Due to the characteristics of two-phase structure, by correctly controlling the chemical composition and heat treatment process, the dual phase stainless steel valve has the advantages of both ferritic stainless steel valve and austenitic stainless steel valve. It combines the excellent toughness and weldability of austenitic stainless steel valve with the high strength and chloride stress corrosion resistance of dual phase stainless steel valve, It is these superior properties that make the dual phase stainless steel valve develop rapidly as a weldable structural material.
Duplex stainless steel valves have the following performance characteristics:
(1) molybdenum containing duplex stainless steel valves have good chloride stress corrosion resistance under low stress. Generally, 18-8 austenitic stainless steel valves are prone to stress corrosion fracture in neutral chloride solution above 60 ° C. in trace chloride and hydrogen sulfide industrial media, heat exchangers, evaporators and other equipment made of this kind of stainless steel have the inclination of stress corrosion fracture, while duplex stainless steel valves have good resistance.
(2) Molybdenum containing duplex stainless steel valve has good pitting corrosion resistance. With the same equivalent value of pitting resistance (pre = CR% + 3.3mo% + 16N%), the critical pitting potential of duplex stainless steel valve is similar to that of austenitic stainless steel valve. The pitting corrosion resistance of duplex stainless steel valve and austenitic stainless steel valve 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 and wear corrosion resistance. Under the condition of some corrosive media, it is suitable for making dual phase stainless steel water pumps, dual phase stainless steel valves and other power equipment.
(4) 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 in solid solution state reaches 25%, and the toughness value AK is more than 100J.
(5) It has good weldability and small tendency of hot cracking. Generally, preheating is not required before welding and heat treatment is not required after welding. It can be welded with 18-8 austenitic stainless steel or carbon steel.
(6) The hot working temperature range of duplex stainless steel valve containing low chromium (18% Cr) is wider than that of 18-8 austenitic stainless steel, and the resistance is small. It can be rolled directly to produce steel plate without forging. The hot working of duplex stainless steel containing high chromium (25% Cr) is slightly more difficult than that of austenitic stainless steel. It can produce plate, pipe, wire and other products.
(7) When cold working, the work hardening effect is greater than that of 18-8 austenitic stainless steel. In the initial stage of deformation of pipe and plate, large stress needs to be applied to deform.
(8) Compared with austenitic stainless steel valve, it has large thermal conductivity and small linear expansion coefficient. It is suitable for equipment lining and production of composite plate. 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 brittleness tendencies of high chromium ferritic stainless steel, which is not suitable for working conditions higher than 300 ° C. The lower the chromium content in duplex stainless steel valves, σ The less harmful the equal brittle phase is.