Nickel superalloys. Different strengths. Aerospace vs chemistry.

Inconel 718 combines: (1) High strength at temperature (1035 MPa yield to 650°C). (2) Good fatigue life for rotating components. (3) Weldability. (4) Established supplier base. (5) Moderate cost vs other superalloys. It's the workhorse for gas turbine discs, rotating engine parts, and aerospace fasteners. Variants: Inconel 625 (solid solution, similar temperature), Inconel X-750 (older precipitation-hardened grade).

C-276 handles combinations of oxidizing and reducing environments — most alloys favor one or other. Plus: high chloride resistance (PREN 65), tolerates wet chlorine, handles sulfuric, hydrochloric, and phosphoric acids, stress corrosion cracking resistant. For process plants with mixed or uncertain chemistry, C-276 is the catch-all alloy. Premium cost but single material solves multiple problems.

Inconel 625: solid solution strengthened, not heat-treatable. Better corrosion resistance than 718. Used for: welded assemblies (no post-weld aging needed), oil and gas sour service (NACE-qualified), chemical processing. Inconel 718: precipitation hardened (aged), higher strength (1035 vs 460 MPa yield), harder to weld. Used for: structural aerospace, rotating engine parts. Generally: 625 for chemistry, 718 for mechanical.

Both are notoriously difficult. Work hardening (stainless behavior but worse), low thermal conductivity (heat concentrates at tool), sticky chips. Techniques: sharp carbide tooling (change often), slow cutting speeds (20-30 m/min), heavy feed to stay ahead of work hardening, flood coolant, rigid setup essential. Machining cost 3-5× equivalent steel. Ceramic or CBN tooling economical for production volumes. Plan extra machining time and cost in quoting.

Inconel 718: $50-80/kg. Hastelloy C-276: $60-100/kg. Compare to: stainless 316L $5-8/kg. Duplex 2507 $15-20/kg. Ti-6Al-4V $60-80/kg. Pure nickel 200: $25-35/kg. Monel 400: $30-50/kg. Specify nickel superalloys only when performance justifies — often 5-10× stainless cost. Review carefully whether duplex stainless or specialty steel would serve application.

Rene 41, Waspaloy: very high temperature aerospace (700-900°C). Haynes 230: oxidation resistance to 1150°C, gas turbine combustor. Haynes 25 (L605): cobalt-base for very high temp. MP35N: non-magnetic high strength + corrosion. Nimonic 90: older British aerospace alloy. For specific extreme applications, consult specialty superalloy supplier — many niche alloys for specific needs. Inconel and Hastelloy cover 80% of superalloy applications.