What is Inconel® 625 Stainless Steel ?
Inconel® 625 stainless steel, with a chromium-nickel and low carbon content, is used for its outstanding corrosion resistance especially at
elevated temperatures. This alloy has similar physical properties and fabrication characteristics as Type 304 at room temperature. The unique
chemistry of Inconel® 625 increases the corrosion resistance in salt water applications and against high temperature oxidation. In the medical
field, it has served the MRI compatible market due to its high nickel content that keeps a low magnetic permeability even at high strengths.
Inconel® 625 is more expensive than 304, but is readily available.
Inconel® 625 Products Form
- Bar
- Wire
- Sheet
- Plate
- Forgings
- Pipe fittings
- Flanges
- Seamless & Welded pipe
- Seamless Tube & Welded tube
- Weld Rod
Applications for Inconel® 625
Product and technology applications of Inconel 625 include:
- Seawater components
- Flare stacks
- Aircraft ducting systems
- Fabrication with Inconel 625
- Specialized seawater equipment
- Chemical process equipment
- Turbine shroud rings
- Engine thrust-reverser systems
- Jet engine exhausts systems
- Boiler furnaces
Equivalents of Inconel® 625
| STANDARD | INCONEL 625 |
| UNS | N06625 |
| WERKSTOFF NR. | 2.4856 |
| EN | NiCr22Mo9Nb |
| BS | NA 21 |
| GOST | ХН75МБТЮ |
| OR | ЭИ602 |
| JIS | NCF 625 |
| AFNOR | NC22DNB4M |
Chemical Composition(%) for Inconel® 625
| C | Si | Mn | P | S | Cr | Ni | Cb+Ta | Co | Mo | Fe | Al | Ti |
| 0.1 max | 0.5 max | 0.5 max | 0.015 max | 0.015 max | 20.0-23.0 | 58.0 min | 3.15-4.15 | 1.0 max | 8.0-10.0 | 5.0 max | 0.4 max | 0.4 max |
Mechanical Properties
Inconel alloy 625 is a highly sought-after alloy due to its impressive mechanical properties. It has excellent fatigue strength, tensile strength, and a high degree of creep rupture under temperatures as high as 1500F. Furthermore, its stress corrosion cracking resistance and oxidation resistance make it suitable for many extreme applications. UNS N06625 also offers superior weldability and formability compared to many other similar materials – making it an ideal choice for parts that need to be deeply formed or complexly joined. All in all, Inconel 625 is an incredibly strong and versatile solution in the competitive world of metal alloys.
| PROPERTY | 21°C | 204 °C | 316 °C | 427 °C | 538 °C | 649 °C | 760 °C | 871 °C |
| Ultimate Tensile Strength /Mpa | 992.9 | 923.9 | 910.1 | 910.1 | 896.3 | 820.5 | 537.8 | 275.8 |
| 0.2% Yield Strength /MPa | 579.2 | 455.1 | 434.4 | 420.6 | 420.6 | 413.7 | 406.8 | 268.9 |
| Elongation % | 44 | 45 | 42.5 | 45 | 48 | 34 | 59 | 117 |
| Coefficient of Thermal Expansion µm/m⁰C | – | 13.1 | 13.3 | 13.7 | 14 | 14.8 | 15.3 | 15.8 |
| Thermal Conductivity /kcal/(hr.m.°C) | 8.5 | 10.7 | 12.2 | 13.5 | 15 | 16.4 | 17.9 | 19.6 |
| Modulus of Elasticity/ MPa | 2.07 | 1.93 | 1.93 | 1.86 | 1.79 | 1.65 | 1.59 | – |
Physical Properties
| ENSITY | 8.44 g/cm 3 / 0.305 lb/in 3 |
| MELTING POINT | 1290 -1350 (°C) / 2350 – 2460 (°F) |
| SPECIFIC HEAT @ 70°F | 0.098 Btu/lb/°F |
| PERMEABILITY AT 200 OERSTED (15.9 KA) | 1.0006 |
| CURIE TEMPERATURE | -190 (°C) / < -320 (°F) |
| YOUNG’S MODULUS (N/MM2) | 205 x 10 |
| ANNEALED | 871 (°C) / 1600 (°F) |
| QUENCH | Rapid Air |
Corrosion Resistance
The high alloy content of INCONEL alloy 625 enables it to withstand a wide variety of severe corrosive environments. In mild environments such as the atmosphere, fresh and sea water, neutral salts, and alkaline media there is almost no attack. In more severe corrosive environments the combination of nickel and chromium provides resistance to oxidizing chemicals, whereas the high nickel and molybdenum contents supply resistance to nonoxidizing environments. The high molybdenum content also makes this alloy very resistant to pitting and crevice corrosion, and niobium acts to stabilize the alloy against sensitization during welding, thereby preventing subsequent intergranular cracking. Also, the high nickel content provides freedom from chloride ion stresscorrosion cracking.
Heat Resistance
Inconel 625 is a titanically-alloyed nickel-chromium material designed for exceptional heat resistance. It is specifically protected against crevice corrosion and attack in many acidic environments, making it uniquely suited for use in industries where increased temperatures often lead to a breakdown of standard materials. Inconel 625 has been used in marine engineering, nuclear power productions, and other applications where prolonged exposure to high temperatures can be an issue. So if you need a material that won’t fail under intensive heat, Inconel 625 is the ideal solution.
Heat Treatment
Inconel Alloy 625 has three basic heat treatments:
(1)High Solution Anneal – 2000/2200°F (1093/1204°C), air quench or faster.
(2)Low Solution Anneal – 1700/1900°F (927/1038°C), air quench or faster.
(3)Stress Relieve – 1650°F (899°C), air quench.
The time at the above temperatures depends on volume and section thickness. Strip, for example, would require shorter times than large sections. Temperatures for treatments No. 1 and 2 are generally held for 1/2 to 1 hour, 1 to 4 hours for treatment No. 3.
Treatment No. 1 is not commonly used for applications below 1500°F (816°C). It is generally used above 1500°F and where resistance to creep is important. The high solution anneal is also used to develop the maximum softness for mild processing operations such as cold rolling or drawing.
Treatment No. 2 is the used treatment and develops an optimum combination of tensile and rupture properties from ambient temperatures to 1900°F (1038°C). Ductility and toughness at cryogenic temperatures are also very good.
Treatment No. 3 is recommended for application below 1200°F (649°C) when maximum fatigue, hardness, tensile and yield strength properties are desired. Ductility and toughness at cryogenic temperatures are excellent. When a fine grain size is desired for fatigue, tensile and yield strengths up to 1500°F (816°C), treatment No. 3 is sometimes used.
Hot Forming
The hot-working temperature range for Alloy 625 is 1650–2150°F (900–1177°C). Heavy working needs to occur as close to 2150°F (1177°C) as possible, while lighter working can take place down to 1700°F (927°C).
Hot-working should occur in uniform reductions to prevent duplex grain structure
Cold Forming
Inconel Alloy 625 can be cold-formed by the standard shop fabrication practices. The alloy should be in the annealed condition. Work hardening rates are higher than the austenitic stainless steels.
Machinability
Inconel 625 is difficult to machine (class D-2). Heavy machines, sharp tools, slow speeds and deep uninterrupted cuts to remove the work hardened layer are needed.
Welding
Inconel 625 is readily welded by GMAW (MIG), GTAW (TIG), SMAW (manual) and SAW processes. Preheat, post heat and post weld heat treatment are not required. The area around the weld must be clean to prevent contamination of the weld pool. Argon shielding gas is used.
| Normal Service | Higher Strength | Best Corrosion Resistance | |
| Welding Electrode | Inconel WE 112 | N/A | Inco Weld WE 686CPT |
| Filler Metal | Inconel FM 625 | Inco Weld FM725NDUR | Inco Weld FM 686CPT |
| Flux Cored Wire | Inco Cored 625DH | N/A | N/A |