Precipitation behaviour of 25% Cr ‐ 5.5% Ni austenitic stainless steel containing 0.87% nitrogen

In this paper, a 25Cr ‐ 5.5Ni steel (mass contents in %), which originally had a ferritic‐austenitic duplex microstructure (DIN material no. 1.4460), and to which mass contents of 0.87% nitrogen were added to become fully austenitic was studied. The phase transformations that occurred between 700 and 1350°C were studied using several complementary techniques. Firstly, various treatments were carried out in the range 1050‐1350°C for 1h to select the best temperature for solution heat treatment. Chromium nitride dissolution and absence of ferrite were was observed at 1250°C for 1h. Subsequently, the specimens were aged in the range 700‐1100°C, for 90s up to 100h. The first phase to precipitate was chromium nitride. Ferrite precipitation occurred after long aging times, followed by sigma phase precipitation. A TTT diagram has been proposed.