Rust is the most insidious enemy of all iron structures. It imperceptibly but surely destroys them both in air and in water, turning strong structures into fragile ruins. It would seem that steel, being an improved iron alloy, should be more resistant to rust. But it is also poorly protected from it. We encounter the consequences of corrosion in everyday life every day: rust spoils cars, damages household appliances and violates the integrity of buildings. However, there is an exception – stainless steel. As you can understand from the name, it is not susceptible to rust. What makes this material so unique? Let's figure out what is hidden the secret of stainless steel durability.
Stainless steel is an expensive material with unique properties. Image: aradbranding.com
What Causes Rust
In simple terms, rust appears on metal structures and equipment due to the reaction of iron with oxygen and moisture. When metal is in contact with water and air for a long time, oxygen penetrates the metal structure and begins to slowly destroy it from the inside.
Rust is an iron oxide that forms on the surface of metal objects when exposed to oxygen and moisture, causing them to corrode. Source: myfreetextures.com
According to All The Science, it's like bits of oxygen are eating away at the metal, creating a rusty coating on the surface. In a salty environment, like seawater, the process is even faster. Water penetrates into the tiny cracks in the metal, which accelerates the deterioration. Thinner metals rust faster and can completely disintegrate.
Rust can destroy even very large structures. For example, it almost destroyed the infamous Titanic, which has been lying at the bottom of the Atlantic Ocean since that fateful year of 1912.
The current state of the Titanic underwater. Photo: artnet.com
What metal doesn't rust
Stainless steel, which is more commonly known as stainless steel, is an alloy that is resistant to corrosion. There are different grades of stainless steelwhich may contain chromium, nickel, carbon, nitrogen and many other compounds.
According to Live Science, stainless steel remains rust-resistant thanks to its special composition. Unlike regular steel, which is almost entirely made up of iron (around 99%) except for a few additives, stainless steel always contains an important element: chromium. It is this element that protects the steel from oxidation. In regular steel, iron reacts vigorously with oxygen, forming rust, which destroys the metal. But in stainless steel, chromium creates a protective layer on the surface that prevents oxygen from penetrating the iron.
Stainless steel is used to make pipes and many other products that often come into contact with water. Image: tekhmet.ru
This protective layer, just a few nanometers thick, is invisible to the eye, but it does its job reliably. If this coating is damaged, it can restore itself. Water, oxygen, and other substances are not dangerous for chromium, because it is inert, that is, it does not react with the environment. This fact makes stainless steel ideal for use where hygiene and cleanliness are important – for example, in medicine and cooking.
In fairness, it should be noted that under certain conditions even stainless steel can become rusty. For example, it corrodes in salt water, as well as if welding technologies are violated.
Read also: What is the secret of the Qutub column – an iron pillar that does not rust for hundreds of years
Who invented stainless steel
The history of stainless steel began in 1912, when the English metallurgist Harry Brearleywas trying to create an alloy to protect gun barrels from corrosion. Over the course of several months, he experimented with various combinations of iron, carbon, chromium, and nickel.
Although none of the alloys he created worked for the gun barrels, Brearley noticed that one material he had thrown out in his backyard did not rust even after several weeks of sitting outside. Inspired by this discovery, he continued his experiments and in 1915 introduced the world to the new material we know today as stainless steel.
Harry Brearley invented stainless steel by accident. Image: fishki.net
Since then, stainless steel has become extremely popular and now accounts for about 4% of all steel used annually worldwide. Despite its popularity, stainless steel remains expensive to produce to this day: its cost is three to five times higher than that of regular steel.
Special additives such as molybdenum (for underwater use of steel structures) can further increase the price. Therefore, in most cases, ordinary steel is used, which is protected by paint or other coatings.
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If you are interested in learning more about other amazing metals and their properties, we invite you to read our articles “The Most Valuable Metals on Earth” and “The Most Interesting Metals on Earth”.