Duplex stainless steel is a new star in stainless steel. Since the discovery of duplex structure in the 1920s, duplex stainless steel has developed for three generations. The first generation of duplex stainless steel is represented by AISI329 steel, which contains high chromium and molybdenum and has good local corrosion resistance, but has a high carbon content. The second generation duplex stainless steel is an ultra-low carbon type, containing molybdenum, copper or silicon, and the representative steel type is SAF2205. The third generation of duplex stainless steel is super duplex stainless steel, with brands such as SAF2507, UR52N+, Zeron 100, etc. This type of steel has low carbon content, high molybdenum and nitrogen content, 40-45% ferrite content, and excellent hole resistance. Corrosion performance.
In the iron-based solid solution structure of duplex stainless steel, the ferrite phase and the austenite phase account for approximately half each, but the minimum phase content must reach more than 30%. Duplex stainless steel combines the advantages of austenite’s plasticity and toughness and ferrite’s high strength and corrosion resistance, greatly reducing the shortcomings of the two phases, making it an ideal structural material.
Chemical composition and mechanical properties of duplex stainless steel
The alloy elements of duplex stainless steel mainly include chromium, nickel, molybdenum and nitrogen. These elements not only determine its corrosion resistance, but also determine its mechanical properties. The yield strength of duplex stainless steel is 2-3 times that of austenitic stainless steel. The yield strength of SAF2507 steel is higher due to the strengthening effect of nitrogen. Austenitic stainless steel has more slip surfaces inside, so its elongation is significantly higher than that of duplex stainless steel.
Room temperature mechanical properties of typical duplex stainless steel grades
Steel type standard grade σ0.2/MPa σb/Mpa δ5/% AK/J
AISI304 UNS S30400 210 515~690 45 >300
SAF2304 UNS S32304 400 600~820 25 300
SAF2205 UNS S31803 450 680~880 25 250
SAF2507 UNS S32750 550 800~1000 25 230
Corrosion resistance of duplex stainless steel
Duplex stainless steel not only has good mechanical properties, but also has excellent pitting corrosion resistance, stress corrosion resistance, corrosion fatigue resistance and other properties. Its joints also have good resistance to pitting corrosion and chloride stress corrosion cracking, and the intergranular corrosion performance is not lower than that of the base material, but the resistance to H2S stress corrosion cracking is poor. The worst corrosion resistance of the joint is the seam zone (HAZ), which is mainly caused by the precipitation of the second phase (chromium nitride) in the seam zone to form a “chromium-poor” layer.
Limitations of Duplex Stainless Steel
Compared with austenitic stainless steel, the disadvantages of duplex stainless steel are as follows:
1. The universality and versatility of applications are not as good as those of stainless steel, and the use temperature must be controlled between -50°C~250°C.
2. The plasticity is lower than that of austenitic stainless steel, and the cold and hot working processes and forming properties are slightly worse.
3. There is a medium-temperature brittle zone, and the heat treatment and welding process systems need to be strictly controlled to avoid the appearance of harmful phases, otherwise the performance will be damaged.
Welding of duplex stainless steel
Duplex stainless steel has good welding performance and low tendency of hot cracking. It does not require preheating during welding and does not require heat treatment after welding. Compared with the welding of austenitic stainless steel, the tendency of hot cracking of the weld is low; when welding with ferritic stainless steel In comparison, the degree of embrittlement of the welded joint after welding is low; and the degree of coarsening of the single-phase ferrite phase in the welding heat affected zone (HAZ) is also low.
The key to welding duplex stainless steel is to maintain an appropriate amount of ferrite and austenite in the weld metal and welding heat affected zone (HAZ).
Tianjin Anton Metal Manufacture Co., Ltd. is a company specializing in the production of various nickel-based alloys, Hastelloy alloys and high-temperature alloy materials. The company was established in 1989 with a registered capital of 10.0 million, specializing in the production and sales of alloy materials. Anton Metal’s products are widely used in aerospace, chemical industry, electric power, automobile, nuclear energy and other fields, and can also provide customized alloy material solutions according to customer needs. If you need to know the price consultation of alloy materials or provide customized alloy material solutions, please feel free to contact the sales staff.
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Post time: Nov-25-2023
