Alloy 20 Introduction (marketing department of Shanghai HY Industry Co., Ltd)
Alloy 20/UNSN08020/Incoloy20/2.4660/nicr20cumo/Nicrofer3620NB/F20/CN7M/Carpenter 20 CB 3TM/NAS 335X/NS143/NS 1403/0Cr20Ni28Mo3Cu3Nb/20Cb -0Cr20Ni28Mo3Cu3Nb/20Cb is an iron-nickel based corrosion resistant alloy that appeared in 1963. It is a high nickel deformable austenitic stainless steel with good corrosion resistance to H2SO4 and HNO3 and their mixed acids. However, when dissolving the nuclear fuel stainless steel cladding, this steel was found to produce stress corrosion fracture in 3 mol/L H2SO4. To solve this problem, it was found through research that increasing the amount of nickel in the steel from 27%-29% to 33%-38% under conditions where the other alloy compositions were essentially the same as Carpenter 20Cb, improved both the stress corrosion fracture resistance of the steel and greatly improved the corrosion resistance and workability of the steel in reducing acids, leading to the creation of the 20Cb-3 alloy. Since this alloy has good corrosion resistance in many chemical process media, including highly aggressive inorganic acid solutions, chlorine gas and various media containing chlorides, dry chlorine gas, formic and acetic acid, acid anhydride, seawater and brine, it has become an ideal material for media transport and is used in a large number of applications in flue gas scrubber towers, wet metallurgy and sulfuric acid industrial installations.
Weldability and welding process of Alloy20 alloy:
For a long time, many people have been debating: Is Alloy20 a stainless steel or a nickel alloy? This is because the 32-38% nickel content is right on the 36% cut-off. This blurs the categorization of the material. Generally speaking, there is no problem calling an alloy a nickel alloy because it contains more nickel elements, but classifying it as Ni-Based Alloy is not very suitable at this stage. The latest ASTM A240 standard includes Alloy20, which supports from the side that Alloy20 has been classified as stainless steel. At the time of customs declaration, as the larger part of Alloy20 nickel content in about 33%, customs will also be this material tariff by stainless steel classification to deal with. Similar materials are N08904 (904L), N08926 (1.4529), etc. This material was earlier classified as a nickel alloy series and implemented a separate ASTM B series of standards. But a decade ago, these super stainless steels were already subject to tariffs according to stainless steel!
Controversy does not affect its corrosion performance. Alloy20 has excellent resistance to stress corrosion cracking, good resistance to local corrosion, satisfactory corrosion resistance in many chemical process media, resistance to chlorine and various media containing chlorides, dry chlorine, formic and acetic acid, acid anhydride, seawater and brine, etc. At the same time, Alloy20 is resistant to oxidation-reduction complex media corrosion, commonly used in sulfuric acid environments and sulfuric acid solutions containing halogen ions and metal ions, such as wet metallurgy and sulfuric acid industrial installations. In addition, Alloy20 contains niobium, which improves the resistance to sensitization and intergranular corrosion.
In welding, Alloy 20 has the common characteristics of nickel alloys, which generally do not produce cold cracks when welding, but are more prone to hot cracks. Because nickel and sulfur, phosphorus, etc. can form low melting point eutectic, solidification often forms coarse dendritic austenite crystals, low melting point impurities more easily concentrated in the grain boundaries, in the grain solidification shrinkage stress and the role of welding stress, not fully solidified grain boundaries low melting point material is easy to be pulled apart to form thermal cracks, so the sulfur and phosphorus content of the welded material should be strictly controlled.
Although the alloy was originally designed for the sulfuric acid industry, Alloy 20 is now a popular choice for many industries. In addition to its widespread use in petrochemical process equipment, Alloy20 is often used in synthetic rubber manufacturing equipment, pharmaceuticals, plastics, organic and heavy chemical processing, storage tanks, piping, heat exchangers, pumps, valves and other process equipment, pickling and pickling equipment, chemical process piping, blisters, food and dye production. In addition, this high temperature alloy is used in heat exchangers, mixing tanks, metal cleaning and pickling equipment, and piping.
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