2007 Volume 47 Issue 3 Pages 479-485
Performing the solution nitriding treatment under pressurized nitrogen gas atmosphere, the microstructure change and the relationship between the nitrogen gas pressure and the solute nitrogen content in Fe–Cr alloys were investigated. The microstructure of the ferritic Fe–Cr alloys changed to an austenitic structure by the pressurized solution nitriding treatment at 1473 and 1573 K. However, in the case that their martensite temperature did not decrease sufficiently lower than room temperature, martensitic transformation occurred during the cooling process. Examination of the interaction on nitrogen activity with the thermodynamic method confirmed that the deviation between the experimental and theoretical solute nitrogen contents in Fe–Cr alloys widened greatly in the high nitrogen region over 3 at% N because of the strong N–N interaction in austenite. The interaction parameter eN[N] between N atoms in austenite iron at 1473 K was obtained as 0.120. The temperature dependence of eN[N] is expressed as follows:
eN[N]=217/T−0.0273
