Inconel 625 / Alloy 625: standards, composition and properties
Nickel alloy 625 · UNS N06625, 2.4856, CW6MC, ERNiCrMo-3
Alloy 625 is a solid-solution-strengthened Ni-Cr-Mo-Nb alloy, used where resistance to pitting, crevice corrosion and stress corrosion cracking is required together with good strength from -196 °C to about 1,000 °C. The same composition gets different names by form: B443 (plate), B446 (bar), B444/B704/B705 (tubes and pipe), B564 (forgings), B366 WPNCMC (fittings), CW6MC as a casting (A494) and ERNiCrMo-3 / ENiCrMo-3 as welding and overlay consumable.
One composition, several standards
The name changes with the product form. When specifying, cite the standard, grade and class.
| Form | ASTM/ASME | Grade/class | EN | ABNT/others |
|---|---|---|---|---|
| Forging (flanges, blocks, rings) | ASTM B564 / ASME SB-564 | N06625 annealed | 2.4856 (VdTÜV 499; DIN 17754*) | AMS 5666; ISO 9725*; NACE MR0175/ISO 15156-3; API 6A (forgings with CRA overlay) |
| Bar and rod | ASTM B446 / ASME SB-446 | N06625 Grade 1 or Grade 2 | 2.4856 (DIN 17752*; VdTÜV 499) | AMS 5666; JIS G4901 NCF625*; BS 3076 NA21*; GB GH3625 / NS3306 |
| Plate, sheet and strip | ASTM B443 / ASME SB-443 | N06625 Grade 1 or Grade 2 | EN 10095 2.4856; DIN 17750*; VdTÜV 499 | AMS 5599 (annealed); AMS 5869 (solution annealed)*; JIS G4902 NCF625*; BS 3072 NA21* |
| Seamless tube | ASTM B444 / ASME SB-444 | N06625 Grade 1 or Grade 2 | 2.4856 (DIN 17751*) | AMS 5581; JIS G4903 NCF625TP; BS 3074 NA21* |
| Welded tube and pipe | ASTM B704 (tube) / B705 (pipe); ASME SB-704 / SB-705 | N06625 Grade 1 or Grade 2 | 2.4856 | AMS 5581 (seamless and welded); general requirements B751 / B775 |
| Welding fittings | ASTM B366 / ASME SB-366 | WPNCMC (N06625) | — | Dimensions ASME B16.9 / B16.11; ASME B16.5 flanges group 3.8 via B564* |
| Casting | ASTM A494 / ASME SA-494 | CW6MC (N26625) | 2.4856 cast: G-NiCr22Mo9Nb* | Valves and pumps; NACE MR0175 when solution annealed |
| Wire and electrode (welding and overlay) | AWS A5.14 / ASME SFA-5.14; AWS A5.11 / SFA-5.11 | ERNiCrMo-3 (N06625); ENiCrMo-3 (W86112) | ISO 18274 S Ni 6625; ISO 14172 E Ni 6625 | AMS 5837 (wire)*; EQNiCrMo-3 strip for electroslag cladding |
| Clad / lined pipe | API 5LD | CRA 625 on carbon steel | — | Weld overlay (Fe ≤ 5 % or ≤ 10 % at the surface, per specification) |
If the order does not state the grade, B443, B444 and B446 supply Grade 1 (annealed); for creep service above 593 °C specify Grade 2. Standard 625 is not covered by API 6ACRA, which deals with the precipitation-hardenable alloys (718, 725, 925, 716/625 Plus, 945).
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Hot-rolled bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Plate (> 10 mm, width ≥ 600 mm) | 7506.20.00 | 7506.20 | 7506.20.3000 | 7506 20 00 |
| Seamless pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 12 00 |
| Welded pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 12 00 |
| Flange and fitting | 7507.20.00 | 7507.20 | 7507.20.0000 | 7507 20 00 |
Class in Dustre's NCM table (INF 004): nickel alloy.
*: US and EU codes are for reference; confirm with your customs broker. NCM codes with * were checked by Dustre against the current NCM, outside the INF 004 table. HS = first 6 digits of the NCM.
Chemical composition by standard (%)
The ranges of each standard side by side, to see where they differ.
| Standard | C max | Mn max | Si max | P max | S max | Cr | Mo | Nb+Ta | Fe max | Ti / Al max | Ni | Others |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ASTM B443/B444/B446/B564/B704/B705 N06625 | 0.10 | 0.50 | 0.50 | 0.015 | 0.015 | 20.0–23.0 | 8.0–10.0 | 3.15–4.15 | 5.0 | 0.40 / 0.40 | 58.0 min | Co 1.0 max (if determined) |
| AMS 5599 / 5666 | 0.10 | 0.50 | 0.50 | 0.015 | 0.015 | 20.0–23.0 | 8.0–10.0 | 3.15–4.15 | 5.0 | 0.40 / 0.40 | 58.0 min | Co 1.0; additional limits (Ta, B) per AMS* |
| VdTÜV 499 (2.4856) | 0.03 (EN 10095: 0.10) | 0.5 | 0.4 | 0.01 | 0.01 | 21–23 | 8–10 | 3.2–3.8 | 5 | 0.4 / 0.4 | 58–71 | Co 1 |
| 625LCF, UNS N06626 (AMS 5879) | 0.03 | 0.50 | 0.15 | 0.015 | 0.015 | 20.0–23.0 | 8.0–10.0 | 3.15–4.15 | 5.0 | 0.40 / 0.40 | bal. | N 0.02; Co 1.0 |
| ASTM A494 CW6MC (N26625) | 0.06 | 1.00 | 1.00 | 0.015 | 0.015 | 20.0–23.0 | 8.0–10.0 | 3.15–4.50 (Nb) | 5.0 | — | bal. | — |
| AWS A5.14 ERNiCrMo-3 | 0.10 | 0.50 | 0.50 | 0.02* | 0.015 | 20.0–23.0 | 8.0–10.0 | 3.15–4.15 | 5.0 | 0.40 / 0.40 | 58.0 min | Cu 0.50*; others 0.50* |
| ASTM B805 N07725 (725) | 0.03 | 0.35 | 0.20 | 0.015 | 0.010 | 19.0–22.5 | 7.0–9.5 | 2.75–4.00 | bal. | Ti 1.00–1.70 / Al 0.35 | 55.0–59.0 | — |
Mechanical properties by standard
Minimum values at room temperature, in the stated delivery condition.
| Standard and condition | YS min | UTS min | Elong. | RA | Hardness |
|---|---|---|---|---|---|
| FORGINGS | |||||
| ASTM B564 N06625 annealed, up to 102 mm | 414 MPa (60 ksi) | 827 MPa (120 ksi) | 30 % | — | — |
| ASTM B564 N06625 annealed, > 102 to 254 mm | 345 MPa (50 ksi)* | 758 MPa (110 ksi)* | 25 %* | — | — |
| AMS 5666 annealed (bar, forging, ring) | 414 MPa (60 ksi)* | 827 MPa (120 ksi)* | 30 %* | — | ATI cites 483 / 897 MPa and 40 % for bar; confirm in AMS* |
| ROLLED | |||||
| ASTM B443 Grade 1 (annealed) | 414 MPa (60 ksi) | 827 MPa (120 ksi) | 30 % | — | — |
| ASTM B443 Grade 2 (solution annealed) | 276 MPa (40 ksi) | 690 MPa (100 ksi) | 30 % | — | — |
| ASTM B446 Grade 1, up to 102 mm | 414 MPa (60 ksi) | 827 MPa (120 ksi) | 30 % | — | — |
| ASTM B446 Grade 1, > 102 to 254 mm | 345 MPa (50 ksi) | 758 MPa (110 ksi) | 25 % | — | — |
| ASTM B446 Grade 2 (solution annealed) | 276 MPa (40 ksi) | 690 MPa (100 ksi) | 30 % | — | — |
| AMS 5599 annealed (sheet/strip) | 414 MPa (60 ksi) | 827 MPa (120 ksi) | 30 % | — | — |
| VdTÜV 499 Grade 1, plate ≤ 50 mm | 380 MPa | 760 MPa | 35 % | — | — |
| PIPE, FITTINGS AND CASTINGS | |||||
| ASTM B444 Grade 1 (annealed) | 414 MPa (60 ksi) | 827 MPa (120 ksi) | 30 % | — | — |
| ASTM B444 Grade 2 (solution annealed) | 276 MPa (40 ksi) | 690 MPa (100 ksi) | 30 % | — | — |
| ASTM B704 / B705 Grade 1 and Grade 2 | same values as B444* | same values as B444* | 30 %* | — | — |
| ASTM B366 WPNCMC | per starting material (B564/B444/B443) | per starting material | — | — | — |
| ASTM A494 CW6MC | 275 MPa (40 ksi) | 485 MPa (70 ksi) | 25 % | — | — |
Grade 1 vs. Grade 2 of alloy 625
Grade 1 is annealed at ≥ 871 °C: fine grain, higher YS (414 MPa) and UTS (827 MPa), recommended for service up to 593 °C, including corrosive and cryogenic. Grade 2 is solution annealed at ≥ 1,093 °C: coarser grain, YS 276 MPa and UTS 690 MPa, but better creep and rupture strength above 593 °C. The composition is the same; what changes is the heat treatment and, therefore, the allowable stresses in ASME. Grade 2 may receive a stabilizing anneal at ≥ 982 °C to reduce sensitization. Without indication in the order, ASTM standards supply Grade 1.
Heat treatments required by the standards
| Standard | Delivery condition | Temperature |
|---|---|---|
| ASTM B443 / B444 / B446 Grade 1 | Annealed | ≥ 871 °C (1600 °F) |
| ASTM B443 / B444 / B446 Grade 2 | Solution annealed, with or without stabilization | ≥ 1,093 °C (2000 °F); stabilization ≥ 982 °C (1800 °F) |
| VDM / VdTÜV 499 (2.4856) | Annealed (Grade 1) / solution annealed (Grade 2) | 950–1,050 °C (980 °C preferred) / 1,080–1,160 °C (1,120 °C preferred), rapid water cooling |
| AMS 5869 | Solution annealed | 1,175–1,230 °C (2150–2250 °F)* |
| ASTM A494 CW6MC | Solution annealed and water cooled | ≈ 1,175 °C (2150 °F) min* |
| ASTM B805 N07725 | Solution annealed + aged | > 1,040 °C; 730 °C/8 h, furnace cool to 620 °C/8 h, air |
Variants in the family
| Variant | Standards | Difference | YS / UTS |
|---|---|---|---|
| 625LCF (UNS N06626) | AMS 5879; AMS 5599 | C ≤ 0.03, Si ≤ 0.15, N ≤ 0.02; vacuum melted and fine grained for low-cycle fatigue (bellows, expansion joints) | 414 / 827 MPa; elong. 40 % (AMS 5879) |
| 625 Plus (UNS N07716) | ASTM B805*; API 6ACRA; NACE MR0175 | 625 with Ti and Nb adjusted for precipitation hardening | ≈ 827 MPa min aged* |
| 725 (UNS N07725) | ASTM B805, B872, B983, B1007; API 6ACRA; NACE MR0175 | 625 chemistry with Ti 1.0–1.7 %; age hardenable, same corrosion resistance | 827 / 1,034 MPa (bar ≤ 76 mm, aged); hardness < 43 HRC |
| 925 (UNS N09925) | ASTM B805, B637; API 6ACRA; NACE MR0175 | Fe-Ni-Cr-Mo-Cu-Ti (Ni 42–46 %, Mo 2.5–3.5 %); lower cost and lower pitting resistance than 625/725 | 758 / 965 MPa (110 / 140 ksi); 26–38 HRC |
| CW6MC (N26625) | ASTM A494 / SA-494 | Cast version: Si and Mn up to 1.0 %, Nb up to 4.50 % | 275 / 485 MPa |
| ERNiCrMo-3 overlay (Fe 5 / Fe 10) | AWS A5.14; API 6A; API 5LD | Weld overlay on carbon or low-alloy steel; dilution limits the Fe at the surface (≤ 5 % or ≤ 10 %) | Depends on the substrate |
Corrosion, PREN and temperature
- PREN ≈ 51: Cr + 3.3 Mo; in 10 % FeCl3, CPT ≈ 75 °C and CCT ≈ 55 °C (VDM). Resistant to pitting and crevice corrosion in seawater, including heated.
- Chlorides and SCC: Ni ≥ 58 % makes the alloy practically immune to chloride stress corrosion cracking, unlike austenitic stainless steels.
- Temperature: Grade 1 up to 593 °C (B443/B444); TÜV approves Grade 1 from -196 to 450 °C. Grade 2 is used above ~600 °C and up to ~1,000 °C in oxidation. Allowable stress limits: ASME II-D, table 1B: Section VIII Div. 1, Grade 1 (annealed) up to 649 °C and Grade 2 (solution annealed) up to 871 °C; Section I, Grade 1 up to 593 °C.
- Embrittlement: prolonged exposure between ~600 and 800 °C precipitates phases (gamma double prime, delta) and reduces room-temperature ductility and toughness; consider in long service in that range*.
- NACE MR0175/ISO 15156-3: annealed or solution-annealed 625 is listed in the solid-solution nickel alloy table (A.13), with no hardness requirement in the annealed condition; restrictions apply to cold-worked material. MR0103: hardness ≤ 35 HRC.
- Sensitization: with C up to 0.10 %, thermal cycles may precipitate carbides; Grade 2 with stabilization at ≥ 982 °C or low C (VdTÜV 499: C ≤ 0.03 %) reduces the risk.
Overlay and cladding with ERNiCrMo-3
- Use: alloy 625 is the most common CRA overlay on valves, wellheads (API 6A), flanges and clad pipe (API 5LD) over carbon or low-alloy steel (e.g. 4130, F22, A694).
- Dilution: the specification defines the maximum Fe at the finished surface, usually Fe ≤ 5 % ("Fe5") or ≤ 10 % ("Fe10"), which defines the number of layers and minimum thickness.
- Processes: hot-wire TIG, pulsed MIG/MAG, submerged arc or electroslag strip (EQNiCrMo-3); low heat input to control dilution.
- PWHT of the substrate: when the base steel requires stress relief, deposited 625 generally tolerates the cycle, but the qualification must verify hardness and corrosion after PWHT*.
- Usual tests: surface chemistry (Fe), liquid penetrant, ultrasonic bond testing, hardness and, when specified, ASTM G48.
Welding
| Item | Usual practice |
|---|---|
| Wire (TIG/MIG/SAW) | AWS A5.14 ERNiCrMo-3 (ISO 18274 S Ni 6625) |
| Covered electrode | AWS A5.11 ENiCrMo-3 (ISO 14172 E Ni 6625) |
| Cladding strip | AWS A5.14 EQNiCrMo-3 (ISO 18274 B Ni 6625) |
| ASME IX group | P-No. 43; F-No. 43 |
| Preheat | Not needed (only remove moisture) |
| Interpass | ≤ 150 °C |
| Heat input | Low, stringer beads; TIG/MIG ≤ 8 kJ/cm, electrode ≤ 7 kJ/cm (VDM) |
| PWHT | Not required for 625; root shielding with pure argon |
| Dissimilar (625 to carbon steel/stainless) | ERNiCrMo-3 is the usual choice |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
International equivalents
| System | Designation |
|---|---|
| UNS | N06625 (wrought/forged); N26625 (cast); N06626 (625LCF) |
| EN / W.Nr. | 2.4856 NiCr22Mo9Nb (EN 10095) |
| ISO | NiCr22Mo9Nb / NW6625 |
| AFNOR | NC22DNb |
| BS | NA21 (BS 3072 to 3076)* |
| JIS | NCF625 (G4901/G4902)*; NCF625TP (G4903) |
| GB | NS3306 (GB/T 15007, corrosion resistant); GH3625 (high temperature) |
| Trade names | Inconel 625, Alloy 625, VDM Alloy 625, Nicrofer 6020 hMo, Haynes 625 |
| ABNT / SAE / AISI | No designation of its own; use UNS/ASTM |
The equivalents indicate similar composition, not automatic interchange: C, Si, P and S limits and the mechanical properties vary between ASTM, EN/VdTÜV, AMS and JIS. One source (Austral Wright) cites W.Nr. 2.3856, probably a typo for 2.4856.
Typical applications
| Form or industry | Where it is used |
|---|---|
| Oil and gas | Overlay on valves and wellheads (API 6A), clad pipe, control lines, flanges and fittings in sour service |
| Marine and offshore | Seawater systems, bellows, firewater piping, cables and fasteners |
| Chemicals and petrochemicals | Heat exchangers, columns, equipment with acids and chlorides |
| Aerospace | Exhaust ducts, bellows and expansion joints (625LCF), turbine components (AMS 5599/5666) |
| Power | Flue gas scrubbers (FGD), boilers, overlay on waste boiler walls |
| Nuclear and cryogenics | Reactor components and service at -196 °C (Grade 1) |
| Castings | Pumps, impellers and valve bodies in CW6MC |
| Strip and band | Banding and strapping of piping and lines in oil and gas and offshore (strip per ASTM B443); EQNiCrMo-3 strip for electroslag cladding |
Frequently asked questions
Are Inconel 625 and UNS N06625 the same thing?
Yes. Inconel is a Special Metals trademark; the generic composition is UNS N06625 (W.Nr. 2.4856), produced by several manufacturers and specified by form in B443, B444, B446, B564, etc.
When to order Grade 1 or Grade 2?
Grade 1 (annealed) for service up to 593 °C and where a higher YS is wanted. Grade 2 (solution annealed) for creep service above 593 °C. If the order does not specify, ASTM standards supply Grade 1.
Does 625 meet NACE MR0175?
Yes, in the annealed or solution-annealed condition it is listed in ISO 15156-3 as a solid-solution nickel alloy, with no hardness requirement in the annealed condition. Check the environmental limits of the applicable table.
What is the difference between 625 and 725?
725 has the chemistry of 625 with 1.0–1.7 % Ti and is age hardenable: YS of 827 MPa vs. 414 MPa for annealed 625, with similar corrosion resistance. It is covered by API 6ACRA; standard 625 is not.
Is there Inconel 625 strip? What is it for?
Yes. 625 strip is rolled per ASTM B443 (plate, sheet and strip). In oil and gas it is used for banding and strapping of piping and lines exposed to seawater and chemicals: it is formed to different diameters, applied in hard-to-reach places and lasts longer than carbon steel or common stainless. There is also EQNiCrMo-3 strip, a consumable for electroslag cladding.
