HY Co21(UNS R30021)

Introduction:

HY Co21  Material grades and equivalents: Stellite 21/ UNS R30021

HY Co21 (UNS R30021/Stellite 21) cobalt is a cobalt alloy. Cited properties are appropriate for the annealed condition. It has a moderately high thermal conductivity among cobalt alloys. In addition, it has a very low melting temperature and a fairly low tensile strength.

 

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    Description

    HY Co21(UNS R30021 , Stellite 21

    HY Co21 Material grades and equivalents:UNS R30021,  Stellite 21

    HY Co21 (UNS R30021/Stellite 21) 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 HY Co21 (UNS R30021/Stellite 21) composition. It was also one of the first heat-resistant alloys trialled for use in jet engines.

    HY Co21 (UNS R30021/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 HY Co21 (UNS R30021/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.

    HY Co21 (UNS R30021/Stellite 21) has excellent cavitation, galling and metal-tometal 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.

    HY Co21 (UNS R30021/Stellite 21) has excellent resistance to thermal and mechanical shock. Optimum high temperature strength is obtained by solution heat treatments at 1200-1240ºC (2190 – 2265ºF) followed by quenching, and aging in the temperature range 700-1150°C (1290-2100°F).

    HY Co21 (UNS R30021/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.

    Corrosion Resistance

    HY Co21 (Stellite 21) is resistant to oxidizing and reducing gaseous atmospheres up to 1150°C (2100°F). Because its ternary alloying element is Mo and not W, it has higher resistance to reducing or complex environments (e.g. sulphuric acid, hydrochloric acid, and sour gas) than CoCrW alloys such as Stellite® 6. The typical electrode potential in sea water at room temperature is approx. -0.3 V (SCE). Like stainless steels, HY Co21 (UNS R30021/Stellite 21) corrodes primarily by a pitting mechanism and not by general mass loss in seawater and chloride solutions. More information regarding corrosion resistance can be provided on request.

    Chemical composition:

    Co

    Cr

    W

    C

    Ni

    Mo

    Fe

    Si

    Other

    Bal.

    28

    0.25

    3

    5.2

    <3.0

    <1.5

    <0.5

    Mechanical properties:

    ASME/AWS

    Hardness(HRC)

    (SF)A 5.21 ER CoCr-E

    28-40

    Characteristic as below:

    HY Co21(UNS R30021/ Stellite 21) has excellent resistance on high heat, corrosion and abrasion.

    Processing conditions and application:

    Recommended use for making fuild valve,brass casting die , vlave seat, etc.