Effect of nitrogen and carbon on the early stage of austenite recrystallisation in iron–niobium alloys

The effect of nitrogen and carbon on the early stage of static recrystallisation of hot-deformed austenite in a binary Fe–Nb alloy was investigated using a three-dimensional atom probe (3DAP). Double compression tests reveal that the onset of the recrystallisation is retarded by the addition of nitrogen or carbon to the Fe–Nb binary alloy, with nitrogen having a much stronger effect. Nb-interstitial complexes were desorbed from the matrix of the Fe–Nb–N alloy in the form of NbN2+ and NbN3+. FeN ion complexes were also desorbed from the Fe–Nb–N alloy kept for a longer holding time after deformation. In contrast, no NbC and FeC complexes were desorbed from the Fe–Nb–C alloy. A combination of transmission electron microscopy and AP analysis shows that the retardation of the early stage of the recrystallisation can be caused by solute interstitial atoms and small substitutional–interstitial atomic clusters, not by finely dispersed niobium carbonitrides.