Material Family

Nickel-Molybdenum Alloy (Thermally Stable, Low Iron, Low Carbon)

A direct, improved successor to B-2, with optimized chemistry for stability.

Common Designations

UNS N10675, Hastelloy B-3, W.Nr. 2.4600

The modern benchmark for severe, hot reducing acid service with improved fabricability. "Hastelloy" and "B-3" are trademarks of Haynes International.

Chemical Composition (Typical wt.%)

Ni: ≥ 65.0 (Balance)
Mo: 27.0 - 32.0
Cr: 1.0 - 3.0
Fe: 1.0 - 3.0
Mn: ≤ 3.0
Co: ≤ 3.0
C: ≤ 0.010
Si: ≤ 0.10
Al: ≤ 0.50
Ti: ≤ 0.20

High Molybdenum (Mo) for reducing acid resistance. Controlled, low levels of Cr & Fe improve thermal stability without compromising resistance to HCl. Addition of Al/Ti aids stability.

Mechanical Properties (Annealed Plate)

Tensile Strength (Rm): 827 - 1034 MPa
Yield Strength (Rp0.2): 414 - 690 MPa
Elongation (A): 40 - 55%

Exhibits higher typical strength than B-2 while maintaining excellent ductility.

Physical Properties

Density: ~9.22 g/cm³
Melting Range: 1370 - 1420 °C

Similar high density to B-2 due to high molybdenum content.

Key Corrosion Resistance Attributes

• Equal or superior resistance to B-2 in pure hydrochloric acid (HCl) across all concentrations and temperatures.• Excellent resistance to sulfuric (H₂SO₄), phosphoric (H₃PO₄), and acetic acids under strictly reducing conditions.

• ⚠️ Same Major Limitation: Poor resistance to oxidizing agents (e.g., Fe³⁺, Cu²⁺ ions, HNO₃, oxygen). Oxidant contamination must be avoided.

Matches B-2's legendary reducing acid performance but with a crucial practical advantage:

Key Advancement: Thermal Stability

Dramatically improved resistance to embrittlement caused by precipitation of intermetallic phases (mu, sigma) when held in or slowly cooled through the 550-1050°C range. This makes it far less sensitive during welding and heat treatment than B-2.

This is the primary reason to choose B-3 over B-2 for new designs. It allows safer fabrication and provides greater long-term microstructural stability in service.

Key Standards (Plate)

ASTM B333 / ASME SB-333 (Grade UNS N10675)

Procured under the same ASTM standard as B-2, but to the N10675 composition.

Fabrication Note

Significantly easier and safer to weld and fabricate than B-2. While controlled procedures are still recommended, the risk of forming brittle phases in the heat-affected zone (HAZ) is greatly reduced.

Post-weld heat treatment is less frequently required, simplifying construction.

Typical Applications

• Hydrochloric Acid (HCl) Synthesis, Pickling, and Handling at High Temperatures.
• Sulfuric Acid (H₂SO₄) Recovery and Concentration Systems.
• Acetic Acid and Chemical Intermediate Production.
• Tubing for High-Temperature, High-Pressure Hydrogen Service.

Used in the same severe reducing processes as B-2, but where fabricability, weld integrity, and long-term thermal stability are critical concerns.