Electrochemical dissolution behavior of stainless steels with different metallographic phases and its effects on micro electrochemical machining performance

To investigate the anodic dissolution of stainless steels with diverse metallographic phases and its impact on micro electrochemical machining (micro-ECM) performance, the electrochemical behavior of representative ferritic stainless steel (SUS430), martensite stainless steel (SUS440C), dual-phase stainless steel (2205 DSS), and austenite stainless steel (SUS316L) in neutral solutions were examined by analyzing potentiodynamic results and electrochemical impedance spectroscopy (EIS). The growth and chemical compositions of passive films on the stainless steels were evaluated using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). EIS results indicate that the passive film formed on SUS430 (ferritic phase) and SUS440C (martensite phase) in NaClO₃ exhibited greater stability compared to that formed in NaNO₃, which is attributed to the thicker passive film formed in NaClO₃ and higher Fe²⁺/Fe³⁺ ratio as well as Cr₂O₃/Cr(OH)₃ ratio. The SUS316L (austenite phase) exhibits almost the opposite behavior compared to the SUS430 and SUS 440C. The impact of the electrochemical behavior on the evolution of dissolution region and surface topography was discussed from the micro-ECM experimental results. The 2205 DSS exhibits a much higher corrosion resistance, but local corrosion zones were observed at the edges of microgrooves, leading to approximate material removal rate values compared to single-phase steels. The metallographic phases influence the composition, structure, and density of the passive films, and determine the ECM performance. This study demonstrates the relationships between the MRRs and the metallographic phases of stainless steel, which provides a feasible idea for optimizing the matches of the electrolyte composition and stainless steel workpiece.