Inconel 625
Also: Alloy 625, Inconel 625, IN625, UNS N06625, Nickel alloy 625, W.Nr. 2.4856, NiCr22Mo9Nb, Haynes 625, Nicrofer 6020 hMo, ERNiCrMo-3 (filler)
Inconel 625 is the corrosion superalloy: 830 MPa (120 ksi) tensile, resists chlorides, acids and oxidation to 980 °C (1800 °F), easy to weld. Values annealed.
Sourcing Inconel 625 parts or stock?
- Machine shops that work with nickel alloys · 84
- Forging companies that work with nickel alloys · 17
- 3D Printing companies that work with nickel alloys · 10
- All U.S. manufacturers working with nickel alloys · 189
- Find specialty alloy suppliers
At a glance
| Density | 8.44 g/cm³ (0.305 lb/in³) |
|---|---|
| Tensile strength | 827 MPa (120 ksi) min; typically 930 MPa (135 ksi) |
| Yield strength | 414 MPa (60 ksi) min; typically 517 MPa (75 ksi) |
| Hardness | About 95 HRB (175-220 HB) |
| Elongation | 30% min; typically 40-45% |
| Modulus of elasticity | 207 GPa (30 Msi) |
| Thermal | Melts at 1290-1350 °C (2350-2460 °F); thermal conductivity ~9.8 W/m·K; oxidation resistant to about 980 °C (1800 °F); tough to cryogenic temperatures |
| Composition | Ni 58% min, Cr 20-23%, Mo 8-10%, Nb+Ta 3.15-4.15%, Fe up to 5%, Ti up to 0.4%, Al up to 0.4%, C up to 0.1% |
Typical values, Annealed (ASTM B443 Grade 1, annealed at about 870-980 °C). Grade 2 solution annealed at about 1090-1200 °C for creep service: 690 MPa (100 ksi) tensile and 276 MPa (40 ksi) yield minimum. Confirm against the mill certificate and the purchase spec.
- MachinabilityPoor
- About 15% of the free-machining steel benchmark; it work-hardens severely under a rubbing tool and holds heat at the edge. Rigid setups, sharp positive-rake carbide, low speed, heavy constant feed and flood coolant; do not let the tool dwell.
- WeldabilityExcellent
- The easiest superalloy to weld: TIG, MIG, plasma and laser with ERNiCrMo-3 filler, as-welded with no post-weld heat treatment, and the weld metal matches the parent in corrosion resistance. Also the standard filler for dissimilar and clad joints.
- FormabilityGood
- Forms cold in the annealed condition with high forces and springback; deep draws and spins with intermediate anneals. Hot work at 925-1150 °C (1700-2100 °F). No post-forming heat treatment needed except to restore ductility.
- Corrosion resistanceExcellent
- Resists pitting and crevice corrosion in seawater and chlorides (PREN about 50), chloride stress-corrosion cracking, most organic and mineral acids, and sour gas (NACE MR0175 listed). Oxidation resistant to about 980 °C (1800 °F). Hastelloy C-276 is stronger in hot, wet chlorine and strongly reducing acids.
Inconel 625 is a nickel-chromium-molybdenum alloy with niobium, strengthened by the molybdenum and niobium in solid solution rather than by heat treatment. That makes it usable as welded and as formed, with no aging cycle to schedule, and gives it a combination that few alloys match: about 830 MPa (120 ksi) minimum tensile annealed, high strength and creep resistance from cryogenic to about 980 °C (1800 °F), and corrosion resistance across oxidizing and reducing media, chlorides, seawater and sour gas.
It is the general-purpose alloy for corrosive high-temperature service: flue gas scrubbers, chemical process piping and reactors, seawater systems and subsea wellhead overlays, aircraft exhaust and bellows, rocket combustion chambers made by additive manufacturing, and nuclear components. Its filler metal, ERNiCrMo-3, is also the most used nickel welding wire, for joining dissimilar metals and for cladding steel with a corrosion-resistant layer.
ASTM B443 sells it in Grade 1 (annealed at a lower temperature, for higher strength below about 600 °C / 1100 °F) and Grade 2 (solution annealed at a higher temperature for creep resistance above that). Long exposure between about 600 and 750 °C (1100-1400 °F) slowly precipitates a gamma double-prime phase that raises strength and cuts ductility, which matters for parts that must stay tough after years of hot service. Machining is slow and work-hardening, as with all nickel alloys.
Heat treatment
Not age-hardened in practice; strength comes from solid solution and cold work. Anneal at about 870-980 °C (1600-1800 °F) for Grade 1 strength, or solution anneal at about 1090-1200 °C (2000-2200 °F) for Grade 2 creep resistance, followed by rapid cooling. Stress relief is rarely needed after welding; if specified, use the anneal. Avoid long holds between about 600 and 750 °C (1100-1400 °F), which slowly precipitate gamma double-prime and reduce ductility.
Tempers and conditions
- Annealed (ASTM B443 Grade 1)
- Solution annealed (ASTM B443 Grade 2)
- Cold worked (strip and wire)
Stock forms
- Plate
- Sheet and strip
- Round bar
- Seamless and welded pipe and tube
- Forgings and rolled rings
- Welding wire and overlay
- Powder for additive manufacturing
Relative cost
Tier 5 of 5. Roughly 10-15x the price of 304 stainless per pound, similar to or a little above Inconel 718 because of the molybdenum and niobium; machining runs 8-12x aluminum time. Weld overlay on steel is the economical way to get 625 corrosion resistance on large parts.
Typical applications
- Chemical process reactors, columns and piping
- Flue gas desulfurization scrubbers and ducting
- Seawater piping, pumps and heat exchangers
- Subsea wellhead and valve weld overlays
- Aircraft exhaust systems, bellows and ducting
- Additively manufactured rocket engine combustion chambers and injectors
- Nuclear reactor components and steam generator parts
- Springs and fasteners for hot corrosive service
Process compatibility
How Inconel 625 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | PoorPoor | Slow and work-hardening; carbide at low speed with heavy feed and flood coolant. Expect 8-12x the cycle time of 6061. |
| Welding | ExcellentExcellent | ERNiCrMo-3 filler by TIG, MIG or plasma, as-welded, no post-weld heat treatment; the reference alloy for corrosion-resistant fabrication. |
| TIG Welding | ExcellentExcellent | Low heat input, stringer beads, argon shielding; weld metal matches the parent in corrosion resistance. |
| Laser Welding | GoodGood | Laser and EB welds are clean and narrow; used for bellows, thin-wall ducting and additive part repair. |
| Sheet Metal Fabrication | GoodGood | Sheet cuts, forms and welds into scrubber liners, ducting and bellows; allow for high forming forces and springback. |
| Press Brake Forming | GoodGood | Bend annealed sheet at about 1-2x thickness inside radius with 5-10 degrees of overbend; forces run 2-3x those for 304 stainless. |
| Deep Drawing | FairFair | Draws with polished, lubricated tooling and intermediate anneals; work hardening limits draw ratios. |
| Laser Cutting | GoodGood | Fiber lasers cut sheet and plate to about 12 mm (1/2") with nitrogen assist; the edge is clean and only slightly hardened. |
| Waterjet Cutting | ExcellentExcellent | Cuts any plate thickness with no heat-affected zone; the usual route for thick corrosion-resistant plate parts. |
| Metal 3D Printing | ExcellentExcellent | One of the best-behaved printed metals: laser powder bed and directed energy deposition for rocket chambers, heat exchangers and impellers, followed by stress relief or HIP. |
| Forging | GoodGood | Forged flanges, fittings and rings at 925-1150 °C (1700-2100 °F); high flow stress needs heavy equipment. |
| Electropolishing | GoodGood | Electropolishes to a bright, clean surface for pharmaceutical and food process parts. |
| Heat Treating | Not recommendedNot recommended | Cannot be hardened by heat treatment, and holding it at 600-750 °C (1100-1400 °F) embrittles it. Only annealing applies; buy Inconel 718 if strength must come from aging. |
| Carburizing | Not recommendedNot recommended | No martensitic transformation, so it cannot be case hardened; nickel alloys also carburize into brittle carbides in hot hydrocarbon atmospheres. |
Compare Inconel 625
Design and sourcing tips
- Specify the grade: "Inconel 625 per ASTM B443 Grade 1" for strength below about 600 °C (1100 °F), "Grade 2" for creep service above it; AMS 5599 or 5666 for aerospace.
- Use it as welded: no post-weld heat treatment is needed, so design welded fabrications freely and keep 718 for parts that need aged strength.
- Consider 625 weld overlay or cladding on carbon steel for large corrosion-exposed parts; solid 625 is reserved for thin sections and complex shapes.
- Avoid long service between 600 and 750 °C (1100-1400 °F) where the part must stay ductile; specify a periodic anneal or a different alloy.
- For hot, wet chlorine, hypochlorite or hot concentrated reducing acids, compare Hastelloy C-276 before settling on 625.
- Keep machined features simple and move detail to laser cutting, forming and welding, which 625 does far more cheaply than milling.
Frequently asked questions
- What is Inconel 625 used for?
- Anything that is hot and corrosive at the same time: chemical process piping and reactors, flue gas scrubbers, seawater systems, subsea wellhead overlays, aircraft exhausts and bellows, and printed rocket engine parts. Its filler metal (ERNiCrMo-3) is also the standard wire for welding dissimilar metals and cladding steel.
- Can Inconel 625 be heat treated to make it stronger?
- Not usefully. It is a solid-solution alloy and reaches its strength as annealed; the only heat treatments are annealing and solution annealing. Long exposure at 600-750 °C (1100-1400 °F) does precipitate a hardening phase, but it embrittles the alloy rather than improving it. For an age-hardened superalloy, use Inconel 718.
- Is Inconel 625 easier to weld than 718?
- Yes. 625 is welded as is, with matching ERNiCrMo-3 filler and no post-weld heat treatment, and the weld resists corrosion as well as the parent metal. 718 welds well but needs to be solution treated and aged afterward to recover strength. For fabricated assemblies 625 is the simpler alloy.
- Is Inconel 625 magnetic?
- No. Inconel 625 is a fully austenitic nickel alloy and is non-magnetic in all conditions, including after welding and cold work. This also means a magnet will not distinguish it from 718 or from austenitic stainless.
- How does Inconel 625 compare to Hastelloy C-276?
- Both are nickel-chromium-molybdenum alloys. 625 has more chromium and niobium and is stronger and better at high temperature and in oxidizing conditions; C-276 has more molybdenum plus tungsten and resists hot wet chlorine, hypochlorite, ferric and cupric chlorides and hot reducing acids better. 625 is the choice for hot structural and mixed service, C-276 for the most aggressive wet chemistry.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B443 and ASTM B446 (property minimums by grade and form)
- AMS 5599 and AMS 5666
- Special Metals Inconel alloy 625 data sheet
- ASM Handbook, Volume 2 (Properties and Selection: Nonferrous Alloys)
