Hangbo Alloy Group
Shanghai · Est. 2012
Incoloy 800, 800H and 800HT share almost the same nominal chemistry yet diverge sharply in carbon, aluminum, titanium and creep-rupture ceiling. This guide shows where they differ and how to specify the right grade, heat treatment and grain size by UNS number so a high-temperature pressure part is never quietly downgraded.
Incoloy 800, 800H and 800HT are three of the most confused grades in the nickel-iron-chromium family. They share almost the same nominal chemistry, the same look, and in many product forms the same ASTM product specification — yet they have very different carbon, aluminum and titanium limits and, most importantly, very different creep-rupture ceilings. Specify the wrong one and a pressure part that should last twenty years in a reformer or pyrolysis furnace may be operating well outside its design basis from day one.
This guide is written for engineers and buyers who must choose between the three grades for high-temperature service: ethylene pyrolysis coils, hydrogen reformer outlet piping, superheater tubes, and furnace hardware. It explains exactly where 800, 800H and 800HT diverge, why those small chemistry differences change the allowable temperature by hundreds of degrees, and how to write a purchase order that locks in the grade, the heat treatment and the grain size you actually need. Every number here ties to the published UNS and ASTM or ASME definitions.
We write this as a manufacturer, not a trader. Hangbo Alloy Group in Shanghai produces Incoloy 800, 800H and 800HT in bar, seamless tube, plate and forging form and supplies the mill test certificate that names the grade, the UNS number, the heat treatment and the grain size. Trademarks such as Incoloy belong to their respective owners; the controlling definitions are the UNS numbers N08800, N08810 and N08811 and the applicable ASTM and ASME specifications.
Where you need the full failure-mode picture, our pillar guide on nickel alloy procurement pitfalls covers certification and melting-route verification, and our creep and stress-rupture guide explains the metallurgy behind the temperature ceilings discussed below.
Incoloy 800, 800H and 800HT are all iron-nickel-chromium alloys built around roughly 32–35 percent nickel, 19–23 percent chromium and the balance iron, with small aluminum and titanium additions for stability. The 800 grade is the general-purpose version; 800H and 800HT are deliberate high-temperature creeps-strength evolutions of the same base. The single most important fact for a specifier is that they are not interchangeable at temperature, even though a mill can make all three look identical on the shop floor.
The family split happened because the original 800 chemistry, with carbon capped only at 0.10 percent and aluminum and titanium each only minimum-controlled, does not deliver predictable long-term creep rupture above moderate temperature. 800H tightened the carbon band and required a coarse grain size to raise the creep limit; 800HT then controlled both aluminum and titanium at higher minimums to push the ceiling further. Reading the grade name alone is never enough — you must read the UNS number and the ordered condition.
The nominal nickel, chromium and iron are essentially the same across the three grades. The real differences are carbon, aluminum, titanium, and the combined aluminum-plus-titanium contents, which is why a composition table for these grades must show those elements in detail.
| Element (% unless noted) | Incoloy 800 (UNS N08800) | Incoloy 800H (UNS N08810) | Incoloy 800HT (UNS N08811) |
|---|---|---|---|
| Nickel | 30.0 – 35.0 | 30.0 – 35.0 | 30.0 – 35.0 |
| Chromium | 19.0 – 23.0 | 19.0 – 23.0 | 19.0 – 23.0 |
| Iron | Balance | Balance | Balance |
| Carbon | 0.10 max | 0.05 – 0.10 | 0.06 – 0.10 |
| Aluminum | 0.15 – 0.60 | 0.15 – 0.60 | 0.25 – 0.60 |
| Titanium | 0.15 – 0.60 | 0.15 – 0.60 | 0.25 – 0.60 |
| Al + Ti (combined) | — | — | 0.85 – 1.20 |
| Manganese, Silicon, Sulfur, Cu | Controlled to the same ASTM limits across the family | ||
Two details decide the grade. First, 800H and 800HT require a minimum carbon of 0.05 and 0.06 respectively, while 800 only caps carbon at 0.10 max — so the higher grades guarantee enough carbon to stabilise the grain and support creep strength. Second, 800HT is the only one of the three with a specified combined aluminum-plus-titanium range of 0.85 to 1.20 percent, and it raises the minimums on both elements individually. That combined control is what delivers its higher creep-rupture strength.
The mechanism is grain-boundary creep. At high temperature and sustained load, a fine-grained material deforms and ruptures along its many grain boundaries far sooner than a coarse-grained one. 800H and 800HT are therefore not just chemistry grades; they are heat-treatment grades, solution-annealed at a high enough temperature to produce a coarse grain (commonly ASTM grain size No. 5 or coarser, as required by the product specification) that resists creep.
Carbon and the aluminum-titanium pair matter because they pin the grain boundaries and stabilise the structure during that high-temperature anneal. Too little carbon, or loosely controlled aluminum and titanium, and the mill cannot reliably grow and hold the coarse grain that the creep allowable depends on. This is why a seller cannot simply “heat-treat 800 into 800H” — the starting chemistry must already meet the N08810 or N08811 limits. The grade is set at the melt, and confirmed at the anneal.
The practical outcome is a clear ladder of allowable service temperature for pressure and structural use, as reflected in the ASME Boiler and Pressure Vessel Code design stress allowables and the ASTM product requirements. The figures below are the commonly cited design ceilings; always confirm against the current code edition and your project’s addenda.
| Attribute | Incoloy 800 (N08800) | Incoloy 800H (N08810) | Incoloy 800HT (N08811) |
|---|---|---|---|
| Design intent | General corrosion + moderate temperature | High-temperature creep service | Maximum creep-rupture service |
| Commonly cited ASME design ceiling | About 593°C (1100°F) per the applicable code | About 649°C (1200°F) per the applicable code | About 760°C (1400°F) per the applicable code |
| Required grain size | Not grain-size controlled for creep | Coarse grain (typically ASTM No. 5 or coarser) | Coarse grain (typically ASTM No. 5 or coarser) |
| Heat treatment | Annealed | High-temperature solution anneal | High-temperature solution anneal |
| Creep rupture strength | Lowest of the three | Higher than 800 | Highest of the three |
For buyers the takeaway is blunt: if your equipment sees sustained load above about 600°C, 800 is the wrong choice and you should be specifying 800H or 800HT by UNS number. Between those two, 800HT is the grade when the design pushes toward the upper end of the high-temperature window and you need the extra creep margin the controlled aluminum-titanium chemistry provides.
Matching the grade to the service environment is the whole point. The table maps the three to the applications where they are normally specified.
| Grade | Typical applications | Why it fits |
|---|---|---|
| 800 (N08800) | Heat-exchanger tubing, furnace retorts, carburising equipment, electrical heating-element sheathing | Good oxidation and carburisation resistance at moderate temperature without a creep requirement |
| 800H (N08810) | Reformer and pyrolysis furnace components, superheater tubing, header pipe, high-temperature vessel parts | Coarse-grain creep strength for sustained high-temperature load |
| 800HT (N08811) | Ethylene pyrolysis coils, hydrogen reformer outlet manifolds, the most demanding creep service | Highest creep-rupture strength from controlled Al + Ti |
Our detailed profiles of Incoloy 800, Incoloy 800H and Incoloy 800HT carry the full property and application detail for each, and our furnace fixture selection guide covers related high-temperature choices.
The failure mode here is substitution-by-omission: an inquiry that says only “Incoloy 800” gets filled with the cheapest grade, which may be exactly wrong for a high-temperature pressure part. Write the order so the grade cannot drift.
| What to state | Why it matters | Example wording |
|---|---|---|
| UNS number, not just the name | “800” is ambiguous across the family | “Incoloy 800HT, UNS N08811” |
| ASTM product specification and edition | Confirms chemistry and condition requirements | “ASTM B407 / B408 / B409 (current edition)” |
| Required condition / heat treatment | 800H and 800HT need the coarse-grain anneal | “Solution annealed, coarse grain per spec” |
| Grain size requirement | Creep allowable depends on it | “ASTM grain size No. 5 or coarser” |
| Measured chemistry including C, Al, Ti | Confirms the grade is actually N08810/11 | “Reported composition for all controlled elements” |
| No equivalent without written approval | Stops downgrade to plain 800 | “No substitute grade without written consent” |
At our mill the route that guarantees the grade is stated on the certificate: virgin prime raw material charged into vacuum induction melting with electroslag or vacuum arc remelting, complete descaling before forming, controlled forging and rolling, the coarse-grain solution anneal the grade demands, then finishing and composition, mechanical, ultrasonic or penetrant, dimensional, marking and packing checks on every heat. The UNS number, heat treatment and grain size are reported, not assumed.
Use this table as the backbone of your purchase order. Always confirm the latest revision and any project-specific addenda.
| Product form | Typical ASTM / ASME specification | Note for 800H and 800HT |
|---|---|---|
| Seamless tube and pipe | ASTM B407 / ASME SB-407 | Covers the 800 family; grade by UNS |
| Bar and rod | ASTM B408 / ASME SB-408 | Common for forgings and machined parts |
| Plate, sheet and strip | ASTM B409 / ASME SB-409 | Grain-size and heat-treatment sensitive |
| Design allowables | ASME Boiler & Pressure Vessel Code, Section II Part D | Lists the temperature ceilings by UNS |
| Creep evaluation | See our creep and stress-rupture guide | Background on the grain-size mechanism |
This article is guidance for engineers and buyers, not a substitute for the applicable ASTM, ASME or project specification. Always verify the current edition and any code case or addendum that governs your equipment.
Both are high-temperature creep grades with controlled carbon, but 800HT (UNS N08811) additionally controls aluminum and titanium each at a higher minimum and specifies a combined Al + Ti range of 0.85 to 1.20 percent. That tighter control raises the creep-rupture strength, so 800HT is used where the design pushes toward the top of the high-temperature window.
No. The grade is set at the melt. 800H and 800HT require minimum carbon of 0.05 and 0.06 percent respectively, and 800HT requires the controlled aluminum-titanium chemistry, none of which plain 800 (capped at 0.10 carbon max, with only minimum aluminum and titanium) guarantees. The high-temperature anneal only develops the coarse grain if the starting chemistry already meets the N08810 or N08811 limits.
The commonly cited ASME design ceiling for 800H is about 649°C (1200°F), and for 800HT about 760°C (1400°F), with plain 800 typically limited to about 593°C (1100°F). Confirm the exact allowable against the current ASME Section II Part D values and your project addenda, because the numbers govern fitness for service.
At high temperature and sustained load, creep and rupture occur along grain boundaries. A coarse grain (commonly ASTM No. 5 or coarser, as the product specification requires) has fewer boundaries per unit volume and resists creep far better than a fine grain. The high-temperature solution anneal exists to produce and lock in that coarse grain.
Specify the UNS number N08811 on the order, name the ASTM B407/B408/B409 product specification and its edition, require the coarse-grain solution anneal and grain-size requirement, and require the reported composition for carbon, aluminum and titanium. Then confirm those values on the EN 10204 3.1 certificate before acceptance.
For the demanding, sustained high-temperature load of a pyrolysis coil, 800HT (UNS N08811) is normally the preferred choice because its controlled aluminum-titanium chemistry gives the highest creep-rupture strength. 800H is appropriate where the design temperature and stress are lower. The final choice should follow the equipment designer’s stress calculation and the applicable code.
The creep behaviour is governed mainly by chemistry and the coarse-grain heat treatment rather than by a mandated double-melt, but consistent chemistry and cleanliness still matter. Specify the melting route if your project requires it, and require it to be stated on the certificate so the material is traceable back to the heat.
If you are unsure whether your equipment needs 800, 800H or 800HT, or you want to confirm a quotation you received specifies the correct UNS number, heat treatment and grain size, send us the grade, product form, dimensions, quantity, service temperature and design stress. We will confirm the right grade for your condition, quote our own virgin-material, double-melted production with the correct coarse-grain anneal, and supply a certificate that names the UNS, heat treatment and grain size. Typical response time is ten minutes, and we ship worldwide from Shanghai.
Email: serena@hangboalloy.com
Phone: +86 166 2109 2936
WhatsApp: +86 166 2109 2936
Send us the grade, product form, dimensions, quantity, service temperature and design stress. We will confirm the correct UNS number and heat treatment for your condition, quote our own virgin-material, double-melted production with the right coarse-grain anneal, and supply a certificate naming the UNS, heat treatment and grain size.