Alloy 706 vs. Alloy 718
(UNS N09706 vs. N07718):
Which Superalloy Should You Choose
for Your Forging Project?

When specifying nickel superalloys for turbine discs, compressor rings, shafts, or high-pressure casings, engineers consistently shortlist two precipitation-hardenable workhorses: Alloy 706 (UNS N09706) and Alloy 718 (UNS N07718). Both carry outstanding high-temperature credentials. Both can be forged into demanding geometries. And both have decades of validated service history in aerospace and industrial gas turbines worldwide.

But they are not interchangeable. The wrong choice can cost you significantly in machining time, post-weld cracking risk, qualification overhead, or operating temperature margin. This guide gives you a rigorous, production-experience-backed analysis so your engineering and procurement teams can make the call with confidence.

Alloy Identities at a Glance

Before comparing specific properties, it helps to understand the engineering rationale behind each alloy and the market context in which it was created.

Jiangsu Liangyi Co., Limited manufactures Alloy 706 open-die forgings and seamless rolled rings in sizes from 30 kg to 30 tons per piece, with seamless rings up to 6,000 mm diameter — one of the widest capability ranges for UNS N09706 available from a single manufacturer.

Chemical Composition: What's Actually Different?

Both alloys share a nickel-chromium-iron base but diverge significantly in iron, niobium, titanium, and molybdenum content. These differences drive real-world fabrication and performance gaps that directly affect production cost and component reliability.

Why Iron Content Matters for Forging

Alloy 706's higher iron content (~38% vs ~18% in Alloy 718) directly reduces raw material cost. More importantly, higher Fe content changes the alloy's flow stress and recrystallization behavior during hot working: Alloy 706 is easier to deform in large open-die and ring-rolling operations, requiring lower press tonnage and enabling larger cross-sections without forming defects. This is why Alloy 706 dominates large land-based turbine disc applications where forging diameters of 1–3 m are common.

The Niobium Difference: Peak Strength vs. Long-Term Stability

In Alloy 718, the dominant hardener is γ'' (gamma double prime) driven by high niobium. This delivers exceptional room-temperature tensile strength. However, γ'' is thermodynamically metastable above approximately 650 °C, where it gradually transforms to the δ (delta) phase, causing progressive loss of creep and tensile strength during prolonged high-temperature service.

Alloy 706 uses a more balanced γ'/γ'' ratio with greater titanium contribution. This produces slightly lower peak strength than Alloy 718, but with a more stable microstructure during long-hold high-temperature service — a critical advantage in industrial gas turbine discs that operate continuously for 8,000–25,000 hours between overhauls.

Mechanical & Thermal Properties

The comparison below uses typical forged, heat-treated values. Always verify against the specific standard and heat treatment required for your application.

Summary: Alloy 718 wins on peak strength — UTS and yield strength are typically 10–12% higher at room temperature, and HCF performance is superior. However, the margin narrows at elevated temperature, and Alloy 706 compensates through better ductility, lower notch sensitivity, and superior microstructural stability during long-duration service — qualities critical in rotating disc applications and long-service industrial gas turbines.

Forging Process Differences

This is where Alloy 706's engineering value becomes most compelling. The alloy was designed to solve fabrication challenges that Alloy 718 creates at large scale — particularly for open-die forging and seamless ring rolling of large-diameter components.

Delayed Hardening: The Manufacturing Advantage Engineers Often Overlook

Alloy 706 resists premature precipitation at aging temperatures for longer than Alloy 718, giving a wider processing window before significant hardening begins. This controls two critical manufacturing risks:

1. Postweld strain-age cracking resistance. Rapid precipitation can lock residual welding strain into the HAZ, causing intergranular cracking during PWHT. Alloy 706's slow hardening kinetics allow residual stresses to relax before the material becomes brittle — a fundamental advantage over Alloy 718.

2. Large-section forging homogeneity. In open-die forgings and large rolled rings up to 6,000 mm diameter, temperature gradients are unavoidable. Delayed hardening keeps the alloy workable throughout the forging window, reducing hot tearing risk and enabling more homogeneous grain structure.

For full dimensional specifications, press capacity, and ring-rolling capability data for Alloy 706, see our Alloy 706 forging manufacturing capabilities page, which details equipment, tolerances, and NDT inspection standards available for every order.

Machinability & Weldability

Machinability: A Clear Alloy 706 Advantage

Both alloys are difficult to machine relative to steel — work hardening, low thermal conductivity, and high strength accelerate tool wear. However, Alloy 706 is measurably easier to machine: lower niobium content reduces hard Laves phase particles that damage cutting edges; higher iron content slightly softens the matrix during roughing cuts. In production, machining shops report Alloy 706 achieves approximately 20–30% higher cutting speeds and 25–35% longer tool life vs equivalent Alloy 718 operations — directly reducing per-part cost, especially significant for complex turbine disc profiles with 200+ hours of machining time.

Weldability: Alloy 706's Design Priority

Alloy 706 was explicitly designed with weldability as a primary objective. The delayed hardening response allows residual stresses in the HAZ to relax before significant hardening, virtually eliminating the postweld strain-age cracking that can afflict Alloy 718 joints. For applications where welded assembly is part of the manufacturing route — compressor casings, turbine frames, pressure vessels — selecting Alloy 706 over Alloy 718 can prevent the most common and costly failure mode in superalloy fabrication.

Application Suitability

The table below reflects real-world market patterns validated by decades of production experience in both alloys.

Cost & Supply Chain Considerations

The true total cost comparison must account for raw material, machining, heat treatment, weld repair scrap rate, and qualification risk — not just price per kilogram.

To compare material options for your specific component and get a production cost estimate, request a custom Alloy 706 forging quote directly from our Jiangyin engineering team — typical response within 24 working hours.

Decision Guide: Choose Alloy 706 or Alloy 718?

There is no universally "better" superalloy. The right choice depends on your specific combination of section size, service temperature, fabrication route, strength requirement, and procurement context.

Frequently Asked Questions