Inconel 625, a superalloy known for its high strength and excellent fabricability, is widely used across various industries. This article dives deep into the unique composition of this nickel-chromium alloy, its physical and mechanical properties, and its various applications.
Composition of Inconel 625
The primary components of Inconel 625 are nickel, chromium, and molybdenum, with niobium added to enhance its strength. Below is a detailed composition table of Inconel 625.
| Element | Percentage |
| Nickel | 58.0 min |
| Chromium | 20.0-23.0 |
| Iron | 5.0 max |
| Molybdenum | 8.0-10.0 |
| Niobium + Tantalum | 3.15-4.15 |
| Carbon | 0.10 max |
| Manganese | 0.50 max |
| Silicon | 0.50 max |
| Phosphorus | 0.015 max |
| Sulfur | 0.015 max |
| Aluminum | 0.40 max |
| Titanium | 0.40 max |
| Cobalt | 1.0 max |
The above table represents the main elements in the Inconel 625 composition. The percentages may vary slightly based on the specific manufacturing process.
Physical Properties of Inconel 625
The physical properties of Inconel 625, such as its density and specific heat, make it an ideal material for various applications. The following table outlines some of these physical properties.
| Property | Value |
| Density | 0.305 lb/cu in |
| Melting Range | 2350-2460 °F |
| Specific Heat | 0.102 Btu/lb°F at 200°F |
| Permeability at 200 Oersted | 1.0006 |
| Curie Temperature | <-320°F |
These properties contribute to the alloy’s resistance to a wide range of temperatures and pressures, making it ideal for high-stress environments.
Mechanical Properties of Inconel 625
Inconel 625 showcases excellent mechanical properties, including high tensile strength, creep strength, and rupture strength. Here’s a glance at some of those properties.
| Property | Value |
| Tensile Strength | 120-160 ksi |
| Yield Strength (0.2% Offset) | 60-110 ksi |
| Elongation | 60-30% |
| Hardness (Brinell) | 175-240 |
These mechanical properties are derived from the stiffening effect of molybdenum and niobium on its nickel-chromium matrix, making the alloy an excellent choice for high-stress applications.
Heat Treatment of Inconel 625
Inconel 625 is typically not strengthened by heat treatment. It can be provided in the annealed, solution annealed, or cold hardened condition. The solution annealed condition is used for applications above 1100°F to achieve optimal creep resistance, while the annealed condition is typically employed in services up to 1100°F.
Workability of Inconel 625
Inconel 625 exhibits good hot and cold workability. Hot-working should be performed above 1600°F to ensure adequate ductility, while cold work is conducted below 1200°F. When the material becomes stiff from cold working, ductility can be restored by a process anneal.
Weldability of Inconel 625
Inconel 625 can be welded using conventional methods. Post-weld heat treatment is usually not necessary to maintain corrosion resistance. The alloy’s mechanical properties follow the same trends as base metal properties when welded.
Corrosion Resistance of Inconel 625
Inconel 625 exhibits excellent corrosion resistance in a wide range of environments, including seawater and various acids. Its high molybdenum content protects against pitting and other forms of localized corrosion.
Applications of Inconel 625
The unique composition and properties of Inconel 625 make it suitable for a wide range of applications, including:
- Aerospace: The alloy’s high tensile strength, oxidation resistance, and excellent weldability make it perfect for use in aircraft ducting systems, engine exhaust systems, and other aerospace applications.
- Marine: Its excellent corrosion resistance makes it ideal for use in seawater applications, such as in undersea communication cables and propeller blades for motor patrol gunboats.
- Chemical Processing: Due to its resistance to a wide range of corrosive environments, Inconel 625 is widely accepted in the chemical processing field.
Trade Names and Standards of Inconel 625
Inconel 625 is also known by several other names, including Sanicro® 625, Haynes 625, Nickelvac 625, Nicrofer 6020, Altemp 625, and Chronic 625. It meets or exceeds many leading industry standards, including those from ASTM, ASME, SAE, AMS, ISO, DIN, EN, and BS.
Conclusion
The Inconel 625 composition is a testament to its versatility, making it a preferred choice for various high-stress environments. Its excellent resistance to oxidation and corrosion, coupled with its high strength and ease of fabrication, makes it a favored material across multiple industries. Understanding the composition and properties of Inconel 625 can help businesses make informed decisions about the best materials for their specific needs.
