PRECIPITATION BEHAVIOR OF 25-PERCENT CR-5.5-PERCENT NI AUSTENITIC STAINLESS-STEEL CONTAINING 0.87-PERCENT NITROGEN

In this paper, a 25Cr-5.5Ni steel (mass contents in %), which original ly had a ferritic-austenitic duplex microstructure (DIN material no. 1 .4460), and to which mass contents of 0.87% nitrogen Were added to bec ome fully austenitic was studied. The phase transformations that occur red between 700 and 1350 degrees C were studied using several compleme ntary techniques. Firstly, various treatments were carried out in the range 1050-1350 degrees C for Ih to select the best temperature for so lution heat treatment. Chromium nitride dissolution and absence of fer rite were was observed at 1250 degrees C for Ih. Subsequently the spec imens were aged in the range 700-1100 degrees C, for 90s up to 100h. T he first phase to precipitate was chromium nitride. Ferrite precipitat ion occurred after long aging times, followed by sigma phase precipita tion. A TTT diagram has been proposed.