1. Description
2.4606 belongs to the low-carbon Ni-Cr-Mo-W group of corrosion-resistant alloys. It is used where the process medium changes between oxidising and reducing conditions.
Chromium provides passivity in oxidising media. Molybdenum provides resistance in reducing acids. Tungsten acts with molybdenum and increases resistance to localised pitting and crevice attack in chloride and mixed-halide service. The alloy is a single-phase solid solution and contains no strengthening precipitates, so the microstructure remains stable and there are no phases that can over-age.
The carbon limit of 0.010 % matters in fabrication. It suppresses grain-boundary carbide precipitation during welding, so the heat-affected zone keeps corrosion resistance close to that of the parent metal, and post-weld solution annealing can often be omitted on site.
Key values
- Chromium
- 19–23 %
- Molybdenum
- 15–17 %
- Tungsten
- 3.0–4.4 %
- Carbon max
- 0.010 %
- PREN typical
- ≈ 80Cr + 3.3(Mo + 0.5W)
- Density
- 8.73g/cm³ (0.315 lb/in³)
- Tensile min
- 690MPa (100 ksi)
- Elongation min
- 45 %solution annealed
PREN is calculated as Cr + 3.3 × (Mo + 0.5 W) on mid-range composition. Across the full permitted composition range the value falls between about 74 and 86.
2. Designations and standards
The following names all refer to the same alloy. A purchase order or drawing may use any one of them.
| EN / Werkstoff number | 2.4606 |
|---|---|
| EN chemical designation | NiCr21Mo16W |
| UNS number | N06686 |
| Common trade names | Alloy 686, Inconel® 686, Nickel Alloy 686 |
| Alloy family | Low-carbon nickel-chromium-molybdenum-tungsten, single-phase austenitic |
| ASME material group | P-No. 43 |
| ASME design stresses | Section II Part D Table 1B; Code Case 2198 for Section VIII Div. 1 to 800 °F |
| Sour service listing | NACE MR0175 / ISO 15156-3 |
| German approval | VdTÜV Werkstoffblatt 515 |
| Matching weld consumable | ERNiCrMo-14 / ENiCrMo-14 |
| Legacy DIN standard | DIN 17744 |
Inconel® is a registered trademark of Special Metals Corporation and is used here only to identify the alloy grade. Jiangyin Jiangnan Metal is not affiliated with the trademark holder.
Product-form standards
| Standard | Product form |
|---|---|
| ASTM B564 / ASME SB-564 | Nickel alloy forgings. Primary specification for rings, discs, shafts and blocks. |
| ASTM B462 | Forged or rolled pipe flanges, forged fittings, valves and parts for corrosive high-temperature service |
| ASTM B574 / SB-574 | Rod and bar |
| ASTM B575 | Plate, sheet and strip |
| ASTM B622 | Seamless pipe and tube |
| ASTM B619 / B626 | Welded pipe and welded tube |
| ASTM B366 | Factory-made wrought fittings |
| EN 10204 | Inspection documents, type 3.1 or 3.2 |
| EN 10228-3 / SEP 1921 / ASTM A388 | Ultrasonic examination of forgings |
3. Chemical composition
Composition limits follow ASTM B564 and ASTM B574 for UNS N06686, in weight percent.
| Element | Specified limits | Function |
|---|---|---|
| Nickel (Ni) | Balance | Matrix. Resistance to reducing acids and chloride stress-corrosion cracking |
| Chromium (Cr) | 19.0 – 23.0 | Passivity in oxidising media |
| Molybdenum (Mo) | 15.0 – 17.0 | Reducing-acid and crevice corrosion resistance |
| Tungsten (W) | 3.0 – 4.4 | Acts with Mo. Raises localised corrosion resistance |
| Iron (Fe) | 5.0 max | Residual from raw material |
| Titanium (Ti) | 0.02 – 0.25 | Carbon and nitrogen stabiliser |
| Carbon (C) | 0.010 max | Held low to protect the weld heat-affected zone |
| Manganese (Mn) | 0.75 max | Deoxidiser |
| Silicon (Si) | 0.08 max | Restricted to limit intermetallic phases |
| Phosphorus (P) | 0.04 max | Residual |
| Sulphur (S) | 0.02 max | Residual. Controlled for hot workability |
Cobalt is not restricted by ASTM but is often capped by agreement. Nuclear and radiation-service orders frequently require Co ≤ 0.10 %. State any such limit on the enquiry and it will be carried through to the melt specification. Where a customer specification is tighter than ASTM, for example Fe ≤ 2.0 %, we confirm before order whether the ingot source can meet it.
4. Mechanical and physical properties
| Property | ASTM B564 / B574 minimum | Typical, metric | Typical, imperial |
|---|---|---|---|
| Tensile strength, Rm | 690 MPa (100 ksi) | 720 MPa | 104,700 psi |
| Yield strength, Rp0.2 | 310 MPa (45 ksi) | 365 MPa | 52,800 psi |
| Elongation, A | 45 % | 60 – 71 % | 60 – 71 % |
| Modulus of elasticity, E | not specified | 207 GPa | 30,000 ksi |
| Shear modulus, G | not specified | 77 GPa | 11,200 ksi |
| Poisson’s ratio | not specified | 0.34 | 0.34 |
| Density | 8.73 g/cm³ / 0.315 lb/in³ |
|---|---|
| Melting range | 1330 – 1380 °C / 2425 – 2515 °F |
| Structure | Face-centred cubic, single-phase austenitic, non-magnetic |
| VdTÜV approved service temperature | up to 400 °C (Werkstoffblatt 515) |
Typical values are indicative of forged product in the solution annealed condition and are not guaranteed properties. The mill certificate issued with each heat governs. Results vary with section size, forging reduction and test location.
5. Comparison with C-276 and Alloy 22
These three alloys are often compared during material selection. The difference between them is the chromium and molybdenum content.
| Alloy | UNS | W.-Nr. | Cr % | Mo % | W % | PREN ≈ | Typical use |
|---|---|---|---|---|---|---|---|
| 2.4606 / Alloy 686 | N06686 | 2.4606 | 19–23 | 15–17 | 3.0–4.4 | 80 | Highest combined Cr, Mo and W of the three. Mixed oxidising and reducing service, free halides, severe crevice risk |
| Hastelloy C-276 | N10276 | 2.4819 | 14.5–16.5 | 15–17 | 3.0–4.5 | 68 | Reducing acid service. Long-established grade, usually lower cost |
| Hastelloy C-22 / Alloy 22 | N06022 | 2.4602 | 20–22.5 | 12.5–14.5 | 2.5–3.5 | 72 | Strongly oxidising service, flue gas desulphurisation and pollution control. Lower Mo than 686 |
For stable reducing service, C-276 is normally sufficient. For strongly oxidising service, Alloy 22 is well proven. 2.4606 is specified where the process alternates between oxidising and reducing conditions, where free chlorides or fluorides are present, or where crevice corrosion has already occurred under a gasket or under a deposit.
6. Forged products and size range
| Forged form | Size range | Typical end use |
|---|---|---|
| Seamless rolled rings | OD 200 – 4,000 mm, height ≤ 1,000 mm | Valve bodies, pressure-vessel shell courses, pump casings |
| Forged discs and blanks | Ø 100 – 2,000 mm | Tube sheets, blind flanges, impeller blanks |
| Forged round, square and flat bars | Ø 20 – 800 mm, length ≤ 8,000 mm | Valve stems, fasteners, machined components |
| Forged flanges | DN15 – DN2000, ASME B16.5 / B16.47, EN 1092-1 | Piping and vessel connections in corrosive duty |
| Shafts and spindles | Ø 50 – 800 mm, length ≤ 8,000 mm | Chemical pumps, agitators, plunger pumps |
| Sleeves, bushings, hollow bars | OD 100 – 1,500 mm | Wear surfaces, liners, stuffing boxes |
| Tube sheets and forged plates | up to 2,500 mm | Shell-and-tube heat exchangers, condensers |
| Valve bodies, blocks, nozzles, cross bars | To customer drawing | Ball, gate, globe, check and plug valves; wellhead equipment |
| Single-piece forged weight | 10 kg – 20,000 kg | General |
Send the drawing and the finished weight will be confirmed with the quotation, together with the forging reduction ratio achievable on that section.
7. Manufacturing and heat treatment
- Melting. Ingot is produced by EAF with AOD or VOD refining, followed by electroslag remelting (ESR) or vacuum arc remelting (VAR) where the specification or the section size requires improved cleanliness and reduced segregation.
- Open-die forging. Cogging and upsetting break down the as-cast structure. The part is then forged to shape with the reduction ratio and finishing temperature controlled to give a uniform recrystallised grain. Ring blanks are pierced and rolled on the ring mill.
- Solution annealing. Typically 1120 to 1180 °C followed by rapid cooling or water quench, to dissolve any intermetallic phase formed during forging and restore full corrosion resistance.
- Machining. Rough or semi-finish turning and boring to the allowance specified, or finish machining to drawing.
- Inspection and certification. See section 8.
Ageing of 2.4606
2.4606 is a solid-solution alloy. It contains no gamma-prime or gamma-double-prime strengthening phases, so an ageing cycle does not increase strength. Long exposure between roughly 600 and 1000 °C can precipitate mu and P intermetallic phases, which reduce both ductility and corrosion resistance. The required treatment is solution annealing followed by rapid cooling. Where higher strength is needed it is obtained by cold work, and the resulting hardness must then be checked against any NACE MR0175 limit.
8. Testing and certification
- Chemical analysis by optical emission spectrometry on every heat, with positive material identification (PMI) on the finished forging where required.
- Tensile testing at room temperature to ASTM E8 / ISO 6892-1. Elevated-temperature tensile on request.
- Hardness testing, Brinell or Rockwell, mandatory where NACE MR0175 / ISO 15156-3 applies.
- Grain size to ASTM E112.
- Corrosion testing to ASTM G28 method A for intergranular attack and ASTM G48 for pitting and crevice, where the specification requires it.
- Ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388, to the acceptance class stated on the order.
- Liquid penetrant examination to ASTM E165 / ASME V Article 6.
- Dimensional report against the drawing, with marked-up sketch.
- Certification, EN 10204 type 3.1 as standard. Type 3.2 witnessed by TÜV, SGS, BV, DNV, Lloyd’s Register or the customer’s own inspector on request.
Traceability is maintained from ingot heat number through forging, heat-treatment charge and final inspection. Heat and job numbers are hard-stamped or vibro-etched on each piece.
9. Applications
| Industry | Typical 2.4606 forged components |
|---|---|
| Oil and gas, subsea | Wellhead and Christmas tree bodies, valve blocks and seat rings, hangers, forged bars for stems. Sour service to NACE MR0175 |
| Chemical process | Reactor nozzles, agitator shafts, pump casings and sleeves for mixed acid, HF and halide duty |
| Flue gas desulphurisation and pollution control | Scrubber and absorber internals, damper shafts, forged rings for ducting |
| Pulp and paper | Bleach plant equipment, digester components, forged discs and tube sheets |
| Waste incineration | Quench and scrubber components in chloride-bearing flue gas |
| Seawater and desalination | Pump shafts, sleeves and bushings, heat-exchanger tube sheets |
| Pressure vessels and heat exchangers | Forged flanges, tube sheets, shell rings, nozzle forgings |
| Pharmaceutical and biochemical | Reactor and vessel components where product purity forbids iron pickup |
| Valves and pumps | Bodies, bonnets, stems, seat rings, discs for ball, gate, globe, check and plug valves |
10. Ordering information
The following information allows a quotation to be prepared accurately. A drawing alone is usually enough to start.
- Grade and specification. 2.4606, NiCr21Mo16W, UNS N06686 or Alloy 686, plus the governing standard. ASTM B564 for forgings, ASTM B462 for flanges and valve parts.
- Drawing or dimensions. A 2D drawing, a 3D model, or finished dimensions with the machining allowance required on each face. For rings: OD, ID and height.
- Condition and heat treatment. Solution annealed and quenched, plus any hardness cap.
- Testing and certification. EN 10204 3.1 or 3.2, the ultrasonic standard and acceptance class, and any corrosion test.
- Quantity. Piece count, and whether the order will repeat.
- Delivery terms. Incoterm and destination port, for freight and packing.
11. Frequently asked questions
What is 2.4606 material?
2.4606 is the European Werkstoff number for NiCr21Mo16W, a single-phase austenitic nickel-chromium-molybdenum-tungsten alloy also known as Alloy 686 and UNS N06686. It contains 19 to 23 % chromium, 15 to 17 % molybdenum and 3.0 to 4.4 % tungsten, with carbon limited to 0.010 %. It resists oxidising and reducing acids, pitting and crevice attack in halide media, and corrosion in as-welded heat-affected zones.
Is 2.4606 the same as Alloy 686 and UNS N06686?
Yes. 2.4606 (EN Werkstoff number), NiCr21Mo16W (EN chemical designation), UNS N06686 and the trade names Alloy 686 and Inconel® 686 all refer to the same alloy. A purchase order may use any of these designations.
Can 2.4606 be age-hardened or precipitation hardened?
No. 2.4606 is a single-phase solid-solution alloy and contains no strengthening precipitates, so an ageing cycle does not increase strength. Long exposure between roughly 600 and 1000 °C can precipitate mu and P intermetallic phases, which reduce ductility and corrosion resistance. The required heat treatment is solution annealing at approximately 1120 to 1180 °C followed by rapid cooling or water quench. Higher strength can be obtained only by cold work.
Which standards cover 2.4606 forgings?
Forgings in UNS N06686 are covered by ASTM B564 and ASME SB-564, and by ASTM B462 for forged flanges, fittings, valves and parts in corrosive high-temperature service. Rod and bar are covered by ASTM B574, plate and sheet by ASTM B575, seamless pipe and tube by ASTM B622. The alloy is ASME P-No. 43 and is listed in NACE MR0175 / ISO 15156-3 for sour service.
What are the minimum mechanical properties of 2.4606 forgings?
In the solution annealed condition, ASTM B564 and B574 require a minimum tensile strength of 690 MPa (100 ksi), a minimum 0.2 % offset yield strength of 310 MPa (45 ksi) and a minimum elongation of 45 %. Typical measured values on forged product are about 720 MPa tensile strength, 365 MPa yield strength and 60 to 70 % elongation.
Should I specify 2.4606 or Hastelloy C-276?
2.4606 contains 19 to 23 % chromium against 14.5 to 16.5 % in C-276, with the same 15 to 17 % molybdenum. It therefore performs better in oxidising and in mixed oxidising and reducing service, and matches C-276 in reducing acids. Its pitting resistance equivalent number is about 80, against about 68 for C-276. C-276 is normally sufficient for stable reducing service where cost governs. 2.4606 is specified where the medium alternates, where free halides are present, or where crevice corrosion has already occurred.
Is 2.4606 approved for sour service?
Yes. UNS N06686 is listed in NACE MR0175 / ISO 15156-3 for H2S-containing oil and gas production, subject to the hardness and condition limits in that standard. We supply 2.4606 forgings solution annealed with hardness testing and full traceability, so compliance can be shown on the certificate.
What certification and testing do you supply?
An EN 10204 3.1 mill certificate is supplied as standard, or 3.2 witnessed by TÜV, SGS, BV, DNV or Lloyd’s Register on request. Testing covers chemical analysis and PMI, room-temperature tensile, hardness, grain size to ASTM E112, corrosion testing to ASTM G28 method A or ASTM G48 where specified, and ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388.
Who manufactures 2.4606 open-die forgings in China?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It produces 2.4606 (Alloy 686 / UNS N06686) seamless rolled rings, flanges, round bars, discs, shafts, sleeves, bushings, tube sheets and valve components to customer drawing. Enquiries: sales@steelforgepieces.com, +86 189 2135 9659.
What is the minimum order quantity?
The minimum order is one piece, including single prototypes and spare-part forgings. Lead time depends on ingot availability and part size and is confirmed with each quotation. Send the drawing or required dimensions, quantity, specification and test requirements to sales@steelforgepieces.com.
13. Manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China. We forge rings, seamless rolled rings, flanges, round bars, discs, shafts, sleeves, bushings, tube sheets and machined components in carbon steel, alloy steel, tool steel, stainless steel and nickel alloys, including 2.4606 / Alloy 686 / UNS N06686. Work is made to customer drawing, from single prototypes to repeat production, and certified to EN 10204 3.1 or 3.2.
Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Tel: +86 189 2135 9659
Email: sales@steelforgepieces.com
Web: www.steelforgepieces.com