1. The second generation of duplex steel stainless steel pipe has the characteristics of ultra-low carbon, low nitrogen, typical composition Cr5% Ni0.17%n and 2205 higher nitrogen content than the first generation of duplex steel stainless steel pipe, which improves the resistance to stress corrosion and pitting resistance of acidic media with high chloride ion concentration. Nitrogen is a strong austenite forming element. The addition of nitrogen in duplex stainless steel not only improves the plasticity and toughness of the steel without obvious damage, but also improves the strength of the steel, and inhibits the precipitation and delay of carbides.
2. Organizational function: In the greenhouse, austenite and ferrite account for about half of the solid solution, which has the characteristics of biphase structure. It retains the characteristics of small number of ferritic stainless steel conductors, resistance to pitting, cracking and chloride stress corrosion, with good toughness, low embrittlement temperature, resistance to intergranular corrosion and mechanical properties and good weldability.
3. Under the same pressure grade conditions can save materials, the yield strength and stress corrosion resistance of duplex steel stainless steel pipe is almost 1 times that of austenitic stainless steel, the linear expansion coefficient is less than the austenitic stainless steel of the austenitic stainless steel system, and the low carbon steel is close to it. Cold forging is not as good as austenitic stainless steel.
4. Weldability: duplex steel stainless steel pipe 2205 has good weldability, welding cold, hot crack sensitivity is small, usually no preheating before welding, no heat treatment after welding. Due to the small tendency of single-phase ferrite and high nitrogen content in the heat affected zone, the welding wire energy can be controlled at this time when the welding material is reasonably selected, and the comprehensive performance is good.
5. Hot crack: The sensitivity of hot crack is much lower than that of austenitic stainless steel. This is because the nickel content is not high, the impurities that are easy to form low-melting eutectic are low, the liquid film with low melting point is not easy to produce, and the rapid growth of the grain danger does not exist at high temperatures.
6. Brittleness of heat affected zone: The main problem of welding of duplex steel stainless steel pipe is the heat affected zone. Due to the rapid cooling effect of the heat affected zone in the non-equilibrium state of the welding heat cycle, more cooled ferrite is always retained, which tends to increase the sensitivity of corrosion and hydrogen-induced cracking.
7. Welding metallurgy: During the welding process of duplex stainless steel, under the action of thermal cycling, the microstructure and heat-affected zone of the weld metal have undergone a series of changes. At high temperatures, the microstructure of duplex stainless steel is precipitated by ferrite and austenite during cooling. The amount of austenite precipitation is affected by many factors.
Post time: Jun-26-2023