2205 Duplex Stainless Steel
The main alloy elements of 2205 duplex stainless steel are Cr, Ni, Mo and N, of which Cr content is 22%. Cr and Mo increase the content of ferrite, while Ni and N are austenite stable elements, and some steel types also contain Mn, Cu, W and other elements. Cr, Ni and Mo can improve the corrosion resistance, especially the resistance to pitting and crack corrosion in the environment containing chloride. N is the enhancement of austenite forming element, which increases the corrosion resistance of duplex stainless steel. Nitrogen can retard the precipitation of metal gaps and reduce the tendency to form sigma phase in duplex stainless steel.
The mechanical properties of duplex stainless steel are related to tempering temperature of steel plate, and the higher the tempering temperature, the lower the strength. When the tempering temperature is 600 degrees, the yield strength is 400 MPa and the tensile strength is 650 MPa. The metallographic structure of duplex stainless steel is composed of two phases of alpha ferrite (black) and gamma austenite (white), which have the characteristics of approximately equal volume fraction. Therefore, duplex stainless steel has dual characteristics of austenitic stainless steel and ferritic stainless steel. Compared with ferritic stainless steel, its toughness is high, its ductile brittle transition temperature is low, its intergranular corrosion resistance and welding performance are significantly improved. At the same time, it retained the characteristics of high thermal conductivity, small expansion coefficient of stainless steel. Compared with austenitic stainless steel, the yield strength and fatigue strength of the austenitic stainless steel are significantly improved, about 2 times of that of austenitic stainless steel. It also improved the properties of intergranular corrosion, stress corrosion and corrosion fatigue. Nitrogen plays an important role in strengthening 2205 duplex stainless steel. However, when the mass fraction of nitrogen exceeds 0.2%, the strength of austenite is stronger than ferrite due to the interstitial strengthening of nitrogen. The increase of ferrite content will lead to the decrease of impact toughness and the precipitation of nitrogen in ferrite, resulting in the formation of chromium nitride. Because nitrogen is less soluble in ferrite than in austenite. Cold processing can reduce the impact toughness of 2205 duplex stainless steel and improve the transition temperature of toughness and brittleness. The transition time will be within the range of 280-350 ℃ results in the decrease of toughness.