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 :
A TIN-PLATED STEEL SHEET FOR AEROSOL CAN BOTTOM COVERS HAVING HIGH-PRESSURE STRENGTH AND METHOD OF PRODUCING SAME.



2 APPLICANT (S)

Name : JSW STEEL COATED PRODUCTS 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 a tin-plated steel sheet for an aerosol CAN ends/bottom cover and a method for producing the same, and particularly to a steel sheet for an aerosol can bottom having a high-pressure strength and a method for producing the same.

BACKGROUND OF THE INVENTION
The aerosol CANs are filled with propellant for ejecting the contents. The contents inside the CAN are in a high-pressure state with pressure ranging from 12 to 18 bars. Therefore, tin-plated material of thickness in the range of 0.30mm to 0.39mm with yield strength in the range of 550-610 Mpa is most suitable for making the bottom covers of aerosol cans to resist high-pressure inside the cans without failure. However, there are certain difficulties associated with the production of high-strength tin plates of thickness more than 0.30mm. Conventionally to produce high strength Tin plated material of YS more than 500 Mpa, double reduction method is used where annealed material is subjected to a secondary reduction of more than 33% to strengthen the material by strain hardening mechanism. But in this case the thickness of the required material is more than 0.30mm and the annealed material will require to have a thickness of more than 0.50 mm to achieve the required 33% reduction during secondary rolling. Designed for producing thinner gauge materials, the Double cold reduction mills have the capability of feeding material with a maximum input thickness of 0.50mm restricting the use of annealed material of less than 0.50mm.

US9315877B2 reveals a method of for the production of steel sheets for bottom covers of aerosol cans where the thickness of the sheet is between 0.27 to 0.34mm which includes, as chemical composition, C: 0.025 to 0.065 mass %, Mn: 0.10 to 0.28 mass %, P: 0.005 to 0.03 mass %, Al: 0.01 to 0.04 mass %, N: 0.0075 to 0.013 mass %, Si: limited to 0.05 mass % or less, S: limited to 0.009 mass % or less, and the balance consisting of Fe and unavoidable impurities, wherein yield point YP in rolling direction after aging treatment is in range of 460 to 540 Mpa. This process involves a further process of aging treatment leading to a high cost of production. Also due to aging treatment, the material has a yield point elongation which may lead to defects like Stretcher strains.
US9506131B2 disclosed a steel sheet containing C: 0.02% or more and 0.10% or less, Si: 0.01% or more and 0.5% or less, P: 0.001% or more and 0.100% or less, S: 0.001% or more and 0.020% or less, N: 0.007% or more and 0.025% or less, Al: 0.01% or more and {-4.2×N (%)+0.11}% or less, Mnf: 0.10% or more and less than 0.30% where Mnf is defined by equation Mnf=Mn-1.71×S, and the balance being Fe and inevitable impurities, in which the steel sheet has a thickness of 0.35 (mm) or less, the product of the lower yield point (N/mm2) of the steel sheet (mm) is 160 (N/mm). The method uses higher nitrogen (>0.0070%) percentage in order to carry out natural strain aging of the material for 10 days after giving a pre-strain of 10%. Natural aging of 10 days increases the time of production significantly.
The prior arts mentioned above need a further aging process to increase the strength of the material. This adds to the cost and time of production. Further due to aging treatment the material has yield point elongation which can lead to issues like stretcher strain. Also to facilitate aging the chemistry of raw material requires the presence of Nitrogen in excess of 70ppm. This is detrimental to steel quality and can lead to issues like pin holes.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed toward the generation of tin-plated steel sheets for the bottom covers of aerosol cans.

A still further object of the present invention is directed to provide tin-plated steel sheets with good formability.

A still further object of the present invention is to provide the tin-plated steel sheet material with pressure resistance to withstand the high-pressure condition inside the aerosol cans.

A still further object of the present invention is to produce aerosol cans from said tin-plated steel sheets without yield point elongation, and which will not be affected by further natural aging.

A still further object of the present invention is directed to the production of tin-plated steel sheet material with required properties through double reduction to eliminate the additional process involved after tin-plating as mentioned in the prior arts.

SUMMARY OF THE INVENTION

The present invention provides a tin-plated steel sheet adapted for aerosol can bottom covers having high-pressure strength comprises the base steel sheet composition in terms of weight %: C: 0.03 - 0.06 %; Mn: 0.2 - 0.4%; Si: 0.005 – 0.03%; P: 0.005 - 0.02%; Al: 0.02 - 0.06%; S: 0.005 - 0.01 %; N: 0.0001 - 0.005 %; the balance being Fe and other unavoidable impurities.

In one aspect of the present invention, the tin-plated steel sheet is having thickness in the range of 0.30 - 0.39mm, yield strength in the range of 550 - 610 MPa, tensile strength in the range of 560 - 620 MPa, total elongation in the range of 2.5 - 5% and hardness HR30Tm in the range of 73 - 76.

In another aspect of the present invention, the tin-plated steel sheet in the form of aerosol can bottom is capable to withstand pressure as per the 2021-FEA standards for aerosol containers.

In another aspect of the present invention, thetin-plated steel sheet is free of yield point elongation and stretcher strains during forming of can bottom covers.

Further, the present invention provides a method of manufacturing tin-plated steel sheet adapted for aerosol can bottom covers having high-pressure strength comprises following steps.

Step 1: Converter Smelting: Obtaining molten steel from basic oxygen furnace (BOF) and RH degasser comprises following chemical composition in terms of weight %: C: 0.03 - 0.06 %; Mn: 0.2 - 0.4%; Si: 0.005 – 0.03%; P: 0.005 - 0.02%; Al: 0.02 - 0.06%; S: 0.005 - 0.01 %; N: 0.0001 - 0.005 %; the balance being Fe and other unavoidable impurities.

Step 2: Slab Continuous Casting: Refining and continuous casting the molten steel to obtain a solid slab.

Step 3: Hot Rolling: The solid slab is reheated to a temperature of 1150 - 1250 °C. The reheated slab is subjected to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 - 1080°C. The rough rolled steel is subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C - Ac3+100 °C. The finished rolled steel is cooled at an average run-out table cooling rate in the range of 10 to 30 °C/second to obtain a hot-rolled coil.

Step 4: Acid Pickling: Pickling the hot-rolled coil in a continuous line with concentrations of acid HCl to remove the surface scale to form a hot-rolled pickled coil.

Step 5: Cold Rolling Reduction: Cold rolling the hot-rolled pickled coil or the hot-rolled coil to form a cold-rolled coil. The cold reduction of thehot-rolled pickled coil in the range of 75 - 80%.

Step 6: Continuous Annealing: Continuously annealing the cold-rolled coil to obtain an annealed steel. The annealing soaking temperature is 700-720 ?. The annealing soaking time is 40 - 200s. The cold-rolled steel is over-aged at the temperature from 420- 430 ?. The skin pass elongation of the annealed steel to an annealed steel coil.

Step 7: Secondary Rolling Reduction: The annealed steel coil is subjected to secondary rolling reduction, wherein the rolling reduction is 20-24% to obtain secondary rolled steel coil.

Step 8: Tinning: Electro tinning on the secondary rolled steel coil to obtain the tin-plated steel sheet having a hardness grade of TH580. The reflow temperature is controlled to 230 to 265 ?.

To facilitate the production of high strength Tin plated steel sheet of thickness range of 0.30mm to 0.39mm through a double cold reduction route, the material was annealed at a temperature of 700-720 Deg Celsius in a continuous annealing line to get fine-grained microstructure. The microstructure thus obtained had grains with ASTM grain number 10 which are 20% smaller than the grains of annealed material generally used for Double reduced material, with microstructure of base steel having 98-99% ferrite phase and 1-2% pearlite phase and grains are oriented in the rolling direction as well as has an excellent anisotropic property of ?R values ranging from 0.8-1. As a result, the annealed material produced was of higher strength as compared to annealed material generally used for double reduced material. The final properties could be achieved with 22-24% reduction during secondary rolling instead of 33% due to the high strength of the input material. Hence the thickness of the annealed material could be controlled within 0.50mm which is within the process capability of a double cold reduction mill.

A further aspect of the present invention is directed to Aerosol can having can bottom obtained of having high-pressure strength base steel sheet composition in terms of weight %:
C: 0.03 - 0.06 %;
Mn: 0.2 - 0.4%;
Si: 0.005 – 0.03%;
P: 0.005 - 0.02%;
Al: 0.02 - 0.06%;
S: 0.005 - 0.01 %;
N: 0.0001 - 0.005 %;
the balance being Fe and other unavoidable impurities, and wherein the tin-plated steel sheet is having thickness in the range of 0.30 - 0.39mm, yield strength in the range of 550 - 610 MPa, tensile strength in the range of 560 - 620 MPa, total elongation in the range of 2.5 - 5% and hardness HR30Tm in the range of 73 - 76.

A still further aspect of the present invention is directed to said aerosol can wherein the can bottom covers can withstand pressure as per the 2021-FEA standards for aerosol containers.

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

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING

Figure 1: the micrograph showing microstructure of base steel having 98-99% ferrite phase and 1-2% pearlite phase with grain oriented in rolling direction.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWING AND EXAMPLES

The present invention provides a tin-plated steel sheet for aerosol can bottom covers having high-pressure strength comprises the base steel sheet with following chemical composition in terms of weight %: C: 0.03 - 0.06 %; Mn: 0.2 - 0.4%; Si: 0.005 – 0.03%; P: 0.005 - 0.02%; Al: 0.02 - 0.06%; S: 0.005 - 0.01 %; N: 0.0001 - 0.005 %; the balance being Fe and other unavoidable impurities. The tin-plated steel has good formability, ageing resistance and surface tin coating, its chemical compositions and method of manufacturing are described here under with explanation on metallurgical factors deciding the range of constituents in a composition.

The tin-plated steel sheet is having thickness in the range of 0.30 - 0.39mm, yield strength in the range of 550 - 610 MPa, tensile strength in the range of 560 - 620 MPa, total elongation in the range of 2.5 - 5% and hardness HR30Tm in the range of 73 - 76. The tin-plated steel sheet is used to make the can bottom to withstand pressure as per the 2021-FEA standards for aerosol containers. The tin-plated steel sheet is devoid of yield point elongation and no stretcher strains are avoided during forming of can bottom covers.

Hereinafter, the steel composition is described hereunder with an explanation on metallurgical factors governing the ranges of the constituents in a composition according to a preferred embodiment wherein all the elements are in weight % are demonstrated.

Carbon (0.030-0.060 wt.%) - While carbon increases the steel strength, it reduces the cold workability and the deep drawability of the cold-rolled steel sheet remarkably and thus the higher limit of the cold-rolled sheet is set at 0.1 wt.%. For improving the R-value i.e. drawabilty it is desirable to reduce the C level less than 0.06 wt.%. Lowering the carbon content below 0.02 wt.% results in poor ageing properties since below 0.02 wt.% steel is the complete a-ferrite region in the iron-cementite phase diagram resulting in no cementite formation. Consequently, more free carbon will be available in the steel matrix which deteriorates the ageing property. Cementite formed in grain boundaries its precipitate size should be greater than 1µm which helps in reducing solute carbon and suppress the YPE for better ageing resistance. To avoid YPE and to have yield strength within the desired limit, the level of Carbon is between 0.02-0.06 wt. percent.
Mn (0.2-0.4) wt. % - The Mn ranges from 0.3 to 0.5 % is most desirable given that S remains in the favorable range of 0.008wt% or less. Keeping the Mn level 0.1wt% with higher Sulphur content may result in surface irregularities such as red shortness, edge crack sliver, etc. The lower limit of Mn is kept at 0.3% to ensure the surface properties deteriorate and embrittlement may occur due to hot brittleness as the amount of Mn is insufficient to fix S. More than 0.5 %Mn makes the steel hard and the deep draw ability lower.
Al (0.02-0.06) wt. % – Al wt% ranges from 0.02-0.06 and is intended for fixing free N which results in aging if left unfixed. In addition, less than 0.02 % Al will delay the AlN precipitation causing the insufficient growth of ferrite grains and deteriorating the {111} texture. An optimized volume fraction of AlN in steel matrix in combination with NbC precipitate results in excellent drawability and reduced ?r value as described in the present invention. The same is achieved by optimizing hot rolling and cold rolling parameters to avoid Ostwald ripening phenomenon which results in coarse precipitate size along with low r-bar values.
Nitrogen (0.005wt% or less) -The upper limit for N is 0.005%; it is advisable to keep it to a minimum level. Higher N content requires a higher Al addition to fix extra N and increase the volume of AlN precipitates which strengthens the material, ultimately deteriorating the drawing property.
P (0.005-0.02) wt. %: -. P is an element that improves the strength at a low cost, and the amount of addition thereof varies depending on a target strength level. When the added amount exceeds more than 0.02 wt.% the yield strength level increases significantly. In addition, a higher amount of P promotes the formation of surface defects and significantly reduces the corrosion resistance of the base metal. So, the maximum limit of P is kept at 0.02 %.
Si (0.005-0.03) wt.%: Itis an element utilized for increasing the strength of steel. As the silicon content increases the ductility noticeably deteriorates. Since silicon deteriorates tin coating properties by forming SiO2 type of oxides (scale) on the surface. It is advantageous to add as low amount of silicon to the steel as is possible, the added amount of silicon is preferably 0.03 wt.% or less.

Following abbreviations, terminologies and expressions are used to describe the manner of implementation of the present invention:
SRT -Slab Reheating Temperature
FT-Finishing Temperature
CT- Coiling Temperature
Ac1 & Ac3 – Critical temperatures in iron-carbide diagram
El – Elongation (%)
UTS - Ultimate Tensile Strength (MPa)
YS - Yield Strength (MPa)
SPM - Skin Pass Elongation (%)

Hereinafter, the manufacturing method of the non-oriented electrical steel sheet of this invention is demonstrated in detail.

A method of manufacturing tin-plated steel sheet for aerosol can bottom covers having high-pressure strength comprises following steps.

Step 1: Converter Smelting: Obtaining molten steel from basic oxygen furnace (BOF) and RH degasser comprises following chemical composition in terms of weight %: C: 0.03 - 0.06 %; Mn: 0.2 - 0.4%; Si: 0.005 – 0.03%; P: 0.005 - 0.02%; Al: 0.02 - 0.06%; S: 0.005 - 0.01 %; N: 0.0001 - 0.005 %; the balance being Fe and other unavoidable impurities.

Step 2: Slab Continuous Casting: Refining and continuous casting the molten steel to obtain a solid slab.

Step 3: Hot Rolling: The solid slab is reheated to a temperature of 1150 - 1250 °C. The reheated slab is subjected to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 - 1080°C. The rough rolled steel is subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C - Ac3+100 °C. The finished rolled steel is cooled at an average run-out table cooling rate in the range of 10 to 30 °C/second to obtain a hot-rolled coil.

Step 4: Acid Pickling: Pickling the hot-rolled coil in a continuous line with concentrations of acid HCl to remove the surface scale to form a hot-rolled pickled coil.

Step 5: Cold Rolling Reduction: Cold rolling the hot-rolled pickled coil or the hot-rolled coil to form a cold-rolled coil. The cold reduction of the hot-rolled pickled coil in the range of 75 - 80%.

Step 6: Continuous Annealing: Continuously annealing the cold-rolled coil to obtain an annealed steel. The annealing soaking temperature is 700-720 ?. The annealing soaking time is 40 - 200s. The cold-rolled steel is over-aged at the temperature from 420- 430 ?. The skin pass elongation of the annealed steel to an annealed steel coil. By annealing the material in lower temperatures of 700-720 ?, the annealed steel coil has finer grains of ASTM grain number 10 as compared to the annealed material is generally used for double reduce material.

Step 7: Secondary Rolling Reduction: The annealed steel coil is subjected to secondary rolling reduction, wherein the rolling reduction is 20-24% to obtain secondary rolled steel coil.

Step 8: Tinning: Electro tinning on the secondary rolled steel coil to obtain the tin-plated steel sheet having a hardness grade of TH580. The reflow temperature is controlled to 230 to 265 ?.

The microstructure of base steel has 98-99% ferrite phase and 1-2% pearlite phase as shown in Figure 1. The grains are oriented in the rolling direction as well as has an excellent anisotropic property of ?R values ranging from 0.8-1 due to lower secondary reduction percentage of 22-24% considering high strength double reduced material. These microstructural properties ensure minimum earing formation in formed bottom covers which in turn leads to significant decrease in loss due to trimming of ears.

Hereinafter, the present invention will be described specifically by way of examples.

Examples

Complete description of steel according to the present advancement and comparative steel grades are illustrated in following table 1 to table 4 and the weight percent range of constituents and the selective process parameters according to the invention are validated through following examples 1 & 2:

Table 1: Elemental Compositions in weight % of the inventive steel sheets along with comparative examples.

Table 2: Hot rolling and cold rolling of inventive with comparative steel sheets having chemical compositions as per Table 1.

Table 3: Tin Coating Parameters of inventive with comparative steel sheets having chemical compositions as per Table 1.
Table 4: Mechanical properties of comparative steels having chemical composition as per table 1 and being processed as per Table 2 and Table 3
Table 1
Sample No C Mn S P Si Al N
1 0.040 0.35 0.003 0.01 0.03 0.04 0.005
2 0.030 0.25 0.003 0.01 0.02 0.03 0.004
3 0.050 0.30 0.01 0.015 0.03 0.03 0.004
4 0.015 0.45 0.01 0.02 0.02 0.04 0.003
5 0.45 0.35 0.007 0.017 0.014 0.057 0.0025
6 0.055 0.029 0.006 0.018 0.013 0.060 0.0035

Table 2

Hot Rolling Parameters Cold Rolling Parameters
Sample No SRT°C Roughing Mill temp°C FT°C CT°C Cold Reduction %


1 1200 1065 885 650 77
2 1230 1070 890 660 77
3 1220 1070 908 680 77
4 1210 1080 910 684 77
5 1210 1060 890 665 77
6 1215 1055 895 651 77

* SRT- Slab reheating temperature, FT- hot finish rolling temperature, ROT- Run out table at hot coil mill, CR%- Cold rolling reduction %, SS- soaking section, OAS-Over-Ageing Section, SPM- Skin pass elongation
Table 3
CAL and Tin Coating Parameters
Sample No SS TEMP SS Residence Time OAS TEMP Secondary reduction % at DCR Tin induction Reflow Temperature
1 760 95 430 22 250
2 740 95 430 22 250
3 720 95 430 22 250
4 720 90 430 24 250
5 720 90 430 24 250
6 700 90 430 24 250

Table 4

Sample No Mechanical Properties Pressure Resistance (15 Bar pressure test) Remarks
YS TS Elongation % Yield Point Elongation Hardness (HR 30T)
1 480 485 6 0 68 Leakage at 12 bars C
2 520 530 5 0 70 No leakage C
3 560 565 4.5 0 73 No leakage I
4 510 520 4.5 0 72 No leakage C
5 580 585 3.5 0 74 No leakage I
6 605 615 2.5 0 76 No leakage I

*I - Present inventive example, C- Comparative Examples, G- Good, NG- Not Good
The mechanical property YS, TS, El, and Yield point elongation was done as per IS-1993-2018
The pressure test is done as per 2021-FEA standards for aerosol containers.

It can be appreciated from Table 1 to Table 4 that steel sheets remarked as “I” are satisfying all the scopes of present invention. These steels exhibit improved Yield strength of 550-610 MPa, Tensile strength of 560-620 MPa, total elongation in the range of 2.5% to 5%, hardness level (HR30T) in the range of 73 to 76 and excellent pressure resistance. Whereas, Steel remarked as ‘C’ doesn’t comply with at least one of the scope of the present invention and does not conform with minimum one or more of the end product attributes as mentioned in the scope of the present invention. For example, steel no. 4 has a low carbon concentration less than 0.02. This lead to low yield strength. Similarly, sample 1 and 2 are having YS less than 550 MPa and hardness is less than 73 HR30T which is out of scope of present invention and sample 1 failed in pressure test at customer end after CAN formation.

It is thus possible to produce tin plated steel of Yield strength of 550-610 MPa, Tensile strength of 560-620 MPa, total elongation of 2.5% or more, hardness level (HR30T) in the range of 73 to 76, Excellent pressure resistance invention using steel grade with composition by weight %: C: 0.06-0.06 %; Mn: 0.2- 0.4%; Si: 0–0.03%; P: 0-0.02%; Al: 0.02-0.06%; S: 0.01 % or less; N: 0.005 % or less; and the balance being Fe and other unavoidable impurities, and annealing it in a temperature range of 700 to 720 °C in continuous annealing line followed by subjecting it to a secondary reduction of 22-24%.
, Claims:We Claim:
1. A tin-plated steel sheet adapted for aerosol can bottom covers having high-pressure strength comprising of base steel sheet composition in terms of weight %:
C: 0.03 - 0.06 %;
Mn: 0.2 - 0.4%;
Si: 0.005 – 0.03%;
P: 0.005 - 0.02%;
Al: 0.02 - 0.06%;
S: 0.005 - 0.01 %;
N: 0.0001 - 0.005 %;
the balance being Fe and other unavoidable impurities, and wherein the tin-plated steel sheet is having thickness in the range of 0.30 - 0.39mm, yield strength in the range of 550 - 610 MPa, tensile strength in the range of 560 - 620 MPa, total elongation in the range of 2.5 - 5% and hardness HR30Tm in the range of 73 - 76.

2. The tin-plated steel sheet as claimed in claim 1,in the form of aerosol can bottom which can withstand pressure as per the 2021-FEA standards for aerosol containers.

3. The tin-plated steel sheet as claimed in claim 1,which is free of yield point elongation and stretcher strains during forming of can bottom covers.

4. A method of manufacturing tin-plated steel sheet adapted for aerosol can bottom covers having high-pressure strength comprises following steps:

converter smelting: obtaining molten steel from basic oxygen furnace (BOF) and RH degasser comprises following chemical composition in terms of weight %:
C: 0.03 - 0.06 %;
Mn: 0.2 - 0.4%;
Si: 0.005 – 0.03%;
P: 0.005 - 0.02%;
Al: 0.02 - 0.06%;
S: 0.005 - 0.01 % ;
N: 0.0001 - 0.005 %;
the balance being Fe and other unavoidable impurities;

slab continuous casting: refining and continuous casting the molten steel to obtain solid slab;

hot rolling: the solid slab is reheated to a temperature of 1150 - 1250 °C, the reheated slab is subjected to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 - 1080°C, the rough rolled steel is subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C - Ac3+100 °C, the finish rolled steel is cooled at an average run-out table cooling rate in the range of 10 to 30 °C/second to obtain a hot-rolled coil;

acid pickling: pickling the hot-rolled coil in a continuous line with concentrations of acid HCl to remove the surface scale to form a hot-rolled pickled coil;

cold rolling reduction: cold rolling the hot-rolled pickled coil or the hot-rolled coil to form a cold-rolled coil, wherein the cold reduction of hot-rolled pickled coil in the range of 75 - 80%;

continuous annealing: continuously annealing the cold-rolled coil to obtain an annealed steel, wherein during the continuous annealing, the annealing soaking temperature is 700-720 ?, the annealing soaking time is 40 - 200s, cold-rolled steel is over-aged at the temperature from 420- 430 ?, skin pass elongation of the annealed steel to an annealed steel coil;

secondary rolling reduction: the annealed steel coil is subjected to secondary rolling reduction, wherein the rolling reduction is 20-24% to obtain secondary rolled steel coil; and

tinning: electro tinning on the secondary rolled steel coil to obtain the tin-plated steel sheet having a hardness grade of TH580, wherein the reflow temperature is controlled to 230 to 265 ?.

5. The method of manufacturing tin-plated steel sheet adapted for aerosol can bottom covers having high-pressure strength as claimed in claim 4, wherein the step of double cold reduction rolling is carried out under controlled conditions of higher front, back tension and use of emulsion wherein oil concentration ranges from 3-4%. such as to provide tin-plated steel sheet having thickness in the range of 0.30 - 0.39mm, yield strength in the range of 550 - 610 MPa, tensile strength in the range of 560 - 620 MPa, total elongation in the range of 2.5 - 5% and hardness HR30Tm in the range of 73 – 76, with microstructure of base steel having 98-99% ferrite phase and 1-2% pearlite phase and grains are oriented in the rolling direction as well as has an excellent anisotropic property of ?R values ranging from 0.8-1.

6. The method of manufacturing tin-plated steel sheet adapted for aerosol can bottom covers having high-pressure strength as claimed in claim 4, wherein the tin-plated steel sheet is used to make the can bottom to withstand pressure as per the 2021-FEA standards for aerosol containers.

7. The method of manufacturing tin-plated steel sheet adapted for aerosol can bottom covers having high-pressure strength as claimed in claim 4, wherein the tin-plated steel sheet is free of yield point elongation and stretcher strains during forming of can bottom covers.

8.Aerosol can having can bottom obtained of having high-pressure strength base steel sheet composition in terms of weight %:
C: 0.03 - 0.06 %;
Mn: 0.2 - 0.4%;
Si: 0.005 – 0.03%;
P: 0.005 - 0.02%;
Al: 0.02 - 0.06%;
S: 0.005 - 0.01 %;
N: 0.0001 - 0.005 %;
the balance being Fe and other unavoidable impurities, and wherein the tin-plated steel sheet is having thickness in the range of 0.30 - 0.39mm, yield strength in the range of 550 - 610 MPa, tensile strength in the range of 560 - 620 MPa, total elongation in the range of 2.5 - 5% and hardness HR30Tm in the range of 73 - 76.

9.The aerosol can as claimed in claim 8 wherein the can bottom can withstand pressure as per the 2021-FEA standards for aerosol containers.

Dated this the 9th day of June, 2022
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199