Hot deformation behaviour and recrystallization mechanisms in a niobium stabilized austenitic stainless steel
Résumé
316Nb austenitic stainless steels are used in nuclear industry for their excellent corrosion resistance and high temperature mechanical properties. In thick-walled components, work hardening, dynamic recovery and recrystallization govern hot workability. Static recovery and static or post-dynamic recrystallization can induce further metallurgical evolution during cooling. In addition, solute atoms and niobium-rich precipitates may significantly affect recrystallization mechanisms. Obtaining a homogeneous microstructure requires deep understanding of the hot deformation behaviour and mechanisms of this material. The influence of hot deformation conditions on recrystallization was determined from torsion tests. Metallographic and electron backscatter diffraction examinations showed extended dynamic recovery, which delays dynamic recrystallization. A particular dynamic recrystallization mechanism explains progressive elimination of annealing twin boundaries. Coarse initial grain size, solute drag, and pinning of grain boundaries and dislocations by fine Nb(C,N) particles hinder dynamic recrystallization which is not the dominant microstructural evolution mechanism in the studied conditions.