The duplex stainless steel valve has the following performance characteristics: (1) The molybdenum-containing duplex stainless steel valve has good resistance to chloride stress corrosion under low stress. Generally, 18-8 type austenitic stainless steel valves are prone to stress corrosion cracking in neutral chloride solutions above 60°C. Heat exchangers and evaporators made of this type of stainless steel are used in trace chloride and hydrogen sulfide industrial media. Equipment has a tendency to produce stress corrosion cracking, while duplex stainless steel valves have good resistance. (2) The molybdenum-containing duplex stainless steel valve has good pitting corrosion resistance. With the same equivalent value of pitting corrosion resistance (PRE=Cr%+3.3Mo%+16N%), the critical pitting corrosion potential of the duplex stainless steel valve is similar to that of the austenitic stainless steel valve. The pitting corrosion resistance of duplex stainless steel valves and austenitic stainless steel valves is equivalent to AISI 316L. The pitting and crevice corrosion resistance of high-chromium duplex stainless steel valves containing 25% Cr, especially nitrogen, exceeds AISI 316L. (3) It has good corrosion fatigue resistance and wear corrosion resistance. Under certain corrosive medium conditions, it is suitable for making duplex stainless steel water pumps, duplex stainless steel valves and other power equipment.
(4) The comprehensive mechanical properties are good. It has high strength and fatigue strength, and the yield strength is twice that of 18-8 type austenitic stainless steel. The elongation in the solid solution state reaches 25%, and the toughness value AK is above 100J.
(5) Good weldability, small tendency of hot cracking, generally do not need preheating before welding, no heat treatment after welding, can be welded with 18-8 type austenitic stainless steel or carbon steel and other dissimilar types.
(6) The hot working temperature range of the duplex stainless steel valve containing low chromium (18%Cr) is wider than that of the 18-8 type austenitic stainless steel, and the resistance is small. It can be directly rolled to produce steel plates without forging. The hot working of duplex stainless steels containing high chromium (25%Cr) is slightly more difficult than that of austenitic stainless steels, 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, a large stress is required to deform. (8) Compared with the austenitic stainless steel valve, the thermal conductivity is large and the linear expansion coefficient is small, which is suitable for the lining of equipment and the production of composite plates. It is also suitable for making the tube core of heat exchanger, and the heat exchange efficiency is higher than that of austenitic stainless steel.
(9) There are still various brittle tendencies of high-chromium ferritic stainless steel, which should not be used in working conditions higher than 300°C. The lower the chromium content in the duplex stainless steel valve, the less harmful the brittle phase such as σ is.