Microstructural and Passivation Response of Severely Deformed AISI 304 Steel Surface: The Role of Surface Mechanical Attrition Treatment

The present study investigates the microstructural and passivation behavior of surface mechanical attrition treated (SMAT) AISI 304 stainless steel in a 0.6 M NaCl solution at room temperature. SMAT process, which is more advanced than the classical shot-peening, causes 2-3 times improvement in surface hardness of the steel. Ball size, a vital SMAT parameter, plays a significant role in controlling the microstructure and corrosion behavior of the steel. Larger diameter (6 mm) balls induce thicker deformed layer (450 μm), a higher proportion of deformation-induced martensite (~ 50%), a higher density of dislocations and twins, and higher lattice strain. TEM results confirm the presence of {111} twins throughout the deformed layer. SMAT enhances the corrosion properties of the steel. Specimen SMATed with 4-mm-diameter-balls displays the lowest corrosion rate (1.80 × 10−4 mmpy). SMAT increases the pitting resistance of the steel surface. XPS is utilized to understand the passivation mechanism of steel comprehensively. SMAT alters the proportion of Cr2O3, Cr(OH)3, Fe2O3, and FeO compounds in the passive layer. SMAT increases the thickness of the passive layer.