Stellite alloy welding can combine two pieces of metal to withstand high temperatures. It can also be used to repair parts damaged by wear or corrosion.
Strength
Stellite is an excellent hard-facing material, a process that layers tougher alloys over weaker, less expensive metals. Hard-facing increases the life of critical components in harsh environments, such as engine parts and aerospace parts that operate at high temperatures.
Stellitic alloys have a unique microstructure that makes them very hard. They have a hypoeutectic dendritic structure that is strengthened by a network of small carbide particles. They also have low thermal expansion and good chemical resistance.
Due to its excellent wear resistance, stellite is often applied to the seat surfaces of valves. This reduces the erosion of hot gases, extending the interval between maintenance and re-grinding. However, stellite is not suitable for seawater applications. Instead, a cobalt-based alloy called Ultimet or Triballoy is better for this application.
Durability
Welding is a process that joins dissimilar metals using high heat to melt and fuse them. This creates a strong connection between the two pieces that can withstand extreme conditions and temperatures. It is also very durable, which means it can withstand much abuse without deteriorating or breaking down.
Metallurgical analysis has been performed to study the microstructure of a typical Stellite weld overlay zone (WOZ) deposited on low alloy steel by gas-based cold spraying. The results show that the WOZ has a typical hypoeutectic dendritic structure with plenty of carbide precipitates and a network of co solid solutions. The WOZ also contains some hard and brittle Co-Fe phases.
Weldability
Stellite welding creates powerful connections that can withstand extreme temperatures and conditions. The process involves cleaning and preheating the pieces before bringing them together under an arc heat source or laser beam. Afterward, the welded parts are cooled and further processed as needed for their specific application. Common post-weld processing techniques include grinding, machining, plating, coating, and sandblasting.
The weldability of Stellite alloys is due to their high melting point and low thermal expansion. They are also non-magnetic and resist corrosion. This makes them ideal for use in harsh environments.
Stellite is available in a variety of forms, including rods and electrodes. They can be used for various applications, including hardfacing for valve seats, saw teeth, and acid-resistant machine tools. They can be welded using various methods, including TIG, GTAW, and oxyacetylene. However, it is important to note that some welding methods require a shield gas to protect against cobalt fumes.
Cost
In addition to its high wear resistance, Stellite has good flexibility and is easy to weld. Before welding, the surfaces that will be joined must be cleaned and preheated to prevent thermal stress and cracking. Preheating can be accomplished using grinding, wire brushing, or abrasive blasting.
The XRD analysis of the welding coating reveals the presence of a-Co and M7C6 (M = Fe, Cr) phases. The a-Co phase exhibits the highest peak intensity and contributes significantly to the hardness of the welding coating. However, M7C6 is also important and contributes to the toughness of the coating. This is attributed to the fact that the M7C6 carbides are denser and more dispersive than those of a-Co.
