Same alloy, different trade name: HS-25 is Haynes International's original "Haynes Stellite 25" designation for the identical wrought cobalt-chromium-tungsten-nickel alloy sold today as Haynes 25, and also marketed by other producers as L-605, Stellite 25, and Udimet L-605 (UNS R30605). All of these names refer to the same chemistry and the same AMS 5537 / AMS 5759 specifications. For that reason, the composition and machining data on this page are drawn directly from FM Carbide's Haynes 25 reference page to keep the two pages consistent.

This is a solid-solution-strengthened cobalt alloy that combines excellent high-temperature strength with good resistance to oxidizing environments up to about 980°C/1800°F for prolonged exposure, along with strong resistance to sulfidation. It is the strongest of the readily fabricable cobalt-base alloys and is particularly notable for excellent resistance to metal galling and cavitation. Historic and current applications include military and commercial gas-turbine engine components (rings, blades, combustion-chamber parts) and ball bearings/bearing races, where its cold-worked strength and wear resistance are put to direct use.

Because HS-25 is chemically identical to Haynes 25, its machining behavior is identical as well and is generally considered more difficult than most nickel-base superalloys. Thermal conductivity is very low - on the order of 10.5 W/m-K at room temperature, well below typical nickel superalloys - so heat generated in the cut has essentially nowhere to go except into the tool, driving accelerated crater wear and edge deformation if speeds are not controlled.

This alloy work-hardens very rapidly, to the point that frequent intermediate anneals are needed just to cold-form the material - a strong signal of how aggressively it work-hardens under cutting forces as well. Any hesitation, rubbing, or light/inconsistent feed leaves a hardened layer that is significantly tougher to cut on the next pass, making a steady, adequate chip load essential.

This chemistry also retains strength at elevated temperature better than most nickel solid-solution alloys, so tool edges stay under heavy mechanical and thermal load throughout the cut. Its exceptional resistance to galling, a benefit in bearing and wear applications, is a liability at the cutting edge: the same tenacity against metal-to-metal adhesion that resists wear in service also promotes strong built-up edge and edge chipping in the cut if tools are not sharp, coated, and run with generous coolant.