Inconel 706 is a precipitation-hardenable nickel-iron-chromium alloy designed as a lower-cost alternative to Inconel 718. It contains less nickel, molybdenum, and niobium than Inconel 718, and adds titanium and aluminum for age-hardening. The alloy offers good high-temperature strength up to about 650°C (1,200°F) while providing improved machinability and lower raw material cost.

The nominal chemical composition is: nickel 39.0 to 44.0 percent, iron balance (approximately 37 percent), chromium 14.5 to 17.5 percent, niobium (plus tantalum) 2.5 to 3.3 percent, titanium 1.5 to 2.0 percent, molybdenum 2.0 to 3.0 percent, aluminum 0.4 to 0.6 percent, and smaller amounts of carbon, manganese, silicon, and cobalt.

Key mechanical properties (typical, aged condition):

● Tensile strength: 1,000 to 1,200 MPa

● Yield strength (0.2% offset): 700 to 900 MPa

● Elongation: 15 to 25 percent

● Hardness: 30 to 38 HRC

● Density: 8.06 g/cm³

Inconel 706 exhibits good tensile and creep-rupture properties at temperatures up to 650°C. It has excellent machinability in the solution-annealed condition, significantly better than Inconel 718. The alloy also offers good oxidation resistance and moderate corrosion resistance, though it is less resistant to pitting and crevice corrosion than higher-molybdenum alloys like Inconel 625.

Common standards: ASTM B670 (plate, sheet, strip), B637 (bar, forgings), AMS 5538 (sheet), AMS 5702 (bar, forgings).

Typical applications include:

● Gas turbine engines: discs, shafts, spacers, and compressor components, particularly in larger industrial turbines where cost is a factor.

● Automotive: turbocharger rotors and high-temperature fasteners.

● Aerospace: structural components requiring moderate high-temperature strength.

● Nuclear: reactor components and hardware.

Comparison with Inconel 718: Inconel 706 has lower nickel and niobium content, making it less expensive and easier to machine. However, it has slightly lower creep strength and oxidation resistance at the upper end of its temperature range (above 650°C). For many applications below 650°C, Inconel 706 is an acceptable substitute. For maximum strength and corrosion resistance at higher temperatures, Inconel 718 remains the preferred choice.

Selection guidance: Choose Inconel 706 for gas turbine and high-temperature components operating below 650°C where cost reduction is important and the performance requirements do not demand the full capability of Inconel 718. For sour gas or highly corrosive environments, higher-molybdenum alloys (Inconel 625, 725) are more suitable.