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 :
SINGLE REDUCED COLD ROLLED STEEL SHEET FOR TINPLATE OF HIGHER THICKNESS WITH EXCELLENT AGING RESISTANCE AND FORMABILITY AND PRODUCTION METHOD THEREOF.


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 cold rolled steel sheet for tinplate with higher thickness 0.55-0.6mm in single reduced category with good formability along with ageing resistance with end applications in electronic media many parts and frames,with composition in terms of weight % comprising: C: 0.015-0.05 %; Mn: 0.15- 0.3%; Si: 0–0.02%; P: 0-0.015%; Al: 0.02-0.06%; S: 0.01 % or less; N: 0.005 % or less;V: 0.002-0.025 % and B: 0.001-0.002 %;and the balance being Fe and other unavoidable impurities; wherein B/N ratio range from 0.2to 2for ageing resistance after tin coating.
The advancement favors generation of cold rolled high strength steel sheet for tinplate wherein the said steel sheet has yield strength of 250-340 MPa, ageing resistance of 6 months and more, Tensile strength of 310-380 MPa, total elongation of 32% or more and hardness level (HR30T) in the range of 54 to 61.

BACKGROUND OF THE INVENTION
Tinplated sheet through continuous annealing route after Tin coating, stretch marks and waviness is a major limitation which restricts the application of tin coated steel sheet in drawing applications due to aging nature of steel sheet after temper rolling. And producing higher thickness 0.55-0.6mm is challenging considering tension setting in continuous annealing line as well as achieving intended mechanical properties and there after maintaining shape for next processes which further results with associated surface defects like scratches, flow marks and others.
Through improving the ageing resistancebetter formability can be achieved. To facilitate, ferriteMaterials has been utilized where interstitial elements like C, N and S are fixed using V and or Ca and B in ferrite matrix that results in excellent ageing resistance and uniform tin coating.
Aging phenomenon is known to be reappearance of yield point in which strength of metal increases and ductility decreases and a low value of strain rate sensitivity on heating at a relatively low temperature after cold-working. This is due to the diffusion of C and N atoms to the dislocations during the aging to form new solute atmospheres anchoring the dislocations. Nitrogen plays a more important role in the strain-aging of iron than carbon because it has a higher solubility and diffusion coefficient and produces less complete precipitation during slow cooling.

It is thus important to eliminate aging in drawing steels specially produced through continuous annealing route because the reappearance of yield point can lead to difficulties with surface markings or stretch marks due to localized heterogeneous deformation.
In the present work, Line tension setting were optimized to process higher thickness 0.55-0.6mm sheet without formation of wrinkles, also annealing temperature and Single cold reduction mill elongation for stand 1 or stand 2 optimized in order to meet mechanical properties requirements for final application with higher thickness requirements 0.55 to 0.6 mm.

KR20080038142A
Method of producing Soft black plates having thickness range 0.17-0.55mm with hardness HR30T of 51±3 for tinning comprise (wt.%) up to 0.005 C, 0.20-0.30 Mn, 0.03-0.06 Al, up to 0.03 Si, 0.03-0.06 Ti, up to 0. 012 P, up to 0.015 S, up to 0.003 N, up to 0.004 O, and the balance Fe and other inevitable impurities. The method for producing the soft black plates involves the following steps: steelmaking, continuous casting, hot rolling, and combination of pickling and cold tandem rolling, continuous annealing, and temper rolling. The main process parameters in the method are as follows: slab delivering temperature is 1190-1250 deg. C, final rolling temperature is 880-920 deg. C, coiling temperature is between 560 deg. C and 620 deg. C, annealing temperature is 730-760 deg. C, holding time is 25-50 seconds, temper elongation is 1.2-2.2%.

JP4559918B2
The present invention relates to a tin plate excellent in workability and a steel plate for TFS (tin-free steel) in a thickness range of 0.15-0.6 mm and a method for producing the same.
Steel plates for tinplate and TFS are subjected to temper rolling according to the tempering degree of tin to produce T1 to T5 (target Rockwell hardness (HR30T) is 49 ± 3 to 65 ± 3), and secondary rolling (Single reduce) In general, DR6 to DR10 (target Rockwell hardness (HR30T) is 70 ± 3 to 80 ± 3) are manufactured by rolling, and are manufactured according to Rockwell hardness. Therefore, when manufacturing a hard tinplate, it manufactured so that C might be made high and it might become the hardness range of a predetermined refining degree. However, even if the hardness is within the predetermined range, it is not preferable because the workability is required at the same time, and it is not preferable, and if it is extremely low C in order to satisfy the workability, the workability is satisfactory. Even if it was possible, the hardness was lower than a predetermined value, which was not preferable.
By mass, C: 0.0030 to 0.0060%, Si: 0.04% or less, Mn: 0.60% or less, P: 0.005% or more, 0.03% or less, S: 0.02% Hereinafter, Al: more than 0.005%, 0.1% or less, N: 0.005% or less, the balance is made of Fe and inevitable impurities, the plate thickness is a tin plate excellent in workability, characterized by having a hardness level (HR30T) of 67 ± 3 to 76 ± 3 and a ?r value indicating in- plane anisotropy of ± 0.2 or less. And steel sheet for TFS.Then, after hot rolling with a finish rolling temperature of Ar 3 temperature or higher and a coiling temperature in the range of 650 ° C. ± 50 ° C., cold rolling with a rolling reduction of 85% to 95%, followed by recrystallization Annealing is performed at a temperature higher than that, and secondary rolling is performed at a rolling reduction of 8 to 35%, so that the sheet thickness is 0.2 mm or less and the hardness level (HR30T) is 67 ± 3 to 76 ± 3.

Problem to be solved by the Present Invention:
The Present invention aims to solve the problem of the prior arts by providing the good ageing resistance for 6 months and also change in yield strength after 6 months within 30 Mpa with alloying of vanadium, Ti, Ca and B with Single cold rolling of 1.2 % or more with process consisting of over ageing section Temperature 380 to 430 °C to suppress the yield point elongation ensuring ageing guarantee for 6 months at 30°C. The Ratio of B/N to be minimum 0.2 to ensure the ageing guarantee and also providing difference in yield strength after processed condition and after 6 hrs of heating at 100 °C and tested condition is around 20 to 30 Mpa.
The continuous annealing has such a serious disadvantage that no satisfactory ageing resistance can be given to Al-killed steel, and thus the remarkable quality and less production cycle time of the continuous anneal¬ing have not been fully obtained in the case of the Al-¬killed steel up to now because of less AlN precipitation which is required to fix N.

Along with above to achieve intended mechanical properties annealing cycle and Single cold reduction stretching were optimized along with speed of continuous annealing line to process 0.55-0.6 mm steel sheet.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide Cold rolled steel sheet for tinplate with higher thickness 0.55-0.6 mm having excellent aging resistanceand method of manufacturing the same.

A still further object of the present invention is directed to provideCold rolled steel sheet for tinplatehaving selective composition and processing to achieve the desired hardness and tin coating property.

A still further object of the present invention is directed to providecold rolled steel sheet for tinplate has yield strength of 250-340 MPa, ageing resistance of 6 months and more, Tensile strength of 310-380 MPa, total elongation of 32% or more and hardness level (HR30T) in the range of 54 to 61.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to cold rolled steel sheet for tinplate with excellent ageing resistance and higher thickness 0.55-0.6 mm with having a steel slab composition in terms of weight % comprising:
C: 0.015-0.05 %;
Mn: 0.15- 0.3%;
Si: 0–0.02%;
P: 0-0.015%;
Al: 0.02-0.06%;
S: 0.01 % or less;
N: 0.005 % or less;
V: 0.002-0.025% ;
B: 0.001-0.002 %;
and the balance being Fe and other unavoidable impurities; and wherein B/N ratio range from 0.2to 2providing for desired excellent ageing resistance after tin coating with Target hardness level (HR30T) in the range of 54 to 61.

A further aspect is directed to provide saidcold rolled steel sheet comprising anyone or more element selected from the group consisting of 0.0005% to 0.003% of Ti, and less than 0.003 % Ca.

A still further aspect of the present invention is directed to provide said cold rolled steel sheet which is tin coated and comprises, in terms of area fraction relative to entire microstructure of steel, 95% or more of ferrite phase, 5 % or less of pearlite phase along with carbide, nitride and sulphide precipitates for excellent stretch formability with ageing resistance.

A still further aspect of the present invention is directed to provide saidcold rolled steel sheet having Yield strength of 250-340 MPa, ageing resistance of 6 months and more, Tensile strength of 310-380 MPa, total elongation of 32% or more and hardness level (HR30T) in the range of 54 to 61.

A further aspect of the present invention is directed to aprocess to manufacturing Cold rolled steel sheet for tinplate as described above, comprising the steps of:
reheating the said steel slab composition to reheating temperature in the range from 1170°C -1230 °C;
said reheated slab being subjected to roughing rolling in roughing mill with roughing mill delivery temperature of 1070°C or less;
said rough rolled steel being subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C to Ac3+100 °C.
coiling the finish rolled steel at with average run out table cooling rate of 10 °C/second or more; and
acid Pickling the Cold rolling the said hot rolled steel sheet with cold reduction of atleast 65%.

A further aspect of the present invention is directed to provide saidprocess for manufacturing Cold rolled steel sheet for tinplate wherein cold rolled steel is subjected to continuous annealing following the steps comprising;
annealing the cold rolled steel sheet at soaking section critical temperature range from Ar3 °C to Ar3+100 °C with residence time ranging from 35 to 160 seconds;
over-aging Temperature the steel from SS temperature up to a temperature range of 380 to 430 °C;
subjecting to skin pass elongation or Single cold reduction of 1 % to 3 %;
subjecting to tin deposition through electrolytic process at reflow temperature from 200 to 300°C.

The above objects and advantages of the present invention are described hereunder in details with reference to non-limiting accompanying examples:

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING
Figure 1: shows the Microstructure of steel according to present invention having 95% or more of ferrite phase and 5 % or less of pearlite phase.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWING AND EXAMPLES

The Present invention relates to cold rolled steel sheet for tinplate having excellent ageing resistance and Target hardness level (HR30T) in the range of 54 to 61 with composition in terms of weight % comprising:
C: 0.015-0.05 %;
Mn: 0.15- 0.3%;
Si: 0–0.02%;
P: 0-0.15%;
Al: 0.02-0.06%;
S: 0.01 % or less;
N: 0.005 % or less;
V: 0.002-0.025 %;
B: 0.001-0.002 %;
and the balance being Fe and other unavoidable impurities;
whereinB/N ratio range from 0.2to 2 for excellent for excellent ageing resistance after tin coating.
Cold rolled steel sheet for tinplate wherein the said steel sheet has Yield strength of 250-340 MPa, ageing resistance of 6 months and more, Tensile strength of 310-380 MPa, total elongation of 32% or more and hardness level (HR30T) in the range of 54 to 61.

The cold rolled steel sheet of present invention which is tin coated and having microstructure comprising in terms of area fraction relative to entire microstructure of steel, 95% or more of ferrite phase, 5 % or less of pearlite phase along with carbide, nitride and sulphide precipitates for excellent stretch formability with ageing resistance.
Figure 1 shows the Microstructure of steel having 95% or more of ferrite phase and 5 % or less of pearlite phase.

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 (%)

A cold rolled steel sheet for tinplate with improved ageing resistance and surface tin coating according to present invention, its chemical compositions and method of manufacturing are described hereunder with explanation on metallurgical factors deciding the range of constituentsin a composition according to a preferred embodiment wherein all the elements are in weight % as follows:

Carbon (0.015-0.05wt%) - 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. drawability it desirable to reduce the C level less than 0.05 wt%. Lowering the carbon content below 0.015 wt% results in poor ageing property since below 0.015 wt% steel is in complete a-ferrite region in Iron-Cementite phase diagram resulting no cementite formation. Consequently more free carbon will be available in steel matrix which deteriorates the ageing property. Cementite formed in grain boundaries its precipitate size should be greater than 1µm which in helps in reducing solute carbon and suppress the YPE for better ageing resistance. Keeping low carbon <0.02 % also requires vacuum degassing the molten steel which add more cost of production. To avoid YPE and to have yield strength within the desired limit, the level of Carbon is between 0.015-0.05 wt percent.

Mn (0.15-0.3) wt. % - The Mn ranges from 0.15 to 0.3 % is most desirable for the given low carbon steel grade provided that S remains in the favorable range of 0.010wt% 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. here keeping the level to minimum is advisable for providing a soft material, however, the lower limit is 0.1% as below it the surface property deteriorates 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.

Vanadium 0.0020 to 0.025%: Vanadium is strong carbide former, reduces solute carbon in the mild steel and forms Vanadium Carbide, as it forms coarser carbide particles it restricts the yield strength within 340Mpa and promotes the ageing resistance. To achieve stretcher strain free material minimum vanadium to be added is 0.002 and to restrict yield strength maximum vanadium is to be 0.025. To achieve the desired properties vanadium is restricted to 0.002 to 0.025 more preferably 0.005 to 0.02.

B (0.001-0.002 wt%)–Advantage of adding B is two-fold. Firstly, B acts as a strong Nitride former forming BN and complex carbo nitrides B(C, N) helpful in fixing C and N in order to avoid aging problem in low carbon steel sheet after temper rolling.
But it is desirable that the ratio of B and N shall be 0.2 to 2 to fix the N partially and get the desired ageing guarantee of min 6 Months as well as yield strength less than 340 Mpa. As the total amount of B increases, the ferrite grains become finer because of decrease in BN precipitate size which increases the yield strength of material. On the other hand if the ratio of B and N ratio is less than 0.2 then it results free N which deteriorate in the ageing property.

Al (0.02-0.06) wt. % – Al wt% ranges from 0.02-0.06 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 deteriorates 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 describes the present invention. Same is achieved by optimize 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 minimum level. Higher N content requires to higher Al addition to fix extra N and increase the volume of AlN precipitates which strengthens the material, ultimately deteriorating the drawing property.

P (0-0.015) wt%:When P is added in amount exceeding more than 0.02 wt% the yield strength level increases significantly. In addition, higher amount of P promotes formation of surface defects after tin coating and also lowers corrosion resistance of tinplate. So, maximum limit of P is kept 0.015 %.

Si (0-0.02) wt%: It is 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 surface. It is advantageous to add as low an amount of silicon in the steel as is possible, the added amount of silicon is preferably 0.02 wt% or less.

Description of the process of manufacturing:
To achieve Slab chemistry as described in scope of the invention, Heat from basic oxygen furnace (BOF) is processed through RH degasser and subsequently continuously casted. Special measures are taken to hot roll resulted slabs by keeping slab reheating temperature in the range of 1170°C to 1230°C intended to control roughing mill delivery temperature under 1070°C and finishing mill entry temperature under 1070°C to check surface defects like rolled in scale. During hot rolling, finishing mill temperature is varied in the range from Ac3 °C to Ac3+100 °C. After finish rolling, Run out table cooling rate from finishing mill to coiler of more than 9 0C/sec was maintained to achieve coiling temperature range of 620 to 680 °C. Hot rolled coils were subsequently processed through pickling coupled with tandem cold rolling mill to remove the oxide surface present in the surface and to provide selective cold reduction of 65% or more.

Annealing the cold rolled steel sheet at soaking section critical temperature range from Ar3 °C to Ar3+100 °C with residence time ranging from 35 to 160 seconds;
Over-aging Temperature the steel from SS temperature up to a temperature range of 380 to 430 °C;
Subjecting to skin pass elongation or Single cold reduction of 1 % to 3 %;
Subjecting to tin deposition through electrolytic process at reflow temperature from 200 to 300°C.

Subsequent to pickling and cold rolling to desired thickness, cold rolled steel strip are processed through continuous annealing line where electrolytic cleaning removes rolling emulsion present on the surface. Cleaned surface passes through the preheating and heating section where the strip is heated at the rate of 1-5 0C/sec up to soaking section temperature. Soaking section temperature was maintained in the range from Ar3 °C to Ar3+100 °C to achieve ferrite and pearlite
Phases in microstructure. Annealing time is kept in the range from 35 to 160 seconds to allow sufficient time for annealed and homogenization of austenite microstructure. Following soaking section, annealed strip sheet passes through Over-aging section to a temperature range of 380 to 430 °C and followed by Single stand skin pass mill where skin pass elongation ranges from 1 to 3% in order to get desired mechanical properties.After Skin pass, said steel is subjected to Tin deposition through Electrolytic process where pure tin is Anode and Cathode-Sheet and Electrolyte- Stannous + phenyl sulfonic acid. Tin deposited on steel sheet and strong bond is formed due to formation of iron tin alloy at temperature ranges from 200 to 300 °C.

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 trough following examples 1 & 2:
Table 1: Elemental Compositions in weight % of the inventive steel sheets along with comparative example.
Table 2:Hot rollingandcoldrollingof 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 3Figure 1. Microstructure of steel having 95% or more of ferrite phase and 5 % or less of pearlite phase

Table 1
Chemical Composition in %
Sample No C MN S P SI AL N B V B/N Others Remarks
1 0.029 0.15 0.004 0.01 0.02 0.04 0.003 0.002 0.015 0.67 Ca:0.0015 I
2 0.05 0.3 0.007 0.012 0.02 0.03 0.005 0.001 0.005 0.2 B: 0.001 I
3 0.005 0.15 0.01 0.015 0.018 0.03 0.003 0.0005 0.008 0.16 Nb: 0.007 C
4 0.002 0.2 0.01 0.014 0.011 0.04 0.004 0.0004 0.005 0.12 Nb:0.003 C

*I - Present inventive example, C- Comparative Examples
*Underline boxes indicates “outside the appropriate range”

Example 1
It can be appreciated from Table 1 to Table 4 that steel sheets remarked as “I” are satisfying all the scopes of present invention and improved ageing resistance to avoid wrinkling problem and improved Tin coating without bare spot on the surface. These steels exhibits improved yield strength of 250-340 MPa, ageing resistance of 6 months and more, Tensile strength of 310-380 MPa, total elongation of 32% or more and hardness level (HR30T) in the range of 54 to 61.Whereas, Steel remarked as ‘C’ from Table 1 to Table 4 doesn’t comply with atleast 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. example steel no. 3 and 4 has does not comply with required ratio of B/N ratio and has poor Tin coating surface.

Table 2

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


1 1205 1060 900 650 82
2 1205 1040 880 660 89
3 1220 1065 902 570 68
4 1210 1070 890 560 75

*I - Present inventive example, C- Comparative Examples
Note: Steel marked as 1 and 2have the chemical composition of present inventive steel, and however they are processed at different conditions to validate the claimed process. In sample no 1 and 2Single reduction skin pass elongation varied as 1.6% and 2.4% which resulted YS more than 250 MPa and hardness more than 54 HR.
* SRT- Slab reheating temperature, FT- hot finish rolling temperature,ROT- Run out table at hot strip mill, CR%- Cold rolling reduction %, SS- soakingsection ,OAS-Over-Ageing Section, SPM- Skin pass elongation.

Table 3
CAL and Tin Coating Parameters
Sample No Thickness (mm) SS TEMP SS Residence Time OAS TEMP Single Reduction Skin Pass Tin Coating Temperature
1 0.55 740 90 410 1.9 200
2 0.6 760 95 420 2.4 250
3 0.58 790 57 350 0.7 180
4 0.6 810 80 360 0.9 320

Table 4
Mechanical Prop Coating Properties
Sample No YS TS Elongation % Aging Resistance (Months) Hardness (HR 30T) Tin Coating Cost Remarks
1 285 321 36 6 60 G Low I
2 261 334 38 6 58 G Low I
3 222 301 42 8 48 NG High C
4 231 310 40 9 49 NG High C

*I - Present inventive example, C- Comparative Examples, G- Good, NG- Not Good
Example 2;

In sample 3 and 4 where in sample 3 is having Yield strength less than 250 MPa and hardness is less than less than 54 HR30T and poor coating property which is out of scope of present invention.
In case of sample 3 and 4, Tin coating property is also not goodwhich is out of scope of current invention. As per Table 4, Sample 3 and 4 gives good aging resistance but at higher cost.

It is thus possible by way of the present invention to provideCold rolled steel sheet having thickness in the range of 0.55-0.6 mm through continuous annealing route for tinplate having excellent ageing resistance and Target hardness level (HR30T) in the range of 54 to 61 with composition in terms of weight % comprising:
C: 0.015-0.05 %; Mn: 0.15- 0.3%; Si: 0–0.02%; P: 0-0.015%; Al: 0.02-0.06%; S: 0.01 % or less; N: 0.005 % or less;V: 0.002-0.025 % and B: 0.001-0.002 %; and the balance being Fe and other unavoidable impurities; wherein B/N ratio range from 0.6 to 2 for excellent for excellent ageing resistance after tin coating.

The advancement favors generation of cold rolled higher thickness tinplated sheet having thickness in the range of 0.55-0.6 mm withYield strength of 250-340 MPa, ageing resistance of 6 months and more, Tensile strength of 310-380 MPa, total elongation of 32% or more and hardness level (HR30T) in the range of 54 to 61.
, Claims:We Claim:
1. Cold rolled steel sheet for tinplate with excellent ageing resistance and higher thickness 0.55-0.6 mm with having a steel slab composition in terms of weight % comprising:
C: 0.015-0.05 %;
Mn: 0.15- 0.3%;
Si: 0–0.02%;
P: 0-0.015%;
Al: 0.02-0.06%;
S: 0.01 % or less;
N: 0.005 % or less;
V: 0.002-0.025 % ;
B: 0.001-0.002 %;
and the balance being Fe and other unavoidable impurities; and wherein B/N ratio range from 0.2to 2providing fordesired excellent ageing resistance after tin coating with Target hardness level (HR30T) in the range of 54 to 61.

2.) Cold rolled steel sheet as claimed in claim 1 comprising anyone or more element selected from the group consisting of 0.0005% to 0.003% of Ti, and less than 0.003 % Ca;

3)Cold rolled steel sheet as claimed in anyone of claims 1 or 2 which is tin coated and comprises, in terms of area fraction relative to entire microstructure of steel, 95% or more of ferrite phase, 5 % or less of pearlite phase along with carbide, nitride and sulphide precipitates for excellent stretch formability with ageing resistance.

4)Cold rolled steel sheet as claimed in anyone of claims 1 to 3 having Yield strength of 250-340 MPa, ageing resistance of 6 months and more, Tensile strength of 310-380 MPa, total elongation of 32% or more and hardness level (HR30T) in the range of 54 to 61.

5.) A process to manufacturing Cold rolled steel sheet for tinplate as claimed in anyone of claims 1 to 4, comprising the steps of:
reheating the said steel slab composition to reheating temperature in the range from 1170°C -1230 °C;
said reheated slab being subjected to roughing rolling in roughing mill with roughing mill delivery temperature of 1070°C or less;
said rough rolled steel being subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C to Ac3+100 °C.
coiling the finish rolled steel at with average run out table cooling rate of 10 °C/second or more; and
acid Pickling the Cold rolling the said hot rolled steel sheet with cold reduction of atleast 65%.

6.) The process for manufacturing Cold rolled steel sheet for tinplate as claimed in claim 5, wherein cold rolled steel is subjected to continuous annealing following the steps comprising;
Annealingthe cold rolled steel sheet at soaking section critical temperature range from Ar3 °C to Ar3+100 °C with residence time ranging from 35 to 160 seconds;
Over-aging Temperature the steel from SS temperature up to a temperature range of 380 to 430 °C;
Subjectingto skin pass elongation or Single cold reduction of 1% to 3%;
Subjecting to tin deposition through electrolytic process at reflow temperature from 200 to 300°C.

Dated this the 8th day of March, 2023
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199