The zinc plays a part in protecting the surface of steel strips from corrosion and rusting. Both galvanneal and galvanized steels undergo zinc coating processes in a mill. They also pass through a hot-dip coating process, but galvanneal passes through an extra annealing process.
Read more about the differences and functions of galvanized and Galvanneal.
Galvanneal vs. Galvanized Corrosion
The thickness of the coating on the surface of galvanized steel contributes to its corrosion performance. The zinc-iron coating thickness of galvanneal plays a role in the corrosion and rusting protection of the steel.
Most of the applications of galvanized steel are for painting after fabrication. The thickness of the zinc-alloy coating on Galvanneal also has a role in protecting against corrosion.
Product Specifications
Galvanneal and galvanized steels are the same standards, the ASTM A 653/A 653M. The American Society for Testing and Materials (ASTM) designates Galvannealed with an A grade like A60 and A40.
ASTM designates Galvanized with a G grade like G60 or G40. The number denotes the weight of the coating.
Here is a list of common variations in galvanized steel:
- G30 – .30 ounces of coating per square foot
- G60 – .60 ounces of coating per square foot
- G90 – .90 ounces of coating per square foot
Galvanneal steel compositions:
- Zeta alloy layer-5.2 to 6.1 percent iron and 0.7 percent aluminum
- Delta alloy layer-7.0 to 11.5 percent iron and 3.7 percent aluminum
- Gamma alloy layer-15.8 to 27.7 percent iron and 1.4 percent aluminum
Differences in Appearance and Usage
Galvanized steel has a spangled metallic appearance, while Galvanneal has a dull, gray, and matte surface. Galvanized steel is resilient as the paint coating can withstand saltwater and external elements.
Galvanized steel has anti-corrosion and anti-rust mechanisms that are useful in making several products that may come in contact with water. It is ideal for homes beside coastal areas. It is available in various forms like galvanized wire or galvanized pipes.
Building exteriors also use galvanized steel to protect from corrosion and rusting.
Here are the uses of galvanized steel:
- Body parts of automobiles, trucks, and buses
- Steel frames for houses and buildings
- Household appliances, such as hair dryers, air conditioning casings, and washing machines
- Electronic and computer parts
- Highway signs
- Protective gears
- High tension electrical towers
- Wrought-iron gates, window and door bars
- Metal pails & buckets
- Wall and hanging ornaments
- Window & door coverings
- Utility holes & gutters
Galvanneal steel has more benefits and uses than galvanized steel. The process of Galvanneal is for painting purposes. Its zinc coating is more absorbent than galvanized steel because the paint adheres to its surface.
The zinc coating of galvanneal is more robust and resistant to scratching. The applications of galvanneal steel depend on the amount of carbon or alloy.
Galvannealed steel with high-strength, thick and low alloy is a good fit for building structures, deep drawing, marine applications, high-tensile stress conditions, and welding operations.
Galvannealed with low carbon is ideal for automobile frames. It is prevalent in shipbuilding, construction, transport, and automobile manufacturing.
Differences in Process
Both Galvanneal and Galvanized have a zinc coating to prevent corrosion and rusting. Although they went through a hot-dip coating process, Galvanneal passed through an annealing process.
This method aims to diffuse the alloy between the steel and the molten zinc coating. It leads to a lusterless surface than the galvanized steel. The annealing process increases the paint’s adhesion and the galvanneal material’s formability.
The annealing process takes place in a Galvanneal furnace. The steel strip undergoes reheating at a controlled temperature from 500 degrees C to 600 degrees C for a few seconds. A zinc bath with small aluminum portions is ready for dipping the metal sheet.
As soon as the strip of metal emerges from the hot bath, the air knives remove the pressurized zinc to get the desired coating weight. The strip goes into the furnace approximately 10 to 15 feet above the knives.
The iron-zinc diffusion-reaction restarts and starts breaking down the layer of iron-zinc aluminum when the temperature rises. Reheating of the strip happens while the zinc is still in its liquefied state.
The strip undergoes several seconds of heating and ten seconds of soaking. The appearance of Galvanneal becomes dull matte grey when enough iron is diffusing into the coating.
The galvanization process begins by immersing a steel sheet in molten zinc at 850 degrees F—the zinc layers bond to the steel substrate at a specific molecular level. Zinc offers protection to the strip from oxidation when there is exposure to corrosive elements.
Differences Between Galvanneal and Galvanized Steel
Galvannealed and galvanized steel have zinc coatings to protect them from corrosion and rust. Both have properties that make them unique, such as coating, appearance, specifications, weldability, etc.
Coating
The galvanized steel coating is mostly zinc with a small portion of iron, zinc, and aluminum bonding layer. Usually, the bulk composition of the zinc-iron alloy is 90 percent zinc and 10 percent iron.
The annealing process on the Galvanneal leads to forming three coating layers: zeta, delta, and gamma. The gamma layer has the highest level of iron content.
The coating of Galvanneal is stronger than the galvanized steel, meaning that the former is more resilient and complex than the latter. During press forming and bending, the coating of Galvanneal cracks and produces powder.
Appearance
Galvanized steel looks more attractive than Galvannealed material because it has a shiny texture. Galvanneal passes through an annealing process, leading to a rough, dull, and matte surface.
The annealing process results in a zinc-iron (Zn-Fe) alloy. You can paint, coat, or add finishing to the galvanized steel. Their speckled patterns ensure that there are no identical galvanized pieces.
The matte texture of galvannealed steel is ideal for painting as the paint bonds more than galvanized steel. Galvannealed steel is appropriate if you want a flat paint coating.
Weldability
The annealing process of Galvanneal is an ideal material in all types of structures as it possesses welding characteristics than the galvanized steel. Galvanneal has an iron coating that makes the steel easier to weld than galvanized material.
The electrical resistance, melting point, and hardness of Galvanneal make the material last for years compared to galvanized steel.
Paintability
If you want to coat your steel with paint, Galvanneal is a good choice. The surface of Galvanneal has high porosity, making it more paintable than galvanized steel. The dull and gray surface of Galvanneal allows the paint to adhere.
Formability
The annealing process of galvannealed steel produces a ductile and firm surface, leading to higher formability. The coating of galvanized steel is softer, which results in higher machinability.
The coating in galvanized steel is softer than Galvanneal. The flexibility and soft layer in galvanized materials are lubricants and quickly get scratched.
Since the Galvanneal coating is hard, it does not get scratches during transporting and handling. It is easy to stretch and roll according to its application.
Galvanneal vs. Galvanized Cost
Galvanneal is more costly than galvanized steel because of the additional annealing step. The market demand for Galvanneal is high as it offers many advantages over its galvanized counterpart.
Although the surface may look dull, Galvanneal can withstand rusting and corrosion. It is easy to form, weld, and coat with paint.
Conclusion
Have you ever thought about which steel is the best? Learning the difference between Galvanneal and galvanized steels can be tricky because they have good qualities. You have to compare their properties before concluding which one is superior to the other. You still need a professional to guide you in choosing the best steel product.
