Duplex stainless steel

Ferrite and austenite account for about 50% respectively. Generally, the content of less phase also needs to be at least 30% of stainless steel.

Cr content is 18% ~ 28%, Ni content is 3% ~ 10%; Some steels also contain Mo, Cu, Nb, Ti, N and other alloy elements.

Performance characteristics

Duplex stainless steel has the advantages of both ferritic stainless steel and austenitic stainless steel. It has not only the excellent toughness and weldability of austenitic stainless steel, but also the high strength and chloride stress corrosion resistance of ferritic stainless steel.

Compared with austenitic stainless steel:

(1) The yield strength can reach 400MPa ~ 550MPa, which is twice that of ordinary austenitic stainless steel;

(2) The pitting corrosion resistance, stress corrosion resistance and corrosion fatigue resistance have also been significantly improved.

Compared with ferritic stainless steel:

(1) High toughness, low brittle transition temperature, intergranular corrosion resistance and welding performance are significantly improved;

(2) It retains some characteristics of ferritic stainless steel, such as brittleness at 475 ℃, high thermal conductivity, low coefficient of linear expansion, superplasticity and magnetism.

Classification of duplex stainless steel

(1) Low alloy type:

Representative brand (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.

(2) Medium alloy type:

Representative brand (22cr-5ni-3mo-0.15n),PREN value is 32-33, and its corrosion resistance is between AISI 316L and 6% Mo + n austenitic stainless steel.

(3) High alloy type:

It generally contains 25% Cr, molybdenum and nitrogen, and some also contain copper and tungsten; The standard grade (25cr-6ni-3mo-2cu-0.2n) and PREN value are 38-39. The corrosion resistance of this kind of steel is higher than that of duplex stainless steel with 22% CR.

4) Super duplex stainless steel type:

Standard brand (25cr-7ni-3.7mo-0.3n), PREN value greater than 40, can be applied to harsh medium conditions, the same as super austenitic stainless steel.