On the Achievement of Nanostructured Interstitial Free Steel by Four-Layer Accumulative Roll Bonding Process at Room Temperature

In this study, the four-layer accumulative roll bonding (ARB) process at room temperature for nanostructuring the interstitial free (IF) steel was used for the first time. Hardness and tensile tests were performed and the microstructure was characterized using scanning transmission electron microscopy. It was found that the grain size decreased into the nanostructured domain after fourth cycle, reaching grain sizes of smaller than 100 nm. The stored energy was retained in the material until the continuous dynamic recrystallization led to nanostructuring of the IF steel. The dislocation density was measured by microhardness indentation size effect using the Nix-Gao model. The results indicated that an increase in the number of ARB cycles leads to increase in the dislocation density. The dislocation density increased from 2.02 x 10(9) cm(-2) for initial sample to 9.47 x 10(9) cm(-2) after fourth cycle. The yield strength of the IF steel after fourth cycle was 10.8 times (909 MPa) higher than that of the initial sample (84 MPa). Finally, the contribution of individual mechanisms such as the grain refinement, dislocation, and precipitation in strengthening of the IF steel were evaluated.