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 :
COLD-ROLLED NON-ORIENTED MOTOR LAMINATION STEEL SHEET AND MANUFACTURING METHOD THEREOF.


2 APPLICANT (S)

Name : JSW STEEL LIMITED.

Nationality : An Indian Company incorporated under the Companies Act, 1956.

Address : JSW CENTRE,
BANDRA KURLA COMPLEX,
BANDRA(EAST),
MUMBAI-400051,
MAHARASHTRA,INDIA.




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
The present invention relates to cold-rolled non-oriented motor lamination steel sheet for use as core laminations of motors, generators. More particularly, the present invention relates to a non-oriented electrical steel having desired magnetic properties, which can be used directly in making core laminations of electromagnetic machines without need of a decarburization anneal to develop magnetic properties. The present invention provides a steel sheet which is cost effective and its magnetic properties are also comparable to traditional fully processed and coated electrical steel sheet as well as semi processed steel sheet. Additionally this steel sheet can be optionally annealed to further improve the core losses. Therefore this steel does not provide any production routing limitations or constraints on the punched core lamination making process.
BACKGROUND OF THE INVENTION
The cold rolled non oriented motor lamination steel sheets, CRML in abbreviated form, are traditionally used for making core laminations of small and medium size motors. This traditional CRML steel sheet has to undergo a decarburization anneal process to develop the desired magnetic properties after lamination punching process. This process requires additional equipment set up, its maintenance and additional cost associated with it. Whereas traditional cold rolled non-oriented fully processed and coated steel sheet are more expensive than CRML steel grades. Due to this additional process and cost involved, often the core lamination manufacturer uses low cost alternative cold rolled steel sheet grade where the core losses are much higher. This alternative material imparts lower efficiency in electromagnetic machines and thereby higher greenhouse gas emission associated with it.
In prior art for instance in Indian patent number 237812, discloses a method of production of semi processed electrical steel sheet to achieve core loss of 4.5 W/kg in 0.50 mm thickness after decarburization annealing treatment. This decarburization annealing treatment involve additional cost and requirement of a decarburization annealing furnace and its maintenance.
In yet another prior art for instance in Indian patent application199/MUM/2011, discloses a method for the production of electrical steel having wide range of core losses from 4.0 to 12.0 W/kg at 50Hz 1.5T. Here also the production method employs additional one and/or more annealing step after lamination punching to achieve the desired core loss. This again involve additional processing equipment and associated cost.
In yet another prior art for instance in Indian patent application number 202231018498, discloses a cold rolled electrical steel in 0.50 mm thickness which does not require the decarburizing annealing treatment step. This steel offers the cost advantage to core lamination manufactures but the core losses are 10 to 15W/kg, which is comparatively higher than traditional semi processed and fully processed electrical steel in 0.50 mm thickness. This higher core loss will result in inferior electromagnetic machine efficiency and accordingly have high greenhouse gas emission associated with it.
To solve the above problems of prior arts, the present inventors conducted extensive study to provide a method to manufacture cold-rolled non-oriented motor lamination electrical steel sheet having thickness in the range of 0.50–0.65 mm; exhibit Watt loss at 50Hz and 1.5T, W15/50 ≤ 10.0 Watts/kg and magnetic flux density at 5000 A/m, B50 is in the range of 1.68 to 1.77 T in as received condition without requiring a decarburization annealing process. Thereby making this CRML steel sheet cost effective by eliminating the requirement of additional decarburizing annealing treatment to develop the desired magnetic properties.
Additionally, these laminations can be optionally subjected to a stress relief annealing process after lamination punching, which further reduces core losses to achieve the Watt loss at 50Hz and 1.5T, W15/50 is ≤ 6.6 Watts/kg after stress relief annealing at 750°C to 850°C for 2 to 3 hours under reducing atmosphere comprising of H2 and N2 mixture. The magnetic flux density at 5000 A/m, B50 is in the range of 1.68 to 1.77 T.
The present invention thus providesa non-oriented electrical steel having desired magnetic properties, which can be used directly in making core laminations of electromagnetic machines without need of a decarburization anneal to develop magnetic properties. Thus it is capable of eliminating an additional step of decarburization annealing of punched laminations to develop magnetic properties which has additional cost and complexity associated with it. As for small and medium size motor the cost of raw material often prevents the usage of superior fully processed and coated steel sheet. The present invention provides a solution to the above problem by providing a steel sheet which is cost effective and its magnetic properties are also comparable to traditional fully processed and coated electrical steel sheet as well as semi processed steel sheet.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide a cold rolled non-oriented motor lamination electrical steel having desired magnetic properties, having thickness in the range of 0.50–0.65 mmwhich can be used directly in making core laminations of electromagnetic machines without need of a decarburization annealing to develop magnetic properties.
A further object of the present invention is directed to provide a cold rolled non-oriented motor lamination electrical steel having desired magnetic properties produced by a process eliminating an additional step of decarburization annealing of punched laminations to develop magnetic properties which has additional cost and complexity associated with it.
A still further object of the present invention is directed to provide a cold rolled non-oriented motor lamination electrical steel having desired magnetic properties where the steel sheet is cost effective and its magnetic properties are also comparable to traditional fully processed and coated electrical steel sheet as well as semi processed steel sheet.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide a cold rolled non-oriented motor lamination steel sheet comprising of steel composition having alloying elements in weight%, C: 0.0005-0.01%; Mn: 0.10-0.70%; Si: 0.1-1.0%; Al: 0.0005-0.5%; P: 0.001-0.20%; S: 0.0005-0.02%; N: 0.0005- 0.008%; Ti: 0.0-0.003%; and the balance are Fe and other unavoidable impurities and satisfies the following relation: weight % [Mn]/[S] ≥ 25, and [Nb] + [V] + [Ti] ≤ 0.0050% as non oriented electrical steel having magnetic properties.

According to another advantageous aspect of the present invention, said cold rolled non oriented motor lamination steel sheet comprising of application in core lamination of motors and generators.

A further aspect of the present invention is directed to provide said cold rolled non oriented motor lamination steel sheet wherein the said cold-rolled non-oriented motor lamination steel sheet having thickness in the range of 0.50–0.65 mm , free of any required decarburization annealing, having magnetic properties of Watt loss at 50Hz and 1.5T, W15/50 ≤ 10.0 Watts/kg in as received condition and Watt loss at 50Hz and 1.5T, W15/50 is ≤ 6.6 Watts/kg after stress relief annealing at 750°C to 850°C for 2 to 3 hours under reducing atmosphere comprising of H2 and N2 mixture.

A further aspect of the present invention is directed to provide said cold rolled non oriented motor lamination steel sheet having magnetic flux density at 5000 A/m, B50 is in the range of 1.68 to 1.77 T.

A still further aspect of the present invention is directed to provide a process for the manufacture of Cold rolled non oriented motor lamination steel sheet as described above comprising:
i) providing select alloying elements in weight%, C: 0.0005-0.01%; Mn: 0.10-0.70%; Si: 0.1-1.0%; Al: 0.0005-0.5%; P: 0.001-0.20%; S: 0.0005-0.02%; N: 0.0005- 0.008%; Ti: 0.0-0.003%; and the balance are Fe and other unavoidable impurities and satisfies the following relation: weight % [Mn]/[S] ≥ 25, and [Nb] + [V] + [Ti] ≤ 0.0050% and subjecting to steel making route to continuous casting of steel into slabs;
ii) subjecting the hot slab to reheated to a temperature in the range of 1100 to 1250 °C and thereafter to rough rolling, maintaining the temperature at the end of rough rolling the slab to a temperature in the range 1100 to 950 °C;
iii) subjecting the thus rough rolled steel to a finish rolling to achieve a final temperature of 800 to 950 °C and produce hot coil thus obtained in thickness of 2.0 to 3.0 mm was coiled at a temperature range of 600 to 700 °C and finally cooled to room temperature to thereby provide as non oriented electrical steel having magnetic properties free of any required decarburization annealing for generating its magnetic properties.

A still further aspect of the present invention is directed tosaid processwherein the hot rolled coil thus obtained was pickled with 2 to 18% hydrochloric acid to remove the scales, said pickled hot coil can optionally subjected to annealing by soaking at a temperature in the range of 650 °C to 900 °C for 20 to 180 seconds in the case of continuous annealing or 6 to 16 hours in the case of box annealing.
A still further aspect of the present invention is directed tosaid process comprising cold rolling step wherein the cold rolling reduction is controlled within 50 to 85% to obtain final sheet thickness of 0.50 – 0.65 mm.
Another aspect of the present invention is directed to said process comprising step of subjecting to soaking at final annealing temperature of 650 °C to 900 °C for 20 to 180 seconds in the case of continuous annealing or 6 to 16 hours in the case of box annealing to thereby produce the annealed coils of said cold-rolled non-oriented motor lamination steel sheet of the thickness in the range 0.50 to 0.65 mm.
Yet another aspect of the present invention is directed tosaid process comprising oiling with a suitable rust preventive oil through an electrostatic oil spraying machine to provide resistance to rust during transportation and further processing of making core laminations and wherein the oiling content is controlled to 100 to 350 grams per square meter of surface area.
A still said further aspect of the present invention is directed to process comprising subjecting additionally to step of annealing for stress relief of punching operation at 750°C to 850°C for 2 to 3 hours under reducing atmosphere comprising of H2 and N2 mixture such as to attain the Watt loss after stress relief annealing at 50Hz and 1.5T, W15/50 is ≤ 6.6 Watts/kg and magnetic flux density at 5000 A/m, B50 is in the range of 1.68 to 1.77 T.
The above and other aspects and advantages of the present invention are described hereunder in greater details with reference to following accompanying illustrative drawing and examples.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
[Fig. 1]: It is a flow chart showing schematic representation of process route followed for production of inventive example steel according to present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS AND EXAMPLES
The present invention discloses a method of manufacturing cold rolled non-oriented motor laminations electrical steel sheet comprising of following chemical composition by weight percent as C: 0.0005 to 0.01%; Mn: 0.1 to 0.7%; Si: 0.1 to 1.0%; Al: 0.0005 to 0.5%; P: 0.001 to 0.20%; S: 0.0005 to 0.02%; N: 0.0005 to 0.008%; Ti: 0.0 to 0.003%; and the balance are Fe and other unavoidable impurities and satisfies the following relation: weight % [Mn]/[S] ≥ 25 and [Nb] + [V] + [Ti] ≤ 0.0050%.
According to the present invention, a steel of the chosen composition with the specified range of alloying elements and impurity level the desired thickness of the sheets could be fabricated that finally meets the target magnetic properties. The chosen composition in the steel can be obtained by appropriately alloying the elements during steel making. By using such electrical steel sheet according to the present invention it is possible to provide a cold rolled non-oriented motor lamination electrical steel sheet suitable for use as a core lamination for motors, generators and other electromagnetic machines.
Hereinafter the chemical composition of the steel is described with the reason of limiting the specified ranges of each constituent and the metallurgical significance thereof. According to the preferred embodiment wherein all the elements were demonstrated in weight percent.
Carbon (0.0005 – 0.01 wt %) - Carbon is a harmful element for electrical steel sheets as it increases core loss by carbide precipitate. If the carbon content exceeds 0.01%, carbides such as cementite and alloy carbides precipitate, and due to this the core loss deterioration may become significant during service. If carbon content is more than 0.01%, a decarburization annealing should be performed to reduce the carbon content in the steel sheet which is not prescribed in the present invention. To further improve the magnetic properties, particularly to improve the core loss in as received condition, the upper limit of the C content is preferably 0.005%. The lower limit of carbon is not particularly limited, but, it increases the production time to bring Carbon less than 0.0005% in industrial processes. Therefore, the carbon content is set as 0.0005 – 0.01%, more preferably 0.001 – 0.003%.
Manganese (0.1 – 0.7wt %) – Manganese improves the specific resistivity of the steel and thus helps to reduce the core losses. Manganese also improves the yield strength by solid solution strengthening. It is also effective in coarsening the sulphide precipitate rendering it harmless to the magnetic properties, mainly watt losses. The manganese should be in excess quantity to the stoichiometric ratio of [Mn]/[S] to form coarser precipitates therefore, the minimum amount in the present invention is set to 0.1% for fixing Sulphur. If the manganese addition is more than 0.7 %, it further increases the mechanical strength and causes higher rolling loads during cold reduction. Therefore, the maximum Manganese content is set as 0.7%. More preferably it should be 0.2 to 0.5 % maximum.
Silicon (0.1 – 1.0 wt %) – Silicon is a vital alloying element for electrical steel. It increases the specific resistivity of steel and decreases core loss. The minimum limit specified in the present invention is set to 0.1 %, below that the core loss reduction is not sufficient to achieve the desired watt losses. The upper limit of silicon in present invention is kept as 1.0% which sufficient to achieve the desired watt loss of ≤ 10.0 Watts/kg in as received condition. Additional Silicon over and above will result in added cost and magnetic flux density is adversely affected. More preferably the Silicon should be in the range 0.2 to 0.8%.
Aluminum (0.0005 – 0.5wt %) – Like silicon, Aluminum also increases the specific resistivity of steel, thereby reducing the core losses. The upper limit of Aluminum in present invention is kept as 0.5% which sufficient to achieve the desired watt loss of ≤ 10.0 Watts/kg in as received condition. However, if Aluminum exceeds 0.5 %, magnetic flux density is adversely affected. Therefore, the maximum limit is set to 0.5 %. More preferably, Al may be contained in amounts to 0.4% maximum.
Phosphorous (0.001 - 0.20 wt %) – Phosphorous increases the specific resistivity of the steel and improves favorable texture by preferential segregation to the grain boundaries. However, when it is above 0.20 %, the steel becomes brittle and cold rolling becomes difficult. Therefore, the maximum Phosphorous content is set to 0.20 %. More preferably it is 0.10 % or less, and even more preferably it is 0.08 % or less.
Sulphur (0.0005 - 0.02wt %) – S is a harmful element for electrical steel sheets. Sulphur forms fine precipitates of [M][S] form, where [M] is a metallic element present in steel. The most common sulphide forming elements are Fe, Mn, Cu, Ti and Ca, etc. These fine precipitates deteriorates the core loss. When Sulphur exceeds 0.02 %, the core loss deterioration effect becomes remarkable, therefore, the maximum limit is set to 0.02%. The minimum level is not particularly limited as specified here is 0.0005% because a lower amount of Sulphur than 0.0005% is extremely difficult to obtain in industrial processes.
Nitrogen (0.0005 - 0.008wt %) – Nitrogen is a harmful element for electrical steel sheets. It forms fine metal nitride precipitates with Ti, Al, Fe, etc. These fine precipitates restrict the grain growth by pinning the grains during annealing which adversely affects the core losses, therefore the maximum limit is set to 0.008%. The minimum level is not particularly limited as specified here is 0.0005% because a lower amount of Nitrogen than 0.0005% is extremely difficult to obtain in industrial processes.
Titanium (0.0 - 0.003 wt %) – Titanium is a harmful element for magnetic properties of electrical steel. Ti is a strong nitride and carbide forming element. The fine precipitates of titanium restrict the grain growth by pinning the grains during annealing which deteriorates the core loss, therefore the maximum limit is set to 0.003%. The minimum level is not particularly limited as is an undesirable impurity.
%[Mn]/[S] ≥ 25– Maintaining Manganese to Sulphur ration more than 25 results in fixing the free Sulphur to form coarse sulphide inclusion. This prevents formation of fine sulphide inclusion which can act as a grain growth pinning agent during recrystallization annealing.
[Nb] + [V] + [Ti] ≤ 0.0050%– Elements like Niobium, Vanadium and Titanium are strong carbide and nitride formers. These element if present in sufficient quantity will form carbides, nitrides or carbonitride precipitate which acts as a grain growth pinning agent during annealing. These precipitate if present in finer size distribution then it also pin the magnetic domain movement which results in higher core losses. Therefore combined content of Niobium, Vanadium and Titanium should be controlled less than 0.005%. More preferably less than 0.003%.
Hereinafter, the manufacturing method of the non-oriented electrical steel sheet of this invention is demonstrated in detail. Following abbreviations, terminologies and expressions are used to describe the manner of implementation of the present invention:
SRT – Slab Reheating Temperature
RMX – Roughing Mill Exit Temperature
FT – Finishing Rolling Exit Temperature
CT – Coiling Temperature
HR thk – Hot rolled coil thickness
Final thk – Final thickness after cold reduction
CAL – Continuous Annealing Line
W15/50- Watt loss in W/kg at 1.5T, 50Hz
B50- Magnetic flux density in T at 5000 A/m
The method of manufacturing cold rolled non-oriented motor lamination electrical steel sheets according to present invention is described with reference to accompanying Figure 1 as follows:
1. Steel making and Casting Process: First, the primary steel is made through Basic Oxygen Converter (BOF). The molten steel is decarburized in the converter, was taken out into the ladle, and the ladle was moved to the RH type vacuum degasser. Vacuum decarburization was performed with an RH vacuum degassing apparatus and then alloying additions were made (in RH) to achieve the required chemistry ranges of the steel bath as described in the scope of the invention. Subsequently, the steel melt is cast into slabs through a continuous casting machine.
2. Hot Rolling Process: The continuous casted slabs having the desired chemical composition of the present invention are then charged into the reheating furnace of the hot strip mill. Before hot rolling the slab having the above steel composition is heated in the temperature range of 1100 to 1250 °C. For a reheating temperature of more than 1250 °C, there is a possibility of dissolution of AlN, MnS, etc. precipitates and re-precipitation in finer size distribution during the hot rolling process which deteriorates the core loss. More preferably it is maintained at 1200 °C maximum. Below 1100 °C the hot rolling loads becomes high. The reheated slabs is then subjected to rough hot rolling to obtain a steel plate. Considering the achievement of low core loss and high magnetic flux density, the roughing mill exit temperature is kept as 1100 °C to 950 °C. Subjecting the steel plate to finishing rolling in form of hot rolled strip in tandem rolling stands with finish rolling exit temperature as 800 °C to 950 °C. The finish rolling temperature as a more preferable range is 850°C to 930°C. The finishing mill exit thickness i.e. hot coil thickness is maintained between 2.0 to 3.0 mm. In thickness less than 2.0 mm, controlling the shape or waviness of the strip becomes difficult and for thickness more than 3.0 mm the degree of cold rolling reduction increases which adversely affect the favorable texture development after final annealing which deteriorates the magnetic properties. The coiling temperature is 600°C to 700°C. Coiling temperature when exceed 700°C, results in excessive scale formation on hot-rolled coils and the pickling process becomes difficult. Coiling temperature lower than 600°C results in finer hot band grain size which is not desirable for achieving good core loss.
3. Cold Rolling Process: The hot-rolled steel strip coil obtained by the above hot rolling process is subjected to cold rolling after removing the scale formed on the steel sheet surface during hot rolling by pickling process. The hot rolled coil can be then optionally annealed to improve the magnetic properties further. When hot-rolled sheet optional annealing is performed on the hot-rolled steel sheet, it can be pickled either before or after hot-rolled sheet annealing. The hot-rolled coils which are optionally annealed after a pickling process are subjected to soaking at annealing temperature in the range of 650 °C to 900 °C for 10 to 180 seconds in case of continuous annealing and 6 to 16 hours in case of box annealing. The other conditions of hot band annealing process is not particularly limited. If the hot coil annealing temperature is too low, then complete recrystallization adequate grain growth is not obtained and improvement of magnetic properties is not sufficient, therefore it is defined as 650 °C minimum. A higher hot coil annealing temperature increases the resultant recrystallized grains size excessively, which reduces the yield strength of the material by coarsening the average grain diameters. Therefore, the maximum temperature of hot coil annealing is set as 900°C in the present invention. The adoption of hot coil annealing method as box annealing or continuous annealing both works well as both of the processes suffice for the improvement of magnetic properties. The hot-rolled coils after pickling or pickling and annealing are then subjected to cold rolling to achieve the final thickness. This cold rolling process to achieve the final thickness is done in one stage. The total cold rolling reduction to be controlled within 50 to 85% so that sufficient amount of shear bands are formed after final reduction which will promote favorable theta fiber and Goss texture components after final annealing. Thus improving the magnetic flux density and reduction of core losses. More than 85% cold reduction in final cold rolling process tends flatten the grains along the rolling direction instead of shear banding which promotes unfavorable gamma and alpha fiber components which deteriorates the magnetic flux density and increases the core loss. The final cold rolled thickness is in the range of 0.5 – 0.65 mm.
4. Final Annealing Process: The final cold rolled sheet is then subjected to final annealing and in continuous annealing Line (CAL). The soaking temperature of final annealing is kept between 650 – 900°C and holding time at annealing temperature is kept as 20 – 180 Seconds. If the soaking temperature is less than 650°C, then complete recrystallization do not occur therefore the core losses reduction is not sufficient. Whereas when soaking temperature exceeds 900°C, excessive grain growth take place and average grain size increases excessively and mechanical strength and hardness becomes low, this leads to shape related issues and excessive burr formation during lamination punching operation which is not desirable. The cold-rolled annealed sheet is further oiled on both surfaces with a suitable rust preventive oiling through an electrostatic oil spray machine to provide resistance to rust during transportation and further processing of making core laminations. The oiling content is controlled to 100 to 350 grams per square meter of surface area. Higher oiling quantity in lamination punching application is not desirable because when stress relief annealing treatment is required, the oil on the surface need to follow a separate oil burn off cycle incorporated within it. No skin passing elongation was done in the coils as any deformation after final annealing drastically deteriorates the magnetic properties. The steel sheet thus produced which is final annealed and oiled have required core loss and magnetic flus density as specified in the present invention.
Hereinafter, the present invention will be described specifically by way of examples.
Examples
A steel melt having a chemical composition as given in Table 1 is made through steel making process from converter and further vacuum refined in RH degasser. The steel melt thus produced having chemical composition as prescribed in the present invention were then casted into slabs through a continuous casting route. The slabs thus obtained were then charged in hot strip mill reheating furnace for hot rolling operation. The slabs were heated in furnace to a temperature between 1100 – 1250°C. The slabs after heating were discharged from the furnace for hot rolling followed by a high pressure water jet descaling, the slabs were then moved though roller table to the roughing mill. Roughing reductions were given in the slab such that after last roughing reduction pass exit temperature was maintained between 950 to 1100°C. The steel plate after roughing was then sent to the finishing mill for further reduction in thickness. The finishing mill exit temperature was controlled between 800 to 950°C and the target exit thickness was maintained as 2.0 to 3.0 mm. After finishing rolling the coils were coiled at coiling temperature between 600 to 700°C.

The hot rolled coils thus produced were pickled with concentrations of acid HCl from 2 to 18% to remove the surface scale. Here conditions of pickling operation such as speed, temperature and other parameters are not particularly limited and known conditions of pickling to obtain a pickled surface can be used. Some batches of hot rolled pickled coils were then subjected to hot band annealing treatment. The hot band annealing soaking temperature was kept in the range of 650 °C to 900 °C for 6 to 16 hours in of box annealing furnace. The other conditions of hot band annealing process is not particularly limited.

The hot rolled pickled coils and hot band annealed coils were then subjected to cold rolling. The cold rolling was done in one stage. The total cold rolling reduction from hot rolled to final cold rolled thickness was controlled between 50 to 85%. A cold rolling reduction higher than 85% lead to reduction in proportion of favorable theta and Goss texture and unfavorable gamma texture proportion increases. The cold rolled sheet thus obtained were then subjected to final recrystallization annealing and oiling process.
The final recrystallization annealing and coating is performed in production Continuous Annealing Line (CAL). The conditions of final annealing parameters are presented in table 2. The annealed sheet is oiled on both surfaces with a suitable rust preventive oiling through an electrostatic oil spray machine to provide resistance to rust during transportation and further processing of making core laminations. The oiling content is controlled to 100 to 350 grams per square meter of surface area.No skin passing elongation was done in the coils as any deformation after final annealing drastically deteriorates the magnetic properties. After this process a sample is drawn to evaluate the electromagnetic properties. These properties results are listed in table 2. The process flow of inventive steel example is shown in figure 1. In the given process flow bypassing the skin passing reduction is vital because any deformation after final annealing drastically deteriorates the magnetic properties.
Additionally, some samples were treated with stress relief annealing treatment by soaking at 750°C to 850°C for 2 to 3 hours under reducing atmosphere comprising of H2 and N2 mixture. The samples are then tested for evaluation of magnetic properties after stress relief annealing. These properties results are listed in table 3.

Table 1: Steel chemical composition (Wt%)
Steel No C Mn Si Al P S N Ti [Mn]/[S] [Nb]+[V]+[Ti] Remarks
1 0.0018 0.23 0.36 0.0014 0.052 0.0036 0.0012 0.0001 64.4 0.0019 Inventive example
2 0.0014 0.23 0.38 0.0030 0.055 0.0047 0.0013 0.0003 48.9 0.0009 Inventive example
3 0.0013 0.25 0.37 0.0013 0.062 0.0049 0.0019 0.0002 51.9 0.0016 Inventive example
4 0.0027 0.23 0.58 0.210 0.068 0.0070 0.0026 0.0002 32.9 0.0011 Inventive example
5 0.0024 0.27 0.61 0.219 0.073 0.0061 0.0016 0.0011 44.3 0.0024 Inventive example
6 0.0028 0.28 0.53 0.201 0.082 0.0072 0.0010 0.0004 38.9 0.0015 Inventive example
7 0.0021 0.25 0.48 0.002 0.066 0.0041 0.0010 0.0003 61.0 0.0007 Comparative example
8 0.032 0.18 0.30 0.004 0.017 0.014 0.0028 0.0003 13.0 0.0008 Comparative example
Balance Fe and other unavoidable impurities

Table 2: Electromagnetic properties as annealed condition
Steel No HR Thk (mm) Hot Band Annealing(°C) % Cold Reduction Final Thk (mm) Final Annealing temperature (°C) % SPM Elongation W15/50 (W/kg) B50 (T) Remarks
1 2.8 --- 82.1 0.50 784 0 6.65 1.72 Inventive example
2 2.8 --- 82.1 0.50 793 0 6.11 1.73 Inventive example
3 2.8 --- 82.1 0.50 789 0 6.50 1.73 Inventive example
4 2.8 --- 82.1 0.50 788 0 5.82 1.73 Inventive example
5 2.8 710 76.8 0.65 800 0 6.63 1.76 Inventive example
6 2.8 710 76.8 0.65 803 0 6.47 1.76 Inventive example
7 2.8 --- 76.8 0.65 710 4.0 10.60 1.70 Comparative example
8 2.8 --- 82.1 0.50 802 1.6 12.08 1.72 Comparative example

Table 3: Electromagnetic properties after stress relief annealing treatment
Steel No Final Thk (mm) Stress Relief Annealing temperature (°C) W15/50 (W/kg) B50 (T) Remarks
1 0.50 790 5.77 1.71 Inventive example
2 0.50 790 5.64 1.71 Inventive example
3 0.50 790 5.44 1.72 Inventive example

The watt loss W15/50 at 1.5T, 50Hz and magnetic flux density B50 in as received condition for inventive steel example numbers 1 to 6 are within the prescribed range for both 0.50 mm and 0.65 mm thickness grade. Whereas steel samples other than invention examples where at least one of the elementsof the present invention scope does not comply and does not meet at least one of the end product quality attributes. For example steel number 7 complies with the prescribed chemical composition but processed with 4.0% Skin pass elongation after final annealing resulted in higher watt loss, which is more than 10.0 W/kg at 1.5T, 50 Hz. In another comparative example steel number 8 does not complies with prescribed chemical composition, carbon is high and processed with 1.6% skin pass elongation after final annealing which was specified to bypass as per present inventive process flow recommendation, resulted higher watt loss of 12.08 W/kg at 1.5T, 50 Hz in as received condition.

Inventive steel number 1 to 3 was further treated at 790°C for 2 to 3 hours under reducing atmosphere comprising of H2 and N2 mixture. The Watt loss after stress relief annealing is achieved as ≤ 6.6 Watts/kg at 50Hz and 1.5T, and magnetic flux density at 5000 A/m, B50 is in the prescribed range of 1.68 to 1.77 T. Therefore the cold-rolled non-oriented motor lamination steel sheet thus produced are suitable for use as core laminations of motors and generators is cost effective and its magnetic properties are also comparable to traditional fully processed and coated electrical steel sheet as well as semi processed steel sheet.
, Claims:We Claim:

1. Cold rolled non oriented motor lamination steel sheet comprising of steel composition having alloying elements in weight%, C: 0.0005-0.01%; Mn: 0.10-0.70%; Si: 0.1-1.0%; Al: 0.0005-0.5%; P: 0.001-0.20%; S: 0.0005-0.02%; N: 0.0005- 0.008%; Ti: 0.0-0.003%; and the balance are Fe and other unavoidable impurities and satisfies the following relation: weight % [Mn]/[S] ≥ 25, and [Nb] + [V] + [Ti] ≤ 0.0050% as non oriented electrical steel having magnetic properties.
2. The cold rolled non oriented motor lamination steel sheet as claimed in claim 1 comprising of core lamination of motors and generators.
3. The cold rolled non oriented motor lamination steel sheet as claimed in claim 1 wherein the said cold-rolled non-oriented motor lamination steel sheet having thickness in the range of 0.50–0.65 mm having free of any required decarburization annealing to develop desired magnetic properties of Watt loss at 50Hz and 1.5T, W15/50 ≤ 10.0 Watts/kg in as received condition and Watt loss at 50Hz and 1.5T, W15/50 is ≤ 6.6 Watts/kg after stress relief annealing at 750°C to 850°C for 2 to 3 hours under reducing atmosphere comprising of H2 and N2 mixture.
4. The cold rolled non oriented motor lamination steel sheet as claimed in anyone of claims 1 or 2 having magnetic flux density at 5000 A/m, B50 is in the range of 1.68 to 1.77 T.
5. A process for the manufacture of Cold rolled non oriented motor lamination steel sheet as claimed in anyone of claims 1 to 4 comprising :
i) providing select alloying elements in weight%, C: 0.0005-0.01%; Mn: 0.10-0.70%; Si: 0.1-1.0%; Al: 0.0005-0.5%; P: 0.001-0.20%; S: 0.0005-0.02%; N: 0.0005- 0.008%; Ti: 0.0-0.003%; and the balance are Fe and other unavoidable impurities and satisfies the following relation: weight % [Mn]/[S] ≥ 25, and [Nb] + [V] + [Ti] ≤ 0.0050% and subjecting to steel making route to continuous casting of steel into slabs;
ii) subjecting the hot slab to reheated to a temperature in the range of 1100 to 1250 °C and thereafter to rough rolling, maintaining the temperature at the end of rough rolling the slab to a temperature in the range 1100 to 950 °C;
iii) subjecting the thus rough rolled steel to a finish rolling to achieve a final temperature of 800 to 950 °C and produce hot coil thus obtained in thickness of 2.0 to 3.0 mm was coiled at a temperature range of 600 to 700 °C and finally cooled to room temperature to thereby provide as cold rolled non-oriented motor lamination steel sheet having magnetic properties free of any required decarburization annealing for generating its magnetic properties.

6. The process as claimed in claim 5 wherein the hot rolled coil thus obtained was pickled with 2 to 18% hydrochloric acid to remove the scales, said pickled hot coil can optionally subjected to annealing by soaking at a temperature in the range of 650 °C to 900 °C for 20 to 180 seconds in the case of continuous annealing or 6 to 16 hours in the case of box annealing.
7. The process as claimed in anyone of claims 5 or 6 comprising cold rolling step wherein the cold rolling reduction is controlled within 50 to 85% to obtain final sheet thickness of 0.50 – 0.65 mm.
8. The process as claimed in anyone of claims 5 to 7 comprising step of subjecting to soaking at final annealing temperature of 650 °C to 900 °C for 20 to 180 seconds in the case of continuous annealing or 6 to 16 hours in the case of box annealing to thereby produce the annealed coils of said cold-rolled non-oriented motor lamination steel sheet of the thickness in the range 0.50 to 0.65 mm.
9. The process as claimed in anyone of claims 5 to 8 comprising oiling with a suitable rust preventive oil through an electrostatic oil spraying machine to provide resistance to rust during transportation and further processing of making core laminations and wherein the oiling content is controlled to 100 to 350 grams per square meter of surface area.
10. The process as claimed in anyone of claims 5 to 9 comprising subjecting additionally to step of annealing for stress relief of punching operation at 750°C to 850°C for 2 to 3 hours under reducing atmosphere comprising of H2 and N2 mixture such as to attain the Watt loss after stress relief annealing at 50Hz and 1.5T, W15/50 is ≤ 6.6 Watts/kg and magnetic flux density at 5000 A/m, B50 is in the range of 1.68 to 1.77 T.

Dated this the 11th day of March, 2025
Anjan Sen
Of Anjan Sen & Associates
(Applicants’ Agent)
IN/PA-199