High temperature alloys
UNS Number | UNS N07718 |
Industry Name | Alloy 718, Inconel 718, W.Nr.2.4668, NiCr19Fe19Nb5Mo3 |
Product Forms | Billets, Bars, Forgings, Plates, Strips, Powders |
General Characteristics
Alloy 718 is a nickel-based precipitation-hardened alloy, strengthened by niobium-rich γ'' precipitates. It maintains stable performance from -250°C up to 650°C, featuring high strength, good creep resistance and weldability. It can be readily fabricated into forgings and bars, widely adopted for large components in aerospace and oil & gas industries, such as turbine parts, valve seats, hangers.
Compared with similar nickel alloys, Alloy 718 has lower high-temperature strength than Inconel 738, yet superior weldability and resistance to strain-age cracking, making it more suitable for complex parts. Against solid-solution strengthened Inconel 625, Alloy 718 delivers higher strength at room and moderate temperatures. However, its γ'' phase will coarsen under long-term exposure above 650°C, leading to gradual strength loss.
At the same time, alloy 718 offers good corrosion resistance against seawater and hydrogen sulfide, frequently used for downhole oilfield parts. Its limitation lies in the obvious performance drop beyond 650°C, so alternative grades are selected for continuous ultra-high temperature service.
Alloy 718 chemical compositions
Ni | Fe | Mn | C | Si | S | Cr | Al | Ti | Nb+Ta | Mo | P | Co | Pb | Se | Bi | Ca | B | Mg | |
Min | 50 | Balance | 17 | 0.4 | 0.8 | 4.87 | 2.8 | ||||||||||||
Max | 55 | 0.35 | 0.045 | 0.35 | 0.01 | 21 | 0.6 | 1.15 | 5.2 | 3.3 | 0.01 | 1 | 0.001 | 0.0005 | 0.00005 | 0.003 | 0.006 | 0.006 |
The rich and complex chemical composition of Alloy 718 brings multiple synergistic advantages.
Nickel acts as the base matrix, providing excellent corrosion resistance and structural stability. Chromium delivers oxidation and general corrosion protection, while niobium, paired with iron, enables precipitation hardening via γ'' phase precipitates, which endow the alloy with outstanding tensile and creep strength at intermediate temperatures.
Molybdenum further boosts matrix strength and resistance to pitting corrosion.
This multi-element design distinguishes it from simpler nickel alloys. Unlike solid-solution strengthened grades such as Inconel 625, Alloy 718 can achieve much higher strength after aging treatment, without sacrificing weldability.
The balanced element ratio in 718 greatly mitigates the risk of strain-age cracking after welding, allowing fabrication of large forgings and complex welded assemblies.
Aerospace||High temp fasteners
Technical Standards | Product Form |
ASTM B637 | Bar, Forging, Forged Billet |
AMS 5662 | Bar, Forging, Ring |
AMS 5663 | Bar, Forging, Ring |
AMS 5664 | Bar, Forging, Ring |
ASTM B670 | Plate, Sheet, Strip |
AMS 5596 | Plate, Sheet, Strip |
AMS 5597 | Plate, Sheet, Strip |
AMS 5589 | Seamless tube |
AMS 5590 | Seamless tube |
ASTM B829 | Seamless tube |
AMS 5832 | Wire, Welding Wire |
ASTM F3056 | Additive Manufacturing Powder |
AMS 7929 | Additive Manufacturing Powder |
AMS 5583 | Castings |
Product form | Size range (mm) |
Forged bar | Dia.70-500 |
Rolled bar | Dia.2.0-70 |
Flat bar | T4-50*W60-300 |
Wire | Dia.0.25-18.0 |
Forged ring | OD 30-350* ID 30-350 |
Strip | 0.15-3.0 * 20-200 |
Plate | 1-25 * ≤1200 * ≤1200 |
Seamless tube | OD 6.0-200 * 0.6-20 |
Alloy 718 thermal conductivity
θ/°C | 11 | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 | 1000 |
W/(m·°C) | 13.4 | 14.7 | 15.9 | 17.8 | 18.3 | 19.5 | 21.2 | 22.8 | 23.6 | 27.6 | 30.4 |
Alloy 718 Coefficient of Thermal Expansion
θ/°C | 20-100 | 20-200 | 20-300 | 20-400 | 20-500 | 20-600 | 20-700 | 20-800 | 20-900 | 20-1000 |
α | 11.8 | 13 | 13.5 | 14.1 | 14.4 | 14.8 | 15.4 | 17 | 18.4 | 18.7 |
Alloy 718 Structure-Phase Transition Temperature
γ "phase is the main strengthening phase, and its peak stable temperature is 650°C, the initial solid solution temperature is 840-870°C, and the complete solid solution temperature is 950°C.
γ 'phase is also the strengthening phase of the alloy718, but the amount is less than γ' phase, its precipitation temperature is 600°C, the complete dissolution temperature is 840°C.
δ phase: Initial precipitation temperature of is 700°C, precipitation peak temperature is 940°C, the dissolution begins at 980°C, and the complete dissolution temperature is 1020°C.
Alloy 718 modulus of elasticity
θ/℃ | 20 | 100 | 200 | 300 | 400 | 450 | 500 | 550 | 600 | 650 | 700 |
E/GPa | 204 | / | / | 181 | 176 | / | 160 | 160 | 150 | 146 | 141 |
Alloy 718 embrittlement
In the presence hydrogen, Nickel alloy 718 is particularly susceptible to embrittlement. Alloy 718 failed prevalently through a combination of transgranular and intergranular cracking behavior.
Is Alloy 718 magnetic?
Non-magnetic.