating to 400±10°C for 90±10 minutes; 2.Heating to 780±10°C under reduced atmosphere for 90±10 minutes 0.50 0.25
ES2 1. Heating to 400±10°C for 90±10 minutes; 2.Heating to 700±10°C under reduced atmosphere for 90±10 minutes 0.50 0.25

ES3 1. Heating to 400±10°C for 90±10 minutes; 2.Heating to 700±10°C under reduced atmosphere for 90±10 minutes 0.55 0.20
ES4 1.Heating to 400±10° C for 90±10 minutes; 2. Heating to 600±10°C for 90±10 minutes in ambient air 0.52 0.24
ESS 1. Heating to 400±10°C for 60±10 minutes;
2. Heating to 600±10°C for 90±10 minutes in
ambient air 0.50 0.22
ES6 1. Heating to 400±10°C for 30±10 minutes
2. Heating to 550±10°C for 90±10 minutes in
ambient air 0.55 0.20
ES7 1. Heating to 400±10°C for 30±10 minutes
2. Heating to 500±10°C for 60±10 minutes in
ambient air 0.52 0.25
Table 2: Comparative value of core loss of electrical steel (ESI to ES7) produced according to invention with conventional fully processed CRNO grades.

Sr. Fully processed Maximum Core Electrical steel Max. Core loss of
No CRNO Grade loss of CRNO produced indigenously heat
Name grade at 50Hz, according to the treated grade at
1.5T(W/kg) invention 50Hz, 1.5T(W/kg)
1 50C400 (M43) 4.00 ESI 4.00
2 50C470 4.70 ES2 4.50
3 50C530 (M 45) 5.30 ES3 4.50
4 50C600 6.00 ES4 6.00
5 50C630 6.30 ES5 6.30

6 50C700 (M 47) 7.00 ES6 7.00
7 50C800 8.00 ES7 8.00
According to table 2, it is clear that the single grade of semi-processed electrical steel having (0.2 to 1.2 weight % Silicon + 0.2 to 0.3 weight % Aluminum) on subjection to method of the invention i.e. heat treatments combinations as specified results in the core loss values similar to fully processed CRNO grades as specified.

We claim;
1. A method for the production of electrical steel having wide range of
magnetic properties from 4.0 W/Kg to 12.0 W/Kg at 50Hz 1.5T;
said method comprises
a punching of laminations of semi-processed electrical steel by using a machine press or stamping press;
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 400° C for 30 to 120 minutes; and / or
c. subjecting punched laminations to heat treatment at temperature in the
range of 500° C to 600° C for 30 to 120 minutes; and / or
d. subjecting punched laminations to heat treatment at temperature in the
range of 700° C to 850° C under reduced atmosphere for 30 to 120
minutes.
2. The method as claimed in claim 1, wherein the semi processed electrical steel used has Si and A\ content in the range of 0.4 to 1.5 weight %.
3. The method as claimed in claim 1, wherein the semi processed electrical steel has Si content is in' the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %.
4. A method for the production of electrical steel having wide range of magnetic properties from 7.0 W/Kg to 12.0 W/Kg at 50Hz 1.5T;
said method comprises
a punching of laminations of semi-processed electrical steel by using a
machine press or stamping press; and
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 400° C for 30 to 120 minutes.

5. The method as claimed in claim 4, wherein the semi processed electrical steel used has Si and Al content in the range of 0.4 to 1.5 weight %.
6. The method as claimed in claim 4, wherein the semi processed electrical steel used has Si content is in the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %.
7. A method for the production of electrical steel having wide range of magnetic properties from 5.0 W/Kg to 7.0 W/Kg at 50Hz, 1.5T;
said method comprises a punching of laminations of semi-processed electrical steel by using a machine press or stamping press;
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 400° C for 30 to 120 minutes; and
c. subjecting punched laminations to heat treatment at temperature in the
range of 500° C to 700° C for 30 to 120 minutes.
8. The method as claimed in claim 7, wherein the semi processed electrical steel used has Si and Al content in the range of 0.4 to 1.5 weight %.
9. The method as claimed in claim 7, wherein the semi processed electrical steel used has Si content is in the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %
10.A method for the production of electrical steel having wide range of magnetic properties from 4.0 W/Kg to 5.0 W/Kg at 50Hz 1.5T;
said method comprises
a punching of laminations of semi-processed electrical steel by using a
machine press or stamping press;
b. subjecting punched laminations to heat treatment at temperature in the
range of 300° C to 400° C for 30 to 120 minutes;

c. subjecting punched laminations to heat treatment at temperature in the
range of 500° C to 600° C for 30 to 120 minutes; and
d. subjecting punched laminations to heat treatment at temperature in the
range of 700° C to 850° C under reduced atmosphere for 30 to 120
minutes.
1 l.The method as claimed in claim 10, wherein the semi processed electrical steel used has Si and Al content in the range of 0.4 to 1.5 weight %.
12.The method as claimed in claim 10, wherein the semi processed electrical steel used has Si content is in the range of 0.2 to 1.2 weight % and Al content is in the range of 0.2 to 0.3 weight %.