Hastelloy C-22 Alloy
General characteristics of Hastelloy C
Hastelloy C-22 is a nickel-chromium-molybdenum-tungsten alloy with outstanding resistance to pitting, crevice corrosion and stress-corrosion cracking. The alloy is very resistant to a host of aggressive corrosive media. It resists the formation of grain boundary precipitates in the weld heat-affected zone and hence is suitable for most chemical process applications in the as-welded condition.
The corrosion resistance of this alloy renders it suitable for many industrial applications, including, among others, electro-galvanizing rolls, flue gas scrubber systems, nuclear fuel processing, phosphoric acid production and sulfur dioxide cooling towers.
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’s welding characteristics are similar to those of C-276 alloy. Gas-tungsten-arc welding (GTAW) and shielded-metal-arc welding (SMAW) are commonly used to weld C-22 alloy.
It is recommended that the alloy be in the solution-annealed condition for welding, and that C-22 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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