The mechanism of pitting initiation and propagation at deformation bands intersection of cold-rolled metastable stainless steel in acidic ferric chloride solution

Pitting initiation and propagation at the deformation bands intersection of cold-rolled 14Cr10Mn stainless steel in acidic ferric chloride solution with a pH of 1.3 were investigated by a scanning electron microscope equipped with electron back scatter diffraction and a high-resolution transmission electron microscopy. The experimental results show that the pits with regular morphology are a sort of dislocation etch pit with strict triggering conditions. The pitting corrosion resistance of the etch pits is closely related to the orientations in the increasing order of {100}〈001〉 < {110}〈112〉 < {111}〈110〉. The pit wall will expand to the periphery along the trend of retaining the close-packed plane, leading to an increase in pit depth after the pitting initiation is triggered. We believe that hydrogen ions compete with chloride ions and preferentially adsorbed on the dislocation outcrops in the austenite around α′-martensite and form hydrogen atoms occupying vacancies to prevent chloride ions from eroding the metal matrix. The results also reveal that the vacancy bands formed by the slip of edge dislocations, and the vacancy groups formed by the dissolve of partial dislocation outcrops are patterns for triggering dislocation etch pits.