Alloy 800HT Overview
Alloy 800HT (UNS N08811 / W.Nr. 1.4959) is a controlled-composition nickel-iron-chromium alloy developed for elevated-temperature service. Its chemistry and heat treatment are controlled to support high-temperature strength, structural stability and resistance to oxidation, carburization and selected furnace atmospheres.
800HT is not selected only by maximum temperature. Design stress, exposure time, atmosphere, thermal cycling, fabrication, product form and the governing pressure or equipment code must be reviewed together. For long-term high-temperature service, the ordered condition and applicable allowable stresses are essential purchasing information.
Alloy 800HT Product Specification
| Item |
Supply Reference |
| Grade |
Alloy 800HT |
| UNS designation |
N08811 |
| W.Nr. |
1.4959 |
| Alloy family |
Nickel-iron-chromium high-temperature alloy |
| Available product forms |
Plate, sheet, strip, rod, bar, forgings, pipe, tube, fittings and specified wire products |
| Critical order information |
Product standard, dimensions, heat treatment, design code, testing and certification |
Supply Forms and Applicable Standards
| Product Form |
Common ASTM / ASME Reference |
| Rod and bar |
ASTM B408 / ASME SB-408 |
| Forgings and forging stock |
ASTM B564 / ASME SB-564 |
| Plate, sheet and strip |
ASTM B409 / B906 and ASME SB-409 / SB-906 |
| Seamless pipe and tube |
ASTM B407 / B829 and ASME SB-407 / SB-829; heat-exchanger tube may reference ASTM B163 |
| Welded pipe and tube |
ASTM B514 / B775 for welded pipe; ASTM B515 / B751 for welded tube |
| Fittings |
ASTM B366 / ASME SB-366 |
| Wire |
Required wire specification, dimensions and acceptance criteria must be confirmed separately; ASTM B408 is not a wire standard |
Alloy 800HT Technical Data
Chemical composition reference — the original page values are retained below. Final acceptance follows the ordered product specification and material certificate.
| Grade |
Range |
Ni |
Cr |
Fe |
C |
Mn |
Si |
Cu |
S |
Al |
Ti |
| 800HT |
Min |
30 |
19 |
Balance |
0.05 |
— |
— |
— |
— |
0.15 |
0.15 |
| Max |
35 |
23 |
0.10 |
1.5 |
1.0 |
0.75 |
0.015 |
0.60 |
0.60 |
Mechanical properties reference at 20°C — actual values vary with product form, dimensions and condition.
| Tensile Strength |
0.2% Yield Strength |
Elongation |
| 500 MPa |
210 MPa |
35% |
| Service Factor |
Engineering Note |
| Oxidation and carburization |
Useful resistance in many high-temperature furnace and process atmospheres; actual gas chemistry must be reviewed |
| Creep and rupture strength |
Long-term strength depends on temperature, stress, grain structure, heat treatment and the applicable design code |
| Stress-corrosion cracking |
High nickel content can improve resistance in selected environments, but process chemistry and temperature control material selection |
| Fabrication |
Forming, welding and post-fabrication treatment must follow qualified procedures for the ordered product and service |
Discuss 800HT Dimensions and Service Conditions
Alloy 800HT Applications
| Industry |
Typical Equipment |
| Industrial heating |
Radiant tubes, furnace fixtures, muffles, retorts, baskets and heat-treatment equipment |
| Petrochemical processing |
High-temperature piping components, headers, pigtails and process fittings |
| Power and thermal systems |
Selected superheater, reheater and heat-recovery components subject to code approval |
| Chemical processing |
Components exposed to elevated-temperature oxidizing or carburizing environments |
| Synthetic gas plants |
High-temperature equipment used in ammonia, methanol and related gas-production systems |
Quality Inspection and Documentation
| Inspection Item |
Available Review |
| Material identity |
Chemical composition, grade, heat / batch number and traceability |
| Dimensions and surface |
Thickness or diameter, tolerances, flatness / straightness, edges and visual condition |
| Mechanical testing |
Room-temperature or elevated-temperature tests according to the ordered standard when required |
| Heat treatment |
Supply condition and heat-treatment record should match the grade and product specification |
| Additional inspection |
PMI, ultrasonic, hydrostatic, eddy-current or other NDT as applicable to product form and order |
| Documents |
EN 10204 3.1 or specified certificate, inspection reports, marking and project documentation |
Packaging and Export Delivery
| Plate and sheet |
Surface protection, moisture barrier and reinforced wooden cases or pallets |
| Bar and forgings |
Bundles or cases with end protection and heat / batch identification |
| Pipe and tube |
End caps, bundled protection, waterproof wrapping and wooden cases where required |
| Strip and wire |
Coils or spools with interleaving, moisture protection and rigid outer packing |
RFQ Confirmation Checklist
| Please Provide |
Required Detail |
| Grade and standard |
UNS N08811, product specification, code and required edition |
| Product form and dimensions |
Thickness or diameter, width, length, tolerances and quantity |
| Service conditions |
Design temperature, stress, atmosphere, pressure and expected service life |
| Processing |
Cutting, machining allowance, forming, welding, surface and heat treatment |
| Quality and delivery |
Certificate, tests, NDT, marking, packing and destination |
Request an Alloy 800HT Quotation
Send the product standard, form, dimensions, service conditions, quantity and required documentation.
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