Hangbo Alloy Group
Shanghai · Est. 2012
UNS N06686 / W.Nr. 2.4606 — Nickel-chromium-molybdenum-tungsten superalloy with PREN > 50 for the most aggressive chemical environments on Earth.
Inconel 686 (UNS N06686 / W.Nr. 2.4606) is a super corrosion-resistant nickel-chromium-molybdenum-tungsten alloy that represents the pinnacle of wrought nickel alloy corrosion resistance. Developed by Special Metals Corporation, 686 was engineered specifically for the most aggressive chemical environments where even Hastelloy C-276 and Inconel 625 may experience localized attack. With a Pitting Resistance Equivalent Number (PREN) exceeding 50, it offers exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-containing oxidizing and reducing acids, seawater, and mixed chemical media.
The defining metallurgical feature of Inconel 686 is its exceptionally high chromium (19-23%), molybdenum (15-17%), and tungsten (3.0-4.4%) content, combined with ultra-low carbon (≤0.010%) and silicon (≤0.08%) levels. This chemistry provides a level of corrosion resistance that surpasses virtually all other wrought nickel-base alloys, including Hastelloy C-276, Inconel 625, and Alloy 59. The alloy's balanced Cr-Mo-W system ensures protection in both oxidizing and reducing conditions, a versatility that few materials can match.
Unlike precipitation-hardenable superalloys, Inconel 686 is strengthened primarily by solid-solution mechanisms. This gives it excellent thermal stability, outstanding weldability, and freedom from strain-age cracking concerns. The alloy can be readily formed, welded, and machined using procedures similar to other Ni-Cr-Mo alloys, making it suitable for complex fabrications such as multi-pass welded vessels, clad plate constructions, and intricate process piping systems.
At Hangbo Alloy Group, Inconel 686 is supplied in plates, sheets, bars, seamless tubes, welded tubes, fittings, and welding wire per ASTM, ASME, and DIN/EN specifications. We support chemical process operators, offshore platform builders, pollution control system manufacturers, and nuclear fuel reprocessors with mill-direct supply, full certification, and custom fabrication services.
The chemistry of Inconel 686 is optimized to deliver the highest possible corrosion resistance in a wrought nickel alloy. The combination of high chromium, molybdenum, and tungsten provides protection across the full spectrum of oxidizing and reducing chemical environments.
| Element | Min % | Max % |
|---|---|---|
| Nickel (Ni) | Balance | Balance |
| Chromium (Cr) | 19.0 | 23.0 |
| Molybdenum (Mo) | 15.0 | 17.0 |
| Tungsten (W) | 3.0 | 4.4 |
| Iron (Fe) | — | 5.0 |
| Titanium (Ti) | 0.02 | 0.25 |
| Carbon (C) | — | 0.010 |
| Manganese (Mn) | — | 0.75 |
| Silicon (Si) | — | 0.08 |
| Phosphorus (P) | — | 0.040 |
| Sulfur (S) | — | 0.020 |
Inconel 686 has a face-centered cubic (FCC) austenitic structure in the solution-annealed condition. Its physical properties are comparable to other high-Cr-Mo nickel alloys, facilitating design calculations and welding to similar base metals.
| Property | Value | Unit |
|---|---|---|
| Density | 8.49 | g/cm³ |
| Melting Range | 1338 – 1380 | °C |
| Specific Heat (20°C) | 420 | J/kg·K |
| Thermal Conductivity (20°C) | 9.5 | W/m·K |
| Electrical Resistivity (20°C) | 1.25 | μΩ·m |
| Modulus of Elasticity (20°C) | 210 | GPa |
| Mean CTE (20–100°C) | 11.5 | μm/m·°C |
| Mean CTE (20–600°C) | 13.8 | μm/m·°C |
| Magnetic Permeability | 1.002 | (non-magnetic) |
Inconel 686 is supplied in the solution-annealed condition, typically heat treated at 1100-1150°C followed by rapid cooling. The alloy exhibits excellent ductility and toughness, with elongation around 45% that allows bending, forming, and moderate cold working.
| Property | Annealed Value |
|---|---|
| Tensile Strength | 760 MPa (110 ksi) |
| Yield Strength (0.2% offset) | 380 MPa (55 ksi) |
| Elongation in 2 inches | 45% |
| Reduction of Area | 55% |
| Hardness | 95 HRB |
| Charpy V-notch Impact (RT) | 200 J min |
Inconel 686 was specifically developed to resist the most aggressive forms of chemical attack. Its performance in pitting, crevice corrosion, and stress corrosion cracking is superior to virtually all other wrought nickel alloys.
The Pitting Resistance Equivalent Number (PREN = %Cr + 3.3×%Mo + 16×%N) for Inconel 686 exceeds 50, among the highest of any wrought alloy. In ASTM G48 pitting and crevice corrosion tests in ferric chloride solution, 686 significantly outperforms Inconel 625, Hastelloy C-276, and even Alloy 59. This makes it the alloy of choice for seawater heat exchangers, offshore platform components, and chemical process equipment handling chloride-bearing acids.
Inconel 686 offers outstanding resistance to mixed oxidizing-reducing acids, including sulfuric-hydrochloric mixtures, sulfuric-nitric combinations, and phosphoric acid with halide contaminants. Its balanced Cr-Mo-W system ensures that neither oxidizing nor reducing conditions cause rapid attack. In many mixed acid environments, 686 provides corrosion rates an order of magnitude lower than C-276.
The alloy demonstrates excellent resistance to chloride stress corrosion cracking (SCC) in both boiling magnesium chloride solutions and actual process environments. This is critical for applications such as nuclear fuel reprocessing, where chloride SCC of lower-grade alloys has caused catastrophic failures.
Inconel 686 is selected wherever the most severe corrosion conditions exist. Its field-proven performance has made it the ultimate material of choice in several ultra-demanding industries.
Hangbo Alloy Group supplies Inconel 686 in the full range of product forms required by the chemical processing, offshore, and nuclear industries. Material is supplied in the solution-annealed condition with EN 10204 3.1 mill test certificates and full traceability.
Inconel 686 has excellent weldability by gas tungsten arc welding (GTAW/TIG), gas metal arc welding (GMAW/MIG), and shielded metal arc welding (SMAW). Its austenitic structure and ultra-low carbon content minimize sensitization concerns.
| Standard | Description |
|---|---|
| ASTM B575 | Plate, Sheet, and Strip |
| ASTM B574 | Bar, Rod, and Wire |
| ASTM B622 | Seamless Pipe and Tube |
| ASTM B619 / B775 | Welded Pipe |
| ASTM B626 / B751 | Welded Tube |
| ASTM B366 | Fittings |
| ASTM B564 | Forgings |
| ASME SB-575 / SB-574 / SB-622 | Boiler and Pressure Vessel Code |
| DIN/EN W.Nr. 2.4606 | German/European Material Designation |
Shanghai Hangbo Alloy Group is a professional manufacturer and global supplier of Inconel 686 (UNS N06686 / W.Nr. 2.4606). We provide plates, sheets, bars, seamless tubes, welded tubes, fittings, and welding wire with full material certification per ASTM, ASME, and EN standards. Mill-direct pricing, ISO 9001:2015 quality system, and fast delivery to 50+ countries worldwide.
Inconel 686 (UNS N06686 / W.Nr. 2.4606) is a super corrosion-resistant nickel-chromium-molybdenum-tungsten alloy designed for the most aggressive chemical environments. With higher Cr, Mo, and W content than Inconel 625 and Hastelloy C-276, 686 offers exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking.
Nominal composition: Ni balance (min 50%), Cr 19.0–23.0%, Mo 15.0–17.0%, W 3.0–4.4%, Fe max 5.0%, Ti 0.02–0.25%, C max 0.010%, Mn max 0.75%, Si max 0.08%. The combination provides PREN values exceeding 50, among the highest of any wrought nickel alloy.
Inconel 686 has a density of approximately 8.49 g/cm³ (0.307 lb/in³) and a melting range of 1338–1380°C (2440–2515°F).
Typical annealed properties: tensile strength ~760 MPa (110 ksi), yield strength ~380 MPa (55 ksi), elongation ~45%, hardness ~95 HRB. The alloy retains excellent ductility and toughness across a wide temperature range.
Key standards: ASTM B575 (plate/sheet/strip), ASTM B574 (bar/rod), ASTM B622 (seamless pipe/tube), ASTM B619/B775 (welded pipe), ASTM B626/B751 (welded tube), ASTM B366 (fittings), ASTM B564 (forgings), and W.Nr. 2.4606.
Inconel 686 resists corrosion through its exceptionally high Cr (21%), Mo (16%), and W (3.7%) content, giving it a PREN above 50. This makes it highly resistant to pitting, crevice corrosion, and stress corrosion cracking in chloride-containing environments, sulfuric acid, hydrochloric acid, and mixed oxidizing-reducing acids.
Inconel 686 is suitable for continuous service up to 450°C (840°F) in corrosive environments. For high-temperature structural applications without corrosion concerns, it can be used up to 800°C (1470°F).
Primary applications: chemical process equipment for aggressive media, pollution control scrubbers, seawater and brine components, pulp and paper bleach plants, flue gas desulfurization, oil and gas sour gas handling, pharmaceutical processing, and nuclear fuel reprocessing.
Yes, Inconel 686 has excellent weldability using GTAW, GMAW, and SMAW processes. Matching filler metals such as ERNiCrMo-14 or ENiCrMo-14 are recommended. No preheat is required, and post-weld heat treatment is generally not necessary for corrosion resistance.
Hangbo Alloy Group supplies Inconel 686 in round bars, plates/sheets/strips, seamless tubes/pipes, welded tubes/pipes, fittings, forgings, and welding wire. All products are delivered with EN 10204 3.1 mill test certificates and full traceability.
Inconel 686 has significantly higher Cr, Mo, and W content than both Inconel 625 and Hastelloy C-276, giving it superior pitting and crevice corrosion resistance. Its PREN exceeds 50 compared to approximately 45 for C-276 and 40 for 625. However, 625 offers higher strength at elevated temperatures, and C-276 may be more cost-effective for less severe environments.
Inconel 686 is a premium ultra-corrosion-resistant alloy. Typical mill-direct pricing ranges from $45–70/kg for bars, $55–85/kg for plates, and $70–120/kg for seamless tubes, depending on size and quantity. Lead times are typically 10–14 weeks for custom mill orders; Hangbo Alloy maintains strategic inventory for 3–5 week delivery. MOQ is generally 50 kg for stock sizes and 200–500 kg for custom sizes. Contact hangbo@nickel-alloy.com for a competitive quote.
Request a quotation for Inconel 686 plates, tubes, bars, or welding wire for chemical processing, offshore, or nuclear applications. We stock standard sizes and accept custom orders.