| The contradiction between continuously increasing requirement of stainless steels and limited Ni resources has become more and more serious in recent years. In addition, human organs exhibit irritability to austenitic stainless steel with Ni as bioengineering materials. As a result, great attention is now focused on resource-saving stainless steels, that is high-nitrogen stainless steel having not only low cost but also excellent mechanical properties, corrosion resistance, oxidization resistance and wear resistance etc. However, the precipitation of carbides, nitrides and intermetallics may occur in austenite of this advanced steel material during thermal processes, welding and service at the elevated temperatures, which reduce austenitic stability. The precipitation of second phases will heavily damage various working and service properties of materials. Therefore, investigation on precipitation behavior and its effects on properties are of academic significance and practical importance.This research take the Fe-22Cr-16Mn-1.5Ni-0.4Si-0.1C-0.6N high nitrogen austenite stainless steel as the object of study, Through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermodynamic calculation, we systemically investigated the thermodynamic and kinetic behaviors of precipitation during isothermal aging. The major conclusions are as follows:1.Fe-22Cr-16Mn-1.5Ni-0.4Si-0.1C-0.6N steel precipitation maximum temperature of950℃, minimum temperature of550℃, precipitation temperature range550-950℃. Precipitated the most sensitive temperature750-800℃, the precipitation of the corresponding incubation period for the10min(precipitation amount to1%as the precipitation started).2.Fe-22Cr-16Mn-1.5Ni-0.4Si-0.1C-0.6N steel after solid solution precipitates during aging mainly (Cr,Fe,Mn)2(N,C) phase,(Cr,Fe,Mn)23(C,N)6phase and σ phase.(Cr,Fe,Mn)2(N,C) phase of the Cr2N hep structure, within550℃-950℃ have precipitated.(Cr,Fe,Mn)2(N,C) compared to the first form of discrete particles in the grain boundaries, the temperature below950℃, with the aging time to extend the M2N cellular precipitation in the form of crystal growth; in temperature above800℃, M2N also an independent rod in the grain interior.(Cr,Fe,Mn)23(C,N)6phase, the Cr23C6fcc structure, cellular precipitation in coexistence with the M2N. σ phase is tetragonal, the following aging at850℃, when the cell structure will be developed to a certain extent in order to rough strip in front of cellular structure. |
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