Standards
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 925 Chemical Composition (UNS N09925)
Per Special Metals Technical Bulletin Table 1 — limiting chemistry for nickel-iron-chromium age-hardenable alloy
Incoloy 925 (UNS N09925) is an age-hardenable nickel-iron-chromium alloy with deliberate additions of molybdenum, copper, titanium and aluminum. Each element plays a specific role: nickel provides chloride stress-corrosion cracking resistance, chromium gives oxidising-environment resistance, molybdenum drives pitting and crevice corrosion resistance, copper extends the reducing-acid envelope, and the titanium + aluminum additions form the gamma prime Ni3(Al, Ti) precipitates during age hardening that double the alloy's yield strength. The composition is governed by Special Metals SMC HA 46 internal specification and harmonised across ASTM B805 (bar, forgings) and ASTM B983 (sheet, plate, strip).
Need Incoloy 925 with certified chemistry? Email info@torqbolt.com with product type, size and quantity. Every order ships with EN 10204 3.1 manufacturer's MTC documenting actual heat-lot chemistry vs the specified limits below. Full Incoloy 925 datasheet + sample MTC available on request.
Limiting Chemical Composition — UNS N09925
| Element | Min % | Max % | Role |
|---|---|---|---|
| Nickel (Ni) | 42.0 | 46.0 | Cl-SCC resistance, austenite stabiliser |
| Chromium (Cr) | 19.5 | 22.5 | oxidising-environment resistance |
| Iron (Fe) | 22 min | balance | matrix, cost-effective base |
| Molybdenum (Mo) | 2.5 | 3.5 | pitting, crevice, sour service |
| Copper (Cu) | 1.5 | 3.0 | reducing-acid resistance |
| Titanium (Ti) | 1.9 | 2.4 | gamma-prime former (age hardening) |
| Aluminum (Al) | 0.1 | 0.5 | gamma-prime former (age hardening) |
| Manganese (Mn) | — | 1.0 max | deoxidiser, residual |
| Silicon (Si) | — | 0.5 max | deoxidiser, residual |
| Niobium (Nb) | — | 0.5 max | residual / carbide former |
| Carbon (C) | — | 0.03 max | controlled to limit M23C6 at grain boundaries |
| Sulfur (S) | — | 0.03 max | controlled to limit hot-cracking susceptibility |
Source: Special Metals Corporation: INCOLOY® alloy 925 Technical Bulletin, Table 1. Identical chemistry envelope is replicated in ASTM B805 and ASTM B983 standards.
Element-by-Element — Why Each Number Is What It Is
Nickel 42.0–46.0%, the dominant alloying element. Nickel above ~30% is what gives Incoloy 925 its near-immunity to chloride stress-corrosion cracking, the failure mode that destroys 304/316 stainless in seawater and chloride-bearing produced fluids. The 42–46% window is the sweet spot: high enough to defeat Cl-SCC, low enough to keep the alloy affordable vs solid-solution nickel alloys like Incoloy 825 (38–46%) and Monel K-500 (63%).
Chromium 19.5–22.5%, provides the passive Cr₂O₃ oxide film that resists oxidising acids, hot air, and steam. The 19.5% minimum is the threshold for stable passivation in chloride media; the 22.5% maximum prevents sigma-phase precipitation during age hardening. Compare with Duplex 2205 (22–23% Cr): similar chromium, but 2205 lacks Incoloy 925's nickel and copper, so it loses to 925 in reducing acids and at temperatures above 300°F.
Molybdenum 2.5–3.5%, the single most important element for sour-service performance. Molybdenum drives the Pitting Resistance Equivalent Number (PREN = Cr + 3.3·Mo + 16·N): Incoloy 925 scores ~32, well above 304 (~19) and 316 (~25), placing it in the "qualified for sour service" envelope of NACE MR0175 / ISO 15156. Below 2.5% Mo, pitting resistance collapses; above 3.5%, ductility suffers.
Copper 1.5–3.0%, extends the alloy's resistance into reducing acids (sulfuric, phosphoric) where pure austenitic stainless fails. Copper is the metallurgical fingerprint that distinguishes Incoloy 925 from Inconel 718 (no Cu) and aligns it with Incoloy 825 (1.5–3.0% Cu, no Ti/Al). This is also why Incoloy 925 is favoured for downhole completions exposed to acid stimulation treatments.
Titanium 1.9–2.4% + Aluminum 0.1–0.5%, the age-hardening pair. During the controlled age treatment at 1365°F (740°C), Ti and Al precipitate as nano-scale Ni₃(Al, Ti) gamma-prime particles inside the austenite matrix. These coherent precipitates roughly double the alloy's yield strength, taking 0.2% YS from ~50 ksi (annealed) to ~110 ksi minimum (per ASTM B805). The Ti:Al ratio (~5:1) is critical, too much Al promotes gamma double-prime, which has different ageing kinetics.
Carbon ≤0.03% + Sulfur ≤0.03%, tightly controlled residuals. Carbon above 0.03% triggers M₂₃C₆ chromium carbide precipitation at grain boundaries during ageing, which depletes adjacent matrix of chromium and creates intergranular corrosion paths. Sulfur is hot-cracking poison, the 0.03% maximum protects weld integrity.
Comparison vs Adjacent Alloys
| Alloy | UNS | Ni % | Cr % | Mo % | Cu % | Ti % | Age-hardenable? |
|---|---|---|---|---|---|---|---|
| Incoloy 925 | N09925 | 42–46 | 19.5–22.5 | 2.5–3.5 | 1.5–3.0 | 1.9–2.4 | Yes (gamma-prime) |
| Incoloy 825 | N08825 | 38–46 | 19.5–23.5 | 2.5–3.5 | 1.5–3.0 | 0.6–1.2 | No (solid solution) |
| Inconel 718 | N07718 | 50–55 | 17–21 | 2.8–3.3 | ≤0.30 | 0.65–1.15 | Yes (gamma double-prime) |
| Incoloy 926 | N08926 | 24–26 | 19–21 | 6–7 | 0.5–1.5 | No (super-austenitic) | |
| Monel K-500 | N05500 | 63 min | 27–33 | 0.35–0.85 | Yes (gamma-prime) |
The takeaway: Incoloy 925 sits in a unique niche, the strength of an age-hardenable nickel alloy with the corrosion envelope of a solid-solution nickel-iron-chromium alloy. Incoloy 825 shares the chemistry but cannot age-harden (lacks Ti). Inconel 718 shares the strength but has no Cu (loses in reducing acids). See the Inconel vs Incoloy comparison for full selection logic.
UNS N09925 Naming & Trademark
"Incoloy 925" is a registered trademark of Special Metals Corporation. The unified numbering designation UNS N09925 is the standards-body-neutral identifier used in ASTM, ASME, and NACE/ISO documentation. The two are interchangeable on certificates, an MTC may state "Incoloy® alloy 925 (UNS N09925)" or simply "UNS N09925." Other regional designations:
- Werkstoff Nr. 2.4858, German/European DIN material number
- EN designation: NiFe30Cr21Mo3Ti, European chemistry-based designation
- NACE MR0175 Table A.10, sour-service qualified designation
- API 6A CRA category 4d, precipitation-hardened nickel alloy classification for wellhead service
TorqBolt MTC, What We Document
Every Incoloy 925 product TorqBolt ships carries an EN 10204 3.1 manufacturer's MTC (3.2 third-party witnessed available on request). The chemistry section reports actual heat-lot values vs the limiting composition above:
- Heat number traceability, every fastener, bar, or plate links back to the melt heat via stamping or tag
- All 12 elements reported, Ni, Cr, Fe, Mo, Cu, Ti, Al, Mn, Si, Nb, C, S (plus P, residuals on request)
- Ladle vs product analysis, both reported when product analysis is contractually required
- Dual-spec compliance, chemistry evaluated against both ASTM (B805 / B983) and customer specification simultaneously
- NACE MR0175 / ISO 15156 stamp, certifying chemistry conforms to sour-service envelope when ordered against NACE MR0175
See the full Incoloy 925 datasheet for mechanical, physical, and corrosion data sheets that accompany each chemistry report.
Common Incoloy 925 Products We Manufacture
| Product | Standard | Size Range | Application |
|---|---|---|---|
| Stud Bolts | ASTM B805 / API 6A / NACE MR0175 | 1/4" to 4" | Wellhead, Christmas tree, sour service |
| Heavy Hex Nuts | ASTM B805 / ASME B18.2.4.6M | M6 to M64 / 1/4" to 4" | Companion to stud bolts |
| Hex Bolts | ASTM B805 / ASME B18.2.1 | 1/4" to 2" | Structural, flange bolting |
| Washers | ASTM B805 | 1/4" to 3" | Load distribution, sour-service |
| Pipe | ASTM B983 | 1/2" to 12" NPS | Sour-service flowlines |
| Plate & Sheet | ASTM B983 | 3mm to 50mm thk | Pressure vessels, cladding |
Frequently Asked Questions
Is Incoloy 925 the same as Inconel 925? No. "Inconel 925" is a common misnomer, Special Metals does not market a 925 grade under the Inconel trademark. The correct designation is Incoloy 925 (UNS N09925). The "Inconel vs Incoloy" naming convention reflects iron content: Incoloy alloys contain significant iron (Incoloy 925 has 22% min Fe), while Inconel alloys are nickel-rich with low iron. See the Inconel vs Incoloy comparison for the full naming logic.
What's the difference between UNS N09925 and Werkstoff 2.4858? They are the same alloy under different naming systems. UNS (Unified Numbering System) is the North-American standard used in ASTM/ASME/NACE; Werkstoff Nr. is the European DIN designation. An MTC must report both when shipping into European markets governed by EN/PED.
Can the chemistry envelope vary between bar and plate? No, the limiting composition in ASTM B805 (bar/forgings) and ASTM B983 (sheet/plate/strip) is identical and matches Special Metals SMC HA 46. Heat-treatment requirements differ between product forms (see heat treatment specification), but chemistry does not.
Does Incoloy 925 contain cobalt? Cobalt is not a controlled element in UNS N09925. For nuclear applications requiring <0.05% Co (per ASME Section III), TorqBolt can supply low-Co heats with cobalt reported on the MTC, specify "low cobalt" at RFQ stage.
Request a Quote
For Incoloy 925 with EN 10204 3.1 MTC documenting heat-lot chemistry, contact TorqBolt:
- 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 restricted-element requirements (low cobalt, Hg-free, etc.).
References: Special Metals Corporation: INCOLOY® alloy 925 Technical Bulletin (Table 1). 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. NACE MR0175 / ISO 15156-3 Table A.10. INCOLOY® and INCONEL® are registered trademarks of Special Metals Corporation.
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