Evaluation of Corrosion Progression in X210Cr12 Tool Steel in a Marine-like Chloride Environment Using SEM/EDS and PCA Techniques

Corrosion of high-chromium tool steels in marine environments is a major concern for structural materials, as chloride-rich conditions accelerate material degradation and reduce service life. The corrosion process involves complex interactions among passive film degradation, localized pitting, and surface defect evolution. This study investigates the corrosion progression of X210Cr12 tool steel immersed in a 3.5 wt.% NaCl solution, representing a marine-like chloride environment. Corrosion progression was monitored by combining mass loss measurements, SEM/EDS characterization, quantitative image analysis, and principal component analysis (PCA). The results reveal three distinct stages of surface degradation: initial pit nucleation, pit propagation accompanied by formation of new defects and growth of already existing ones, and pit coalescence with accelerated mass loss after 90 days of exposure, which can be associated with pronounced chromium depletion and degradation of the protective surface layer. The cumulative mass loss increased from 0.024 g after 30 days to 0.153 g after 120 days, while the calculated corrosion rate increased from 0.067 to 0.107 mm/year. Image analysis showed an increase in the degraded surface area from 0.089% to 13.34% at 120 days. EDS measurements indicated a pronounced decrease in surface chromium content accompanied by increasing oxygen content in corroded regions. PCA identified the most informative morphological descriptors, showing that size-related parameters dominated in the early stages of corrosion, while shape-related descriptors became more important during advanced stages of degradation. The proposed methodology provides a data-driven approach for monitoring corrosion progression and identifying morphological parameters associated with different stages of surface degradation under marine-like chloride conditions.