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.

Contents Introduction Facilities & Products Technical Trends Technical Developments Prospects

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

Film Formation Rates of Various Methods

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

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

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

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

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

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)

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

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

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

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

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 1980 1990 2000 E/M Levitation

: 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

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

Development of Operation Technology - EGL ②Charge transfer Cathode Zn2+ 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

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

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%

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

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- →H2 ( 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

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

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

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)

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