Galvanized steel coil (also called GI coil or galvanized coil) is carbon steel sheet that has been hot-dip coated with zinc to provide superior corrosion resistance. The zinc coating acts as a sacrificial anode — it corrodes preferentially to protect the underlying steel from rust. Huaxia-Steel supplies hot-dip galvanized carbon steel coil in thicknesses from 0.3mm to 4.0mm, with zinc coating weights from Z60 to Z350 g/m², to ASTM A653, EN 10346, and JIS G3302 standards.
Product Overview: Galvanized Steel Coil
Galvanized steel is one of the most versatile corrosion-protected steel products in the world. It combines the strength and formability of cold-rolled carbon steel with the long-term corrosion protection of a zinc coating. The continuous hot-dip galvanizing process ensures uniform coating thickness across the entire coil surface. The resulting spangle pattern — the crystalline zinc structure visible on the surface — can be controlled from large (regular spangle) to zero (skin-passed or temper-rolled) depending on aesthetic and paint adhesion requirements.
| Property | Specification |
|---|---|
| Base material | Cold-rolled carbon steel (DC01-DC06, SPCC, Q195, S235JR) |
| Thickness range | 0.3mm to 4.0mm |
| Width range | 600mm to 1,500mm (standard), up to 2,000mm available |
| Coil inner diameter | 508mm or 610mm |
| Coil weight | 3-8 MT per coil (custom available) |
| Zinc coating | Z60, Z80, Z100, Z120, Z180, Z275, Z350 g/m² |
| Surface treatment | Chromated, oiled, anti-fingerprint, or dry |
| Spangle | Regular, minimized, zero (skin-passed) |
Zinc Coating Weight Comparison
| Designation | Coating (g/m² total both sides) | Coating per side (g/m²) | Approx. thickness per side (µm) | Typical service life* |
|---|---|---|---|---|
| Z60 | 60 | 30 | 4 | 2-5 years rural |
| Z100 | 100 | 50 | 7 | 5-10 years rural |
| Z120 | 120 | 60 | 8 | 8-12 years rural |
| Z180 | 180 | 90 | 13 | 10-20 years rural |
| Z275 | 275 | 138 | 20 | 20-40 years rural |
| Z350 | 350 | 175 | 25 | 30-50+ years rural |
*Service life estimates for rural/light industrial environments. Coastal, heavy industrial, or tropical environments will reduce service life. Actual life depends on exposure conditions, maintenance, and whether the galvanized surface is painted or left bare.
Available Grades and Standards
| Standard | Grade | Yield (MPa) | Tensile (MPa) | Elongation (%) | Application |
|---|---|---|---|---|---|
| EN 10346 | DX51D+Z | 140-300 | 270-500 | 22-26 | General forming, construction |
| EN 10346 | DX52D+Z | 140-300 | 270-420 | 24-28 | Deep drawing |
| EN 10346 | DX53D+Z | 140-260 | 270-380 | 28-32 | Extra deep drawing |
| EN 10346 | S220GD+Z | 220 min | 300 min | 18-20 | Structural, moderate strength |
| EN 10346 | S350GD+Z | 350 min | 420 min | 16-17 | Structural, high strength |
| ASTM A653 | CS Type B | 170-380 | 290 min | 20-26 | Commercial steel |
| ASTM A653 | SS Gr.50 | 340 min | 450 min | 12-16 | Structural Grade 50 |
| JIS G3302 | SGCC | 205 min | 270 min | — | General purpose |
| JIS G3302 | SGC400 | 245 min | 400 min | 16-18 | Structural |
Hot-Dip Galvanizing Process
The continuous hot-dip galvanizing line (CGL) transforms cold-rolled steel coil into galvanized coil through these steps:
- Cleaning: The coil passes through an alkaline degreasing bath to remove rolling oil and surface contaminants.
- Annealing: The strip is heated to 700-800°C in a reducing atmosphere (hydrogen-nitrogen) furnace. This recrystallizes the cold-rolled microstructure, restoring ductility and preparing the surface for zinc adhesion.
- Hot-dip coating: The strip enters a molten zinc bath at approximately 460°C. The zinc reacts with the steel surface to form intermetallic alloy layers (gamma, delta, zeta phases) topped with a pure zinc (eta) layer.
- Air knife wiping: Immediately after exiting the zinc bath, high-pressure air knives wipe excess zinc from both surfaces, controlling the final coating thickness.
- Cooling and post-treatment: The coated strip is cooled and may receive a chromate passivation treatment (for storage corrosion resistance) and/or oiling (for formability).
- Skin passing / temper rolling: Optional cold reduction (0.5-2%) to eliminate yield point elongation, control surface roughness, and produce a zero-spangle finish.
Applications
| Industry | Application | Recommended Grade | Typical Coating |
|---|---|---|---|
| Construction | Roofing sheets, wall cladding, purlins, decking | DX51D+Z, S220GD+Z | Z180-Z275 |
| Automotive | Body panels, structural components, underbody | DX53D+Z, DX54D+Z | Z100-Z140 |
| Appliances | Washing machines, refrigerators, HVAC ducting | DX51D+Z, DX52D+Z | Z100-Z180 |
| Electrical | Cable trays, enclosures, switchgear cabinets | DX51D+Z | Z100-Z180 |
| Agriculture | Grain silos, barn roofing, fencing, irrigation pipe | DX51D+Z, S220GD+Z | Z275-Z350 |
| General fab | Storage racks, shelving, furniture, signs | DX51D+Z | Z100-Z180 |
Tolerances
| Dimension | Tolerance (EN 10143) |
|---|---|
| Thickness 0.3-0.4mm | ±0.04mm |
| Thickness 0.4-0.6mm | ±0.05mm |
| Thickness 0.6-0.8mm | ±0.06mm |
| Thickness 0.8-1.0mm | ±0.07mm |
| Thickness 1.0-1.5mm | ±0.09mm |
| Thickness 1.5-2.0mm | ±0.11mm |
| Thickness 2.0-4.0mm | ±0.13mm |
| Width (all thicknesses) | +7 / -0mm (mill edge), +2 / -0mm (slit edge) |
Quality Assurance
- Zinc coating weight test: Triple-spot test per ASTM A90/A90M or EN 10346 Annex A — confirmed on every coil
- Coating adhesion test: Bend test (180° over mandrel) — no flaking or peeling of zinc coating
- Surface quality inspection: Visual inspection for spangle uniformity, surface defects (pin holes, bare spots, zinc runs), and edge quality
- Mechanical properties: Tensile test in rolling direction — yield, tensile, elongation per applicable standard
- Dimensional verification: Thickness gauge (continuous automatic), width measurement, coil weight
- EN 10204 3.1 MTC: Full chemistry (ladle + product), mechanicals, and coating weight on every coil shipped
Packaging and Shipping
Galvanized coils are packaged for sea freight as follows:
- Coil wrapping: Inner wrapping (VCI paper) + outer wrapping (waterproof tarpaulin or plastic film) + steel circumferential strapping (4-6 bands per coil) + edge protectors (steel or plastic corner guards)
- Coil orientation: Eye-to-sky (vertical) or eye-to-side (horizontal) per customer preference and container type
- Container loading: 20' GP accommodates 2-4 coils (15-25 MT); 40' HC accommodates 4-6 coils (25-28 MT)
- Securing: Wooden wedges and steel straps ensure coils do not shift during ocean transit
- Breakbulk: Available for very heavy coils (10+ MT) or when shipping to ports without container handling equipment
Conclusion
Galvanized steel coil provides the most cost-effective combination of formability, strength, and corrosion resistance available in coated steel products. With zinc coating weights from Z60 to Z350 g/m², forming grades from commercial (DX51D) to extra deep drawing (DX53D), and structural grades up to S350GD, there is a galvanized steel specification for nearly every application. The key to reliable procurement is specifying the exact standard, grade, coating weight, and surface treatment in your purchase order — and sourcing from mills with certified continuous galvanizing lines and consistent quality documentation.
Need galvanized steel coil for your manufacturing or construction project? Contact Huaxia-Steel for factory-direct pricing, EN 10204 3.1 MTC, custom slit widths, and global containerized shipping from ISO-certified Chinese mills.
