Effect of Milling Parameters on the Stability of the Passive Film of AISI 304 Stainless Steel

AISI 304 stainless steel samples were milled with different feed rates and depths of cut. The effect of the milling parameters on the surface residual stresses was assessed by x-ray diffraction. The chemical composition of the passive film was examined by x-ray photoelectron spectroscopy. The corrosion behavior and pitting corrosion susceptibility in 3.5 wt.% NaCl solution were investigated by potentiodynamic polarization curves. The Mott-Schottky approach was employed to study the semiconducting properties of the passive films. Milling imparted higher surface stresses to the metal surface. Compressive stresses were favored at slower feed rates and higher depths of cut. Chromium enrichment was observed after milling, leading to an increased stability of the passive film for the milled samples with respect to the as-received material. The corrosion behavior and doping densities of the passive films were also affected by milling. There is a strong relationship between milling parameters, surface stresses, chemical composition of the passive film and its corrosion behavior.