What is Nimonic 263 Alloy? UNS N07263, Equivalent Grades (2.4650, Chinese GH263) & Typical Applicati

Nimonic 263 (UNS N07263 / W.Nr. 2.4650) is a precipitation-hardenable (γ′ strengthened) nickel-chromium-cobalt-molybdenum superalloy​ originally developed by Rolls-Royce in the UK for aero-engine combustor liners, transition ducts, and afterburner casings​ operating in the 650–850°C (1200–1560°F) creep range. Its defining characteristics versus other Ni-base alloys are:

• Age-hardenable via γ′ (Ni₃(Ti,Al)) precipitation​ → significantly higher creep strength than solid-solution alloys (Inconel 625, Hastelloy X) in the 700–800°C bracket.

• Good resistance to Strain-Age Cracking (SAC)​ after welding → can be fusion-welded and then precipitation-aged without post-weld crack sensitivity seen in René 41 or Waspaloy.

• Excellent sheet-formability (comparable to Inconel 625)​ in the solution-annealed condition → suited to complex rolled/bent combustor assemblies.

• Nominal chemistry: Ni–20Cr–20Co–5.9Mo–0.40Ti–0.06Al–≤0.30Fe–0.06C.

This article provides the technical definition, composition limits, property overview, grade equivalents, and typical applications per BS HR 10 / AMS 5872.

1. UNS, Trade Name & International Equivalents

⚠️ Nimonic 263 is not​ Inconel 718 (UNS N07718). 718 is stronger at RT and 650°C peak but has narrow quenching window + SAC sensitivity; 263 is optimized for large thin-walled welded fabricationsthat are aged post-weld.

2. Nominal Chemical Composition (per BS HR 10 / AMS 5872)

*Some specs show Al 0.30–0.60%; typical production aims low (≤0.15%) to minimize γ′ volume for controlled aging & SAC resistance.

3. Key Physical Properties (Solution-Annealed + Aged, 20°C Unless Noted)

4. Typical Mechanical Properties

Condition A — Solution Annealed (SA, as-delivered for forming):​

Soft, ductile, Rm ≈ 750–850 MPa; Rp0.2 ≈ 300–380 MPa; A₅₀ ≥ 35–45%.

Condition B — Solution Annealed + Aged (SA+A):​

Common aging: 800°C × 8 h / AC or 700–760°C × 16 h​ (per BS HR 10 / aerospace practice — single-step, not two-step like 718).

Elevated-Temperature Tensile (Aged Condition — Typical):

• Creep Rupture (representative):​ 750°C / 200 MPa ≈ 100–200 h; 800°C / 140 MPa ≈ 100 h; 815°C / 105 MPa ≈ 50–100 h (for preliminary estimation — not design allowables).

• Strain-Age Cracking (SAC) Resistance:​ Significantly better than René 41 / Waspaloy — welded assemblies can be aged directly after GTAW/GMAW without intermediate stress-relief cracking in most thicknesses (< ~6 mm sheet typical for combustor).

5. Heat Treatment & Aging Practice

• Solution Anneal (SA):​ 1120–1150°C × (time per section, e.g. 5–15 min/mm thin sheet) → rapid air cool or water quench (thin gauge air cool acceptable)​ → soft condition for forming.

• Aging (Precipitation Hardening):​

  • Recommended: 800°C × 8 h / furnace cool or air cool​ (BS HR 10 typical)

  • Alternative: 700–760°C × 16 h (slightly lower peak strength, finer γ′)

  • Single-stage only​ — unlike Inconel 718 (two-stage 720°C + 620°C), Nimonic 263 uses one hold.

• Post-Weld:​ Welded (as-welded) → solution-annealed region around HAZ + weld → full part can be aged directly (provided no severe restraint / thickness > ~10 mm check for residual stress cracks — usually OK for combustor gauge).

• Do NOT over-age > 850°C long:​ γ′ coarsens / converts → strength drops; η (Ni₃Ti hexagonal) may form on extreme over-aging.

6. Welding & Fabrication

• Weldability:​ Good (GTAW/GMAW/EBW). Filler: matching N07263 wire​ preferred; Inconel 625 (ERNiCrMo-3) sometimes used for dissimilar but lowers creep strength — not recommended for primary load-bearing aged assemblies.

• Formability:​ In SA condition, similar to Inconel 625 — springback noticeable but manageable with proper tooling; minimum bend radius ~ 2–3 × thickness (cold) for annealed sheet.

• Machining:​ Work-hardens; rigid set-up, low SFM (8–15 m/min), high feed, TiAlN coated carbide, coolant flood.

7. Typical Applications by Industry

8. Comparison Snapshot (Selection Context)

→ Select Nimonic 263​ when: large thin-walled welded fabrications (combustor/duct) need creep strength above Hastelloy X/625 AND good post-weld age-crack resistance AND sheet formability.

→ Select Inconel 718​ when: maximum 650°C yield/ultimate + good fatigue required (disk, bolt, thick fitting) — not thin-wall large weldments.

9. Summary

Nimonic 263 (UNS N07263 / W.Nr. 2.4650 / BS HR 10 / AMS 5872) is a γ′-hardenable Ni–20Cr–20Co–6Mo–0.4Ti superalloy​ offering:

• Creep strength in 650–850°C​ range superior to solid-solution Ni-base alloys

• Low susceptibility to strain-age cracking​ → weld + age in one step for thin-gauge fabrications

• Good sheet formability in solution-annealed condition; oxidation resistance to ~980°C (Cr₂O₃)

• Typical applications: aero-engine combustor liners, transition ducts, exhaust cones, gas-turbine hot-section sheet metal

It is not​ a substitute for disc alloys (Inconel 718 / René 41 at lower T, Udimet 720 / René 80 at higher T) nor for severe oxidation > 1050°C (select Haynes 188 / Inconel 617).