S-590 is a multiphase iron-cobalt-chromium-nickel heat-resisting alloy that gets its high-temperature strength from a dense dispersion of carbide-forming elements - molybdenum, tungsten, and niobium (columbium) - rather than from gamma-prime age hardening. This carbide-strengthened, multiphase structure is the defining feature of the S-500-series alloy family, and it is what allows S-590 to hold useful strength and corrosion resistance in the 1100-1400°F (595-760°C) range typical of turbine exhaust and combustion hardware.

Because iron, cobalt, and nickel are present in roughly equal proportions alongside chromium near 20%, S-590 sits between the fully iron-base heat-resisting steels and the nickel- or cobalt-base superalloys in both cost and capability. It has a long service history in gas-turbine and jet-engine components operating at moderate-to-high temperature, including turbine buckets, bolts, and exhaust-system hardware, where its combination of strength, oxidation resistance, and relative machinability (for a heat-resisting alloy) made it a practical choice before high age-hardenable nickel superalloys became the default.

S-590 presents a different machining profile than the age-hardenable nickel superalloys, but it is not an easy material to cut. Its strength comes from a dense population of molybdenum, tungsten, and niobium carbides distributed through the iron-cobalt-nickel-chromium matrix. That carbide population is abrasive to cutting edges in much the same way that carbide-rich tool steels or high-alloy cast irons are abrasive - tool wear tends to be dominated by flank abrasion from hard second-phase particles rather than purely by adhesive/diffusion wear.

The alloy still work-hardens under cutting stress like other Fe-Co-Ni-Cr HRSA grades, so a light, hesitant cut leaves a hardened skin that is harder to remove on the next pass than the parent material would have been. Combined with only moderate thermal conductivity, this means heat and mechanical load both build up at the cutting edge if feed rates are too low or engagement is inconsistent.

Because the carbide phases in S-590 are not gamma-prime and do not dissolve or soften with modest temperature changes, edge wear tends to progress steadily rather than catastrophically, which makes it more forgiving of moderate speed increases than fully age-hardened nickel alloys - but abrasion-resistant carbide grades, sharp edges, and consistent chip loads remain essential.