Characteristics of nano/ultrafine-grained austenitic TRIP steel fabricated by accumulative roll bonding and subsequent annealing

In this paper, microstructure and mechanical properties of nano/ultrafine-grained (UFG) austenitic Fe-24Ni-0.3C steel fabricated by accumulative roll bonding (ARB) and subsequent annealing were studied. The results indicated that after 6 cycles of the ARB process, elongated UFG austenite with mean grain size of about 300 nm was obtained. Annealing treatment of 6-cycle ARB processed austenite at temperatures between 773 and 873 K resulted in formation of partly and fully recrystallized austenites with mean grain sizes between 750 nm to 2.5 mu m. Discontinuous yielding accommodated with Luders band deformation was observed in the stress strain curves of the ARB processed specimens. Microstructural observation indicated that the Udders band propagation corresponding to the propagation of the region where deformation-induced martensitic transformation occurred. It was found that deformation-induced martensitic transformation provided extra strain hardening ability, resulting in significant enhancement of uniform elongation in UFG metastable austenitic steel having ultrahigh strength and considerable uniform elongation. (C) 2016 Elsevier Inc. All rights reserved.