Hastelloy C-276 Nickel Alloy
General characteristics of Hastelloy C – 276 Alloy
Alloy C-276 resists the formation of grain boundary precipitates in weld heat-affected zones, hence its suitability for most chemical process applications in the as-welded condition. If, however, attack of a C-276 alloy weld joint is experienced as it may be in certain environments, C-22 weld filler metal should be considered.
The alloy has excellent resistance to a wide variety of chemical process environments.
The alloy is used in flue gas desulfurization systems. It has excellent resistance to pitting and stress corrosion cracking, and resists wet chlorine gas, hypochlorite and chlorine dioxide. The alloy is also resistant to seawater and brine solutions.
The alloy is forged between 2250/1750ºF (1230/955ºC) following a soak at forging temperature of 30 minutes per inch of billet or ingot section thickness. Forging should be started immediately the stock is removed from the reheat furnace and 25/40% reductions help to retain as much internal heat as possible. For optimum corrosion resistance, forged parts should be subsequently annealed. See Heat Treatment.
The alloy is normally supplied in the solution-annealed condition. This treatment is carried out at 2050ºF (1120ºC) followed by water quench or rapid air cool. The treatment is performed after hot working to ensure optimum corrosion resistance and between cold- working operations.
The alloy is considered moderate to difficult to machine, but can be machined using conventional methods. The alloy has a high work hardening rate, and efficient machining requires rigid and overpowered machines, sharp tools, preferably carbide-tipped, and heavy, constant feeds.
The alloy welds in a similar manner to C-22 alloy. Gas-tungsten-arc welding (GTAW) and shielded-metal-arc welding (SMAW) are commonly used to weld C-276 alloy.
It is recommended that the alloy be in the solution-annealed condition for welding, and that C-276 filler metal be used.
Submerged-arc-welding is not recommended for this alloy as there is high heat input with this method and slow cooling of the weld. Neither is Oxyacetylene welding recommended, due to the danger of carbon pickup in the weld.
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