The increasing demand for high-strength, corrosion-resistant steels in advanced engineering applications has driven the search for materials that eliminate hazardous coatings like cadmium while maintaining robust mechanical performance. This study investigates the effect of carburization on the microstructure, corrosion behavior, and surface hardness of the CSS-42L stainless steel. Under sulfur dioxide salt fog testing, noncarburized CSS-42L coupons exhibited no signs of general or localized corrosion across combined galvanic and crevice, galvanic, and individual exposure conditions. In contrast, carburized CSS-42L samples displayed general corrosion on flat surfaces, pitting along sidewalls, and edge cracking, with a significant increase in the corrosion rate compared with the equivalent untreated samples. Microstructural analyses via optical microscopy confirmed a gradient in the carburized samples, from a high-carbon martensitic surface enriched with M₇C₃ and M₂₃C₆ carbides to a tempered martensitic core. Electron backscatter diffraction phase maps also revealed carbide morphologies and distribution. Hardness profiles further corroborated these gradients, with surface values reaching approximately 785 HV compared with approximately 360 HV for the core, matching the uniform hardness of noncarburized samples. Overall, the results demonstrate that although carburization enhances surface hardness, it compromises corrosion resistance due to chromium depletion and carbide precipitation. These findings underscore the design potential and limitation of selective carburization strategies to enhance mechanical performance.