Duplex stainless steel

Duplex Stainless Steel (DSS) refers to about 50% of ferrite and austenite each, and generally requires a minimum content of 30% stainless steel. In the case of lower C, Cr content of 18% to 28%, Ni content of 3% to 10%. Some steel also contains Mo, Cu, Nb, Ti, N and other alloying elements.

This kind of steel combines the characteristics of austenitic and ferritic stainless steel. Compared with ferrite, the steel has higher plasticity and toughness, no brittleness at room temperature, significantly improved intergranular corrosion resistance and weldability, and at the same time retains iron The body of stainless steel 475 ℃ brittleness and high thermal conductivity, with superplasticity and other characteristics. Compared with the austenitic stainless steel, high strength and resistance to intergranular corrosion and chloride stress corrosion significantly improved. Duplex stainless steel has excellent resistance to pitting corrosion, but also a nickel-saving stainless steel.

Duplex stainless steel

The first is a low-alloy type, which stands for UNS S32304 (23Cr-4Ni-0.1N). It contains no molybdenum in the steel and has a PREN value of 24-25. It can be used instead of AISI 304 or 316 in terms of stress corrosion resistance.

The second type belongs to the alloy type, the representative grade is UNS S31803 (22Cr-5Ni-3Mo-0.15N), PREN value of 32-33, the corrosion resistance between AISI 316L and 6% Mo + N austenitic stainless steel between.

The third type is a high alloy type, generally containing 25% Cr, also contains molybdenum and nitrogen, and some also contain copper and tungsten, the standard grade UNSS32550 (25Cr-6Ni-3Mo-2Cu-0.2N), PREN value of 38-39 , This type of steel corrosion resistance than 22% Cr duplex stainless steel.

The fourth category is super duplex stainless steel type, containing high molybdenum and nitrogen, the 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 and mechanical properties, comparable with super austenitic stainless steel.