Introduce 2205 duplex stainless steel components and chromium, nitrogen, molybdenum, nickel and corrosion influence on the performance of the duplex stainless steel

The chemical composition of 2205 duplex stainless steel is generally believed that ferrite and austenite facies duplex stainless steel is 30% ~ 70%, can obtain good performance. But duplex stainless steel is often referred to as a ferrite and austenite is roughly half, in the current commercialized, in order to obtain the toughness and processing properties, tend to be larger the proportion of the austenite. Main alloy elements, especially nickel chromium, molybdenum and nitrogen and the interaction between is very complex. In addition to the phase equilibrium, the main problem of duplex stainless steel and its chemical composition is at higher temperatures is harmful to the formation of intermetallic phase. σ Phase and & chi; Phase formed in high chromium and molybdenum stainless steel, and the priority in the ferritic phase precipitation. Nitrogen added greatly delayed the formation of the phase. So keep enough amount of nitrogen in solid solution is very important. With the increase of duplex stainless steel manufacturing experience, people more and more realized the importance of the control element of narrow range. 2205 duplex stainless steel ( UNS S31803） Set composition range is too wide, experience has shown that in order to get the corrosion resistant performance and avoid the formation of the intermetallic phase, chromium, molybdenum and nitrogen content of S31803 should maintain in the scope of content of ceiling, thus raises the composition narrow the scope of the improved 2205 UNS S32205 dual phase steel. S32205 ingredient is today the commercialization of typical components of 2205 duplex stainless steel. In this article, unless otherwise specified, usually 2205 means S32205. The following simple introduce chromium, nitrogen, molybdenum, nickel alloy elements on the mechanical property of duplex stainless steel, the influence of the physical properties and corrosion characteristics. Nitrogen, nitrogen austenitic and improve the resistance to pitting and crevice corrosion of duplex stainless steel, it also can significantly improve the strength of the steel. In fact it is a valid solid solution strengthening elements and low cost of alloy elements. Improved nitrogen duplex stainless steel toughness due to its high content of austenite and fewer intermetallic phase. N't stop intermetallic phase precipitation, but can delay the formation of the intermetallic phase, that there is enough time for duplex stainless steel processing and manufacturing. Nitrogen is added to the high corrosion resistance of high chromium and molybdenum content austenitic and duplex stainless steel, to offset their & sigma; The tendency of phase. Nitrogen is strong austenite formed elements, replacing parts of the nickel in austenitic stainless steel. Nitrogen can reduce fault can be enhanced and the work hardening rate of austenite. It is also through solid solution strengthening improved the strength of the austenite. Duplex stainless steel is generally adding nitrogen and adjust the content of nickel in order to achieve the appropriate balance. Ferrite formation of element chromium and molybdenum and nickel austenite formation elements and nitrogen balance each other to obtain dual phase structure. Nickel, nickel is stable elements austenitic nickel prompted the crystal structure of stainless steel from the body centered cubic structure ( Ferrite) Into a face-centered cubic structure ( Austenitic) 。 Ferritic stainless steel nickel containing very little or no nickel, nickel content duplex stainless steel is low to medium, such as 1. 5% ~ 7%, and 300 series austenitic stainless steel containing at least 6% of the nickel. Adding nickel delayed the austenitic stainless steel in the harmful to the formation of the intermetallic phase, but the delay effect of nickel in the duplex stainless steel is much less than the nitrogen effectively. Face-centered cubic structure made of austenitic stainless steel has good toughness. In approximately half duplex stainless steel is austenitic organization, so the toughness of the dual phase steel significantly higher than that of ferritic stainless steel. Chromium, chromium content in the steel must be not less than 10. 5% to form stable chromium passivation membrane, protect the steel against atmospheric corrosion. The corrosion resistance of stainless steel with chrome content increases. Chromium ferritic form element, add chromium steel can make body centered cubic structure of ferrite formation. Chromium content in the steel is high, need to add more nickel to form austenite or bipolar ( Ferrite, austenite) Organization. High chromium content also can promote the formation of intermetallic phase. Austenitic stainless steel at least 16% chromium content, duplex stainless steel containing at least 20% chromium. Chromium also can increase the oxidation resistance of steel at high temperature, the effect of chromium is very important, it affect the heat treatment after welding or scale or the formation and removal of heat tint. Duplex stainless steel pickling and remove heat tint than austenitic stainless steel. Molybdenum, molybdenum can improve the ability of resistance to pitting and crevice corrosion of stainless steel. When at least 18% chromium content in stainless steel, molybdenum in chloride environment, the ability of resistance to pitting and crevice corrosion is three times of chromium. Molybdenum is ferrite formation elements, and at the same time increase the tendency of the stainless steel forming intermetallic phase. Therefore, the molybdenum content of austenitic stainless steel is usually less than about 7. The molybdenum content of 5%, duplex stainless steel is less than 4%.