The effect of interstitial N upon the cohesion of a Σ3[110](111) grain boundary was investigated by means of ab initio electronic structure calculations. These revealed that free interstitial N produced a marked strengthening, reduced the magnetic moments of the grain-boundary Fe-atoms and had an embrittling effect at the grain boundaries.

The Effect of Interstitial N on Grain Boundary Cohesive Strength in Fe. M.Kim, C.B.Geller, A.J.Freeman: Scripta Materialia, 2004, 50[10], 1341-3