Inconel 718 properties
Chemical composition
Section titled “Chemical composition”The typical composition of Inconel 718 (UNS N07718) is:
| Element | Content (% by weight) |
|---|---|
| Nickel (Ni) | 50,00 – 55,00 |
| Chromium (Cr) | 17,00 – 21,00 |
| Iron (Fe) | Balance |
| Niobium (Nb) + Tantalum (Ta) | 4,75 – 5,50 |
| Molybdenum (Mo) | 2,80 – 3,30 |
| Titanium (Ti) | 0,65 – 1,15 |
| Aluminum (Al) | 0,20 – 0,80 |
| Cobalt (Co) | 1,00 max. |
| Manganese (Mn) | 0,35 max. |
| Silicon (Si) | 0,35 max. |
| Carbon (C) | 0,08 max. |
| Phosphorus (P) | 0,015 max. |
| Sulfur (S) | 0,015 max. |
| Boron (B) | 0,006 max. |
| Copper (Cu) | 0,30 max. |
Mechanical properties
Section titled “Mechanical properties”Solution treated condition
Section titled “Solution treated condition”| Product | Yield strength (0,2%) min. | Tensile strength min. | Elongation min. (%) |
|---|---|---|---|
| Sheet / strip | 550 MPa (80 ksi) | 965 MPa (140 ksi) | 30 |
| Plate | 725 MPa (105 ksi) | 1035 MPa (150 ksi) | 30 |
Solution treated and precipitation aged condition
Section titled “Solution treated and precipitation aged condition”| Product | Yield strength (0,2%) | Tensile strength | Elongation min. (%) |
|---|---|---|---|
| All forms | 1035 MPa (150 ksi) | 1240 MPa (180 ksi) | 12 |
Physical properties
Section titled “Physical properties”| Property | Value |
|---|---|
| Density (solution treated) | 8,19 g/cm³ (0,296 lb/in³) |
| Density (aged) | 8,22 g/cm³ (0,297 lb/in³) |
| Melting range | 1260 – 1338 °C (2300 – 2440 °F) |
| Young’s modulus (at -189 °C) | 216 GPa |
| Young’s modulus (at 1093 °C) | 99 GPa |
| Poisson’s ratio (range) | 0,25 – 0,402 |
Thermal properties
Section titled “Thermal properties”| Property | Value |
|---|---|
| Thermal conductivity (average 0–100 °C) | 6,5 W/m·K (11,2 BTU·ft/ft²·hr·°F) |
| Specific heat | 0,435 J/g·°C (0,104 BTU/lb·°F) |
Corrosion resistance
Section titled “Corrosion resistance”Inconel 718 alloy exhibits good resistance to oxidation and corrosion in the atmospheres encountered in jet engines and gas turbines, within the temperature range where the alloy maintains its mechanical strength.
Heat treatment
Section titled “Heat treatment”Precipitation hardening is achieved through the following typical cycle:
- Solution treatment: 982 °C (1800 °F) for 1 hour.
- Aging: 718 °C (1325 °F) for 8 hours, followed by furnace cooling at 55 °C/h (100 °F/h) to 621 °C (1150 °F) and holding for 8 hours.
Machining
Section titled “Machining”Machining of Inconel 718 is demanding due to its high strength and work-hardening tendency. Carbide tools with positive rake angles, low cutting speeds (typically 10 – 30 m/min), abundant coolant, and rigid machine setups are recommended.
Welding
Section titled “Welding”Inconel 718 can be welded by conventional processes such as TIG (GTAW) or plasma. ERNiFeCr-2 filler material is used. To restore mechanical properties in the weld zone, post-weld heat treatment (solution treatment + aging) is necessary.
Applications
Section titled “Applications”- Jet engine components (disks, shafts, blades).
- Stationary gas turbines.
- Cryogenic systems and storage tanks.
- Downhole tools and high-strength bolts in the petrochemical industry.
Comparison with similar materials
Section titled “Comparison with similar materials”| Alloy | Density (g/cm³) | Tensile strength (aged) | Maximum service temperature |
|---|---|---|---|
| Inconel 718 | 8,22 | 1240 MPa (180 ksi) | ~ 700 °C (1300 °F) |
| Inconel 625 | 8,44 | 1035 MPa (150 ksi) | ~ 815 °C (1500 °F) |
| Inconel X-750 | 8,28 | 1100 MPa (160 ksi) | ~ 815 °C (1500 °F) |
| Waspaloy | 8,16 | 1310 MPa (190 ksi) | ~ 870 °C (1600 °F) |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the tensile strength of Inconel 718 after aging?
Section titled “What is the tensile strength of Inconel 718 after aging?”The alloy achieves a minimum tensile strength of 1240 MPa (180 ksi) in the solution treated and precipitation hardened condition.
What is the density of Inconel 718?
Section titled “What is the density of Inconel 718?”The density in the aged condition is 8,22 g/cm³ (0,297 lb/in³), slightly higher than the 8,19 g/cm³ of the solution treated condition.
At what temperature does Inconel 718 melt?
Section titled “At what temperature does Inconel 718 melt?”Its melting range is between approximately 1260 °C and 1338 °C (2300 – 2440 °F).
What is the thermal conductivity of Inconel 718?
Section titled “What is the thermal conductivity of Inconel 718?”It exhibits an average thermal conductivity of 6,5 W/m·K (11,2 BTU·ft/ft²·hr·°F) in the range of 0 to 100 °C.
How much nickel does Inconel 718 contain?
Section titled “How much nickel does Inconel 718 contain?”The nickel content is between 50% and 55% by weight.
What strength does it retain at cryogenic temperatures?
Section titled “What strength does it retain at cryogenic temperatures?”At -196 °C, the tensile strength of Inconel 718 exceeds 1800 MPa, making it suitable for cryogenic applications.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=4459
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/metals-galvanic-series-seawater-d_1495.html
- steelnumber.com: https://www.steelnumber.com/en/search_form_eu.php