Note on designation: no independent alloy standard, AMS specification, or manufacturer datasheet for a "Multimet N-156" grade could be verified. Every trade reference and specification (UNS, AMS, DIN, and manufacturer literature) points to Multimet N-155 (also written N155), a trademark of Haynes International for the iron-nickel-cobalt-chromium heat-resisting alloy originally developed as "Multimet." The data on this page reflects the verified N-155 specification; the "N-156" figure appears to be a legacy transcription error carried over from the original source material.

Multimet N-155 is an iron-nickel-cobalt-chromium heat-resisting superalloy (HRSA) that gets its high-temperature properties from solid-solution strengthening and carbide/nitride dispersion rather than gamma-prime age hardening. Because it does not depend on precipitation hardening, it retains good strength and ductility after long-term exposure and is straightforward to weld and fabricate compared with age-hardenable Ni-base grades. It is rated for continuous service to about 1500°F/815°C under stress and can tolerate brief excursions to 2000°F/1095°C with good oxidation resistance.

The alloy has a long service history in jet-engine and gas-turbine hot-section hardware: tailpipes and tail cones, afterburner components, exhaust manifolds, combustion chambers, and turbine blades and buckets. Its balanced iron-nickel-cobalt matrix makes it noticeably more machinable than the higher-nickel, precipitation-hardened superalloys it is often specified alongside.

Multimet N-155 is generally easier to machine than the fully age-hardenable nickel superalloys, but it is still a heat-resisting alloy and behaves nothing like a stainless steel of similar hardness. Its iron-rich matrix gives it somewhat better thermal conductivity than high-nickel grades, which helps move heat away from the cutting edge, but the combined nickel-cobalt-chromium content still limits heat dissipation well below what carbon or alloy steels allow, so heat concentrates at the tool-chip interface more than shop experience with steel would suggest.

Because N-155 strengthens through solid solution and carbide/nitride dispersion rather than gamma-prime precipitation, it work-hardens under cutting stress in the same way most HRSA materials do: a light, hesitant, or interrupted cut burnishes a hardened skin into the surface that is tougher to remove on the next pass. Maintaining a steady, adequate chip load so the edge stays under the previously work-hardened layer is essential.

The niobium, molybdenum, and tungsten additions form carbide and nitride particles that add abrasive wear on top of the adhesive wear mechanisms common to nickel-cobalt alloys. Sharp, positively-raked coated carbide edges, moderate cutting speeds, rigid setups, and generous coolant flow are the standard countermeasures, similar to other Fe-Ni-Co HRSA grades.