As a furniture manufacturer, the most frequent question about stainless steel furniture clients have asked us was, it won’t rust, right?
In most cases, stainless steel furniture does not rust in a normal environment. But it is not really “completely rust-free.” it will be corroded and rusted under certain extreme conditions, such as high humidity & salinity area, chemical environment (chlorine, hydrochloric acid, or sulfuric acid), etc.
In this article, we will focus on why stainless steel is corrosion-resistant, how it can be rusted and how to deal with it.
Why is stainless steel furniture corrosion-resistant?
Stainless steel furniture attracts people not only because of its beautiful finishes but also from the durability of its raw material-stainless steel, which is corrosion-resistant and helps it long-last. Who does not want a durable piece of furniture, right?
But why can stainless steel resist corrosion? The answer is its component – chromium.
Besides iron and carbon, the other key component of stainless steel is “chromium.” Chromium mixes with water or oxygen in the air to form a protective barrier of chromium oxide, which prevents oxygen and water from interacting with the iron content of the stainless steel. This protective layer is also known as the “passivation layer.”
When the stainless steel is scratched, and the passivation layer is damaged, the chromium will react with oxygen in a new round to restore the passivation layer, then continue to protect the stainless steel from corrosion.
However, it is important to note that chromium oxide does not heal itself unlimited. Once it is complete damage, it will not restore.
What caused stainless steel furniture rust?
The most direct reason stainless steel furniture rusts is that the passivation layer is completely damaged or depleted and insufficient to provide protection. For the below conditions, stainless steel is at a higher risk of corrosion, which could lead to rust.
1. Chemical environment
Chlorine weakens the stainless steel “passivation layer” – chromium oxide, resulting in partial corrosion, and the beneath ferrous (iron-containing) steel will be exposed to oxygen. Iron reacts with the oxygen in water/air to create rust (iron oxide), which is also known as pitting corrosion.
Hydrochloric acid or sulfuric acid
Hydrochloric acid and sulfuric acid are extremely acidic and corrosive and will erode the surface of stainless steel, destroying its passivation layer, chromium oxide. Losing the protection of chromium, the raw steel of stainless steel is exposed to air, and the iron content in it is easily oxidized, forming iron oxide and contributing to increased corrosion.
2.High humidity and high salinity
Besides indoor furniture, stainless steel is also used for outdoor furniture. Suppose stainless steel outdoor furniture is placed on the beach. In that case, the high humidity and salinity conditions can result in saline corrosion, and the iron in the stainless steel can oxidize to create iron oxide. High humidity and high salinity will accelerate the rate of oxidation, which will promote more corrosion to occur and lead to structural damage to the steel.
3. Inappropriate stainless steel
As previously stated, stainless steel mainly relies on chromium oxide for corrosion protection. However, if the stainless steel does not have sufficient chromium content when the top layer of chromium oxide is scraped off, it can not form a new chromium oxide layer.
10.5% is the minimum chromium requirement for stainless steel. According to the different grades of stainless steel, chromium content also varies. The higher the chromium content, the better the corrosion resistance. Inappropriate stainless steel will shorten its service life.
For example, in specific environments, as mentioned before: containing chlorides, high humidity, high salinity, etc., the minimal 10.5% chromium content of stainless steel is not enough to withstand these situations; a higher grade of stainless steel is needed,such as “marine grade” stainless steel, 316.
4. Stainless steel suffered damage
Once stainless steel suffered extreme strikes or was hit by sharp objects leading to serious dents, scratches, and chisel marks on the surface or exposing the original steel inside, it will easily be eroded after physical damage.
The stainless steel surface is permanently damaged
Wipe the stainless steel with tools like abrasives, steel wool, steel brushes, etc., which will destroy the surface layer of stainless steel and damage its passivation layer, lowering the chromium and causing it to lose its protective function.
6. Stainless steel processing may cause rust
Stainless steel in processing will also meet some rare rusting situations, such as sensitized corrosion and iron contamination.
Stainless steel is often welded during furniture production. In high-temperature welding, stainless steel may occur sensitization phenomenon: carbon combined with the surrounding chromium forms chromium carbide. This sensitization leads to a local lack of chromium in the welded area, resulting in a discontinuous passivation layer and a weakened chromium oxide, which leads to partial rusting.
Iron, carbon steel dust pollution
When iron or carbon steel undergoes a series of processes such as cutting, welding, polishing, etc., it will make some iron/carbon steel dust. If stainless steel is also placed in the same space, the iron/carbon steel dust will likely fall on the surface of the stainless steel. If not cleaned quickly, over time, this dust will pollute the stainless steel, damaging the chromium oxide surface, reducing the healing ability of the passivation layer, and leading to rust on the surface.
How to remove rust from stainless steel furniture?
If stainless steel furniture rusts, it can be refreshed and restored to its luster by some of the following methods.
The all-purpose “baking soda”
You can use baking soda to clean it for light or minor rust. Mix baking soda and water to a paste, then use a soft cloth dipped in a little to gently wipe the surface of stainless steel, clean and dry the water stains.
If the range of rust is slightly larger, you can directly cover the rusted area with baking soda, then moisten it with water, wipe it with a soft cloth, clean, and dry the water stains.
White vinegar is also a good helper in removing rust stains. You can use a soft cloth soaked in white vinegar to wipe in the rusty position of stainless steel furniture. Or spray vinegar directly on the rusty area (note to avoid other areas), leave it for a while, wipe with a soft cloth, clean it and wipe dry the water stains.
Chemical rust remover
If rust is serious, you can use chemical rust remover products for cleaning, but you need to take good protection as most of them contain phosphoric acid or oxalic acid, which are harmful to the skin and need to be safe.
Moreover, these chemical rust removers are very corrosive and can harm the essence of stainless steel, so you need to pay attention to the amount and time used.
1. Wipe the stainless steel (especially brushed finishes) should be wiped in the direction of the metal texture, not arbitrarily multi-directional wipe; otherwise, a chaotic pattern will appear.
2. It is important to keep the stainless steel dry at any time; after cleaning need to wipe dry water stains.
3. The above rust removal is for unplated/sprayed/colored stainless steel. If the stainless steel has been colored, you should contact professional suppliers for help.