EXHAUST VALVES MATERIAL AND PROPERTIES

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Properties required :

•              Maintain strength at high temperatures.

•              Have good creep resistance.

•              Easily machined.

•              Good corrosion and erosion resistance.

•              Good compatibility with guide materials.

•              Good wear resistance.

Typical Nickel based alloy :

            C         Fe       Cr        Ti         Al        Co       Mo       Ni

            0.1       1.0       15        1.0       5          20        4          Remainder

Valve stems may be surface hardened to improve wear (Chromed, Nitrided, etc.)

Valve faces often have Stellite layer welded on which gives a hard corrosion resistant finish which is maintained at high temperatures.

Stellite            Co       Cr        Mo       C         W(Tungsten)

                        50        20        18        2          10       

Valve seats are often alloy steel with Stellite facing. Again this gives good corrosion and erosion resistance  to prolong life.

Valve cages are usually cast iron with the stem guide being a separate item usually pearlitic cast iron. This gives cheap easy manufacture and the guide material has good compatibility.