Coarsening Tendency of Ultra-fine Ferrite in Low Carbon Steels

The coarsening tendency of ultra-fine ferrite grains produced by deformation-enhanced transformation was investigated at simulated coiling temperatures by thermal simulating tests in four low carbon steels containing different C and Mn contents. Results show that the ultra-fine microstructures are quite stable. No apparent coarsening and static recrystallization of ferrite grains were detected and they are ascribed to the effective pinning by the second/minor phases. The evolution of second phases in four steels was different. During holding at coiling temperatures the transformation of austenite to perlite proceeded in a divorced manner owing to the strong deformation of austenite. Orientation mapping in EBSD measurements was also applied to reveal the changes of (mis)orientations of ferrite grains during holding.