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 it 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. (C) 2002 Elsevier Science B.V. All rights reserved.