Corrosion properties of polished and shot-peened austenitic stainless steel 304L and 316L with and without plasma nitriding

In this study, two austenitic steels - 304L and 316L - were used in a solution annealed condition with either polished or shot-peened surfaces. Furthermore, these samples were tested without plasma nitriding, with plasma nitriding or annealing and a combined nitriding and post annealing process. The microstructural properties were examined by optical microscopy (OM) and scanning electron microscopy (SEM), phases were analyzed by X-ray diffraction (XRD) and the corrosion properties were tested by means of potentiodynamic polarization testing in 5% NaCl solution. Statistical evaluations were carried out to identify significant effects between the microstructure and nitriding conditions and the corrosion properties. The results indicate, that plasma nitriding improves the corrosion resistance of both steels with polished surfaces, while shot-peening increases the corrosion rates. Surface hardness measurements show the positive influence of plasma nitriding to surface hardness. Furthermore, a correlation between specimen treatment and the corresponding microstructures, the nitriding and the annealing process and the corrosion resistance will be presented.