Formation of Nanostructured Surface Layer Induced by Surface Mechanical Attrition Treatment (SMAT) in Spring Steel

Surface mechanical attrition treatment (SMAT) is measured to be a current approach for obtaining a nanostructured layer on the treated metal. In this paper, a nanostructured surface layer up to 450 +/- 20 mu m thick was induced on commercially used spring steel by SMAT. The effect of SMAT on microstructural features has been systematically characterized by optical microscope (OM) for cross-sectional observation, transmission electron microscopy (TEM) and X-ray diffractometry (XRD) analysis. The result shows an increase in strain in the surface layer due to grain refinement process. This involves an increase in dislocation density, formation of thin martensitic layers and twinned martensite. The SMAT also induce craters which is approximately circular depression in the surface prompt an increase in roughness value from 0.572 mu m to 1.978 mu m and decreases slightly upto 1.871 mu m when SMAT goes upto 75 min. These changes resulted in an increase of mechanical properties which were characterized as hardness increment, yield strength, tensile strength and also increases the % elongation after certain time of SMAT.