Short answer: Incoloy 825 is a nickel-iron-chromium alloy with molybdenum and copper, used mainly for sulphuric and phosphoric acid service. Inconel 625 is a nickel-chromium-molybdenum alloy with niobium, chosen where higher strength, chloride resistance and high-temperature service are needed. 825 is the cheaper of the two; 625 is stronger and more corrosion resistant.
Inconel 625 at a glance
Incoloy 825 Vs Inconel 625
Inconel is a nickel based superalloy. According to the amount of nickel present in the alloy and by considering many other parameters, we can grade Inconel differently. And the two such grades are Inconel 625 and Incoloy 825. The main difference between the two is that Inconel 625 contains a high amount of nickel as compared to Incoloy 825.
What is Inconel 625?
Inconel 625 contains a high amount of nickel than other grades of Inconel, and it is nickel-based superalloy. At higher temperature it has high strength and great resistivity. Against corrosion and oxidation it shows great protection. In nuclear and marine applications these specific advantages make it very useful.
Inconel 625 alloy service temperature ranges from cryogenic to 982°C. The alloy high strength is due to the stiffening effect of niobium and molybdenum, which locates in the nickel-chromium matrix. Therefore Inconel alloy does not need precipitation hardening treatments. Inconel 625 is an excellent choice for seawater applications due to high tensile strength, high corrosion-fatigue strength and resistance to chloride-ion stress-corrosion cracking. Apart from this, it exhibits excellent toughness and ductility at low temperature.
Inconel Alloy 625 Chemical Composition
| Inconel | Element (% by mass) | ||||||||||||||
| Ni | Cr | Fe | Mo | Nb | Co | Mn | Cu | Al | Ti | Si | C | S | P | B | |
| 625 | 58.0 | 20.0–23.0 | 5.0 | 8.0–10.0 | 3.15–4.15 | 1.0 | 0.5 | 0.4 | 0.4 | 0.5 | 0.1 | 0.015 | 0.015 | ||
Alloy 625 equivalent grades
| STANDARD | WERKSTOFF NR. | UNS | GOST | AFNOR | JIS | BS | EN | OR |
| Inconel 625 | 2.4856 | N06625 | ХН75МБТЮ | NC22DNB4M | NCF 625 | NA 21 | NiCr22Mo9Nb | ЭИ602 |
Inconel 625 mechanical properties
| Density | Melting Point | Tensile Strength | Yield Strength (0.2%Offset) | Elongation | |
| 625 | 8.4 g/cm3 | 1350 °C (2460 °F) | Psi – 135,000 , MPa – 930 | Psi – 75,000 , MPa – 517 | 42.5 % |
What is Incoloy 825?
When compared to other Inconel grades, Incoloy 825 contains a moderate amount of nickel and is a nickel based superalloy. It consist a higher melting point but has low yield strength and a low tensile strength. And it contains chromium and nickel along with titanium, molybdenum and copper. It specifically provides an exceptional corrosion resistance to aqueous corrosion. Beside this, it exhibits oxidizing resistance and reducing acids such as phosphoric and sulfuric acids.
Difference between Inconel 625 and Incoloy 825
| Inconel 625 | Incoloy 825 | |
| Defination | It is nickel based superalloy which contains a high amount of nickel than any other grade of Inconel | It is nickel based superalloy which contains a moderate amount of nickel as compared to any other grade of Inconel |
| Nickel Content | It contains about 58% of nickel | It contains about 36-48% of nickel |
| Tensile Strength | It has very high tensile strength and yield strength | It has comparatively low tensile strength and yield strength |
| Elongation | It’s elongation is about 42.52% | It’s elongation is about 30% |
Incoloy 825 chemical composition
| Alloy | Ni | Cr | Fe | Mb | Ti | Cu | Mn | C | S | Al | Si |
| Incoloy 825 | 38.0 – 46.0 | 19.5 – 23.5 | 22.0 min | 2.5 – 3.5 | 0.6 – 1.2 | 1.5 – 3.0 | 1.0 max | 0.05 max | 0.03 max | 0.2 max | 0.5 max |
Alloy 825 equivalent grades
| ALLOY | WERKSTOFF NR. | UNS | GOST | AFNOR | JIS | BS | EN | OR |
| Incoloy 825 | 2.4858 | N08825 | ЭП703 | NFE30C20DUM | NCF 825 | NA 16 | NiCr21Mo | XH38BT |
Alloy 825 mechanical properties, density and melting point
| Density | Melting Point | Tensile Strength | Yield Strength (0.2%Offset) | Elongation |
| 8.14 g/cm3 | 1400 °C (2550 °F) | Psi – 80,000 , MPa – 550 | Psi – 32,000 , MPa – 220 | 30 % |
Which one to specify
If the duty is sulphuric or phosphoric acid at moderate temperature, 825 does the job at a lower price and with better availability in bar and tube. If the duty involves chlorides, seawater, or temperatures where creep strength matters, 625 is the correct choice and paying less for 825 is a false economy.
Related reading
- Incoloy 825 (N08825) — full grade data, composition and supply forms.
- Inconel 625 (N06625) — the AMS 5666 grade data.
- Common types of nickel alloys — where both grades sit in the wider family.
- Inconel 601 — the oxidation-resistant alternative for furnace service.
You get chemical composition, mechanical properties and a price — with inspection certificates to EN 10204 3.1 issued against the heat number.
