The material of duplex steel pipe fittings refers to stainless steel with ferrite and austenite accounting for about 50% each, and generally the content of lesser phases needs to reach at least 30%. In the case of low C content, the Cr content is 18%~28%, and the Ni content is 3%~10%. Some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N. Super duplex stainless steel type, containing high molybdenum and nitrogen, standard grade UNS S32750 (25Cr-7Ni-3.7Mo-0.3N), some also contain tungsten and copper, PREN value greater than 40, suitable for harsh medium conditions, with Good corrosion resistance and mechanical properties, comparable to super austenitic stainless steel.
The representative grade of duplex steel elbow is UNS S31803 (22Cr-5Ni-3Mo-0.15N), the PREN value is 32-33, and its corrosion resistance is between AISI 316L and 6%Mo+N austenitic stainless steel. Duplex stainless steel contains about 50% to 60% austenite and 50% to 40% ferrite after normal solution treatment (heating at 1020°C to 1100°C and water cooling). As the heating temperature increases, the ratio of the two phases does not change significantly. The continuous use temperature range of duplex stainless steel is -50 to 250°C, the lower limit depends on the brittle transition temperature of the steel, the upper limit is limited by the brittleness of 475°C, and the upper limit temperature cannot exceed 300°C. Duplex stainless steel needs rapid cooling after solid solution treatment, and slow cooling will cause the precipitation of brittle phases, which will lead to the decrease of the toughness of the steel, especially the localized corrosion resistance. The lower limit temperature of hot working and hot forming of high chromium molybdenum duplex stainless steel should not be lower than 950°C, super duplex stainless steel should not be lower than 980°C, low chromium molybdenum duplex stainless steel should not be lower than 900°C, to avoid the precipitation of brittle phases during processing Surface cracks caused by the process cannot be treated with stress relief at 650-800 °C commonly used for austenitic stainless steel, and solution annealing is generally used. After surfacing duplex stainless steel on the surface of low alloy steel, when the overall stress relief treatment at 600-650 °C is required, the toughness and corrosion resistance brought about by the precipitation of brittle phases must be considered, especially the localized corrosion resistance. In order to avoid the drop problem, the heating time in this temperature range should be shortened as much as possible. The heat treatment of low alloy steel and duplex stainless steel clad plate should also be considered in the same way.
Duplex steel elbow material:
ASTM / ASME SA789/790 UNS S31803 , S32205 , S32750 , S32760 .
ASTM A182 F51, F53, F55
ASTM A815 UNS S31803, S32205, S32750, S32760
Size range: outer diameter 21.3~1219MM, wall thickness: SCH 10S~SCH XXS
Author: Maria
Post time: Jun-26-2023