Effects of Applied Stress on Atmospheric Corrosion and Pitting Characteristics of 304 Stainless Steel

The effects of applied stress, ranging from tensile to compressive, on atmospheric pitting corrosion of stainless steel 304L (SS304L) were analyzed through laboratory exposure and localized corrosion experiments. Pitting characteristics, analyzed through optical profilometry, scanning electron microscopy, and electron backscatter diffraction, were obtained after exposure for 50 days of an SS304L four-point bend bar to simulated seawater conditions at 50°C and 35% RH. Additionally, localized electrochemical measurements were carried out on an unexposed SS304L four-point bend bar to analyze the effects of applied stress on the corrosion susceptibility in analogous chloride solutions. In the tested, simulated seawater environment, the applied stress showed no effect on the pitting characteristics due to the aggressivity of the 4g/m2 loading of simulated seawater. Pitting depth, surface area, roundness, and distribution were found to be largely stochastic and rely on the available cathodic area and preexisting microstructure. However, through localized corrosion experiments in more benign environments, containing lower Cl- concentrations, the effects of stress on corrosion susceptibility start to become noticeable from the open circuit potential (OCP) measurements. A measurable decrease in the OCP indicated increased susceptibility to corrosion in the region of applied tensile stress as compared to the compressively stressed region. These findings indicate that stress may be less of a contribution to corrosion susceptibility than Cl- concentration under the exposure conditions examined. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2020-4490 A