Discover the latest trends and innovations in the nickel alloy industry. We provide expert insights and in-depth analysis on the newest developments in nickel alloys.
Incoloy 925 (UNS N09925 / often referenced to Special Metals Carpenter 925®) is an age-hardenable (precipitation hardening) Ni-Fe-Cr alloy derived from the Incoloy 825 (N08825) composition base, with intentionally increased Titanium and added Aluminum to form γ′ precipitates (Ni₃(Ti,Al)) during aging. It is designed for sour gas (H₂S/CO₂) oil & gas downhole service requiring high yield strength (≥ 110 ksi / 758 MPa) and NACE MR0175 / ISO 15156 SSC resistance, combined with good general corrosion resistance similar to Alloy 825. It is not a high-temperature creep alloy like Incoloy 800HT, nor a general-purpose acid-process alloy like 825 in the annealed (non-aged) condition—its primary advantage is strength + sour-environment SCC resistance.
Chemical Composition (UNS N09925 per ASTM B805 / ASME SB805)
|
Element |
Weight % |
Functional Significance |
|---|---|---|
|
Nickel (Ni) |
38.0 – 46.0 |
Austenite stabilizer; matrix for γ′ formation; Cl⁻ SCC immunity |
|
Chromium (Cr) |
19.5 – 22.5 |
Oxidation resistance; general acid (HNO₃) & CO₂ corrosion resistance |
|
Iron (Fe) |
≥ 22.0 (Balance) |
Matrix element; cost reduction vs. full Ni-base |
|
Molybdenum (Mo) |
2.5 – 3.5 |
Pitting / crevice corrosion resistance (PREN ≈ 35–38) |
|
Copper (Cu) |
1.5 – 3.0 |
Enhances resistance to reducing acids (H₂SO₄, H₃PO₄ — similar to 825) |
|
Titanium (Ti) |
1.80 – 2.40 |
Key hardener — forms γ′ (Ni₃Ti/Al); raised vs. 825 (0.6–1.2%) to enable age hardening |
|
Aluminum (Al) |
0.10 – 0.50 |
Co-precipitates with Ti as γ′ (Ni₃(Al,Ti)); controls aging response |
|
Carbon (C) |
≤ 0.03 |
Extra-low to prevent Cr-carbide sensitization after aging |
|
Manganese (Mn) |
≤ 1.0 |
— |
|
Silicon (Si) |
≤ 0.50 |
— |
|
Sulfur (S) |
≤ 0.010 |
Tightened vs. 825 — critical for SSC performance |
|
Phosphorus (P) |
≤ 0.030 |
— |
Common product forms: ASTM B805 (bars/forgings/rod), B704 (seamless tube), B705 (welded tube — less common for aged product).
Chinese equivalent typically ordered as "Incoloy 925 rod/forging per UNS N09925 + NACE MR0175".
Heat Treatment: Solution + Aging (Critical!)
Unlike Incoloy 825 (single-step solution anneal only), Incoloy 925 must be age hardened to develop design strength:
Solution Treat (ST): 900–980°C (typically 910–930°C), hold, rapid water quench → soft condition (Rm ≈ 690–830 MPa, Rp0.2 ≈ 380–480 MPa), suitable for machining.
Age Hardening (AH): 620–720°C (typical 650–680°C) × 8–16 h, air or furnace cool → γ′ (Ni₃(Ti,Al)) precipitates → strength increases substantially.
Delivery Condition:
Solution-annealed only:for customer final machining + own aging.
Solution-annealed + Aged:ready for installation (hardness ~28–38 HRC; machine beforeaging if complex geometry).
⚠️ Over-aging (>740°C or excess time) causes η-phase (Ni₃Ti) coarsening → slight strength drop, toughness rise — follow approved procedure.
Mechanical Properties (Aged / Precipitation-Hardened Condition — ASTM B805 Minimum Values)
|
Property |
ASTM B805 Minimum |
Typical Mill Range |
|---|---|---|
|
Tensile Strength, Rm |
≥ 965 MPa (140 ksi) |
1000–1170 MPa |
|
Yield Strength, Rp0.2 |
≥ 758 MPa (110 ksi) |
790–930 MPa |
|
Elongation, A₅₀ |
≥ 12% |
15–20% |
|
Reduction of Area, Z |
≥ 45% |
50–60% |
|
Hardness (HRC) |
— |
28–38 HRC (typical 30–34 HRC) |
|
Charpy V-Notch @ −46°C (−50°F) |
≥ 34 J (25 ft‑lbf) |
Typically 40–60 J |
|
Young's Modulus, E (RT) |
~196–200 GPa |
— |
Common oilfield grade: 110 ksi yield strength class (≥758 MPa). 120 ksi class (≥827 MPa YS) is achievable with tighter process control and confirmed by some mills on request.
Physical Properties (Solution Treated / Aged — Approximate)
|
Property |
Value |
|---|---|
|
Density |
8.14 g/cm³ (use 8.15 kg/dm³ for weight calc.) |
|
Melting Range |
1345–1400°C (2460–2550°F) |
|
Crystal Structure |
FCC (fully austenitic) — non-magnetic in ST & aged condition |
|
Modulus of Elasticity (E, 20°C) |
~197 GPa |
|
Coefficient of Thermal Expansion (20–300°C) |
~14.5 × 10⁻⁶ /K |
|
Thermal Conductivity (100°C) |
~11.5 W/(m·K) |
|
Specific Heat (20°C) |
~460 J/(kg·K) |
|
Electrical Resistivity (20°C) |
~1.10 µΩ·m |
Corrosion Resistance Summary (Similar to Alloy 825 but SSC-Capable at High Strength)
|
Environment |
Performance |
Note |
|---|---|---|
|
Sour Gas (H₂S/CO₂, Cl⁻ — NACE MR0175 limits) |
★★★★☆ (SSC resistant @ ≥110 ksi YS within ISO 15156 envelope) |
Primary design application — downhole completions |
|
CO₂ (Sweet) Corrosion, ≤150°C |
★★★★☆ |
Far better than 13Cr / Cr-Mo tubulars |
|
Chloride SCC (aqueous) |
★★★★★ (fully austenitic) |
Immune vs. 300-series SS |
|
Pitting / Crevice (PREN≈35–38) |
★★★★ |
Comparable to 825; < super duplex / 625 |
|
Sulfuric / Phosphoric Acid (dilute, moderate T) |
★★★★ |
Like 825 (Cu effect); not for strong HCl/HF |
|
Seawater Full Immersion (long term) |
★★ Moderate |
OK for SCC; point corrodes slower than 316 but less than 625 — use 625 or super duplex if pitting governs |
|
High-Temp Oxidation / Creep (>650°C press.) |
✗ Not intended |
Use Incoloy 800HT / Inconel 600+ |
Typical Applications
Downhole tubular accessories, polished bore receptacles, packer mandrels & components
Subsurface safety valve (SSSV) stems / spools
High-strength fasteners / hanger components in sour (H₂S) offshore environments
Pump shafts for sour crude / produced water pumps
Not used for: high-temp furnace tubes (→800HT), general process vessels/tanks (→825), strong reducing acid service (→C-276)
