Multimet N-155 is an iron-nickel-cobalt-chromium multiphase heat-resisting alloy, one of the earlier solid-solution-strengthened superalloys developed for service across an unusually broad temperature range. Its balanced iron-nickel-cobalt-chromium matrix, reinforced with molybdenum and tungsten, gives it high strength at temperatures up to about 1500°F under heavy stress, and useful strength with good oxidation resistance up to roughly 2000°F under lighter loading. Because its high-temperature properties come from solid-solution strengthening rather than an age-hardening precipitate, N-155 does not depend on a precise heat-treatment cycle to reach its working strength, which makes it comparatively easy to fabricate and weld relative to precipitation-hardened superalloys.

That combination of broad-range strength, good ductility, and straightforward fabricability made N-155 a mainstay of early jet-age aerospace hardware, and it is still specified today for tailpipes and tail cones, exhaust manifolds, combustion chambers, afterburner components, turbine blades, shafts and rotors, and high-temperature bolts. It is normally supplied and machined in the solution-annealed condition.

Multimet N-155 machines similarly to Haynes 556 in that both are solid-solution-strengthened iron-nickel-cobalt-chromium multiphase alloys with no gamma-prime phase - a real advantage over precipitation-hardened nickel superalloys, but still a meaningfully tougher cut than an austenitic stainless steel. The combined nickel, cobalt, and chromium content stiffens the iron matrix considerably, and low thermal conductivity keeps cutting heat concentrated at the tool edge rather than escaping into the chip.

Work hardening is a real factor: light or interrupted cuts leave a hardened surface skin that is harder to machine on the following pass, so maintaining a steady, adequate chip load matters more with N-155 than with plain stainless. Chips tend to be tough and stringy, and cobalt content contributes to abrasive wear at the cutting edge. Rigid setups, sharp positive-rake coated carbide, moderate cutting speeds, and consistent feed rates that keep the tool cutting rather than rubbing are the standard approach for this alloy.