Surface mechanical attrition treated AISI 304L steel: role of process parameters

In the present work, AISI 304L steel was used to investigate the effect of surface mechanical attrition treatment (SMAT) parameters on the hardness and microstructure. The surface modified by SMAT was examined using an optical microscope, SEM, electron backscattered diffraction, X-ray diffraction and microhardness measurements. The surface hardness of specimens was more than two times the hardness of non-treated core for all SMAT parameters. High density of shear bands (which formed nanosize rhombic blocks) was observed near the treated specimen surface. Density of shear bands was reliant on the size and number of balls. Deformation induced martensite (α′) was formed in surface mechanical attrition treated region. Volume per cent of α′ was enhanced with an increase in SMAT duration and number of balls. However, it was reduced with an increase in gap between vibrating plate and specimen surface. Microstructure evolution at various SMAT parameters was effectively explained using newly introduced terminology called ‘peening intensity’.