A nickel-base SOLID-SOLUTION alloy. Its strength comes from the stiffening effect of molybdenum and niobium on the nickel-chromium matrix; no precipitation-hardening cycle is applied and none is required.
Forms
Round bar · flat bar · plate · sheet · tube · forging. All forms are supplied to order.
Standards
AMS 5599 — sheet, strip, plate; ANNEALED (Grade 1 branch). · AMS 5869 — sheet, strip, plate; SOLUTION HEAT TREATED (Grade 2 branch). · AMS 5879 — sheet, strip, foil; cold rolled and annealed (does not cover plate). · AMS 5666 — bars, forgings, extrusions, rings and stock for forgings, extrusions and rings; ANNEALED. · AMS 5581 — seamless or welded tubing; ANNEALED. · AMS 5837 — welding wire (equivalent to AWS A5.14 ERNiCrMo-3). · ASTM B443 / ASME SB-443 — plate, sheet, strip; Grade 1 and Grade 2. · ASTM B446 / ASME SB-446 — rod and bar; Grade 1 and Grade 2. · ASTM B564 / ASME SB-564 — forgings. · ASTM B444 / ASME SB-444 (+ B829) — seamless pipe and tube; Grade 1 and Grade 2. · ASTM B704 / ASME SB-704 — welded tube. · ASTM B705 / ASME SB-705 — welded pipe. · ASTM B366 / ASME SB-366 — factory-made wrought fittings. · DIN 17750 (sheet/plate) · DIN 17752 (rod and bar) · DIN 17753 (wire) · DIN 17754 (forgings) · ISO 6207 / 6208 / 9723 / 9724 / 9725 · VdTÜV 499 · NACE MR0175 / ISO 15156-3 (sour service). The AMS numbers split by product form AND by annealing class; an order must state both. Grade 1 (annealed) branch: AMS 5599 · AMS 5879 · AMS 5666 · AMS 5581. Grade 2 (solution heat treated) branch: AMS 5869.
Advantage
Without any precipitation-hardening cycle, the annealed material meets a specification minimum of 827 MPa tensile / 414 MPa yield (ASTM B443/B446/B444 Grade 1) — a yield level more than double that of austenitic stainless steels — while at the same time being practically immune to chloride-induced…
Welding
Filler metal: AWS A5.14 ERNiCrMo-3 (AMS 5837; UNS N06625) — matching composition. Covered electrode: AWS A5.11 ENiCrMo-3 (UNS W86112, INCONEL Welding Electrode 112). ASME Section IX base metal grouping: P-No 43 (nonferrous P-Numbers carry no Group Number); filler metal F-No 43.
Limits
1) Long-term intermediate-temperature exposure: held for long periods in the intermediate temperature band, annealed 625 suffers a severe loss of room-temperature impact strength. The mechanism is precipitation of γ” (Ni₃Nb) and δ (orthorhombic Ni₃Nb) together with M23C6/M6C carbides on the grain boundaries.
Compiled from manufacturer data sheets · confirm against the current specification before ordering
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Standards by Product FormWelding, Heat Treatment and MachiningWhich Alloy for Which Duty?Frequently Asked Questions
Inconel 625 (2.4856), also widely known as Alloy 625, is one of the most widely used of all nickel alloys. The grade is formed essentially from three elements: nickel, chromium and molybdenum, so it can also be described as a nickel-chromium-molybdenum alloy. It has a very high degree of corrosion resistance and shows excellent resistance to many organic and mineral acids. Able to retain its mechanical properties even at extremely high temperatures, Alloy 625 also retains that high mechanical strength at extremely low, cryogenic temperatures.
Its corrosion resistance changes little even when the material is loaded, and it retains its very high corrosion resistance even under stress. The grade can operate at temperatures as high as approximately 1000 °C, and its resistance to oxidation is very high even at those temperatures.
The material shows very good resistance to many acids. Thanks to this property it can be used even in highly aggressive acids such as nitric acid, phosphoric acid and hydrochloric acid.
The applications of this grade are the demanding ones that require high strength. It is used in oil and gas production, in marine vessels and components subject to very high stress, on offshore oil platforms, on various surfaces in contact with chemicals, in the aerospace industry and in nuclear reactors.
Chemical Composition (NiCr22Mo9Nb) · Inconel 625 (2.4856)
DEFENCE METAL
Ni
min 58.0%
Cr
20.0-23.0%
Fe
max 5.00%
Mo
8.00-10.0%
Nb+Ta
3.15-4.15%
C
max 0.10%
Mn
max 0.50%
Si
max 0.50%
P
max 0.015%
S
max 0.015%
Al
max 0.40%
Co
max 1.00%
Ti
max 0.40%
Mechanical Properties at Room Temperature
DEFENCE METAL
Density (specific gravity)
8440 kg/m³
Melting Temperature
1290–1330°C
Standards and Equivalents · Inconel 625
DEFENCE METAL
Trade name
Inconel 625
UNS
N06625
W.Nr (DIN/EN)
2.4856
EN chemical symbol
NiCr22Mo9Nb
AMS
5599 · 5666 · 5837
Available forms
Round bar · Flat bar · Plate · Sheet · Tube · Forgings All forms are supplied to order.
Standards by Product Form
STANDARDS BY PRODUCT FORM
DEFENCE METAL
Product form
Standards
Round bar, flat bar
AMS 5666 (bars, forgings, extrusions, rings; ANNEALED) · ASTM B446 / ASME SB-446 Grade 1 (annealed) and Grade 2 (solution annealed) · DIN 17752 · ISO 9723
Forging
AMS 5666 (ANNEALED) · ASTM B564 / ASME SB-564 · DIN 17754 · ISO 9725
Plate
AMS 5599 (ANNEALED) · AMS 5869 (SOLUTION HEAT TREATED) · ASTM B443 / ASME SB-443 Grade 1 and Grade 2 · DIN 17750 · ISO 6208
AMS 5837 (welding wire) · AWS A5.14 ERNiCrMo-3 (UNS N06625) · AWS A5.11 ENiCrMo-3 (covered electrode, UNS W86112) · DIN 17753 · ISO 9724
Wrought fitting
ASTM B366 / ASME SB-366
The map lists only the product forms we sell, the specifications that correspond directly to them and their companion general-requirement specifications. Where one form carries two AMS numbers, the difference is the ANNEALING GRADE: AMS 5599 is annealed (Grade 1 branch), AMS 5869 is solution heat treated (Grade 2 branch). The grade must be stated on the order together with the number. There is no AMS specification that delivers bar, forgings or rings solution annealed; Grade 2 bar is ordered only against ASTM B446 Grade 2. AMS 5879 is for sheet, strip and foil; it does not cover plate. AMS 5401 and AMS 5402 are casting specifications for the same composition; they do not substitute for the wrought forms we sell and are therefore not on the map. ASTM B366 is a specification for wrought fittings, not for fasteners.
Two things must be stated together when ordering Inconel 625: the product form and the grade (Grade 1 or Grade 2). ASTM B443 and B446 cover the same material in two different heat-treated conditions with different mechanical minimums. Note also that for welded products ASTM B704 is tube and ASTM B705 is pipe — some supplier catalogues have these reversed, so check the certificate.
Grade 1: low and intermediate temperature, best strength · Grade 2: above ~815 °C, creep-critical
ASME Sec. VIII Div. 1
Grade 1: 649 °C · Grade 2: 871 °C
The condition normally held in stock and used in most applications is Grade 1 (annealed). If you need Grade 2 for a creep-critical part, state it explicitly on the order — otherwise Grade 1 will be supplied.
Welding, Heat Treatment and Machining
HEAT TREATMENT — SCHEMATIC
DEFENCE METAL
GRADE 1 — Anneal
Step
GRADE 1 — Anneal
Summary
The standard delivery condition. The branch with the highest room-temperature strength.
Temperature
Specification requirement: 1600 °F (871 °C) minimum — ASTM B443 / B446 / B444. Producer practice bands: 1700-1900 °F (927-1038 °C, Special Metals) · 950-1050 °C, preferably 980 °C (VDM Metals) · 1600-1900 °F (871-1038 °C, Corrosion Materials) · mill anneal 1925 ± 25 °F (1052 ± 14 °C, Haynes International)
Time
The specifications give no soak time. Special Metals says ‘for times commensurate with thickness’; no numerical soak time could be confirmed by 4 independent sources, so none is stated here.
Cooling
Air cool or faster (Corrosion Materials). VDM Metals calls for rapid water quenching and accepts air cooling below 3 mm thickness. Special Metals states that the rate of cooling after heating has no significant effect.
Purpose
Service at 593 °C (1100 °F) and below. The standard delivery condition for corrosion service. Room-temperature yield and tensile minimums are highest in this branch (414 / 827 MPa).
The high-temperature branch. Coarser grain, lower room-temperature yield strength, higher creep and rupture strength.
Temperature
Specification requirement: 2000 °F (1093 °C) minimum — ASTM B443 / B446 / B444. Producer practice bands: 2000-2200 °F (1093-1204 °C, Special Metals and Corrosion Materials) · 1080-1160 °C, preferably 1120 °C (VDM Metals) · at or above 1093 °C (Haynes International)
Time
The specifications give no soak time; no numerical soak time could be confirmed by 4 independent sources, so none is stated here.
Cooling
Air cool or faster (Corrosion Materials). VDM Metals calls for rapid water quenching.
Purpose
Service above 593 °C (1100 °F), where creep and stress-rupture resistance are required. Room-temperature minimums drop (276 / 690 MPa).
Specifications
AMS 5869 (sheet, strip, plate) · ASTM B443 Grade 2 · ASTM B446 Grade 2 · ASTM B444 Grade 2. There is NO AMS specification that delivers bar, forgings or rings solution annealed.
DEFENCE METAL
Stabilization anneal — optional extra step within Grade 2
Step
Stabilization anneal — optional extra step within Grade 2
Temperature
1800 °F (982 °C) minimum
Cooling
Air cool or faster
Purpose
Applied after the solution anneal; increases resistance to sensitization.
Specifications
ASTM B443 · ASTM B446 · ASTM B444 — the text reads ‘with or without subsequent stabilization anneal’, so it is not mandatory.
Note
This step is defined inside Grade 2; it is not a separate grade.
DEFENCE METAL
After welding
Step
After welding
Temperature
A postweld solution anneal (at or above 1093 °C) may be applied where maximum corrosion resistance is required; it is not a general requirement for corrosion service.
Note
No postweld heat treatment is required to maintain properties; the weld metal keeps its high strength and ductility with no postweld heat treatment.
DEFENCE METAL
Range to avoid
Step
Embrittlement band under long-term exposure — this is NOT a hardening cycle
Temperature
The band differs between sources: ASME code note 1000-1400 °F (538-760 °C) · ATI 1200-1600 °F (649-871 °C) · Haynes International above 593 °C · Alleima above 600 °C · peer-reviewed study 700 and 750 °C
Time
The effect accumulates over long times; in the peer-reviewed measurement it stabilised after 2000 h at 750 °C.
Result
Room-temperature impact energy fell from roughly 314 J to roughly 10 J (750 °C, aged up to 5000 h, peer-reviewed study). The ASME code note uses the wording ‘severe loss of impact strength at room temperature’.
Mechanism
Fine disk-shaped γ” (Ni₃Nb) precipitates + needle-like or plate-like δ (orthorhombic Ni₃Nb) + Cr-rich M23C6 and Mo-rich M6C carbides on the grain boundaries.
Note
Inconel 625 does not precipitation harden. This band is not an ageing recipe; it is the service band to be AVOIDED. The producer recommendation for sustained service is an upper limit of 593 °C.
The diagram is schematic; the time axis is not to scale. Inconel 625 DOES NOT PRECIPITATION HARDEN — it is a solid-solution alloy; there is therefore no ageing cycle (no H900, H1075 and so on) and no ageing diagram has been drawn. The diagram shows the two annealing grades of ASTM B443 / B446 / B444. No published TTT/CCT curve was used, so no curve is drawn. The diagram is schematic; the time axis is not to scale. No published TTT/CCT curve was used, so no curve is drawn. Grade 1 and Grade 2 are ALTERNATIVES to each other; they are not applied one after the other. An order is placed against one of them. No specification gives a numerical soak time, and none could be confirmed by 4 independent sources, so none is written on the diagram; the time is set by section thickness. ASTM B443, B446 and B444 define the grades identically: Grade 1 = annealed at 871 °C minimum, Grade 2 = solution annealed at 1093 °C minimum (with or without a 982 °C stabilization anneal). Sources disagree on the cooling rate: Special Metals states that the rate of cooling has no significant effect, while VDM Metals calls for rapid water quenching. Both are shown; no average was taken.
Welding
GTAW (TIG), GMAW (MIG), SMAW, submerged-arc and plasma welding are all applicable. The matching filler is ERNiCrMo-3 wire (AWS A5.14 / AMS 5837), or ENiCrMo-3 (AWS A5.11) for covered-electrode welding. The alloy’s greatest practical advantage: no preheat and no post-weld heat treatment are required — strength, ductility and corrosion resistance are retained as welded, and the alloy resists intergranular attack even in the as-welded condition. Keep interpass temperature below 150 °C. Do not substitute a different nickel-alloy filler; the corrosion resistance of the weld metal will suffer.
Heat treatment
The alloy strengthens by solid-solution hardening rather than precipitation — strength comes from molybdenum and niobium in solution in the nickel-chromium matrix — so no ageing treatment is applied. Annealing (Grade 1) is carried out above 871 °C, in practice between 927 and 1038 °C; solution annealing (Grade 2) between 1093 and 1204 °C. Both are followed by air cooling or faster. Stress relief is carried out between 593 and 816 °C. The standards do not specify a fixed soak time; it is commensurate with section thickness.
Machining
Machine in the annealed condition. The alloy work-hardens rapidly, generates high heat during cutting and resists chip removal. The machine must be rigid and amply powered, with tool overhang kept to a minimum. Always use sharp tooling; a tool with a 0.38 mm wear land should be treated as blunt. Maintain a heavy, steady feed to keep a positive cutting action and never dwell in the cut, which produces a work-hardened layer. Depth of cut must reach below the work-hardened layer left by the previous pass. Typical turning speeds: 4–11 m/min with HSS, 14–34 m/min with coated carbide; feed 0.13–0.50 mm/rev. Hot working is done between 900 and 1177 °C.
Which Alloy for Which Duty?
Nickel-base alloys are not interchangeable — each is optimised around a different priority. A short guide:
Selection Guide · Nickel-Base Alloys
DEFENCE METAL
Inconel 625
Chloride and seawater service, pitting and crevice corrosion, sour service; no post-weld heat treatment required
Mixed oxidising and reducing acid environments
Frequently Asked Questions
Should I order Grade 1 or Grade 2?
For service below roughly 815 °C, order Grade 1 — it is what is held in stock and it offers higher strength (min. 827 MPa tensile / 414 MPa yield). For creep-critical parts running continuously above 650 °C, ask for Grade 2 (min. 690 / 276 MPa): the grain structure is coarser and creep resistance is better. State Grade 2 explicitly on the order.
Are AMS 5599 and ASTM B443 interchangeable for plate?
Not exactly. Both cover the same chemistry (UNS N06625), but AMS 5599 is an aerospace specification with different testing, traceability and acceptance criteria. In practice material is supplied dual-certified (AMS 5599 + ASTM B443 Gr 1). Pressure-vessel work requires the ASME SB-443 marking; aerospace work requires the AMS 5599 certificate. Do not accept singly certified material in place of the other.
Is post-weld heat treatment required?
No. Inconel 625 is a solid-solution-strengthened alloy with no precipitation hardening, so neither preheat nor post-weld heat treatment is needed. According to manufacturer data, strength, ductility and corrosion resistance are retained as welded. Use AWS A5.14 ERNiCrMo-3 wire or AWS A5.11 ENiCrMo-3 covered electrodes.
STRENGTH VALUES
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
ASTM Grade 1 · bar ≤ 102 mm
—
414
827
30%
ASTM Grade 1 · bar 102-254 mm
—
345
758
25%
ASTM Grade 1 · cold-rolled sheet/strip
—
414
827
30%
ASTM Grade 1 · hot-rolled sheet/plate
—
379
758
30%
ASTM Grade 1 · seamless tube
—
414
827
30%
ASTM Grade 2 · all forms
—
276
690
30%
AMS 5599 · sheet, strip, plate
—
414
827
30%
AMS 5666 · bar ≤ 102 mm
—
414
827
30%
Every row is a SPECIFICATION MINIMUM, not a manufacturer typical value, and the figures are for room temperature. The ASTM rows and the AMS rows are separate specification families; an order is accepted against one of them, not both. GRADE 1 (annealed) and GRADE 2 (solution annealed) are two delivery conditions of the same material: the room-temperature yield minimum of Grade 2 is about one third lower than Grade 1, while Grade 2 is what is called for above 593 °C for creep and rupture strength. The ASTM rows and the AMS rows are separate families; an order is accepted against one of them, not both. The Grade 2 room-temperature minimums of ASTM B443, B446 and B444 are identical: 690 / 276 MPa / 30%. The mechanical minimums of AMS 5869 (solution heat treated sheet/strip/plate) could not be confirmed by 4 independent sources and are therefore not in the table; when ordering to that specification the values must be confirmed from the specification text. For AMS 5666 above 102 mm, the values 758 / 345 MPa and 25% were found in only two sources and are therefore not in the table. The hardness column is empty: ASTM B443/B446 state no room-temperature hardness requirement for N06625, and the 287 HB maximum quoted for the AMS family was found in only two sources. Long-term service of Grade 1 material above 593 °C causes a loss of impact strength; the table shows room-temperature delivery minimums only, not values after long-term service.
