Strengthening mechanisms and optimization of structure and properties in a nanostructured IF steel

Nanostructured interstitial free (IF) steel has been produced by accumulative roll-bonding (ARB) for 6 cycles, and post-process treatments by recovery annealing and cold rolling up to 50% thickness reductions have been employed to explore the optimization of structure and mechanical properties. Structural parameters including boundary spacing, misorientation angle, and dislocation density have been quantified by means of transmission electron microscopy and mechanical properties have been determined by tensile testing for the as-ARB processed samples and for the post-process treated samples. Annealing-induced hardening and low-strain cold rolling (<30%) induced softening have been observed, which is accounted for by the availability of mobile dislocations and dislocation sources in different sample conditions. Tailoring the structural scale and dislocation density by additional cold rolling has been verified to be a promising way for optimizing the mechanical properties of nanostructured IF steels produced by warm ARB. Based on the experimental findings, guidelines are discussed for optimizing structure and mechanical properties of samples deformed to very high strains.