Effect of prior plastic deformation and deformation rate on the corrosion resistance of AISI 321 austenitic stainless steel

In this work, the role of prior plastic deformation and rate of deformation on the corrosion behavior of plastically-deformed metastable AISI 321 austenitic stainless steel in 3.5 wt% NaCl solution was investigated. Samples were deformed under dynamic (epsilon(T) = 8.8 x 10(3) s(-1)) and quasi-static (epsilon(T) = 4.4 x 10(3) s(-1)) loading conditions to a common true strain of similar to 0.86 using a split Hopkinson pressure bar and Instron R5500 mechanical testing systems, respectively. While the specimen subjected to quasi-static compression experienced substantial deformation-induced martensitic transformation, phase transformation was significantly suppressed in the specimen subjected to dynamic loading due to temperature rise during impact. The yield strength of the specimen under dynamic impact loading is higher than that of the specimen compressed under quasi-static loading condition. However, the specimen deformed under quasi-static loading shows higher strain-hardening rate compared to the specimen subjected to dynamic impact load which is dominated by thermal softening at true strain beyond similar to 0.6. Using the Tafel polarization and impedance spectroscopic techniques, the deformed specimens were found to be more resistant to chloride-induced intergranular corrosion at room temperature compared to the undeformed ones. The specimen subjected to quasi-static loading exhibits significantly higher corrosion resistance in comparison with those subjected to dynamic loading. This could be attributed to the formation of a denser passive film on the specimen subjected to quasi-static loading on exposure to the test electrolyte over time. In addition to the role of particles on pitting formation in metals exposed to corrosive environment, the current work affirms the important role of prior plastic deformation on the corrosion behavior of the investigated alloy. Evolution of twins and stable-end orientation (preferred crystallographic orientation) in both parent (austenite) and product (martensite) phases nullified what would have been the negative effects of plastic deformation (due to the associated deformation-induced martensitic phase and stored defects) on the corrosion resistance of the investigated stainless steel.