Guides / Materials

Incoloy 800H and 800HT: Grades, Specs and Machinability for Buyers

October 16, 2026

Incoloy 800H and 800HT show up on furnace, reformer and heat exchanger drawings, and they sit in the cost range between stainless steel and the Inconel grades. They are easier to machine than 718 or 625, but they come with a set of grade rules that trips up buyers. Pick the wrong version and the part can fail a code review or fail early in service.

The alloy family

Incoloy is a Special Metals trademark. The 800 family is an iron-nickel-chromium alloy with roughly 30 to 35 percent nickel, 19 to 23 percent chromium and the balance mostly iron. It resists oxidation, carburization and many corrosive environments at high temperature, and it is austenitic, meaning its structure stays stable up to the melting point. A small addition of titanium and aluminum gives modest hardening and stability.

Three versions matter to buyers: 800, 800H and 800HT. Their chemistry is nearly the same, but their carbon limits, minimum titanium plus aluminum and required heat treatment differ. Those differences control creep strength, the slow stretching of metal under load at high temperature. Our buyer’s guide to Inconel machining covers the more common nickel-based grades for comparison.

Grades compared

Grade	UNS	Carbon	Al + Ti	Typical anneal	Main use
800	N08800	0.10 max	0.30 to 1.20	About 980 °C or higher	Moderate temperature, general corrosion
800H	N08810	0.05 to 0.10	0.30 to 1.20	About 1,120 °C or higher	High-temperature creep service
800HT	N08811	0.06 to 0.10	0.85 to 1.20	About 1,150 °C or higher	Highest creep strength

Check the product specification for exact limits, because they vary slightly by form. The point for a buyer is that the three grades are not interchangeable on a drawing. A designer who chooses 800H for creep service wants its coarse grain and its controlled carbon. A material certificate for plain 800 does not satisfy that requirement even though the alloy looks the same.

Where it is used

Typical uses are in hydrocarbon and chemical processing and in power generation. Examples include outlet headers and pigtails on steam methane reformers, process heater and furnace components, heat exchanger tubes and tubesheets, superheater tubing and hardware inside high-temperature process vessels. Machined parts include flanges, nozzles, rings, fittings, supports and fixtures. Many parts are fabricated by welding before or after machining.

Design codes control temperature limits. 800H and 800HT carry higher allowable stresses than 800 at temperatures where creep governs, which is why the grade call-out matters to the engineer. Check the governing code or customer specification, and quote only the grades it allows.

Material specifications

Product forms are covered by ASTM specifications. B408 covers rod and bar. B409 covers plate, sheet and strip. B564 covers forgings. Seamless pipe and tube fall under B407, condenser and heat exchanger tube under B163 and welded pipe and tube under B514 and B515. Quote the specification and the grade, and ask for certificates showing the heat number, chemistry, mechanical properties, grain size and heat treatment.

Some mills dual-certify a heat to more than one grade when it meets both. That is legitimate, but you should confirm that the certificate covers the grade your drawing calls for. Our note on mill certificates and PMI for Inconel explains what each document proves. Positive material identification confirms the alloy family but cannot always separate 800 from 800H, since the difference is mostly carbon, so the certificate carries the proof.

How it machines

Incoloy 800H is an austenitic alloy that work-hardens, so it needs sharp tools and a steady cut, but it is much less demanding than aged Inconel 718. It machines more like a tough austenitic stainless steel such as 316 than like a precipitation-hardened superalloy. It is gummy, forms long chips and builds up an edge on the tool at low speeds.

Typical practice uses coated carbide at speeds somewhat lower than for 316, high-pressure coolant where available and positive-rake geometry. Heavy enough feeds keep the tool under the hardened layer. Our note on why Inconel work hardens covers the mechanism, and 800H shows it at a milder level.

Operation	Tool	Typical speed	Notes
Turning, rough	Coated carbide	40 to 80 m/min	Positive rake, chip breaker
Turning, finish	Fine-grain carbide	50 to 90 m/min	Sharp edge, steady feed
Milling	Carbide end mill	30 to 60 m/min	Climb milling, rigid setup
Drilling	Solid carbide	20 to 40 m/min	Through-tool coolant
Thread milling	Carbide thread mill	30 to 60 m/min	Preferred for large threads

These are typical planning ranges. Real values come from the shop’s tooling and experience.

Grain size and condition

800H and 800HT are supplied solution annealed to a coarse grain, which gives creep strength. The coarse grain is not a machining problem, but it matters for finishing. Coarse-grained material can show a slightly rougher surface after cutting, and thin parts can show variation in properties between grains. Heavy cold work from machining followed by high-temperature service can lead to local grain changes, so some specifications call for a stress relief or restrict the amount of cold work. If your part has such a requirement, it will be in the specification, so quote it.

Welding and fabrication

800H and 800HT weld well with matching or compatible nickel-base filler metals, and welded fabrication is common. Weld procedures should follow the governing code and be qualified for the grade. Post-weld heat treatment is sometimes required for creep service. Our guide on welding Inconel for buyers outlines the general points that apply to the 800 family as well.

Thermal expansion and size

Alloys in this family expand more than carbon steel when heated, roughly 15 to 17 micrometers per meter per degree Celsius against about 12 for steel. For a flange or ring that mates with a carbon steel part, the difference matters at operating temperature, and designers allow for it in the clearances. For the shop, the effect shows up in measurement. A large ring measured warm from the machine reads larger than the same ring at 20 degrees Celsius, so shops stabilize parts and measure in a controlled room. If your tolerance is tight on a large diameter, say what temperature the dimension applies at, which is normally 20 degrees Celsius.

Typical parts

Part	Typical form	What matters to the shop
Reformer outlet header or pigtail	Pipe or forging	Wall thickness, weld preparation, grade traceability
Furnace support or hanger	Plate or bar	Hole position, many identical parts
Heat exchanger tubesheet	Plate or forging	Drilled hole pattern, flatness, ligament control
Flange or nozzle	Forging or plate	Bore size, sealing face finish
Process vessel internals	Plate, bar	Welds, fit-up, cleanliness

Many of these parts are large and heavy, and some shops lack the machine size to handle them. Ask about maximum swing and table size, and about crane capacity, before you send a quote request for a large item.

Inspection and documentation

Typical inspection covers dimensions, surface finish, weld inspection and a review of material documents. Parts for pressure service can call for penetrant testing of welds and machined edges and for hydrostatic or pneumatic pressure tests of the finished assembly. Heat treatment records and grain size reports come from the mill or an outside lab. Our page on first article inspection for Inconel parts shows how a release package is normally assembled, and the same approach works for 800H parts.

Cost and lead time

Incoloy 800H costs less per kilogram than Inconel 625 or 718, because it contains less nickel. Bar, plate and tube in common sizes are stocked by distributors, and lead times for standard items are shorter than for superalloys. Machining cost is moderate: tool wear is lower than on Inconel, but work hardening and long chips still call for good practice. Large rings and forgings, however, can take weeks or months from the mill.

Why the grade call-out saves money

Buyers sometimes ask whether plain 800 would do instead of 800H to save cost or time. The price difference between grades is usually small, and the risk is large. A part made from the wrong grade can be rejected at inspection, which costs the whole machining spend, or it can pass inspection and fail early in service, which costs far more. Quote the grade the drawing names, ask the designer in writing before accepting any substitute, and keep the certificate that proves the grade with the part records. The same discipline applies to stock that sits in a warehouse for months, since bars with similar looks and different grades share the same racks.

What to include on the RFQ

• Grade name and UNS number, such as 800H (N08810) or 800HT (N08811).
• Product specification and form, with heat treatment condition.
• Grain size requirement, if the specification sets one.
• Design code or customer specification.
• Welding requirements and filler metal, if fabricated.
• Certificates, PMI and inspection needs.

Closing checklist

Check that the drawing names one grade, with a specification and condition, that the certificate you require lists that grade, and that welding and heat treatment are stated. When you are ready, send an RFQ and we match you with up to three shops that already machine nickel alloys. Ask each whether it has run 800H or 800HT and how it checks the grade on the incoming certificate. For the other grades used above 600°C, read our guide to high temperature nickel alloys.

Frequently asked questions

Keep reading

• Waspaloy and Rene 41 Machining: The Harder Superalloys Compared With Inconel
• Inconel X-750 vs 718: Which Alloy for Springs and High-Temperature Fasteners