Galvanized Steel: Types, Specifications, Properties & Applications
ASTM A653 / A123 / A153 (Hot-Dip Galvanized) · Published: 2026-07-25 · Updated: July 2026
Galvanized steel is carbon steel coated with a layer of zinc to protect the underlying steel from atmospheric corrosion. The zinc acts as both a physical barrier and a sacrificial (galvanic) anode—even if the coating is scratched, the surrounding...
Galvanized steel is carbon steel coated with a layer of zinc to protect the underlying steel from atmospheric corrosion. The zinc acts as both a physical barrier and a sacrificial (galvanic) anode—even if the coating is scratched, the surrounding zinc corrodes preferentially, protecting the exposed steel from rust. The zinc coating extends the service life of carbon steel by 30-80 years in atmospheric exposure, depending on coating thickness and environment. Three principal galvanizing processes produce galvanized steel products: (1) Hot-Dip Galvanizing (HDG) per ASTM A123/A653—the steel is immersed in molten zinc at ~450°C, forming a metallurgically bonded zinc-iron alloy coating 50-200 µm thick. This is the heaviest, most durable coating and the standard for outdoor structural steel, utility poles, and highway guardrail. (2) Electrogalvanizing (EG)—zinc is electroplated from an aqueous electrolyte, producing a thin (5-15 µm), uniform, smooth coating used for automotive body panels and appliances where paint adhesion and surface finish are critical. (3) Galvannealing—the hot-dip coated steel is immediately annealed at ~500-550°C to fully alloy the zinc with iron, producing a harder, more paintable surface used for automotive exposed panels. Coating weight is specified in oz/ft² (G90, G60, G40 for ASTM A653 sheet) or mil thickness. For outdoor structural applications, G90 (0.90 oz/ft² total both sides) is the minimum recommended; heavier coatings (G185, G210) extend service life proportionally. Compare galvanized steel's properties to astm-a36/">ASTM A36 carbon steel for structural applications, or to 304-stainless-steel/">304 stainless steel when superior corrosion resistance is required.
Quick Facts
| Category | Carbon Steel |
| Standard | ASTM A653 / A123 / A153 (Hot-Dip Galvanized) |
| Density | 7.85 g/cm³ (base steel) |
| Yield Strength | 205-345 MPa (depends on base steel grade) |
| Tensile Strength | 340-450 MPa (depends on base steel grade) |
Detailed Mechanical Properties
| Elongation | 15-25% (depends on base steel) |
| Hardness | Base steel hardness; zinc coating 60-120 HV |
| Modulus Of Elasticity | 200 GPa (base steel) |
Physical Properties
| Melting Point | 1420-1530 °C (base steel); zinc coating melts at 419 °C |
| Thermal Conductivity | 50 W/m·K (base steel) |
| Zinc Coating Thickness | 5-200 µm (process-dependent) |
| Coating Adhesion | Metallurgical bond (HDG) / electroplated bond (EG) |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| HDG (Hot-Dip Galvanized) | Compare |
| EG (Electrogalvanized) | Compare |
| Galvannealed | Compare |
| Zn-coated steel | Compare |
| EN 10346 | Compare |
Heat Treatment & Processing
| Note | Hot-dip galvanizing performed at 445-460°C may slightly temper some quenched-and-tempered base steels. Galvanized steel cannot be subsequently heat-treated without destroying the zinc coating (zinc melts at 419°C, boils at 907°C). |
Welding & Fabrication
| Preheat | Remove zinc 5-10 cm from weld zone; preheat per base steel grade |
| Filler Metal | Match base steel grade (E70XX for A36 base); use low-silicon filler to reduce zinc spatter |
| Interpass Temp | Per base steel grade |
| Pwht | Not compatible with zinc coating; must be performed before galvanizing |
| Weldability Rating | Good — with zinc removal; poor if welded through coating (fume hazard, porosity) |
Related Materials
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Frequently Asked Questions
How long does galvanized steel last outdoors?
Service life depends on zinc coating thickness and environment. In rural atmospheres, G90 galvanized sheet lasts 30-50 years; in urban/industrial, 20-40 years; in coastal, 15-25 years; in severe industrial or marine splash, 5-15 years. Hot-dip galvanized structural steel (ASTM A123) with thicker coatings (100-200 µm) typically achieves 50-80 year life in temperate rural environments.
Can galvanized steel be welded?
Yes, but the zinc coating must be removed from the weld zone first (5-10 cm on each side) to prevent zinc vapor porosity and zinc-induced weld cracking. Welding through galvanized coating produces zinc oxide fumes that cause 'welding fume fever' (metal fume fever). After welding, the damaged coating must be repaired with zinc-rich paint or metallizing spray to restore corrosion protection. AWS D19.0 governs welding of galvanized steel.
What is the difference between galvanized and stainless steel?
Galvanized steel is carbon steel with a sacrificial zinc coating—cheaper but limited coating life (30-80 years) and vulnerable to coating damage. Stainless steel (304, 316) has chromium alloyed throughout the steel—self-healing, indefinitely corrosion-resistant, but 3-5× more expensive. For permanent outdoor structures, stainless is superior; for cost-sensitive applications with periodic replacement, galvanized is economical.
What does G90 mean for galvanized steel?
G90 is an ASTM A653 coating weight designation meaning 0.90 oz/ft² of zinc total on both sides (equivalent to ~275 g/m² or ~19 µm per side). G60 = 0.60 oz/ft² (183 g/m², ~13 µm/side). G90 is the minimum recommended for outdoor structural sheet; lighter G60 is used for indoor appliances; heavier G185/G210 is used for severe environments.
Does galvanized steel rust?
Eventually yes—once the zinc coating is consumed (sacrificial corrosion) or mechanically damaged, the underlying carbon steel rusts like uncoated steel. Galvanizing extends service life but does not make steel corrosion-proof. In chloride environments (coastal, de-icing salts), zinc corrodes 5-10× faster than in rural atmospheres, reducing galvanized service life significantly.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu
Structural & Carbon Steel — Engineering Reference
Structural steels are the backbone of construction and heavy industry. Grades in this category are specified primarily by their yield strength, tensile strength, and weldability — the three properties that determine whether a building stands or a bridge holds.
ASTM A36/A572/A516, EN 10025, JIS G3101/G3106, GB/T 700/1591
Building frames, bridges, pressure vessels, shipbuilding, offshore platforms, pipelines
When selecting a structural grade, match the required yield strength to the design load, but also verify Charpy impact values if the structure will operate below freezing — many structural steels undergo a ductile-to-brittle transition at low temperatures.