Resistant to scratches and friendly to paint, galvannealed steel has a matte finish that’s also more durable than galvanized coatings.
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What is Galvannealed Steel?
When compared to galvanized steel, galvannealed steel offers improved painting and welding characteristics. However, galvannealed tends to powder during the forming process, particularly in areas of compression. The tendency for powdering is known to increase with increasing coating weights. Conversely, we can minimize powdering by reducing the galvannealed coating weight. Even though lowering the coating weight lowers material costs and improves the manufacturing process, some are hesitant to reduce the specified coating weight due to corrosion concerns.
The corrosion performance of galvannealed is more challenging to determine than the corrosion performance of galvanized. The iron present in the galvannealed coating will cause a “red rust” discoloration on the surface of unpainted galvannealed, which is cosmetic in nature. However, we measure standard salt spray corrosion testing to the degree of red rust resulting from base metal corrosion. Discerning between the two is difficult. As most galvannealed is painted after fabricating, collecting data on the painted sheet rather than bare may be more appropriate.
We can perform corrosion testing on painted galvannealed using a scribe-creep test. There is statistical evidence in cyclic corrosion testing that increasing coating weight from A40 to A60 has a marginal effect on the scribe-creep test (Reference: “Effects of Coating Weight and Pretreatment on the Painted Corrosion Performance of Coated Steel Sheet,” SAE Paper Number 970732, Theresa C. Simpson and Jay D. Hoffman of Bethlehem Steel Corporation, 1997.)
Reducing the coating weight of galvannealed offers many benefits, including lowering material cost, decreasing the tendency to powder, and reducing related issues in the manufacturing process. It also appears that reducing the coating weight may only have minor implications on the corrosion performance of painted galvannealed. For all of these reasons, reducing the coating weight on painted galvannealed could be a viable option. When determining if this is an appropriate change, factors such as performance requirements and applicable industry standards should be considered, and appropriate testing should be performed.
Both galvanized steel and galvannealed steel are base steels with a thin layer of corrosion-resistant zinc on the outside. However, they differ in how the zinc adheres to the steel.
With galvanized steel, the base metal is hot dipped in molten zinc. Galvannealed steel follows this same process but passes through a low-pressure, high-volume air knife that blows off excess zinc before it dries. The metal is then placed into a furnace where the heat allows the zinc and steel to be alloyed.
Galvannealed steel has a thinner zinc coating than galvanized steel, but that layer is bonded with the baking process.
Painting Galvannealed Steel
One of the most significant advantages of galvannealed steel is that, unlike other steels, it accepts paint very well. This makes it a popular metal for doors, door frames, and any steel-fabricated product that needs a painted application. In fact, galvannealed steel doesn’t require any special primers before applying paint.
Coating Galvannealed Sheet Stock
Galvannealed sheet stock, as mentioned above, has a zinc-iron alloy, which gives it a powdery finish (the heavier the coating, the more powdering). This is why galvannealed steel has a thinner exterior coating than galvanized steel.
However, this coating is what allows the paint to so readily adhere to it. It’s worth noting that galvannealed steel should be formed into its final product before painting to prevent cracking of the brittle zinc coating and paint.
Uses and Applications Benefits of Galvannealed Steel
Galvannealed steel is lower on the cost spectrum than other steels, but it still performs well. There are many benefits for using galvannealed steel, including:
- Life expectancy. Galvannealed steel retains its corrosive-resistant properties for many years, especially when painted.
- Superb paint adhesion characteristics. Because of its powdery, zinc-iron coating, galvannealed steel gives the paint an already-primed surface. That means saving on primer if you choose to paint your steel.
- Minimal maintenance. The zinc coating acts as a rust inhibitor. Its slow oxidation rate gives it long-lasting protection against atmospheric corrosion.
Because of its durability, you’ll find galvannealed steel used in bridges, guardrails on highways, signs, and fencing, in recreation centers, and any areas that require long-term, maintenance-free protection from corrosion and heavy use.
Advantages and Disadvantages of Galvanneal
Perhaps the biggest advantage of galvannealed steel is its rust resistance properties, but many would say its paintability.
On its own, it has a matte grey color that has become popular in the architectural industry. But its ability to adhere to paint without needed primers makes it a cost-effective way to get specific colors with paint.
It’s also easy to form into whatever shape is needed and can withstand damp or salty environments.
However, galvannealed steel does come at a higher cost than galvanized. And if your project is going to be prone to scratches, galvanized steel could be preferable.
Need Galvanized Steel For Your Next Project?
If you need galvanized steel manufactured and processed for your next project, contact us below to coordinate with one of our experts. We offer a variety of steel products, including cold-rolled steel, aluminized steel, galvanized steel, and stainless steel. We can discuss your project needs and provide you with the galvanized steel you need at the best price.
