Table of Contents
Introduction
Got a high-heat, high-stress project? Inconel 738 is up for the job. This nickel-based superalloy is built for intense environments, with properties that stand up to extreme heat and corrosion. From gas turbines to aerospace, Alloy 738 delivers reliability where it counts. In this article, we explore Alloy 738’s unique properties, specifications, applications, and how it compares to other superalloys.
What is Inconel 738?
Inconel 738 (UNS N07738) is a nickel-chromium-cobalt alloy that performs in extreme heat and chemically aggressive environments. Engineered for strength and corrosion resistance, it’s found in industries where components face high stress and oxidation, such as gas turbines and jet engines. The alloy’s balanced mix of nickel, chromium, and cobalt gives it superior durability for demanding applications.
What Are the Specifications of Inconel Alloy 738?
738 Inconel Equivalent
| Specification | Equivalent |
| UNS | N07738 |
| AMS | 5391 |
| ASTM | B637 |
| DIN | W.Nr. 2.4652 |
| EN | 2.4652 |
| JIS | NCF 738 |
Inconel 738 Chemical Composition
| Element | Composition (%) |
| Nickel (Ni) | Balance |
| Chromium (Cr) | 15.7 – 16.3 |
| Cobalt (Co) | 8.0 – 9.0 |
| Molybdenum (Mo) | Max 1.5 |
| Titanium (Ti) | 3.4 – 3.6 |
| Aluminum (Al) | 3.2 – 3.4 |
| Carbon (C) | Max 0.17 |
| Manganese (Mn) | Max 0.5 |
| Silicon (Si) | Max 0.5 |
| Boron (B) | 0.005 – 0.015 |
| Zirconium (Zr) | Max 0.10 |
Inconel Metal 738 Mechanical Properties
| Property | Value |
| Tensile Strength | 135 ksi (min) |
| Yield Strength | 100 ksi (min) |
| Elongation | 5 – 12% |
| Hardness (Rockwell C) | 40 – 45 HRC |
Inconel Metal 738 Physical Properties
| Property | Value |
| Density | 8.11 g/cm³ |
| Melting Point | 1205-1290°C |
| Thermal Conductivity | 11.2 W/m·K (at 20°C) |
| Specific Heat | 0.103 cal/g°C |
Nickel Alloy 738 Corrosion Resistance
| Environment | Corrosion Resistance Performance |
| Oxidizing Atmospheres | Excellent resistance up to 1800°F (982°C), retaining structural integrity. |
| Sulfur-bearing Environments | High resistance in oxidizing sulfur conditions, performing well up to 1700°F (927°C). |
| Aqueous Environments | Limited resistance; Inconel 738 is not ideal for sustained exposure in wet or humid conditions. |
| Carburizing Atmospheres | Good resistance to carburization up to 1500°F (816°C), maintaining surface stability. |
Nickle Alloy 738 Heat Treatment
| Heat Treatment Process | Temperature Range |
| Solution Treatment | 2100°F – 2150°F (1149°C – 1177°C) |
| Precipitation Hardening | 1400°F – 1600°F (760°C – 871°C) |
In recent advancements, additive manufacturing methods like Electron Beam Powder Bed Fusion have enabled significant microstructural-property enhancements in 738 Inconel, as shown in this study on microstructural-property relationships in additively manufactured Inconel 738.
How Does Inconel Alloy 738 Benefit You?
- Withstands High Temperatures: This alloy holds up at temperatures up to 1800°F (982°C), making it ideal for equipment facing constant, intense heat.
- Resists Oxidation: Thanks to its high chromium and aluminum content, it forms a durable oxide layer that protects against oxidation in high-temperature settings, extending the life of your equipment.
- Corrosion-Resistant: In sulfur-rich and other corrosive environments, this material stays tough, providing essential corrosion resistance for applications like gas turbines and chemical processing.
- Fatigue and Creep Resistance: Designed to resist stress over time, it withstands constant, repeated cycles without breaking down, making it perfect for equipment that’s in action long-term.
- Castable for Complex Shapes: This alloy casts easily, allowing manufacturers to shape it without compromising strength, making it a flexible choice for turbine blades and other complex forms.
What is Inconel 738 Used For?
- Aerospace: Engine turbine blades, combustion liners.
- Power Generation: Hot section components in gas turbines.
- Industrial Gas Turbines: Blades, combustion chambers, other high-heat parts.
- Chemical Processing: High-temperature equipment exposed to corrosive environments.
How Does Inconel Alloy 738 Compare to Other Alloys?
Inconel 738 vs 718
Inconel 738 and 718 are both strong in high heat, but they suit different needs.
Alloy 738’s higher chromium and cobalt content give it better resistance to oxidation and creep, so it excels in turbine blades and similar uses. Inconel 718 is easier to weld, making it more suitable for structural components that don’t face the same extreme temperatures.
Inconel 738 vs Inconel 625
Inconel 738 and Inconel 625 both resist corrosion, but they shine in different places.
738 Inconel is made for high-temperature durability, so it’s ideal for gas turbines and aerospace parts. 625 Inconel, with its molybdenum and niobium, performs better in marine settings where pitting and crevice corrosion are common but isn’t as heat-resistant as 738.
Conclusion
Inconel 738 is a superalloy crafted for intense environments, with strength and corrosion resistance that make it a staple in industries like aerospace and power generation. It’s engineered to perform at high temperatures, offering reliability in applications where heat, corrosion, and stress are constant.
For more on high-performance alloys like Alloy 738, reach out to learn how it can work for your projects.
FAQs
What is INCONEL 738 standard?
INCONEL 738 is typically specified under ASTM B637 for bars, forgings, and other high-performance components. This standard covers the production and mechanical property requirements of nickel-based alloys used in applications that demand high strength and corrosion resistance at elevated temperatures.
Is Inconel 738 easy to machine?
It’s tough to machine, but it’s well-suited for casting, allowing complex shapes for aerospace and industrial parts.
What industries use Inconel 738?
Inconel 738 is widely used in aerospace, power generation, and industrial gas turbine sectors. It’s especially valued in environments requiring components that can handle high temperatures and stress.
Read More:
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