1. Overview of Inconel625 (NO6625) alloy
Inconel 625 (NO6625) alloy is a high-temperature alloy that is solid solution strengthened and deformed. It mainly strengthens the nickel-chromium matrix through solid solution of refractory metals niobium and molybdenum. It has many outstanding performance characteristics, good organizational stability, and can maintain its own structural stability in high temperature environments and is not easy to change.
It has excellent corrosion resistance and has excellent resistance to various corrosive media in oxidizing and reducing environments. Inorganic acids such as nitric acid, phosphoric acid, sulfuric acid, hydrochloric acid and their mixed acids, Inconel 625 alloy can show excellent corrosion resistance. In addition, in chloride media, the alloy has excellent resistance to pitting, crevice corrosion, intergranular corrosion and erosion, and can effectively resist chloride ion reduction stress corrosion cracking. Even in seawater and industrial gas environments, or in contact with salt solutions at high temperatures, it will hardly cause corrosion.
At the same time, the fatigue and creep properties of Inconel 625 alloy are also relatively good, so that it can maintain a good performance state under repeated forces and long-term stress, and is not prone to fatigue cracks, excessive deformation and other problems.
With these excellent properties, Inconel 625 alloy is widely used in many important fields. In the aerospace field, it is often used to manufacture aircraft engine parts, such as turbine parts, aircraft nozzles, combustion chamber components and other high-temperature parts; in the petroleum industry, it can be used in the manufacture of corrosion-resistant and high-temperature resistant equipment such as oil well casings, valves and pipeline systems; in the chemical industry, equipment that requires corrosion resistance, such as chemical reactors, distillation towers, catalyst carriers, etc., often uses it; in the nuclear industry, corrosion-resistant parts in nuclear reactors and nuclear fuel processing equipment will also use Inconel625 alloy; and in marine engineering, desalination plant equipment, offshore oil extraction equipment, and offshore platform support structures and other parts facing the threat of seawater corrosion can obtain long-term and reliable corrosion protection by using Inconel 625 alloy.
2. Chemical composition and microstructure characteristics
(I) Chemical element composition
The main chemical elements of Inconel 625 alloy include nickel (Ni), chromium (Cr), molybdenum (Mo), niobium (Nb), etc., and also contain a small amount of iron (Fe), cobalt (Co), titanium (Ti), carbon (C) and other elements. The following is the role of each element in the alloy
(II) Microstructure characteristics
For rolled Inconel 625 alloy, it presents a typical austenite morphology, with a large number of fine deformation twins and segregation, and the presence of carbide second phase. Its grain size is (15±2.5)μm, with more high-angle grain boundaries and larger dislocation density, and preferential growth in the (111) direction.
The Inconel 625 alloy prepared by SLM (selective laser melting) has finer cellular crystals inside the molten pool, coarser cellular crystals outside the molten pool, and columnar crystals growing perpendicular to the molten pool boundary. The grain size inside the molten pool is in the range of 0.2-2μm. The SLM-formed alloy has the strongest grain texture characteristics on the XZ plane, the strongest (001) orientation, and its dislocation density is lower than that of the rolled alloy. The grain boundary orientation difference is mainly distributed in the range of 20° - 55°.
These different microstructures have an important influence on the properties of the alloy. For example, at 900°C, the oxidation resistance of the rolled Inconel 625 alloy is better than that of the SLM alloy. This is mainly attributed to the fact that the rolled alloy has more dislocations and twins. The higher dislocation density is conducive to improving the oxidation resistance of the Inconel 625 alloy. Different grain morphology, size and grain boundary characteristics will also affect the strength, hardness, fatigue resistance and other mechanical properties of the alloy to a certain extent, making them suitable for different working conditions and processing requirements.
3. Excellent performance
(I) Corrosion resistance
Inconel 625 alloy has excellent performance in corrosion resistance and can easily cope with a variety of corrosive media. In the face of acidic media, such as nitric acid, hydrochloric acid, sulfuric acid, etc., and their mixed acids, the alloy shows extremely low corrosion rate.
It is precisely because of this excellent corrosion resistance that Inconel 625 alloy is widely used in many fields. In the chemical industry, it is often used to manufacture equipment and pipelines working under various corrosive media, such as reactors, heat exchangers, pumps and valves, etc., to ensure that the equipment can operate stably for a long time and reduce the frequency of maintenance and replacement; in the field of marine engineering, components such as desalination plant equipment and offshore oil production equipment that are threatened by seawater corrosion can effectively resist seawater erosion and operate reliably.
(II) High temperature performance
Inconel 625 alloy has good performance from low temperature to high temperature environment (such as around 980℃).
For this reason, Inconel 625 alloy has key applications in high temperature scenes such as aerospace engines, such as for the manufacture of high temperature engine parts, combustion chambers, nozzles, etc. In these high temperature and performance-demanding parts, the alloy can work stably to ensure the normal operation of aerospace equipment.
(III) Antioxidation performance
Inconel 625 alloy has excellent antioxidation performance, which is mainly due to the synergistic effect of various elements in its chemical composition. Among them, chromium will form a dense chromium oxide film on the surface of the alloy at high temperature. This film can effectively prevent the penetration of oxidizing substances such as oxygen and prevent the internal metal from being further oxidized. Nickel gives the alloy good basic oxidation resistance, allowing it to maintain its own stable performance in an oxidizing environment. At the same time, elements such as molybdenum and niobium also indirectly contribute to the alloy's oxidation resistance and improve its overall oxidation resistance.
(IV) Mechanical properties
The tensile strength of Inconel 625 alloy is relatively good. The tensile strength can reach 830MPa or above at room temperature. In a high temperature environment, it can also maintain a high tensile strength level within the corresponding temperature range, ensuring that it is not easy to be broken when subjected to tension. In terms of yield strength, it is usually ≥415 MPa, which means that it can maintain a stable shape and performance before the force reaches a certain level, and will not easily undergo plastic deformation.
4. Diverse product specifications and supply status
Inconel 625 alloy has diverse product specifications and supply status. Common product forms include seamless pipes, steel plates, round steel, forgings, flanges, welded pipes, supporting welding materials, etc., which can meet the diverse needs of customers in different fields.
