Nimonic 90 vs Inconel 718 - Creep Strength and Temperature
Date: 2026年9月20日 Categories: News Views: 303
By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012
Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360
Quick Answer: Should I Use Nimonic 90 or Inconel 718 Above 650°C?
Inconel 718 (UNS N07718) is the default high-strength superalloy up to about 650°C, where its gamma-double-prime phase still provides a minimum yield strength of 1030 MPa, and it is far easier to weld than Nimonic 90. Above 650°C that strengthening phase transforms and 718 loses its advantage, while Nimonic 90 (UNS N07090) — strengthened by gamma-prime with 15-21% cobalt — retains creep and rupture strength to roughly 815-920°C. So: 718 for discs, shafts, casings and bolts below 650°C; Nimonic 90 for blades, vanes and hot fixtures above it.
Key Takeaways
- The strengthening phase decides the application. Gamma-double-prime (718) is very strong but unstable above about 650°C; gamma-prime (Nimonic 90) is stable at much higher temperature.
- 718 has the higher proof strength at room temperature — 1030 MPa minimum versus roughly 750-850 MPa typical for Nimonic 90 — but that comparison is meaningless at 800°C.
- Nimonic 90 contains 15-21% cobalt, which is why it typically costs 1.4-2 times as much per kilogram as 718.
- 718 welds well; Nimonic 90 does not. Nimonic 90 is strain-age crack sensitive and is normally a cast or forged, non-welded component.
- Never choose on tensile strength alone at temperature. Above 650°C, design is governed by creep and stress-rupture data, not by room-temperature UTS.
What Are Nimonic 90 and Inconel 718?
Nimonic 90 is a nickel-chromium-cobalt alloy strengthened by the precipitation of gamma-prime (Ni3(Al,Ti)) phases, with titanium and aluminium as the key additions and 15-21% cobalt supporting the gamma-prime solvus. The grade was developed for gas-turbine blades and remains a standard material for high-temperature components where creep resistance rather than proof strength is the design driver.
Inconel 718 is a nickel-chromium-iron alloy strengthened by gamma-double-prime (Ni3Nb) precipitation, with niobium plus molybdenum providing the chemistry and a controlled titanium-aluminium addition. It was designed to combine high strength with excellent weldability and cost, and it became the most widely used superalloy in the aerospace industry.
Both are specified by trade name plus a UNS number: Nimonic 90 is UNS N07090, Inconel 718 is UNS N07718. Our Nimonic 80A bar and Inconel alloy supplier pages cover the forms we stock.
Composition Comparison (wt.%)
| Element | Nimonic 90 (N07090) | Inconel 718 (N07718) | Per standard |
|---|---|---|---|
| Nickel | Balance | 50.0-55.0 | BS HR 501 (verify current edition) / ASTM B637 |
| Chromium | 18.0-21.0 | 17.0-21.0 | BS HR 501 / ASTM B637 |
| Cobalt | 15.0-21.0 | 1.0 max | BS HR 501 / ASTM B637 |
| Titanium | 2.0-3.0 | 0.65-1.15 | BS HR 501 / ASTM B637 |
| Aluminium | 1.0-2.0 | 0.20-0.80 | BS HR 501 / ASTM B637 |
| Niobium + Tantalum | — | 4.75-5.50 | ASTM B637 |
| Molybdenum | — | 2.80-3.30 | ASTM B637 |
| Iron | 1.5 max | Balance (~18) | BS HR 501 / ASTM B637 |
| Carbon | 0.13 max | 0.08 max | BS HR 501 / ASTM B637 |
| Manganese | 1.00 max | 0.35 max | BS HR 501 / ASTM B637 |
Table note: Values are specification limits from the cited documents; confirm the current edition of the British Standard before issuing a purchase order. The clean discriminator in a PMI check is cobalt and niobium: 15-21% Co with no niobium means Nimonic 90; 4.75-5.5% Nb with cobalt at or below 1% means 718.
Mechanical Properties Comparison
| Property | Nimonic 90, aged | Inconel 718, solution treated + aged | Per standard |
|---|---|---|---|
| UTS at 20°C | ~1200-1300 MPa (typical) | 1240 MPa min | BS HR 501 / ASTM B637 |
| 0.2% yield at 20°C | ~750-850 MPa (typical) | 1030 MPa min | BS HR 501 / AMS 5662 / ASTM B637 |
| Elongation at 20°C | ~20-25% (typical) | 12% min | BS HR 501 / AMS 5662 |
| Hardness | ~330-410 HB (typical) | ~331-401 HB (typical) | ASTM E10 / ASTM E18 |
| Strength capability | Creep and rupture limited to ~815-920°C depending on stress | Strength limited to ~650°C | — |
| Oxidation resistance | Good to ~900°C | Good to ~700°C, degrading above | — |
Table note: For Nimonic 90, property figures are stated as typical values because the applicable national specification should be consulted for guaranteed minima; for 718 the figures are minimum values from ASTM B637 / AMS 5662. Above 650°C all design work must be based on stress-rupture and creep data such as that produced under ASTM E139, not on room-temperature tensile strength.
The apparent paradox is important: 718 has the higher room-temperature yield strength, yet it is the weaker material at 800°C. This is not a contradiction — it is the direct consequence of two different strengthening mechanisms.
Why the Strengthening Phase Sets the Temperature Limit
| Feature | Nimonic 90 (gamma-prime) | Inconel 718 (gamma-double-prime) |
|---|---|---|
| Strengthening phase | Ni3(Al,Ti), gamma-prime | Ni3Nb, gamma-double-prime |
| Phase stability at temperature | Stable to high temperature | Transforms to delta phase above ~650°C |
| Consequence of overheating | Gradual overaging | Rapid loss of strength |
| Room-temperature proof strength | Moderate | Very high |
| Creep / rupture strength above 700°C | Strong | Falls away above ~650°C |
| Cobalt required | 15-21% | Not required |
| Weldability | Poor; strain-age cracking risk | Excellent |
Table note: Phase-transformation temperatures are established from published superalloy metallurgy and are given as approximate engineering guidance; confirm against material data sheets for design work.
This is why the two alloys occupy different positions in a gas turbine. Blades and vanes sit in the hot gas path and are creep-limited, so they use gamma-prime alloys such as Nimonic 90 and its higher-strength relatives. Discs, shafts, casings and fasteners sit behind a cooling system, are strength- and fatigue-limited, and use 718.
Heat Treatment
| Step | Nimonic 90 | Inconel 718 |
|---|---|---|
| Solution treatment | ~1080°C (typical practice) | ~955-980°C per AMS 5662 / AMS 5663 |
| Aging | ~700°C for ~16 h (typical practice) | 720°C for 8 h, furnace cool to 620°C, hold 8 h |
| Cooling after solution treatment | Controlled — rapid cooling can cause cracking in heavy sections | Air cool typically acceptable |
| Post-weld heat treatment | Not generally weldable; see below | Solution treat + age after welding when required |
| Distortion on aging | Low | Low |
Table note: Heat-treatment schedules shown for Nimonic 90 are typical industry practice and must be confirmed against the applicable specification and section thickness; 718 schedules follow the referenced AMS documents. Always work to the drawing and the material specification, not to a generic table.
Welding and Fabrication
Inconel 718 is one of the most weldable high-strength superalloys, which is a major reason for its dominance. It resists strain-age cracking, can be welded in the solution-treated condition and aged afterwards, and is used for large fabricated structures as well as for rotating parts.
Nimonic 90 sits at the opposite end. It is sensitive to strain-age cracking, and welded joints generally cannot recover the parent-metal creep properties. Most Nimonic 90 components are therefore forged, rolled or cast and then finish machined, with joining avoided or achieved by other means.
Machining. Both alloys are difficult: they work-harden rapidly, generate high cutting temperatures and require rigid setups, sharp tooling and generous coolant. Nimonic 90 is generally considered the more difficult of the two to machine because of its higher elevated-temperature strength — the tool sees a hotter, harder chip.
A practical observation from our own processing: customers sometimes ask for Nimonic 90 bar in a condition that allows easier machining before final aging. That is reasonable, but the bar must then be aged to the correct schedule after machining, and the aging step must be specified on the drawing. Bar sold "as rolled" that is installed without aging will not achieve the design properties — and the failure mode is creep, which only appears after months in service.
Where the duty is cooler and the budget tighter, the iron-nickel-chromium alternatives on our Incoloy 825 / 800H supplier page are worth reviewing, and the duplex & PH stainless range covers lower-temperature fixtures and hardware that do not require gamma-prime strengthening at all.
Which Alloy for Which Application?
| Application | Best choice | Why |
|---|---|---|
| Turbine blades and vanes above 700°C | Nimonic 90 | Gamma-prime creep strength in the hot gas path |
| Turbine discs and shafts | Inconel 718 | Strength plus fatigue life below 650°C |
| High-temperature bolts and fasteners | Inconel 718 | Proof strength plus weldability; see note on creep below |
| Combustion chamber liners and hot fixtures | Nimonic 90 | Oxidation and creep resistance at temperature |
| Heat-treatment furnace baskets, trays and jigs | Both, by load and temperature | 718 for lower-temperature high-load, Nimonic 90 for hotter |
| Exhaust valves and valve seats | Nimonic 90 | Hot, cyclic, creep-limited duty |
| Cryogenic pressure vessels and piping | Inconel 718 | Toughness plus strength at low temperature |
| Large welded fabrications at 600-650°C | Inconel 718 | Weldability decides the choice |
| Instrumentation and spring components | Inconel 718 | Elastic properties and formability |
Design note on high-temperature fasteners. 718 bolts are common to about 650°C, but bolted joints are creep-limited because a bolt under sustained load relaxes if the material creeps. Above roughly 650°C, creep relaxation — not tensile strength — controls joint integrity, and an upgrade to a gamma-prime alloy or a design change is required.
Price Reference (2026, EXW Shanghai)
| Form | Nimonic 90 | Inconel 718 | Comment |
|---|---|---|---|
| Round bar | \$65-95/kg | \$38-60/kg | Cobalt content drives the gap |
| Plate / sheet | \$70-105/kg | \$42-66/kg | Thickness and width add spread |
| Forging / ring | Quote by drawing | Quote by drawing | Yield and NDT drive cost |
| Wire | \$80-130/kg | \$48-80/kg | Drawing and cleaning dominate |
Table note: Reference range only — floats with LME nickel price, and Nimonic 90 additionally tracks cobalt levels. 2026, EXW Shanghai, USD/kg. Confirm against current raw-material levels, size and certification requirements.
Standard Index
| Standard | Title / scope | Covers | Form |
|---|---|---|---|
| ASTM B637 | Precipitation-hardening and cold-worked Ni alloy bar, forging | Composition + mechanical | bar, forging |
| AMS 5662 | 718 solution-treated and aged bar, forging, ring | Mechanical + heat treatment | bar, forging |
| AMS 5663 | 718 solution-treated and aged bar, forging, ring (variant) | Mechanical + heat treatment | bar, forging |
| AMS 5596 | 718 sheet, strip, plate | Mechanical + heat treatment | sheet, plate |
| BS HR 501 | Nimonic 90 bar and forging (verify current edition) | Composition + mechanical | bar, forging |
| BS HR 502 | Nimonic 90 sheet and strip (verify current edition) | Composition + mechanical | sheet, strip |
| ASTM E8/E8M | Tension testing of metallic materials | Test method | — |
| ASTM E139 | Conducting creep, creep-rupture and stress-rupture tests | Test method | — |
| ASTM E1476 | Standard guide for metals identification (PMI) | Test method | — |
How We Verify These Grades Before Shipment
Both alloys are expensive and both are targets for substitution, so our release process is explicit:
- OES verification of cobalt and niobium. For Nimonic 90 we confirm cobalt within 15-21% and titanium and aluminium levels consistent with the gamma-prime chemistry; for 718 we confirm niobium within 4.75-5.50% with cobalt at or below 1%. A "Nimonic 90" delivery showing no cobalt is not Nimonic 90.
- Hardness and condition confirmation. The supply condition (aged or as-rolled) is confirmed against the purchase order, because the buyer's machining strategy depends on it and the design properties depend on the final age.
- Certificate reconciliation. EN 10204 3.1 or 3.2 documentation is matched line by line against the stencilled heat number, and the reconciliation is photographed into the batch record.
A substitution case worth noting: material offered as Nimonic 90 for a furnace fixture came in with Co 0.4%, Ti 2.4%, Al 1.4% — a gamma-prime chemistry, but without the cobalt that stabilises it for the intended temperature. It would have been acceptable on a drawing that specified only "nickel-chromium-titanium alloy" and would have crept early in service. Specification by UNS number plus the correct British or AMS document prevents exactly this. See our related technical guides and alloy technical knowledge center for more on verification practice.
FAQ
Q1: Which alloy is stronger at 800°C, Nimonic 90 or Inconel 718?
Nimonic 90 is far stronger at 800°C. Inconel 718's gamma-double-prime strengthening phase transforms to the delta phase above roughly 650°C and its strength falls steeply, while Nimonic 90's gamma-prime phase remains stable and retains creep and stress-rupture capability to approximately 815-920°C depending on stress level.
Q2: Why is Inconel 718 so much more expensive than Nimonic 90?
The opposite is true — Nimonic 90 is the more expensive grade, typically 1.4-2 times the price of 718 per kilogram, because it contains 15-21% cobalt. 718 achieves its strength with niobium and molybdenum, which are cheaper additions, and it also contains roughly 18% iron, reducing the nickel requirement.
Q3: Is Nimonic 90 easy to weld?
No. Nimonic 90 is sensitive to strain-age cracking and welded joints do not recover the parent material's creep properties. Most components are forged, rolled or cast. Inconel 718, by contrast, is one of the most weldable high-strength superalloys and is routinely welded in the solution-treated condition and aged afterwards.
Q4: Which alloy has higher yield strength at room temperature?
Inconel 718, by a clear margin: 1030 MPa minimum per AMS 5662 and ASTM B637, against roughly 750-850 MPa typical for aged Nimonic 90. This room-temperature advantage reverses at high temperature and is not a sound basis for selecting a hot-section material.
Q5: Can Inconel 718 be used at 700°C?
Only with caution and never as a long-term load-bearing material. Its gamma-double-prime strengthening is unstable in that range, strength drops significantly and creep relaxation becomes the controlling mechanism. Where sustained load at 700°C and above must be carried, a gamma-prime alloy such as Nimonic 90 should be used instead.
Q6: What heat treatment does Inconel 718 require?
The standard schedule is solution treatment at roughly 955-980°C followed by a two-step age: hold at 720°C for 8 hours, furnace cool to 620°C, then hold at 620°C for 8 hours. This is the schedule referenced by AMS 5662 and AMS 5663, and it is what produces the 1240 MPa tensile and 1030 MPa yield minimum values.
Q7: What are the UNS numbers?
Nimonic 90 is UNS N07090, also known as Werkstoff 2.4632. Inconel 718 is UNS N07718. Both should appear on the purchase order and on the EN 10204 certificate alongside the governing specification.
Q8: Can I substitute 718 for Nimonic 90 to save cost?
Only below about 650°C. In colder duties 718 is often the better engineering and commercial choice, with higher proof strength and much better weldability. In a hot, creep-limited duty the substitution will fail in service even though the room-temperature data looks superior.
Q9: Which grade is used for turbine blades?
Nimonic 90 and its gamma-prime relatives are the traditional blade materials because blades are creep-limited in the hot gas path. Modern high-pressure blades often use more highly alloyed single-crystal or directionally solidified grades, but Nimonic 90 remains in service for many industrial and smaller aero applications.
Q10: How do I verify I received the correct grade?
Ask for OES analysis of cobalt, niobium, titanium and aluminium — cobalt at 15-21% with no niobium confirms Nimonic 90, while niobium at 4.75-5.50% with cobalt at or below 1% confirms 718 — and confirm the supply condition and aging state by hardness and certificate reconciliation against the stencilled heat number.
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Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier
Email: sales@hangboalloy.com | WhatsApp (Lisa): +86 13611656360 | www.nickel-alloy.com
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