Galvanized steel” refers to the process of coating the surface of a steel sheet with zinc to make it less susceptible to corrosion and rust, thus extending its useful life.
Will galvanized steel rust?
In our daily life, galvanized steel sheets are a common type of steel sheet. The cars we drive are made with them and have a good reputation. But, will they rust?
- Galvanized steel plates can rust and the degree of rust varies depending on the environment in which they are located. For example, if a galvanized steel plate is placed outdoors for a long period of time, it will eventually rust. On the other hand, if it is kept indoors and protected from water and corrosive liquids, it will take longer to rust.
- The rust of galvanized steel plates is a natural phenomenon because they contain impurities such as iron, zinc and other metals that make them susceptible to corrosion and rust.
- Although galvanized steel plates have some degree of corrosion and rust resistance, their ability to resist corrosion and rust is limited. If they are exposed to aggressive environments for a long time, they will end up rusting.
- Galvanized steel plates are divided into two types: cold galvanized steel plates and hot galvanized steel plates. Cold galvanized steel plates are more susceptible to rust, while hot galvanized steel plates are less prone to rust.
Why does galvanized steel sheet rust?
- The uneven thickness of the galvanized steel plate can cause rust, as the thick parts will drive the rusting process, causing the entire plate to rust.
- Galvanized steel sheets used in homes are generally not suitable for placement in humid environments. If they are exposed to high humidity for a long period of time, this can result in rapid rusting of the board.
What causes galvanized sheet metal to rust?
(1). Throughout the useful life of a galvanized sheet, the first form of corrosion is the oxidation of the zinc coating on the surface, leading to the formation of “white rust”. Over time, the “white rust” on the surface will further react with carbon dioxide and other contaminants in moist air to form “black spots.”
When the galvanized sheet is in use for a long period of time and the corrosion of the galvanized layer is severe, the steel base loses the protective function of zinc, known as “sacrificial corrosion protection”, and begins to oxidize, forming “red rust”. . ”
Once the steel base begins to oxidize, the rate of corrosion accelerates and the galvanized sheet reaches the end of its useful life.
(two). Furthermore, there are two special forms of corrosion in galvanized sheets known as “black shift”.
One occurs after a period of use, when elements such as lead in the zinc coating cause dull parts of the zinc flake to turn black. Although the blackened zinc coating still protects the steel base, it affects its service life. This problem was ameliorated by using antimony instead of lead in promoting the formation of zinc flakes.
Another situation occurs during the transport of galvanized sheet, where the low winding tension causes the layers of the steel strip to loosen and parts of the steel coil rubbing against the skid result in oxidation. The white oxide is removed, producing black spots on the surface of the galvanized sheet, damaging the passivation film, reducing the thickness of the galvanized layer and shortening its service life, affecting its appearance.
(3). Galvanized steel sheets have excellent corrosion resistance in dry or non-polluting environments. However, in polluted environments, its service life is greatly reduced and it must be pre-coated to form a color plate, also known as color coated plate, before use.
(4). Generally, corrosion of galvanized steel sheets is not due to uniform corrosion of the galvanized coating on the surface, but rather to initial corrosion of the coating at points where the coating and substrate are poorly adhered, resulting in severe local corrosion and loss of performance.
In this regard, the adhesion of the zinc coating, especially the overall adhesion, is more crucial than the thickness of the zinc coating. If the local adhesion of the zinc coating is poor, even a thicker coating will rust due to poor adhesion, a problem that galvanizing production technicians must recognize, similar to the “bucket principle”.
H How long does it take for galvanized steel to rust ?
Generally, the galvanized steel available on the market today includes 80g spangle-free galvanized sheets and 60g spangles.
These materials can provide rust protection for up to three years without spangles in outdoor conditions, while spangled sheets may begin to show signs of white rust in about two years.
Properly coated galvanized steel can resist rust for a long period of time, but will eventually transition from bright white to light gray.
However, if the steel is not treated properly before coating, it may develop rust stains or even begin to peel within three to five months.
It is important to emphasize that no material is completely immune to rust.
The performance of aluminum and galvanized sheets can vary in different environments, and the quality of aluminized and galvanized steel produced by different factories can also impact their resistance to rust.
Even 200 series stainless steel coated with aluminum and zinc, which is a higher grade than galvanized sheet, is not immune to rust.
Likewise, 300 and 400 series aluminum and zinc coated stainless steel, which are of even higher quality, can still rust in certain environments.
How long does galvanized steel not rust?
- When properly coated, galvanized steel can last approximately 20 years without significant changes to its surface, turning from a bright white to a light gray over time.
- However, if proper treatment is not provided, rust can begin to form within three to five months.
It should also be noted that the service life of galvanized steel can be affected by the environment in which it is used. If it is in a dry environment for a long period of time, its lifespan may be longer, but if it is in a constantly humid environment, its lifespan may be reduced.
