Super Alloy Allvac 718™ (UNS N07718)

Topics Covered

Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Other Designations
Fabrication and Heat Treatment
     Machinability
     Forming
     Welding
     Heat Treatment
     Forging
     Hot Working
     Cold Working
     Annealing
     Aging
     Hardening
Applications

Introduction

Super alloys have good creep and oxidation resistance. They can function at very high temperatures and severe mechanical stress, and also where high surface stability is required. They can be strengthened by solid-solution hardening, work hardening, and precipitation hardening. They contain a number of elements in a variety of combinations to achieve the desired result.

Allvac 718™ is a nickel-chromium alloy having high corrosion resistance, temperature resistance and strength. The datasheet given below gives more details about Allvac 718™.

Chemical Composition

The following table shows the chemical composition of Allvac 718™.

Element Content (%)
Nickel, Ni 54
Chromium, Cr 19
Iron, Fe 17
Niobium, Nb 5.2
Molybdenum, Mo 3.1
Titanium, Ti 0.9
Aluminum, Al 0.5
Carbon, C 0.02

Physical Properties

The physical properties of Allvac 718™ are highlighted in the following table.

Properties Metric Imperial
Density 8.19 g/cm3 0.296 lb/in³
Melting point 1327°C 2420°F

Mechanical Properties

The mechanical properties of Allvac 718™ are displayed in the following table.

Properties Metric Imperial
Tensile strength 1345 MPa 195100 psi
Yield strength (@ strain 0.200%) 1104 MPa 160100 psi
Poisson’s ratio 0.284 0.284
Elongation at break 22% 22%
Reduction of area 35% 35%
Hardness, Brinell (estimated from Rockwell C value for Brinell test with 3000 kg load/10 mm diameter ball) 389 389
Hardness, Knoop (estimated from Rockwell C value) 425 425
Hardness, Rockwell C 42 42
Hardness, Vickers (estimated from Rockwell C value) 407 407

Other Designations

Other designations that are equivalent to Allvac 718™ are included in the following table.

MS 5589 AMS 5662 ASTM B637 GE B14H89 GE B50TF15
AMS 5590 AMS 5663 ASTM B670 GE B50 TF14 PWA 1009
AMS 5596 AMS 5664 DIN 2.4668 GE B50 TF69 PWA 1010
AMS 5597 AMS 5832 DIN 2.4688 GE B50TF14 PWA 1033
RBO 170-153 SPS M275 SPS M637

Fabrication and Heat Treatment

Machinability

Allvac 718™ can be machined using conventional machining methods which are used for iron-based alloys. Machining operations are performed using commercial coolants. High -speed operations such as grinding, milling or turning, are performed using water-based coolants.

Forming

Allvac 718™ can be formed using all conventional techniques

Welding

Allvac 718™ is welded using gas-tungsten arc welding, shielded metal-arc welding, gas metal-arc welding, and submerged-arc welding methods

Heat Treatment

Allvac 718™ is heat treated by annealing at 1038°C (1900°F) followed by cooling.

Forging

Allvac 718™ is forged at 927 to 1122°C (1700 to 2050°F).

Hot Working

Allvac 718™ is hot worked at 899°C to 1122°C (1650 to 2050°F). If the temperature falls below 899°C (1650°F), this alloy must be reheated again.

Cold Working

Allvac 718™ can be cold worked using standard tooling.

Annealing

Allvac 718™ is annealed at 1038°C (1900°F) followed by cooling.

Aging

Allvac 718™ has two different types aging heat treatments. In the first type of treatment, this alloy is aged at 719°C (1325°F) for 8 h followed by cooling in a furnace. It is then held at that temperature for 10 h followed by again cooling in air in order to achieve good rupture properties and highest room temperature strength. In the second type of treatment, this alloy is aged at 760°C (1400°F) followed by cooling in a furnace. It is then held at that temperature for 10 h followed by cooling in air again to achieve good transverse ductility, especially in heavy sections.

Hardening

Allvac 718™ can be hardened by cold working.

Applications

Allvac 718™ is mainly used in cryogenic storage tanks and gas turbine hot section components.

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