Sealing and hardfacing
Stellite 6
Cobalt-chromium-tungsten hardfacing alloy
A cobalt-based hardfacing alloy. Deposited by welding on valve seat and disc faces; resists wear, erosion, galling and corrosion at high temperature. The "hardfaced" material of the API 600 trim codes.
- HARDNESS
- —
- —
- —
- TEMPERATURE
- −200 … +650 °C
- COST
Chemical composition
The values in this section are being verified.
Mechanical properties
The values in this section are being verified.
Service temperature
−200 °C+650 °C−200−1000100200300400500600700800
Retains its hardness up to ~500 °C; 540–650 °C in valve and steam service. The limit is usually set by the base material.
Media suitability GENERAL TREND
Fresh water
Seawater
Steam
Hydrocarbons, oil
Dilute acid
Caustic
Air, gas
Low temperature
Emsal assessment. The final choice is made from corrosion tables, taking concentration, temperature, chloride content and flow velocity into account.
Strengths and weaknesses
Strengths
- Hardness and wear resistance at high temperature
- Highly resistant to galling
- Resistant to erosion and cavitation
Weaknesses
- Expensive (cobalt)
- Overlay welding needs a qualified procedure; risk of cracking
- Difficult to machine, grinding required
Manufacturing and use
- ECONOMY
- High.
- MANUFACTURING METHODS
- Overlay by TIG / PTA / oxy-acetylene · Cast part
- TYPICAL VALVE PARTS
- Seat face · Disc face · Stem guide
Source: AWS A5.21 ERCoCr-A. Values compiled and verified by Emsal Vana; for binding values, refer to the current edition of the standard and the material certificate.