Material Family

Nickel-Molybdenum Alloy (Low Iron, Low Carbon)

The absence of chromium is its defining characteristic, optimizing it for pure reducing conditions.

Common Designations

UNS N10665, Hastelloy B-2, W.Nr. 2.4617

The premier alloy for severe reducing acid service. "Hastelloy" is a trademark of Haynes International.

Chemical Composition (Typical wt.%)

Ni: ≥ 69.0 (Balance)
Mo: 26.0 - 30.0
Fe: 2.0 max
Cr: 1.0 max
Co: 1.0 max
C: ≤ 0.010
Si: ≤ 0.08
Mn: ≤ 1.0

Extremely High Molybdenum (Mo) provides resistance to reducing acids. Very Low Chromium (Cr) and Iron (Fe) are critical to prevent attack by oxidants.

Mechanical Properties (Annealed Plate)

Tensile Strength (Rm): 760 - 965 MPa
Yield Strength (Rp0.2): 350 - 550 MPa
Elongation (A): 40 - 60%

High strength and excellent ductility in the annealed condition.

Physical Properties

Density: 9.22 g/cm³
Melting Range: 1330 - 1380 °C

One of the densest common nickel alloys due to high molybdenum content.

Key Corrosion Resistance Attributes

• Unparalleled resistance to hydrochloric acid (HCl) at all concentrations and temperatures up to the boiling point.• Excellent resistance to sulfuric (H₂SO₄), phosphoric (H₃PO₄), and acetic acids under reducing conditions.• Good resistance to hydrogen chloride (HCl) gas.

• ⚠️ Major Limitation: Very poor resistance to oxidizing agents (e.g., Fe³⁺, Cu²⁺ ions, HNO₃, oxygen, chlorine). Presence of even ppm-level oxidants can cause severe corrosion.

A specialist alloy with an extremely specific and powerful application window. Must be used in strictly oxygen-free, reducing environments.

Key Standards (Plate)

ASTM B333 / ASME SB-333 (Primary Standard), DIN 2.4617

ASTM B333 covers plate, sheet, and strip for nickel-molybdenum alloys.

Fabrication & Heat Treatment

Critical Sensitivity: Prolonged exposure in the 550-1050°C range can cause precipitation of intermetallic phases, drastically reducing ductility and corrosion resistance. Must be rapidly cooled after annealing and welding.

Fabrication requires strict thermal control. Post-weld heat treatment is often necessary to restore optimal properties.

Form Availability

Plate, Sheet, Bar, Pipe, Tube, Fittings

Available for specialized chemical plant construction.

Typical Applications

• Hydrochloric Acid (HCl) Production, Pickling, and Handling Systems.
• Sulfuric Acid (H₂SO₄) Recovery and Concentration Plants.
• Acetic Acid and Anhydride Reaction Vessels.
• Non-Oxidizing Organic Acid Processes (e.g., formic acid).
• Chemical Catalysts and Intermediates Production.

Used almost exclusively in highly controlled, strictly reducing chemical processes.