Influence of Cold Deformation and Phase Transformation on the Electrochemical Corrosion Behavior of Nitrogen‐Alloyed Stainless Steel in Chloride Solution

Nitrogen‐alloyed stainless steels exhibit outstanding corrosion resistance in chloride solution. However, cold deformation and phase transformation can influence the materials surface properties and, therefore, corrosion behavior. A nitrogen‐alloyed stainless steel with 20 wt% chromium, 0.13 wt% nitrogen, and subject to plastic deformation of up to 36% is electrochemically tested in a 5 wt% sodium chloride solution by linear polarization and electrochemical impedance spectroscopy. The steel's corrosion behavior is distinctly influenced by its deformation state. Before polarization, a negative influence of plastic deformation on the corrosion resistance of the alloy can be determined. However, after anodic polarization, the susceptibility to corrosion due to cold deformation and phase transformation decreases. While the electrochemical resistance of the protective surface film decreases due to deformation‐induced film rupture and the formation of anodes at the surface, the permeability of the double layer also decline. This is caused by the increased activation of the surface due to the formation of local anodes and, therefore, an increase in the formation of protective species that retard further dissolution processes. In addition, increasing plastic deformation results in the surface ratio between anodes and cathodes becoming more favorable, and in a decrease in the anodic current density. The influence of plastic deformation on the electrochemical corrosion behavior of a cast austenitic Fe–19Cr–4Ni–3Mn–0.13C–0.13N stainless steel is investigated in a 5 wt% sodium chloride solution. The results indicate a negative influence of plastic deformation on the virgin surface. However, anodic polarization and a following impedance spectroscopy reveals an increase of corrosion resistance due to plastic deformation and phase transformation.