Studies Of High Nitrogen Austenitic Stainless About The Second Phase In The Behavior Of Precipitation

The second phase of high nitrogen austenitic stainless steel and nickel preci pitation of thermodynamic process was studied in this paper, mainly including the effect of heat treatment temperature, heat treatment time on the morphology,size a nd the stability of the thermodynamics. The change process of the second phase m orphology and the size of the change process were examined by electron microscop e, X-ray diffraction and microhardness testing techniques. The mine conclusions wer e as following:Through the process of the solution and slow colding treatment of test steel, t he best heat treatment process of the second photo of layered precipitation was diff usion annealing for 8 hours in the isothermal heat treatment furnace at 1140℃ and then furnace cooling. Slice layer precipitation were mainly along the boundary. The precipitations wre Cr2N and their thickness were about 50nm; the middle structure of the precipitation was γ’and its thickness was about 200nm; The thickness of de position was related to material surface oxide layer thickness in heat treatment proce ss,which was about lmm.In order to make the nitrides precipitating from slice layer redissolute to the austenite matrix to obtain fine and uniform granular precipitation, the re-dissolution temperature of high nitrogen austenitic stainless steel after colding treatment were lower than the temperature of austenitizing completly. Lamellar precipitation began to fuse at 950℃;Lamellar precipitation were perfectly fusing into granular after insulation 8h at 1120℃and water quenching.The obtioned particle size was about 10-100nm.Through the study of the thermodynamic stability of lamellar precipitates and granular precipitation, its morphology and size had no change after heat treating at 550-750℃ for different time.Granular precipitation did not grow up before 700℃. There were two secondary precipitation of lamellar second phase appeared at 750 ℃ and its size was smaller than the slow cooling treatment,which was about 10-20nm.