M. Abbasi - Department of Materials Engineering, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran
A. Kermanpur - Department of Materials Engineering, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran
A. Najafizadeh - Department of Materials Engineering, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran
Y. Mazaheri - Department of Materials Engineering, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran

The formation of nano/ultrafine grained ferrite in low carbon steels containing different amounts of niobium was investigated using thermomechanical treatment which consisted of annealing of ۸۵% cold rolled martensite with different parameters. The specimens were characterized by optical and scanning electron microscopy and Vickers hardness test. A lamellar dislocation cell structure was formed during cold rolling. An increase in hardness was found during annealing with the addition of the Nb element. The mean grain size of the specimens annealed at ۵۵۰ ºC for ۳۰۰ s was approximately similar (ranging from ۷۹ to ۸۷ nm) for both chemical compositions. Increasing annealing temperature to ۶۰۰ ºC or annealing time to ۲.۷ ks led to a severe grain growth in the steel without Nb,but no considerable changes in Nb containing steel were observed.

Ultrafine/Nano grained structure, Niobium, Cold rolled martensite, Grain growth