24 July 2021 Inconel®
INCONEL® alloy 725 Nickel Based Alloy
INCONEL® alloy 725 (UNS N07725) is a nickel- chromium-molybdenum-niobium alloy that is highly resistant to corrosion and is age hardenable for extremely high strength. It has essentially the same corrosion resistance as INCONEL alloy 625, which is widely used in a broad range of severely corrosive environments. The strength of age-hardened INCONEL alloy 725 is of the order of twice that of annealed alloy 625. Because the strength of alloy 725 is developed by heat treatment, not by cold work, ductility and toughness remain high. Also, strength can be imparted to large or non-uniform sections that cannot be strengthened by cold work.
The chemical composition of INCONEL alloy 725 is given in Table 1. High levels of nickel and chromium provide corrosion resistance in reducing and oxidizing environments. The substantial molybdenum content enhances resistance to reducing media and provides a high degree of resistance to pitting and crevice corrosion. Additionally, the combination of elements makes the alloy resistant to hydrogen embrittlement and stress- corrosion cracking.
The properties of INCONEL alloy 725 are used for a range of applications that require outstanding corrosion resistance along with high strength. The alloy is used for hangers, landing nipples, side pocket mandrels and polished bore receptacles in sour gas service, where it resists the effects of hydrogen sulfide, chloride, and carbon dioxide. The alloy is also attractive for high strength fasteners in marine applications, where it resists corrosion, pitting and crevice attack in sea water.
Chemical Composition:
The following table shows the chemical composition of Inconel 725™.
| Elements | Content (%) |
|---|---|
| Nickel, Ni | 55 - 59 |
| Chromium, Cr | 19 - 22.5 |
| Iron, Fe | 9 |
| Molybdenum, Mo | 7 - 9.50 |
| Niobium, Nb (Columbium, Cb) | 2.75 - 4 |
| Titanium, Ti | 1 - 1.70 |
| Aluminum, Al | 0.35 |
| Manganese, Mn | 0.35 |
| Silicon, Si | 0.20 |
| Carbon, C | 0.030 |
| Phosphorous, P | 0.015 |
| Sulfur, S | 0.010 |
Physical Properties:
The physical properties of Inconel 725™ are given in the following table.
| Properties | Metric | Imperial |
|---|---|---|
| Density | 8.3 g/cm³ | 0.3 lb/in³ |
| Melting point | 1271-343ºC | 2320-2449ºF |
Mechanical Properties:
The mechanical properties of Inconel 725™ are displayed in the following table.
| Properties | Metric | Imperial |
|---|---|---|
| Tensile strength | 855 MPa | 124000 psi |
| Yield strength (@0.2%) | 427 MPa | 62000 psi |
| Modulus of elasticity | 204 GPa | 29600 ksi |
| Poissons ratio | 0.31 | 0.31 |
| Elongation at break | 57% | 57% |
| Hardness, Rockwell C | 5 | 5 |
Thermal Properties:
The thermal properties of Inconel 725™ are displayed in the following table.
| Properties | Metric | Imperial |
|---|---|---|
| Thermal expansion co-efficient (@21-100°C/69.8-212°F) | 13 µm/m°C | 7.22 µin/in°F |