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Inconel 738LC, also known as IN738LC or Alloy 738LC, is the low-carbon version of the cast nickel-based superalloy IN738.
The designation“LC” stands for “Low Carbon.”
Compared with the conventional higher-carbon grade, IN738LC uses adjusted carbon and minor-element chemistry to help control carbide formation, improve casting behavior, and reduce certain cracking concerns.
However, IN738LC remains a highly alloyed, gamma-prime-strengthened material, so welding and repair operations still require carefully controlled procedures.
The alloy contains approximately 60% nickel, with significant additions of chromium, cobalt, titanium, aluminum, tungsten, molybdenum, tantalum, and niobium.
Its high-temperature strength comes primarily from two strengthening mechanisms:
Solid-solution strengthening:Elements such as tungsten, molybdenum, and cobalt contribute to the strength and stability of the nickel-rich matrix.
Precipitation strengthening:Aluminum, titanium, tantalum, and niobium promote the formation of gamma-prime (γ′) precipitates, which provide resistance to deformation at elevated temperatures.
IN738LC typically contains a high volume fraction of γ′ precipitates, commonly around 40–45%, depending on composition and heat treatment.
This microstructure helps the alloy maintain strength under prolonged thermal and mechanical loading.
| Property | Typical Information |
|---|---|
| Alloy name | Inconel 738LC / IN738LC |
| Alloy family | Nickel-based cast superalloy |
| Strengthening mechanism | Solid solution + γ′ precipitation |
| Nickel content | Approximately 60–62 wt.% |
| Density | Approximately 8.1–8.2 g/cm³ |
| Melting range | Approximately 1230–1315°C |
| Typical processing | Vacuum melting and investment casting |
| Main characteristics | Creep resistance, high-temperature strength, oxidation and hot corrosion resistance |
| Main applications | Gas turbine blades, vanes, shrouds, and other hot-section castings |
Values are representative and may vary according to material specifications, casting conditions, and heat treatment.
The carefully balanced chemical composition of Inconel 738LC is responsible for its high-temperature mechanical properties and environmental resistance.
Nickel provides the primary matrix, while chromium supports oxidation and corrosion resistance. Elements such as aluminum, titanium, tantalum, and niobium form strengthening precipitates, and tungsten and molybdenum contribute to solid-solution strengthening.
| Element | Typical Range (wt.%) | Main Function |
|---|---|---|
| Nickel (Ni) | Balance (~61%) | Base matrix and high-temperature stability |
| Chromium (Cr) | 15.5–16.5 | Oxidation and hot corrosion resistance |
| Cobalt (Co) | 8.0–9.0 | Solid-solution strengthening and microstructural effects |
| Tungsten (W) | 2.4–2.8 | High-temperature solid-solution strengthening |
| Molybdenum (Mo) | 1.5–2.0 | Creep and strength enhancement |
| Tantalum (Ta) | 1.5–2.0 | γ′ precipitation strengthening |
| Niobium (Nb) | 0.6–1.1 | Precipitation and carbide strengthening |
| Titanium (Ti) | 3.2–3.7 | Formation of γ′ strengthening precipitates |
| Aluminum (Al) | 3.2–3.7 | γ′ formation and protective oxidation behavior |
| Carbon (C) | 0.09–0.13 | Carbide formation and grain-boundary strengthening |
| Boron (B) | 0.007–0.012 | Grain-boundary cohesion |
| Zirconium (Zr) | 0.03–0.08 | Grain-boundary properties and stability |
| Iron (Fe) | ≤ 0.50 | Controlled residual element |
These are reference composition ranges for this article, not a universal certification specification. Exact limits should be confirmed against the applicable material or customer specification.
Carbon plays an important role in the performance of nickel-based casting superalloys.
It contributes to carbide formation, which can improve grain-boundary strength and high-temperature creep resistance when properly controlled.
However, excessive or poorly distributed carbides may contribute to undesirable microstructures and cracking problems during casting or subsequent processing.
The low-carbon design of IN738LC helps balance carbide formation, casting characteristics, and mechanical performance.
This controlled approach is especially important when manufacturing complex turbine components through investment casting.
The physical properties of IN738LC influence casting design, thermal behavior, structural analysis, and component performance in high-temperature environments.
| Property | Typical Value |
|---|---|
| Density | 8.11 g/cm³ |
| Melting range | 1230–1315°C |
| Thermal conductivity at 100°C | 11.4 W/m·K |
| Thermal conductivity at 900°C | 21.5 W/m·K |
| Electrical resistivity at 20°C | 1.25 µΩ·m |
| Mean thermal expansion coefficient, 20–100°C | 12.0 × 10⁻⁶/K |
| Mean thermal expansion coefficient, 20–900°C | 16.2 × 10⁻⁶/K |
| Specific heat capacity at 20°C | 430 J/kg·K |
| Young's modulus at 20°C | 210 GPa |
| Young's modulus at 850°C | 150 GPa |
The values above are indicative reference data. They should not be treated as certified design values without confirmation from the applicable technical datasheet or actual material testing.
Gas turbine components experience repeated heating and cooling cycles, making thermal expansion and dimensional stability important considerations.
IN738LC combines relatively high mechanical strength with good resistance to high-temperature deformation.
Its thermal conductivity, expansion behavior, and elastic modulus must be considered during component design, particularly where tight dimensional tolerances, thermal gradients, or cyclic loading are involved.
One of the main advantages of IN738LC is its ability to retain useful mechanical strength at elevated temperatures.
Through precipitation strengthening and suitable heat treatment, the alloy develops a microstructure capable of resisting deformation under sustained loads.
| Mechanical Property | Indicative Value |
|---|---|
| Room-temperature tensile strength | 950–1150 MPa |
| Room-temperature 0.2% yield strength | 750–880 MPa |
| Room-temperature elongation | Approximately 4–8% or higher, depending on condition |
| Brinell hardness | Approximately 340–400 HBW |
| Rockwell hardness | Approximately 35–42 HRC |
Mechanical properties depend on casting geometry, defect population, specimen orientation, heat treatment, and testing conditions. These ranges are for general technical reference only.
Creep resistance is one of the most important reasons IN738LC is used in gas turbine components.
Creep refers to the gradual deformation of a material under sustained stress at elevated temperatures.
IN738LC is engineered to resist this deformation through its high γ′ precipitate content, solid-solution strengthening elements, and controlled grain-boundary chemistry.
Stress-rupture performance is normally evaluated at specified combinations of temperature, applied stress, and time.
For example, engineering evaluations may involve long-duration tests at temperatures around 815–870°C.
However, actual rupture life cannot be defined by temperature alone. It depends on the applied stress, casting structure, heat treatment, and acceptance specification.
For critical turbine applications, engineers should rely on verified stress-rupture test reports and qualified design data rather than generalized property tables.
Proper heat treatment is essential for developing the desired microstructure and mechanical properties of IN738LC castings.
A commonly referenced heat treatment consists of two main stages.
1120°C for 2 hours, followed by accelerated air cooling or an appropriate controlled cooling process.
This stage helps adjust the cast microstructure and influences the distribution of strengthening phases.
845°C for 24 hours, followed by air cooling.
The aging stage promotes the formation and development of γ′ precipitates, contributing to the alloy's high-temperature strength.
The γ′ phase is central to the performance of IN738LC.
Its size, distribution, and volume fraction influence mechanical strength, creep resistance, and high-temperature behavior.
A suitable heat treatment helps establish the required precipitation structure while managing the effects of the original casting microstructure.
Exact cycles should be selected according to the relevant material specification, casting geometry, and component requirements.
IN738LC offers several valuable properties for high-temperature casting applications.
The alloy's high γ′ precipitate content provides effective strengthening at elevated temperatures.
This makes it suitable for components exposed to sustained mechanical loads, such as turbine blades and other hot-section castings.
Tungsten, molybdenum, and γ′-forming elements work together to resist time-dependent deformation.
This is particularly important in industrial gas turbines operating for extended periods under high thermal and mechanical loads.
With approximately 16% chromium, IN738LC provides useful resistance to oxidation and certain high-temperature corrosive environments.
Chromium contributes to protective oxide scale formation, while aluminum also plays an important role in oxidation behavior.
This combination is beneficial for turbine components exposed to combustion gases and environments containing corrosive deposits.
However, actual hot corrosion resistance depends on temperature, fuel composition, salt contaminants, coatings, and operating conditions.
The low-carbon composition helps manage carbide formation and casting microstructure.
Compared with higher-carbon variants, it offers a different balance between carbide strengthening, grain-boundary behavior, and processing characteristics.
IN738LC is designed to maintain a useful strengthening microstructure during high-temperature operation.
Its long-term stability depends on service temperature, exposure duration, applied stress, and thermal history.
For severe service, changes in γ′ morphology, carbide distribution, and possible detrimental phases must be considered.
IN738LC is primarily used for precision cast components that require a combination of high-temperature strength, creep resistance, and environmental durability.
In aerospace applications, IN738LC may be selected for appropriately qualified hot-section castings, including:
Turbine blades
Turbine guide vanes
Shroud segments
Nozzle components
Other high-temperature structural castings
These components experience thermal cycling, mechanical loading, and exposure to hot combustion gases.
Material selection depends on the engine design, component location, qualification requirements, and operating conditions.
Industrial gas turbines are a major application area for IN738LC.
Typical applications include:
Turbine rotor blades
Stationary turbine vanes
Nozzle guide vane segments
Shrouds and hot gas path components
Selected high-temperature sealing and structural castings
Power-generation turbines often operate over extended service intervals, making creep resistance, oxidation resistance, and long-term component reliability particularly important.
Marine and offshore turbine systems may encounter corrosive environments associated with airborne salts, fuel contaminants, and hot combustion gases.
IN738LC can be considered for qualified turbine hot-section components where its strength and corrosion-resistance characteristics are appropriate.
Protective coatings and environmental control may still be necessary for severe salt-related hot corrosion conditions.
IN738LC may also be evaluated for specialized turbine or propulsion components requiring high-temperature strength and casting capability.
Suitability must be established through application-specific design, testing, and qualification.
The main distinction between IN738 and IN738LC lies in the adjusted carbon and minor-element composition.
Both alloys belong to the same family of precipitation-hardened nickel-based casting superalloys and share similar strengthening mechanisms.
| Feature | IN738 | IN738LC |
|---|---|---|
| Alloy type | Nickel-based cast superalloy | Nickel-based cast superalloy |
| Carbon design | Higher-carbon variant | Low-carbon variant |
| Strengthening | γ′ precipitation + solid solution | γ′ precipitation + solid solution |
| Carbide behavior | Greater carbon availability for carbide formation | Adjusted carbide formation and distribution |
| Weldability | Crack-sensitive | Still crack-sensitive; controlled procedures required |
| Typical use | High-temperature turbine castings | High-temperature turbine castings |
| Selection basis | Design and qualified specification | Design and qualified specification |
The lower carbon content of IN738LC does not automatically make it easy to weld.
Because the alloy contains substantial aluminum and titanium, it remains susceptible to cracking during welding and post-weld heat treatment.
For this reason, welding, brazing, and component repair must be carefully evaluated using qualified procedures.
For casting manufacturers and buyers, selecting the correct alloy grade is only one part of ensuring reliable material quality.
The production of IN738LC also requires control over raw materials, melting conditions, chemical composition, cleanliness, and subsequent processing.
Vacuum induction melting (VIM) is commonly used in the production of nickel-based superalloy master alloys.
A controlled vacuum environment helps reduce exposure to atmospheric gases and supports the production of clean alloy material.
Because IN738LC contains reactive elements such as aluminum and titanium, controlling oxygen, nitrogen, and other impurities is particularly important.
Major alloying elements must be carefully controlled to achieve the intended γ′ precipitation behavior, oxidation resistance, and mechanical performance.
Trace elements and impurities also require attention because they can influence solidification, grain-boundary behavior, and casting quality.
IN738LC is commonly processed through investment casting to manufacture complex turbine components.
Casting parameters such as mold temperature, melt temperature, solidification conditions, and feeding design influence defect formation and final microstructure.
Depending on customer requirements, relevant quality verification may include:
Chemical composition analysis
Oxygen, nitrogen, and hydrogen analysis
Metallographic examination
Mechanical property testing
Non-destructive inspection
Heat treatment records
Batch traceability and inspection documentation
For master alloy buyers, agreeing on chemical composition limits, product form, inspection methods, and acceptance criteria before production is essential.
Inconel 738LC is mainly used in high-temperature turbine castings, including blades, vanes, shrouds, and other gas turbine hot-section components that require creep resistance and environmental durability.
LC stands for Low Carbon. It identifies the modified carbon chemistry of the IN738 alloy family.
IN738LC is a nickel-based alloy containing approximately 16% chromium, 8.5% cobalt, 3.4% aluminum, 3.4% titanium, and smaller amounts of tungsten, molybdenum, tantalum, niobium, carbon, boron, and zirconium.
Exact composition limits depend on the applicable material specification.
IN738LC has a typical melting range of approximately 1230–1315°C. The actual solidus and liquidus temperatures may vary with composition.
The density of IN738LC is commonly reported at approximately 8.1–8.2 g/cm³.
A commonly referenced treatment is solution heat treatment at 1120°C for 2 hours, followed by accelerated cooling, then aging at 845°C for 24 hours.
Specific heat treatment requirements should follow the qualified material specification.
No. Although IN738LC is a low-carbon variant, its high γ′-forming element content makes it susceptible to weld cracking and strain-age cracking. Specialized welding or repair procedures are required.
IN738LC is used for high-temperature applications, often in a temperature range approaching 900°C. However, the allowable service temperature depends on stress, required life, component geometry, coatings, and operating environment. There is no single maximum temperature suitable for every application.
Inconel 738LC is an important nickel-based casting superalloy for high-temperature turbine applications.
Its carefully balanced composition provides a combination of precipitation strengthening, creep resistance, high-temperature strength, and oxidation and hot corrosion resistance.
The low-carbon formulation helps control carbide-related microstructural characteristics, while appropriate heat treatment develops the γ′ precipitate structure required for high-temperature performance.
For material buyers and casting manufacturers, understanding IN738LC chemical composition, processing requirements, and property limitations is essential for selecting the appropriate material and establishing reliable quality requirements.
If you are sourcing IN738LC master alloy for investment casting or other qualified high-temperature alloy applications, selecting a supplier with appropriate melting capabilities, chemical composition control, inspection procedures, and material traceability is an important step.
Contact our team to discuss your required composition, master alloy form, order quantity, inspection requirements, and technical specifications.
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