Abstract: An effective approach to enhance the surface degradation characteristics of laser powder bed fusion (LPBF) type 420 stainless steel involves the incorporation of spherical cast WC/W₂C to create LPBF metal matrix composites (MMCs). However, the corrosion behavior of stainless steel and cast WC/W₂C varies inversely across different pH levels, and the phenomenon of pitting corrosion in LPBF MMCs under varying pH conditions remains insufficiently explored. In LPBF 420 + 5wt% WC/W₂C MMCs, pits form adjacent to cast WC/W₂C in acidic and neutral environments, attributed to the presence of chromium-rich carbides and galvanic coupling effects. The dissolution of the reinforced particles facilitates pit nucleation in alkaline conditions. Notably, in-situ reaction layers exhibit superior corrosion resistance to the matrix or the reinforced particles across all pH levels. The distinct corrosion mechanisms influence the pitting corrosion behavior, with the corrosion ranking based on critical pitting potential being neutral > alkaline > acidic, contrasting the observed kinetics of pit growth (alkaline > acidic > neutral).