Cold rolling deformation-induced microstructural evolution and corrosion performance optimization in 254 SMO super-austenitic stainless steel bipolar plates for PEMFCs

This study examined the influence of cold rolling deformation on the microstructural evolution and corrosion performance of 254 SMO super-austenitic stainless steel (SASS) bipolar plates in a simulated cathode environment for proton exchange membrane fuel cells (PEMFCs). The results show that corrosion resistance of 254 SMO SASS exhibits a trend of first increasing and then decreasing with the increase in cold rolling reduction levels, reaching its optimal at 75% reduction level, which is mainly associated with the presence of high-density dislocations and large-quantity low-angle grain boundaries (LAGBs). These high-density crystal defects provide abundant active sites for the nucleation of highly dense and Cr-rich passivation films. When the reduction level reaches 83%, the beneficial effects of increased LAGBs and high-density dislocations are outweighed by the pronounced lattice distortion and unbalanced crystallographic texture that disrupts the preferential orientation for the growth of compact passivation films. In addition, for the severely deformed 254SMO SASS (83% reduction level), the occurrence of dislocation entanglements and deformation twins will form a large number of “micro domains” within the microstructure and composition, which constitutes microscopic galvanic corrosion couples, thereby corrosion resistance being deteriorated.