| High nitrogen austenitic stainless steels have excellent corrosion resistance, good mechanical properties and excellent process performance in many corrosive medias. Furthermore, by using nitrogen element as a substitute for nickel element, they can not only increase the comprehensive properties of stainless steels, save nickel resources, but also improve the biocompatibility between stainless steel and the body. However, in certain heat conditions, the second-phase precipitation of nitrogen-containing austenitic stainless are complex. They have not only many kinds of precipitated phases, but also the precipitation mechanism of the nitride and σ phase may have many differences from the general austenitic stainless steel. Therefore, we study on its precipitation behavior is important to the academic research and practice.In the present study, a kind of high-nitrogen austenitic stainless steels completely replacing Ni by Mn and N were selected as the research object. We systemically investigated the thermodynamic and kinetic behaviors of Fe-18Cr-16Mn-2Mo-1.1N steel during isothermal aging. And we conclude that the features of precipitated phases, growth mechanism and types of precipitated phases. The major conclusions are as follows:1. The temperature region of Fe-18Cr-16Mn-2Mo-1.1N steel precipitation is between650℃and950℃. According to the isothermal precipitation kinetics curve of M2N, we conclude that the nose temperature of M2N precipitation is determined to be at850℃and the corresponding incubation period is only a few minutes.2. The nitride microstructure of Fe-18Cr-16Mn-2Mo-1.1N steel is lamellar-structure which is parallel on austenite matrix. With the increase of aging temperature and time, the lamellar thickness and spacing of layers increased in size. 3. The precipitate of Fe-18Cr-16Mn-2Mo-1.1N steel include M2N-phase with close-packed hexagonal structure, which has layered and granular features. In addition, in the matrix we also found a very small amount of granular M23C6-phase and the clumpy intermetallic compounds σ-phase in the grain boundaries and intragranular areas. |
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