Modification of the Corrosion Properties of a Model Fe-8Ni-18Cr Steel Resulting from Plastic Deformation and Evaluated by Impedance Spectroscopy

A model {minor elements}-free Fe-8Ni-18Cr alloy (wt%) was elaborated by foundry, then cut in several cylindrical parts which were subjected to compression tests leading to different plastic deformation rates. The axis surface of the obtained samples were characterized in corrosion by impedance spectroscopy in an acid sulphuric solution. The obtained EIS results were plotted in the complex plan of Nyquist and the diagrams were all semicircular but with an average radius decreasing when the deformation rate increased. The plastic deformation obviously induced a decrease in charge transfer resistance, revealing a detrimental effect of the corrosion behaviour as the most often reported in studies involving stationary methods of electrochemical characterization of corrosion. It was also found that the capacitance tends to increase with the rate of plastic deformation by compression. 1. Introduction A lot of fabrication processes induce for metals and alloys more or less severe plastic deformation for obtaining the required shapes for the pieces (e.g., cold or hot rolling, forging, stamping, etc.). Such permanent deformations, by multiplying defects and dislocations, can be responsible of significant changes in the mechanical properties as well as of modification of the surface reactivity. The effect of plastic deformation on the mechanical behaviour of the alloys is well known (e.g., increased hardness and elastic resistance) [1] but it is not really the same about the consequences on the corrosion behaviour since the observations are rather scattered on this subject. Indeed, numerous studies have been done in the past about the influence of mechanical deformation (e.g., cold-rolling) on the corrosion behaviour of metals and alloys (aluminium- [2], magnesium- [3], or titanium-based [4]), and also of stainless steels in various solutions [5–7]. If it was sometimes found that plastically deformed iron-based alloys are more resistant against aqueous corrosion than before deformation [8, 9] the contrary was more frequently observed, as reported in many works. Between all these earlier works the studied alloys were different from one another, concerning their fabrication details or their chemical compositions which contained or not elements able to influence the corrosion behaviour even if they are present in low quantities. The aim of the present work is to study the effect of a plastic deformation of an alloy on its corrosion behaviour by avoiding some of the previous possible causes of results dispersion. A ternary alloy was elaborated by foundry, including a