Effects of microstructure on the susceptibility of austenitic and martensitic stainless steels to pitting and intergranular corrosion in aqueous chloride environments
Sikri, Tarun Vabhav Pratap
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Stainless steels are utilized for their high toughness and resistance to general corrosion. Austenitic (300 series) stainless steels are the most popular because they are ductile and can be easily formed into desired geometries. They can also be case hardened to form alternating layers of martensitic and austenitic microstructures for applications that require high toughness and resistance to surface wear. However their usage is limited in comparison to other ferrous alloys due to higher initial costs and susceptibility to pitting and intergranular (IGC) corrosion. A microcell was developed to study these localized corrosion phenomena in microstructural regions of interest by performing polarization (spot) tests within well defined areas on metallic surfaces. Spot tests across profiles of welded 304 stainless steel confirmed that sensitization, greater acidities and higher chloride contents increase susceptibility and greater additions of chromium and nickel reduce susceptibility to localized corrosion. Spot tests across a case hardened (CSS 42L) stainless steel profile revealed that the austenitic sensitized outer layer was more susceptible to localized attack compared to the martensitic matrix. A more complete understanding of how microstructure affects these localized corrosion processes will lead to better alloy modifications, service environments and maintenance making this class of material a more sustainable alternative.