Inconel 740H is a precipitation-hardenable nickel-chromium-cobalt-molybdenum alloy specifically developed for ultra-supercritical (USC) power plants operating at steam temperatures up to 760°C (1,400°F) and pressures above 35 MPa. It is an improved version of Inconel 740, with modified composition (higher niobium, reduced silicon) to enhance creep strength and long-term microstructural stability.

The nominal chemical composition is: nickel 47–52%, chromium 23–26%, cobalt 18–22%, molybdenum 0.2–0.8%, niobium 1.3–2.3%, titanium 0.1–0.8%, aluminum 0.8–1.3%, and iron up to 2%. The alloy is strengthened by gamma prime (Ni3(Al,Ti,Nb)) precipitates.

Key mechanical properties (aged condition):

● Tensile strength: 1,000–1,200 MPa

● Yield strength (0.2% offset): 600–800 MPa

● Elongation: 20–30%

● Density: 8.15 g/cm³

Inconel 740H offers outstanding creep-rupture strength up to 760°C, excellent oxidation and corrosion resistance in high-temperature steam and combustion atmospheres, and good weldability and fabricability. It is the leading candidate for USC boiler tubing, headers, and piping.

Standards: ASME Code Case 2702 (for Section I construction), ASTM pending.

Applications: superheater and reheater tubes, steam headers, and piping in advanced USC coal-fired power plants.

Compared to Inconel 617 and 625, Inconel 740H provides higher creep strength at 700–760°C specifically for steam turbine applications. For gas turbine or lower-temperature service, other alloys may be more suitable.