Stellite 8 is the wear-industry designation for a cobalt-chromium-molybdenum cast alloy that shares its base chemistry with ASTM F75 (UNS R30075, also referenced as ISO 5832-4), the internationally standardized Co-Cr-Mo casting alloy. Unlike the tungsten-carbide-strengthened Stellite grades (4, 6, 7, 12), this branch of the family substitutes molybdenum for tungsten as the principal solid-solution and carbide-forming strengthener, giving it a distinct combination of corrosion resistance, biocompatibility, and moderate wear resistance rather than the maximum abrasion resistance of the high-carbon Stellites.

That shared chemistry gives this alloy a genuinely dual role: in industrial hardfacing and wear-component service it is specified for pump and valve components operating in corrosive or erosive media, while the identical base chemistry cast under ASTM F75 / UNS R30075 is one of the most established alloys in orthopedic implant manufacturing, used for cast hip and knee prosthesis components under the same standard family (ISO 5832-4). This is a genuine metallurgical overlap, not a coincidence of naming - both applications draw on the alloy's combination of corrosion resistance and moderate strength in the cast, unwrought condition.

Cast Co-Cr-Mo alloys in the Stellite 8 / F75 family machine similarly to the wear-resistant Stellite grades in some respects and differently in others. Like the tungsten-strengthened Stellites, the alloy is work-hardening, has poor thermal conductivity relative to steel, and retains its strength at elevated temperature, so heat concentrates at the tool-chip interface and there is no useful thermal-softening effect to lean on at higher speeds. Unlike the higher-carbon abrasion-resistant grades, its molybdenum-based strengthening and low carbon content (0.35% max) mean it does not carry the same volume of massive primary carbides, which tends to make it somewhat more forgiving to machine than Stellite 1, 12 or 190, while still being significantly harder to cut than any conventional steel.

As-cast microstructure can vary meaningfully with casting process (investment casting versus sand casting) and any post-cast heat treatment, which in turn affects machinability - parts machined directly from as-cast stock can present a coarser, more variable carbide structure than wrought or hot-isostatic-pressed material. Rigid setups, sharp positive geometries, hard PVD/CVD-coated carbide grades suited to superalloys, constant adequate chip load to avoid work-hardening, and generous coolant are the standard approach.