Cr15 Super Martensitic Stainless Electrochemical Corrosion Studies

In this paper, the corrosion resistance of the super martensitic stainless steel(SMSS) with different content of tungsten and copper under content of several heat treatments was surveyed by the electrochemical experiment. The pitting corrosion resistance of SMSS was discussed in various environment of different Cl-concentrations, pH, CO2 conditions and adding Na2SO4, NaHCO3 in corrosive solution. What's more, it was analyzed at several temperature and immersion times.The microstructures of grains coarsens with the rising quenching temperature of the tempered at 650℃; and which become refinement with the rising tempering temperature of the quenched at 1050℃. The reversed austenite is generated at the tempered condition, but the content is the highest under the tempered 650℃.The super martensitic stainless steel of different organization and component was measured with potentiondnamic scanning, it can be obtained polarization curve, In several heat treatments, the super martensitic stainless which quenched at 1050℃and then tempered at 650℃has the best pitting corrosion resistance.It's to continue in-depth for super martensitic stainless steel with optimum heat treatment. The pitting corrosion resistance of SMSS decreases gradually when the Cl-concentration increased. Compared with in the NaCl solution without CO2, the corrosion potential and maintaining passivity current density of stainless steel are relatively positive in the solution with CO2, it shows that the corrosion rate of stainless steel is higher with CO2. However, the maintaining passivity region and pitting potential is increasing, it indicates that super martensitic stainless steel can form a dense layer corrosion passive film with CO2, the matrix is protected effectively.It can be observed the acceleration experiment in ferric chloride solution, the kinds of stainless steel had undergone severe corrosion. At the same time the corrosion of stainless steel with W and Cu is relatively lighter.It can also obtained through above experimental data, the corrosion resistance of stainless steel of containing W is superior to non-W elements; the corrosion resistance of stainless steel that is containing Cu higher is superior. It's to continue in-depth for super martensitic stainless steel which has the best corrosion resistance. With the pH decreased and temperature increased, the corrosion resistance of super martensitic stainless steel gradually declined. Within 0-72h, the stainless steel was measured with polarization curve, the maintaining passivity current density is gradually decreased and pitting potential gradually increased following the extension of immersion time. It can be seen from electrochemical impedance spectroscopy, the capacitance arc is greater as the time goes on. the stainless steel was measured with electrochemical noise, the noise resistance is to be increased with the increase of immersion time. It indicates that super martensitic stainless steel can form a dense layer corrosion passive film with a certain time, and the film adsorbed on the matrix, so the corrosion resistance of stainless steel is improved.