Inconel 825 (UNS N08825/W.Nr. 2.4858/Incoloy825) comprising nickel, iron, chromium, molybdenum, copper, and titanium, known for its exceptional resistance to corrosion. This combination of elements gives the inconel alloy outstanding resistance to many corrosive environments, as well as high strength and good weldability. Additionally, Inconel 825 has excellent formability and machinability, making it a popular choice for many engineering applications.
Table of Contents
- Inconel 825 Chemical Composition
- Physical and Mechanical Properties of Inconel 825
- Heat Treatment of Inconel 825
- Corrosion Resistance of Inconel 825
- Applications of Inconel 825
- Welding and Fabrication of Inconel 825
- Machining and Forming of Inconel 825
Inconel 825 Chemical Composition
Inconel 825 (UNS N08825/W.Nr. 2.4858) is a nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium for exceptional corrosion resistance in an array of hazardous environments. The chemical composition of Inconel 825 is optimized to provide excellent resistance to oxidation, pitting, crevice corrosion, stress-corrosion cracking, intergranular corrosion, and chloride-ion-induced stress corrosion cracking.
Nickel is the major alloying component of Inconel 825; it comprises about 58% of the alloy mass. Nickel provides good general corrosion resistance and excellent resistance to stress-corrosion cracking in chloride-containing environments. Molybdenum enhances the pitting and crevice corrosion resistance of Inconel 825 as well as adds increased strength at elevated temperatures. Copper increases strength at temperatures ranging from cryogenic to moderate levels while also providing improved resistance to reducing acids such as Sulphuric acid and phosphoric acid. Lastly, Titanium serves as a grain refiner and further improves the structural integrity of Inconel 825 at higher temperatures.
Physical and Mechanical Properties of Inconel 825
Inconel 825 is highly resistant to pitting, crevice corrosion, and chloride-ion stress corrosion cracking, as well as reducing environments such as sulfuric and phosphoric acid solutions. This superior resistance has made the alloy a popular choice for many demanding applications in a variety of industries including chemical processing, pharmaceuticals, oil & gas, and heat exchangers, In addition to its excellent corrosion resistance properties,
Alloy 825 also exhibits impressive physical properties such as high strength at elevated temperatures up to 1150°C (2100°F). The alloy has a density of 8.4 g/cm3 (0.30 lbs/in3). Its melting range is between 1290°C – 1350°C (2350°F – 2460°F). The mechanical features of Inconel 825 depend on the heat treatment applied to it and include high tensile strength up to 930 MPa (135 ksi) or greater in some conditions depending on the product form.
It also features good fatigue strength and creep strength at elevated temperatures up 1100°C (2000°F). The modulus of elasticity is 207 GPa (30 Msi). Additionally, Inconel 825 offers superior formability when hot or cold worked compared to other nickel alloys due to its higher work hardening rate which makes it easier to produce complex shapes with tight tolerances.
Heat Treatment of Alloy 825
INCOLOY® alloy 825 is a composition of nickel, iron, chromium, molybdenum, copper, and titanium, combined to form a highly durable and corrosion-resistant alloy. Heat treatment of this alloy can affect its properties, and the heat treatment process must be carefully controlled to ensure the desired results.
The most common type of heat treatment for Alloy 825 is annealing. During annealing, the alloy is heated to a specific temperature for an extended period before it is slowly cooled. This allows for redistribution of the alloy’s crystalline structure which improves ductility and toughness while also reducing hardness and strength.
Solution heat treatment (also known as precipitation hardening) involves heating the material above its recrystallization temperature and then rapidly quenching it to cool it quickly. This can greatly improve mechanical properties such as tensile strength, yield strength, and creep resistance by introducing a second phase which strengthens the material due to precipitation hardening.
Corrosion Resistance of Incoloy 825
Incoloy 825 has exceptional resistance to the high amounts of nickel within the alloy which provides to stress corrosion cracking and resistance to chloride-ion as well as molybdenum and copper which give outstanding resistance to reducing environments such as those containing stress corrosion cracking and phosphoric acids. Molybdenum also increases the alloy’s immunity to pitting and crevice corrosion.
In addition to these beneficial elements, alloy 825 also has excellent properties when exposed to stress corrosion cracking such as nitric acid due to its high chromium content which creates a strong oxide film on top of the alloy’s surface. The titanium content further adds stability to this protective layer, resulting in superior oxidation resistant to compared with other alloys in its class. Furthermore, Incoloy 825 has good resistance to aqueous corrosion when exposed to temperatures from cryogenic up to about 550°C or 1,020°F depending on the environment.
Applications of Incoloy 825
Incoloy 825 is widely used across a variety of industries due to its exceptional corrosion resistance properties. Applications include chemical process equipment plants, oil and gas, flue gas desulfurization systems, food processing facilities, paper mills, power generation plants and more. The price of Incoloy 825 depends on the form that you purchase it in – plates tend to be much more expensive than bars or pipe/tubing pieces – however, it still represents a great value when you consider the level of protection it provides against corrosion damage over time.
Welding and Fabrication of Incoloy 825
Welding
Welding Incoloy 825 can be accomplished using traditional arc welding methods such as TIG, MIG, and SMAW as well as innovative technologies like laser welding or EBW (electron beam welding). When welding Incoloy 825, a preheat temperature of 350-450°F should be applied prior to welding to prevent cracking in the heat-affected zone. It’s also important to use filler metals with enough nickel content to match the base material for maximum corrosion protection and strength. Nickel-based filler metals such as Inconel Alloy 625 are recommended when welding Incoloy 825 because they provide superior strength and corrosion resistance compared to those with lower nickel content.
Fabrication
Fabrication of Incoloy 825 can be done using cutting tools made out of high-speed steel or cobalt alloys with good wear resistances such as K183M12 or K371M21C4V1 which can withstand high temperatures without losing their hardening properties. Grinding wheel materials should also be chosen carefully – carbide-tipped wheels are highly recommended because they have less abrasive build-up than regular steel wheels which can cause vibrations during grinding or finishing processes. Furthermore, the grinding process mustn’t produce any sparks which may ignite combustible materials nearby since Inconel is an inherently flammable metal alloy due to its high chromium content present in its chemical composition.
Machining and Forming of Incoloy 825
Machining:
Incoloy 825 is considered relatively difficult to machine due to its work-hardening properties, but proper tooling and coolant selection can help improve the process. High-speed steel or carbide tools are commonly used for machining this material, as well as cobalt or titanium nitride cutters for more abrasive conditions. When working with Incoloy 825, it is important to choose the right cutting speed and feed rate to avoid built-up edge formation, which can lead to premature failure of the cutting tool. Additionally, using positive rake angles can help reduce cutting forces while also promoting chip evacuation. The use of sufficient lubricants or coolants during the machining process will also help reduce temperature build-up in order to prevent thermal stress from forming in the workpiece material.
Forming:
Incoloy 825 has excellent formability characteristics which make it well-suited for various manufacturing processes such as bending, deep drawing, spinning and welding operations. The alloy’s high strength makes it easy to deform without sacrificing too much toughness or ductility during forming operations. It is important to pay attention to temperature when forming Incoloy 825 since this material has a lower temperature limit before it begins losing its malleability and formability properties. Additionally, proper lubrication should be used during forming operations to prevent sticking between the tool surface and the workpiece material surface area from occurring.
