GH738 in Power Generation: Combustion Components & High-Temperature Fasteners

Material selection for gas turbines and industrial power generators demands a precise balance between high-temperature strength, fatigue resistance, and environmental stability. GH738 (UNS N07001 / Waspaloy)​ is a precipitation-hardening nickel-based superalloy specifically engineered for these extreme conditions. With a service ceiling up to 815°C (1500°F) in rotating parts, it outperforms many generic stainless steels and lower-grade alloys in combustion zones. Shanghai COCESS Special Alloys Co., Ltd​ supplies GH738 in bar, forging stock, ring rolls, and wire forms, fully compliant with ASTM B637 and AMS specifications, ensuring the microstructural integrity required for critical power generation components.

Metallurgical Design and Chemical Composition

GH738 achieves its strength through a high volume fraction of gamma-prime (γ') precipitates, Ni₃(Al, Ti), distributed within a solid-solution strengthened matrix. The high cobalt content (12-15%) is critical for stabilizing the gamma prime phase and enhancing high-temperature creep resistance.

Chemical Composition (Weight %):

• Nickel (Ni): Balance (Approx. 55-58%)

• Chromium (Cr): 18.0 – 21.0% (Oxidation and sulfidation resistance)

• Cobalt (Co): 12.0 – 15.0% (Solid solution strengthening, γ' stability)

• Molybdenum (Mo): 3.5 – 5.0% (Solid solution strengthening)

• Titanium (Ti): 2.75 – 3.25% (Primary γ' former)

• Aluminum (Al): 1.20 – 1.60% (Primary γ' former)

• Iron (Fe): ≤ 2.0%

• Carbon (C): 0.03 – 0.10% (Carbide formation)

• Boron (B): 0.003 – 0.010% (Grain boundary strengthening)

• Zirconium (Zr): 0.02 – 0.08% (Grain boundary strengthening)

Physical and Mechanical Properties

The alloy exhibits excellent retention of properties at elevated temperatures, making it suitable for continuous service up to 650°C-815°C in critical stress-bearing parts.

Physical Constants:

• Density: 8.22 g/cm³ (0.297 lb/in³)

• Melting Range: 1330 – 1360 °C (2425 – 2475 °F)

• Elastic Modulus (20°C): ~214 GPa (31 x 10³ ksi)

• Coefficient of Thermal Expansion (20-100°C): 12.47 x 10⁻⁶/°C

Typical Mechanical Properties (Fully Heat Treated Condition):

• Room Temp Tensile Strength: 1200 – 1380 MPa (174 – 200 ksi)

• Room Temp Yield Strength (0.2%): 800 – 895 MPa (116 – 130 ksi)

• Room Temp Elongation: 15 – 25%

• Hardness: 32 – 42 HRC

• 815°C (1500°F) Tensile Strength: ~400 MPa (58 ksi)

• 815°C (1500°F) Stress Rupture: Exceeds 100 hours at 390 MPa (approx. 57 ksi)

Application in Combustion Components

In power generation gas turbines, the combustion section and early stages of the turbine experience the highest temperatures and thermal gradients. GH738 is specified for:

• Combustor Casings & Transitions: Where high-temperature oxidation resistance and structural stability are mandatory.

• Turbine Discs (Rotors): The alloy's superior low-cycle fatigue (LCF) life at 650°C-760°C makes it a standard for discs holding turbine blades.

• Stationary Seals & Shrouds: Components requiring dimensional stability under thermal cycling.

  Its ability to resist oxidation (low mass gain rate at 900°C-1000°C) and maintain strength in the 760°C-870°C range ensures long component life in land-based power plants.

High-Temperature Fasteners and Hardware

GH738 is a premier material for critical fasteners in turbine assemblies, used for bolts, nuts, and studs operating up to 730°C-815°C.

• Stress Rupture Strength: Fasteners made from GH738 maintain high preload tension and resist stress relaxation better than Alloy 718 at temperatures exceeding 600°C.

• Fatigue Performance: The alloy provides reliable performance in threaded fasteners subjected to vibration and thermal expansion cycles.

• Manufacturing Form: Supplied as hot-rolled or forged bar, subsequently machined into precision fasteners, often requiring the standard triple-step heat treatment (Solution + Stabilization + Aging) to achieve specified mechanical properties.

Supply Standards and Availability

Shanghai COCESS provides GH738 (Waspaloy) materials strictly according to the following key standards:

• Bars, Forgings, Rings: ASTM B637, AMS 5708, AMS 5706

• Sheet, Plate, Strip: AMS 5544

• Wire: AMS 5828

All materials are supplied with full traceability, Ultrasonic Testing (UT) options where applicable, and EN 10204 3.1/3.2 certification. For technical datasheets, current stock sizes, or inquiries regarding GH738 for your gas turbine or power generation projects, contact Shanghai COCESS Special Alloys Co., Ltd.

Website: https://en.cocessalloys.com
Email: sales@cocessalloys.com