Surface Nanocrystallization of EN8 Steel: Correlation of Change in Material Characteristics with Corrosion Behavior

Abstract

The present paper addresses the influence of surface mechanical attrition treatment on the characteristic properties of EN8 steel and, to analyze the correlation between the change in properties of the treated steels with their corrosion behavior in 0.6 M NaCl and borate buffer, evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy studies. Surface mechanical attrition treatment of EN8 steel induced plastic deformation, enabled surface nanocrystallization, increased the surface roughness, microstrain and defects/dislocations and, imparted compressive residual stresses. The change in properties of EN8 steel following treatment has caused a deleterious influence on its corrosion resistance in 0.6 M NaCl but an improvement in corrosion behavior in borate buffer. The possible reasons for the change in corrosion behavior of the treated EN8 steel are suggested. Pictorial models are proposed to explain the evolution of surface roughness and the mechanism of corrosion attack of the treated EN8 steels in 0.6 M NaCl and borate buffer.Carbon steels are widely used as structural materials in many industries due to their low cost and ability to provide reasonably good mechanical properties besides being weldable. However, the structural components fabricated using carbon steels encounter failures during service, particularly due to surface related failures such as fatigue, wear and corrosion. Hence, modifying the surface properties of carbon steels becomes not only essential but also mandatory to enhance their service life and utility. A variety of severe plastic deformation (SPD) processes have been explored and such treatments have enabled carbon steels to achieve superior mechanical properties, improved tribological behavior and imparted them with the ability to inhibit fatigue crack initiation. 1-4 However, corrosion resistance of carbon steels subjected to SPD has been a debatable issue. 5-15 Reduction in grain size, increase in the extent of dislocations, microstrain and surface roughness, change in texture and change in residual stress were considered as the major factors that have influenced the corrosion resistance of steels after SPD. The corrosivity of the medium, solubility of corrosion products and the ability of the corrosive medium to promote passivation, further increase the complexity by another dimension. For instance, a reduction in grain size caused a deleterious effect on the corrosion resistance of steel in H 2 SO 4 and H 2 SO 4 + Na 2 SO 4 5,6 whereas it promoted passivation of steel in borate buffer. 15 Similarly, a change in texture offered an improvement in corrosion resistance of steel in H 2 SO 4 + Na 2 SO 4 12 while a reduction in grain size without a change in texture showed the opposite trend. 5 Likewise, carbon steel subjected to supersonic fine-particles bombarding showed a decrease in corrosion resistance in 3.5 wt% NaCl while the trend was reversed in saturated Ca(OH) 2 . 11 The increase in surface roughness and formation of micro-cracks were suggested as reaso...

A Facile Method to Modify the Characteristics and Corrosion Behavior of 304 Stainless Steel by Surface Nanostructuring toward Biomedical Applications

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