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VDM® Alloy 718

Alternative and trade names
Nicrofer 5219 Nb, Inconel 718
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Description

VDM® Alloy 718 is an age hardenable nickel-chrome-iron-molybdenum alloy. The age hardening is achieved by specific additions of niobium, titanium and aluminum. It can be delivered in solution annealed or hardened condition.


VDM® Alloy 718 is characterized by:

  • Good processing properties in the solution-annealed condition
  • Good mechanical short and long-term properties, and great fatigue strength in the age hardened condition
  • Good creep resistance up to 700°C
  • Good oxidation resistance up to approx. 1100°C
  • Excellent mechanical properties in low temperatures

Related Standards

Properties

Electrical

Electrical resistivity ρel

1.18E-6 Ω·m at 20 °C

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General

Density ρ

8.26 g/cm³ at 20 °C

Magnetic

Curie temperature Tc

-195 °C at 20 °C

Typical material property in solution annealed condition

Relative magnetic permeability μrel

1 [-] at 20 °C

Mechanical

Creep limit Rp,creep

783 MPa at 550 °C

Rp 1.0/10⁴ h according to DIN EN 10302 for solution annealed and age hardened condition

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Creep strength Rm,creep

810 MPa at 550 °C

Rm/10⁴ h according to DIN EN 10302 of the solution annealed and age hardened condition

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Elastic modulus E

204 GPa at 20 °C

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Elongation A

12 % at 20 °C

Typical mechanical properties in the solution annealed and age hardened condition

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Hardness, Brinell HB

277 [-] at 20 °C

Typical mechanical property for rod and bar in the solution annealed condition

Tensile strength Rm

1280 MPa at 20 °C

Typical mechanical properties in the solution annealed and age hardened condition

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Yield strength Rp0.2 Rp0.2

1030 MPa at 20 °C

Typical mechanical properties in the solution annealed and age hardened condition

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Thermal

Coefficient of thermal expansion α

1.41E-5 1/K at 20 °C

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Melting point Tm

1257 - 1342 °C

Specific heat capacity cp

460 J/(kg·K) at 20 °C

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Thermal conductivity λ

11.5 W/(m·K) at 20 °C

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Chemical properties

Element

Weight %

Comment

Fe

-

balance

Ni

50 - 55 %

Cr

17 - 21 %

Nb

4.75 - 5.5 %

Mo

2.8 - 3.3 %

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Technological properties

Application areas

Based on its high-temperature resistance up to 700 °C, its excellent oxidation and corrosion resistance, and its good workability, VDM® Alloy 718 is used in many demanding applications. Originally, it was developed and used for static and rotating components in aircraft turbines such as housings, mounting elements and turbine disks, where tough requirements apply for creep resistance and fatigue behavior, in particular for the rotating applications. Due to its properties, its good workability and efficiency, the material is additionally widely used for static and rotating components in stationary gas turbines, rocket drives and spacecraft, motor vehicle turbo chargers, high-strength screws, springs and mounting elements, and for heat-resistant tools in forgeries, extruders and separating shearers. The variant VDM® Alloy 718 CTP, which is laid out specifically for the requirements of the oil and gas industry, finds increasing uses in drilling equipment and pump shafts. The components used must ensure an efficient and safe oil and gas extraction with increasing drilling hole depth and pressures and temperatures becoming more critical, and withstand the acid gas environment (H₂S, CO₂, chloride) that is prevalent there (see special data sheet VDM® Alloy 718 CTP).

Corrosion properties

Based on the high chrome and molybdenum concentrations, VDM® Alloy 718 has a good resistance in many media against abrasive and local corrosion such as pitting. By virtue of its high nickel content, VDM® Alloy 718 also has good resistance against stress corrosion cracking.

General machinability

While VDM® Alloy 718 in the solution annealed condition is easier to process and the strain on tools is less, better surface quality is achieved in the hardened condition. The best results in terms of the surface quality of the finished product are achieved by pre-treatment before hardening and by finishing in the hardened condition. As the alloy is more prone to work-hardening than other low alloyed materials, low cutting speeds and appropriate feed rates should be used and the tool should stay engaged at all times. Sufficient chip depths are important to get below the work-hardened surface layer.

Other

VDM® Alloy 718 has an austenitic structure; multiple phases can be precipitated. By means of different heat treatments, graduated mechanical properties of the material can be reached. The excellent mechanical properties of VDM® Alloy 718 result from the γ’’-formation during the precipitation hardening.

This material data has been provided by VDM Metals.

All metrics apply to room temperature unless otherwise stated. SI units used unless otherwise stated.
Equivalent standards are similar to one or more standards provided by the supplier. Some equivalent standards may be stricter whereas others may be outside the bounds of the original standard.