Chromium is used in electroplating for glossy chrome plating, hard and black chromium plating, as a catalyst in the chemical industry but also in steel production. Chromium is one of the most important alloying elements for producing rustproof and heat-resistant steels.
Chromium added to carbon steel in percentages usually greater than 11% creates stainless steel. At this percentage and greater, the corrosion resistance of a steel vastly increases, and oxidation of the iron is prevented in many conditions. The iron does not oxidize because the chromium will oxidize first and form a protective layer over the steel. Chromium also helps to improve mechanical properties, even in smaller amounts. It will increase the steel’s strength, hardness, and ability to be heat treated.
In Steel(up to 13%): Chromium is a powerful alloying element in steel. It strongly increases the hardenability of steel and markedly improves the corrosion resistance of alloys in oxidizing media. In common alloy steels such as 4340, it has a content of around 1%. In high alloy tool steel, in ranges between 3%-13%.
In Stainless Steel (up to 30%): When amounts of chromium around 11% or greater are used, and nickel composition is higher than 8%, austenitic stainless steel is created. The chromium forms a thin film of reaction products that shields the metal substrate from oxidation attack. The protective film (called passive film) is only 1.0-2.0 nm, reducing the corrosion rate to a negligible level. Typical stainless alloys such as 316 have 17% chromium content.
In Super Alloys (Up to 50%): Where stainless steels may fail is where nickel-based superalloys come into play. Most HSRA’s contain around 20% of chromium (For example, Inconel 718).
In Aluminium Alloys (Up to 0.5%): Chromium is added in small quantities to Aluminium alloys to control the grain structure and prevent recrystallization. It also reduces stress corrosion y and improves toughness. Although it is a small quantity, it is critical for high-quality Aluminium.