• LPBF 420 + 5wt% WC/W2C MMCs exhibit pH-dependent pitting mechanisms: pits form near carbides in acidic/neutral media, while particle dissolution drives nucleation in alkaline conditions.
• In-situ reaction layers show superior corrosion resistance compared to both matrix and reinforced particles across all pH levels, offering a design pathway for enhanced durability.
• Critical pitting potential ranking (neutral > alkaline > acidic) inversely correlates with pit growth kinetics (alkaline > acidic > neutral), highlighting distinct thermodynamic and kinetic controls.
• The study provides critical insights for optimizing LPBF MMC compositions and service environments to mitigate localized corrosion in chloride-containing solutions.