Excerpt:
Nimonic 90 (UNS N07090, W.Nr. 2.4632) aerospace superalloy technical guide from Hangbo Alloy. Covers the gamma-prime Ni₃(Al,Ti) precipitation-hardening mechanism, Co 15–21% / Cr 18–21% chemistry, solution-and-age heat treatment (8 h/1080 °C + 16 h/700 °C), elevated-temperature tensile and 50–3,000-hour stress-rupture data, turbine-disc forging controls, BS HR 2 / ASTM B637 / AMS specs, and a procurement checklist plus FAQ.
Nimonic 90 (UNS N07090) — Gamma-Prime Strengthened Superalloy for Turbine Discs and Hot-Section Aerospace Service | Hangbo Alloy
Alloy Import Pitfalls Series — Technical Bulletin for Aerospace, Power-Generation, and Precision-Component Buyers
The Certification Chasm Between "Bar Stock" and "Aerospace-Qualified Bar"
Nimonic 90 is not an alloy you buy twice casually. A turbine disc or hot-section forging spends its working life at 700–900 °C under centrifugal and thermal stress, and its metallurgy — a fine dispersion of gamma-prime precipitates in a nickel-chromium-cobalt matrix — is created by a heat-treatment sequence measured in hours and verified in tenths of a percent. Yet in the importing world, "Nimonic 90" bar is frequently offered from stock with no proof of the solution-and-age cycle, no grain-flow verification for the forging direction, and a certificate that lists a chemistry range instead of heat-specific values.
Hangbo Alloy (Shanghai Hangbo Alloy Group, nickel-alloy.com) supplies Nimonic 90 (UNS N07090, W.Nr. 2.4632) to BS HR 2 and ASTM B637, with the controlled forging and heat-treatment practices this page describes. If your drawing says "Nimonic 90, disc forging per AMS/BS HR2," the paragraphs below are the acceptance framework your inspector should be using.
1. Alloy Identity and the Gamma-Prime Mechanism
Nimonic 90 is a nickel-base superalloy strengthened by precipitation of the γ′ phase — Ni₃(Al,Ti) — a coherent, ordered intermetallic that precipitates as fine particles during aging and blocks dislocation movement at high temperature. Cobalt (15–21%) raises the solidus and solutionizes into the matrix, contributing solid-solution strengthening and raising the temperature at which γ′ remains effective; chromium (18–21%) provides oxidation and hot-corrosion resistance; aluminum plus titanium (combined ~3–5%) supply the γ′ former.
| Element | Specified Range (wt %) | Metallurgical Role |
|---|---|---|
| Nickel | Balance | Matrix |
| Chromium | 18.0–21.0 | Oxidation/hot-corrosion resistance |
| Cobalt | 15.0–21.0 | Solid-solution strengthening, higher solvus |
| Titanium | 2.0–3.0 | γ′ (Ni₃(Al,Ti)) former |
| Aluminum | 1.0–2.0 | γ′ former; oxidation resistance |
| Iron | 1.5 max | Residual |
| Manganese | 1.0 max | Residual |
| Silicon | 1.0 max | Residual |
| Carbon | 0.13 max | Carbide control (MC, M₂₃C₆) |
| Boron | 0.02 max | Grain-boundary strengthening |
| Zirconium | 0.15 max | Grain-boundary refinement |
| Sulfur / Lead / Copper | 0.015 / 0.002 / 0.2 max | Trace control for forgeability & ductility |
The alloy is serviceable to roughly 920 °C for lightly loaded parts, with the useful stressed range for turbine hardware concentrating between 700 and 900 °C. Density is 8.18 g/cm³; solidus ≈ 1310 °C, liquidus ≈ 1370 °C.
Heat treatment is the product. Bar and forging stock receive a solution anneal followed by an aging cycle — for bar, the classic route is 8 h at 1080 °C, air cool, then 16 h at 700 °C, air cool. Sheet product is typically solution-treated ~3 min at 1150 °C, fast-cooled, then aged (e.g., 1 h at 925 °C AC + 4 h at 750 °C AC per one standard route). The aging step nucleates the γ′ dispersion; the solution step sets grain size and dissolves carbides so they reprecipitate in the right morphology. A heat that skips or shortens aging delivers room-temperature strength without the high-temperature creep capability — and the deception is invisible to any room-temperature tensile test the importer runs.
| Heat-Treatment Stage | Typical Practice (bar/forging) | Purpose |
|---|---|---|
| Solution anneal | 8 h at 1080 °C, air cool | Dissolve γ′, set grain structure |
| Aging | 16 h at 700 °C, air cool | Precipitate fine γ′ dispersion |
| Optional stabilization | Per spec (e.g., 4 h at 900 °C class) | Coarsen grain-boundary carbides for rupture ductility |
| Verification | Hardness + room-temp tensile + (where required) stress-rupture test | Confirms the treatment actually worked |
2. Governing Specifications — BS HR 2, ASTM B637, and the AMS Web
Nimonic 90 is procured under a dense web of national and industry specifications. The importer's first duty is to state which spec governs, because chemistry is similar but testing and traceability requirements differ sharply.
| Specification | Scope | Notes for Importers |
|---|---|---|
| BS HR 2 | Rod, bar, and forgings (UK) | Classic Nimonic 90 procurement spec; solution + age verified |
| ASTM B637 | Seamless/forged/wrought bar and forgings for high-temp service | US pressure/structural route; UNS N07090 |
| SAE AMS 5829 | Wire (and related mill forms) | Aerospace wire applications |
| BS HR 501 / HR 502 / HR 503 | Related UK forms | Check the exact HR number on your drawing |
| DIN/ISO equivalents | W.Nr. 2.4632 | European sourcing |
The import pitfall: aerospace primes and their Tier-1 suppliers do not accept "equivalent to" substitutions across this web. A BS HR 2 order cannot be closed out with an ASTM B637 certificate that lacks the HR 2 testing supplements, and vice versa. Hangbo Alloy qualifies material against the specific spec named on your PO and provides the associated certificate structure (EN 10204 3.1 with spec-specific testing).
3. Tensile and Stress-Rupture Performance at 700 °C and Above
Because Nimonic 90's value lives above 700 °C, its datasheets present tensile data at temperature — not just room temperature. Typical extruded-bar values (averages over production casts) illustrate the envelope:
| Test Temperature | 0.2% Proof Stress | Tensile Strength | Elongation | Reduction of Area |
|---|---|---|---|---|
| 20 °C | ~813 MPa | ~1251 MPa | ~28% | ~41% |
| 700 °C | ~711 MPa | ~965 MPa | ~13% | ~17% |
| 800 °C | ~573 MPa | ~683 MPa | ~10% | ~16% |
| 900 °C | ~300 MPa | ~346 MPa | ~21% | ~37% |
| 1000 °C | ~48 MPa | ~76 MPa | — | — |
Notice the shape of the curve: proof strength holds above 700 MPa at 700 °C and still exceeds 500 MPa at 800 °C — that retention of load-bearing capacity into the hot section is exactly what γ′ hardening buys and what solid-solution alloys cannot match at these temperatures.
Stress-rupture is the property aerospace engineers design to: the stress a material sustains for a stated life (e.g., 100 or 1000 hours) at temperature. The table below gives typical rupture stresses for Nimonic 90 sheet heat-treated by a 1150 °C solution plus a 750 °C age — representative of the alloy's published capability (elongation at fracture in these tests ranged roughly 0.3–8.5%):
| Temperature | 50 h | 100 h | 300 h | 1000 h | 3000 h |
|---|---|---|---|---|---|
| 700 °C | 464 MPa | 428 MPa | 371 MPa | 320 MPa | 271 MPa |
| 750 °C | 349 MPa | 320 MPa | 275 MPa | 221 MPa | 170 MPa |
| 800 °C | 244 MPa | 218 MPa | 164 MPa | 104 MPa | 59 MPa |
| 850 °C | 163 MPa | 136 MPa | 95 MPa | 54 MPa | 29 MPa |
| 900 °C | 90 MPa | 74 MPa | 48 MPa | 26 MPa | — |
Engineering reading of the rupture table: at 800 °C, Nimonic 90 carries ~218 MPa for 100 hours and ~104 MPa for 1000 hours; at 900 °C the same lives require dropping stress to ~74 and ~26 MPa respectively. This steep stress-life-temperature coupling is why disc and blade designs quote both a temperature and a life, and why a "hot-section alloy" claim must always be tied to a specific rupture life.
4. Turbine Disc and Hot-Section Service — Component Reality
Nimonic 90 serves in gas-turbine discs and blades, turbine and compressor blading for industrial and aero engines, springs, bolts, and casings in the 700–900 °C band, and in diesel-engine and high-performance valve train components where hot strength plus fatigue resistance are required. Its selection rationale versus alternatives:
| Component / Duty | Why Nimonic 90 | Typical Alternative Considerations |
|---|---|---|
| Turbine discs (early-stage engines, industrial turbines) | γ′ strength to ~800 °C, forgeable, established pedigree | Nimonic 80A (lower Co, lower top-end strength); Inconel 718 (lower temperature ceiling ~650 °C, but higher RT strength) |
| Turbine blades / buckets (lower-temp engines) | Creep + fatigue + oxidation balance | Nimonic 105 / 115 (higher solvus, for hotter blades) |
| Bolts and fasteners in hot sections | High-temperature proof strength + relaxation resistance | Waspaloy class for higher temperatures |
| Springs at 300–600 °C | Retention of modulus/relaxation resistance | Nimonic 90 standard in high-performance valves |
The engineering shorthand: Nimonic 90 is the workhorse disc and hot-section alloy where service stays below ~900 °C and where a forged, fine-grained, γ′-aged microstructure — not a cast or single-crystal structure — is the cost-effective solution.
5. Advanced Forging Controls at Hangbo Alloy
Turbine disc integrity is made in the forge, not the furnace. The controls Hangbo Alloy applies to Nimonic 90 disc and bar forging are the ones aerospace buyers should audit:
| Control | Hangbo Alloy Practice | Why It Matters |
|---|---|---|
| Forging temperature range | Hot working centered in the ~1050–1150 °C class range; no working below the safe finishing temperature | Cold-die or low-finish-temperature working cracks γ′ and leaves residual strain |
| Reduction and finish-temperature control | Controlled reduction per pass; finish above the recrystallization-safe floor | Sets final grain size and grain-flow orientation |
| Reheat discipline | No prolonged soaking; furnace cut-back on delays; no exceeding the maximum hot-working ceiling | Overheating coarsens grain and can initiate incipient melting at carbide sites |
| Post-forge heat treatment | Full solution + age per BS HR 2 / drawing (e.g., 8 h/1080 °C AC + 16 h/700 °C AC) | Creates the service γ′ dispersion — non-negotiable |
| Grain flow / macro-etch | Macro-etch inspection confirming flow lines follow the disc contour | Misoriented flow = anisotropic rupture life |
| Traceability | Heat-lot identity maintained from melt through forging and heat treatment | Aerospace requires melt-to-part pedigree |
| Destructive verification | Room- and elevated-temperature tensile; stress-rupture samples where specified | Proves the heat treatment, not just the chemistry |
Hot working of Nimonic 90 demands attention to the alloy's resistance to deformation: the working range is narrow, tools and dies should be preheated (≈500 °F class practice) to avoid chilling, and heavy reductions must not overheat the work. Hangbo Alloy's forging team documents actual temperature, reduction, and finish conditions per part — the records a prime's metallurgist will ask for at first-article approval.
6. Procurement and Acceptance Checklist
| Check | Acceptance Criterion |
|---|---|
| UNS / trade name | N07090 / Nimonic 90 / W.Nr. 2.4632 — all on the MTC |
| Governing spec | BS HR 2, ASTM B637, or AMS as named on the PO |
| Chemistry | Heat-specific values vs. Section 1 table; Co, Ti, Al, B verified |
| Heat treatment | Solution + age cycle recorded with times and temperatures |
| Mechanicals at temperature | Elevated-temperature tensile and rupture data per spec |
| Forging record | Reduction, temperatures, finish temperature, grain flow |
| Traceability | Melt-to-part heat identity; EN 10204 3.1 structure |
| Third-party verification | Witness testing, PMI, and macro-etch on request |
Technical FAQ — Nimonic 90 (UNS N07090)
1. What is Nimonic 90 and what UNS number covers it?
Nimonic 90 is a gamma-prime (Ni₃(Al,Ti)) precipitation-hardened nickel-cobalt-chromium superalloy, designated UNS N07090 (W.Nr. 2.4632). It serves gas-turbine discs, blades, bolts, springs, and hot-section hardware at service temperatures up to about 920 °C.
2. How is Nimonic 90 precipitation-hardened?
A solution anneal (for bar, typically 8 h at ~1080 °C, air cool) dissolves alloying elements, then an age (typically 16 h at ~700 °C, air cool) precipitates a fine coherent γ′ dispersion that blocks dislocation motion at high temperature. Cobalt raises the solvus; chromium and aluminum give oxidation resistance. Skipping or altering the age cycle destroys high-temperature capability without necessarily failing a room-temperature test.
3. What are the stress-rupture properties of Nimonic 90 at 800 °C and above?
Typical rupture stresses for solution-and-aged Nimonic 90 at 800 °C are about 218 MPa for 100 hours, 164 MPa for 300 hours, and 104 MPa for 1000 hours; at 900 °C the corresponding values fall to roughly 74 MPa for 100 hours and 26 MPa for 1000 hours. Full 50–3000 h tables for 700–900 °C appear in Section 3.
4. Which specifications cover Nimonic 90 bar and forgings?
BS HR 2 covers rod, bar, and forgings in the UK system; ASTM B637 covers bar and forgings for high-temperature service in the US system; SAE AMS 5829 and related BS HR numbers address wire and other forms. Specify the exact governing spec on the purchase order — certificates are not freely interchangeable across this web.
5. What is the difference between Nimonic 90 and Nimonic 80A?
Both are γ′-hardened nickel-base alloys, but Nimonic 90 adds 15–21% cobalt (80A has none by design), which raises high-temperature strength and the effective service ceiling. 80A is a lower-cost choice for moderate temperatures; 90 is specified where the 700–900 °C envelope demands more.
6. Can Nimonic 90 be forged, and what temperature range is used?
Yes. Nimonic 90 is hot worked in a relatively narrow range centered around 1050–1150 °C, with careful control of reduction and finishing temperature to develop the required grain structure. Tools and dies are preheated to avoid chilling, and prolonged soaking at hot-working temperature is avoided. Post-forge solution and aging are mandatory to restore service properties.
7. What service temperature limit applies to Nimonic 90?
The alloy is rated for service to approximately 920 °C for suitable applications; stressed turbine hardware is typically designed within 700–900 °C where the rupture-life data in Section 3 apply. Above ~900 °C, designers normally move to higher-solvus alloys such as Nimonic 105/115 or cast superalloys.
8. Is Nimonic 90 used for turbine discs or only blades?
Both — and its disc pedigree is one of its defining credentials. Forged Nimonic 90 discs operate in industrial and aero gas turbines where the rim temperature stays in the alloy's capability band. Disc procurement emphasizes forging reduction, grain flow, and finish-temperature control, not just chemistry.
9. Why does a Nimonic 90 certificate list cobalt, boron, and zirconium?
Cobalt (15–21%) is a deliberate strengthening addition, not an impurity. Boron (≤0.02%) and zirconium (≤0.15%) are microalloying additions that strengthen grain boundaries and improve rupture ductility. Trace elements such as lead (≤0.002%) are limited because they embrittle grain boundaries at service temperature — verifying them is part of aerospace-grade acceptance.
10. Does Hangbo Alloy supply Nimonic 90 with full aerospace traceability?
Yes. Hangbo Alloy supplies Nimonic 90 bar, forgings, and rolled products to BS HR 2 and ASTM B637 with melt-to-part heat-lot traceability, documented forging and heat-treatment records, EN 10204 3.1 mill certificates, and optional third-party witness testing and macro-etch/grain-flow inspection. We treat the forging and heat-treatment record as part of the product — because in this alloy, it is.
Alloy Import Pitfalls Series — Hangbo Alloy (Shanghai Hangbo Alloy Group, nickel-alloy.com). Data are typical engineering values compiled from recognized industry sources for material selection; governing documents are the applicable specifications (BS HR 2, ASTM B637, AMS) and the certified mill report. Contact Hangbo Alloy for Nimonic 90 stock, forging services, and aerospace-grade documentation.
