Inconel 718: Composition, Characteristics, and Applications in Casting

HDCMFG
November 22, 2023

What Is Inconel 718?

Inconel 718 is a robust nickel-based superalloy recognized for its high strength and corrosion resistance in extreme conditions. Comprising primarily nickel, chromium, iron, and other alloys, it excels in various demanding applications. The alloy’s unique composition, coupled with precise heat treatment, contributes to its outstanding strength, durability, and resistance to oxidation and corrosion, making it a preferred material for critical components in challenging environments.

The “718” in Inconel 718 Represents What

The 718 in Inconel 718 does not give the number any embodiment of the alloy’s qualities or elements like in other material codes. However, it is not a unique number that differentiates it from the other Inconel alloys but rather its part of the series of numbers that define the alloy itself. The Inconel family of alloys is a group of nickel-chromium superalloys that cover the performance requirements regarding the resistance to corrosion, high temperature endurance, as well as the structural strength. The designation of the numbering system, which includes “718,” is really a designation or an identifier of the particular molybdenumated composition that was involved in the development and commercialization of this alloy. Incoloy 718 is rather yarded for its high altitude, compressive, and creep corruption properties till about 1300 °F (700 °C) and is aptly used in gas turbine engines, aerospace and oil and gas drilling equipment.

Chemical Composition of Inconel 718

Component Elements Properties	Metric	English
Aluminum, Al	0.20 – 0.80 %	0.20 – 0.80 %
Boron, B	<= 0.0060 %	<= 0.0060 %
Carbon, C	<= 0.080 %	<= 0.080 %
Chromium, Cr	17 – 21 %	17 – 21 %
Cobalt, Co	<= 1.0 %	<= 1.0 %
Copper, Cu	<= 0.30 %	<= 0.30 %
Iron, Fe	17%	17%
Manganese, Mn	<= 0.35 %	<= 0.35 %
Molybdenum, Mo	2.8 – 3.3 %	2.8 – 3.3 %
Nickel, Ni	50 – 55 %	50 – 55 %
Niobium, Nb (Columbium, Cb)	4.75 – 5.5 %	4.75 – 5.5 %
Phosphorus, P	<= 0.015 %	<= 0.015 %
Silicon, Si	<= 0.35 %	<= 0.35 %
Sulfur, S	<= 0.015 %	<= 0.015 %
Titanium, Ti	0.65 – 1.15 %	0.65 – 1.15 %

Influence of Chemical Composition on the Properties of Inconel 718

Inconel 718, an outstanding nickel-based superalloy appreciated for its extraordinary mechanical properties, as well as the ability to withstand high temperatures and corrosion is by design a carefully balanced composition of chemicals. Nickel forms the frame of the alloy which strengthens it and makes it resistant to corrosion and then chromium reinforces its resistance to oxidation. Niobium and titanium are sources of strengthening, forming precipitates during the heat treatment that provide rigidness and stability. Strength and creep resistance are given by molybdenum, whereas precipitation strengthening is what aluminium brings. Iron, as well as trace elements such as carbon, sulfur and silicon impact weldability and corrosion traits. The interaction between these elements is the essential ingredient in designing Inconel 718 to meet application needs.

Physical Properties of Inconel 718

Physical Properties	Metric	English
Density	8.19 g/cc	0.296 lb/in³

Mechanical Properties of Inconel 718

Mechanical Properties	Metric	English
Tensile Strength, Ultimate	1100 MPa @Temperature 650 °C	160000 psi @Temperature 1200 °F
Tensile Strength, Ultimate	1375 MPa @Temperature 23.0 °C	199400 psi @Temperature 73.4 °F
Tensile Strength, Yield	1100 MPa @Strain 0.200 %	160000 psi @Strain 0.200 %
Tensile Strength, Yield	980 MPa @Strain 0.200 %, Temperature 650 °C	142000 psi @Strain 0.200 %, Temperature 1200 °F
Elongation at Break	25%	25%
Elongation at Break	18 % @Temperature 650 °C	18 % @Temperature 1200 °F
Rupture Strength	593 MPa @Temperature 649 °C, Time 3.60e+6 sec	86000 psi @Temperature 1200 °F, Time 1000 hour
Rupture Strength	703 MPa @Temperature 649 °C, Time 360000 sec	102000 psi @Temperature 1200 °F, Time 100 hour

Electrical Properties of Inconel 718

Electrical Properties	Metric	English
Electrical Resistivity	0.000125 ohm-cm	0.000125 ohm-cm
Magnetic Permeability	1.0011	1.0011
Curie Temperature	-112 °C	-170 °F

Thermal Properties of Inconel 718

Thermal Properties	Metric	English
CTE, linear	13.0 µm/m-°C @Temperature 20.0 – 100 °C	7.22 µin/in-°F @Temperature 68.0 – 212 °F
Specific Heat Capacity	0.435 J/g-°C	0.104 BTU/lb-°F
Thermal Conductivity	11.4 W/m-K	79.1 BTU-in/hr-ft²-°F
Melting Point	1260 – 1336 °C	2300 – 2437 °F
Solidus	1260 °C	2300 °F
Liquidus	1336 °C	2437 °F

Common Application of Inconel 718

Inconel 718 finds widespread application across various industries due to its exceptional properties. Common uses include aerospace components, industrial machinery, and applications requiring high-strength, corrosion-resistant materials. Its versatility makes it a go-to choice in situations where reliability and durability are paramount, such as in manufacturing turbine engines, rocket motors, and components exposed to extreme temperatures and harsh environments.

Benefits of Using Inconel 718 in Investment Casting

The utilization of Inconel 718 in investment casting offers a range of significant benefits:

High Temperature and Corrosion Resistance:
- Maintains strength in extreme heat and exhibits exceptional corrosion resistance.
Impressive Mechanical Properties:
- Boasts high tensile and yield strength, ensuring robust performance.
Durability and Longevity:
- Components offer lasting durability, enhancing overall equipment reliability.
Resistance to Fatigue and Creep:
- Exhibits resistance to fatigue and creep deformation for prolonged stability.
Ease of Forming and Machining:
- Facilitates the creation of intricate components during the investment casting process.
Wide Range of Customization:
- Allows for the production of custom-designed components tailored to specific needs.

In summary, Inconel 718’s utilization in investment casting offers a versatile, durable, and reliable solution for critical components in various industries.

Challenges of Using Inconel 718 in Investment Casting

High Melting Point: Demands specialized equipment and high-energy requirements.
Fluidity and Mold Filling: Inconel 718 has poor fluidity, requiring careful mold design for proper filling.
Thermal Stresses: Susceptibility to thermal stresses may lead to cracking during casting.
Oxidation and Decarburization: Prone to oxidation and decarburization, necessitating special atmospheres or coatings.
Grain Size Control: Precise control of cooling rates and solidification parameters is crucial for the desired microstructure.
Surface Finish and Porosity: Achieving a smooth finish is difficult due to high viscosity; and susceptibility to gas porosity.
Post-Casting Heat Treatment: Requires careful control to avoid additional stresses or distortion.
Cost Considerations: Inconel 718 is a premium alloy, impacting overall economic feasibility.

Despite these challenges, the exceptional properties of Inconel 718 often make it a preferred choice in specific applications, necessitating a careful balance of expertise and resources for successful utilization.

Inconel 718 Compared to Inconel 625 in Investment Casting

Inconel 718 and Inconel 625, compared in the realm of investment casting, exhibit distinct characteristics. Inconel 718, with its higher nickel content, boasts superior strength and temperature resistance, making it a prime choice for aerospace and industrial applications but at a higher cost. In contrast, Inconel 625, renowned for exceptional corrosion resistance, finds its niche in chemical processing and marine industries, offering a cost-effective solution. The decision between them hinges on specific application requirements, budget considerations, and the desired balance among temperature resistance, mechanical strength, and corrosion resistance, guiding manufacturers in optimal material selection for investment casting.

Cost Consideration When Custom Inconel 718 Casting Parts

Material Cost: Inconel 718 is a premium alloy with high material costs.
Specialized Equipment: The high melting point requires costly specialized equipment.
Energy Requirements: The casting process demands elevated energy consumption.
Post-Casting Processes: Heat treatment for optimal properties adds to costs.
Process Complexity: Intricate mold design and precise controls increase labor and operational costs.
Waste and Scrap: Challenges in casting may lead to higher waste levels, impacting cost efficiency.
Quality Assurance: Rigorous testing and inspection processes contribute to production costs.
Tooling and Maintenance: The abrasive nature may increase wear on tooling, requiring regular maintenance.

Careful consideration of these factors is essential for determining the economic feasibility of Inconel 718 investment casting, balancing its performance benefits with associated costs.

Custom Inconel 718 Investment Casting Parts

When seeking custom Inconel 718 investment casting parts from manufacturers, it’s crucial to research reputable companies with proven expertise in handling Inconel 718. Assess their capabilities, ensuring they meet your specific design and dimensions requirements. Verify the manufacturer’s commitment to quality assurance, material traceability, and compliance with industry standards. Discuss lead times, obtain detailed cost estimates, and establish clear communication channels for collaborative production. Additionally, inquire about after-sales support and warranty policies. This comprehensive approach ensures the reliable production of tailored Inconel 718 parts for your specific application.