Abstract
The role of grain size and strain rate on the corrosion behavior of plastically-deformed Ti-stabilized austenitic stainless steel (AISI 321) in saline media was investigated. The as-received coarse-grained alloy (CG: ~37 µm) was subjected to thermomechanical processing to develop fine (FG: ~3 µm) and ultrafine (UFG: ~0.24 µm) grained structures. These samples were deformed under high (dynamic) and low (quasi-static) strain-rate conditions to a similar true strain of ~0.86. Microstructural analyses on specimens after deformation prior to corrosion study suggests a shift from the estimated stacking fault energy value of the steel. Electrochemical tests confirm the highest corrosion resistance for UFG specimens due to the formation of the most stable adsorbed passive film. This is followed by FG and CG specimens in that order. For the three grain sizes, the corrosion resistance of specimen deformed under quasi-static loading condition is higher than that subjected to dynamic impact loading while the corrosion resistance of undeformed samples is the least. This work also confirms the non-detrimental effect of TiCs in AISI 321 austenitic stainless steel on its corrosion resistance. However, TiNs were observed to be detrimental by promoting pitting corrosion due to galvanic coupling of TiNs with their surrounding continuous phase. The mechanism of pitting in AISI 321 in chloride solution is proposed.
Highlights
The role of grain size and strain rate on the corrosion behavior of plastically-deformed Ti-stabilized austenitic stainless steel (AISI 321) in saline media was investigated
The strain hardening could be attributed to activation of different deformation and/ or strengthening mechanisms
Thermal softening leads to thermo-mechanical instability and loss of load-carrying capability as the temperature of the specimen is raised during the dynamic deformation process
Summary
The role of grain size and strain rate on the corrosion behavior of plastically-deformed Ti-stabilized austenitic stainless steel (AISI 321) in saline media was investigated. The as-received coarse-grained alloy (CG: ~37 μm) was subjected to thermomechanical processing to develop fine (FG: ~3 μm) and ultrafine (UFG: ~0.24 μm) grained structures These samples were deformed under high (dynamic) and low (quasi-static) strain-rate conditions to a similar true strain of ~0.86. In a separate study[6], UFG structured AISI 321 steel developed via thermomechanical processing exhibited lower corrosion resistance than coarse grain (CG) specimens in 0.1 M NaCl solution at room temperature. The role of grain size, prior deformation, and strain rate on the degradation pattern of AISI 321 stainless steel in corrosive environments are not exhaustively covered in the literature. This is the motivation for the present study. The aim is to ascertain how these loading conditions affect the corrosion behavior of AISI 321 steel
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