What is Nimonic 90 Alloy? UNS N07090, Equivalent Grades (2.4632, Chinese GH90/GH4090) & Typical Appl

Nimonic 90 (UNS N07090 / W.Nr. 2.4632) is a precipitation-hardenable (γ′ strengthened) nickel-chromium-cobalt superalloy​ originally developed by Henry Wiggin & Co. (later part of Inco / Special Metals heritage) for high-temperature rotating and stressed components​ such as gas turbine blades, vanes, high-temperature springs, and fasteners operating in the 650–870°C (1200–1600°F) range. Its distinguishing features versus other Nimonic-series alloys are:

• High γ′ volume fraction​ from relatively high Al + Ti (≈ 3.8–4.8 wt% total: Ti 2.2–3.0%, Al 1.0–2.0%) → superior creep and stress-rupture strength vs. Nimonic 263 or solid-solution alloys in the same temperature band.

• Two-stage aging (precipitation hardening)​ required to optimize γ′ size/distribution → higher strength but greater susceptibility to Strain-Age Cracking (SAC) in welded thick/restrained sections compared to Nimonic 263.

• Nominal chemistry: Ni–19.5Cr–18Co–2.6Ti–1.5Al–(≤0.5 Mo)–(≤3.0 Fe max).

This article provides the technical definition, chemical limits, property overview, grade equivalents (including Chinese GH90 / GH4090 reference), and typical applications per BS HR 1 / AMS 5829.

1. UNS, Trade Name & International Equivalents

⚠️ Nimonic 90 is not​ Inconel 718 (UNS N07718). Inconel 718 is stronger at peak (especially < 650°C) and has a wider safe quenching window for thick sections, but Nimonic 90 can operate usefully to ≈ 870°C in creep (vs. 650°C practical limit for 718 in long-term design). Nor is it a direct substitute for Nimonic 263 — 90 is for forged/machined stressed parts, 263 is for welded sheet-metal fabrications.

2. Nominal Chemical Composition (per BS HR 1 / AMS 5829)

Key: (Al+Ti)total ≈ 3.8–4.8%​ → significantly higher γ′ volume fraction than Nimonic 263 (≈0.5%) or Hastelloy X / Inconel 625 (none).

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

4. Typical Mechanical Properties

Condition A — Solution Annealed (SA, as-delivered for machining/pre-form):​

Soft, Rm ≈ 800–950 MPa; Rp0.2 ≈ 350–450 MPa; A₅₀ ≥ 30–40%.

Condition B — Solution Annealed + Double-Aged (typical: 1080–1150°C SA → 700–750°C × 16 h / AC + 650°C × 16 h / AC):

Elevated-Temperature Tensile (Aged — Typical):

Creep / Stress-Rupture (representational for estimation only — not design allowables):

• 750°C / 220 MPa ≈ 100–300 h

• 815°C / 150 MPa ≈ 100–200 h

• 870°C / 100 MPa ≈ 50–150 h

• 900°C / 70 MPa ≈ marginal (upper use limit for sustained load)

→ Nimonic 90 has higher creep-rupture strength than Nimonic 263 or Hastelloy X​ in the 700–870°C range due to higher γ′ fraction; it is not​ a disc alloy for > 950°C sustained centrifugal load (select Udimet 720 / René 80 for that).

5. Heat Treatment & Aging Practice

• Solution Anneal (SA):​ 1080–1150°C × (soak per section, e.g. 1–2 h + time for upset) → oil or water quench​ (must be rapid enough to retain γ′ solutes — thicker sections need verified quench rate).

  Typical production: 1120–1140°C → water/oil quench.

• Aging (Double-Stage — typical BS HR 1 practice):​

  1st stage: 700–750°C × 16 h / furnace cool or air cool​

  2nd stage: 650°C × 16 h / air cool​

  → Produces bimodal γ′ (primary coarse + secondary fine) for optimum strength & stress-rupture.

• Alternative single-stage (less common):​ 700°C × 24 h — gives slightly lower peak strength.

• Over-aging caution:​ > 1050°C or prolonged 800–900°C exposure → η phase (Ni₃Ti hex) forms at γ′ expense → strength drops.

• Post-Weld:​ Welded assemblies (if attempted on thick/restrained parts) may require full re-solution + re-age; thin-gauge or low-restraint welds using matched filler canbe direct-aged but SAC risk exists — usually Nimonic 90 is machined/forged THEN welded in sub-assemblies or used as forged bar/spring, not large welded fabrications (that's Nimonic 263's role).

6> Welding, Forming & Machining

• Weldability:​ Fair — high Al+Ti → HAZ γ′ re-precipitates on cooling → Strain-Age Cracking (SAC) risk in thick/restrained joints.

  • Filler: matching N07090 wire preferred for strength recovery; Inconel 82 (ERNiCr-3) sometimes used for non-critical joints (lower creep).

  • Usually welded in solution-annealed condition; PWHT = re-solution + double-age (expensive for large assys) or local stress relief + age if geometry permits.

  • Not recommended for large thin-wall welded fabrications​ (use Nimonic 263 or Hastelloy X for those).

• Forming:​ In SA condition can be warm-formed (650–800°C) or cold-formed with intermediate anneals; more springback than austenitic SS.

• Machining:​ Work-hardens; rigid setup, low SFM (8–15 m/min), high feed, TiAlN coated carbide, flood coolant — similar to Inconel 718 or other γ′ Ni-base.

7. Typical Applications by Industry

8. Comparison Snapshot (Selection Context)

→ Select Nimonic 90​ when: part is forged/machined or spring/wire, requires maximum creep @ 650–870°C among Nimonic family, and welding is minimal / carefully controlled.

→ Select Nimonic 263​ when: part is a large thin-walled welded fabrication​ (combustor liner) needing post-weld age without SAC.

→ Select Inconel 718​ when: peak strength @ ≤ 650°C + thick-section quench-capable + fatigue critical (disc/bolt).

9. Summary

Nimonic 90 (UNS N07090 / W.Nr. 2.4632 / BS HR 1 / AMS 5829) is a γ′-hardened Ni–19.5Cr–18Co–2.6Ti–1.5Al superalloy​ offering:

• Creep & stress-rupture strength in the 650–870°C​ range superior to solid-solution Ni-base and Nimonic 263;

• Double-stage aging​ (700–750°C + 650°C) to develop optimal γ′ distribution;

• Good oxidation resistance to ≈ 1040°C (Cr₂O₃ + minor Al₂O₃ sub-layer);

• Typical applications: gas turbine blades & vanes, high-temperature springs, fasteners, lock rings;

• Not​ a direct substitute for Nimonic 263 in welded sheet-metal fabrications (SAC sensitivity) nor for disc alloys > 950°C sustained centrifugal load.