Claims:We Claim:

1. Galvanized structural steel comprising of steel composition having

C – 0.040 to 0.08 % by wt. preferably 0.06 % by wt;
Mn- 0.7 to 1.50 % by wt. preferably 1.00 % by wt;
P-0.0 % to 0.025% by wt. preferably 0.015 % by wt;
S- 0.0 to 0.02 % by wt. preferably 0.007 % by wt;
Si-0.0 to 0.03 % by wt. preferably 0.01% by wt;
Al- 0.020 to 0.06 % by wt. preferably 0.035 % by wt; and
Nb.- 0.005 to 0.020 % by wt. preferably 0.01 % by wt;
which is Zinc coated and of thickness in the range of 2.0 to 3.2 mm preferably 3.0 mm having Yield Strength minimum 450 MPa, preferable 470 MPa to 500 MPa, Tensile Strength minimum 480 MPa, preferable 500 MPa to 530 MPa, and Elongation minimum 10 % at 50 mm gauze length, preferable 18 % to 21% preferably.

2. The galvanised structural steel as claimed in claim 1 which is non-skin pass and stretch levelled having thickness of 2.0 to 3.2 mm. preferably 3.0 mm and zinc coating thickness more than 600 GSM, preferable in the range of 625 to 640 adapted for column post and grain silos.
3. The galvanised structural steel as claimed in anyone of claims 1 or 2 having finish size of 2.965 to 3.035 mm X 1250 to 1255 mm preferably 3.00 X 1250.
4. The galvanised structural steel as claimed in anyone of claims 1 to 3 comprising galvanised coils having thickness 3.00 mm, Width 1250 mm and zinc Coating GSM 630;
5. A process for manufacture of galvanized structural steel as claimed in anyone of claims 1 to 3 including:
i)providing HR coil of steel composition having
C – 0.040 to 0.08 % by wt. preferably 0.06 % by wt;
Mn- 0.7 to 1.50 % by wt. preferably 1.00 % by wt;
P-0.0 % to 0.025% by wt. preferably 0.015 % by wt;
S- 0.0 to 0.02 % by wt. preferably 0.007 % by wt;
Si-0.0 to 0.03 % by wt. preferably 0.01% by wt;
Al- 0.020 to 0.06 % by wt. preferably 0.035 % by wt; and
Nb.- 0.005 to 0.020 % by wt. preferably 0.01 % by wt;
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 galvanizing involving (a) annealing (b) coating of cold rolled steel strip to increase corrosion resistance strip (c ) stretch levelling to impart antifluting property of galvanized steel strip and desired shape involving tensile stress and bending stress and (d) passivation of the galvanized surface, preferably Chrome Free passivation with Min Salt Spray 600 Hrs (First Red rust) such as to produce the galvanized structural steel with Zinc coated and of thickness in the range of 2.965 to 3.035 preferably 3.0 mm and having Yield Strength minimum 450 MPa, preferable 470 to 500 MPa,Tensile Strength minimum 480 MPa, preferable 500 to 530; and Elongation minimum 10 % at 50mm gauge lengthpreferable 18 to 21%.
6. The process as claimed in claim 5 is directed to said process wherein said step of cold rolling is carried out involving coils of sizes 2.88 x 1250 to 2.94 X 1255 preferably about 2.915 X 1250 , length 850 to 860 Mtrs preferably about 851 Mtrs ,weight 24.5 Mt to 30.5 Mt preferably about 24.965 Mt. , Input HR thickness 2.8 to 4.0 mm mm preferably about 3.5 mm with cold reduction in the range of 15-25 %, preferably about 16 %.

7. The process as claimed in anyone of claims 5 or 6 involving a zinc bath comprising of Al % 0.12 % to 0.13 % preferably about 0.127 %, Pb % 0.07 % to 0.08% preferably about 0.073 % and Fe % 0.020 % to 0.03 % preferably about 0.025 % and rest is Zn
8. The process as claimed in anyone of claims 5 to 7 wherein said step of galvanizing is carried out involving select temperature control in various furnace sections including select exit temperatures comprising in Non-Ox. Furnace (NOF) 705 to 725 preferably 7150C,Radiant Tube Furnace (RTF) 727 to 747 preferably 7370C, soaking furnace 750 to 770 preferably 7610C and Jet Cooling Furnace (JCF) 595 to 615 preferably 6060C.
9. The process as claimed in anyone of claims 5 to 8 wherein said step of galvanizing involve furnace operative parameters including subjecting coil of size 2.00 x1250 mm to 3.2 x 1250 mm preferably 3.00*1250 mm to line steed of 24 mpm to 28 mpm preferably about 25.6 meters per minute 40 TPH to 50 TPH preferably about 45 Mt./Hrs, Furnace tension 1880 Kgf to 1920 Kgf preferably about 1900 Kgf, Pot tension 3950 Kgf to 4050 Kgf preferably about 4000 Kgf, Air Knife RPM 1650 to 1710 RPM preferably about 1680 RPM, Air Knife Pressure 0.2 to 0.21 kg/cm2 preferably about 0.203 kg/cm2 and air knife gap 475 to 495 preferably about 480-488 mm.

Dated this the 29th day of November, 2021
Anjan Sen
Of Anjan Sen & Associates
(Applicants’ Agent)
IN/PA-199
, 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 :
GALVANIZED STRUCTURAL STEEL WITH IMPROVED CORROSION RESISTANCE AND PROCESS FOR ITS MANUFACTURING.



2 APPLICANT (S)

(i) Name : JSW STEEL LIMITED;

Nationality : An Indian Company.

Address : Dolvi Works, Geetapuram, Dolvi, Taluka Pen, Dist. Raigad, Maharashtra-402107,India; Having the Registered Office at
JSW CENTRE,BANDRA KURLA COMPLEX,BANDRA(EAST), MUMBAI-400051, STATE OF MAHARASHTRA, INDIA.


(ii) Name: JSW STEEL COATED PRODUCTS LIMITED;

Nationality: An Indian Company.

Address: Tarapur; B-6, Tarapur M.I.D.C. Industrial Area, Navapur Road, BOISAR-401205, STATE OF 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
Present invention relates to development of cold rolled Galvanized Structural Steel and more specifically to Galvanized, Non skin pass, Stretch leveled, 3.0 mm thick, Zinc Coating 600 GSM, Structural Steel Grade material for the application of Columnpost and Grain Silos.

BACKGROUND OF THE INVENTION
Galvanizing is a technique of coating a protective Zinc coating on Steel or iron, to prevent it’s rusting. The usual practice to produce galvanized steel is through hot dip galvanizing method Zinc acts as a sacrificial material protecting the base metal iron from corroding or when scratch is formed. Galvanized steel in present era plays an important role in everyday lives. It has various field of usage such as transport, construction, power transmission, and where ever long life is needed. Preheated steel strip coming from the annealing furnace is passed through a molten zinc bath at 460°C. The thickness of the film deposited on to the strip as it emerges from the bath is controlled by jet stripping, which consists in forcing excess zinc to flow back in to the bath by directing a high velocity and horizontally extended gas jet at the moving strip.

Corrosion resistance:
Corrosion reactions require four components: viz., an anode, a cathode, an electrical circuit and an electrolyte. Galvanic corrosion is the corrosion that results when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte. The difference in electrical potential that exists between the different metals serves as the driving force for electrical current flow through the electrolyte. This current results in corrosion of one of the metals. The larger the potential difference, the greater the probability of galvanic corrosion. Galvanic corrosion only causes deterioration of one of the metals. The less resistant, active metal becomes the anodic corrosion site. The stronger, more noble metal is cathodic and is protected. When zinc and steel are in contact in the presence of an electrolyte, a current will flow from the steel to the zinc, so that the zinc becomes an anodic electron - producing region while the steel is cathodic and consumes electrons, preventing it from combining with oxygen and forming rust. This property of zinc is used in many applications as a galvanic protector of steel. The zinc coating also acts as a barrier, further protecting the steel.

The purpose of this Development was to add high strength and High Durable Galvanized product in product basket and supplying for application of Solar mounting structures & Grain Silos.

Present invention thus develop cold rolled structural steel product to cater to requirement of Galvanized structural steel having Non skin pass, Stretch leveled, 3.0 mm thick, Zinc Coating 600 GSM suitable complying to the requirement of AS 1397 G450 &IS 277 2018 GP 450 MPa. Coating Z-600 GSM, suitable for application in column post for solar power plant installations and grain silos and the like with improved corrosion resistance, to add new product in existing capability, and develop GI Higher thickness & 600GSM zinc coating.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide cold rolled Galvanized Structural Steel which is processed as Galvanized, Non skin pass, Stretch leveled, 3.0 mm thick, Zinc Coating 600 GSM.

A further object of the present invention is directed to provide cold rolled Galvanized Structural Steel Grade material for the application of Column post and Grain Silos.

A still further object of the present invention is directed to provide cold rolled Galvanized structural steel which conforms to complying to the requirement of as per as 1397 Grade G450 & IS 277 2018 Grade GP 450, Coating Z-600 GSM.

A still further object of the present invention is directed to provide cold rolled Galvanized structural steel which is subjected to Stretch Levelling to achieve anti-fluting property of the Galvanized steel and to get desired shape by applying tensile stress & bending stress.

A still further object of the present invention is directed to provide cold rolled Galvanized structural steel wherein the Zn coating is further subjected to passivation chemical treatment of the Galvanized or Galvalume surface with a superficial layer of Cr, chromic acid or any other passivation chemical to improve corrosion resistance.

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

C –0.040 to 0.08 % by wt. preferably 0.06 % by wt;
Mn- 0.7 to 1.50 % by wt. preferably 1.00 % by wt;
P-0.0 % to 0.025% by wt. preferably 0.015 % by wt;
S- 0.0 to 0.02 % by wt. preferably 0.007 % by wt;
Si-0.0 to 0.03 % by wt. preferably 0.01% by wt;
Al- 0.020 to 0.06 % by wt. preferably 0.035 % by wt; and
Nb.- 0.005to0.020 % by wt. preferably 0.01 % by wt;
which is Zinc coated and of thickness in the range of 2.0-3.2mm preferably 3.0 mm having Yield Strength minimum 450 MPa MPa preferably about 470-500 MPa,Tensile Strength minimum 480 MPa preferably about 500-530 MPa; and Elongation minimum 10% at 50 mm gauze length preferably minimum 18-21%.

A further aspect of the present invention is directed to said galvanised structural steel which is non-skin pass and stretch levelled having thickness of 2.0-3.2 mm preferably 3.0 mm and zinc coating more than 600 GSM, preferable 625 GSM to 640 GSM adapted for column post and grain silos.

A still further aspect of the present invention is directed to said galvanised structural steel having finish size of preferably 3.00 X 1250.

A still further aspect of the present invention is directed to said galvanised structural steel comprising galvanised coils having thickness 3.00 mm, Width 1250 mm and zinc Coating GSM 630 ;

Another aspect of the present invention is directed to a process for manufacture of galvanized structural steel as described above including:

i)providing HR coil of steel composition having
C – 0.040 to 0.08 % by wt. preferably 0.06 % by wt;
Mn- 0.7 to 1.50 % by wt. preferably 1.00 % by wt;
P-0.0 % to 0.025% by wt. preferably 0.015 % by wt;
S- 0.0 to 0.02 % by wt. preferably 0.007 % by wt;
Si-0.0 to 0.03 % by wt. preferably 0.01% by wt;
Al- 0.020 to 0.06 % by wt. preferably 0.035 % by wt; and
Nb.- 0.005 to 0.020 % by wt. preferably 0.01 % by wt;
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 galvanizing involving (a) annealing (b) coating of cold rolled steel strip to increase corrosion resistance strip (c ) stretch levelling to impart antifluting property of galvanized steel strip and desired shape involving tensile stress and bending stress and (d) passivation of the galvanized surface, preferably Chrome Free passivation with Min Salt Spray 600 Hrs (First Red rust), such as to produce the galvanized structural steel with Zinc coated and of thickness in the range of 2.0mm to 3.2 mm preferably 3.0 mm and having Yield Strength of minimum450 MPa, preferably about 470-500MPaTensile Strength minimum 480 MPa, preferably 500-530 MPa; and Elongation 10% minimum at 50 mm gauze length, preferable 18% to 21%.

A still further aspect of the present invention is directed to said process wherein said step of cold rolling is carried out involving coils of sizes 2.88 x 1250 to 2.94 X 1255 preferably about 2.915 X 1250 , length 850 to 860 Mtrs preferably about 851 Mtrs ,weight 24.5 Mt to 30.5 Mt preferably about 24.965 Mt. , Input HR thickness 2.8 to 4.0 mm mm preferably about 3.5 mm with cold reduction in the range of 15-25 %, preferably about 16 %.

A still further aspect of the present invention is directed to said process involving a zinc bath comprising of Al % 0.12 % to 0.13 % preferably about 0.127 %, Pb % 0.07 % to 0.08% preferably about 0.073 % and Fe % 0.020 % to 0.03 % preferably about 0.025 % and rest is Zn.

Another aspect of the present invention is directed to said process wherein said step of galvanizing is carried out involving select temperature control in various furnace sections including select exit temperatures comprising in Non-ox Furnace (NOF) 704 0C to724 0C preferably 7140C ,Radiant Tube Furnace (RTF) 725 0C to 745 0C preferably 7370C, soaking furnace 7500C to 770 0C preferably 7610C and Jet Cooling Furnace (JCF) 595 0C to 6150C preferably 6060C.

Yet another aspect of the present invention is directed to said process wherein said step of galvanizing involve furnace operative parameters including subjecting coil of size of 2.00 x1250 mm to 3.2 x 1250 mm preferably 3.00*1250 mm to line steed of 24 mpm to 28 mpm preferably about 25.6 meters per minute 40 TPH to 50 TPH preferably about 45 Mt./Hrs, Furnace tension 1880 Kgf to 1920 KgfKgf preferably about 1900 Kgf , Pot tension 3950 Kgf to 4050 Kgf preferably about 4000 Kgf, Air Knife RPM 1650 to 1710 RPM preferably about 1680 RPM, Air Knife Pressure 0.2 to 0.21 kg/cm2 preferably about 0.203 kg/cm2 and air knife gap 475 to 495 preferably about 480-488 mm.

The above and other objects and advantages of the present invention is described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1: process flow chart for producing the galvanized structural steel according to present invention.

Figure 2: shows the graphical plot of Coil No TG3A1E0862 to TG3A1E0865, 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).

Figure 3: shows the screen shot of stress-strain diagram of the processed GI coils complying to the requirement of AS 1397 Grade g450 &IS 277 2018 GP 450.

Figure 4(a-c): showing the microstructure of top and bottom surfaces of base steel metal and coated surfaces.

Figure 5: shows application of the invented steel in column post for solar segments and grain silo structures.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
The present invention is directed to provide cold rolled Galvanized Structural Steel which is processed as Galvanized, Non-skin pass, Stretch leveled, 3.0 mm thick, Zinc Coating 600 GSM, complying to the requirement of as per AS1397 & IS 277 2018 Grade GP 450, Coating Z-600 GSM.

Experimental procedure:
This report deals with the trials conducted at Galvanizing Line(CSD3) at Tarapur Plant of Applicants through following activities:
• Selection of suitable raw material

• Cold rolling

• Galvanizing in CSD

• Mechanical Testing

• Data compilation and analysis

The inventive steel grade was produced through following Process Path:
Hot Rolled Coil (HR coil) ------> HR Coil Slitting ------> Pickling ------> Cold Rolling ------> Galvanizing ------> Packing

Accompanying Figure 1 shows the flow process chart for producing the galvanized structural steel according to present invention showing detailed process steps.

Detail of HR COIL:
a. Raw Material HR Grade 97(JDHSH41AKN) selected for applying the above steps including galvanizing process.
Chemistry: HR Grade: IS 11513 CR6 from applicant’s JSW Steel Limited, Dolvi plant.

CR coil no HR Coil No Size(mm) C% Mn% P% S% Si% Al% Nb%
TM1A1E0376 2120200706 3.50x 1250 0.06 0.975 0.012 0.007 0.005 0.034 0.012
TM1A1C0420 2110117107 3.50 x 1250 0.052 1.034 0.016 0.006 0.009 0.028 0.010

b. ColdRolling Detail:

Coil No.

Size(mm*mm)
Length

Mtr.
Weight

Mt. Input
Thick. mm
OutPut

Thick.mm %
Reduction
TM1A1E0376 2.915X1250 851 24.965 3.49 2.915 166
TM1A1C0420 2.915 X 1250 982 24.800 3.49 2.915 16

c. Galvanizing:
Zinc Bath Chemistry: following table shows the bath chemistry showing level of elements other than balance amount being Zinc:

Bath Chemistry
Al% Pb.% Fe.%
0.127 0.073 0.025

Furnace parameters:

CR NO TM1A1E0376 TM1A1C0420 UOM
GI Coil No. TG3A1E0862TO0865 TG3A1C1162
Size 3.00*1250 3.00*1250 mm X mm
Line Speed 25.6 24 Meter per minute
TPH 45.2 42.4 Mt./Hrs.
NOF 714 711 Degree Centigrade
RTF 737 740 Degree Centigrade
SF 761 768 Degree Centigrade
JCF 606 606 Degree Centigrade
Furnace Tension 1900 1900 Kgf
Pot Tension 4000 4000 Kgf
AirKnife RPM 1680 1680 RPM
AirKnifePressure 0.203 0.203 (kg/cm2)
AirKnife Gap 480-488 479-489 Mm

Accompanying Figure 2 shows the graphical plot of Coil No TG3A1E0862 to TG3A1E0865, 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).

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 desired temperature, soaking the strip.
2. Zn Pot: Coating of Cold Rolled Steel strip with a layer of Zinc & alloy to increase corrosion resistance of the strip.
3. Stretch Levelling: To achieve antifluting property of the Galvanized steel strip & to get desired shape by applying tensile stress & bending stress.
4. Passivation: Chemical treatment of the Galvanized or Galvalume surface with a superficial layer of Cr, chromic acid or any other passivation chemical to improve corrosion resistance.

c. The GI product obtained is to comply as follows:
Finish Size–3.00X1250mm

Mechanical Properties Required for AS 1397 Grade G 450
Yield Strength - 450 MPa (Min)
Tensile Strength - 480 MPa (Min)
Elongation -10 % in 50 mm Gauge Length.

Mechanical Properties Required for IS 277 Grade GP450
Yield Strength - 450 MPa (Min)
Tensile Strength - 480 MPa (Min)
Elongation -9 % in 50 mm Gauge Length.

Zinc Coating Mass :600 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
Z600 600 540 240

d. Testing and conclusions:
The galvanized structural steel produced according to the above stated process was subjected to mechanical testing and the results are shown in following table:

Zinc Coating in GSM : Tested Coating weight values Given Below
Coil Number Minimum Coating Mass g/m2
Total Both Surfaces One Surface
Triple Spot Single Spot Single Spot
TG3A1E0862 630 560 255
TG3A1E0863 640 570 260
TG3A1E0864 625 565 260
TG3A1E0865 630 570 260

Details of passivation treatment carried out as follows:
Passivation: Chrome Free Passivation:
Chromium(VI)-free passivation for galvanized and alloy – galvanized steel strip to improve bare corrosion protection.

Scope:
Product Details: Gardo® T P 1 0 7 2 4 / 1

Product information: chromium(VI)- and fluoride-free passivation,
Application: by coater or squeezing rollers
Coating weight: between 15 - 25 mg/m² chromium
Suitable for: galvanized steel.
Physical properties:
Appearance: acidic aqueous solution
Colour: dark green
pH value (10 g/L, 20 °C): 2.9
Density (20 °C): 1.161 g/cm³.
Operating Parameters :
Product Concentration Application through PMT 0C Coiling Temperature 0C
Gardo TP 45% Chemical Coater 70 45

Chromium Coating: Mg per meter square & Salt Spray Results:
Coil No Thickness (MM) Chrome Coating mg/m2 Salt Spray as per ASTM B 117
Top Bottom
TG3A1E0862 3.0 18.0 22.0 675 Hrs -2 % First Red Rust
TG3A1E0863 3.0 22.0 24.0 672 Hrs -2 % First Red Rust
TG3A1E0864 3.0 25.0 22.0 696 Hrs -2 % First Red Rust
TG3A1E0865 3.0 19.0 22.0 675 Hrs -2 % First Red Rust

Mechanical Properties:
Minimum Mechanical Properties as per AS 1397 Grade G450 Note 3 as follows,
Yield Strength- 450 MPa (Min), Tensile Strength - 480 MPa (Min), Elongation -10 % In 50 mm Gauge Length.

Actual tested values given below Table.

Galvanized Coil Nos Thickness Width Zinc Coating GSM Weight Sample Yield Strength Tensile Strength MPa % Elongation in 50 GL
mm mm Mt MPa
TG3A1E0862 3.00 1250 630 6.185 Edge 470 512 21
Center 484 532 20
TG3A1E0863 3.00 1250 630 6.13 Edge 475 510 20
Center 490 525 19
TG3A1E0864 3.00 1250 630 5.91 Edge 485 510 20
Center 495 530 18
TG3A1E0865 3.00 1250 630 6.345 Edge 480 520 20
Center 495 525 19

Accompanying Figure 3 shows the screen shot of stress-strain diagram of the processed GI coils are complying to the requirement of AS 1397 Grade G450 & IS 277 2018 Grade GP 450

Accompanying Figure 4(a-c): showing the microstructure of top and bottom surfaces of base steel metal and coated surfaces. Microstructure of the basemetal in 500x magnification of optical microscope shows ferrite matrix with 10 percent of cementite distributed along the grain boundaries which gives the material the required strength.

e. Results/Conclusion:
Mechanical properties Yield strength, Tensile strength & Elongation are achieved as per AS 1397 GRADE G450& IS 277 G450, Zinc Coating Z-600 GSM. We can supply the material for column post application for Solar Segment.

Benefit:
Galvanized, Non-skinpass, Stretch leveled material, as per AS 1397 GRADE G450 or IS 277 G450 can be used for the structural Application. End Application: Grain Silos and Structural application[Refer Figure 5].

Present invention thus provides galvanized steel sheet having Chrome free passivation suitable for the Grain Silo complying to the ROHS norms & higher strength steel with minimum elongation 16 %, beyond the requirement given in the standard for Grade Ys 450 OR G450, the requirement of elongation for G450 is 10 % whereas the actual elongation in this development is =18 %. & ROHS, Chrome Free passivation with Min Salt Spray 600 Hrs (First Red rust).