Steel is a metal that is manufactured into hundreds of products because of its strength, durability, and shine. The definition of stainless steel is a steel that is resistant to tarnishing and rusting. Stainless steel is composed of about seven different metals, but most of it is iron, which can rust in humid environments.
Iron in regular steel rusts, so it makes one wonder, does stainless steel also rust? The answer is yes. Stainless steel can rust under the following conditions:
- Loss of chromium oxide barrier
- Chemical reactions
- Reactions with water
- Reactions to heat
While stainless steel is resistant to tarnishing, it can rust under the right circumstances. Please read on to find out what is causing your stainless steel to rust. At the end of this article, is a section on how you can remove surface rust and stains from your stainless steel cookware.
Condition #1: Loss of Chromium Oxide Barrier
Stainless steel is composed of iron, carbon, chromium, and other metals. Chromium is mixed inside of stainless steel to give it extra strength and a protective coating against rust. This protective coating is called chromium oxide and occurs when the chromium in the stainless steel reacts with the oxygen in the atmosphere. This chromium oxide barrier bonds to the steel and remains there as long as oxygen is present.
Rust comes from iron reacting with oxygen and water. The chromium oxide barrier is very resistant to water and prevents iron from reacting with oxygen and water. As long as the barrier is in place, the stainless steel is protected from the elements that could cause it to rust. Should the chromium oxide layer get damaged, the chromium on the surface of the steel will replace the barrier.
However, when the chromium oxide is exposed to certain elements and materials, these things can tear the barrier away and expose the iron. Without the chromium oxide barrier, the stainless steel will eventually rust because of this exposure. The solution is to keep the chromium barrier intact and away from things that can damage it.
Some of these items that can damage the barrier come from common cleaning agents that are improperly used to clean stainless steel.
Condition #2: Chemical Reactions
Using the wrong cleaning agents on stainless steel can damage the protective barrier and cause the appearance of rust. Most cleaners contain elements such as iodine, alcohol, ammonia, and other acidic chemicals. These are primarily used to remove dirt or stains, but they can also remove the chromium oxide barrier from stainless steel.
Another chemical known as chlorine not only causes the stainless steel to rust, but it can also damage the steel in another way. Through a process called pitting corrosion, chlorine can cause holes or pits to form in stainless steel. The process of pitting corrosion causes the iron within the stainless steel to leave and take the chromium with it, leaving holes behind for water and air to get through to metals such as iron.
This only occurs in situations that have a high concentration of chloride or salt in the atmosphere.
Steel brushes and steel wools should not be used to clean stainless steel because these items contain carbon steel, which can be left behind during cleaning, and begin to rust. As the carbon steel rusts, it causes the exposed iron of the stainless steel to rust with it. Instead of using steel wool, use products and sponges designed to clean stainless steel.
Condition #3: Reactions With Water
Saltwater damages a majority of metals, including stainless steel. Saltwater helps facilitate a reaction between iron and oxygen in the water. Saltwater aids in this process by exchanging electrons between iron and oxygen to form rust. This rusted form of iron crumbles away and leaves behind a layer of fresh iron to begin the process again.
Saltwater and iron have a stronger reaction to each other because saltwater has more free-flowing ions than freshwater. Iron is more likely to rust in the presence of saltwater instead of freshwater because the free ions accelerate the chemical reactions. Unless the iron within the stainless steel is well protected, the water will rust the iron.
Stainless steel is resistant to saltwater because of its chromium oxide layer. However, if exposed to saltwater over a long period of time, the stainless steel’s barrier will eventually corrode, and the steel will begin to show signs of rust.
Special paints designed to repel saltwater or a coating of zinc can help keep the effects of saltwater exposure. Special paints can stop saltwater from contacting the stainless steel’s surface. A specialized coating of zinc can also keep the effects of saltwater away from the stainless steel.
Condition #4: Reactions to Heat
Stainless steel is a heat-conducting type metal and is used in products designed to handle high temperatures. Some items that contain stainless steel are ovens, furnace parts, boiler rooms, engines, and more. Stainless steel can handle high amounts of heat, but temperatures that are between 842°F to 1562°F (450°C to 850°C) for a long time, soon becomes a problem.
Such temperatures are normally found in industrial jobs like welding and not in regular amenities such as cooking.
During high temperatures, through a process called intergranular corrosion, the carbons within the steel react with chromium and form chromium carbides. Chromium carbides are not resistant to rust like the chromium oxide barrier and are formed when carbon reacts with chromium. Chromium carbides form along molecular cracks in the stainless steel called grain boundaries.
These areas are less resistant to rust and compromise the stainless steel’s barrier at the molecular level. Since the chromium has fused with the carbon, there is a hole in the area where the chromium once was.
The stainless steel now has a hole in its defenses, giving oxygen and moisture the chance to slip in, react with the iron, and create rust.
Intergranular corrosion can be prevented by making sure the steel does not remain in these temperatures for long periods or by carefully cooling down the steel so that it does not form chromium carbides.
Tips for Removing Surface Rust From Stainless Steel
If you have rust on a stainless steel item, do not give up hope, for it can be restored. Stains or rusts located on the surface of the stainless steel are called surface stains. These can be removed using a solution and a bit of scrubbing. Baking powder is a home remedy that can restore rusted stainless steel kitchen appliances back to normal.
For this process, you will need a tablespoon of baking soda, two cups of water, a toothbrush, and a cloth. Scrub baking soda onto the surface of the appliance using the toothbrush. The baking soda will loosen up the rust without leaving any marks on the steel. Once the rusted area is covered up, use two cups of water to rinse off the area. Dry the stainless steel with a cloth, and the rust will be gone.
If you want to use a premade solution to get the job done, there are products that you can buy. There are stainless steel cleaners such as CitriSurf products that remove rusts and stains from stainless steel items and the Cerama Bryte product, which removes and protects stainless steel from rust and stains.
The CitriSurf77 Plus and the CitriSurf 2310 removes rust and passivates the stainless steel items. Passivation is a process that removes rust from a steel object but leaves behind protective components such as chromium. These components react with oxygen to form a protective barrier, called chromium oxide. These products come in gels or sprays.
Cerama Bryte Protective Stainless Steel Cleaning Polish is a liquid product that removes stains and smudges off of stainless steel items. It can remove food stains, water spots, and fingerprints. It leaves behind a protective coating to prevent future spots from appearing and gives your steel a nice shine. Just put a little of the product on a cloth, wipe the surface of your stainless steel object, and you are done.
If you would like to have more information about removing and preventing rust from stainless steel, read this article.
Rust on Stainless Steel: Final Thoughts
Stainless steel does not rust, as easily as other metals, but it can appear to rust under the right conditions. The chromium inside steel is the main ingredient for keeping the stainless steel rust-free. The chromium creates a layer called the chromium oxide layer, which protects the steel from rust. As long as proper precautions are taken to keep this layer safe, then rust will not form on the steel.
Be careful not to use any chemicals that are acidic or binding to chromium as these can strip away the barrier. Make sure that your stainless steel is not exposed to saltwater for long periods of time because it will weaken the barrier and draw out the iron to form rust.
Finally, make sure that you do not expose stainless steel to extremely high temperatures for a long period of time. By following these proper precautions, your stainless steel will remain stain and rust proof for a long time.