As the saying goes, "A sharp knife doesn't rust if not sharpened." Iron rusting is one of its major drawbacks. To prevent rusting and protect steel, people have to paint ironware, galvanize it, or coat it with "chromium"... However, once the "coating" is worn out, iron will still be devoured by rust. People really want to create a kind of steel that doesn't rust!
In 1913, British metallurgist Henry Brearley was dedicated to developing a new alloy steel for making gun barrels, as the existing gun barrels were too prone to wear and tear. He tried one formula after another but failed to achieve his goal. He threw the scrap materials into the yard. Exposed to the elements, the steel soon became rusty. One day, while passing by the scrap pile, he suddenly noticed a piece of steel that shone brightly and didn't rust at all. Surprised by this strange phenomenon, he conducted in-depth research and discovered that the steel contained a large amount of chromium. Chromium, a shiny metal commonly known as "chromium", could coat the surface of steel to make it shiny and beautiful, but the inner steel would still rust. However, once chromium was melted into steel and the chromium content reached over 12%, the steel could resist corrosion without any coating. Brearley drew inspiration from the scrap pile and invented stainless steel.
However, at first, people didn't believe that there could be steel that didn't rust. Therefore, Brearley's invention didn't initially gain popularity. Later, one of his friends used stainless steel to make Western-style cutlery. After many people used this new type of cutlery, they realized its benefits of not rusting. Thus, stainless steel began to gain popularity. In 1916, Brearley obtained a patent for stainless steel and was henceforth hailed as the "Father of Stainless Steel". Today, making cutlery is just one of the many applications of stainless steel. In food factories, workers use huge stainless steel pressure cookers to cook food; in hospital operating rooms, stainless steel surgical instruments gleam brightly; in chemical plants, even tall reaction towers are often made of stainless steel; in synthetic ammonia plants, more than 20 types of stainless steel with different properties are needed to manufacture production equipment... In watches, stainless steel accounts for over 60% of the weight. A "full-steel watch" refers to one whose case and back are all made of stainless steel; a "semi-steel watch" refers to one whose back is made of stainless steel while the case is made of brass or other metals (coated with chromium).
Of course, stainless steel not rusting only applies under normal circumstances. There's no metal that doesn't rust, but stainless steel is more resistant to corrosion. People have conducted such experiments: placing two 20-gram pieces of stainless steel and ordinary carbon steel in dilute nitric acid and boiling them for a day and a night. The result showed that the ordinary steel was severely corroded, leaving only 13.6 grams, while the stainless steel still had 19.8 grams remaining.