Galvanized steel is steel that has been coated with a thin layer of zinc. A galvanizing process is used to apply a zinc coating to the surface of steel or iron sheets to prevent corrosion. In this process, the steel is cleaned and then submerged in a bath of molten zinc. As the steel is drawn up from the bath, the zinc coating forms and bonds to the surface through metallic bonding. When exposed to air, the zinc coating develops a protective patina that shields the steel below from corrosion. The zinc acts as a sacrificial anode that corrodes in place of the steel. Galvanized steel is widely used for constructing fences, pipes, outdoor structures, and metal roofing because the zinc coating provides long-term corrosion resistance in many environmental conditions.
What Is the Difference between Galvanized Steel and Regular Steel?
Galvanized steel resists corrosion much better but has a slightly higher cost, while regular steel is cheaper but more prone to rusting.
- Galvanized steel has a thin coating of zinc applied to the surface, while regular steel is uncoated. The zinc coating is what provides galvanized steel with enhanced corrosion resistance.
- Corrosion resistance: Thanks to the zinc coating, galvanized steel has much higher corrosion resistance than bare or regular steel. The zinc coating protects the steel underneath from rusting or corroding. Regular uncoated steel is more prone to corrosion when exposed to moisture, acids, salts, etc.
- Appearance: Galvanized steel has a silver-gray, shiny appearance right after the galvanizing process. As it weathers, it develops a duller, flaky patina. Regular steel typically shows signs of rust or corrosion over time when outdoors.
- Strength: The zinc coating does not significantly affect the mechanical or structural properties of the steel. So galvanized and regular steel has comparable strength, hardness, etc. The zinc layer is very thin.
- Cost: Galvanized steel costs more than regular steel due to the additional galvanizing process. But it provides enhanced durability and lifespan that can offset the higher initial price.
What Are the Types of Galvanized Steel?
Hot-dip galvanizing is the most common and provides the best all-around corrosion performance for structural and outdoor applications. The main types of galvanized steel are:
- – Hot-dip galvanized steel: This is the most common type. It involves dipping steel into a bath of molten zinc. This results in a uniform zinc coating on all sides of the steel for superior corrosion protection.
- – Electrogalvanized steel: In this process, steel is electroplated with a thin zinc coating. It provides less corrosion resistance than hot dip. Often used for parts that can’t be submerged or for aesthetic/decorative purposes.
- – Galvannealed steel: The zinc-coated steel is then annealed to form an alloy layer between zinc and steel for added corrosion protection and paintability. Used in automotive, appliance, and construction industries.
- – Painted galvanized steel: For applications needing color coating, hot-dip galvanized steel can be painted for both corrosion protection and aesthetics. The zinc acts as a primer promoting paint adhesion.
- – Zinc-aluminum alloy coated steel: Contains small amounts of aluminum added to zinc coatings. Provides enhanced corrosion resistance, formability, and weldability over standard hot-dip galvanized.
- – Amalgam method: Zinc and other metals like aluminum, tin, or lead are electro-deposited on steel to form a corrosion-resistant alloy coating. Used in some critical fastener applications.
What Are the Properties of Galvanized Steel?
| Property | Details |
| Chemical Composition | Base Material: Iron alloyed with carbon (steel)<br>Coating: Zinc |
| Structure | Base: Ferrous, body-centered cubic crystal structure<br> Coating: Hexagonal close-packed crystal structure of zinc |
| Corrosion Resistance | High – Zinc coating protects the steel through galvanic corrosion where zinc atoms sacrificially corrode first |
| Tensile Strength | Between 350-550 MPa depending on steel grade. Not significantly affected by thin zinc coating. |
| Ductility | The zinc coating layer is very thin so the density is the same as base steel at 7.75 g/cm3. |
| Hardness | Zinc coating is softer than steel (0.25 GPa vs typical steel of 2.5-4 GPa). |
| Density | The zinc coating layer is very thin so the density is same as base steel at 7.75 g/cm3. |
| Melting Point | Base steel: 1,500°C (2,632°F) |
| Thermal Expansion | Similar to base steel: 11-13 x 10^-6/K |
| Electric Conductivity | Slightly lower than steel but still electrically conductive. |
| Paintability | Zinc layer compatible with most paint types for additional corrosion protection & aesthetics. |
What Industries utilize Galvanized Steel?
1. Fences
Galvanized steel fences can last decades with minimal maintenance. Regular steel fences would require much more frequent repair/replacement due to rusting.
2. Pipes and ductwork
Galvanized steel is widely used for water pipes, ventilation ducts, and other outdoor plumbing applications since it protects against corrosion from moisture.
3. Construction beams and supports
For buildings and structures near salt water or in coastal areas, galvanized steel beams and columns are specified to prevent rust corrosion over time.
4. Hardware and fasteners
Bolts, nuts, screws, nails, etc. used in outdoor applications are often galvanized for longer lifespans.
5. Electrical transmission towers
The high strength need for these supports is fulfilled by galvanized steel which also withstands weather exposure.
6. Shipping and storage containers
The galvanized coating protects containers even during overseas transport exposure to elements.
7. Agriculture equipment
Implements, gates, and other machinery used in wet, muddy fields perform better with galvanized steel.
8. Roofing and siding
The coatings on metal roofing and steel house siding are typically galvanized for decades of use without maintenance.
What Are the Pros and Cons of Galvanized Steel?
Galvanized steel offers significant longevity benefits through corrosion resistance, though it has a small cost and weight penalty over plain carbon steel. With proper handling, its risks are generally manageable.
| Pros | Cons |
| High corrosion resistance – Zinc coating protects steel from rusting for decades. | More expensive than plain carbon steel initially due to galvanizing process. |
| Low maintenance – Once installed, galvanized steel requires little ongoing upkeep. | Zinc coating is slightly softer than steel, so may dent or scrape more easily. |
| Recyclable – Both the steel and zinc can be recycled at the end of life. | Thermal conductivity is lower than plain steel, reducing heat transfer properties. |
| Facilitates rust-proofing and rain drainage. | Sensitive to over-thick coatings which can crack and peel over time. |
| Forms strong bonds for welding and painting. | Zinc coating provides some weight penalty vs plain steel. |
| Widely available as a construction/industrial material. | Imperfections in hot-dip galvanizing leave marks and may reduce corrosion protection. |
| More expensive than plain carbon steel initially due to the galvanizing process. | More toxic than plain steel if galvanized materials are burned without emission controls. |
| Compatible with most environments and structures. | Can present inhalation risks if (hot-dip) galvanizing fumes are inhaled without protection. |