UNS N06686 Forgings Alloy 686 forged rings, flanges, bars, discs and shafts to ASTM B564

OverviewWhat is UNS N06686?

UNS N06686 is the UNS designation for a low-carbon nickel-chromium-molybdenum-tungsten alloy. ASTM B564 lists it among the nickel alloys supplied as forgings. The alloy is austenitic and single-phase. It carries no strengthening precipitates, so all of its strength comes from solid solution.

Every element in the composition has a job. Nickel and molybdenum carry the resistance in reducing acids such as hydrochloric and dilute sulphuric. Chromium handles oxidising media, including nitric acid and hot oxidising chlorides. Molybdenum and tungsten together raise resistance to localised attack, which means pitting and crevice corrosion. Localised attack is normally what ends the service life of a part in seawater or process brine. Iron is held to 5% maximum. Carbon is held to 0.010% maximum, which keeps grain-boundary carbide precipitation low during welding, so the heat-affected zone retains its corrosion resistance without post-weld heat treatment.

That carbon limit counts for more in a forging than in sheet. Forgings are thick, they cool slowly through the sensitisation range, and nozzle attachment welds or weld repairs are common. Low carbon and the absence of an ageing response are what make N06686 predictable in heavy section.

EquivalentsDesignations and equivalent standards

Werkstoff and EN designations are given for identification. Where a purchase order cites a European standard, we certify against that standard as well as against ASTM B564.

ChemistryChemical composition of UNS N06686

Composition limits below are the ASTM B564 requirements for UNS N06686, in weight percent. Every heat is supplied with a ladle analysis. A product check analysis is run on request.

Some purchasers restrict cobalt for nuclear service, or restrict Al plus Ti. State any tightened element limits on the enquiry. We place the melt order against your limits rather than against the generic table.

MechanicalMechanical properties of N06686 forgings

Two sets of numbers appear below. The first column is what ASTM B564 requires, which is what an inspector checks against. The second column is what solution-annealed forgings normally deliver. Use the typical column for design margin only.

Typical values are indicative of hot-forged, solution-annealed sections and are not for design or specification. The guaranteed values are the ASTM B564 minima, verified on a test coupon representing the forging.

PhysicalPhysical properties

Physical property values are typical published data for the alloy and are given for information. For elevated-temperature design data, refer to the applicable ASME Section II Part D tables.

PerformanceCorrosion behaviour

Localised corrosion resistance across the Ni-Cr-Mo family scales with combined chromium, molybdenum and tungsten content. UNS N06686 runs roughly 21% Cr, 16% Mo and 3.7% W nominally, one of the highest combined loadings available in a weldable, forgeable, single-phase alloy. What that means in service:

• Pitting and crevice corrosion. Critical pitting and crevice temperatures in acidified ferric chloride, ASTM G48 methods C and D, exceed those of Alloy C-276 and Alloy 625. Published data places the alloy above 85 °C.
• Mixed acids. Resistant to oxidising and reducing conditions at the same time. That is the situation in flue-gas desulphurisation scrubbers, pickling lines and waste incineration, where the chemistry swings.
• Chlorides. Tolerates chloride levels well beyond 100,000 ppm and low-pH acid mixtures, the regime that defeats 316L and even 6Mo austenitics.
• Seawater. Resistant to general, galvanic and localised attack and to hydrogen embrittlement, both annealed and cold worked.
• Welded joints. The 0.010% carbon ceiling limits grain-boundary precipitation, so the heat-affected zone keeps its corrosion resistance without post-weld heat treatment.

Corrosion data are drawn from published alloy producer literature and are indicative. Behaviour depends on the specific medium, concentration, temperature, velocity, aeration and contaminants. Qualify the alloy against your own service conditions or your licensor's material selection.

ProcessHow we forge UNS N06686

The hot working window for this alloy is narrow and the material is stiff under the press. Finishing below the recrystallisation temperature leaves residual strain that shows up later as cracking, or as a failed intergranular corrosion test. Our route for N06686:

1. Melting and raw material

Bar and billet are procured double melted: electric arc furnace with argon-oxygen or vacuum-oxygen decarburisation, followed by electroslag remelting. ESR tightens sulphur and phosphorus, breaks up segregation and gives a sound centre. That matters because N06686 forgings usually go into pressure-retaining service with volumetric NDT.

2. Open-die forging

Heating to 1,150 to 1,180 °C, with soak time set by section thickness so the core reaches temperature. Forging finishes above about 950 °C. Below that the alloy work-hardens sharply and the risk of surface cracking rises, so heavy sections are reheated instead of being pushed. Minimum forging reduction ratio from billet is 3:1, higher where the drawing calls for it, to break down the cast structure and give uniform grain flow.

3. Ring rolling

Seamless rolled rings are pierced and expanded on a radial-axial ring mill. This produces circumferential grain flow, which is why a rolled ring outperforms a ring cut from plate in both fatigue and corrosion service.

4. Solution annealing

Solution treatment at approximately 1,120 °C followed by rapid cooling. Heavy sections are water quenched. Cooling quickly through the precipitation range keeps the carbides and intermetallics in solution. Furnace time-temperature charts are recorded and issued with the certificate. No ageing treatment is applied.

5. Machining and finishing

Rough machining to the drawing with an agreed allowance, or finish machining to print. The alloy work-hardens, so it needs rigid setups, sharp positive-rake tooling, low speeds and heavy feeds. We quote a machining allowance we can hold.

ProductForged forms and size range

Delivery condition options: as-forged with scale, shot-blasted, rough turned or bored with machining allowance, or finish machined to drawing. Pickled and passivated surfaces are supplied where the downstream process requires them.

QualityTesting, inspection and certification

ApplicationsWhere UNS N06686 forgings are used

Flue-gas desulphurisation and pollution control

Scrubber internals, absorber nozzles, forged rings and flanges working in chloride-rich acidic condensate. This was one of the first applications for the alloy. Scrubber chemistry swings between oxidising and reducing, which is the condition 686 handles better than most.

Chemical and petrochemical processing

Reactor and column nozzles, forged tube sheets and flanges for shell-and-tube heat exchangers, pressure vessel components, agitator and pump shafts, sleeves and bushings for chemical and plunger pumps.

Oil, gas and subsea

Wellhead and Christmas tree components, subsea and deepwater production hardware, valve bodies, bonnets, seat rings and stems, forged blocks and manifolds. Where sour service applies, confirm the NACE MR0175 / ISO 15156-3 condition and hardness limits on the order.

Waste incineration and waste to energy

Boiler and duct components, scrubber hardware, forged rings and tube sheets in condensing chloride environments.

Pulp and paper

Bleach plant hardware, digester components, forged discs and rolls in chlorine dioxide and chloride service.

Marine and desalination

Seawater pump and valve components, shafts, sleeves, high-strength cold-worked bolting, heat exchanger tube sheets in brine.

Power generation

Forged rings, spindles, gears and casings in gas compressors, turbines and gear boxes handling corrosive process gas, plus nitrogen generator and industrial air compressor hardware.

SelectionUNS N06686 compared with C-276, Alloy 625 and Alloy 22

These four alloys overlap and buyers often ask which to specify. Alloy 686 gives the highest localised corrosion resistance of the group and costs the most. C-276 is the long-established workhorse. Alloy 625 is chosen where niobium-strengthened elevated-temperature properties matter. Alloy 22 sits between C-276 and 686, with better performance than C-276 in oxidising conditions.

We forge all four grades. If the grade is not settled, send the medium, concentration, temperature, pressure and the code the part is built to. We will quote the alternatives and forge to whichever grade your engineer confirms.

Related grades: Hastelloy C-276 forgings, Hastelloy C-22 forgings, Inconel 625 forgings, Hastelloy C-2000 forgings.

OrderingHow to order UNS N06686 forgings

Send a drawing if you have one. If you do not, rough dimensions are enough to start. A complete enquiry contains:

1. Grade and specification. UNS N06686 to ASTM B564, plus any additional standard your code requires.
2. Shape and dimensions. Drawing, or OD × ID × height for rings, Ø × length for bars.
3. Quantity and whether the order repeats.
4. Delivery condition. As-forged, rough machined with allowance, or finish machined.
5. Testing. UT class, IGC test, PMI, impact testing, anything beyond the standard package.
6. Certification. EN 10204 3.1, or 3.2 and which inspection body.
7. Destination port and required Incoterm: EXW, FOB Shanghai, CIF or DDP.

Quotation within 24 hours on working days. Email sales@steelforgepieces.com · Call or WhatsApp +86 189 2135 9659.

CatalogueOther nickel alloy forgings we produce

By product form: forged tubes, forged spindles, open-die forgings.

Data sources and revision

Composition and mechanical requirements on this page are stated to ASTM B564 / ASME SB-564. Corrosion and physical property statements summarise published alloy producer literature for Alloy 686. Typical values are indicative and are not design allowables. Work from the current edition of the applicable standard and from your own qualification testing. INCONEL® is a registered trademark of Special Metals Corporation and Hastelloy® is a registered trademark of Haynes International. Trade names are used here for identification only.

Prepared by the sales engineering team, Jiangyin Jiangnan Metal Co., Ltd. · Published 14 May 2019 · Last updated 29 August 2026.