Inconel 725 (NC15Fe) solid solution strengthened nickel-based alloy
Alloy 725 is a nickel-chromium-iron-based solid solution strengthened alloy. It has good high-temperature corrosion resistance and oxidation resistance, excellent hot and cold processing and welding process properties, and has satisfactory thermal strength and high plasticity below 700°C. Alloys can be strengthened by cold working or joined by resistance welding, fusion welding or brazing.
Inconel 725 has the following features:
1. It has good resistance to corrosion by reducing, oxidizing and nitriding media.
2. It has good resistance to stress corrosion cracking at room temperature and high temperature.
3. It has good resistance to corrosion by dry chlorine gas and hydrogen chloride gas.
4. It has good mechanical properties at zero, room temperature and high temperature.
5. It has good creep rupture resistance and is recommended for use above 700°C.
Metallographic structure of Inconel 725:
Inconel 725 has a face-centered cubic lattice structure.
Corrosion resistance of Inconel 725:
Alloy 725 is corrosion resistant to a variety of corrosive media. The composition of chromium gives this alloy better corrosion resistance under oxidizing conditions than Nickel 99.2 (Alloy 200) and Nickel 99.2 (Alloy 201, low carbon). At the same time, the higher nickel content gives the alloy good corrosion resistance in reducing conditions and alkaline solutions, and can effectively prevent chlorine-iron stress corrosion cracking. Alloy 725 has good corrosion resistance in organic acids such as acetic acid, acetic acid, formic acid, stearic acid, and moderate corrosion resistance in inorganic acids. It has excellent corrosion resistance in high-purity water used in primary and secondary circulation in nuclear reactors. The particularly outstanding performance of 725 is its ability to resist corrosion from dry chlorine and hydrogen chloride, and its application temperature can reach 650°C. At high temperatures, annealed and solution-treated alloys have good resistance to oxidation spalling and high strength in the air. The alloy is also resistant to ammonia gas and nitriding and carburizing atmospheres. However, when the redox conditions alternate, the alloy will be corroded by some oxidizing media (such as green death liquid).
Inconel 725 process performance and requirements:
Thermal processing
1. Thermal processing temperature range is 1200℃~900℃, and the cooling method is water quenching or rapid air cooling.
2. To obtain good corrosion resistance and the most suitable crystal structure, heat treatment is required after heat processing.
3. Materials can be fed directly into the heated furnace.
Cold working
1. Cold working materials should be in an annealed or solution heat treated state. The work hardening rate of 725 alloy is close to that of austenitic stainless steel, so similar processing equipment can be selected.
2. Intermediate annealing should be performed during the cold working process.
3. When the cold working amount is greater than 5%, the workpiece needs to be solution treated.
4. To reduce material wear, the mold should be made of alloy tool steel, carbide or cast steel.
Inconel 725 welding process
The alloy has good welding performance and can be connected by various methods such as arc welding, argon arc welding, resistance welding and brazing. Large or complex welded structural parts should be annealed at 870°C for 1 hour after welding to eliminate welding stress.
Inconel 725 parts heat treatment process
The heat treatment process of parts should be carried out according to the heat treatment system of the corresponding material standard. Annealing of sheet and strip parts should be carried out in a protective atmosphere.
Application scope of Inconel 725: 1. Thermowells in corrosive atmospheres
2. Vinyl chloride monomer production: resistant to chlorine gas, hydrogen chloride, oxidation and carbonization corrosion
3. Oxidation of uranium into hexafluoride: resistant to hydrogen fluoride corrosion
4. Fields of production and use of corrosive alkali metals, especially environments where sulfides are used
5. Preparation of titanium dioxide using chlorine gas method
6. Production of organic or inorganic chlorides and fluorides: resistance to chlorine and fluorine corrosion
7. Nuclear Reactor
8. Retorts and components in heat treatment furnaces, especially in carbonizing and nitriding atmospheres
9. For catalytic regenerators in petrochemical production, alloy 725 is recommended for applications above 700°C to obtain longer service life.
