Hastelloy C-276 alloy
Hastelloy C-276 alloy is a tungsten-containing nickel-chromium-molybdenum alloy with a very low silicon carbon content and is considered to be a versatile corrosion-resistant alloy. Mainly resistant to wet chlorine, various oxidizing chlorides, chloride solutions, sulfuric acid and oxidizing salts, have good corrosion resistance in low temperature and medium temperature hydrochloric acid. Therefore, in the past 30 years, in the harsh corrosive environment, such as chemical, petrochemical, flue gas desulfurization, pulp and paper, environmental protection and other industrial fields have a wide range of applications.
1 .Excellent corrosion resistance for most corrosive media in both oxidizing and reducing atmospheres.
- Excellent resistance to pitting, crevice corrosion and stress corrosion. The higher Mo and Cr contents make the alloy resistant to chloride ion corrosion, and the W element further improves the corrosion resistance. At the same time, Hastelloy C-276 is one of only a few materials resistant to moisture chlorine, hypochlorite and chlorine dioxide. It has high concentrations of chloride solutions such as ferric chloride and copper chloride. Significant corrosion resistance. It is suitable for various concentrations of sulfuric acid solution and is one of the few materials that can be applied to hot concentrated sulfuric acid solution.
Tensile strength: σb ≥ 730Mpa, elongation: δ ≥ 40%, hardness: HRB ≤ 100.
The Hastelloy C-276 alloy is thermoformed immediately at 1150 ° C and quenched with water. Cold deformation processing of Hastelloy C-276 alloy increases its strength.
Hastelloy C-276 alloy has similar formability to ordinary austenitic stainless steel. However, since it is stronger than ordinary austenitic stainless steel, there is more stress during the cold forming process. In addition, this material has a much faster work hardening speed than ordinary stainless steel, so mid-way annealing is required during extensive cold forming processes.
The physical properties of the Hastelloy C-276 alloy are as follows:
Material composition: 57Ni-16Cr-16Mo-5Fe-4W-2.5Co*-1Mn*-0.35V*-0.08Si*-0.01C* * is the maximum a margin
Executive Standard: UNS N10276, ASTM B575, ASME SB575, DIN/EN 2.4819
Petrochemical equipment, heat exchangers, flue gas desulfurization equipment, fluid chemical pumps, fluorine chemicals, etc.
6.Welding and heat treatment:
The welding properties of Hastelloy C-276 are similar to those of ordinary austenitic stainless steel. Before using a welding method to weld C-276, measures must be taken to minimize the corrosion resistance of the weld and heat affected zone. TIG welding, GMAW, submerged arc welding or other welding methods that minimize the corrosion resistance of welds and heat affected zones. However, it is not suitable for welding methods such as oxyacetylene which may increase the carbon content or silicon content of the weld and heat affected zone of the material.
For the selection of welded joint forms, reference can be made to the successful experience of the ASME Boiler and Pressure Vessel Code for Hastelloy C-276 alloy welded joints.
The welding groove is preferably machined, but the machining will bring about work hardening, so it is necessary to polish the machined groove before welding.
A suitable heat input speed is used during welding to prevent the occurrence of hot cracks.
In most corrosive environments, Hastelloy C-276 alloys can be used in the form of welded parts. However, in very demanding environments, C-276 materials and weldments are solution heat treated to achieve the best corrosion resistance.
The welding of Hastelloy C-276 alloy can be selected as the welding material or filler metal. If it is required to add certain components to the weld of Hastelloy C-276 alloy, like other nickel-based alloys or stainless steel, and these welds will be exposed to corrosive environments, then the welding rods or welding wires used for welding are required to have The base metal is resistant to corrosion.
The solution heat treatment of Hastelloy C-276 alloy consists of two processes: (1) heating at 1040 ° C ~ 1150 ° C; (2) rapid cooling to black state (about 400 ° C) within two minutes, such treated material Has good corrosion resistance. Therefore, it is ineffective to perform stress relief heat treatment only on Hastelloy C-276 alloy. Before the heat treatment, it is necessary to clean all the dirt which may generate carbon during the heat treatment, such as oil stain on the surface of the alloy.
The surface of Hastelloy C-276 alloy will produce oxides during welding or heat treatment, which will reduce the Cr content in the alloy and affect the corrosion resistance, so it should be surface cleaned. A stainless steel wire brush or a grinding wheel can be used, followed by immersion in a mixture of nitric acid and hydrofluoric acid in an appropriate ratio, and finally rinsed with water.
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