All About Galvanized Steel

By July 25, 2017News

In the world of flatroll steel, galvanized remains a top choice for corrosion protection, price, availability, and versatility. Galvanized steel is steel that has been applied with a protective zinc coating, which inhibits oxidation, or rusting and corrosion.

At Pacesetter, we offer a number of galvanized products, including:

  • Galvanized steel (with oil or a standard chemical treatment added for additional corrosion resistance). Regular galvanized is approximately 99.7% zinc coated.
  • Galvannealed offers a surface with more of a matte finish and more porosity. Its paint adhesion properties are excellent. The coating is composed of approximately 90% zinc and 10% iron.
  • Galvalume coatings are 55% aluminum, 43.5% zinc, and 1.5% silicon. Galvalume features excellent barrier-coating protection as well as galvanic protection.
  • Other options are a Zinc-Aluminum-Magnesium product, and Aluminized, which ranges from a nearly pure aluminum coating over the base steel to 89% aluminum and the balance silicon. Aluminized is popular where corrosion protection is required on hot applications such as dryer vents and mufflers. Electrogalv is a less common, but available option.
  • Chemical Treatments (chem-treat) on these products covers as broad a spectrum as the products themselves:
  • Bonderized, Phosphatized and Acrylic Coated: Provided with specific customer needs in mind i.e. paintability or adhesion.
  • Standard Chrome-6 chem-treat, as well as RoHS compliant Chrome-3

It’s interesting and helpful to understand steel and galvanizing, as well as its history and applications.

The History of Galvanized

In 1742 the French chemist Melouin submitted a treatise to the French Royal Academy explaining how a zinc coating could be applied to iron, and it drew interest. Its first application was for kitchen utensils.

In 1780 an Italian, Luigi Galvani, discovered that electrical shock could be created with the contact of two differing metals, setting the stage for the “electrogalv” process, and ultimately “galvanizing” was derived from his name.

One of the underrated scientific greats, Michael Faraday of England, discovered and wrote on metal alloys, magnetism, and electricity in the early 1800’s, which contributed greatly to industrialized galvanization processes.
In 1837, Stanislas Sorel filed a patent in France for a process of protecting iron from rust in larger batches, using a zinc bath – the precursor to the modern zinc bath on Galv lines. By 1850, British industry was consuming 10,000 tons of zinc per year for iron and steel coating.

Methods of Galvanization

How does galvanization work on flat-roll steel?

  • Hot-dip galvanizing (hot dipped galvanized or HDG): The most common method for galvanization occurs on continuous galvanizing lines, where coils are welded together end-to-end and run through a bath of molten zinc. In industry parlance regular HDG is referred to as “GI”.
  • Galvannealed: Produced on the same lines as GI, Galvanneal is created by reheating the coil strip just above the air knives to bond, or alloy the zinc to the steel substrate. Most people know that Galvanneal has a coating that is about 10% iron. However, iron is not added to the zinc bath. Rather, some of the aluminum content used in GI production is reduced, and the iron content is picked up when the bond between zinc and steel occurs in the reheat process. In industry parlance galvanneal is abbreviated as “GA”.
  • Electrogalvanizing: A process quite different from hot dip galvanizing, the zinc coating is applied to the steel in an electroplating process, where the anode is zinc, the cathode is steel, and the electrolyte is zinc sulfate. In other words, electrically applied rather than dipped in zinc. This process consumes a lot of electricity, but leaves an excellent finish. Its main application has been on exposed automotive. In industry parlance electrogalv is referred to as “EG”.

Applications & Advantages

Today, galvanized steel has an enormous array of usages. You encounter it in some way, shape, or form every day. It’s used in construction products, HVAC systems, roofing, automotive, agriculture, power transmission, hardware, piping, and much more.

Why galvanized, and not cheaper uncoated steel, or other coatings or materials?

  • Low long term cost. Where the initial cost of galvanizing is higher than alternative coatings or no coating, galvanizing is often more economical in the long term because of its longevity in the field and high degree of protection.
  • Low short term cost. Stainless steel, for example, is also used where corrosion protection is needed. However, only in the most demanding or specialized applications (food, medical) would the high cost of stainless steel justify its use over galvanized steel.
  • Long life. The life expectancy of galvanized coatings can exceed 60 years in many environments, and 20 years plus even in severe urban and coastal applications.
  • Galvanic Protection / Barrier Protection: The base steel is protected from the elements by the zinc, zinc/alloy coating. Life expectancy over uncoated steel multiplied many times over.
  • Adaptable/Practical. Weldability, paintability, formability are all there, and galvanized coatings are compatible with grades from highly formable EDDS to ultra-high strength steels.
  • Available. Most major steel mills make galvanized steel.
  • The Pacesetter Advantage! Pacesetter is a recognized leader in the service center sector in the purchasing, processing, efficiency, and quality aspects of galvanized steel.