Features of Duplex Stainless Steel
Duplex Stainless Steel (DSS) refers to stainless steel with ferrite and austenite each accounting for about 50%. Generally, the content of fewer phases needs to be at least 30%. In the case of low C content, the Cr content is 18% to 28%, and the Ni content is 3% to 10%. Some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N.
This type of steel has the characteristics of austenitic and ferritic stainless steel. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and significantly improved intergranular corrosion resistance and welding performance, while still maintaining iron The 475℃ brittleness, high thermal conductivity, and superplasticity of element stainless steel. Compared with austenitic stainless steel, it has high strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting corrosion resistance and is also nickel-saving stainless steel.
Due to the characteristics of the two-phase structure, through correct control of the chemical composition and heat treatment process, the duplex stainless steel has the advantages of both ferritic stainless steel and austenitic stainless steel. It combines the excellent toughness and weldability of austenitic stainless steel with iron The high strength and resistance of the body stainless steel
The chloride stress corrosion performance of duplex stainless steel is combined together. It is these superior properties that make duplex stainless steel develop rapidly as a weldable structural material. Since the 1980s, it has become martensitic, austenitic, and ferritic stainless steel. A side-by-side steel category. Duplex stainless steel has the following performance characteristics:
(1) Molybdenum-containing duplex stainless steel has good chloride stress corrosion resistance under low stress. Generally, 18-8 type austenitic stainless steel is prone to stress corrosion cracking in neutral chloride solution above 60°C. Heat exchangers, evaporators, and other equipment made of this type of stainless steel in trace chloride and hydrogen sulfide industrial media There is a tendency to produce stress corrosion cracking, but duplex stainless steel has good resistance.
(2) Duplex stainless steel containing molybdenum has good pitting corrosion resistance. When having the same pitting corrosion resistance equivalent value (PRE=Cr%+3.3Mo%+16N%), the critical pitting potential of duplex stainless steel and austenitic stainless steel are similar. The pitting corrosion resistance of duplex stainless steel and austenitic stainless steel is equivalent to AISI 316L. The pitting and crevice corrosion resistance of 25% Cr, especially nitrogen-containing high-chromium duplex stainless steel exceeds AISI 316L.
(3) It has good corrosion fatigue and wears corrosion resistance. Under certain corrosive media conditions, it is suitable for making pumps, valves, and other power equipment.
(4) Good comprehensive mechanical properties. It has higher strength and fatigue strength, and its yield strength is twice that of 18-8 austenitic stainless steel. The elongation in the solid solution state reaches 25%, and the toughness value AK (V-notch) is above 100J.
(5) Good weldability, low thermal cracking tendency. Generally, preheating is not required before welding and no heat treatment is required after welding. It can be welded with dissimilar types such as 18-8 austenitic stainless steel or carbon steel. Duplex stainless steel
(6) The hot working temperature range of duplex stainless steel with low chromium (18%Cr) is wider than that of 18-8 type austenitic stainless steel, and its resistance is small. It can be directly rolled to produce steel plates without forging. The hot working of duplex stainless steel containing high chromium (25%Cr) is slightly more difficult than austenitic stainless steel, and products such as plates, tubes, and wires can be produced.
(7) The work hardening effect of cold working is greater than that of 18-8 type austenitic stainless steel. In the initial stage of deformation of the tube and plate, greater stress is required to deform.
(8) Compared with austenitic stainless steel, it has higher thermal conductivity and lower linear expansion coefficient, making it suitable for lining equipment and producing composite plates. It is also suitable for making heat exchanger tube cores, and its heat transfer efficiency is higher than that of austenitic stainless steel.
(9) There are still various brittleness tendencies of high chromium ferritic stainless steel, and it is not suitable for working conditions higher than 300°C. The lower the chromium content in duplex stainless steel, the less harmful the brittle phases such as σ.