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Inconel and Incoloy Alloys

Inconel and Incoloy are the nickel-chromium-iron family: 50–75 % nickel with 15–25 % chromium (Inconel) or 30–45 % nickel in an iron base (Incoloy), most with molybdenum, niobium, aluminum or titanium added for a specific job. The chromium oxide keeps them sound in air to 1,000–1,200 °C, the nickel makes them immune to chloride stress cracking, and the age-hardening members reach alloy-steel strength that holds where steel has gone soft: Inconel 718 yields about 1,035 MPa at room temperature and keeps most of it to 650 °C. They are dense (8.2–8.5 g/cm³), slow to machine and specified by the environment.

Popular Inconel grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
Inconel 7185509658.19PoorVery goodStructural parts and fasteners to 650 °C; the default
Inconel 6254909308.44PoorExcellentWeldable corrosion and heat alloy; bellows, ducting
Inconel 6002556208.47PoorVery goodChloride and caustic service; oxidation to 1,095 °C
Inconel 6013106908.11PoorVery goodFurnace fixtures and radiant tubes to 1,200 °C
Inconel X-7508151,2008.28PoorFairAge-hardened springs and bolts to about 700 °C
Incoloy 800H2205207.94PoorVery goodCreep-rated furnace tube and pigtails, 600–900 °C
Alloy 8253106908.14PoorExcellentSulfuric and phosphoric acid; sour-gas equipment

All 81 Inconel grades

Choose Inconel for

Gas-turbine discs, casings, seals and fasteners; jet and rocket engine parts; exhaust and afterburner sheet metal; furnace fixtures, radiant tubes, muffles and heat-treating baskets; nuclear steam generators and reactor internals; chemical-plant welds in chlorides; cryogenic valves and fittings — parts that must hold shape and strength between 550 and 1,200 °C or resist chloride cracking that no stainless survives.

Look elsewhere when

The temperature stays below about 550 °C (310S, 17-4 PH or a Cr-Mo steel costs a fraction and machines three to five times faster); the environment is a reducing or mixed acid or wet chlorine (Hastelloy C276 or Hastelloy C-22); the part is a rotating turbine component above 650 °C (Waspaloy or Haynes 282, since 718 over-ages); the medium is hydrofluoric acid or seawater without heat (Monel 400); or the part is bulky and only needs oxidation resistance, where 253 MA or 310S does the job.

Yield strength against max service temp, Inconel & Incoloy (Ni-Cr-Fe) among every nickel alloy grade

No materials in view have both of these properties.

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Inconel by application

Hot structural parts
Inconel 718 for discs, shafts, housings, fasteners and brackets to 650 °C; Inconel X-750 for springs, bolts and blade retainers; Inconel 725 where high strength must also resist sour brine.
Hot sheet metal and ducting
Inconel 625 for bellows, exhaust and afterburner ducting, flare tips and heat shields to about 980 °C; Inconel 617 and Inconel 601 for combustor cans and ducting that run hotter or cycle harder.
Furnace and heat-treating hardware
Inconel 601 for fixtures, baskets, radiant tubes and burner parts to 1,200 °C; Incoloy 800H and Incoloy 800HT for tubes and hangers rated by creep at 600–900 °C; Inconel 600 where the atmosphere is caustic or carburizing rather than merely hot.
Corrosion with heat
Inconel 625 and Alloy 825 for chemical-plant welds, acid coolers and sour-gas trim; Inconel 690 for nuclear steam-generator tubing and nitric acid; Incoloy 925 for age-hardened sour-service tool components.

Working with Inconel

Machining
Among the slowest metals to cut: 718 runs at about 20–30 m/min with coated carbide (10–20 % of mild-steel speed) or several times that with whisker-reinforced ceramics, with instant work hardening and the heat going into the tool. Rigid setups, sharp positive geometry, heavy constant feed, no dwelling. Machine 718 and X-750 solution-annealed and age afterwards, leaving grinding stock on close features.
Welding
Inconel 625 and Inconel 600 weld easily by TIG, MIG and SMAW — ERNiCrMo-3 for 625 and dissimilar joints, ERNiCr-3 for 600 and Incoloy 800H — with no preheat, no post-weld treatment and interpass below 150 °C. Inconel 718 is welded annealed with ERNiFeCr-2 and then aged; X-750 is the strain-age-cracking risk and is solution-treated and aged after welding. Sulfur, lead and zinc embrittle nickel welds.
Heat treatment
718 is solution-treated at about 955–980 °C, then aged 8 h at 720 °C, furnace-cooled to 620 °C and held for a total of 18 h (AMS 5662), reaching about 1,035 MPa yield and 36–44 HRC. X-750 ages 20–24 h at 705–845 °C. The solid-solution grades are only annealed. Aging shifts dimensions by a small, repeatable amount; tight features are finish-ground afterwards.
Forming and finishing
625, 600, 601 and 800H sheet bend, spin and roll like a stiff stainless with more springback; 718 sheet is formed only annealed. Heat tint is pickled or blasted off, fatigue-critical 718 features are shot-peened, and turbine hot-section parts get aluminide or thermal-barrier coatings.

Other nickel alloy series

Inconel and Incoloy Alloys — frequently asked

What is Inconel?

Inconel and Incoloy are the nickel-chromium-iron family: 50–75 % nickel with 15–25 % chromium (Inconel) or 30–45 % nickel in an iron base (Incoloy), most with molybdenum, niobium, aluminum or titanium added for a specific job. The chromium oxide keeps them sound in air to 1,000–1,200 °C, the nickel makes them immune to chloride stress cracking, and the age-hardening members reach alloy-steel strength that holds where steel has gone soft: Inconel 718 yields about 1,035 MPa at room temperature and keeps most of it to 650 °C. They are dense (8.2–8.5 g/cm³), slow to machine and specified by the environment.

Which grade of Inconel should I use?

Inconel 718 for anything that carries load hot, to 650 °C: turbine discs and shafts, fasteners, brackets, valves, cryogenic and rocket-engine parts — 1,035 MPa yield, weldable, the most-used superalloy by far. Inconel 625 when the job is corrosion or oxidation with fabrication: a single-phase alloy at about 415 MPa yield that welds and forms like a heavy stainless, for bellows, exhaust ducting, flare tips and chemical-plant welds, and the filler for half the family. Inconel 600 for chloride and caustic service and oxidation to about 1,095 °C; Inconel 601 with 23 % chromium and aluminum for furnace fixtures and radiant tubes to 1,200 °C; Inconel 617 for combustor cans that need creep strength at 1,000 °C. Inconel X-750 is the age-hardening spring and bolt alloy to about 700 °C. On the Incoloy side, Incoloy 800H and Incoloy 800HT are the creep-rated furnace-tube grades for 600–900 °C, and Alloy 825 is the acid alloy for sulfuric and phosphoric service and sour gas.

Which grade of Inconel is the strongest?

718 has the highest yield strength in the series at 1,170 MPa; N07773 follows at 1,030 MPa. Values are for each grade's default condition.

Which grade of Inconel is easiest to machine?

CY5SnBiM (machinability good, 55/100), then CZ-100 (35/100).

Inconel 600 or 601 for furnace parts?

Inconel 601 for heat: its 23 % chromium and 1.4 % aluminum grow an oxide that stays put through thermal cycling, so fixtures, baskets and radiant tubes last to about 1,200 °C in carburizing and oxidizing atmospheres. Inconel 600 tops out around 1,095 °C in air but is the better alloy for chemistry — caustic soda, chloride stress cracking, dry chlorine, nuclear water — and is a little easier to form and weld. If the drawing is about temperature, it is 601.

What is the difference between Inconel and Incoloy?

Inconel alloys are nickel-based (more than half nickel); Incoloy alloys are iron-based with 30–45 % nickel, cheaper per kilogram and aimed at a different job. Incoloy 800H and Incoloy 800HT carry creep ratings to about 900 °C for furnace tube; Alloy 825 is the acid alloy for sulfuric, phosphoric and sour service. When chlorides, hotter service or strength above 700 MPa enter the picture, the nickel content has to rise and the alloy becomes an Inconel — 625 for corrosion plus heat, 718 for strength.