Section 01 · OverviewWhat Is UNS N10665 / Alloy B-2?
UNS N10665 is a binary nickel-molybdenum superalloy engineered for outstanding performance in strongly reducing chemical environments — particularly hydrochloric acid at any concentration and temperature. It is commercially marketed under the registered trademark HASTELLOY® B-2 by Haynes International, Inc., but is also widely specified by its international equivalents: Alloy B-2, W.Nr. 2.4617 (European DIN), and Nimofer 6928. All designations refer to the same alloy chemistry.
The alloy's defining features are a very high molybdenum content (26–30%), a very high nickel balance (≥62%), and deliberately suppressed levels of chromium (≤1%), carbon (≤0.02%), silicon (≤0.10%), and iron (≤2%). Each restriction exists for a specific electrochemical reason explained in detail throughout this guide. Jiangsu Liangyi Co., Limited manufactures Alloy B-2 open-die forgings and seamless rolled rings to ASTM B564, with weights from 30 kg to 30,000 kg and rings up to 6,000 mm OD.
UNS N10665 / Alloy B-2 is not a general-purpose corrosion-resistant alloy. It is a specialist material optimized for one environment: non-oxidizing, reducing acid service — especially HCl at any concentration and temperature up to boiling. Using it in oxidizing environments or where ferric/cupric ions are present can lead to rapid, catastrophic failure.
The alloy was developed as a significant improvement over the original Hastelloy® B. By reducing carbon to ≤0.02% and silicon to ≤0.10%, Alloy B-2 virtually eliminated the grain-boundary carbide and silicide precipitation that previously made welds in the original alloy vulnerable to intergranular corrosion — a phenomenon historically known as "knife-line attack."
Section 02 · ChemistryChemical Composition of UNS N10665 (Alloy B-2)
The alloy chemistry is governed by ASTM B619, B622, and B626 for wrought products and ASTM B564 for forgings. The full composition limits for UNS N10665 / Alloy B-2 / W.Nr. 2.4617 are:
| Element | Min (%) | Max (%) | Purpose in alloy |
|---|---|---|---|
| Nickel (Ni) | Balance | — | Austenitic matrix; baseline corrosion resistance |
| Molybdenum (Mo) | 26.0 | 30.0 | Primary corrosion resistance in reducing acids — the defining element |
| Iron (Fe) | — | 2.0 | Controlled low to prevent oxidation susceptibility |
| Chromium (Cr) | — | 1.0 | Intentionally minimized — provides no benefit and reduces performance in HCl service |
| Carbon (C) | — | 0.02 | Ultralow to prevent HAZ carbide precipitation and knife-line attack after welding |
| Silicon (Si) | — | 0.10 | Ultralow to prevent HAZ silicide precipitation |
| Manganese (Mn) | — | 1.0 | Deoxidizer during melting; no corrosion function |
| Cobalt (Co) | — | 1.0 | Incidental; similar electrochemical behavior to Ni |
| Phosphorus (P) | — | 0.04 | Impurity limit — grain boundary segregation control |
| Sulfur (S) | — | 0.03 | Impurity limit — hot cracking prevention during forging |
Why Is Chromium Deliberately Limited to ≤1.0%?
This is the most common question from engineers familiar with stainless steels and UNS N10276 (HASTELLOY® C-276). In oxidizing environments, chromium forms a protective Cr₂O₃ passive film — the principle behind stainless steels. But in reducing environments such as hydrochloric acid, chromium provides no protective benefit and can actively accelerate corrosion. The chromium ceiling of ≤1.0% in UNS N10665 is therefore a deliberate performance optimization, not a limitation.
Section 03 · PropertiesMechanical and Physical Properties of UNS N10665
Minimum Mechanical Requirements — Solution-Annealed Condition (ASTM B564)
Physical Properties
| Property | Value | Units |
|---|---|---|
| Density | 9.22 | g/cm³ (0.333 lb/in³) |
| Melting range | 1330–1380 | °C (2425–2520 °F) |
| Specific heat capacity | 373 | J/kg·K at 20 °C |
| Thermal conductivity | 11.1 | W/m·K at 20 °C |
| Thermal expansion coefficient | 10.8 | µm/m·°C (20–100 °C) |
| Electrical resistivity | 1.37 | µΩ·m |
| Modulus of elasticity | 217 | GPa (31.5 × 10⁶ psi) |
| Poisson's ratio | 0.30 | dimensionless |
"The exceptional corrosion performance of UNS N10665 in hydrochloric acid is not the result of a passive film, but of sluggish dissolution kinetics — the high molybdenum content slows the anodic reaction to near-zero rates at any acid concentration."
— Principle of Ni-Mo alloy corrosion mechanism, solid-solution strengthening theorySection 04 · Critical WarningTemperature Limits: The 540–870 °C Forbidden Zone
Never expose UNS N10665 / Alloy B-2 to service temperatures between 540 °C and 870 °C (1,000 °F and 1,600 °F). In this range, ordering reactions precipitate Ni₄Mo intermetallic phases at grain boundaries, causing severe and irreversible embrittlement. If your process involves temperatures in this range — even transiently — specify UNS N10675 (also marketed as HASTELLOY® B-3) instead, which is thermally stabilized through additions of Cr, Ti, and Zr.
Below 540 °C (1,000 °F), UNS N10665 maintains excellent ductility and corrosion resistance. Above 870 °C (1,600 °F), ordering reactions dissolve and the alloy recovers — which is the basis of the solution annealing heat treatment used to produce finished forgings. The approved service range for UNS N10665 is cryogenic temperatures to approximately 538 °C (1,000 °F).
Section 05 · CorrosionCorrosion Resistance: Where UNS N10665 Excels and Where It Fails
Outstanding Resistance To:
Do Not Use UNS N10665 In:
Oxidizing acids, oxidizing chloride solutions, and streams containing ferric (Fe³⁺) or cupric (Cu²⁺) ions. UNS N10665 has virtually no chromium and cannot form a protective passive film in oxidizing conditions. Concentrated nitric acid, chromic acid, and ferric or cupric chloride solutions will corrode this alloy at high rates. Even trace contamination of a reducing acid stream with Fe³⁺ or Cu²⁺ ions can trigger rapid attack. For mixed or oxidizing environments, specify UNS N10276 (HASTELLOY® C-276) instead.
Section 06 · ComparisonUNS N10665 vs UNS N10276 vs UNS N10675
Also sold as HASTELLOY® B-2
- Maximum HCl resistance at all concentrations
- 26–30% Mo for reducing acid dominance
- Poor in oxidizing or mixed environments
- Avoid 540–870 °C range in service
- Lower cost than UNS N10675
- Broad resistance in oxidizing and reducing environments
- 16% Mo + 15% Cr + 4% W chemistry
- Tolerates mixed oxidizing/reducing streams
- Best choice when Fe³⁺ or Cu²⁺ ions are present
- Weaker than N10665 in pure HCl service
- Better thermal stability than N10665
- Added Cr, Ti, Zr for phase stability
- Safe through the 540–870 °C range
- Slightly broader acid resistance envelope
- Higher cost — specify when N10665 hits temperature limits
Section 07 · ManufacturingThe UNS N10665 Forging Process — Step by Step
Forging is the preferred manufacturing method for UNS N10665 (Alloy B-2) pressure-containing components due to the refined grain structure and superior mechanical properties it provides over castings. The seven-step process described below applies to every custom UNS N10665 forged part produced at Jiangsu Liangyi, beginning with vacuum induction melting (VIM), followed by electroslag remelting (ESR) or vacuum arc remelting (VAR).
Section 08 · FabricationWelding UNS N10665 (Alloy B-2): Key Considerations
The alloy's ultralow carbon and silicon content was specifically engineered to make welding viable in the as-welded condition — but proper technique remains essential for corrosion-critical applications.
Filler metal: Use ERNiMo-7 (AWS A5.14) for GTAW/GMAW. For SMAW, use ENiMo-7 electrodes. Do not substitute NiCrMo fillers (used for UNS N10276), as the resulting weld metal will behave differently in reducing acid service.
Heat input control: Minimize heat input per pass to reduce time in the 540–870 °C sensitization range. Use stringer beads rather than weave passes. Control interpass temperature to below 100 °C.
Post-weld heat treatment: For ASME code-stamped pressure equipment and the most critical corrosion service, post-weld solution annealing at 1,065–1,175 °C followed by rapid water quench restores full corrosion resistance to the HAZ and weld metal.
Section 09 · ApplicationsIndustries and Applications for UNS N10665 Forgings
| Industry | Typical Component | Critical Requirement |
|---|---|---|
| Chemical Processing | Reactor vessels, heat exchanger shells, agitator shafts, vessel flanges | Resistance to HCl, H₂SO₄, H₃PO₄ at elevated temperature and pressure |
| Pharmaceutical / Fine Chemicals | Reaction vessel internals, pump casings, valve bodies | Acid purity — no contamination from alloy dissolution |
| Petrochemical Refining | HCl alkylation unit components, acid recirculation system parts | Severe HCl service in acid alkylation processes |
| Chlor-Alkali Production | Electrolyzer components, brine treatment equipment, pump impellers | Wet chlorine, HCl, sodium hypochlorite service |
| Mining / Hydrometallurgy | Autoclave internals, agitator shafts, pressure leach reactor parts | Hot, concentrated mineral acid under pressure |
| Industrial Gas | HCl synthesis reactor internals, gas handling valve bodies | High-temperature dry and wet HCl gas service |
| Semiconductor | Acid distribution manifolds, wet bench hardware | Ultra-high-purity acid handling without trace metal ion release |
Section 10 · StandardsApplicable Specifications for UNS N10665 Forgings
| Standard | Scope |
|---|---|
| ASTM B564 | Nickel alloy forgings — primary standard governing UNS N10665 forging composition, mechanical requirements, and testing |
| ASME SB-564 | ASME BPVC equivalent of ASTM B564 — required for code-stamped pressure equipment |
| ASTM B619 | Welded nickel and nickel-cobalt alloy pipe for UNS N10665 |
| ASTM B622 | Seamless nickel and nickel-cobalt alloy pipe and tube for UNS N10665 |
| ASTM B626 | Welded nickel and nickel-cobalt alloy tube for UNS N10665 |
| ASTM A388 | Ultrasonic examination of heavy steel forgings — used for UT inspection |
| EN 10204-3.1 | Material test certificate — inspection and certification by the manufacturer's own quality personnel. Issued as standard with all Jiangsu Liangyi deliveries. |
| EN 10204-3.2 | Material test certificate — inspection by an independent third-party inspector nominated by the customer. Available upon customer request when customer arranges the inspector. |
| UNS N10665 | SAE/ASTM Unified Numbering System designation for this alloy |
| W.Nr. 2.4617 | European DIN material number equivalent |
EN10204-3.2 certificates require an independent inspector approved by the customer to be present during testing and to countersign the certificate. Jiangsu Liangyi Co., Limited does not self-issue EN10204-3.2 certificates. Customers wishing for 3.2 inspection should nominate their preferred third-party inspection agency (e.g., SGS, Bureau Veritas, TÜV, Intertek) and advise us at order placement so inspection can be scheduled within the production timeline.
Section 11 · ProcurementHow to Specify UNS N10665 Forged Parts: 10-Point Checklist
- Material designation: State UNS N10665 / Alloy B-2 / W.Nr. 2.4617. These are interchangeable designations for the same alloy.
- Applicable standard: Reference ASTM B564 or ASME SB-564 for forgings, including edition year if required.
- Component type: Open-die forging, seamless rolled ring, forged disc, forged flange, forged shaft, or hollow bar.
- Dimensional requirements: Rough forging envelope (min/max per axis) or finish-machined drawing with all tolerances.
- Weight range: Approximate unit weight in kg. Jiangsu Liangyi's range is 30 kg to 30,000 kg per piece.
- Heat treatment: Solution-annealed and water-quenched — standard and mandatory for all UNS N10665 forgings.
- NDT requirements: UT per ASTM A388, PT or MT class, and acceptance criteria per applicable code.
- Material certificate: EN10204-3.1 (standard, issued by Jiangsu Liangyi QC) or EN10204-3.2 (third-party inspector arranged by customer).
- Chemical analysis: Heat analysis and product analysis both required per ASTM B564.
- Quantity and delivery: Number of pieces and confirmed required delivery date.
Section 12 · Our ProductsUNS N10665 Forged Parts from Jiangsu Liangyi Co., Limited
Jiangsu Liangyi Co., Limited has manufactured UNS N10665 (Alloy B-2) open-die forgings and seamless rolled rings since 1997. Our 80,000 m² facility in Jiangyin, Jiangsu Province, China operates forging presses from 2,000 to 6,300 tonnes and ring rolling mills producing seamless rings to 6,000 mm outer diameter. All products are manufactured under ISO 9001:2015 quality management system certification. EN10204-3.1 material test certificates are issued as standard with every delivery.
We manufacture UNS N10665 / Alloy B-2 forged parts in the following standard forms:
Send your dimensions, weight, quantity, and applicable standard. Our technical team responds within 24 hours with a detailed quotation and material availability confirmation.
View UNS N10665 Forged Parts & Request a QuoteSection 13 · FAQFrequently Asked Questions About UNS N10665 / Alloy B-2
UNS N10665 (Alloy B-2, W.Nr. 2.4617, also commercially known as HASTELLOY® B-2) is used in chemical processing equipment handling strongly reducing, non-oxidizing acids — especially hydrochloric acid (HCl) at any concentration and temperature, sulfuric acid at low-to-moderate concentrations, phosphoric acid, acetic acid, and formic acid. Typical forged components include reactor vessels, heat exchanger shells, pump casings, agitator shafts, valve bodies, and flanges.
The UNS designation for HASTELLOY® B-2 alloy is N10665. It is also known by the European DIN designation W.Nr. 2.4617, and the generic designation Alloy B-2. HASTELLOY® is a registered trademark of Haynes International, Inc. Alloys of equivalent chemistry produced by other manufacturers are typically designated UNS N10665 or Alloy B-2.
UNS N10665 must never be exposed to service temperatures between 540 °C and 870 °C (1,000 °F–1,600 °F). In this range, ordering reactions precipitate Ni₄Mo intermetallic phases at grain boundaries, causing severe embrittlement. Approved service range is cryogenic to approximately 538 °C (1,000 °F). If your process exceeds this, specify UNS N10675 instead.
UNS N10665 (Alloy B-2) contains 26–30% Mo and ≤1% Cr, optimized for pure reducing acid service, especially HCl. UNS N10276 (also marketed as HASTELLOY® C-276) contains 16% Mo, 15% Cr, and 4% W, offering broader resistance in both oxidizing and reducing environments. N10276 is preferred when oxidizing contaminants (Fe³⁺, Cu²⁺) are present; N10665 outperforms in pure HCl service. Both HASTELLOY® trademarks are owned by Haynes International, Inc.
Yes. UNS N10665 forgings produced to ASTM B564 / ASME SB-564 are approved materials under the ASME Boiler and Pressure Vessel Code (Section II, Part B). Allowable stress values are listed in ASME Section II Part D for service temperatures up to 538 °C (1,000 °F).
Jiangsu Liangyi Co., Limited holds ISO 9001:2015 quality management system certification. EN10204-3.1 material test certificates are issued as standard with all deliveries. EN10204-3.2 third-party inspection is available upon customer request — customers must nominate and arrange their preferred third-party inspection agency, which then attends and countersigns the certificate during production.
Standard lead times from Jiangsu Liangyi Co., Limited range from 4 to 12 weeks depending on forging size, quantity, and heat treatment schedule. Large-section forgings above 5,000 kg or orders requiring third-party inspection may require additional time. Please contact us with your specific requirements for a confirmed production schedule.
Key Facts: UNS N10665 / Alloy B-2 Nickel-Molybdenum Alloy
- UNS N10665 (W.Nr. 2.4617, Alloy B-2) is a binary nickel-molybdenum alloy with 26–30% Mo and ≥62% Ni. It is commercially marketed as HASTELLOY® B-2 by Haynes International, Inc.
- Outstanding resistance to hydrochloric acid (HCl) at all concentrations and temperatures up to boiling — the best performance of any commercially available wrought alloy in pure HCl service.
- Carbon (≤0.02%) and silicon (≤0.10%) are kept ultralow to prevent HAZ sensitization and knife-line attack after welding.
- Chromium is limited to ≤1.0% — Cr provides no benefit and reduces performance in reducing acid environments.
- Approved service temperature: cryogenic to 538 °C (1,000 °F). The 540–870 °C range causes irreversible Ni₄Mo embrittlement.
- For oxidizing environments or Fe³⁺/Cu²⁺ contamination, specify UNS N10276 (marketed as HASTELLOY® C-276) instead.
- For thermal stability through the 540–870 °C range, specify UNS N10675 (marketed as HASTELLOY® B-3).
- Forging standard: ASTM B564 / ASME SB-564. Heat treatment: solution anneal + water quench.
- Manufacturer: Jiangsu Liangyi Co., Limited, Jiangyin, Jiangsu, China. Established 1997. ISO 9001:2015 certified. Forgings from 30 kg to 30,000 kg; seamless rings to 6,000 mm OD.