"Inconel" and "Incoloy" are both registered trademarks of Special Metals Corporation. They are NOT the same alloy family. The single rule that distinguishes them is iron content: Incoloy alloys contain significant iron (typically 22% minimum) with nickel as the primary alloying element on an iron base; Inconel alloys are nickel-base with low or no iron (typically <20%, often near zero). This 50-year-old naming convention is the source of the most common search query in the nickel-alloy world, "Inconel 925", which is a misnomer. The grade is properly designated Incoloy® alloy 925 (UNS N09925) because it contains 22% minimum iron. This page covers the chemistry rule, the application envelopes, and which alloy wins for which service.
Need help selecting between Incoloy and Inconel? Email info@torqbolt.com with the application (medium, temperature, pressure, sour content), and we will recommend the most cost-effective qualified alloy with full MTC. WhatsApp +91-22-66157017.
The Naming Rule
- Incoloy: Iron-base or nickel-iron-base superalloys with significant iron content (22% minimum, often more). Name origin: Inco + alloy, "Inco" being International Nickel Company, the trademark's originator.
- Inconel: Nickel-base superalloys with nickel typically >50%, alloyed with chromium and (depending on grade) molybdenum, niobium, titanium, aluminium. Iron content is residual (often <5%, never the primary element).
Both trademarks are owned and managed by Special Metals Corporation (Huntington, WV, USA). The naming is historical and does not reflect a hierarchy of "performance", the right alloy depends on the service, not on the brand prefix.
Common Grades — Side-by-Side
| Trademark / Grade | UNS | Ni % | Fe % | Mo % | Strengthening | Primary Service |
|---|---|---|---|---|---|---|
| Incoloy 800 / 800H / 800HT | N08800 / N08810 / N08811 | 30–35 | 39 min (bal) | Solid solution | High-temp furnace, ethylene cracking | |
| Incoloy 825 | N08825 | 38–46 | 22 min (bal) | 2.5–3.5 | Solid solution | Sour-service piping, mild oilfield |
| Incoloy 925 (this site) | N09925 | 42–46 | 22 min (bal) | 2.5–3.5 | Gamma-prime (Ti/Al) | API 6A wellhead bolting, sour service |
| Incoloy 926 | N08926 | 24–26 | bal | 6–7 | Solid solution (super-austenitic) | Severe seawater service |
| Inconel 600 | N06600 | 72 min | 14 max | Solid solution | Heat-resistant tubing, mild corrosion | |
| Inconel 625 | N06625 | 58 min | 5 max | 8–10 | Solid solution (Mo + Nb) | Marine, chemical, severe sour overlay |
| Inconel 718 | N07718 | 50–55 | 17 (bal) | 2.8–3.3 | Gamma double-prime (Nb) | Aerospace, deep sour wells |
| Inconel 725 | N07725 | 55–59 | bal | 7–9.5 | Gamma-prime + Nb | Sour-service tubing, high-strength CRA |
Why "Inconel 925" Is the Most Common Misnomer
Search-query data shows "Inconel 925" gets ~3× the monthly volume of "Incoloy 925" globally, despite the fact that Special Metals has never produced an alloy by that name. Buyers default to "Inconel" because the brand has stronger recognition; mill-test certificates and industry standards always carry the correct INCOLOY® alloy 925 designation. The chemistry rule confirms it: 22% minimum iron disqualifies the grade from the Inconel family.
If you are sourcing material against a customer specification that says "Inconel 925," ALWAYS clarify in writing, the customer almost certainly means INCOLOY 925 (UNS N09925), but mis-spelling on a purchase order can lead to delivery of a different alloy (e.g., Inconel 725, which is a different chemistry, different mechanical envelope, and different price point). The UNS N09925 chemistry page shows what 925 actually is.
Strengthening Mechanism Compared
| Mechanism | Incoloy 925 | Inconel 718 | Inconel 625 |
|---|---|---|---|
| Precipitation phase | Ni₃(Al, Ti), gamma-prime | Ni₃Nb, gamma double-prime | None (solid-solution Mo + Nb) |
| Lattice structure | Coherent FCC, ordered L1₂ | Coherent BCT, ordered DO₂₂ | Disordered FCC matrix |
| Age temperature | 1365°F (740°C) × 8h | 1325°F (718°C) × 8h | None |
| YS after age, ksi | 110 min (760 MPa) | 150 min (1034 MPa) | 60 (414 MPa) typical |
| UTS after age, ksi | 165 min (1140 MPa) | 180 min (1241 MPa) | 120 (827 MPa) typical |
| Sour-service hardness cap | 35 HRC (NACE MR0175 Table A.10) | 40 HRC (Table A.13) | (no age, no cap) |
The takeaway: Inconel 718 is the strongest, but its gamma double-prime is meta-stable and over-ages above ~1200°F. Incoloy 925 sacrifices ~10% strength for a more thermally-stable gamma-prime that holds up to 1100°F. Inconel 625 cannot match either, it is a solid-solution alloy chosen for corrosion, not strength. See the Incoloy 925 vs Inconel 718 page for full selection logic in oilfield service.
Sour-Service Envelope Comparison
| Alloy | NACE / ISO Table | H₂S Partial Pressure max | Temperature max | Cl⁻ max |
|---|---|---|---|---|
| Incoloy 925 | Table A.10 | 1000 psi (6.9 MPa) | 400°F (204°C) | Saturation |
| Incoloy 825 | Table A.7 | 15 psi (0.1 MPa) | 400°F (204°C) | Saturation |
| Inconel 625 | Table A.12 | Any | 450°F (232°C) | Saturation |
| Inconel 718 | Table A.13 | 15 psi (0.1 MPa) | 350°F (177°C) | Saturation |
| Inconel 725 | Table A.14 | Any | 450°F (232°C) | Saturation |
For high-H₂S sour service that also requires high strength, the contenders are Incoloy 925, Inconel 725, and Inconel 718 (the last only up to 15 psi H₂S). For severe-sour low-strength service, Inconel 625 wins on corrosion. For mild sour at lower cost, Incoloy 825 is the volume choice. See the ISO 15156 and NACE MR0175 pages for the full qualification envelopes.
Selection Guide by Application
- API 6A wellhead bolting (sour, high-strength): Incoloy 925 is the volume default. Inconel 718 or 725 for ultra-deep / ultra-high-pressure wells where every ksi of yield matters.
- Sour-service production tubing & flowlines (lower strength): Incoloy 825 for <15 psi H₂S; Incoloy 925 or Inconel 725 for higher H₂S.
- Severe seawater / chloride service: Incoloy 926 (super-austenitic) or Inconel 625 (CRA overlay).
- High-temperature furnace components: Incoloy 800H / 800HT (1100–2100°F).
- Aerospace turbine disks & rings: Inconel 718, the workhorse alloy.
- Acid service (HCl, H₂SO₄): Inconel 625 or specialised Hastelloy C-276 (a Haynes alloy, not Special Metals).
- Cryogenic / LNG service: Monel K-500, Incoloy 925 (PSL-3G qualified to -101°C), or 304/316L stainless if no sour content.
- MWD/LWD downhole tool housings (low magnetic permeability): Incoloy 925 (μr ~1.005) or Inconel 718 (μr ~1.001).
Frequently Asked Questions
Is Incoloy "weaker" than Inconel? No, this is a common myth driven by the cleaner brand of "Inconel." Both families span a wide strength range. Incoloy 925 (110 ksi YS) is stronger than Inconel 600 (35 ksi YS); Inconel 718 (150 ksi YS) is stronger than both. The alloy's strength depends on chemistry and heat treatment, not on which trademark prefix it carries.
Can Incoloy and Inconel be welded together? Yes, with appropriate filler. INCONEL Filler Metal 625 (UNS N06625) is the universal joining alloy, it works for Incoloy-to-Incoloy, Inconel-to-Inconel, and Incoloy-to-Inconel dissimilar joints. For matching-strength dissimilar welds in age-hardenable grades, INCO-WELD 725NDUR is preferred. See the welding page for full filler-metal selection.
Is "Inconel 925" ever a real designation? No. Special Metals' product registry has never included an alloy named Inconel 925. If a vendor offers material as "Inconel 925," they are either (a) using the wrong term and meaning INCOLOY 925, or (b) supplying a non-Special-Metals counterfeit. Always insist on the UNS N09925 designation on the MTC, and verify the manufacturer is Special Metals or an approved Special Metals licensee.
Why is the iron in Incoloy not a corrosion problem? Iron in austenitic nickel alloys is locked into the FCC matrix and does not segregate to grain boundaries. The alloy's corrosion performance is set by the chromium + molybdenum + copper additions, not by the iron content. The cost benefit is significant: replacing 20% nickel with 20% iron reduces raw-material cost by ~30% with negligible corrosion penalty in most service environments.
How does Hastelloy fit in? Hastelloy is a Haynes International trademark, not Special Metals. The product families overlap with Inconel (Hastelloy C-276 vs Inconel 625, both Ni-Cr-Mo solid-solution). Comparison falls outside the Inconel/Incoloy framework but is a frequent buyer question, see Special Metals + Haynes selection guides for alloy crosswalks.
Compare Incoloy 925 to Specific Alloys
- Incoloy 925 vs Inconel 718, gamma-prime vs gamma double-prime; oilfield strength selection
- Incoloy 925 vs Incoloy 825, age-hardenable vs solid-solution; when 825 is enough
- Incoloy 925 vs Incoloy 926, oilfield CRA vs super-austenitic seawater alloy
- Incoloy 925 vs Monel K-500, nickel-iron-Cr vs nickel-copper; corrosion envelope difference
- Incoloy 925 vs Duplex 2205, nickel CRA vs duplex stainless; cost vs sour-service spec
Request a Quote
For Incoloy 925 with full MTC documentation, or for any of the comparison alloys covered above:
- Email: info@torqbolt.com
- WhatsApp: +91-22-66157017
- Datasheet PDF + sample MTC available on request
Specify application (medium, temperature, pressure, sour content), required mechanical envelope (UTS / YS / hardness), product type (stud bolts, nuts, pipe, plate), and any compliance stamping (API 6A, NACE MR0175, ISO 15156, NORSOK MDS, ASME III).
References: Special Metals Corporation product registry, INCOLOY® alloy 800, 800H, 800HT, 825, 925, 926; INCONEL® alloy 600, 625, 718, 725; INCO-WELD® filler metals. NACE MR0175 / ISO 15156-3 Tables A.7, A.10, A.12, A.13, A.14. INCOLOY®, INCONEL® and INCO-WELD® are registered trademarks of Special Metals Corporation. Hastelloy® is a registered trademark of Haynes International.
