Material Family

Nickel-Chromium-Niobium-Molybdenum Precipitation-Hardenable Superalloy

Gains its extreme strength from a controlled aging heat treatment.

Common Supply Conditions

1. Solution Annealed (Soft Condition): For all machining, forging, and welding. 2. Solution Treated & Aged (STA): Directly supplied in the final high-strength condition.

Most bar for fabrication is supplied Solution Annealed; final aging is done post-machining. STA bar is for parts requiring no further heat treatment.

Common Forms (Bar)

Rounds, Hexagons, Squares, Forging Billet, Near-Net-Shape Forgings. Available as hot-rolled, forged, or cold-drawn.

The most common form is round bar for machining. Forging billet is used for critical aerospace components.

Chemical Composition (Typical wt.%)

Ni: 50.0 - 55.0 (Balance)
Cr: 17.0 - 21.0
Fe: Remainder (~18.5)
Nb (+Ta): 4.75 - 5.50
Mo: 2.80 - 3.30
Ti: 0.65 - 1.15
Al: 0.20 - 0.80

Niobium (Nb) is the primary strengthening element for forming the γ" phase. Iron (Fe) content improves workability and reduces cost.

Mechanical Properties (Typical)

Solution Annealed (As-Supplied):
• Tensile: 690 - 965 MPa
• Yield: 275 - 550 MPa
• Elongation: 25 - 45%
After Full Aging (Aged - AMS 5662):
• Tensile: ≥ 1240 MPa
• Yield: ≥ 1035 MPa
• Elongation: ≥ 12%

The dramatic increase in strength after aging is the core value. Strength is more than double that of solid-solution alloys like 625.

Physical Properties

Density: 8.19 g/cm³
Melting Range: 1260 - 1336 °C
Effective Service Temp: -250°C to 700°C (-420°F to 1300°F)

The optimal strength range is up to ~650°C (1200°F).

Key Performance Attributes

• Ultra-High Strength & Excellent Creep Rupture Strength after aging.
• Superior Resistance to Strain-Age Cracking After Welding (a major fabrication advantage).
• Good Oxidation & Corrosion Resistance up to ~700°C.
• High Fatigue Strength and Fracture Toughness.

The premier alloy for high-stress, moderate-temperature components requiring weldability.

Key Standards (Bar)

ASTM B637 (Heat-Treated Bar), AMS 5662 (Aerospace Bar, Heat Treated - most common), AMS 5663 (Solution Heat Treated Bar, for later aging)

AMS 5662 is the leading aerospace procurement standard for aged bar. AMS 5663 is for solution-annealed bar.

Heat Treatment (Aging)

Standard aging: 720°C for 8 hours, furnace cool at 55°C/hr to 620°C, hold 8 hours, air cool. For Solution Annealed bar, this is performed after all machining is complete.

This two-step aging treatment is essential to develop the full γ" and γ' precipitate strengthening.

Machinability & Fabrication

Machinability (Annealed): ~20% (more difficult than 625). Highly abrasive and work-hardening. Requires rigid tooling, positive rake carbide inserts, and constant feed.
Machinability (Aged): Extremely difficult; should be avoided. All heavy machining must be done in the soft, solution-annealed condition.
Weldability: Good in the annealed condition using ERNiFeCr-2 filler.

The "machine soft, then age harden" sequence is critical for manufacturing complex parts.

Typical Bar Applications

• Aerospace: Jet engine turbine discs, shafts, blades, casings, fasteners, landing gear components.
• Oil & Gas: High-strength downhole tools, wellhead components, valve bodies for sour service.
• Power Generation: Turbine blades, bolts, and high-stress fasteners.
• High-Performance Automotive: Turbocharger components, valves, racing engine parts.

The dominant material for critical high-strength rotating and structural components across advanced industries.