Inconel 718 — Nickel alloy Grade Specification, Properties & Equivalents
Inconel 718 is a precipitation-hardening nickel-chromium-molybdenum alloy renowned for its exceptional strength, corrosion resistance, and ability to retain properties at elevated temperatures up to 650°C (1200°F). In India, major users of Inconel 718 include the aerospace sector
Inconel 718 is a precipitation-hardening nickel-chromium-molybdenum alloy renowned for its exceptional strength, corrosion resistance, and ability to retain properties at elevated temperatures up to 650°C (1200°F). In India, major users of Inconel 718 include the aerospace sector for jet engine components, the oil and gas industry for downhole equipment, and chemical processing plants. Its unique balance of weldability, high-yield strength, and creep-rupture strength makes Inconel 718 a preferred choice for critical applications demanding reliability under extreme conditions. The ability to achieve high strength through heat treatment without significant loss of ductility further solidifies Inconel 718
Chemical Composition of Inconel 718
Inconel 718 Chemistry Standards
| Element | % Range |
| Nickel (Ni) | 50.00 - 55.00 |
| Chromium (Cr) | 17.00 - 21.00 |
| Iron (Fe) | Inf. 5.00 |
| Molybdenum (Mo) | 2.80 - 3.30 |
| Niobium + Tantalum (Nb+Ta) | 4.75 - 5.50 |
| Cobalt (Co) | Inf. 1.00 |
| Aluminum (Al) | 0.40 - 1.00 |
| Titanium (Ti) | 0.65 - 1.15 |
| Carbon (C) | Inf. 0.08 |
| Manganese (Mn) | Inf. 0.35 |
| Silicon (Si) | Inf. 0.35 |
| Phosphorus (P) | Inf. 0.015 |
| Sulfur (S) | Inf. 0.015 |
Mechanical Properties of Inconel 718
Inconel 718 Mechanical Properties (Typical at Room Temp)
| Property | Value (ASTM B637) |
| Ultimate Tensile Strength (UTS) | 1035 - 1379 MPa (150 - 200 ksi) |
| Yield Strength (YS) (0.2% offset) | 760 - 1070 MPa (110 - 155 ksi) |
| Elongation at break | 20 - 30% |
| Hardness (Rockwell C) | 33 - 42 HRC |
| Density | 8.19 g/cm³ |
| Modulus of Elasticity | 200 GPa |
Inconel 718 Available Forms in India
| Shape | Typical Machined Sizes (mm) | Standard Lengths (m) |
| Bar | 5 - 250 | 3 - 6 |
| Rod | 3 - 20 | 3 - 6 |
| Wire | 0.1 - 5 | Coil / Spool |
| Sheet/Plate | 0.4 - 50 | 1 - 4 |
| Seamless Pipe/Tube | ID 10-100 / OD 15-120 | 3 - 6 |
Inconel 718 Real-world Applications
- Aerospace: Turbine discs, blades, fasteners, and casings for jet engines and rocket motors.
- Oil & Gas: Downhole drilling tools, wellheads, and completion equipment requiring high strength and corrosion resistance.
- Chemical Processing: Components in high-pressure, high-temperature reactors and fluid handling systems.
- Power Generation: Gas turbine components and steam turbine parts.
- Cryogenics: Effective use in equipment for extremely low temperatures.
- Automotive: High-performance turbocharger components and exhaust systems.
- General Engineering: Specialty fasteners and structural components requiring exceptional mechanical integrity.
Inconel 718 Machinability & Weldability
Inconel 718 exhibits moderate machinability, often requiring specialized techniques due to its high strength and work-hardening tendencies. For Inconel 718, use rigid machine tools, sharp, durable cutting tools (carbide or ceramic inserts preferred), and ample coolant. Recommended cutting speeds for Inconel 718 are significantly lower than for mild steels, typically ranging from 15-30 m/min for turning. A common machining strategy involves using positive rake angles and maintaining continuous cuts to avoid work hardening. Milling and drilling Inconel 718 also demand slower speeds and higher feed rates. Weldability of Inconel 718 is considered good for a high-strength alloy. It can be readily welded using processes like Gas Tungsten Arc Welding (GTAW/TIG), Gas Metal Arc Welding (GMAW/MIG), and Resistance Welding. To maintain the properties of Inconel 718, avoid post-weld heat treatment if high strength is required, or follow the solution and aging treatment specified by ASTM B637 for optimal results, which involves solution treating at 980-1010°C followed by aging at 720°C and then 620°C with intermediate cooling. Special attention is needed to avoid contamination during welding of Inconel 718. Stress relief is generally not performed on Inconel 718 after welding due to potential loss of strength.Inconel 718 Heat Treatment & Processing
The primary heat treatment for Inconel 718 is a two-step aging process to achieve its characteristic high strength. Solution treatment is typically performed at temperatures between 980°C and 1010°C (1800°F - 1850°F), followed by rapid cooling (water quench or fan cool) to retain ductility. The subsequent aging consists of two stages: first at 720°C (1325°F) for 8 hours, followed by cooling to 620°C (1150°F) and holding at this temperature for another 8-10 hours, then air cooling. This double-aging process for Inconel 718 results in the precipitation of gamma double prime (γ″) and gamma prime (γ′) phases, providing excellent strength at moderate temperatures. Annealing of Inconel 718, if required for softening, involves heating to 1010°C followed by air or furnace cooling, yielding a microstructure suitable for subsequent forming operations. Normalizing is not a standard treatment for Inconel 718. The processing of Inconel 718 is critical; hot working should typically be done above 950°C, and cold working can be employed after solution treatment.Sourcing Inconel 718 in India
In India, high-quality Inconel 718 is sourced from reputable manufacturers and major mills such as Tata Steel, Jindal Stainless, and from authorized distributors of international producers. Availability is generally good in major industrial hubs like Mumbai, Pune, and Chennai, catering to the demanding aerospace and oil & gas sectors. Minimum Order Quantities (MOQs) for Inconel 718 can vary; for standard bar and plate, MOQs might range from 100 kg to 500 kg, while for specialized forms like seamless tubes or wire, they could be higher. The indicative price band for Inconel 718 in India typically ranges from ₹1200 to ₹2500 per kg, depending heavily on the form, quantity, and prevailing global nickel prices. Buyers should always expect and request a Material Test Certificate (MTC) as per IS/ASTM standards (e.g., ASTM B637) with every supply of Inconel 718, ensuring full traceability and compliance with material specifications; third-party inspection and Positive Material Identification (PMI) can be arranged upon request for critical applications of Inconel 718.Inconel 718 International Equivalents
| Standard | Code |
| ASTM | B637, B446, B704, B705, B572, B366 |
| ASME | SB637, SB446, SB704, SB705, SB572, SB366 |
| UNS | N07718 |
| Werkstoff Nr. | 2.4668 |
| AMS | 5582, 5598, 5599, 5662, 5663, 5664, 5700, 5704, 5705, 5706, 5707, 5708, 5709, 5832 |
| W.Nr. | 2.4668 |
| DIN | 2.4668 |
| GOST | ЭИ437ДУ (EI437DU) - Similar, but not direct equivalent |
FAQs about Inconel 718
What is the typical hardness of Inconel 718 in HRC?
Inconel 718 typically exhibits a hardness in the range of 33 to 42 HRC after the standard double-aging heat treatment, as per ASTM B637 specifications. This hardness contributes significantly to its high tensile and yield strength, making Inconel 718 suitable for demanding applications. Proper heat treatment is crucial to achieve and maintain this hardness level for Inconel 718.
Can Inconel 718 be used for cryogenic applications?
Yes, Inconel 718 demonstrates excellent mechanical properties, including good toughness and ductility, down to cryogenic temperatures. Its strength actually increases at lower temperatures, making Inconel 718 a suitable choice for applications involving liquid hydrogen and other extremely low-temperature environments, unlike many other high-strength alloys that become brittle.
What are the main advantages of using Inconel 718 in India?
The primary advantages of Inconel 718 in India are its exceptional strength-to-weight ratio, excellent corrosion and oxidation resistance, and its ability to maintain properties at high temperatures up to 650°C. This makes Inconel 718 ideal for India's growing aerospace, defense, and oil & gas sectors, offering reliability in critical components where failure is not an option. The availability through domestic suppliers further enhances its viability.
What is the difference between Inconel 718 and Inconel 625?
Inconel 718 and Inconel 625 are both high-performance nickel alloys, but Inconel 718 offers higher tensile and yield strength, particularly at room and intermediate temperatures, due to its precipitation-hardening mechanism. Inconel 625, on the other hand, has superior corrosion resistance, especially against pitting and crevice corrosion, and better ductility at cryogenic temperatures. The choice between Inconel 718 and 625 depends on whether strength or extreme corrosion resistance is the priority.
What is the recommended heat treatment for Inconel 718 bar supplied in India?
For Inconel 718 bar supplied in India to achieve peak mechanical properties, the standard heat treatment involves solution treatment at 980-1010°C followed by rapid cooling, and then a two-stage aging process: 8 hours at 720°C plus 8-10 hours at 620°C, with intermediate cooling. This process, crucial for Inconel 718, develops the strengthening precipitates. Always confirm with the supplier's MTC for the exact heat treatment applied.
What is the typical tensile strength of Inconel 718 bar (ASTM B637)?
According to ASTM B637, the typical Ultimate Tensile Strength (UTS) for Inconel 718 bar ranges from 1035 to 1379 MPa (150 to 200 ksi). The Yield Strength (YS) at 0.2% offset is usually between 760 and 1070 MPa (110 to 155 ksi). These values reflect the high strength achievable with Inconel 718 after proper heat treatment, making it suitable for critical structural components.
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