Stellite®21 (formerly known as Stellite®8) is a corrosion-resistant CoCr alloy developed in the mid-1930s, and applications for biocompatible hip implants and denture alloys were quickly discovered. Many alloys currently used in medical applications are made up of variant 21 of the original Stellite®. It is also one of the earliest heat-resistant materials, an alloy suitable for jet engines.


Stellite® 21 consists of a CoCrMo alloy matrix containing dispersed hard carbides. These carbides can increase the strength of the alloy and increase its hardness, but also reduce the ductility. The type, shape, size and distribution of carbides are strongly affected by the alloy processing history. Therefore, the mechanical properties of Stellite®21 are very dependent on the manufacturing route and any subsequent heat treatment. Due to the low volume fraction of carbides, the cobalt-based alloy matrix dominates the wear and corrosion properties. Stellite®21 has excellent anti-cavitation, anti-wear and anti-metal-to-metal sliding properties, but it is not recommended for severe hard particle wear. The surface can be hardened considerably during wear and even machining, so it is very important to use the correct machining tools and techniques to achieve the best results.


Stellite®21 has excellent thermal shock and mechanical shock resistance. The best high temperature strength is obtained by solution heat treatment at a temperature of 1200 to 1240ºC (2190-2265ºF), followed by quenching and aging in the temperature range of 700-1150°C (1290-2100°F).


Stellite®21 can be used for casting, powder metallurgy treatment or for welding surfacing. It is recommended for applications involving cavitation, corrosion, corrosion and/or high temperature, such as petrochemical and electric valve trim generation. Because of its good impact resistance, it has been widely used in the manufacture of forging or hot stamping dies. It is not recommended to use the oxyacetylene welding deposition method for this alloy.


Argon arc welding deposition


Cobalt, chromium, molybdenum, carbon other hardness ** density melting range basis 26-29 4.5-6. 0 0.20-0.35


Nickel 2.0-3. 0 Fe, Si, Mn 27-40 HRC **


290-430 high pressure**


8.33 g/cm3


0.301 lb/in 3






**Higher values ​​indicate typical work hardened surfaces. Stellite®21 can work at temperatures up to 550HV (48HRC). Hvof and plasma spray deposition


Corrosion resistance


Stellite®21 can resist oxidation and reduction gases up to 1150°C (2100°F). Because its ternary alloying element is Mo instead of W, it is very effective in reducing or complex environments (such as sulfuric acid,


Hydrochloric acid and acid gas) (such as CoCrW alloys such as Stellite®6). The temperature is approximately -0.3 V (SCE). Like stainless steel, Stellite® 21 types of corrosion are mainly through pitting mechanisms rather than through


General mass loss in sea water and chloride solutions.