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 :
ALUZINC COATED STRUCTURAL STEEL SHEET FOR THE APPLICATION OF LOAD CARRYING TROLLEY RAIL AND PROCESS TO PRODUCE THE 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 corrosion resistant coated structural steel and more specifically to cold rolled Aluzinc Coated Steel sheet, Non skin pass, Stretch leveled, 2.5mm thick Al-Zn coating, AZ150GSM, as per IS15961_2012 standard for the application of Load Carrying Trolley Rail. It minimizes the degreasing, phosphating, and powder coating. Aluzinc coating is formed by an alloy coating of Al (55%); Zn(43.4%) and Si(1.6%). This coating offers excellent corrosion resistance in many atmospheric conditions. The steel with Aluzinc coating can be laser cut and can be stamped to shapes. The Aluzinc coating has better wear resistance than other coating like galvanizing. In addition, the Aluzinc coating has six times higher corrosion resistance than galvanizing coating. The coated sheets are weld able, paintable, and resistant to heat up to 315 oC. Aluzinc coating may be made uniform and consistent in quality and finish.

BACKGROUND OF THE INVENTION
Aluzinc coating is a technique of providing a protective aluminum and zinc alloy coating on Steel or iron, to prevent it from rusting. Hot Aluzinc Coating process is one of the most common forms of metal coating. There is requirement of Aluzinc Coated material with AZ150 GSM coating, having Yield Strength 350~380MPa, Tensile Strength 430~500 MPa and Elongation of 20% min in 50mm gauge length, for the application of Load Carrying Trolley Rail. This current invention is about overcoming the challenges to achieve the Mechanical properties which is similar to the Galvanized material. The invention is about shifting the customer from galvanized product to Aluzinc Coated product without altering the properties & end application.

The Aluzinc coated steels are used in petrochemical industry, chemical industry and power plants for its resistance to corrosion, solar reflectivity associated with uniformity in coating, the coating is an insulator and resists heat and for HVAC power unit due to its resistivity. Electronic panels can be made of such Aluzinc coated steel. The Aluzinc coated steels are used in construction, roofing and flashing, industrial doors, fencing, garden shed etc. In the present invention, a high strength steel grade has been Aluzinc coated towards a load carrying trolley rail.

OBJECTS OF THE INVENTION

The basic objective of the present invention is to provide corrosion resistant structural steel and more specifically to Aluzinc coated, non-skin pass steel sheet with 2.5mm thickness, AZ150, as per IS15961_2012 having mechanical properties in specific range as, yield strength in the range of 350 to 380MPa, tensile strength in the range of 430 to 500 MPa and Elongation of 20% minimum.

Another object of the invention is to replace Galvanized 275 GSM plus powder coated material 40 micron with Bare Galvalume chrome free AFP having minimum salt spray requirements of 600 hrs for first red rust.

Further, the object of the present invention is to provide the above specific material to the application of load carrying trolley rail in the industrial racking segment.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to corrosion resistant structural steel having steel composition of

C - 0.05 to 0.08 % by wt. preferably 0.065 % by wt.;
Mn - 0.80 to 1.0 % by wt. preferably 0.9 % by wt.;
P-0.0 % to 0.02% by wt. preferably 0.019 % by wt.;
S- 0.0 to 0.025 % by wt. preferably 0.015 % by wt.;
Si-0.0 to 0.035 % by wt. preferably 0.011 % by wt.;
Al- 0.025 to 0.07% by wt. preferably 0.035 % by wt.;
N- 0.00to 0.007 % by wt. preferably 0.004 % by wt.;
Ti-0.0to 0.015 % by wt. preferably 0.0018 % by wt.;
Nb - 0.008to 0.015 % by wt. preferably 0.0085 % by wt.; and balance Fe,

Having corrosion resistant coating of Aluzinc and of yield strength of 350 MPa minimum preferably 350 to 380 MPa, Tensile Strength of 420 MPa minimum preferably 430 to 500 MPa; and Elongation 20 % minimum preferably 20 to 25 % in 50mm gauge length.

A further aspect of the present invention is directed to said corrosion resistant structural steel which is free of skin pass and stretch leveled having thickness in the range of 2.46 mm to 2.54 mm preferably 2.5 mm and zinc coating AZ150GSM preferably more than 150GSM and having minimum 140GSM for single spot both side and 70GSM for one side.

A still further aspect of the present invention is directed to said corrosion resistant structural steel having finish size of preferably 2.5X1475mm.

A still further aspect of the present invention is directed to said corrosion resistant structural steel wherein said corrosion resistant coating of Aluzinccomprises steel sheet of thickness ranging from 2.46 mm to 2.54 mm preferably 2.5 mm.

Another aspect of the present invention is directed to a process for manufacture of corrosion resistant structural steel as described above including:
i) Providing hot rolled (HR) coil having said steelcomposition;
ii) Carrying out HR coil slitting;
iii) Subjecting to pickling for removal of the oxide layer;
iv) subjecting to cold rolling including mechanical working of mild steel material to below its recrystallization temperature such as to reduce the thickness at cold rolling mills;
v) subjecting to step of Aluzinc Coating process involving (a) annealing (b) coating of cold rolled steel strip to increase corrosion resistance strip (c) stretch leveling to control the flatness of Aluzinc Coated steel strip and desired shape thickness having Yield Strength – 350MPa Minimum preferably 350~380 Mpa, Tensile Strength – 420 MPa minimum preferably about 430~500 MPa; and Elongation 20 % minimum in 50mm gauge length.

Yet another aspect of the present invention is directed to said process wherein said step of controlling flatness is carried out to control the thickness in the range of 2.46mm to 2.54mm preferably 5.5mm and subjecting the Aluzinc coated surface of the steel to step of passivation comprising passivation chemical treatment with a superficial layer of Cr, Chromic acid or any other passivation chemical.

A further aspect of the present invention is directed to said process wherein said step of cold rolling is carried out involving coils of sizes 2.46x 1470 mm to 2.54x 1480 mm preferably 2.5 mm x1475 weight 23 Mt to 30 Mt preferably about 24 Mt. , Input HR thickness 3.97 mm to 4.03 mm preferably about 4.0 mm , output thickness 2.42 mm to 2.49 mm preferably about 2.455mm achieve a reduction in the range of 35 % to 45 % preferably about 40% keeping the pickling tank concentration % in range 10~20% with rinsing tank PH >5.

A still further aspect of the present invention is directed to said process wherein said step of Aluzinc Coating on cold rolled steel strip comprising involving dipping said strip in an Aluminum- zinc based alloy bath comprising of Al % 53 % to 57 % preferably about 55 %, Zn % 40 % to 46 % preferably about 43.5 % and Si % 1.4 % to 1.8 % preferably about 1.5 %, Fe % 0.3 to 0.5 % preferably about 0.4%.

A still further aspect of the present invention is directed to said process wherein said step of Aluzinc Coating is carried out involving selective temperature control in various furnace sections including select exit temperatures comprising in Non-Ox Furnace (NOF) 600 0C to 700 0C preferably 6500C, Radiant Tube Furnace (RTF) 670 0C to 700 0C preferably 6800C for attaining annealing temperature, soaking furnace 670 0C to 700 0C preferably 6800C for soaking time 1 to 2 minutes and Jet Cooling Furnace (JCF) 570 0C to 600 0C preferably 5800C.

A still further aspect of the present invention is directed to said process wherein said step of Aluzinc Coating involve furnace operative parameters including subjecting coil of size of 2.46x1470 mm to 2.54x 1480 mm preferably 2.5 mm x1475 line steed of 40mpm to 55 Mpm preferably about 45 meters per minute, 60 TPH to 80 TPH preferably about 70 Mt./Hrs., Furnace tension 2000 kgf to 3000 kgf preferably about 2500 Kgf , Pot tension 3000 kgf to 4500 kgf preferably about 4000 kgf, Air Knife RPM 1650 to 2500 RPM preferably about 2000 RPM, Air Knife Pressure 60 to 80 m bar preferably about 75 m bar and air knife gap of 10 to15mm preferably about 12mm. The Air knife parameter can be adjustable according to line speed & online coating weight indicator.

A still further aspect of the present invention is directed to said process comprising passivation chemical treatment of the galvanized or galvalume surface with a superficial layer of Cr, Chromic acid or any other passivation chemical.

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

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows the process flow chart for producing the Aluzinc Coated steel according to the present invention.
Figure 2: shows the graphical plot of Coil No VG4ACI0637, VG4ACI0638 showing Strip Temperature at Exit in Deg. Centigrade at different Furnace Sections – Non-ox Furnace (NOF), Radiant Tube Furnace (RTF), Soaking Furnace (SF) and Jet Cooling Furnace(JCF).

DETAILED DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS AND EXAMPLE
The present invention is directed to corrosion resistant coated structural steel as Aluzinc coated steel sheet conforming to Galvalume YS350 grade steel having composition comprising
C -0.05 to 0.08 % by wt. preferably 0.065 % by wt.;
Mn -0.8to 1.0 % by wt. preferably 0.9 % by wt.;
P-0.0 % to 0.02% by wt. preferably 0.019 % by wt.;
S- 0.0 to 0.025 % by wt. preferably 0.015 % by wt.;
Si-0.0 to 0.035 % by wt. preferably 0.011% by wt.;
Al- 0.025 to 0.07% by wt. preferably 0.035 % by wt.; and
N- 0.00to 0.007 % by wt. preferably 0.004 % by wt.;
Ti-0.0to 0.015 % by wt. preferably 0.0018 % by wt.;
Nb - 0.008to 0.015 % by wt. preferably 0.0085 % by wt.;

which is Aluzinc coated steel with yield strength of 350 MPa minimum preferably 350 to 380 MPa, Tensile Strength of 420 MPa minimum preferably 430 to 500 MPa; and Elongation 20 % minimum. A further aspect of the present invention is directed to said Aluzinc Coated steel which is non-skin pass and stretch leveled, having thickness in the range of 2.46 mm to 2.54 mm preferably 2.5 mm and zinc coating AZ150GSM preferably more than 150GSM and having minimum 140GSM for single spot both side and 70GSM for one side in salt spray test.

Normally, the process of Hot Dip Galvanizing for this application, conventionally includes only Indirect heating of the strip in furnace by using RT (Radiant Tubes) in annealing furnace, but in this invention DFF (Direct Fired Furnace) section included before RT furnace. Again the general process includes pre-cleaning section before the RT furnace to ensure the surface cleaning of Raw material for better metallic coating adhesion, whereas the end application needs the intact coating adhesion during the routine movement of trolley on the rails, as gtargeted and achieved by present invention. The adhesion property of Aluzinc coating is inferior to currently being used galvanized material. But in this invention instead of cleaning section, the DFF section is used to burn & clean any impurities attached on surface and successfully achieved the 0T bend test quality & LFQ (Lock Forming Quality). The desired temperature in DFF section achieved by burner A/F ratio balancing.
And the raw material brightness controlled 85% min by pickling line parameters described in invention summary. DFF route is found to be cost beneficial for surface cleaning than pre cleaning section.

During the working in end application environment, there is chance of the material getting in contact with humid atmosphere frequently so the Aluzinc coating requirement given as single spot 140Gsm min. for both side and 70GSM min. for one side which covers about 40micron coating thickness. The Aluzinc coating of AZ150 GSM which is comparatively harder than galvanizing metal coating, can cause the edge waviness due to edge over coating phenomenon. This phenomenon is successfully reduced in present invention by optimizing the Air knife gap profile setting and controlling the aluminum zinc coating profile parallel along the width of strip.

The mechanical strength in conventional material: YS, 380Mpa~450Mpa % yield elongation about 13~18%. But the material will be bended and undergoes roll forming to make the rail. So to avoid the material fracture due to low elongation and higher thickness 2.5mm, the Target YS kept as 350~380Mpa & yield elongation as 20% min.
During initial trial the convention HR grade 71(SH41CLN), having Mn % 0.45max used and the Yield strength <350Mpa observed so to counter it the HR grade with chemical composition specified in HR coil details used after trial runs.

EXPERIMENTAL PROCEDURE
This invention deals with the trials conducted at Continuous Galvanizing Line (CGL4) at Applicant’s Vasind Plant consisting of following activities:
? Selection of suitable raw material
? Cold rolling
? Aluzinc Coating in continuous galvanizing line CGL4
? Mechanical Testing
? Test Result data compilation and analysis

The steel grade of above stated composition was produced through following process route:
Hot Rolled Coil?Hot Rolled Coil Slitting?Pickling?Cold rolling?Aluzinc Coating?Packing

Accompanying Figure 1 shows the process flow chart for producing the galvanized structural steel comprising of the following process steps.

Details of HR Coil:
HR No. Size (mm) Grade
VDNBCG2157 4.0 X 1480 97(JDHS 41A N)
VDI BCG 2141 4.0 X 1480 97(JDHS 41A N)

HR No. Heat No. %C %Mn %P %S %Si %Al %N
VDNBCG2157 B018111 0.0570 0.905 0.019 0.0120 0.011 0.034 0.0041
VDI BCG 2141 B018117 0.0630 0.885 0.011 0.0200 0.002 0.040 0.0050

Chemistry:

Details of CR Coil
HR No. CR No. Size (mm) Reduction %
VDNBCG2157 VL1ACI0113 2.46X 1475 38.5

Furnace Parameters:
Parameters Units Reading
Avg. Line Speed m / min 45
Avg. TPH Mt / Hrs. 75
Avg. DFF Deg. Centigrade 680
Avg. RTF Deg. Centigrade 680
Avg. Soaking Deg. Centigrade 685
Avg. Exit Deg. Centigrade 576
SPM load Ton Nil
Parameters Units Reading
SPM Elong. % Nil
TLL Elong. % 0.4
Spencer Blower Air % Top: 66; Bot : 66
Air knife Pressure rpm 2000
Air knife gap mm 12~15

Accompanying Figure 2 shows the graphical plot of Coil No VG4ACI0637, VG4ACI0638, Showing Strip Temperature at Exit in Deg. Centigrade at different Furnace Sections – Non-ox Direct fired furnace (NOF, DFF), Radiant Tube Furnace (RTF), Soaking Furnace (SF) and Jet Cooling Furnace(JCF).

The process of hot dip Galvanizing coating on Cold Rolled Strip with a layer of zinc to increase the corrosion resistance of Strip included
1. Annealing: Heating of CR strip up to recrystallization temperature, soaking the strip.
2. Aluzinc alloy Pot: Coating of Cold Rolled Steel strip with a layer of Aluminum & Zinc & to increase corrosion resistance of the strip.
3. Stretch Leveling: To achieve anti fluting property of the Galvanized steel strip & to get desired shape by applying tensile stress & bending stress.
4. Passivation: Chemical treatment of the Aluzinc Coated surface with a superficial layer of Anti Fingerprint, thin organic chemical passivation to improve corrosion resistance & Salt spray Test(SST) Hr. life.

The GL product obtained is to comply as follows:
Finish Size–2.5X1475mm

Mechanical Properties required for the end application of load carrying trolley rail
Yield Strength –350~380MPa
Tensile Strength -430~500MPa
Elongation -20 % (Min) In 50 mm Gauge Length.

150 GSM: Specific coating requirements as below,
Coating Class designation Minimum Coating Mass Gram per Square Meter
Total Both Surfaces One Surface
Triple Spot Single Spot Single Spot
AZ150 150 140 70

Properties of GP coils:
Cold Rolled full hard coil No. Galvalume Coil No Thick-ness
(mm) Width (mm) Mechanical Properties
Yield Strength (MPa) Tensile Strength(MPa) Elongation(%)
Required Actual Required (max.) Actual Required (min.) Actual
VL1ACI0113 VG4ACI0637 2.51 1275 350~380 365 430~500 495 20 24
VG4ACI0638 2.512 1274 350~380 368 430~500 490 20 23
A) Mechanical Properties

Tested Coating
Batch No. Minimum Coating Mass Gram per Square Meter
Total Both Surfaces One Surface
Triple Spot Single Spot Single Spot
VG4ACI0637 160 150 78
VG4ACI0638 155 152 75

It is thus possible by way of present invention to achieve top & bottom Coating configuration and mechanical properties as per requirement of end application & compliance with provisions as per IS 15961_2012. Aluzinc coated material can be used for the Load Carrying Trolley Rail Application in the industrial racking segment.
, Claims:We Claim:
1. Corrosion resistant structural steel having steel composition of

C - 0.05 to 0.08 % by wt. preferably 0.065 % by wt.;
Mn - 0.80 to 1.0 % by wt. preferably 0.9 % by wt.;
P-0.0 % to 0.02% by wt. preferably 0.019 % by wt.;
S- 0.0 to 0.025 % by wt. preferably 0.015 % by wt.;
Si-0.0 to 0.035 % by wt. preferably 0.011 % by wt.;
Al- 0.025 to 0.07% by wt. preferably 0.035 % by wt.;
N- 0.00to 0.007 % by wt. preferably 0.004 % by wt.;
Ti-0.0to 0.015 % by wt. preferably 0.0018 % by wt.;
Nb - 0.008to 0.015 % by wt. preferably 0.0085 % by wt.; and balance Fe,

having corrosion resistant coating of Aluzinc and of yield strength of 350 MPa minimum preferably 350 to 380 MPa, Tensile Strength of 420 MPa minimum preferably 430 to 500 MPa; and Elongation 20 % minimum preferably 20 to 25% in 50mm gauge length.
2. The corrosion resistant structural steel as claimed in claim 1 which is free of skin pass and stretch levelled having thickness in the range of 2.46 mm to 2.54 mm preferably 2.5 mm and zinc coating AZ150GSM preferably more than 150GSM and having minimum 140GSM for single spot both side and 70GSM for one side.
3. Corrosion resistant structural steel as claimed in any of claims 1 or 2 having finish size of preferably 2.5X1475mm.
4. Corrosion resistant structural steel as claimed in any of claims 1 to 3 wherein said corrosion resistant coating of Aluzinccomprises steel sheet of thickness ranging from 2.46 mm to 2.54 mm preferably 2.5 mm.
5. A process for manufacture of corrosion resistant structural steel as claimed in anyone of claims 1 to 4 including:
i) Providing hot rolled (HR) coil having said steelcomposition;
ii) Carrying out HR coil slitting;
iii) Subjecting to pickling for removal of the oxide layer;
iv)subjecting to cold rolling including mechanical working of mild steel material to below its recrystallization temperature such as to reduce the thickness at cold rolling mills;
v) subjecting to step of Aluzinc Coating process involving (a) annealing (b) coating of cold rolled steel strip to increase corrosion resistance strip (c) stretch levelling to control the flatness of Aluzinc Coated steel strip and desired shape thickness having Yield Strength – 350MPa Minimum preferably 350~380 Mpa, Tensile Strength – 420 MPa minimum preferably about 430~500 MPa; and Elongation 20 % minimum in 50mm gauge length.
6. The process as claimed in claim 5 wherein said step of controlling flatness is carried out to control the thickness in the range of 2.46mm to 2.54mm preferably 5.5mm and subjecting the Aluzinc coated surface of the steel to step of passivation comprising passivation chemical treatment with a superficial layer of Cr, Chromic acid or any other passivation chemical.

7. The process as claimed in any of claims 5 or 6 wherein said step of cold rolling is carried out involving coils of sizes 2.46x 1470 mm to 2.54x 1480 mm preferably 2.5 mm x1475 weight 23 Mt to 30 Mt preferably about 24 Mt. , Input HR thickness 3.97 mm to 4.03 mm preferably about 4.0 mm , output thickness 2.42 mm to 2.49 mm preferably about 2.455mm achieve a reduction in the range of 35 % to 45 % preferably about 40% keeping the pickling tank concentration % in range 10~20% with rinsing tank PH >5.

8. The process as claimed in anyone of claims 5 to 7 wherein said step of Aluzinc Coating on cold rolled steel strip comprising involving dipping said strip in an Aluminium- zinc based alloy bath comprising of Al % 53 % to 57 % preferably about 55 %, Zn % 40 % to 46 % preferably about 43.5 % and Si % 1.4 % to 1.8 % preferably about 1.5 %, Fe % 0.3 to 0.5 % preferably about 0.4%.

9. The process as claimed in anyone of claims 5 to 8 wherein said step of Aluzinc Coating is carried out involving selective temperature control in various furnace sections including select exit temperatures comprising in Non-Ox Furnace (NOF) 600 0C to 700 0C preferably 6500C, Radiant Tube Furnace (RTF) 670 0C to 700 0C preferably 6800C for attaining annealing temperature, soaking furnace 670 0C to 700 0C preferably 6800C for soaking time 1 to 2minutes and Jet Cooling Furnace (JCF) 570 0C to 600 0C preferably 5800C.

10. The process as claimed in anyone of claims 5 to 9 wherein said step of Aluzinc Coating involve furnace operative parameters including subjecting coil of size of 2.46x 1470 mm to 2.54x 1480 mm preferably 2.5 mm x1475 line steed of 40mpm to 55 Mpm preferably about 45 meters per minute, 60 TPH to 80 TPH preferably about 70 Mt./Hrs., Furnace tension 2000 kgf to 3000 kgf preferably about 2500 kgf , Pot tension 3000 kgf to 4500 kgf preferably about 4000 kgf, Air Knife RPM 1650 to 2500 RPM preferably about 2000 RPM, Air Knife Pressure 60 to 80 m bar preferably about 75 m bar and air knife gap of 10 to15mm preferably about 12mm. The Air knife parameter can be adjustable according to line speed & online coating weight indicator.

11. The process as claimed in any of claims 5 to 10 comprises passivation chemical treatment of the galvanized or galvalume surface with a superficial layer of Cr, Chromic acid or any other passivation chemical.

Dated this the 7th day of March, 2024
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199