Alloy 625 - AMS 5599, AMS 5666, UNS N06625
Inconel® 625 (AMS 5599, UNS N06625) is a nickel-based superalloy with excellent resistance to oxidation and corrosion. The nickel-chromium matrix of this material is reinforced by the addition of molybdenum and niobium, which is alloyed through solid solution strengthening. This process allows alloy Inconel® 625 to maintain high strength and toughness at temperatures ranging from cryogenic up to 1800°F (982°C). It is non-magnetic, austenitic, and displays high tensile strength, fabricability, and brazeability. Due to its high nickel content, this alloy is nearly immune to chloride ion stress-corrosion cracking and pitting, which is commonly found in thin-walled seawater applications like heat exchangers, fasteners, and cable sheathing. We sell alloy 625 materials in sheet, coil, plate and round bar.
625 Inventory Size Ranges
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Characteristics of 625 materials
- High strength and mechanical properties at both cryogenic and high temperatures.
- High oxidation resistance at temperatures up to 1050°C.
- High tensile, creep, and rupture strength.
- Good resistance to oxidizing and reducing acids such as nitric, sulfuric, hydrochloric and phosphoric acid.
- Virtually immune to chloride ion stress-corrosion cracking and pitting, making it ideal for marine applications.
- Excellent weldabilty.
Working with this product
Alloy 625 can be cold formed, hot worked, and machined through most standard methods. Hot forming should be done at temperature ranges of 1700 – 2150°F (927-1177°C), and care should be taken when cold working and machining, as it work hardens more quickly than more traditional austenitic stainless steels. Recommend using rigid, powerful machines with sharp tooling at positive rake angles, with tools changed frequently to maintain sharpness. Heavy constant feeds are advised to maintain a positive cutting action with proper lubrication. All 625 may be welded through typical gas shielded processes.
Heat treatment
This alloy has three primary heat treatments – solution annealing at 2000-2200°F (1093 – 1204°C) with air or rapid quenching, annealing at 1600-1900°F (927-1038°C) with air or rapid quenching, and stress relieving at 1100-1600°F (593 – 900°C) with air quenching. Each process results in different characteristics, with the high temperature annealing used for applications above 1500°F where creep resistance is important. The medium temperature annealing provides optimal tensile and rupture properties up to 1900°F (1038°C), while the stress relieved state is recommended for applications under 1200°F (649°C), where maximum fatigue, hardness and yield strength are required.
Standard Inventory Specifications
Sheet, Coil and Plate:
- UNS N06625
- UNS N06626-625LCF
- AMS 5599
- ASTM B 443 Gr 1
- ASME SB 443 Gr 1
Bar:
- UNS N06625
- UNS N06626-625LCF
- AMS 5666
- ASTM B 446
Other industry standards we comply with:
- EMS95377
- EN 2.4856
- EN 10204
- DFARS Compliant
- RR SABRe Edition 2
- GE Aircraft Engine (GT193)
- GE Aviation S-SPEC-35 AeDMS S-400
- PWA LCS
Common Trade Names
- Alloy 625
- Nickel 625
- Inconel 625 (® Special Metals)
- Haynes 625 (® Haynes International)
Common Applications of 625
- Aerospace components
- Fasteners
- Chemical Processing
- Propeller blades
- Submarine propulsion motors
- Utility boat exhaust ducts
- Steam-line bellows
- Heat Exchangers
- Flue gas desulfurization scrubbers
- Chemical processing equipment for oxidizing and reducing acids
- Marine components exposed to seawater, such as fasteners and cable connectors
Chemical Composition
| Element | Percent by Weight | |
|---|---|---|
| C | Carbon | 0.010 maximum |
| Mn | Manganese | 0.50 maximum |
| P | Phosphorus | 0.015 maximum |
| S | Sulfur | 0.015 maximum |
| Si | Silicon | 0.50 maximum |
| Cr | Chromium | 20.00 - 23.00 |
| Ni | Nickel | Balance |
| Mo | Molybdenum | 8.00 - 10.00 |
| Nb | Columbium | 3.15 - 4.15 |
| Ti | Titanium | 0.40 maximum |
| Al | Aluminum | 0.40 maximum |
| Ta | Tantalum | 0.05 maximum |
| Fe | Iron | 5.00 maximum |
Physical Properties
- Density: 0.303 lb/in3 (8.44 g/cm3 )
- Specific Gravity: 8.44
- Melting Range: 2350 - 2460°F (1280 - 1350°C)
- Specific Heat: 0.098 Btu/lb x °F (410 Joules/kg x °K)
- Magnetic Permeability (75°F, 200 oersted): 1.0006
| Temperature Range | Linear Coefficients of Thermal Expansion1 · 10-6 | Thermal Conductivity2 3 | |||
|---|---|---|---|---|---|
| °C | °F | /°C | /°F | W/m·K | Btu/(hr/ft²/in/°F) |
| -157 | -250 | - | - | 7.3 | 4.2 |
| -129 | -200 | - | - | 7.4 | 4.3 |
| -73 | -100 | - | - | 8.3 | 4.8 |
| -18 | 0 | - | - | 9.2 | 5.3 |
| 21 | 70 | - | - | 9.9 | 5.7 |
| 38 | 100 | - | - | 10.0 | 5.8 |
| 93 | 200 | 12.8 | 7.1 | 10.7 | 6.3 |
| 204 | 400 | 13.1 | 7.3 | 12.6 | 7.3 |
| 316 | 600 | 13.3 | 7.4 | 14.2 | 8.2 |
| 427 | 800 | 13.7 | 7.6 | 15.7 | 9.1 |
| 538 | 1000 | 14.0 | 7.8 | 17.5 | 10.1 |
| 649 | 1200 | 14.8 | 8.2 | 19.0 | 11.0 |
| 760 | 1400 | 15.3 | 8.5 | 20.8 | 12.0 |
| 871 | 1600 | 15.8 | 8.8 | 22.8 | 13.2 |
| 927 | 1700 | 16.2 | 9.0 | - | - |
| 982 | 1800 | - | - | 25.3 | 14.6 |
- Average coefficient from 70°F (21°C) to temperature shown
- Measurements made at Battelle Memorial Institute
- Material annealed 2100°F (1149°C)
| Temperature | microhm-cm | |
|---|---|---|
| °C | °F | |
| 21 | 70 | 128.9 |
| 38 | 100 | 129.6 |
| 93 | 200 | 131.9 |
| 204 | 400 | 133.9 |
| 316 | 600 | 134.9 |
| 427 | 800 | 135.9 |
| 538 | 1000 | 137.9 |
| 649 | 1200 | 137.9 |
| 760 | 1400 | 136.9 |
| 871 | 1600 | 135.9 |
| 982 | 1800 | 134.9 |
| 1093 | 2000 | 133.9 |
Mechanical Properties and Yield Strength
| Temperature | 0.2% Yield Strength | Ultimate Tensile Strength | Elongation Percent | |||
|---|---|---|---|---|---|---|
| °F | °C | psi | MPa | psi | MPa | |
| 1920 | 1065 | 63,000 | 430 | 136,000 | 940 | 51.5 |
A brief history of Inconel 625
Originally developed for high pressure steam lines in power plants in the 1960s, it quickly became apparent that alloy 625 could handle extreme corrosion and oxidation from harsh environments. It was called a "superalloy", because of its ability to withstand high temperatures, stress and corrosion. Molybdenum, chromium, and niobium give this alloy additional creep strength from stressors like high temperatures and other harsh conditions that could deform less resistant alloys over time.
Common applications
Even though researchers initially touted its creep strength at high temperatures, it was also shown that alloy 625 could remain nearly corrosion free at ambient to low temperature elevations, like seawater environments or chemical processing of acids and salts.
It is nearly immune to chloride-ion induced stress cracking, by virtue of its high nickel content, and has been used in propellers and propulsion systems as well as wires used in cable sheathing in marine environments. In addition to saltwater corrosion resistance, the high ductility of 625 makes it ideal for fasteners like hex bolts in underwater environments.
Because of its ease of weldability, Inconel 625 has been used in weld overlays (weld overlay cladding) to improve the strength and corrosion resistance of base metals, such as those found in boiler tubes or petrochemical equipment like wellheads. Cheaper, thick layers of base materials like steel alloys can be weld cladded with alloy 625 even at economical dilutions with the right technique, giving much needed strength and protection against corrosion to these parts.
It is also used in waste-to-energy boilers, where refuse-derived-fuel is used to power steam generators with refuse boilers. Inconel 625 replaced heat resistant materials like ceramic tiles for corrosion protection, primarily as welded cladding and composite tubes, which significantly lowered the cost of maintenance on corroded refractory. By the late 1990s, this alloy was widely seen as the most corrosion resistant alloy at conditions caused by waste combustion.
Vacuum Processing
N06625 vs. N06626 - one method of processing alloy 625 is through Vacuum Induction Melting (VIM), which uses a strong electric current to melt the alloy in a vacuum. Through careful control of the melting process, manufacturers can produce a more uniform microstructure with a fine grain size. Inconel 625 that has undergone this process is known as 625 LCF (Low Cycle Fatigue) – it has better thermal stability and improved resistance to mechanical fatigue. Bellows are an excellent example of a structure that undergoes cyclic temperature conditions and can be improved by the use of 625-LCF.
United Performance Metals is a supplier of both N06625 and N06626 in varying thicknesses.
Modern Innovations
While Inconel 718 remains the most successful super alloy among the Inconel family, this alloy is still finding new ways to impress the engineering world.
Solar power stations that use super-heated salt (potassium and sodium nitrate), have used Inconel 625 in the seamless tubing of the solar receivers. The automotive industry has used Inconel 625 in exhaust manifolds and other components, as a lightweight alternative to steel with exceptional weldability and corrosion resistance against environments like saltwater air and road salts. Tesla used Inconel to replace steel in the contactors for the Model S main battery pack, increasing maximum output from 1300 amps to 1500 amps.
While not as widely used in the aerospace industry as 718, alloy 625 still finds new applications. NASA’s Marshall Space Flight Center recently used selective laser melting (SLM – an additive manufacturing process) to fabricate thruster injectors from Inconel 625. They required less time to design and fabricate at half the cost than traditionally made injectors for these liquid propulsion systems.
As a global distributor and longtime supplier of alloy 625 and 625 LCF, United Performance Metals can help meet your demand for high quality alloys. Call us today or request a quote here.
*The technical data provided is for information only and not for design purposes. It is not warranted or guaranteed.