Duplex stainless steel is the stainless steel material that contains both ferrite phase and austenite phase in the microstructure of the metal. They are about half of each. But in practical applications, the ratio of a phase is better than that of 40-60%. Consider two organizational characteristics, through the organization of correct control of chemical composition and heat treatment process, can make excellent toughness and weldability of austenitic stainless steel and ferritic stainless steel high strength body and resistance performance of chloride stress corrosion of a fusion, will create a double phase stainless steel stainless steel set excellent corrosion resistance and high strength the advantages of easy manufacture and performance.
Advantages of duplex stainless steel
Based on the above behavior, dual phase stainless steel has many advantages, the following will be described in detail.
Excellent resistance to neutral chloride stress corrosion
The duplex stainless steel with chromium content in the range of 18% -22% is under low stress and has excellent resistance to neutral chloride stress corrosion. 18 – 8 type austenitic stainless steel is usually used in more than 70 DEG C in neutral chloride solutions to stress corrosion cracking, heat exchanger, evaporator and other equipment manufactured by the stainless steel in trace chloride and hydrogen sulfide in industrial environment are susceptible to stress corrosion cracking, but duplex stainless steel in this resistance performance is good.
Good corrosion resistance
Duplex stainless steel, if the alloy element molybdenum is added, will form better pitting corrosion resistance. When pitting equivalent value is equal, the critical pitting corrosion potential of duplex stainless steel and austenitic stainless steel is close. The corrosion resistance of duplex stainless steel with Cr content of 18% is equivalent to that of AISI316L stainless steel. The pitting corrosion and crevice corrosion resistance of duplex stainless steels containing 25%Cr, especially those containing oxygen, are even higher than those of AISI316L stainless steel.
Good corrosion resistance, fatigue and corrosion resistance
Duplex stainless steel has good corrosion resistance, fatigue and wear and corrosion resistance, certain conditions have also been used for pumps, valves and other equipment to manufacture raw materials.
The overall mechanical properties are good
The overall mechanical properties of duplex stainless steel are better, the strength and fatigue strength are higher, and the yield strength is two times of type 18-8 austenitic stainless steel.
The weldability of duplex stainless steel is good and the tendency of hot cracking is small. There is usually no need to preheat before welding, without heat treatment after welding, and can be welded to dissimilar steels such as type 18-8 austenitic stainless steel or carbon steel.
The range of hot working temperature is high
The hot working temperature range of duplex stainless steel containing low chromium (l8%Cr) is wider than that of type 18-8 austenitic stainless steel, and the resistance is small. The steel sheet can be rolled directly without forging. The hot work of duplex stainless steel containing high chromium (25%Cr) is more difficult than austenitic stainless steel.
Large thermal conductivity
Compared with austenitic stainless steel, duplex stainless steel has large thermal conductivity and small coefficient of linear expansion. It is suitable for lining and producing composite plate. It is also suitable to be used as the core of heat exchanger.
Disadvantages of duplex stainless steel
Of course, the duplex stainless steel is also flawed, down to this aspect.
First of all, duplex stainless steel has lower heat resistance than austenitic stainless steel. It is usually used in a working environment below 300 degrees centigrade. The degree of hardening followed by cold working than the effect of 18-8 type austenitic stainless steel, to be applied to large initial deformation of the duplex stainless steel pipe, plate deformation in duplex stainless steel, and the internal stress of these tubes, plates are large. In addition, duplex stainless steels have medium temperature brittleness zones (such as sigma and brittleness at 475 degrees), which can affect heat treatment and welding. The processing of duplex stainless steel with chromium content of 25% is more difficult than austenitic stainless steel.
Source: China Stainless Steel Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)