A Corrosion Study of Grain-Refined 304L Stainless Steels Produced by the Martensitic Process

AISI 304L austenitic stainless steel with different grain sizes of 0.5 -12 μm was obtained through the martensitic process. Corrosion behavior of different samples was investigated in a 0.5M HCl solution using open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy tests. Also, the correlation between the grain size and pitting corrosion resistance was assessed by cyclic polarization experiments and immersion tests combined with optical microscopy. The potentiodynamic polarization results demonstrated that grain refinement had little influence on the corrosion potential and corrosion current density. However, cyclic polarization tests showed that the ultrafine grained steel (500 nm grain size) exhibited superior pitting resistance, as compared to the steel with the larger grain size (1- 12 μm). This behavior was confirmed by immersion tests in the 0.5M HCl for 48 hours, thereby showing that the size and the number of pits were decreased by increasing the grain size. The electrochemical impedance spectroscopy results also revealed that grain refinement enhanced the stability of the passive film of 304L stainless steel.