The Fe-N (Iron-Nitrogen) system

The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

“…Thus, in the sequel, with the term equilibrium, always a metastable equilibrium is meant. Note that similar remarks hold for the established Fe-N [8] and Fe-C [9] binary phase diagrams. [7,10,11] As in the present work, the experimental data for the phase constitution of the Fe-N-C system is usually obtained from gas nitrided or gas nitrocarburized specimens consisting originally of pure Fe or of Fe-N or Fe-C alloys.…”

“…[10] The sequence of invariant reactions in the Fe-N-C system possibly met upon cooling at T 1000 K (727°C) can be visualized in a Scheil reaction scheme [39][40][41] as shown in Figure 1. From the binary systems, the congruent transition c [Fe-N, e Ð c 0 , 953 K (677°C) [8] ] as well as the well-established eutectoid reactions e 1 [Fe-C, c Ð a þ h, 1000 K (727°C) [9] ], e 2 [Fe-N, e Ð c þ c 0 , 923 K (650 C) [8] ], and e 3 [Fe-N, c Ð a þ c 0 , 865 K (592°C) [8] ] are inherited, giving rise to two-phase (c 0 þ e) and three-phase (a þ c þ h; c þ c 0 þ e; a þ c þ c 0 ; in that order upon decreasing temperature) fields in the ternary system. In the ternary system, at high temperatures, an equilibrium between c and h exists, vanishing upon cooling and being replaced by the a þ e equilibrium via the U 1 invariant reaction, c þ h Ð a þ e. Upon further cooling, the c phase vanishes via the ternary eutectoid reaction E 1 , c Ð a þ c 0 þ e. Both reactions (U 1 and E 1 ) involving the c phase have been investigated recently in an experimental study of the Fe-N-C system [32] *; the temperature of the invariant reaction U 1 , as first determined in Reference 32 to occur between 868 K and 873 K (595°C to 600°C), was confirmed in Reference 42. in the system Fe-N-C leading to the replacement of the a þ e equilibrium by the c 0 þ h equilibrium upon cooling.…”

Prediction of Phase Composition and Nitrogen Concentration During the Nitriding Process in Low-Alloy Steel

“…A large number of thermodynamic and diffusion kinetics data can be found in [14][15][16][17][18][19][20] . Iron-nitrogen (Fe-N) binary phase diagrams are the base to understand the phase evolution during the nitriding process.…”

“…Iron-nitrogen (Fe-N) binary phase diagrams are the base to understand the phase evolution during the nitriding process. In the past decades, the iron-nitrogen phase diagram Materials Research and Fe-N system has been investigated extensively 14,15 . Moreover, Lakhtin 16 reviewed the diffusion foundations of the nitriding process in carbon steel and alloy steel.…”

“…1 (a)) 14,15 , it is feasible to predict the different Fe-N phases according to the limit solubility values 10,11 . In Fig.…”