Effect of Uniaxial Tension-Induced Plastic Strain on the Microstructure and Corrosion Behavior of 13Cr Martensitic Stainless Steel

This study aims to understand the correlation between the manufacturing process-induced plastic deformation, microstructure, and corrosion behavior of a 13Cr martensitic stainless steel tubing material (UNS S42000). Comparisons were made between the microstructure, crystallographic orientation, and corrosion performance of a texture-free, heat-treated sample and uniaxially tensioned samples to the elongations of 5% and 22%. Cyclic potentiodynamic polarization tests and electrochemical impedance spectroscopy were performed on all samples in aerated 3.5 wt% NaCl electrolyte at room temperature. Overall, the corrosion resistance of the samples was found to decrease with increasing deformation level. A more stable and higher corrosion potential and pitting potential values with a better stability of the passive film were derived for the nondeformed sample, whereas the 5% and 22% elongated samples exhibited lower corrosion and pitting potential values and were characterized by having a less stable passive layer. All samples consistently revealed micropit formation on the lath boundaries where a high concentration of chromium carbide precipitates was detected. Increasing the level of plastic strain in 13Cr stainless steel was found to enlarge the size of sensitized regions along the matrix/coarse chromium carbide precipitates interface, leading to more regions susceptible to initiation and propagation of pitting.