Description:FIELD OF THE INVENTION

The present invention relates to ultra-thin tinplate steel for a stiff end applications and a method for producing the same by involving skin pass mill based reduction with double stands, and particularly relates to said tinplate steel for said stiff end applications having high strength and lower thickness.
The present invention also provides for a manufacturing method of said tinplate steel of lower thickness preferably as a thinner gauge tin plated steel sheet for strip ends application with high strength and less forming application through double cold reduction route, wherein the composition of raw material in terms of mass percentage of elements are - C: 0.015-0.045 %; Mn: 0.1- 0.3%; Si: 0.005-0.025%; P: 0.005-0.025%; Al: 0.02-0.06%; S: 0.015 % or less; N: 0.006 % or less; and the balance being Fe and other unavoidable impurities.

The present advancement favors generation of high strength tin-plated steel wherein the thickness of the said steel is below 0.14 mm and has Yield strength of 480-560MPa, Tensile strength of 520-560 MPa, total elongation of 2% or more, hardness level (HR30T) in the range of 71 to 75.

BACKGROUND OF THE INVENTION

Tin plated material of thickness in the range of less than 0.14 mm with yield strength in the range of 480-560 Mpa are difficult to manufacture domestically and not available for customers. There are certain challenges associated with production of high strength Tin plate of thickness less than 0.14 mm related to high roll force and tension parameters which ultimately affects product surface, shape as this is almost out of lower capability limit of double cold reduction mill. 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 20-31% to strengthen the material by strain hardening mechanism. But in this case the thickness of the required material being less than 0.14 mm, for that to enable total cold rolling reduction percentage actual hot rolled thickness required should be as low as possible which is to be then annealed to finally achieve required reduction during secondary rolling.

JPH1088233A reveals a method to obtain an extra ultra-thin where thickness of the sheet is between 0.05-0.25 mm, a broad steel sheet for can, improved in strength and workability, by using a steel of specific composition corresponding to ultra-low carbon level with hot rolling conditions, temps, and drafts in a high temperature recrystallization region and a low temperature non-recrystallization region, respectively.
C: 0.0005 to 0.0150 wt%, Si: 0.2 wt% or less, Mn: 0.05 to 0.6 wt%, P: 0.02 wt% or less, S: 0.02 wt% or less, Al: 0.15 wt% or less and N : 0.020 wt% or less, the balance being steel and the composition of Fe and unavoidable impurities is melted and made into a slab. Then, after the slab is heated, in the hot rough rolling step, the total draft is 80% or more and rolling at final pass reduction ratio: 20% or more, and then bonding the obtained sheet bar to the preceding sheet bar before finish rolling, and then performing hot finishing rolling at a temperature range of 950 ° C or more in the hot finish rolling process. Rolling rate: Rolled to 70% or more, then Ar 3 to 950 total rolling reduction in a temperature range of °C.: subjected to 55% or more rolling, finishing temperature: the hot rolling ends at Ar 3-50 °C. or higher, then coiled at a temperature range of 550 to 750 ° C. A method for producing a steel sheet for cans, which comprises performing cold rolling and recrystallization annealing after removing the scale, performing a re-annealing, and then applying a skin pass or a secondary rolling with a rolling reduction of 30% or less.
It is thus a long felt need in the art to provide for ultra-thin tinplate steel that would possess necessary characteristics suitable for stiff applications with excellent aging resistance including applications in calendar strips wherein the thickness of the said steel would be in the range of less than 0.14 mm & has Yield strength of 480-560MPa, and hardness level (HR30T) in the range of 71 to 75 with reduced formability and a method of manufacture thereof that would yield said characteristics through double reduction.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide for ultra-thin tinplate steel and a method towards generation of tin plated steel sheet suitable for stiff applications with excellent aging resistance including applications in calendar strips wherein the thickness of the said steel is in the range of less than 0.14 mm & has Yield strength of 480-560MPa, and hardness level (HR30T) in the range of 71 to 75 having reduced formability.

A still further object of the present invention is to provide for a double reduced ultra-thin tinplate steel that would comprise select chemical composition in percentage by weight: C: 0.015-0.045 %; Mn: 0.1- 0.3%; Si: 0.005–0.025%; P: 0.005-0.025%; Al: 0.02-0.06%; S: 0.015 % or less; N: 0.006 % or less; and the balance being Fe and other unavoidable impurities, wherein Mn/Si ratio would be in the range of from 4 to 20 to provide for desired draw ability of said tinplate having thickness in the range of 0.125-0.135 mm.

A still further object of the present invention is to provide for double reduced ultra-thin tin-plated steel through its process of manufacture comprising anyone or more element selected from the group consisting of 0.0005% to 0.03% of V, and less than 0.003 % Ca.

Yet another object of the present invention is to provide for double reduced ultra-thin tin-plated steel having Yield strength of 480-560 MPa, that would have ageing resistance of 6 months or more, Tensile strength of 520-560 MPa, total elongation of 2-4% and hardness level (HR30T) in the range of 71 to 75.

A still further object of the present invention is to provide for ultra-thin tinplate steel and method of manufacturing a double reduced ultra-thin tin-plated steel of hardness grade TH580 having yield strength in the range of 530 to 610 MPa and wherein hot continuous rolling on the solid slab would be performed to obtain a hot rolled steel to comprise the following steps: the solid slab is reheated to a temperature of 1150°C -1250 °C ; the reheated slab is subjected to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 to 1080°C; the rough rolled steel is subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C to 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; the finished rolled steel is then acid pickled to form the hot rolled steel with a cold reduction in the range of 85 to 95%.

A still further object of the present invention is to provide for said method of manufacturing of double reduced ultra-thin tin-plated steel of hardness grade TH520 that would comprise the following steps:
of providing a chemical composition of C: 0.015-0.045 %; Mn: 0.1- 0.3%; Si: 0.005–0.025%; P: 0.005-0.025%; Al: 0.02-0.06%; S: 0.015 % or less; N: 0.006 % or less; and the balance being Fe and other unavoidable impurities, wherein Mn/Si ratio range from 4 to 20 would enable providing for tin coating having refining and continuously casting of the molten steel to obtain a solid slab; carrying out hot continuous rolling on the solid slab to obtain a hot rolled steel;

pickling and cold rolling the hot rolled steel to obtain a cold-rolled steel; on which continuously annealing would be performed on said cold-rolled steel to obtain an annealed steel, wherein during the continuous annealing, the annealing soaking temperature is 700-740 ?, and the annealing soaking time is 40 to 200s and cold-rolled steel is over-aged at the temperature from 420- 430 ?, skin pass mill with double stands where reduction of 22-31% given to the annealed steel and electrolytic tinning on the steel strip to obtain the tinned plate steel of hardness grade TH520, wherein the reflow temperature is controlled to 230 to 265 ?.

A still further object of the present invention is directed to production of material with given properties through double reduction.

SUMMARY OF THE INVENTION

According to a basic aspect of the present invention there is provided ultra-thin tinplate steel comprising of composition in percentage by weight including:
C: 0.015-0.045 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less;
and the balance being Fe, wherein Mn/Si ratio range from 4 to 20 of said tinplate steel having tin coating is of thickness in the range of 0.125-0.135 mm and Yield Strength in the range of 480-560 MPa.

Preferably said ultra-thin tinplate steel is double reduced wherein products after annealing reduction is given from 18 to 31% range using DCR (Double cold reduction mill), which is in general a skin pass mill with two stands.

Said ultra-thin tin-plate steel comprising elements selected from the group consisting of 0.0005% to 0.03% of V, and less than 0.003 % Ca;

According to another preferred aspect of the present invention there is provided said ultra-thin tinplate steel wherein said tinplate steel has ageing resistance of > 6 months, Tensile strength of 520-560 MPa, total elongation of 2-4% and hardness level (HR30T) in the range of 71 to 75.

Preferably said ultra-thin tinplate steel is provided wherein said tinplate steel of area fraction relative to entire microstructure of steel comprises 98-99% ferrite phase, 1-2% pearlite with grains oriented in the rolling direction favoring excellent anisotropy said microstructure having ASTM grain number 10 that are 20% smaller than the grains of annealed double reduced material.

According to another aspect of the present invention there is provided a method of manufacturing ultra-thin tinplate steel comprising the steps of:

(i) Providing steel slabs from select elemental steel composition having
C: 0.015-0.045 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less;
and the balance being Fe, wherein Mn/Si ratio range from 4 to 20; and

carrying out hot continuous rolling on the solid slabs to obtain hot rolled steel following steps of reheating the solid slab to a temperature of 1150°C -1250 °C; subjecting the reheated slab to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 to 1080°C; subjecting the rough rolled steel to finish rolling with finish mill exit temperature ranging from Ac3 °C to Ac3+100 °C; cooling the finish rolled steel at an average run-out table cooling rate in the range of 10 to 30°C/second; acid pickling the finished rolled steel to form hot rolled steel with a cold reduction in the range of 75 to 95%, followed by

continuous annealing said cold rolled steel sheet at a temperature of 700-740 Deg Celsius thereafter subjecting the thus annealed steel to secondary cold rolling reduction of 22 % to 31 % followed by electrolytic tinning at controlled reflow temperature of 230 to 265 ? for tin coating to obtain therefrom ultra-thin tinplated steel of thickness in the range of 0.125-0.135 mm and Yield Strength in the range of 480-560 MPa.

Preferably in said method of manufacturing ultra-thin tinplate steel wherein said hot continuous rolling of solid steel slab to obtain hot rolled steel comprises the following steps:

reheating solid slab to slab reheating temperature (SRT) of 1150°C -1250 °C;

subjecting the reheated slab to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 to 1080°C;

finish rolling the rough rolled steel with finish mill exit temperature ranging from Ac3 °C to Ac3+100 °C.;

cooling the finish rolled steel at an average run-out table cooling rate from finishing mill in the range of 10 to 30°C/second for coiling in temperature range of 620 to 680 °C;

subjecting the finished hot rolled coiled steel to acid pickling with tandem cold rolling to remove oxide surface and to provide selective cold reduction in the range of 75-95% preferably in the range of 85-95%.

More preferably in said method of manufacturing ultra-thin tinplate steel said continuous annealing of cold rolled steel sheet is carried out at soaking section (SS) temperature of 700-740 ? with residence time for annealing soaking of 40 to 200s followed by over-aging cold-rolled steel at temperature from 420- 430 ?, that is then subjected to skin pass mill with double stands where reduction of 22-31% was given to the annealed steel;
said electrolytic tinning on the steel strip is given at controlled reflow temperature in the range of 230 to 265 ? to obtain tinplated steel of hardness grades TH520 having Hardness 67 to 75 HRB and TH580 having hardness range of 69 to 77 HRB, Yield strength of 480-560 MPa, ageing resistance of >6 months’ Tensile strength of 520-560 MPa, total elongation of 2-4% and hardness level (HR30T) in the range of 71 to 75 having excellent pressure resistance.

According to an aspect of the present invention there is provided said ultra-thin tinplate steel and its method of generation suitable for calendar strip wherein the thickness of the said steel is in the range of less than 0.14mm has Yield strength of 480-560MPa, Tensile strength of 520-560 MPa, total elongation in the range of 2-4%, hardness level (HR30T) in the range of 71 to 75 and having excellent resistance to aging to maintain required strength requirements at lower thickness levels.
C: 0.015-0.040 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less
and the balance being Fe and other unavoidable impurities

A still further aspect of the present invention is directed to use double reduction method to achieve the desired properties in the material. The material is subjected to 22-24 % cold reduction after annealing to achieve the final properties.

A still further aspect of the present invention is to reduce the thickness of annealed material to a range which can be processed in double cold reduction mill by annealing the material in lower temperatures of 700-740 Deg Celsius. As a result, the annealed material has finer grains of ASTM grain number 10 as compared to the annealed material is generally used for double reduced material.

Another aspect of the present invention involves processing through following steps: -
a) Steel is processed from hot metal in basic oxygen furnace (BOF), Subsequently continuously casting into slabs and reheating of said slabs having said composition to a reheating temperature in the range from 1190°C -1250 °C;

b) Said Reheated slab being subjected to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 1020°C - 1080°C;
c) Said rough rolled steel being subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C to Ac3+100 °C;
d) Coiling the finish rolled steel at with average run out table cooling rate in the range 10-20 °C/second;
e) Acid Pickling the Cold rolling the said hot rolled steel sheet with cold reduction of At least 75-80%.
A still further aspect of the present invention is directed to said process wherein cold rolled steel sheet for tinplate, wherein cold rolled steel is subjected to continuous annealing following the steps comprising;
a) Usage of low carbon steel chemistry to avoid extra processing cost involved for Ultra low carbon steel grade.
b) Annealing the cold rolled steel sheet at soaking section critical temperature range from 700-740 °C with residence time ranging from 40 to 200 seconds;
c) Over-aging Temperature the steel from SS temperature up to a temperature range of 400 to 430 °C;
d) Subjecting to secondary cold reduction of 22 % to 31 %
e) Subjecting to tin deposition through electrolytic process at reflow temperature from 230 to 265°C,
enabling selectively special steel sheet comprising in terms of area fraction relative to entire microstructure of steel, 98-99% ferrite phase, 1-2% pearlite. The grains are oriented in the rolling direction giving it an excellent anisotropic property.
According to an aspect of the present invention there is provided a double reduced ultra-thin tin-plated steel comprising of chemical composition in percentage by weight:
C: 0.015-0.045 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less;
and the balance being Fe and other unavoidable impurities, wherein Mn/Si ratio range from 4 to 20 providing for tin coating having thickness in the range of 0.125-0.135mm.
2) A double reduced ultra-thin tin-plated steel as claimed in claim 1 comprising anyone or more element selected from the group consisting of 0.0005% to 0.03% of V, and less than 0.003 % Ca;
3) A double reduced ultra-thin tin-plated steel as claimed in anyone of claims 1 to 2 having Yield strength of 480-560 MPa, ageing resistance of 6 months and more, Tensile strength of 520-560 MPa, total elongation of 2-4% and hardness level (HR30T) in the range of 71 to 75.

According to another aspect is provided a method of manufacturing of double reduced ultra-thin tin-plated steel of hardness grade TH580, wherein the hot continuous rolling on the solid slab to obtain a hot rolled steel comprising the following steps: the solid slab is reheated to a temperature of 1150°C -1250 °C ; the reheated slab is subjected to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 to 1080°C; the rough rolled steel is subjected to finish rolling with finish mill exit temperature ranging from Ac3 °C to 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; the finished rolled steel is then acid pickled to form the hot rolled steel with a cold reduction in the range of 85 to 95%.
Preferably the method of manufacturing double reduced ultra-thin tin-plated steel of hardness grade TH520 comprising the following steps:
C: 0.015-0.045 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less;
and the balance being Fe and other unavoidable impurities, wherein Mn/Si ratio range from 4 to 20 providing for tin coating having refining and continuously casting of the molten steel to obtain a solid slab; carrying out hot continuous rolling on the solid slab to obtain a hot rolled steel;
pickling and cold rolling the hot rolled steel to obtain a cold-rolled steel; continuously annealing was done to the cold-rolled steel to obtain an annealed steel, wherein during the continuous annealing, the annealing soaking temperature is 700-740 ?, and the annealing soaking time is 40 to 200s and cold-rolled steel is over-aged at the temperature from 420- 430 ?, skin pass mill with double stands where reduction of 22-31% given to the annealed steel and electrolytic tinning on the steel strip to obtain the tinned plate steel of hardness grade TH520, wherein the reflow temperature is controlled to 230 to 265 ?.

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

BRIEF DESCRIPTION OF FIGURES

Fig. 1: illustrates magnification: 500 X, Microstructure after Double Cold reduction.

DETAILED DESCRIPTION OF THE INVENTION

As discussed hereinbefore, the present invention relates to generation of Ultra-thin gauge high strength tinplated steel wherein the thickness of the said steel is in the range of less than 0.14 mm has Yield strength of 480-560MPa, Tensile strength of 520-560 MPa, total elongation in the range of 2% to 4%, hardness level (HR30T) in the range of 71 to 75 with composition in terms of weight % comprising:
C: 0.015-0.045 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less;
and the balance being Fe and other unavoidable impurities

To facilitate the production of high strength tin plated steel of thickness range less than 0.14 mm through double cold reduction route, a select steel chemical composition was annealed at a temperature of 700-740 Deg Celsius in continuous annealing line to provide for 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. 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 20-31% reduction during secondary rolling.

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 (%)

According to present invention, the cold rolled steel produced for tin plating high strength for tinplate with 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 according to a preferred embodiment wherein all the elements are in weight % as follows:

Carbon (0.015-0.045 wt.%) - While carbon increases the steel strength, it reduces the cold workability and the deep Drawabilty 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 desirable to reduce the C level less than 0.06 wt.%. Lowering the carbon content below 0.02 wt.% results in poor ageing property since below 0.02 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, which is further balanced by secondary cold reduction after annealing. 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. 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 (0.1-0.3) wt. % - The Mn ranges from 0.1 to 0.3 % is most desirable for the given that S remains in the favorable range of 0.008 wt.% or less. Keeping the Mn level 0.1 wt.% with higher Sulphur content may result in surface irregularities such as red shortness, edge crack sliver etc. The lower limit of Mn is kept 0.1% with average Sulphur level to ensure the surface properties 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.
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 (0.006wt% or less) -The upper limit for N is 0.006%; 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 considering continuous annealing route processing.
P (0.005-0.025) wt. %: -. P is as an element which improves the strength at low cost, and the amount of addition thereof varies depending on a target strength level. When added amount exceeds more than 0.025 wt.% the yield strength level increases significantly. In addition, higher amount of P promotes formation surface defects and significantly reduces the corrosion resistance of the base metal. So, maximum limit of P is kept 0.025 %.
Si (0.005-0.025) 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 0.025 wt.% or less.
WORKING EXAMPLES:
Description of the process of manufacturing:
To achieve slab chemistry as described in scope of the invention, (a) Molten steel 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 1150°C to 1250°C intended to control roughing mill delivery temperature in the range of 980-1080°C preferably 1020-1080°C and finishing mill entry temperature in the range of 1020-1080°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 in the range of 75-85%.

(b) Annealing the cold rolled steel sheet at soaking section critical temperature range from 700 °C to 740 °C with residence time ranging from 40 to 200 seconds;
(c) Over-aging Temperature the steel from SS temperature up to a temperature range of 400 to 430 °C;
(d) Subjecting to secondary cold reduction of 22 % to 31 %
(e) Subjecting to tin deposition through electrolytic process at reflow temperature from 230 to 265°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 (SS) temperature. Soaking section temperature was maintained in the range from 700 to 740 °C to achieve ferrite and pearlite Phases in microstructure. Annealing time is kept in the range from 40 to 200 seconds to allow sufficient time for annealed and homogenization of microstructure. Following soaking section, annealed strip sheet passes through Over-aging section to a temperature range of 400 to 430 °C and followed by secondary cold reduction of the annealed material where the reduction percentage ranges from 22 to 31% in order to get desired mechanical properties. After secondary rolling, 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 230 to 265 °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 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 Mn/Si C
1 0.040 0.3 0.006 0.015 0.15 0.04 0.005 2 C
2 0.030 0.25 0.006 0.01 0.02 0.03 0.004 12.5 I
3 0.042 0.20 0.01 0.015 0.018 0.03 0.004 11 I
4 0.015 0.25 0.01 0.02 0.005 0.04 0.003 50 C

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

* SRT- Slab reheating temperature, FT- hot finish rolling temperature, ROT- Run out table at hot strip 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
1 740 95 425 22 250
2 730 95 420 24 250
3 720 90 430 25 250
4 710 95 430 31 250

Table 4

Sample No Mechanical Properties Remarks
YS TS Elongation % Yield Point Elongation Hardness (HR 30T)
1 490 498 4 2.5% 71 C
2 520 530 3.8 0 72 I
3 530 546 3.2 0 73 I
4 550 560 2.5 3% 74 C

*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

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 480-560 MPa, Tensile strength of 520-560 MPa, total elongation in the range of 2% to 4%, hardness level (HR30T) in the range of 71 to 75 and excellent pressure resistance. Whereas, Steel remarked as ‘C’ doesn’t comply with a 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 or mechanical properties tested were on boundary values. For example, steel no. 1 has processed with higher annealing temperature.

It is thus possible to produce a Ultra-thin tin plated steel having a thickness of less than 0.14 mm with Yield strength of 480-560 MPa, Tensile strength of 520-560 MPa, total elongation of 2 % or more, hardness level (HR30T) in the range of 71 to 75, Excellent aging resistance without using Ultra low carbon chemistry with composition by weight %: C: 0.015-0.045 %; Mn: 0.1- 0.3%; Si: 0.005–0.025%; P: 0.005-0.025%; Al: 0.02-0.06%; S: 0.015 % or less; N: 0.006 % or less; and the balance being Fe and other unavoidable impurities, and annealing it in a temperature range of 700 to 740 °C in continuous annealing line followed by subjecting it to a secondary reduction of 22-31%
, Claims:We Claim:

1. Ultra-thin tinplate steel comprising of composition in percentage by weight including:
C: 0.015-0.045 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less;

and the balance being Fe, wherein Mn/Si ratio range from 4 to 20 of said tinplate steel having tin coating is of thickness in the range of 0.125-0.135 mm and Yield Strength in the range of 480-560 MPa.

2. The ultra-thin tinplate steel as claimed in claim 1 that is double reduced ultra-thin tin-plate steel comprising elements selected from the group consisting of 0.0005% to 0.03% of V, and less than 0.003 % Ca.

3. The ultra-thin tinplate steel as claimed in claims 1 or 2 wherein said tinplate steel has ageing resistance of > 6 months, Tensile strength of 520-560 MPa, total elongation of 2-4% and hardness level (HR30T) in the range of 71 to 75.

4. The ultra-thin tinplate steel as claimed in claims 1-3 wherein said tinplate steel of area fraction relative to entire microstructure of steel comprises 98-99% ferrite phase, 1-2% pearlite with grains oriented in the rolling direction favoring excellent anisotropy, said microstructure having ASTM grain number 10 that are 20% smaller than the grains of annealed double reduced material.

5. The method of manufacturing ultra-thin tinplate steel as claimed in anyone of claims 1-4 comprising the steps of :

(i) Providing steel slabs from select elemental steel composition having
C: 0.015-0.045 %;
Mn: 0.1- 0.3%;
Si: 0.005–0.025%;
P: 0.005-0.025%;
Al: 0.02-0.06%;
S: 0.015 % or less;
N: 0.006 % or less;
and the balance being Fe, wherein Mn/Si ratio range from 4 to 20; and

carrying out hot continuous rolling on the solid slabs to obtain hot rolled steel following steps of reheating the solid slab to a temperature of 1150°C -1250 °C; subjecting the reheated slab to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 to 1080°C; subjecting the rough rolled steel to finish rolling with finish mill exit temperature ranging from Ac3 °C to Ac3+100 °C; cooling the finish rolled steel at an average run-out table cooling rate in the range of 10 to 30°C/second; acid pickling the finished rolled steel to form hot rolled steel with a cold reduction in the range of 75 to 95%, followed by

continuous annealing said cold rolled steel sheet at a temperature of 700-740 Deg Celsius thereafter subjecting the thus annealed steel to secondary cold rolling reduction of 22 % to 31 % followed by electrolytic tinning at controlled reflow temperature of 230 to 265 ? for tin coating to obtain therefrom ultra-thin tinplated steel of thickness in the range of 0.125-0.135 mm and Yield Strength in the range of 480-560 MPa.

6. The method of manufacturing ultra-thin tinplate steel as claimed in claim 5 wherein said hot continuous rolling of solid steel slab to obtain hot rolled steel comprises the following steps:

reheating solid slab to slab reheating temperature (SRT) of 1150°C -1250 °C;

subjecting the reheated slab to roughing rolling in roughing mill with roughing mill delivery temperature in the range of 980 to 1080°C;

finish rolling the rough rolled steel with finish mill exit temperature ranging from Ac3 °C to Ac3+100 °C.;

cooling the finish rolled steel at an average run-out table cooling rate from finishing mill in the range of 10 to 30°C/second for coiling in temperature range of 620 to 680 °C;

subjecting the finished hot rolled coiled steel to acid pickling with tandem cold rolling to remove oxide surface and to provide selective cold reduction in the range of 75-95% preferably in the range of 85-95%.

7. The method of manufacturing ultra-thin tinplate steel as claimed in anyone of claims 5 or 6 wherein

said continuous annealing of cold rolled steel sheet is carried out at soaking section (SS) temperature of 700-740 ? with residence time for annealing soaking of 40 to 200s followed by over-aging cold-rolled steel at temperature from 420- 430 ?, that is then subjected to skin pass mill with double stands where reduction of 22-31% was given to the annealed steel;
said electrolytic tinning on the steel strip is given at controlled reflow temperature in the range of 230 to 265 ? to obtain tinplated steel of hardness grade TH520-TH580, Yield strength of 480-560 MPa, ageing resistance of >6 months Tensile strength of 520-560 MPa, total elongation of 2-4% and hardness level (HR30T) in the range of 71 to 75 having excellent pressure resistance.

Dated this the 29th day of June, 2023
Anjan Sen
Of Anjan Sen and Associates
(Applicants Agent)
IN/PA-199