The special chemical composition of stainless steel creates a protective layer on its surface, preventing oxygen from coming into contact with iron and causing rust.
The chemical composition of stainless steel inhibits oxygen in the air and the environment from interacting with the iron in the steel, thereby blocking harmful oxidation reactions. Regular steel rusts when iron reacts with oxygen, forming iron oxide. Although rust is not harmful to humans, it can corrode the iron, making the material less safe and aesthetically displeasing.
Stainless steel has many applications in the food, medical, and various other industries. (Image: WordPress)
Regular steel typically contains 99% iron and about 0.2 – 1% carbon, while stainless steel usually comprises around 62 – 75% iron, 1% carbon, and more than 10.5% chromium. Stainless steel also contains several percent of nickel, which enhances the material’s durability and workability.
Chromium plays a crucial role in preventing rust in stainless steel, according to materials scientist Tim Collins, secretary general of Worldstainless, a non-profit organization in Belgium collaborating with the World Steel Association. Chromium reacts with oxygen in the environment, both in the air and underwater, creating a passive chromium oxide layer (Cr2O3) on the metal surface. This layer prevents oxygen from coming into contact with the iron in the steel, thus preventing the formation of iron rust, Collins explains.
The passive layer on stainless steel is only a few nanometers thick and is not visible. The chromium oxide layer can also self-repair if damaged. It is inert, does not chemically react with other compounds, and does not leak out, making stainless steel highly suitable for food production, surgical applications, and many other uses.
Stainless steel was developed in 1912 by British metallurgist Harry Brearley while researching steel alloys to prevent corrosion in gun barrels. Brearley created an alloy made from iron, carbon, chromium, and nickel, but it was unsuitable for gun barrels, so he discarded it behind his house. After a few weeks, Brearley noticed that the alloy in the yard did not rust, leading him to develop the material and introduce the product in 1915.
According to Collins, stainless steel currently accounts for about 4% of the steel used worldwide each year, nearly 2 billion tons. However, producing stainless steel is very complex and expensive, costing 3 to 5 times more than regular steel production and including special metal components in the alloy (such as molybdenum for underwater applications), making it even pricier. As a result, most applications requiring steel utilize regular or carbon steel instead.
