1. in Surface Treatment of Steel Sheets
Recent Developments
in Surface Treatment of Steel Sheets
Tae-Yeob Kim
Coating & Electrical Steel Research Group
Technical Research Laboratories
Pohang Iron & Steel Co. Ltd.

2. Contents Introduction Facilities & Products Technical Trends
Technical Developments
Prospects

3. Target Properties of Surface Treatment
Characteristics
Mechanical
Hardness, Lubrication, Strength (tensile, bending)
Electrical
Conduction / Insulation, Electromagnetic Shielding
Magnetism, Electrical Contact
Optical
Gloss, Fastness, Chromism, Piezoelectricity, Reflectibility
Thermal
Thermal Conduction / Insulation, Thermoelectricity
Physical
Adhesion, Roughness, Porosity, Soldering, Air Tightness
Chemical
Corrosion Resistance, Printability, Pollution Prevention
Other
Color, Anti-fogging, Hydrophillic / Hydrophobic

4. Film Formation Rates of Various Methods

5. Facilities – CGL (Continuous Galvanizing Line)
Company
Capacity
Products
Remarks
POSCO
# 1
1988
360
GI, GA
wide strip
# 2
1991
# 3
1996
300 GI
Appliance
# 4
2000
450
Automotive
PGL
1990
200
GI (hot)
> 4.5t
Pohang Steel
1989
GI, Al
Union Steel
1980
GI, Galvalume
Dongbu
Steel
GI, GA, Al
Kodae
1998
350
GI, GA, Galvalume
Hyundai Pipe
400
Dongkuk Steel
150

6. Facilities – EGL / ETL (Electrolytic Galvanizing / Tinning Line)
Company
Capacity
Products
Remarks
POSCO
#1 EGL(P)
1986
300
Zn, Zn-NI
Organic
#1 EGL(K)
1990
400
Zn, Zn-Fe
Wide strip
#2 EGL(K)
1997 Zn
Appliances
ETL (P)
190 TP
Revamping(’02)
DongBu
Steel
#1 ETL (I)
1978
180
TP, TFS
#2 ETL (K)
1999
Insoluble, MSA
Dongyang
Tinplate
# 1 ETL
1974 75
TP, EG, Cu
# 2 ETL
1977
125
# 3 ETL
1988
150
Hyundai Pipe (EGL)
1998
450
Zn, Zn-Ni
Automotive
Union Steel (EGL)
275
Dongshin (EGL)
120
Shinwha (ETL)
100

7. Facilities – CCL (Continuous Color Coating Line)
Company
Capacity
Products
Remarks
Pohang
Steel
# 1
1989
100
PCM
# 2
1993
PCM, Al-color
Appliances
# 3
1997 70
PCM, Laminate
Union
1979
DongBu
1980
1995
Dongshin 50
Laminate
PCM, Print
3coat-3bake 30
Sheet coating
# 4

8. Total (Korea) - capacity
Capacity of Japanese Mills (’99)
Company
Works CG EG TP
TFS
NSC
Kimitsu
901
577 -
Nagoya
867
179
159
229
Hirohata 73
367
225
Yawada
334
133
392
210
NKK
Keihin
203
Fukuyama
839
521
232
285
KSC
Chiba
170
168
322
Mizushima
219
258
Sumitomo
Kashima
385
431
Yakayama 78 61
Kobe
Kakogawa
318
447
Nissin
Ishikawa Oh
619
212
Doyokohan
Kutamatsu 85
139
287
Others
2,420
0.3
Total (Japan)
7,859
3,440
1,469
1,144
Total (Korea) - capacity
3,770
1,845
1,120

9. Products – Hot-dip Product Coating Layer Coating Weight (g/m2)
Performances
Applications
Galvanized
(GI) Zn
Steel
60 ~ 300
Corrosion resistance
(Economical)
Construction
Automotives
Galvannealed
(GA)
Zn-Fe Alloy
(10~12% Fe)
30 ~ 90
Weldability
Paintability
Chassis
Flash
Fe-15%Zn GA
3 ~ 6
/ 20 ~ 60
Electropaintability
Automotive
(Outer Panel)
Zn-Al
(Galvalume)
Zn-55% Al
60 ~ 200
Weather durability
Heat resistance
Stove
(Galfan)
Zn-5% Al Al
20 ~ 75
Exhaust System
High-temp. Parts

10. Products – Electroplating
Coating Layer
Coating Weight
(g/m2)
Performances
Applications
Electrogalvanized
(EG) Zn
Steel
3 ~ 50
Corrosion resistance
Formability
Appliances
Automotives
Zn- Alloy
(Zn-Ni, Zn-Fe)
Zn-15% Fe
or Zn-12% Ni
20 ~ 40
Weldability
Paintability
Double-layer
Fe-15%Zn
Zn-Fe
3 ~ 5
/ 20 ~ 40
+ Paintability
Outer panel
Terne
Pb-8% Snl
40 ~ 75
Fuel resistance
Solderbility
Fuel Tank
Radiator
Tinplate
(TP)
Snl
Alloy Layer
1.1 ~ 11.2
Can
Tin-free Steel
(TFS)
Cr Oxide
Metallic Cr
50 ~ 150
mg/m2
Lacquer adhesion
(Econimical)
(without welding)

11. Products – Organic Coating
Coating Layer
Film
Thickness
Performances
Applications
Pre-coat Steel
Plastisol
Phosphate
CG or EG
150 ~ 200 
Decoration
Weather durability
Outdoor panel
Appliances
Anti-fingerprint
Resin
Chromate EG
1 
Anti-fingerprintability
Corrosion resistance
Computer case
Self-lublicaion
Lublicability
Motor case
Organic-coated
Zn-Ni
Spot weldability
Automotive panel
(inner)
Film Laminated
(Adhesive)
Adhesive
50 ~ 100 
Furniture
Internal panel
Laminate Steel
(Heat Sealing)
PET (cry.)
PET (amor)
TFS
15 ~ 25 
Permeation resistance
Formability
Can

12. Technical Trends - Automotives
‘80
‘90
2000~
Panel
Fuel Tank
Exhaust System GA
Zn-Ni, Zn-Fe
Organic Coated
(thick)
Flash (Fe-Zn/GA)
Double-layer
(thin)
Terne
Zn-X
Sn-Zn
Al (hot-dip) Zn
Al / STS
STS

13. GI (High Corrosion Resistant)
Technical Trends – Electrical Appliances / Construction
‘80
‘90
2000~
Electrical
Appliance
Construc
-tion
Phosphate
Chromate
Post-coat
Anti-fingerprint
Self-lublication
Multi-funtional
GI (SR)
Cr-free
GI (High Corrosion Resistant)
GI (SM)
GALVALUME
Lubricative
Post-treatment
GALFAN
Pre-coat

14. Technical Trends – Canmaking
~’70
‘70
‘80
‘90
2000~
Can-making
Substrate
Adhesive
Welding
3-P Laminate TP
TNS
LTS
TFS - Cr
TFS - Ni
Shaped Can
Weldable TFS
Ni-free LTS
Soldering
Al D&I
Steel D&I
2-P Laminate

15. Electrolytic Degreasing Induction Heating (LF, RF)
Development of Operation Technology - CGL
Pre-treatment
Alkaline Degreasing
Electrolytic Degreasing
Furnace
NOF
All RTS
Zn Pot
WC-Co coating
WC-WB-Co
Al2O3-base Oxide
Total Al
Effective Al
Pb-less Pot GA
Air Wiping
N2 Wiping
SPM
Gas Heating & Soaking
New Air
Knife
Induction Heating (LF, RF)
Gas Jet
Mist, Fog Spray
POSGAL
SBT
EBT, EDT, LDT
E/M
Levitation

16. : Increase during GA operation
GA for Automotive External Panels
- Surface Quality : Minimize Dross Formation
- Powdering : Optimize Degree of Alloying
Crack
Initiation
Propagation
Detach
of Layer
Compressive
Stress
ζ, δ1 (P) phase
δ1 phase
Steel Substrate
Γ1 phase 02
Air wiping
Top Dross
2Zn + O2 → 2ZnO
5Al + 2FeZn7 → Fe2Al5 + 14Zn
Dissolution of Fe
Fe + 7Zn → FeZn7 (Bottom Dross)
: Increase during GA operation
FeZn7
ZnO + Fe2Al5

17. Electromagnetic Hot-dip Galvanizing
E/M Wiping
- Downward Wiping via Linear Induction Motor
- Precise contol of coating weight
E/M Levitation
- Vertical Galvanizing using MHD (Magneto-Hydrodynamic) Seal
- Small Pot / Multi Pot (Melt Circulation System)
- Eliminate the sources of surface defects F B U
Strip
Zinc film
Linear
inductor
Zinc pot
MHD Inductor roll GI GA
GALFAN
MHD Channel

18. Development of Operation Technology - EGL
②Charge transfer
Cathode
Zn Zn2+
① Mass Transfer
Zn (ad-atom)
③ Electrocrystallization
Zn (crystalline)
Key Technologies
High Current Density Operation
Limit Current Density : iL = nFCoDo/
∵ Mass Transfer Rate ≪Charge Transfer Rate
Counter Flow or Hydrodynamic Cell Design
Low Power Consumption ( W = i x V = i2 x R )
∵ Cell resistance ≈Electrolyte Resistance
Narrower Anode Gap

19. Modification of Plating Cells
High Current Density Operation
- Counter Flow
- Hydrodynamic Cell
- Narrow Anode Gap (Low Voltage)
Uniform Coating Thickness Profile
- Edge Mask
Stable Electrical Connection
- Hold-down Roll
One-side Coating
- Gravitel, VHC

20. Pb-free Coated Steel for Fuel Tank
- Japan : Pb emission from dust of scapped car (3.00.3 ppm)
- EU : Ban of heavy metallic wastes from scrapped car (2003)
Resin : 1.0~3.0m
Chromate: 50~150mg/m2
Zn-Ni : 20~30g/m2
Steel substrate
 Fuel Resistance
 Corrosion Resistance
 Deep Drawability
 Weldability
 Paintability
Formability
Weldability
Corrosion Resistance
LDR
LDH
F.C.
Spot
Seam
Solder
SST(600h)
Fuel(6M)
Pb-Free
Coat
2.12
36.6
0.121
5.2~8.2 kA
12~16 kA
60%
Red Rust
< 1%
No Rust
Terne
(NSC)
2.11
36.5
0.133
6~8
13~16
80%
<1%

21. Development of Operation Technology – ETL
Facility
Technical Trends
Purposes
Present
Future
Plating Cell
Ferrostan (Soluble)
Halogen (Soluble)
Ferrostan
(Insoluble)
Prevent edge overcoating
Electrolyte
PSA
(Phenol Sulfonic Acid)
MSA, (TSA)
Environment-friendly
High current density
Reflow
Conduction
Combination
(Induction)
Uniform temperature profile
Chemical Treatment
Cr6+-base
(Na2Cr2O7.2H2O, CrO3)
Cr3+, Cr-free

22. Electrotinning Using Insoluble Anode System
- Plating Cell : Insoluble Anode,Edge Mask
- Sn Dissolution Unit
Soluble Anode System
Anodic Rx Sn →Sn2+ + 2e- (100%)
Cathodic Rx Sn2+ + 2e- →Sn (92 ~ 95%)
2H+ + 2e- →H2 (5 ~ 8%)
Insoluble Anode System
Anodic Rx H2O →2H+ + 1/2 O2 + 2e- (100 %)
Cathodic Rx Sn2+ + 2e- →Sn (92 ~ 95%)
2H+ + 2e- →H ( 5 ~ 8%)
Dissolution Unit Sn + 2H+ + 1/2 O2 →Sn2+ + H2O
Company
Dissolution Unit
Insoluble Anode
Developing Stage
NSC
Fluidized Bed + O2
Pt / Ti
Commercial
TKS + Andritz ?
Lab (pilot)
Corus + Lea Ronal
Membrane Reactor
IrO2 / Ti

23. Laminate Steel Sheet - Japan : Beverage Can (TULC : Toyo Ultimate Can)
- EU : Food Cans (Corus, RAG)
Laminating Process
co-PET
film
TFS
Oriented layer
Amorphous layer
Hydrated CrOx
Metallic Cr
Canmaking Process

24. Cr-free Passivation Treatment
Chromate Treatment : Chemical or electrochemical treatment of metal and metallic coatings
in solution containing chromic acid, chromate or dichromate.
 A protective conversion coating is produced on the metallic surface
composed of tri- and hexavalent chromium compound
Purposes of Chromating
- Corrosion resistance : prolongation of corrosion initiation
Barrier Effect : Cr(OH)3
Self-healing Effect : Cr6+  Cr3+
- Adhesion of organic coating
- Decorative coloring : yellow, brown, olive, black
Treatment Methods Dipping (EG, TP)
(simple chemistry) Roll Coating (EG, GI)
- Electrolytic (EG, TP)
Toxidity of Cr6+ : Can cause cancer or cutitis

25. Alternatives for Chromate
Mo-P (molybdate + phosphate)
- Thickness : 0.2~0.4μm
- Coating Composition
: Mo 20%, P ~7%, Zn 18~22%, O 45~50%
- Mo/P molar ratio in electrolyte = 0.33, pH = 2.1
= 0.66, pH = 4.6
Zirconate ( H2ZrF4 + H3PO4 )
- 2Al + H2ZrF4 + 2H2O →ZrO2 + 2AlF3 + 3H2
- 3H2ZrF6 + 4H3PO4 →Zr3(PO4) + 18HF
※ Polymeric Acid + Zr Salts for Paint Adhesion
Silane Coupling Agent
- Non-toxic & Low VOC
- Corrosion Protection & Paint Adhesion
Ex> VS (vinyltriethoxysilane)
/ BTSE (bis-1,2-[triethoxysilyl]ethane)

26. Prospects  Towards Environment-friendly Processes & Products
Cr-free Post-treatments for EG, GI/GA, TP
- Inorganic Compounds : Mo-P, Zirconate, Silane
- Organic Compound : Conducting Polymer
New Coating Products
- Zn-Ni  Zn-X or Composite Coating
- Multi-functional Resin Coating
- Laminate Steel : Heat Sealing, Direct Extrusion
New Electrolytes
- PSA  MSA, TSA, Simple Acidic Electrolytes
- High Performance Additives : Grain Refiner, Anti-Oxidation
High Speed & Compact Coating Processes