Precipitation during the Nitriding in Fe-Cr-C Steels

Nitriding of synthetic steels (quenched and annealed at 590 degrees C) at temperature 550 degrees C for 100 hours, containing Fe-2.93 wt. % Cr-0.354 wt. % C and 0.0072 wt. % Al, confirmed the predominant role of the initial microstructure before nitriding as well as the presence of chromium and Aluminum on the nitrogen enrichment and on the hardening. We have collected the main results concerning the morphology, chemical composition and crystallographic structure of precipitates formed in the alloy studied as well as their evolution depending on the nitriding depth. The observations were carried out using a Transmission Electron Microscopy (TEM) in complementary with the technic of Electron diffraction, EDX analysis under TEM, Scanning Electron Microscopy (SEM) and X-ray diffraction. We explored a new approach to explain the precipitation phenomenon and experimentally validate the fact that the nitrogen in mass fractions are related to the precipitation of mixed nitrides (Fe, Cr, Al) N. We studied the different precipitations of nitrides in synthetic steels. Thermodynamic calculations were made using the Thermo-Calc software in complement of different characterization done. (C) 2017 Elsevier Ltd. All rights reserved.