Stellite™ 21 Alloy

Nominal Composition (Mass %) and Physical Properties

Co Cr Mo C Ni Others Hardness** Density Melting Range
Base 26-29 4.5-6.0 <0.35 <3.0 Fe, Si, Mn 27-40 HRC**
290-430 HV**
8.33 g/cm3
0.301 lb/in3

**Higher values indicate a typical work-hardened surface. Stellite 21 can work harden up to 550HV (48HRC).

Stellite 21

Stellite cobalt-based alloys consist of complex carbides in an alloy matrix. They are resistant to wear, galling, and corrosion and retain these properties at high temperatures. Their exceptional wear resistance is due mainly to the unique inherent characteristics of the hard carbide phase dispersed in a CoCr alloy matrix.

Stellite 21 (previously known as Stellite 8) was developed
in the mid-1930s as a corrosion-resistant CoCr alloy, and rapidly found application as a biocompatible hip implant and denture alloy. Many of the alloys currently used in medical applications are variants of the original Stellite 21 composition. It was also one of the first heat-resistant alloys trialed for use in jet engines.

Stellite 21 consists of a CoCrMo alloy matrix containing dispersed hard carbides which strengthen the alloy and increase its hardness but also decrease the ductility. The type, shape, size and distribution of the carbides is strongly influenced
by the processing history of the alloy, and for this reason the mechanical properties of Stellite 21 are very dependent upon the manufacturing route and any subsequent heat treatments.

Due to the low volume fraction of carbides, the Co-based alloy matrix dominates the wear and corrosion properties. Stellite 21 has excellent cavitation, galling, and metal-to-metal sliding wear resistance, but is not recommended for severe hard particle abrasion. The surface can work harden considerably during wear or even during machining, and the use of correct machining tools and techniques is important to achieve optimal results.

Stellite 21 has excellent resistance to thermal and mechanical shock. Optimum high-temperature strength is obtained by solution heat treatments at 1200–1240C (2190–2265F) followed by quenching and aging in the temperature range 700–1150C (1290–2100F).

Stellite 21 can be cast, powder metallurgically processed, or applied as a weld hardfacing. It is recommended for applications involving cavitation, erosion, corrosion and/or high temperatures, such as valve trim for petrochemical and power generation. Due to its good impact resistance, it has been widely used in the building up of forging or hot stamping dies. The oxyacetylene weld deposition method is not recommended for this alloy. 





Optical Micrograph of a Stellite 21 Investment Casting (as-cast, etched, 200X). The Carbides in Stellite 21 are Usually of the Type (Cr,Mo,Co)23 C6

Stellite 21 can be supplied to the following specifications:

UNS R30021  Rod, Castings
UNS W73041 Wire
UNS W73021  Electrode
AMS 5385 Castings
AMS 5819 Rod, Wire
AWS A5.21 /
AWS A5.21 /
AWS A5.13 /


Stellite 21 Alloy Data Sheet

Check out our Stellite 21 Alloy data sheet for additional information.

View Now
You are about to add to your My Solutions page. Do you want to proceed?
Please adjust the following properties from

ISO Catalog Number

ANSI Catalog Number

to find similar products.


You should be logged to see your dashboard information
Session expired due to inactivity, please login again
The product/s () you were trying to add to the cart is/are not available, please contact customer service
item(s) successfully added to the cart
View Cart

. Please enter the desired qty for the material(s) you want to include in your promotion or Proceed Without Promotion and only your base materials will be added to the cart.

Minimum quantity should be

SAP Material Number ISO Catalog Number Grade    

Thank you for your registration, pending approval & completion of the registration, your access is currently limited. Full utilization of product search capabilities & collaboration space is available and will remain. Please allow 2 business days for registration completion.

Thank you for your successful registration. You now have immediate access to log in and utilize the site.

You are about to leave the Solution building process.

Are you sure you want to leave?