Material Family

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

The modern, advanced successor to B-2, with optimized chemistry for stability.

Common Forms (Bar)

Hot Rolled, Forged, or Cold Finished Rounds, Hexagons, Squares. Also as Forging Billet.

Typically supplied as round bar for machining critical components.

Chemical Composition (Typical wt.%)

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

High Mo for reducing acid resistance. Controlled, low levels of Cr & Fe and additions of Al/Ti dramatically improve thermal stability over B-2.

Mechanical Properties (Annealed, Room Temp)

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

• 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. The primary difference is not corrosion, but fabricability.

Primary Advancement: Thermal Stability

Dramatically improved resistance to embrittlement caused by precipitation of intermetallic phases 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 single most important reason to choose B-3 over B-2. It enables safer, more reliable fabrication and longer service life.

Key Standards (Bar)

ASTM B335 / ASME SB-335 (Standard Specification for Nickel-Molybdenum Alloy Rod - Grade UNS N10675)

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

Machinability & Fabrication

Machinability Rating: Similar to B-2 (~40%). It is somewhat easier to machine than many nickel alloys. Requires standard practices for nickel alloys: sharp tools, positive rakes, adequate coolant.
Weldability: Significantly better 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.

The improved weldability allows for the fabrication of more complex welded assemblies from bar stock.

Typical Bar Applications

• HCl & Reducing Acid Systems: Pump shafts, valve stems, agitators, fasteners for high-temperature service.
• Chemical Processing: Machined components for acetic anhydride, alkylation, and other oxygen-free processes.
• Parts requiring welding or complex machining in reducing acid service, where B-2 would be risky.

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