Laser peening induced mitigation of severe pitting corrosion in titanium stabilized 321 steel

Abstract

Titanium stabilized 321 stainless steel, as a structural component in oil and petrochemical industries, often susceptible to severe pitting corrosion under aggressive corrosion environments (sulfuric acid and chloride ions). This study explores the applicability of laser peening without protective coating (at 6 GW cm(-2) intensity and 75 % pulse overlap rate) to enhance the electrochemical stability of 321 steel against such severe pitting corrosion. Laser peening altered surface-mechanical and electrochemical properties were investigated by AFM, SEM and potentiodynamic polarization/impedance spectroscopy techniques. On the account of laser peening induced compressive residual stress (-408 MPa) hardness enhancement, a stable/dense and uniform oxide film was formed on 321 steel, subsequently mitigating the pitting corrosion. By contrast, unpeened surface exhibited more number of wider and deeper merged pits (maximum diameter of similar to 2197 mu m). Laser peening promoted oxidation has been confirmed via elemental composition analysis. A twentyfold enhancement in charge transfer resistance and improved oxide film resistance, attributed from the laser peening increased defect density as demonstrated by the improved hardness, evidenced a highly electrochemical stability on 321 steel.