AMS 5666 - Nickel 625 (UNS N06625) Bars, Forgings & Rings (Annealed)
What is AMS 5666?
AMS 5666 is the SAE International aerospace material specification for Nickel 625 (UNS N06625), a corrosion and heat-resistant nickel-chromium-molybdenum-niobium alloy, supplied in the forms of bars, forgings, and rings in the annealed condition.
The nominal composition is 62Ni-21.5Cr-9.0Mo-3.65Nb. Nickel 625 is a solid-solution-strengthened alloy; its strength is not derived from precipitation hardening but from the combined solid-solution effect of molybdenum and niobium in the nickel-chromium matrix.
In the annealed condition per AMS 5666, Nickel 625 achieves a minimum tensile strength of 120 ksi (827 MPa) and a minimum yield strength of 60 ksi (414 MPa) with a minimum elongation of 30%.
AMS 5666 is the standard procurement specification for Nickel 625 round bar, flat bar, and forging stock used in chemical processing equipment, marine and submarine propulsion components, exhaust systems, flare stacks, and high-temperature corrosion-resistant aerospace hardware where resistance to aqueous corrosion, pitting, crevice attack, and oxidizing acids is the primary design driver.
AMS 5666 Available Forms and Stocked Sizes
AMS 5666 covers Nickel 625 in long and forged product forms. The SAE/AMS product form definitions are:
Solid section of uniform cross-section (round, rectangular, square, or hexagonal); length significantly greater than cross-section dimension; supplied hot-rolled or cold-finished in random or cut lengths
A part or starting stock shaped by controlled deformation of a heated metal billet under compressive force (hammering or pressing); forgings exhibit improved grain flow and mechanical properties compared to bar stock of equivalent cross-section
A toroidal (donut-shaped) forging produced by a ring-rolling process or open-die forging; used for flanges, sealing rings, structural ring components, and pressure vessel closures
Fighter Jet Metals supplies Nickel 625 per AMS 5666 in round bar from 0.125″ to 14.00″ diameter, flat bar in various cross-sections, forging stock and billets to customer requirement, and rolled or forged ring forms to customer drawings.
All material is supplied in the annealed condition with full certified mill test reports (CMTR) and certificates of conformance.
Applications of AMS 5666
Aerospace & Gas Turbine Applications
- Jet engine exhaust system components – collectors, tailpipes, and afterburner housings operating in high-temperature, oxidizing combustion gas environments
- Engine nacelle structural components and fire-barrier hardware requiring combined heat and corrosion resistance
- Thrust reverser components and cascade vanes exposed to high-velocity exhaust gas
- Transition duct and transition liner components between compressor and combustion sections of gas turbines
- Aircraft fuel manifold fittings and hydraulic line components requiring chloride SCC resistance in marine aircraft
- Bellows, flexible joints, and expansion joints in aircraft exhaust systems
- Gas turbine reaenerator components for industrial turbines in corrosive service environments
Chemical Processing, Oil & Gas, and Industrial Applications
- Chemical plant reactor vessels, agitators, and pressure vessels handling oxidizing acids, hydrochloric acid, and mixed acid environments
- Flare stack tips and components exposed to corrosive combustion gases and elevated temperatures in petroleum refining
- Pollution control equipment – flue gas desulfurization (FGD) system components, scrubber hardware, and gas handling equipment
- Nuclear power plant structural components requiring combined corrosion resistance and radiation stability in coolant environments
- Oil and gas wellhead bars and forging stock for downhole tools operating in sour gas (H₂S + CO₂) environments
- Subsea equipment components requiring resistance to seawater crevice corrosion and cathodic disbondment
- Heat exchangers in chloride-containing environments where stainless steels are susceptible to pitting failure
Defense & Naval Applications
- Submarine propulsion motor shafts and structural components requiring resistance to seawater corrosion under sustained mechanical load
- Submarine auxiliary propulsion motor hardware – bars and forging stock for components requiring both seawater corrosion resistance and strength
- Marine gas turbine exhaust hardware for naval vessels operating in salt-laden atmospheres
- Shipboard heat exchanger components in seawater cooling systems
- Torpedo tube liner components and pressure hull penetration fittings exposed to seawater
- Defense aircraft exhaust system hardware where corrosion resistance in austere environments is required
Chemical Composition - AMS 5666
The following chemical composition limits apply to Nickel 625 (UNS N06625) per AMS 5666:
| Element | Symbol | Minimum % | Maximum % |
|---|---|---|---|
| Nickel | Ni | 58.0 | Balance |
| Chromium | Cr | 20.0 | 23.0 |
| Iron | Fe | - | 5.0 |
| Niobium + Tantalum | Nb+Ta | 3.15 | 4.15 |
| Molybdenum | Mo | 8.0 | 10.0 |
| Cobalt | Co | - | 1.00 |
| Titanium | Ti | - | 0.40 |
| Aluminum | Al | - | 0.40 |
| Carbon | C | - | 0.10 |
| Manganese | Mn | - | 0.50 |
| Silicon | Si | - | 0.50 |
| Phosphorus | P | - | 0.015 |
| Sulfur | S | - | 0.015 |
Molybdenum (8.0–10.0%) is the most critical alloying element in Nickel 625 for corrosion resistance.
Molybdenum provides outstanding resistance to pitting corrosion, crevice corrosion, and reducing acids, particularly hydrochloric and phosphoric acid environments. Niobium + Tantalum (3.15–4.15%) contributes solid-solution strengthening to the nickel-chromium matrix alongside molybdenum – the combined Mo and Nb solid-solution effect is what provides Nickel 625 its useful strength without any precipitation heat treatment.
Chromium (20.0–23.0%) provides resistance to oxidizing acid environments and high-temperature oxidation.
Nickel (58.0% minimum) provides the fundamental resistance to chloride stress corrosion cracking (SCC) that makes Nickel 625 superior to stainless steels and many other alloys in marine and chemical environments.
Iron is limited to 5.0% maximum – in contrast to Inconel 718 where iron is the balance element, Nickel 625 is a true nickel-base alloy with nickel as the balance, which is fundamental to its corrosion performance.
Mechanical Properties - AMS 5666
Minimum mechanical properties required by AMS 5666 for Nickel 625 bars, forgings, and rings in the annealed condition:
| Property | Imperial | Metric |
|---|---|---|
| Tensile Strength (min) | 120,000 psi (120 ksi) | 827 MPa |
| Yield Strength, 0.2% offset (min) | 60,000 psi (60 ksi) | 414 MPa |
| Elongation in 2 in. (min) | 30% | 30% |
Elevated Temperature Properties - AMS 5666
The elevated temperature properties below are representative typical values for Nickel 625 in the annealed condition from published literature (Special Metals Technical Bulletin).
AMS 5666 specifies room-temperature minimums in the annealed condition only.
| Temperature | Tensile Strength (typical) | Yield Strength (typical) | Elongation (typical) |
|---|---|---|---|
| Room Temp (70°F / 21°C) | 135 ksi (931 MPa) | 75 ksi (517 MPa) | 47% |
| 400°F (204°C) | 130 ksi (896 MPa) | 68 ksi (469 MPa) | 44% |
| 800°F (427°C) | 124 ksi (855 MPa) | 55 ksi (379 MPa) | 43% |
| 1000°F (538°C) | 118 ksi (814 MPa) | 50 ksi (345 MPa) | 44% |
| 1200°F (649°C) | 110 ksi (758 MPa) | 45 ksi (310 MPa) | 47% |
| 1400°F (760°C) | 85 ksi (586 MPa) | 35 ksi (241 MPa) | 55% |
| 1600°F (871°C) | 62 ksi (427 MPa) | 27 ksi (186 MPa) | 60% |
Physical Properties - AMS 5666
| Property | Value (Imperial) | Value (Metric) |
|---|---|---|
| Density | 0.305 lb/in³ | 8.44 g/cm³ |
| Melting Range | 2350°F–2460°F | 1290°C–1350°C |
| Modulus of Elasticity | 29.8 × 10⁶ psi | 205 GPa |
| Thermal Conductivity | 6.0 BTU/(hr·ft·°F) | 10.4 W/(m·K) |
| Thermal Conductivity (1800°F) | 8.5 BTU/(hr·ft·°F) | 14.7 W/(m·K) |
| Coefficient of Thermal Expansion | 7.4 × 10⁻⁶ /°F | 13.3 × 10⁻⁶ /°C |
| Specific Heat | 0.098 BTU/(lb·°F) | 410 J/(kg·K) |
| Max Service Temperature (Mechanical Load) | ~1500°F | ~816°C |
| Max Service Temperature (Oxidation Resistance) | 1800°F | 982°C |
| Melt Practice | EF-AOD or VIM + VAR or ESR | - |
AMS 5666 vs AMS 5599 vs AMS 5581 - Which Specification Do You Need?
All three are SAE AMS specifications for Nickel 625 (UNS N06625) in the annealed condition, but they differ in product form and intended application:
| Feature | AMS 5599 | AMS 5869 | AMS 5879 |
|---|---|---|---|
| Alloy | Nickel 625 (UNS N06625) | Nickel 625 (UNS N06625) | Nickel 625 (UNS N06625) |
| Product Forms | Bars, Forgings, Rings | Sheet, Strip, Plate | Seamless Tubing |
| Condition | Annealed | Annealed | Annealed |
| Tensile Min | 120 ksi (827 MPa) | 120 ksi (827 MPa) | See current revision |
| Yield Strength (min) | 60 ksi (414 MPa) | 60 ksi (414 MPa) | See current revision |
| Elongation (min) | 30% | 30% | See current revision |
| Primary Use | Machined components, forged parts, flanges, rings, and structural hardware requiring bar or forging stock | Sheet metal fabrications, stampings, exhaust panels, and formed aerospace components | Heat exchanger tubes, condenser tubing, propulsion system lines, and fluid system tubing |
| Key Advantage | Optimum strength-to-weight for machined and forged corrosion-resistant hardware | Formability and weldability for thin-gage aerospace and chemical processing sheet metal | Wall thickness control and surface finish for fluid system and heat transfer applications |
Specify AMS 5666 when procuring bar stock for machining corrosion-resistant hardware, or when the engineering drawing requires bar, forging stock, or ring forms.
Specify AMS 5599 when procuring flat-rolled material for sheet metal fabrication, cladding, or formed components.
Specify AMS 5581 when procuring seamless tubing for fluid systems, heat exchangers, or propulsion system lines.
Approved Mill Producers
Fighter Jet Metals sources AMS 5666 Nickel 625 bars, forgings, and ring stock from AS9100D-certified mill producers.
All material is supplied with full certified mill test reports (CMTR), heat/lot numbers, chemical analysis reports, and mechanical test certifications traceable to the originating mill heat and melt practice (EF-AOD+VAR or VIM+VAR confirmed on CMTR).
AMS 5666 Machining Guidelines
Nickel 625 in the annealed condition per AMS 5666 is one of the more difficult nickel alloys to machine.
Unlike precipitation-hardened alloys where hardness correlates with machinability, the challenge with Nickel 625 is its extreme toughness, work-hardening tendency, and tendency to generate heat at the cutting edge:
- Work hardening: Nickel 625 work-hardens significantly faster than austenitic stainless steels – any dwell in the cut causes rapid work hardening that dulls tooling and promotes premature tool failure
- Toughness: High elongation (~47% typical) and ductility make chip breaking difficult; tough, stringy chips are characteristic of Nickel 625 machining
- Heat generation: Low thermal conductivity means heat concentrates at the tool-workpiece interface rather than dissipating into the chip
Machining guidelines for annealed AMS 5666 bar stock:
- Cutting speeds: 40–80 SFM for carbide tooling in turning; lower speeds required versus stainless steels
- Feeds: Use aggressive, consistent feeds – light cuts or intermittent contact causes severe work hardening; maintain continuous engagement
- Tooling: Premium carbide grades (PVD TiAlN or AlTiN coated); positive-rake geometry essential; sharp edges mandatory – dull tooling causes immediate work-hardening failure
- Coolant: High-pressure flood coolant required at all times; sulfurized or chlorinated cutting oils provide best tool life in roughing applications
- Depth of cut: Use the maximum depth of cut consistent with setup rigidity – this keeps the tool below the work-hardened layer from the previous pass
- Turning: Rigid setup and minimal overhang; steady rest required for long slender bar stock; avoid interrupted cuts where possible
- Drilling: Premium cobalt or solid carbide drills; high-pressure through-tool coolant required for deep holes; peck drilling with full retract for hole depths beyond 3× diameter
- Chip control: Chip breakers critical for automated machining; stringy chips cause re-cutting and tool breakage
Weldability of AMS 5666
Nickel 625 per AMS 5666 is one of the most readily weldable nickel alloys.
Its solid-solution-strengthened structure does not contain the precipitation-hardening phases that cause strain-age cracking in alloys like Inconel 718 or Waspaloy, making welding straightforward in most applications:
- TIG (GTAW): Primary welding process for Nickel 625 bar and forging assemblies; argon shielding required; filler metal ERNiCrMo-3 (Alloy 625 matching filler) recommended for full corrosion resistance in the weld zone
- MIG (GMAW): Used for higher deposition fabrications; Ar + He shielding gas; ERNiCrMo-3 filler wire
- Plasma Arc (PAW): Used for precision welds on thin-section Nickel 625 components in aerospace exhaust fabrications
- Electron Beam (EBW): Used in vacuum environments for critical aerospace structural welds requiring minimal heat input and narrow heat-affected zone
- Weld overlay / cladding: Nickel 625 (ERNiCrMo-3 or ENiCrMo-3) is extensively used as a weld overlay on carbon steel and stainless steel substrates to provide corrosion protection in chemical plant and oil and gas equipment – a unique application that sets Nickel 625 apart from alloys like Inconel 718
- Pre-weld condition: No pre-heating required for most applications; welding in the annealed condition is preferred
- Post-weld heat treatment: Not required for most corrosion-resistant applications; solution annealing at 1700°F (927°C) or above may be performed to restore maximum corrosion resistance in the weld heat-affected zone for the most demanding chemical processing services
- Contrast with Inconel 718: Nickel 625 welding is significantly simpler than Inconel 718 (AMS 5662/5663) – no risk of strain-age cracking, no mandatory post-weld heat treatment, and matching ERNiCrMo-3 filler is widely available
Melt Practice - AMS 5666
Nickel 625 per AMS 5666 may be produced by two primary melt routes.
The first is an Electric Furnace (EF) charge followed by Argon Oxygen Decarburization (AOD) refining, which removes carbon, sulfur, and other volatile elements under an argon-oxygen atmosphere at reduced cost compared to vacuum processing.
The second is Vacuum Induction Melting (VIM), which establishes tight chemistry control in a vacuum environment and removes dissolved oxygen and nitrogen.
Either primary melt is typically followed by secondary remelting via Vacuum Arc Remelting (VAR) or Electroslag Remelting (ESR) to improve ingot homogeneity, reduce segregation, and produce a consistent grain structure from center to surface.
For critical aerospace applications – including engine exhaust hardware, nacelle components, and structural parts requiring high fatigue resistance – VIM+VAR or EF-AOD+VAR is the standard melt practice.
Always confirm the melt route on the certified mill test report before procurement.
AMS 5666 Cross-Reference Specifications
Sheet, Strip & Plate
Nickel 625 flat-rolled specifications for aerospace, chemical processing, and marine sheet metal fabrication in the annealed condition.
Tubing
Nickel 625 seamless tubing specification for heat exchangers, propulsion systems, and high-temperature corrosion-resistant fluid handling applications.
BOEING SPECIFICATIONS
Boeing and McDonnell Douglas material and process specifications for Nickel 625 in aircraft exhaust systems, engine nacelles, and structural aerospace components.
Gulfstream Specifications
Gulfstream material specification for Nickel 625 in aircraft engine nacelles, exhaust systems, and high-temperature structural applications.
Safran / Honeywell Specifications
Safran and Honeywell Engineering Material Specification for Nickel 625 in gas turbine engine components, heat shields, and aerospace exhaust hardware.
AIRBUS SPECIFICATIONS
Airbus process specification for Nickel 625 in aircraft engine, structural tubing, and high-temperature aerospace component applications.
Trade Names and Equivalent Designations
Nickel 625 per AMS 5666 is known by many trade names and equivalent designations across different standards systems:
| Designation | System | Notes |
|---|---|---|
| Inconel 625 | Trade name | Special Metals / Precision Castparts registered trademark - most widely used commercial name |
| Nickel 625 / Nickel Alloy 625 | Common name | Generic material designation used in procurement |
| ASTM B446 | ASTM specification | Rod, bar, and wire per ASTM system |
| ASTM B564 | ASTM specification | Forgings per ASTM system |
| AMS 5666 | SAE AMS | Annealed bars, forgings, and rings |
| UNS N06625 | UNS (Unified Numbering System) | Standard material identifier in North America |
| DIN 2.4856 / W.Nr. 2.4856 | Werkstoff Nr. (German) | European material number designation |
| NiCr22Mo9Nb | DIN/EN alloy designation | German/European compositional shorthand |
| AMS 5599 | SAE AMS | Annealed sheet, strip, and plate |
| AMS 5581 | SAE AMS | Annealed seamless tubing |
Why Source AMS 5599 from Fighter Jet Metals?
Full mill certifications on every order
Heat number, lot number, chemical analysis, and mechanical test reports included with every shipment
Complete heat-lot traceability
Full chain-of-custody documentation from mill to your door
AS9100-certified aerospace sourcing
Material from AS9100-certified mills only
OEM specification support
Stock and supply to Boeing BMS/DMS, Gulfstream GMS, Honeywell EMS, Safran DMD, and Airbus AIPS requirements
In-house processing
Plate saw cutting, shearing, and laser cutting available; custom-cut sizes to your dimensions
Same-day quote response
Competitive pricing with rapid quote turnaround
Certified Material for Critical Service
Materials supplied in 6Al-4V titanium must meet strict aerospace certification and traceability requirements. Fighter Jet Metals supports sourcing across a wide range of AMS, MIL, and OEM specifications, ensuring compliance with industry standards.
All material is supplied with full mill certifications, complete heat-lot traceability, and detailed documentation. This ensures reliability and suitability for safety-critical aerospace, defense, and high-performance engineering applications.