Inconel 625 is a nickel-chromium-molybdenum alloy with an addition of niobium (columbium). It is known for its outstanding corrosion resistance, high strength, and excellent fabricability. The alloy is solid-solution strengthened (not precipitation hardenable), with niobium stabilizing the matrix and providing high strength without the need for heat treatment.

The nominal chemical composition is: nickel 58.0 percent minimum, chromium 20.0 to 23.0 percent, molybdenum 8.0 to 10.0 percent, niobium (plus tantalum) 3.15 to 4.15 percent, iron up to 5.0 percent, and smaller amounts of carbon, manganese, silicon, aluminum, and titanium.

Key mechanical properties (typical, annealed condition):

● Tensile strength: 830 to 1,030 MPa

● Yield strength (0.2% offset): 410 to 620 MPa

● Elongation: 30 to 45 percent

● Hardness: 85 to 95 HRB

● Density: 8.44 g/cm³

Inconel 625 offers exceptional resistance to pitting, crevice corrosion, and chloride ion stress corrosion cracking. It resists a wide range of corrosive media including seawater, sulfuric acid, hydrochloric acid, nitric acid, and many organic acids. The alloy also maintains high strength and oxidation resistance from cryogenic temperatures up to about 980°C (1,800°F).

Common standards: ASTM B443 (sheet/plate), B444 (seamless pipe/tube), B446 (bar/forging), B366 (fittings). Also ASME SB specifications, AMS 5599 (sheet), AMS 5666 (bar).

Typical applications include:

● Marine and offshore engineering: seawater piping, pump shafts, propeller blades, and risers.

● Chemical processing: reactors, heat exchangers, evaporators, and distillation columns.

● Aerospace: jet engine ducting, thrust reversers, and exhaust systems.

● Oil and gas: sour gas service equipment, downhole components, and flowlines.

● Nuclear and power generation: reactor components and superheater tubing.

Inconel 625 is often compared to Inconel 600 (lower strength, less pitting resistance) and Hastelloy C-276 (similar corrosion resistance but lower strength). For high-temperature strength above 800°C, Inconel 718 or 625 may be chosen based on specific requirements. For most severe marine and chemical environments, Inconel 625 is a top choice due to its combination of high strength, weldability, and broad corrosion resistance.