The Common Material of Stellite Valve Seat


    With good resistance to elevated temperatures, corrosion and thermal fatigue and excellent heat strength, Cobalt Alloy is one of the common materials for sealing surface of stellite valve seats. Particularly it has superior resistance to scratch in a hot state. Therefore, it is commonly used to steam valves of the critical or supercritical parameters, as well as the surfaces of valves with relatively harsh conditions and high requirements for anti-wear and corrosion resistance. Due to excellent properties, cobalt alloys widely used in aerospace, nuclear, power, petrochemical, metallurgy, transportation and machinery, etc.

    According to the application, the process of cobalt can be fallen into casting, forging or welding process.

    1.Forging process

    When the S content is greater than 0.005 %, the ductility of the cobalt is greatly reduced. The ingot containing S greater than 0.015% cannot be forged due to the formation of cracks between the grains. Forged cobalt alloys are most commonly used in the form of sheets. This alloy has high strength and good oxidation resistance at about 982 ℃, which can be welded in a conventional manner and get high strength by cold working. Elgiloy alloy and MP35N alloy are mainly used for springs and fasteners.

    2.Casting process

    cobaltalloy is used in steam turbines and in conditions where high temperature oxidation resistance and vulcanization resistance are required. Strengthening can be obtained by precipitation with carbide (M23C6, M6C) by using solid solution and precipitation heat treatment. With slow precipitation rate, it has no effect on weldability.

    3.Welding process

    The welding process for surfacing a cobalt matrix has become common and reliable for high temperature, wear and corrosion resistance. It is widely used in the aerospace, nuclear, thermoelectric, petroleum, transportation and machinery industries.

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