Hangbo Alloy Group
Shanghai · Est. 2012
UNS N07740H / W.Nr. 2.4663 — Advanced ultra-supercritical (A-USC) power generation superalloy with outstanding creep-rupture strength and steam oxidation resistance up to 760°C.
Inconel 740H (UNS N07740H / W.Nr. 2.4663) is a precipitation-hardened nickel-chromium-cobalt superalloy specifically developed for Advanced Ultra-Supercritical (A-USC) power generation applications. Unlike general-purpose superalloys such as Inconel 718 or Waspaloy, Inconel 740H was engineered from the ground up to withstand the extreme combination of high temperature (up to 760°C), high pressure (350+ bar steam), and long service life (100,000+ hours) required by next-generation coal-fired and combined-cycle power plants.
The alloy achieves its exceptional creep-rupture strength through a high volume fraction of ordered gamma-prime (Ni3(Al,Ti)) precipitates, combined with substantial solid-solution strengthening from cobalt, chromium, and molybdenum. The "H" in 740H denotes a modified composition with optimized carbon, boron, and zirconium levels to improve thermal stability and resistance to topologically close-packed (TCP) phases during long-term exposure at 700-760°C.
What distinguishes Inconel 740H from competing A-USC candidate materials such as Inconel 617, Haynes 230, and Nimonic 263 is its superior creep-rupture strength at the target operating temperature. At 750°C, 740H delivers approximately 100 MPa stress for 100,000-hour rupture life — roughly 60% higher than Inconel 617 and more than double that of Haynes 230. This strength advantage allows thinner tube walls, reduced material consumption, and improved heat transfer efficiency in boiler designs.
The alloy's high chromium content (23-25%) provides excellent steam oxidation resistance, forming a protective Cr2O3-Al2O3 duplex oxide scale that limits metal loss in high-velocity steam environments. Controlled aluminum and titanium additions enhance this protection while also serving as the primary strengthening mechanism. The cobalt content improves solid-solution strengthening and reduces the rate of gamma-prime coarsening at elevated temperatures.
Processing Inconel 740H requires careful control due to its high gamma-prime content. The alloy is typically vacuum induction melted (VIM) followed by vacuum arc remelting (VAR) or electroslag remelting (ESR) to achieve the cleanliness required for boiler tubing. Hot working is performed in the 1050-1150°C range, with solution annealing at 1120-1150°C to dissolve all strengthening phases before the final aging treatment. Cold working is limited in the aged condition due to high strength and rapid work-hardening.
At Hangbo Alloy Group, Inconel 740H is supplied in seamless tubes, pipes, bars, and forgings per ASTM B983, ASME Code Case 2704, and custom A-USC project specifications. We support power plant OEMs, EPC contractors, and research institutions with material supply, heat treatment certification, and full traceability documentation for critical boiler applications.
The chemistry of Inconel 740H is carefully balanced to maximize creep-rupture strength while maintaining thermal stability and oxidation resistance. The aluminum and titanium content is optimized to produce a high volume fraction of gamma-prime (typically 20-25%) without promoting excessive TCP phase formation during long-term exposure. Carbon, boron, and zirconium are controlled to improve grain boundary strength and creep ductility.
| Element | Min % | Max % |
|---|---|---|
| Nickel (Ni) | 47.0 | 52.0 |
| Chromium (Cr) | 23.0 | 25.0 |
| Cobalt (Co) | 15.0 | 20.0 |
| Aluminum (Al) | 1.35 | 1.85 |
| Titanium (Ti) | 1.35 | 1.85 |
| Niobium (Nb) | 0.50 | 2.00 |
| Molybdenum (Mo) | 0.50 | 2.00 |
| Iron (Fe) | — | 3.00 |
| Manganese (Mn) | — | 1.00 |
| Silicon (Si) | — | 1.00 |
| Carbon (C) | 0.03 | 0.08 |
| Boron (B) | 0.001 | 0.006 |
| Zirconium (Zr) | — | 0.05 |
| Sulfur (S) | — | 0.015 |
| Phosphorus (P) | — | 0.015 |
Inconel 740H has a face-centered cubic (FCC) austenitic matrix in the solution-annealed condition. Upon aging, a high volume fraction of coherent gamma-prime precipitates forms uniformly throughout the matrix, producing the exceptional creep strength that distinguishes this alloy. The physical properties reflect its high nickel and cobalt content, with moderate thermal expansion and relatively low thermal conductivity compared to ferritic steels.
| Property | Value | Unit |
|---|---|---|
| Density | 8.15 | g/cm³ |
| Melting Range | 1280 - 1345 | °C |
| Specific Heat (21°C) | 420 | J/kg·K |
| Thermal Conductivity (21°C) | 11.2 | W/m·K |
| Electrical Resistivity (21°C) | 1.30 | μΩ·m |
| Modulus of Elasticity (21°C) | 210 | GPa |
| Mean CTE (21-760°C) | 15.5 | μm/m·°C |
| Curie Temperature | < -196 | °C |
Mechanical properties of Inconel 740H depend strongly on heat treatment condition. The standard heat treatment for A-USC applications consists of solution annealing at 1120-1150°C followed by a two-step age: 850°C for 4-8 hours, then 750°C for 16-24 hours. This produces the optimum combination of tensile strength, creep resistance, and thermal stability for long-term service at 700-760°C.
| Property | Value |
|---|---|
| Tensile Strength | ≥ 1100 MPa (160 ksi) |
| Yield Strength (0.2% offset) | ≥ 700 MPa (102 ksi) |
| Elongation in 2 inches | 15 - 25% |
| Reduction of Area | 20 - 35% |
| Hardness | 28 - 36 HRC |
| Charpy V-notch Impact (room temp) | 40 - 70 J |
Inconel 740H is supplied in either solution-treated or solution-treated plus aged condition. The aging treatment is critical for developing the high volume fraction of gamma-prime precipitates that provide the alloy's exceptional creep-rupture strength. Two common heat treatment schedules are used:
Careful control of heating rate, furnace atmosphere, and cooling medium is essential to avoid distortion, surface oxidation, and unwanted phase formation. Hangbo Alloy Group provides material with full heat treatment certification and can perform NDT inspection including ultrasonic testing, eddy current testing, and radiography on request.
Inconel 740H was specifically developed to maintain exceptional creep-rupture strength at temperatures where conventional austenitic stainless steels and even solid-solution nickel alloys fail. Its strength retention is superior to all competing A-USC candidate materials because of the high volume fraction of gamma-prime precipitates, which remain stable up to about 750°C and contribute to creep resistance through both precipitation strengthening and dislocation pinning mechanisms.
Long-term creep testing by EPRI, DOE, and international research consortia has confirmed that Inconel 740H achieves approximately 100 MPa stress for 100,000-hour rupture life at 750°C — the key design criterion for A-USC boiler tubing. This performance significantly exceeds Inconel 617 (~60 MPa), Haynes 230 (~50 MPa), and Nimonic 263 (~45 MPa) at the same conditions.
| Temperature (°C) | 1000h Rupture Strength (MPa) | 10000h Rupture Strength (MPa) | 100000h Rupture Strength (MPa) |
|---|---|---|---|
| 650 | 380 | 280 | 200 |
| 700 | 260 | 180 | 120 |
| 750 | 170 | 120 | 100 |
| 800 | 100 | 65 | 40 |
Inconel 740H exhibits excellent steam oxidation resistance due to its high chromium content (23-25%) and controlled aluminum addition. In high-velocity steam environments at 700-760°C, the alloy forms a protective Cr2O3-Al2O3 duplex oxide scale that limits metal loss and prevents breakaway oxidation. This performance is critical for A-USC boiler tubing where tube wall thickness is minimized for heat transfer efficiency.
The combination of exceptional creep-rupture strength, steam oxidation resistance, and thermal stability makes Inconel 740H the leading candidate material for next-generation high-efficiency power generation. It is specifically designed for applications where conventional materials cannot achieve the required combination of temperature, pressure, and service life.
Hangbo Alloy Group manufactures and supplies Inconel 740H in a comprehensive range of product forms and sizes, all supported by material test reports and third-party inspection. Our typical supply scope includes:
| Standard | Description |
|---|---|
| ASTM B983 | Seamless Nickel Alloy Pipe and Tube |
| ASME Code Case 2704 | Boiler and Pressure Vessel Code (A-USC Applications) |
| AWS A5.14 | Welding Wire (ERNiCrCoMo-1) |
| EPRI A-USC Specifications | Project-Specific Material Requirements for A-USC Demonstration Plants |
| DOE/OCDO Specifications | U.S. and Japanese A-USC Consortium Material Standards |
Shanghai Hangbo Alloy Group Co., Ltd. is a professional manufacturer and global supplier of nickel-based superalloys including Inconel 740H. We supply seamless tubes, pipes, bars, and forgings for A-USC power plant projects, gas turbines, and high-temperature process equipment with full material certification and third-party inspection.
Typical response time: within 10 minutes during business hours
The density of Inconel 740H is approximately 8.15 g/cm³ (0.295 lb/in³), typical for high-nickel precipitation-hardened superalloys. This value is slightly lower than Inconel 718 (8.19 g/cm³) due to the higher aluminum and titanium content in 740H.
Inconel 740H is designed for long-term service at temperatures up to 760°C (1400°F) in steam environments. Its creep-rupture strength at 750°C exceeds 100 MPa for 100,000 hours, making it the leading candidate material for Advanced Ultra-Supercritical (A-USC) power plant boiler tubing and headers.
Inconel 740H is a nickel-chromium-cobalt superalloy with approximately 47-52% Ni, 23-25% Cr, 15-20% Co, 1.35-1.85% Al, 1.35-1.85% Ti, 0.5-2.0% Nb, 0.5-2.0% Mo, and controlled carbon (0.03-0.08%). The high aluminum and titanium content form the gamma-prime (Ni₃(Al,Ti)) strengthening phase, while cobalt improves solid-solution strengthening and thermal stability.
Key standards include ASTM B983 (seamless nickel alloy pipe and tube), ASME Code Case 2704 (boiler and pressure vessel applications), and proprietary specifications from EPRI and DOE for A-USC power plant projects. Material is typically supplied in solution-annealed and aged condition per project-specific requirements.
Standard heat treatment involves solution annealing at 1120-1150°C for 1-2 hours followed by water quenching, then a two-step age: first age at 850°C for 4-8 hours, then second age at 750°C for 16-24 hours, both with air cooling. This produces a uniform distribution of gamma-prime precipitates with optimal size for creep resistance.
Inconel 740H is a premium superalloy with pricing significantly higher than standard stainless steels. As of 2026, mill-direct pricing for seamless tubes and pipes typically ranges from $80-150 per kg depending on specification, quantity, and delivery requirements. Contact Hangbo Alloy Group at hangbo@nickel-alloy.com or +86-136-1165-6360 for a detailed quotation.
Inconel 740H is available as seamless tubes and pipes (ASTM B983), bars and forgings, plates and sheets, and welding wire (ERNiCrCoMo-1). The most common form for A-USC applications is seamless tubing for boiler superheater and reheater tubes, typically in diameters from 25 mm to 89 mm with wall thicknesses 3-12 mm.
Yes, Inconel 740H is weldable using GTAW (TIG), GMAW (MIG), and SMAW processes with matching filler metal ERNiCrCoMo-1. However, due to its high gamma-prime content, it is more susceptible to strain-age cracking than Inconel 718. Preheating is generally not required, but post-weld heat treatment (full solution + age) is essential to restore mechanical properties and creep resistance.
Inconel 740H offers superior creep-rupture strength at 700-760°C compared to both Inconel 617 and Haynes 230. At 750°C/100,000 hours, 740H achieves approximately 100 MPa creep strength versus ~60 MPa for Inconel 617 and ~50 MPa for Haynes 230. However, 740H has lower fabricability and weldability than these solid-solution strengthened alloys, requiring more careful processing control.
Due to its specialized nature and limited global production capacity, Inconel 740H typically requires 8-16 weeks lead time for standard sizes. Minimum order quantities (MOQ) vary by product form: seamless tubes typically 100-500 kg, bars and forgings 200-1000 kg. Hangbo Alloy Group can source mill-direct material and arrange custom sizes with full MTR and third-party inspection. Contact us for project-specific scheduling.
Inconel 740H exhibits excellent steam oxidation resistance due to its high chromium content (23-25%) and controlled aluminum addition. At 760°C in steam, it forms a protective Cr₂O₃-Al₂O₃ duplex oxide scale with oxidation rates approximately 5-10 times lower than T91/P91 steel and comparable to or better than Inconel 617. The alloy maintains this protection for extended service periods exceeding 100,000 hours.
Primary applications include Advanced Ultra-Supercritical (A-USC) power plant boiler superheater and reheater tubes, steam headers and piping operating at 700-760°C/350+ bar, gas turbine hot-section components, and high-temperature process heaters. The alloy is specifically developed to enable power plant efficiencies above 50% (HHV) by permitting higher steam temperatures than conventional materials.
Hangbo Alloy Group maintains mill-direct supply of Inconel 740H seamless tubes, pipes, bars, and forgings for A-USC power plant projects, gas turbine manufacturers, and high-temperature process equipment builders. Our team can assist with material selection, heat treatment specification, NDT requirements, and export documentation. We support customers in power generation, petrochemical, and advanced energy industries with reliable quality and competitive lead times.
For quotations, material certifications, or technical consultation, contact our sales team or call +86-136-1165-6360. We typically respond within 10 minutes.
Request a quotation for Inconel 740H seamless tubes, pipes, bars, or forgings. We stock standard sizes and accept custom orders for A-USC and high-temperature projects.