Refractaloy 26 is an early-generation iron-nickel-cobalt-chromium precipitation-hardening superalloy, developed in the 1940s-50s alongside contemporaries such as Discaloy and A-286 during the first wave of high-temperature alloy development for jet-engine and steam-turbine service. Unlike the fully austenitic Fe-Ni-Cr grades of that generation, Refractaloy 26 leans on a substantial cobalt addition (~20%) alongside chromium (18%) and iron (16%), with molybdenum, titanium, and a small aluminum addition providing gamma-prime age-hardening response.

Historically, Refractaloy 26 filled the gap between austenitic stainless fasteners and full nickel-base superalloys — strong enough for high-temperature bolting, turbine blades, and steam-seal springs in large steam turbines, but more cost-effective and more readily forged than the higher-nickel grades that followed it. It is standardized under SAE/AISI 690 and AFNOR Z6NKCDT38, and is also cross-referenced under Werkstoff number 1.2888 and UNS R30188.

It carries a continuous service temperature capability in the 650-760°C range with short-term excursions to roughly 870°C, making it well suited to steam-turbine bolting, blades, and springs, as well as other elevated-temperature fastener applications where full nickel-superalloy cost is not justified.

Refractaloy 26 machines like a high-cobalt, iron-diluted nickel superalloy: the cobalt content pushes hot hardness and abrasiveness higher than a plain Fe-Ni-Cr grade, while the substantial iron fraction keeps overall thermal conductivity somewhat better than a full-nickel alloy — a small but real advantage at the cutting edge compared with alloys like René 77 or René 80.

Work hardening remains the dominant concern. Cobalt-bearing precipitation-hardening alloys harden aggressively wherever the tool rubs instead of cutting, so light or interrupted cuts quickly build a hardened skin that is far tougher on the next pass. Constant, adequate chip load is the primary defense. The alloy also retains meaningful strength at elevated temperature, so edge loads stay high even as cutting temperature climbs, promoting notch wear at the depth-of-cut line if speeds run too aggressive.

Because Refractaloy 26 is most often supplied and machined in the aged (precipitation-hardened) condition for fastener and spring applications, expect noticeably higher cutting forces and faster tool wear than in the solution-annealed condition. Sharp, positive-rake carbide with a fine edge preparation, rigid workholding, and abundant coolant are the standard countermeasures, matching practice for other Fe-Ni-Co-Cr superalloys of this era such as A-286 and Discaloy.