Insights of Cold Rolling Processes
Programme Objectives:
➢ Cold Rolling Principle
➢ Process flow of Cold Rolling Mill
➢ Product & Application of Cold Rolled Sheet
➢ Defects in Cold Rolled Sheet
Date:16-07-2020
Time: 10:00 PM – 11:30 PM
Faculty: Binu Shankar Roy
Capability Development, Tata Steel Jamshedpur
Hot Rolling
Hot Rolling : Rolling above Re-Crystallization Temperature
o
• Steel recrystallizes in the range of 550 to 600 C
• Typically temperature of steels are kept withing 0.5Tm to 0.8 Tm, Where Tm is Melting point of steel
Recrystallized
Re-Crystallization Start Grain
Elongated Grains
As Cast Structure
Cold Rolling
Cold Rolling : Rolling below Re-Crystallization Temperature or room temperature
Typical range of cold rolling is less than 0.3 Tm where Tm is melting point of steel in degree Kelvin
Material Strain Hardens after Cold Rolling
Elongated Grains due to With more cold deformation
Equiaxed Grains
cold Deformation grain structure destroyed
Cold Rolling Process
Cold Rolling Technology
What is Cold Rolling ?
❖ Process by which hot rolled strip or stock is
introduced between rollers and then squeezed or compressed to the desired thickness
❖ Amount of strain introduced determines the properties of the finished product
Why is Cold Rolling done ?
❖ Good Formability
❖ Superior Surface Finish
❖ Reasonable Strength
❖ Close Dimensional Tolerance
Products
❖Hot Rolled Pickled & Oiled(HRPO)
❖Hot Rolled Skin Passed & Oiled (HRSPO)
❖Full Hard Cold Rolled (FHCR)
❖Cold Rolled Closed Annealed-(CRCA)
❖Galvanized
Cold Rolling Mill-CRCA Route
HR Coil
COUPLED PICKLING & TANDEM COLD MILL(PLTCM) ELECTROLYTIC CLEANING LINE(ECL)
SKIN PASS MILL(SPM)
H2 BATCH ANNEALING FURNACE(BAF)
RECOILING & INSPECTION LINE (RCL)
COIL PACKAGING LINE SHIPMENT
Cold Rolling Mill-Galvanizing Route
HR Coil
COUPLED PICKLING & TANDEM COLD MILL(PLTCM)
GALV. LINE FOR AUTO / APPLIANCES
RECOILING & INSPECTION LINE (RCL)
Continuous Galvanizing Line #2 (CGL#2)
GA & GI
GALV. LINE FOR ENGG / CONST. MATL. COIL PACKAGING LINE
GI
Continuous Galvanizing Line #1 (CGL#1)
SHIPMENT
Cold Rolling Mill-CRCA Route
HR Coil
COUPLED PICKLING & TANDEM COLD MILL(PLTCM) ELECTROLYTIC CLEANING LINE(ECL)
SKIN PASS MILL(SPM)
BATCH ANNEALING FURNACE(BAF)
RECOILING & INSPECTION LINE (RCL)
COIL PACKAGING LINE SHIPMENT
Grades of Cold Rolled Steel
❖ D/DD - Drawing/Deep Drawing Simple forming/bending applications
❖ EDD - Extra Deep Drawing Deep Drawn components
❖ IF (Interstitial Free) Critical Draw and Stretch Components in
terms of geometry of the component, type and
depth of draw and press parameters
❖ IFHS (Interstitial Free High Strength) For components involving draw and requiring
resistance against dent and impact
Pickling &Trimmer
TCM PL Entry
PL-TCM
Incoming Material Typical Conditions
❖ Incoming Strip Gauge: Min 2.0 mm Max 6.5 mm
❖ Incoming Strip Width: Min 800 mm Max1,580 mm
❖ Incoming Coil Weight: Max. 31 ton
❖ Coil Inner Diameter: 720 mm to 770 mm
❖ Nominal Coil Inner Diameter: 760 mm
❖ Maximum Coil Outer Diameter: 2100 mm
❖ Material Grade: Hot rolled low carbon steel of
CQ, DQ, DDQ, EDDQ, IF, IF-HSS and High strength
steel delivered from the Hot Strip Mill.
❖ Tensile strength: Min. 260 MPa for low carbon steel
Max. 780 MPa for high strength steel
PL-TCM
Exit Material Typical Conditions
❖ Strip Gauge: Min 0.25 mm. Max 3.2 mm.
❖ Strip Width: Min 800 mm
❖ Exit Coil Weight: Max. 31 ton
❖ Coil Inner Diameter: 610 mm
❖ Maximum Coil Outer Diameter: 2,100 mm
❖ Minimum Coil Outer Diameter: 1,000 mm
❖ Type of Wind: Over-wind only
PICKLING
Why is Pickling done ?
❖To remove scales and oxide layers present on the surface of hot
rolled steel Make the steel surface suitable for cold rolling
❖Scales and oxide layers are harder than steel and hence hinder the
process of cold rolling of low carbon steel
Oxide layers in HR Coils
02 - 04 % Fe2O3
12 - 15 % Fe3O4
80 - 85 % FeO
Base Metal
PICKLING
How’s scale and oxide removal are achieved?
❖Prior to Pickling, HR sheets are passed through Tension Leveler
unit, Which actually breaks scale layer in HR Sheet as well as
shape correction is also done in this process.
❖Hot rolled strip is passed through tanks containing hydrochloric
acid wherein the acid dissolves the oxide layer
❖The strip is then rinsed with water to remove any excess acid.
dried and the strip is ready for cold rolling
Tension
Leveller
Pickling
Section
Pickling Process Variables
❖ Temperature : Acid temperature of 80 to 85 degrees centigrade is maintained. This
ensures faster rate of reaction with the acid.
❖ Acid Concentration: Acid concentration in tanks influence the dissolution of scales and
oxides Lower concentration is maintained in the first tank and
increases in the subsequent tanks
❖ Line Speed : Controls the residence time of the strip in the bath
Oxide layer in Acid Bath
HCl
Base Metal
Chemical Reactions
• FeO + 2HCl = FeCl2 + H2O
• Fe2O3 + 6HCl = 2FeCl3 + 3H2O
• Fe3O4 + 8 HCl = FeCl2 + 2FeCl3 + 4H2O
• Fe + 2HCl = FeCl2 + H2 (gas)
• 2FeCl3 + Fe = 3FeCl2
New i-Box Pickling Technique
STRIP
ACID
2-4% 4-6% 6-8% 8 - 12 %
Feature of i-Box Pickling
Same principle and pickling performance as Jet Pickling Tank
– High Pickling Performance
Acid is constantly re-filled inside the box by means of the
pumping effect generated by running strip – Simple
Operation
No continuously operated Acid Pumps is required – Energy
Saving and Less Maintenance
6HI-5-Stand Tandem Cold Mill
Tension Reel
X-Ray Gauge
Shape Meter Roll
TANDEM COLD MILL
Tata Steel Capability
5 Stand 6Hi Tandem Cold Mill coupled to a Continuous Pickling Line (PLTCM)
Features
❖ Automated Shape and Gauge Control
❖ Thickness tolerance achievable - +/- 0.5% of thickness along Centre line with edge drop of
30 microns
❖ Mill Clean System.
Lubrication in Cold Rolling
Main function of the Cold Mill Lubricants:
• Reduction in Friction: Lubricants are needed to reduce the
Rolling Load, produces high quality strip surface with
reduction in Work roll wear.
• Cooling: Emulsion is used which contains 1.5 to 5% of Oil in
Water Solution, Water provides the necessary Cooling
whereas Oil provides lubrication
Emulsion
Hydro-Philic Lipo-Philic
Oil
Water
Emulsion
➢Emulsion contains around 10 to 15 chemical compounds
➢Easter and Mineral Oils contains major part
➢Some amount of fatty acid is also there
➢Antioxidants
➢Anticorrosive Agents
➢Anti staining Agent: Mainly Sulphur-compound
Electrolytic Cleaning Line(ECL)
Cleaning prior to annealing is required To remove:
• Oil
• Grease
• Iron fines
• Mill dirt
• Other undesired materials.
Batch Annealing Furnace(BAF)
Annealing requires
❖ Heating the cold rolled steel to the recrystallization temperature in an inert atmosphere.
❖ Soaking at this temperature for sufficient time for homogenization and necessary changes to occur
❖ Cooling at a predetermined rate
Process Variables
❖ Temperature
❖ soaking time
❖ cooling rate depending on the desired mechanical properties
Annealing Process
Cooling Hood
Heating Hood
Inner Cover
Convector Plate
Full hard Coil
Annealing Base
Batch Annealing Cycle
o
710 C
o
Temperature
550 C
HST CST
Cold Spot Temperature
Hot Spot Temperature
Time
Annealing Stages
Cold Working Recovery Recrystallization Grain Growth
Property
Annealing Temperature
Recovery
After
Cold Recovery
Worked Grain
Recrystallization
Nucleation of
Recrystallized
Grains
Complete Recrystallization
Formation of New
Strain free
Recrystallized grains
Grain Structure
Continuous Annealing Line
Continuous Annealing
Annealing Cycle
Temperature
1200
1000
Soaking
800 Control Cooling
600 Quenching
400
Over Ageing Cooling
200
100 200 300 400 500 600
Time , Second
COMPARISON BAF Vs CAPL
Parameters Batch Annealing Continuous Annealing
Chemistry Suitable for low Carbon low alloy steel Best suited for IF Steels
Uniformity of Variations between outer/ inner wraps Uniform over the length
Mechanical to center of the coil of the coil
Properties
Productivity Lower Higher
Properties with Lower hardness and YS Higher hardness and
identical YS
chemistry other Higher r Bar value
than IF Lower r Bar value
IF Steel Good properties Better properties
Properties achievable with longer achieved with much
cycle time. lower cycle
ANNEALING CYCLE TIMES (APPROX.) FOR
VARIOUS GRADES:-
Grades Cycle Time (Hr.)
• CQ 34
• D/DDQ 36
• EDD 49
• IF 52
Skin Passing/Temper Rolling
Tata Steel’s Capability
➢ Single Stand 4 Hi Skin Pass Mill
Unique features
➢ Skin Passing with temper fluid -Wet skin passing
➢ Ensures freedom from dirt/dents, any foreign particles on strip surface.
Skin Passing/Temper Rolling
Skin Passing is Done
➢ To achieve the optimum mechanical properties (Hardness, YS,)
➢ To prevent occurrence of stretcher strains in annealed steel
Recoiling and Inspection Line(RCL)
Prime function of RCLs are:
➢To inspect the coils for surface, shape and dimensional aspects.
➢ To part the coil as per customer requirement, when required.
➢ To improve the shape by using tension leveller, when required.
➢ To apply rust preventive oil
➢ To trim the coil as per customer requirement
Cold Rolled Grades and
Applications
FPTG, 48
CQ Grade
Chemistry Applications
C 0.10 % max
Mn 0.50 % max
S , Si 0.05 % max
P 0.04 % max
Ti/Nb -
Al 0.02 % min
Mechanical Property
YS -
UTS -
El -
HRB 55 – 65
R bar - Critical Success Factor
n - Hardness and Shape
FPTG, 49
DQ Grade ( SPC 270 C )
Chemistry Applications
C 0.08 % max
Mn 0.40 % max
S , Si 0.03 % max
P 0.03 % max
Ti/Nb -
Al 0.02 % min
Mechanical Property
YS 230 Mpa max
UTS 270 Mpa min
El 35 % min
HRB 55 max
R bar - Critical Success Factor
n - Mechanical Property, Shape
FPTG, 50
EDD Grade (SPC 270 D)
Chemistry Applications
C 0.05 % max
Mn 0.20 % max
S , Si 0.02 % max
P 0.02 % max
Ti/Nb -
Al 0.02 % min
Mechanical Property
YS 180 Mpa max
UTS 270 Mpa min
El 40 % min
HRB
R bar 1.60 min Critical Success Factor
n 0.20 min Good Mechanical Property
FPTG, 51
IF Grade (SPC 270 F – G)
Chemistry Applications
C 0.0035 % max
Mn 0.15 % max
S , Si 0.015 % max
P 0.02 % max
Ti/Nb 0.04/0.02
Al 0.02 % min
Mechanical Property
YS 170 Mpa max
UTS 270 Mpa min
El 45 % min
HRB -
R bar 1.75 min Critical Success Factor
n 0.22 min Good Mechanical & Surface Property
FPTG, 52
IFHS Grade
Chemistry Applications
C 0.004 % max
Mn 0.3 – 0.5%
S , Si 0.02 % max
P 0.04 – 0.07%
Ti/Nb 0.05
B 10 ppm
Mechanical Property
YS 180 - 240 Mpa
UTS 350 Mpa min
El 35 % min
HRB -
R bar 1.40 min Critical Success Factor
n - Good Mechanical Property and Surface
FPTG, 53
HSQ Grade (SPC 440)
Chemistry Applications
C 0.1 % max
Mn 1.50 %
S , Si 0.04 % max
P 0.02 – 0.06
Ti/Nb 0.01 to 0.03
Al 0.02 % min
Mechanical Property
YS Mpa
UTS 440 Mpa min
El 29 % min
HRB -
R bar - Critical Success Factor
n - Good Mechanical Property
FPTG, 54
Thank You !!!
