Nov 19 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesMechanical PropertiesOther DesignationsFabrication and Heat Treatment Machinability Forming Welding Heat Treatment Forging Hot Working Cold Working Annealing Aging HardeningApplications
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.