Influence of Cold Work on Pitting Corrosion Behavior of a High Nitrogen Stainless Steel

Abstract

The effects of cold work on the pitting corrosion resistance of a nickel-free high-nitrogen stainless steel in chloride solution have been investigated by electrochemical tests, surface chemical analysis, immersion tests, and microscopic observations. Potentiodynamic polarization revealed that pitting resistance was degraded by cold work as convinced by the decreased critical pitting potential. This could be due to a less compact and protective anodic passive film based on the results of electrochemical impedance spectroscopy, Mott-Schottky measurement, and X-ray photoelectron spectroscopy analysis. The growth of such an imperfect passive film could be attributed to a high density of deformation bands and other defects introduced by cold work. Scanning electron microscopy observation of the pitted specimens after polarization tests showed no obvious change in size and density of corrosion pits with increasing cold work level, whereas immersion tests showed varied pit density with cold work although the average size of pits did not increase linearly as a function of cold work level. The effects of cold work on the characteristics of passive films are discussed.The beneficial effects of nitrogen on the properties of highalloyed steels have led to a widespread development of highnitrogen stainless steels ͑HNSSs͒ owing to recent advances in processing technologies. 1-3 Nitrogen as an alloying element causes several beneficial effects on the properties of steels, in particular, those related to an excellent combination of high yield strength and good fracture toughness. 1 Nitrogen is also a strong austenitestabilizing element and is expected to substitute for nickel, which is expensive and causes an allergic reaction in human skin. Moreover, nitrogen alloying, especially together with molybdenum, improves resistance to localized corrosion, in general, and resistance to general corrosion in some environments. Therefore, the austenitic HNSSs constitute a group of promising structural materials that possess a favorable combination of mechanical and corrosion-resistance properties.With these increasing demands, it is necessary to investigate the pitting resistance of the HNSSs. Thus far, a number of possible mechanisms by which nitrogen improves the localized corrosion resistance have been reported. 4-7 Cold work is unavoidable for the fabrication of stainless steel ͑SS͒ components. It might affect the pitting corrosion resistance of SSs because deformation substructures, such as planar dislocation arrays 1,8 and deformation twinning, 9 could be introduced. Several investigations have reported the role of cold work on the localized corrosion resistance of SSs. 10-17 Kamachi Mudali et al. 10 have reported that the pitting corrosion resistance of a nitrogen-bearing 316 SS was improved first by cold work in neutral chloride medium and then reduced beyond 20% cold work. Peguet et al. 11 have reported the different role of cold work on the pitting corrosion resistance at different pitting stages, including pit initiation, prop...

Effect of Plastic Deformation on the Corrosion Behavior of a Super-Duplex Stainless Steel

“…It is not possible to report any improvement in corrosion resistance with increasing plastic deformation for the SDSS used in this study. The results are closer to those reported in (Ref [8][9][10] where small reductions in E p occurred at cold-work levels below 20% area reduction. However, there are also some notable differences from the single-phase studies.…”

Effects of Nitrogen on Passivity of Nickel-Free Stainless Steels by Electrochemical Impedance Spectroscopy Analysis

“…With increasing N content from N1 to N3, the pitting potential was shifted to more positive values, indicating an improved pitting resistance with increasing N content. The above results are coincided with the previous work (Ref [7][8][9][10][11][12][13]. Both the maximum current density and passive current density decreased with increasing N content.…”

Surface Nanocrystallization of EN8 Steel: Correlation of Change in Material Characteristics with Corrosion Behavior

“…R pore and CPE correspond to the resistance of the pores/defects inside the film and its capacitance, respectively. 40 The impedance of CPE is given by Z CPE = 1/Q(jω) n , Where 'n' is the CPE exponent. The capacitance element Q (CPE) will be pure capacitance when n = 1 while it will be pure resistance when n = 0.…”