Chromium (Cr)

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Alloying Element – Chromium

Chromium Alloying element

Chromium added to carbon steel in percentages greater than 11% creates Stainless Steel. At this percentage and greater (When combined with Nickel), the corrosion resistance of steel vastly increases, and oxidation of the iron is prevented. 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.

Raw Materials by Chromium content