welding-alloys.com 9 Metallurgy and performance Cobalt based superalloys are designed for wear resistance, corrosion resistance, and high-temperature performance. These alloys primarily consist of cobalt, with significant additions of chromium, tungsten, molybdenum, and carbon. Key alloying elements and their roles: • Chromium (Cr): enhances corrosion resistance, typically comprising 25-35% of the alloy. • Tungsten (W) and Molybdenum (Mo): contribute to solid-solution strengthening, improving the alloy's high-temperature strength and hardness. • Carbon (C): facilitates the formation of hard carbides, significantly increasing wear resistance and hardness. The microstructure of cobalt based superalloys features complex carbides dispersed within a tough, cobalt-rich matrix. This unique structure imparts outstanding hardness and toughness, enabling the alloys to maintain their properties even under elevated temperatures. The inherent low stacking fault energy of the cobalt matrix promotes work hardening, further enhancing wear resistance. During welding or cladding operations, adhering to recommended procedures is crucial to achieve minimal dilution and maintain the desired chemical composition of the deposited layer. Carbon serves as the primary element for increasing hardness, with tungsten and chromium providing secondary effects. While higher carbon content improves abrasion resistance, it may reduce impact resistance, necessitating a balanced approach based on specific application requirements. Typical microstructure of STELLOY cobalt Exhaust valve seat hardfaced with STELLOY 6-G Back to contents page
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