Incorporating the right material in your industrial project is as vital as the design itself. Picking the proper alloy can be the difference between a successful project and a failure. In the world of superalloys, two names often surface—Inconel 625 and Incoloy 825. Both are nickel-based superalloys, however, they differ in their composition and properties. This article delves into the intricacies of these alloys, comparing their characteristics, applications, and pricing.
A Brief Introduction to Superalloys
Superalloys, also known as high-performance alloys, have the ability to function under immense mechanical stress and high temperatures, and in severe corrosive environments. These materials usually have a matrix with an austenitic face-centered cubic crystal structure. A prime example of such alloys is the Inconel family, including Inconel 625, renowned for its superior resistance to heat and corrosion.
Understanding Inconel 625
Inconel 625, an austenitic nickel-chromium-based superalloy, contains a higher amount of nickel compared to other Inconel grades. This alloy is known for its impressive blend of strength, fabricability, and outstanding corrosion resistance, making it highly useful in various industrial applications.
Key Traits of Inconel 625
Inconel 625, with its high nickel content, offers superior strength and excellent resistance to a wide range of corrosive environments. Its particular resistance to oxidation makes it highly useful in nuclear and marine applications. Inconel 625’s service temperature ranges from cryogenic levels to around 982°C. The alloy’s high strength is attributed to the stiffening effect of niobium and molybdenum, situated in the nickel-chromium matrix. Therefore, the Inconel 625 alloy does not necessitate precipitation hardening treatments.
Composition of Inconel 625
The primary elements of Inconel 625 by mass are approximately 58% Nickel, 20-23% Chromium, 5% Iron, 8-10% Molybdenum, and 3.15-4.15% Niobium. Additionally, it contains small amounts of 1% Cobalt, 0.5% Manganese, 0.4% Copper, 0.4% Aluminum, 0.5% Titanium, 0.1% Silicon, 0.015% Carbon, and 0.015% Sulfur.
Inconel 625 Mechanical Properties
Inconel 625 possesses a density of 8.4 g/cm3, a melting point of 1350 °C, a tensile strength of Psi – 135,000, MPa – 930, a yield strength (0.2% offset) of Psi – 75,000, MPa – 517, and an elongation of 42.5%.
The Incoloy 825 Story
Incoloy 825, on the other hand, contains a moderate amount of nickel compared to other Inconel grades. It is a nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium. This alloy offers superior resistance to both reducing and oxidizing acids, and stress-corrosion cracking, and is particularly resistant to pitting and crevice corrosion in aqueous environments.
Key Traits of Incoloy 825
Incoloy 825 is known for its resistance to a variety of corrosive environments. It demonstrates excellent resistance to reducing and oxidizing acids like sulfuric and phosphoric acids. Additionally, the alloy displays resistance to stress-corrosion cracking, pitting, and crevice corrosion.
Composition of Incoloy 825
The primary elements of Incoloy 825 by mass are approximately 38.0 – 46.0% Nickel, 19.5 – 23.5% Chromium, a minimum of 22.0% Iron, 2.5 – 3.5% Molybdenum, 0.6 – 1.2% Titanium, and 1.5 – 3.0% Copper. It also contains a few other elements in smaller quantities.
Incoloy 825 Mechanical Properties
Incoloy 825 has a density of 8.14 g/cm3, a melting point of 1400 °C, a tensile strength of Psi – 80,000, MPa – 550, a yield strength (0.2% offset) of Psi – 32,000, MPa – 220, and an elongation of 30%.
Table: Inconel 625 vs Incoloy 825
| Property | Inconel 625 | Incoloy 825 |
| Nickel Content | ~58% | 38.0 – 46.0% |
| Chromium Content | 20.0–23.0% | 19.5 – 23.5% |
| Iron Content | 5% | >22% |
| Density | 8.4 g/cm3 | 8.14 g/cm3 |
| Melting Point | 1350 °C | 1400 °C |
| Tensile Strength | Psi – 135,000, MPa – 930 | Psi – 80,000, MPa – 550 |
| Yield Strength | Psi – 75,000, MPa – 517 | Psi – 32,000, MPa – 220 |
| Elongation | 42.5% | 30% |
Analyzing the Differences
The major difference between Inconel 625 and Incoloy 825 lies in their nickel content. Inconel 625 is rich in nickel compared to Incoloy 825. This leads to variations in their respective performance at elevated temperatures. Inconel 625 exhibits greater strength at high temperatures due to its higher nickel content, making it suitable for more demanding applications such as gas turbines and nuclear reactors.
In contrast, Incoloy 825, with its moderate nickel content, has a higher melting point but lower yield strength and tensile strength. This makes it an ideal choice for less demanding applications like exhaust manifolds and chemical processing equipment.
Applications of Inconel 625 and Incoloy 825
Both Inconel 625 and Incoloy 825 find use across various industries, thanks to their distinctive properties. They are commonly used in chemical processing equipment, petroleum refining equipment, heat exchangers, pumps, and valves. They also find application in other industrial components exposed to high temperatures and corrosive environments.
Price Comparison
The price of both Inconel 625 and Incoloy 825 varies, largely depending on the product type and dimensions. For example, the price for Alloy 625 with a thickness of 0.4mm and dimensions of 250mm x 250mm starts from around £50.00. On the other hand, for Alloy 825 with a thickness of 0.5mm and dimensions of 250mm x 250mm, prices start from approximately £42.00.
Final Thoughts
Choosing between Inconel 625 and Incoloy 825 depends largely on your specific application and metallurgical requirements. If your project demands higher high-temperature strength and a more challenging application, Inconel 625 may be the better choice. Conversely, if your application is relatively lightweight and requires better corrosion resistance, Incoloy 825 could prove to be a more suitable option. Other factors to consider include cost implications and the availability of the material. Through an understanding of the unique properties of these superalloys, you can make an informed decision that meets your project’s requirements.
