Formation of nanograin surface layers in Interstitial Free (IF) steels

To produce nanocrystalline layers on the surface of the interstitial free (IF) steels, the surface of IF steel sheets was subjected to surface severe plastic deformation (SSPD). This was done by wire-brushing technique at ambient temperature. The surface nanocrystalline layers were successfully formed by adjusting the applied SSPD parameters. The surface layer of the sheet steels, developed by the near surface severe plastic deformation, was then characterized by means of atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) patterns and micro-hardness measurements. The results show that equiaxed nanocrystals with grain sizes ranging from 30 to 200 nm were observed in the near surface regions of sheet steels. The hardness of the nanostructured layer exhibited an increase up to three times higher than that of starting one. The present SSPD process is an effective and useful technique to form nanocrystalline structure in the surface layers ofdifferent materials. The most important achievement is the production of some kind of functionally graded materials in terms of grain-size gradient through the thickness sheet