|Title of Invention||
ANTIMONY BEARING ELECTRICAL STEEL SHEETS AND A METHOD OF PRODUCTION THEREOF
|Abstract||The invention relates to a process for producing electrical steels with the improved magnetic properties, comprising the steps of providing a steel sheet having a hardness of 120-160 Hv, and a steel chemistry of: C≤ 0.05, Mn = 0.2- 0.5, S ≤ 0.015 P ≤ 0.01- 0.1, Si= 0.2 - 0.5, Al ≤ 0.004 or > 0.08, N ≤ 0.005 and Sb ≤ 0.07, the steel sheet having produced through LD 2 - RH - Slab caster- hot strip mill route, hot strip rolling at a finish rolling temperature of 800° to 950°C and then coiling between 650°-720° C, cold rolling of the processed product to a desired thickness (0.35- 1.0 mm) in cold roll mill, annealing the coil between 650°- 850° C, skin pass reduction between 2-9 %; and carrying out a second annealing step for decarburisation and grain growth.|
FIELD OF THE INVENTION
The present invention relates to a process for producing a new electrical steel
with improved magnetic properties.
BACKGROUND OF THE INVENTION
Electrical steels are used in electrical equipments adapted for generation,
distribution and utilization of electrical energy. Based on crystallographic texture
and resulting magnetic properties, electrical steel strips may be generally of two
types: cold rolled non-oriented electrical steel (CRNO) for small motors and
generators, and cold rolled grain oriented electrical steel (CRGO) for larger
motors, generators and transformer applications. Again, CRNO steels are of two
types: Fully Processes (FP) or semi processed (SP) steels. Fully processed
electrical steels generally have higher silicon (>0.5%) and other alloying
elements (Al, P etc.) for which the final magnetic properties are achieved
through annealing at the steel producers' end. CRNO (FP) can be readily used by
the motor generator manufacturer for lamination. These steels are required to be
sent to customers after varnish coating or some special coatings. In contrast
thereto, the semi processed steels (SP) have lower amount of the alloying
elements and are finished to the final thickness by the steel producers and the
final magnetic properties in the punched lamination are achieved though second
annealing treatment (decarburisation grain growth) at the customers' end.
It is often desired to have the following properties in electrical steels for energy
efficient motors: for example, low core loss, high magnetic induction and high
magnetic permeability, because the electrical steels with such improved
properties will reduce the size of the electrical motors and reduce the overall cost
of the electrical equipment due to reduced cost of materials and processing. The
electrical steel presently used for electrical motors / generators for many
appliances leads to wastage of large quantity of electrical energy due to poor
magnetic properties (higher core loss and lower permeability) of the electrical
OBJECTS OF THE INVENTION
It is therefore, the object of the present invention to develop a new electrical
steel with improved magnetic properties (low core loss and high permeability)
which will eliminate the disadvantages of the prior art.
SUMMARY OF THE INVENTION
According to the invention, steel sheet is, made through LD2 - RH - Slab caster
- Hot Strip Mill route. Hot rolled coil is then cold rolled in CRM to 0.63 mm and
then processed through batch annealing-skin passing route. Epstein strip
samples are annealed in continuous annealing furnace along with other charge
(at the normal annealing parameters) at the motor manufacturers place. The
composition of steel used for the purpose according to the invention contains at
least ≤ 0.07 antimony (Sb) apart from other elements.
Magnetic properties of the finally processed steel as evaluated are shown in
figure l(a) - l(c), including a comparative chart in respect of the prior art steel.
The results indicate that steel with antimony addition according to the present
invention, has a significantly lower core loss value of 3.3 - 4.5 W/kg as
compared to the prior art steels for example, ULC and LC steels which are
5.2W/kg and 5.5 - 6.5 W/kg respectively, the core loss value having measured
at 1.5 Tesla and 50 Hz. The mangnetization force required for achieving 1.5 T in
case of the new steel is also much lower as compared to the prior art steels. The
new steel also shows very high permeability values of 3020-4600 G/Oe as
compared to 1500 - 2000 G/Oe for LC and 2400 G/Oe for ULC steels of prior art.
The prior art steel, inspite of having lower thickness (0.5m) of fully processed
coated material, shows higher core loss (4.8 W/Kg) and poor magnetization than
that of the newly developed steel.
MICROSTRUCTURE AND TEXTURE
Microstructures of the new steel in finally processed condition are shown in
Figure 2. The new steel shows a coarser grain size. The texture of the new steel
is evaluated and has been compared with that of the prior art steel. The new
steel shows a high intensity of magnetic properties favourable texture that is
(110) as compared to that of the prior art steel. A typical ODF for the
new steel is presented in Figure 3. The intensity ratio (110) (211) as evaluated
by using XRD is shown in Figure 4. In case of the new steel, the ratio is 5 times
higher than that of the prior art steels, thus indicating a favourable texture for
the magnetic properties.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure la to 1c - show the magnetic properties of the new steel according to
the invention including a comparison with the magnetic
properties of the prior art steels.
Figure 2 - shows the microstructure of the new steel after annealing
according to the invention
Figure 3 - shows a typical oriental distribution function (ODF) for the
new steel including a comparative ODF in respect of the
prior art steel.
Figure 4 - shows the intensity ratio (110/211) of the new steel
including a comparison with that of the prior art steel.
DETAILED DESCRIPTION OF THE INVENTION
(A) MATERIAL SPECIFICATION IN SUPPLY CONDITION:
(i) Steel sheet with 0.35 - 1.0 mm.
(ii) Chemistry of steel specified is given in Table 1.
(iii) Hardness 120 - 160 HV.
Table 1: Chemistry of steel specified for improved magnetic properties
(B) PROCESS ROUTES:
(i) Steel making by LD or any other process
(ii) Secondray steel making: RH and or LF process
(iii) Slab casting
(iv) Hot strip rolling and cooling with an optimum processing
(v) Cold rolling and the annealing in batch annealing furnace /
continuous annealing furnace,
(vi) Second annealing (Decarburisation / grain growth) at a motor
(C) THE ADAPTED PROCESSING PARAMETERS ARE SHOWN IN TABLE 2,
Table 2: Hot rolling and cold rolling parameters specified for processing
of Sb-bearing steel
Finish rolling Coiling CR def Ann Skin Pass def
temperature temperature Temperature
800 - 950°C 550 - 720°C 50 - 80% 650 - 850°C 2 to 9%
• It is observed from the experimented results that addition of Sb in
electrical steel according to the invention, leads to a large improvement in
magnetic properties. After Sb addition, the core loss (1.5T & 50 Hz) is
decreased by 1.8 W/Kg and 2.5 W/Kg than that of the prior art steel for
example ULC and LC, under similar annealing and testing conditions.
Permeability is increased from 1700 - 2400 to 3020 - 4600 G / Oe.
Magnetizing force required to achieve induction of 1.5 T is decreased from
4.1 to 3.0 Oe.
• Magnetic properties of the new steel is found to be superior to those of
fully processed coated material.
• A minimum critical amount of skin pass deformation (2%) is necessary for
grain coarsening throughout the section for improved magnetic properties.
• Microstructure and texture of the new steel is found to be favourable for
their magnetic properties.
• The benefit of Sb addition in the new steel has been obtained in non-
oriented semi-processed electrical steels. A significant benefit of antimony
addition can also be obtained in non-oriented fully processed as well as in
cold rolled grain oriented steel, according to the invention.
FIELD OF APPLICATION
The new steel produced according to the invention, can be used for lamination
applications for motors and generators and other electrical equipments.
ADVANTAGES OF THE INVENTION
(A) TO STEEL MANUFACTURES
• Possibility of reduction in alloying cost due to reduction in Fe-Si, Fe-AI and
• Achieving excellent properties by the addition of a cheaper alloying
element that is Sb.
(B) TO MOTOR MANUFACTURERS
• Reduction in material consumption of steel along with the other materials
that is Cu, Al etc. for motor manufacturing.
• Reduction in motor size due to reduction in size of core.
• Reduction in processing of cost due to less material consumption.
• Increase in production of motor due to use of thicker sheets.
• A large reduction in overall cost of manufacturing of motors.
1. A process for producing electrical steels with the improved magnetic
properties, comprising the steps of:
providing a steel sheet having a hardness of 120 - 160 Hv, and a
steel chemistry of: C ≤ 0.05, Mn = 0.2 - 0.5, S ≤0.015 P ≤0.01 -
0.1, Si = 0.2 - 0.5, Al ≤ 0.004 or > 0.08, N ≤ 0.005 and Sb ≤ 0.07,
the steel sheet having produced through LD 2 - RH - Slab caster -
hot strip mill route;
- hot strip rolling at a finish rolling temperature of 800° to 950° C and
then coiling between 650° - 720° C;
- cold rolling of the processed product to a desired thickness (0.35 -
1.0 mm) in cold roll mill;
- annealing the coil between 650° - 850° C;
- skin pass reduction between 2-9 %; and
- carrying out a second annealing step for decarburisation and grain
2. A process for producing electrical steels with the improved magnetic
properties as substantially described herein with reference to the
The invention relates to a process for producing electrical steels with the
improved magnetic properties, comprising the steps of providing a steel sheet
having a hardness of 120-160 Hv, and a steel chemistry of: C≤ 0.05, Mn = 0.2-
0.5, S ≤ 0.015 P ≤ 0.01- 0.1, Si= 0.2 - 0.5, Al ≤ 0.004 or > 0.08, N ≤ 0.005 and
Sb ≤ 0.07, the steel sheet having produced through LD 2 - RH - Slab caster- hot
strip mill route, hot strip rolling at a finish rolling temperature of 800° to 950°C
and then coiling between 650°-720° C, cold rolling of the processed product to a
desired thickness (0.35- 1.0 mm) in cold roll mill, annealing the coil between
650°- 850° C, skin pass reduction between 2-9 %; and carrying out a second
annealing step for decarburisation and grain growth.
|Indian Patent Application Number||1235/KOL/2007|
|PG Journal Number||29/2012|
|Date of Filing||03-Sep-2007|
|Name of Patentee||TATA STEEL LIMITED|
|PCT International Classification Number||C22C38/00|
|PCT International Application Number||N/A|
|PCT International Filing date|