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Incoloy 925 Physical Properties (UNS N09925)
Density, thermal, electrical and elastic data per Special Metals Technical Bulletin (Tables 4–5)
Incoloy 925 (UNS N09925) is a fully-austenitic age-hardenable nickel-iron-chromium alloy. Because the matrix is single-phase austenite, the alloy is essentially non-magnetic (relative permeability ~1.005), has a moderately low thermal conductivity (11 W/m·K at room temperature) and a thermal expansion coefficient between carbon steel and austenitic stainless steel. The physical-property data below applies to material in the annealed and aged condition; values are taken from Special Metals Corporation's INCOLOY® alloy 925 Technical Bulletin and are consistent across ASTM B805 bar/forgings and ASTM B983 plate/sheet product forms.
Need certified physical-property data? Email info@torqbolt.com with the application and required temperature range. Density, modulus and thermal-expansion values are reported on every TorqBolt MTC; resistivity / magnetic permeability available on request. Full Incoloy 925 datasheet on request.
Density
Density of Incoloy 925 (annealed + aged) at room temperature:
- 8.08 g/cm³ (0.292 lb/in³) at 68°F (20°C)
- 504 lb/ft³ (8080 kg/m³)
- Source: Special Metals Corporation, INCOLOY® alloy 925 Technical Bulletin, Table 4
Specific Heat
Specific heat capacity of Incoloy 925 increases gradually with temperature. Typical values:
| Temperature, °F (°C) | Specific Heat, J/kg·K | Specific Heat, Btu/lb·°F |
|---|---|---|
| 70 (21) | 444 | 0.106 |
| 200 (93) | 460 | 0.110 |
| 400 (204) | 485 | 0.116 |
| 600 (316) | 510 | 0.122 |
| 800 (427) | 535 | 0.128 |
| 1000 (538) | 560 | 0.134 |
Thermal Conductivity
Like most nickel-iron-chromium alloys, Incoloy 925 has a thermal conductivity roughly 1/4 that of carbon steel. This is a deliberate trade-off, the same dense austenite matrix that resists corrosion also impedes heat flow.
| Temperature, °F (°C) | Thermal Conductivity, W/m·K | Btu·in/h·ft²·°F |
|---|---|---|
| 70 (21) | 11.0 | 76 |
| 200 (93) | 12.5 | 87 |
| 400 (204) | 14.2 | 98 |
| 600 (316) | 15.8 | 110 |
| 800 (427) | 17.4 | 121 |
| 1000 (538) | 19.0 | 132 |
Coefficient of Linear Thermal Expansion
The mean linear coefficient of thermal expansion of Incoloy 925 sits between austenitic stainless steel and carbon steel, an important consideration when designing bolted joints between dissimilar metals (Incoloy 925 stud bolts in carbon steel flanges, for example).
| Temperature Range | Incoloy 925, × 10⁻⁶ /°F | Incoloy 925, × 10⁻⁶ /°C | Carbon Steel, × 10⁻⁶ /°F | 304 SS, × 10⁻⁶ /°F |
|---|---|---|---|---|
| 70–200°F (21–93°C) | 7.0 | 12.6 | 6.4 | 9.3 |
| 70–400°F (21–204°C) | 7.4 | 13.3 | 6.8 | 9.6 |
| 70–600°F (21–316°C) | 7.7 | 13.9 | 7.2 | 9.8 |
| 70–800°F (21–427°C) | 7.9 | 14.2 | 7.5 | 10.0 |
| 70–1000°F (21–538°C) | 8.1 | 14.6 | 7.7 | 10.2 |
Modulus of Elasticity (Young's Modulus)
The modulus of elasticity of Incoloy 925 at room temperature is 27.6 × 10⁶ psi (190 GPa). It decreases gradually with rising temperature. The single-phase austenitic matrix means the modulus is independent of section thickness or production route, the typical ±5% spread seen in dual-phase alloys (duplex stainless, for instance) does not apply here.
| Temperature, °F (°C) | Modulus, × 10⁶ psi | Modulus, GPa | Shear Modulus, GPa |
|---|---|---|---|
| 70 (21) | 27.6 | 190 | 73 |
| 200 (93) | 27.0 | 186 | 71 |
| 400 (204) | 26.0 | 179 | 69 |
| 600 (316) | 25.0 | 172 | 66 |
| 800 (427) | 24.0 | 165 | 63 |
Poisson's Ratio
Typical Poisson's ratio for Incoloy 925 at room temperature is 0.30. This value is used in finite-element analysis for wellhead, Christmas tree and pressure-vessel components. See the mechanical properties page for the corresponding tensile and yield strength data.
Magnetic Permeability
Incoloy 925 is essentially non-magnetic. The maximum relative magnetic permeability at room temperature is approximately 1.005–1.05 in the annealed and aged conditions. This makes the alloy suitable for applications where ferromagnetic materials cannot be used, for instance, MWD/LWD downhole tool housings near magnetometer instruments, and topside instrument valving in sensitive measurement loops.
Electrical Resistivity
Electrical resistivity of Incoloy 925 at room temperature is approximately 1.14 μΩ·m (114 μΩ·cm). It rises gradually with temperature:
| Temperature, °F (°C) | Resistivity, μΩ·m |
|---|---|
| 70 (21) | 1.14 |
| 200 (93) | 1.16 |
| 400 (204) | 1.19 |
| 600 (316) | 1.22 |
| 800 (427) | 1.25 |
Melting Range
Incoloy 925 melting range is 2475–2550°F (1357–1399°C). The relatively narrow range simplifies welding (see welding procedure) but the long ageing cycle (see heat treatment) means most fabrication is performed in the solution-annealed condition before final ageing.
Comparison vs Adjacent Alloys
| Property | Incoloy 925 | Incoloy 825 | Inconel 718 | Carbon Steel | 304 SS |
|---|---|---|---|---|---|
| Density, g/cm³ | 8.08 | 8.14 | 8.19 | 7.85 | 7.93 |
| Modulus, GPa @ 20°C | 190 | 196 | 200 | 200 | 200 |
| Thermal cond, W/m·K @ 20°C | 11.0 | 11.1 | 11.4 | 52 | 16 |
| CTE 21–93°C, × 10⁻⁶ /°C | 12.6 | 14.0 | 13.0 | 11.5 | 17.3 |
| Magnetic permeability | 1.005–1.05 | 1.005 | 1.001 | 200–500 | 1.02 |
Frequently Asked Questions
Is Incoloy 925 magnetic? No. Incoloy 925 is essentially non-magnetic with a relative permeability of ~1.005–1.05 at room temperature. The fully-austenitic matrix has no ferromagnetic phase. This is one of the key differentiators vs duplex stainless steels (which contain ~50% ferrite and are strongly magnetic).
Why does the modulus of elasticity matter for bolting design? The modulus determines stretch-per-load on a stud bolt. At 27.6 × 10⁶ psi (190 GPa), Incoloy 925 stretches ~3% more than carbon steel for the same applied load, a small but important consideration for tensioned-bolt joint design and for ultrasonic bolt-load measurement (the bolt-stretch-vs-frequency calibration is alloy-specific).
What is the operating temperature range? Incoloy 925 is qualified for service from cryogenic temperatures (down to -196°C / -320°F per API 6A PSL-3G) up to ~600°F (315°C) for sustained sour service. Above ~750°F (400°C), gamma-prime over-ageing softens the alloy, for higher-temperature service consider Inconel 718 or Incoloy 718Plus.
How does thermal expansion affect bolting? Incoloy 925 stud bolts in a carbon steel flange will load-up as the joint heats, because Incoloy 925 (CTE ~12.6 × 10⁻⁶ /°C) expands less than the surrounding austenitic stainless flange material (CTE ~17 × 10⁻⁶ /°C). This is usually a benefit (joint stays tight at temperature) but must be checked at design stage to avoid over-stressing the bolt.
Request a Quote
For Incoloy 925 with EN 10204 3.1 MTC documenting density, modulus and thermal-expansion values:
- Email: info@torqbolt.com
- WhatsApp: +91-22-66157017
- Datasheet PDF + sample MTC available on request
Specify product type (stud bolts, nuts, pipe, plate), size range, quantity, applicable standards (ASTM B805, ASTM B983, API 6A, NACE MR0175), and any application-specific physical-property requirements (low magnetic permeability for MWD tools, density tolerance for ballast applications, etc.).
References: Special Metals Corporation: INCOLOY® alloy 925 Technical Bulletin (Tables 4 and 5). ASTM B805 Standard Specification for Forgings and Forging Stock for Nuclear and General Use Wrought Precipitation Hardened UNS N09925. ASTM B983 Standard Specification for Precipitation Hardened UNS N09925 Plate, Sheet, and Strip. INCOLOY® is a registered trademark of Special Metals Corporation.
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