Influence of microstructure and roughness level on corrosion resistance of the austenitic stainless steel welded joint

The influence of microstructure and surface roughness of the X5CrNi18-10 austenitic stainless steel-welded joint on resistance to uniform, pitting, and intergranular corrosion, as well as on the stability of the passive film, was evaluated. The microstructure was revealed by optical microscopy and scanning electron microscopy, whereas surface topography and roughness levels were determined by atomic force microscopy. Corrosion characteristics were obtained by the electrochemical potentiokinetic reactivation method with double loop, electrochemical impedance spectroscopy method, as well as by potentiodynamic measurements. The degree of sensitization of heat-affected zone (HAZ) was significantly lower than the threshold value required for the occurrence of intergranular corrosion. However, HAZ showed a significantly greater tendency to pitting and uniform corrosion compared to weld metal and base metal. No effect of roughness levels (RMS from 3.6 to 54 nm) on the pitting potential value of the welded joint was observed (unlike in HAZ). The polished surface shows significantly higher corrosion resistance than the grinded surface. Generally, polishing improved corrosion resistance, especially in HAZ, which is very important because HAZ is a critical place for the occurrence of pitting and other types of corrosion.