CORROSION AND PASSIVE PROPERTIES OF BULK ULTRAFINE-GRAINED 304L STAINLESS STEEL

Samples of ultrafine-grained 304L stainless steel with an average grain size of (130 +/- 30) nm were prepared by using equal channel angular pressing (ECAP) technique after 6 passes with route Bc at 500 degrees C. The electrochemical behaviors and the passive properties of the material in 0.05 mol/L H2SO4+0.25 mol/L Na2SO4 solution were examined by using polarization curves and Mott-Schottky analysis. As compared with the coarse-grained counterpart, the ultrafine-grained 304L stainless steel sample exhibits a lower corrosion potential (-505 mV) and a higher corrosion current density (11.7 mu A/cm(2)), indicating the accelerated trend of the active dissolution, and has a broadening of passive region (-341-847 mV) with lower passive potential (-341 mV) and passivation current density (4.5 mu A/cm(2)). Both of the passive films exhibit n-type semi-conductor behaviors at potentials ranging from 0 to 0.7 V. The ultrafine grains of 304L stainless steel are helpful in forming more stable Passive films with the reduced donor density and the diffusion coefficient of the charge carrier.