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 fabrication, welding, and machining. 2. Solution Annealed & Aged (STA): For direct installation where high strength is required without further heat treatment.

Most pipe is supplied in Solution Annealed condition; final aging is done post-fabrication. Direct-supplied STA pipe is for non-welded assemblies.

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):
• 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 over other PH superalloys).
• Good Oxidation & Corrosion Resistance up to ~700°C.
• High Fatigue Strength and Fracture Toughness.

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

Key Standards (Pipe)

ASTM B637 (Seamless Pipe and Tube - Heat Treated)
ASTM B670 (Seamless Pipe and Tube - Solution Heat Treated, for later aging)
AMS 5589 (Aerospace Seamless Pipe)

ASTM B637 covers aged material; ASTM B670 covers solution-annealed material for fabrication.

Heat Treatment (Aging)

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

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

Common Sizes & Forms

OD Range: Typically 1/8" to 8" NPS for seamless.
Wall Thickness: Light wall to heavy wall schedules.
Forms: Primarily Seamless (SMLS). Welded forms are less common due to the high-strength requirement.

Often used for machined components, high-pressure manifolds, and hydraulic lines rather than large-diameter process piping.

Typical Applications

• Aerospace: Engine fuel and hydraulic piping, bleed air ducts, afterburner liners.
• Oil & Gas: High-strength downhole tubing, tool joints, wellhead components for sour service.
• Power Generation: High-pressure steam lines, turbine bypass systems.
• High-Performance Racing: Turbocharger housings, exhaust systems.

The dominant material for critical high-strength piping in jet engines and demanding downhole environments.