Age hardening in stable austenitic stainless steel wires with a chemical composition of Fe-18％Cr-12％Ni and different N contents was investigated to clarify the role of N. Age hardening could be enhanced by increasing the drawing ratio and N content. The highest age-hardening effect was observed at 800 K in the N-bearing specimens. In addition, severe drawing induced low-temperature age hardening at 450–600 K. Differential scanning calorimetry (DSC) analysis revealed that age hardening at 800 K may be attributed to particle dispersion strengthening by Cr₂N. Meanwhile, the exothermic peaks observed at 450–600 K were controlled by the pipe diffusion of N. However, nitride precipitates and clusters could not be detected by 3D atom probe anaysis, which implies the formation of atomic-scale N products, such as I-S pairs, at the dislocations.

To clarify the effect of alloying elements (Me) on the grain boundary segregation behavior of nitrogen (N) in α-iron, the grain boundary segregation of N and alloying elements in the Fe–1.0 at.％Me–N (Me：Al, Ti, V, Cr, Mn, Nb or Mo) ternary system was thermodynamically evaluated using the parallel tangent law proposed by Hillert. In this study, the Gibbs energy of the liquid phase in the Fe–1.0 at.％Me–N ternary system was applied to that of the grain boundary. The calculations predicted co-segregation of N and alloying elements for alloys with Al, Ti, V, Cr or Nb additions. In contrast, co-segregation behavior was not predicted in the case of Mn or Mo addition. The tendency of co-segregation of N and alloying elements corresponded well with the formation tendency of metal nitrides.