S 816 is one of the oldest wrought cobalt-base superalloys still referenced in industry, developed in the early 1950s (originally by Allegheny Ludlum, later carried under UNS R30816 and the older ASTM Grade 671 designation) for gas-turbine hardware operating in the 1200-1500°F (650-815°C) range. Unlike the wear-resistant "Stellite" hardfacing alloys that share the cobalt-chromium-tungsten family tree, S 816 was engineered for structural, load-bearing service: turbine blades, buckets, bolting, and hot-section fasteners that need to hold strength and dimensional stability under sustained heat, not just resist abrasive wear.

The alloy gets its strength from a combination of solid-solution hardening (chromium, tungsten, molybdenum) and carbide/intermetallic strengthening contributed by niobium and tantalum, both roughly matched in the composition at 3.5-4.5%. This places S 816 in the same broad "high-temperature structural" category as Haynes 188 and Stellite 188 elsewhere in this library - alloys chosen for retained strength and oxidation resistance at temperature, as opposed to the much higher-carbon Stellite hardfacing grades (1, 12, 19, 100, 151) that are chosen specifically for wear resistance on non-structural, sacrificial wear surfaces.

S 816 shares the core difficulty profile of cobalt-base superalloys: very low thermal conductivity concentrates cutting heat at the tool-chip interface instead of carrying it away in the chip, which accelerates crater wear and edge deformation if speeds are not controlled. Because the alloy is designed to hold its strength at elevated temperature by design, there is no meaningful thermal softening to lean on the way there sometimes is with steel - the cutting edge stays under full mechanical load even as local temperatures climb.

Work hardening is aggressive under interrupted or light cuts, so a steady, adequate chip load matters more here than on comparable nickel alloys. The niobium and tantalum additions that give S 816 its high-temperature strength also form hard secondary carbides that add an abrasive wear component on top of the adhesive and thermal wear mechanisms common to the cobalt family, so expect shorter tool life than on a nickel superalloy of similar nominal hardness.

Because S 816 is a structural alloy rather than a hardfacing grade, its carbide volume fraction is much lower than the Stellite hardfacing alloys (1, 12, 19, 100, 151) covered elsewhere in this library - it machines more like Haynes 188 than like a hardfacing deposit. Sharp, positively-raked coated carbide, rigid low-deflection setups, and generous coolant flow remain essential.