Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 800H Density and Physical Properties
Incoloy 800H (UNS N08810) has a room-temperature density of 7.94 g/cm3 (0.287 lb/in3), Young's modulus of 196 GPa (28.5 x 10^6 psi), Poisson's ratio of 0.339, thermal conductivity of 11.5 W/m/K at 21 deg C and electrical resistivity of 0.989 micro-ohm-metre at 21 deg C. The alloy is non-magnetic in the solution-annealed condition with relative permeability of approximately 1.014 at room temperature, and remains non-magnetic across the full service temperature range. The 800HT (UNS N08811) variant shares the same physical property envelope within engineering uncertainty. This page documents the full set of physical properties at room temperature and across the design service envelope, with the test methods and the engineering implications for piping design, heat-transfer calculations and instrumentation selection.
Room Temperature Physical Properties
| Property | Value (SI) | Value (US) | Test method |
|---|---|---|---|
| Density | 7.94 g/cm3 | 0.287 lb/in3 | ASTM B311 (sintered) / ASTM B962 (wrought) |
| Melting range | 1357 to 1385 deg C | 2475 to 2525 deg F | Differential thermal analysis (DTA) |
| Young's modulus (E) | 196 GPa | 28.5 x 10^6 psi | ASTM E111 (tensile) / ASTM E1875 (resonance) |
| Shear modulus (G) | 76 GPa | 11.0 x 10^6 psi | ASTM E143 |
| Poisson's ratio | 0.339 | 0.339 | Derived from E and G |
| Thermal conductivity (k) | 11.5 W/m/K | 80 BTU-in/hr-ft2-deg F | ASTM E1461 laser flash |
| Specific heat capacity (cp) | 460 J/kg/K | 0.11 BTU/lb/deg F | ASTM E1269 DSC |
| Electrical resistivity | 0.989 micro-ohm-m | 595 ohms-circular-mil/ft | ASTM B193 |
| Magnetic permeability (mu_r) | 1.014 | 1.014 | ASTM A342 (DC hysteresigraph) |
| Curie temperature | not applicable (paramagnetic) | not applicable | n/a |
| Coefficient of thermal expansion (alpha) | 14.4 um/m/K at 100 deg C | 8.0 x 10^-6 /deg F | ASTM E228 dilatometry |
Physical Properties Across the Service Envelope
| Temperature | Young's modulus E (GPa) | Thermal conductivity k (W/m/K) | Specific heat cp (J/kg/K) | Electrical resistivity (micro-ohm-m) |
|---|---|---|---|---|
| 21 deg C (70 deg F) | 196 | 11.5 | 460 | 0.989 |
| 100 deg C (212 deg F) | 193 | 12.5 | 480 | 1.020 |
| 200 deg C (392 deg F) | 188 | 14.0 | 500 | 1.063 |
| 300 deg C (572 deg F) | 183 | 15.5 | 515 | 1.102 |
| 400 deg C (752 deg F) | 177 | 17.0 | 525 | 1.139 |
| 500 deg C (932 deg F) | 170 | 18.6 | 540 | 1.175 |
| 600 deg C (1112 deg F) | 163 | 20.3 | 555 | 1.208 |
| 700 deg C (1292 deg F) | 156 | 22.0 | 575 | 1.236 |
| 800 deg C (1472 deg F) | 148 | 23.7 | 595 | 1.255 |
| 900 deg C (1652 deg F) | 139 | 25.5 | 615 | 1.265 |
| 982 deg C (1800 deg F) | 130 | 27.0 | 635 | 1.272 |
Indicative values from the Special Metals technical bulletin Table 5. Note thermal conductivity rises with temperature (opposite to carbon steel), characteristic of austenitic alloys.
Thermal Diffusivity (Transient Heat Transfer)
The thermal diffusivity alpha_T = k / (rho * cp) governs the transient temperature response on heat-up and cool-down. At room temperature alpha_T = 11.5 / (7940 * 460) = 3.15 x 10^-6 m2/s. At 815 deg C alpha_T = 24 / (7770 * 600) = 5.15 x 10^-6 m2/s. The thermal diffusivity of 800H is approximately 25 percent below carbon steel at room temperature and approximately 15 percent below 304H stainless across the service envelope. The practical implication is a slower transient temperature response, the heat-up time for a 50 mm thick 800H pressure vessel section is approximately 30 percent longer than the equivalent carbon-steel section. Critical for thermal-shock-controlled service such as ethylene cracker decoking cycles.
Elastic Modulus Decay with Temperature
| Temperature | E (GPa) | Decay vs RT (percent) | G (GPa) | Decay vs RT (percent) |
|---|---|---|---|---|
| 21 deg C (RT) | 196 | 0 (reference) | 76 | 0 (reference) |
| 540 deg C | 168 | -14 percent | 64 | -16 percent |
| 815 deg C | 147 | -25 percent | 56 | -26 percent |
| 982 deg C | 130 | -34 percent | 49 | -36 percent |
Magnetic Permeability + Eddy-Current Implications
Incoloy 800H is paramagnetic with relative permeability mu_r = 1.014 at room temperature in the solution-annealed condition. Cold work raises mu_r slightly (typically to 1.05 to 1.10 at 20 percent cold reduction) due to strain-induced martensite transformation, but the effect is reversed by the solution anneal. The non-magnetic character is important for: (1) instrumentation enclosures near sensitive magnetic equipment, (2) eddy-current NDT inspection (the paramagnetic response is uniform across the cross-section, unlike ferritic steels), (3) MRI-compatible components (when cold work is controlled). The Curie temperature is not applicable because the alloy is paramagnetic, not ferromagnetic.
Test Methods + Certification
Density is reported on the EN 10204 type 3.1 mill test certificate when called for, measured to ASTM B962 immersion method. Young's modulus is reported by ultrasonic resonance per ASTM E1875 or by tensile test per ASTM E111. Thermal conductivity is reported to ASTM E1461 laser flash on a representative sample (not heat-specific). Magnetic permeability is reported to ASTM A342 with the DC hysteresigraph on a polished representative sample. Heat-specific testing of physical properties is not standard practice for production lots; the published Special Metals values are the design reference.
Physical Property Comparison vs Adjacent Grades
| Property | Incoloy 800H | 304H | Inconel 600 | Inconel 625 |
|---|---|---|---|---|
| Density (g/cm3) | 7.94 | 8.00 | 8.47 | 8.44 |
| Young's modulus RT (GPa) | 196 | 193 | 207 | 208 |
| Thermal conductivity RT (W/m/K) | 11.5 | 16.2 | 14.8 | 9.8 |
| Specific heat RT (J/kg/K) | 460 | 500 | 444 | 410 |
| Electrical resistivity RT (micro-ohm-m) | 0.989 | 0.720 | 1.030 | 1.290 |
| Magnetic permeability RT (mu_r) | 1.014 | 1.008 | 1.010 | 1.005 |
Engineering Implications
- The 7.94 g/cm3 density translates to approximately 7.94 kg/m for a 6 mm round bar, useful for shipping weight calculations on forged bar shipments.
- The 196 GPa Young's modulus is approximately equal to 304H stainless and approximately 5 percent below Inconel 600, so deflection calculations transfer cleanly between these materials.
- The 11.5 W/m/K thermal conductivity is approximately 30 percent below 304H stainless, design heat exchanger tubes with the lower conductivity in mind for U-tube + LMTD calculations.
- The thermal conductivity RISES with temperature (opposite to carbon steel), reaching 27 W/m/K at 982 deg C, characteristic of austenitic alloys due to electronic conductivity dominating phonon conductivity.
- The 0.989 micro-ohm-m electrical resistivity is approximately 1.4x higher than 304H stainless and approximately 60x higher than copper, relevant for resistance-heating element design.
- The paramagnetic character is preserved across the service envelope, eddy-current NDT inspection is straightforward, no magnetic-permeability-driven false signals.
- See thermal expansion for the alpha curve that pairs with these physical properties.
Frequently Asked Questions
What is the density of Incoloy 800H?
7.94 g/cm3 (0.287 lb/in3) at room temperature in the solution-annealed condition. The 800HT variant has the same density within the engineering uncertainty.
Is Incoloy 800H magnetic?
No, Incoloy 800H is paramagnetic with relative permeability mu_r = 1.014 in the solution-annealed condition. Cold work raises mu_r slightly via strain-induced martensite but the effect is reversed by the solution anneal.
What is the melting point of Incoloy 800H?
1357 to 1385 deg C (2475 to 2525 deg F) melting range. The alloy is a solid solution, so it has a melting range rather than a single melting point.
Why does thermal conductivity rise with temperature?
Austenitic Ni-Fe-Cr alloys have their conductivity dominated by electronic conduction rather than phonon conduction. At higher temperature the increased electron mean free path lifts the conductivity. This is opposite to carbon steel, where the phonon scattering dominates and conductivity falls with temperature.
What is the electrical resistivity at high temperature?
1.272 micro-ohm-m at 982 deg C, approximately 30 percent above the room-temperature value. Used in heating-element + thermocouple-protection-tube design calculations.
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