Electrochemical method of quantitative determination of stainless steel susceptibility to intercrystalline corrosion

A rapid electrochemical method based on a new high-efficiency electrolyte has been developed. The method permits not only to reveal, but also to evaluate qualitatively the inclination of stainless steels towards the intercrystalline corrosion in the region of the active-passive transition potentials, that is under conditions simulating a conventional testing. The study is made with the steel-KH18N9T. The samples of steel are quenched, sensitized at 650 deg C, then the depth of the intercrystalline corrosion is determined metallographically. Prior to conducting the electrochemical measurements the samples are activized by the cathode current. The anodic potentiodynamic curves are plotted at a rate 2.4 V/hr. To ensure a distinct differentiation of the anodic behavior of stainless steels having different degree of the inclination to the intercrystalline corrosion, a new electrolyte, is based on chlorine acid with the additions of NaCl, exhibiting a high selective effect on chromium-depleted grain boundaries. A linear dependence is determined between the logarithm of the anodic solubility current density in solutions of HClO4+NaCl at a constant potential of the activation portion in the region of the active-passive transition and the depth of the intercrystalline corrosion. It is found that the method developed is applicable not only to insufficiently stabilized steels, but to steels of a standard chemical composition, as well as to low-carbon steels. However, application of this method to every new type of steel requires a preliminary refining of the method, that is, the determination of the optimum concentration of NaCl and the potential ensuring the maximum differentiation of the sample dissolving rate of the given steel exhibiting a different degree of the inclination to the intercrystalline corrosion