Correction: this page previously described Haynes 25 as a nickel-based alloy. That is incorrect. Haynes 25 (UNS R30605) is a cobalt-base superalloy - cobalt is the majority element at roughly 51% - alloyed with chromium, tungsten, and a comparatively small nickel addition. It is also known as Alloy L-605, Stellite 25, and Udimet L-605, and is cross-referenced to AMS 5537 (sheet/strip/plate), AMS 5759 (bar and forging stock), AMS 5796/5797 (welding wire/rod), and Werkstoff-Nr. 2.4964.

Haynes 25 is a solid-solution-strengthened cobalt alloy that combines excellent high-temperature strength with good resistance to oxidizing environments up to 1800 degF (980 degC) for prolonged exposure, along with strong resistance to sulfidation. It is the strongest of the cobalt-base alloys that still retain good fabrication characteristics, and it is particularly notable for excellent resistance to metal galling and cavitation - among Haynes' own cobalt alloys, only Ultimet and Haynes 6B outperform it in wear/galling tests.

Historic applications include military and commercial gas turbine engine components (rings, blades, combustion chamber parts) and, notably, ball bearings and bearing races, where its cold-worked strength and wear resistance are put to direct use. In modern gas turbines it has largely been superseded by newer alloys such as Haynes 188 and Haynes 230, but it remains in active production and specification.

Haynes 25 is generally considered more difficult to machine than most nickel-base superalloys, and cobalt-base alloys as a family carry their own distinct set of challenges beyond the usual nickel-alloy playbook. 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.

Haynes International's own fabrication data notes explicitly that the alloy "work-hardens very rapidly," to the point that frequent intermediate anneals are needed just to form the material cold - 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.

Haynes 25 also retains strength at elevated temperature better than most nickel solid-solution alloys - it is described by Haynes as stronger than nickel-base solid-solution alloys and the strongest of the fabricable cobalt 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.