Duplex steel and Super Duplex stainless steel pipe
Stainless steel pipe is roughly divided into 8 categories:
Austenitic stainless steel pipe
Super austenitic stainless steel pipe
(Super) duplex stainless steel pipe
Nickel base alloy tube
Martensitic stainless steel
Ferritic stainless steel
Titanium alloy pipe
recipitation hardening stainless steel pipe
Brand:
S31803 / s32250, S32750, s32760, etc
Product details
(super) duplex stainless steel pipe
Duplex stainless steel has the characteristics of both austenitic stainless steel and ferritic stainless steel because it has austenitic + ferritic duplex structure and the content of the two phases is basically the same. The yield strength can reach 400MPa ~ 550MPa, which is twice that of ordinary austenitic stainless steel. Compared with ferritic stainless steel, duplex stainless steel has higher toughness, lower brittle transition temperature, significantly improved intergranular corrosion resistance and welding performance; At the same time, it retains some characteristics of ferritic stainless steel, such as brittleness at 475 ℃, high thermal conductivity, low coefficient of linear expansion, superplasticity and magnetism. Compared with austenitic stainless steel, duplex stainless steel has higher strength, especially the yield strength is significantly improved, and the properties of pitting corrosion resistance, stress corrosion resistance and corrosion fatigue resistance are also significantly improved.
Duplex stainless steel can be subdivided into:
The first type is low alloy type, representing the brand UNS s32304 (23cr-4ni-0.1n). The steel does not contain molybdenum, and the prEN value is 24-25. It can be used instead of AISI304 or 316 in terms of stress corrosion resistance.
The second type belongs to medium alloy type. The representative brand is UNS S31803 (22cr-5ni-3mo-0.15n), and the prEN value is 32-33. Its corrosion resistance is between AISI 316L and 6% Mo + n austenitic stainless steel.
The third type belongs to high alloy type, which generally contains 25% Cr, molybdenum and nitrogen, and some also contain copper and tungsten. The standard brand is unss32550 (25cr-6ni-3mo-2cu-0.2n), and the prEN value is 38-39. The corrosion resistance of this kind of steel is higher than that of duplex stainless steel with 22% CR.
The fourth type is super duplex stainless steel, which contains high molybdenum and nitrogen. The standard brand is UNS S32750 (25cr-7ni-3.7mo-0.3n). Some also contain tungsten and copper. The prEN value is greater than 40. It can be applied to harsh medium conditions. It has good corrosion resistance and mechanical properties, which is comparable to super austenitic stainless steel.
Product application
It is used for heat exchangers, chillers and devices resistant to seawater, high temperature and concentrated nitric acid in oil refining, chemical fertilizer, papermaking, petroleum and chemical industry.
Product features
1. Corrosion resistance
Excellent overall corrosion resistance and local corrosion resistance, especially stress corrosion resistance, pitting corrosion resistance, crevice corrosion resistance, intergranular corrosion resistance, corrosion fatigue resistance and wear resistance.
2. Good weldability
When welding this kind of steel, the crack tendency is very low, and preheating and post weld heat treatment are not required. Due to the high content of N in the base metal, the single-phase ferrite zone will not be formed in the weld near the seam, and the austenite content is generally not less than 30%. Applicable welding methods include argon tungsten arc welding and electrode arc welding. Generally, in order to prevent grain coarsening in the near seam area, low linear energy welding shall be used as far as possible.
3. Good comprehensive mechanical properties
It has high strength and fatigue strength, and the yield strength is twice that of 18-8 austenitic stainless steel. The elongation of solid solution can be up to more than 40%.
Product standard
ASTM A789 / ASME SA789
ASTM A790 / ASME SA790
GB/T 21833
