MAR-M 918 is a cast cobalt-base superalloy from the Martin Metals family, built around a balanced 52% cobalt / 20% nickel / 20% chromium matrix - the DIN designation CoCr20Ni20Ta captures that balance directly. What sets MAR-M 918 apart from other cast cobalt grades in this family is a comparatively high tantalum addition (4.5%) with only a very small carbon content (0.05%), meaning the alloy's strength comes primarily from tantalum-driven carbide and solid-solution strengthening rather than a dense carbon-rich carbide network. This alloy is mainly used in gas turbine hot-section components and is annealed at 1191°C (2175°F) for 4 hours; it does not respond to further heat treatment beyond that anneal.

MAR-M 918 has a density of 8.8 g/cm³ and a melting point of 1399°C (2550°F), both independently documented physical properties. Because the equal 20/20 nickel-chromium balance sits closer to a conventional heat-resistant alloy chemistry than some of its more heavily carbide-strengthened relatives, MAR-M 918 is somewhat more forgiving to fabricate and machine using techniques common to iron- and nickel-base alloys, though it still demands the conservative approach used across this entire alloy family.

MAR-M 918's balanced cobalt-nickel-chromium matrix behaves like other heat-resistant cast superalloys in this family, but with a lighter carbide load than grades built around heavy tungsten or high-carbon tantalum-carbide strengthening. That does not make it an easy material to cut - it is still a cast, cobalt-rich superalloy that retains hardness at temperatures where most tool materials would soften enough to fail quickly - but the wear mode tends to be somewhat more uniform than on the more heavily carbide-strengthened MAR-M grades, since there is less of a dispersed hard-carbide phase to abrade the edge unevenly.

Work hardening remains a primary concern: the cobalt-nickel matrix hardens under mechanical and thermal load at the cutting edge, so any dwell, light finishing pass, or interrupted engagement produces a hardened skin that resists the next pass more than the bulk material did. Because the alloy does not respond to further heat treatment beyond its initial anneal, its as-received hardness and structure will be consistent from lot to lot, which helps with predictable tool-life planning once a baseline is established.

Standard countermeasures apply: sharp, positive-rake carbide geometry, conservative and consistent cutting speeds, rigid workholding with minimal overhang, and continuous coolant delivery to manage the heat that this alloy's poor thermal conductivity concentrates at the tool-chip interface. Water-based coolants are appropriate for high-speed operations such as grinding, milling, or turning on this grade.