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Duplex Stainless Steel
Description of material
MV274MDE is a duplex stainless steel with a special chemical balance designed to offer better machinability than other duplex grades. This is obtained by a specific steelmaking process that is able to produce the high machinability that is the special feature of enhanced machinability steels without jeopardizing in any significant way the main characteristics of duplex grades. Going into details, MV274MDE offers a better stress corrosion cracking, but with a slightly lower cryogenic toughness and pitting/ crevice corrosion, compared to other duplex stainless steels.
Propeller shafts, spindles, pumps and valves parts, rings, flanges, nuts, bolting.
Argon Oxygen Decarburization
MV274MDE has a higher amount of ferrite in its structure than other duplex grades. For this reason, it offers higher stress corrosion cracking, while pitting and crevice corrosion will be a little lower. It is useful to point up that this grade is micro-resulphurized with specific inclusions, but cannot be considered as free machining stainless steel compared to type 430F or type 303. It’s important to point out that the surface of every kind of stainless steel should be free of contaminants, tint and scale, and passivated for optimum corrosion resistance.
In the annealed condition, it has good cold deforming properties and a cold working hardening capacity lower than other duplex grades. Original mechanical properties and corrosion resistance are restored by a new annealing and fast cooling.
MV274MDE offers a very good machinability, if compared to the poorer machinability of other duplex and super-duplex grades.
MV274MDE has an enhanced machinability due to a special steelmaking process designed to produce a special picture of inclusions in the matrix. Therefore, this structure could cause a different morphology and surface oxides on the weld bead in case of autogenous welding. This can be overcome when a filler metal is used, with accurate setting of welding parameters. Corrosion resistance and the original balance of Ferrite/Austenite is restored by a new annealing or the use of over-alloyed duplex fillers. Preheating and post-welding heat treatment is normally not necessary.
Large shapes and ingots require a suitable preheating. Avoid overheating or reaching the upper limit of forging temperature. Both small pieces, rolled rings or bars could be either air or rapid quenched after forging. However, an annealing with fast cooling after every kind of hot working is mandatory for best mechanical properties and corrosion resistance. Slow or improper cooling rates generate a precipitation of deleterious intermetallic phases causing a considerable reduction of both toughness and corrosion resistance.