Strengthening
Solid Solution
What is Hastelloy B-2? Hastelloy B-2 (UNS N10665) is a nickel-molybdenum alloy with outstanding resistance to hydrochloric acid at all concentrations up to the boiling point. Its Ni-Mo solid-solution matrix — with chromium deliberately kept below 1.0% — provides near-zero corrosion rates in reducing acid environments where stainless steels and even most nickel alloys fail rapidly. This chemistry makes B-2 the benchmark material for HCl distillation columns, acid recovery plants, and chemical process equipment handling pure reducing media. However, its extremely low chromium content means it cannot tolerate oxidizing contaminants; for mixed environments,
Hastelloy C-276 is the correct choice. HT PIPE supplies Hastelloy B-2 in plates, seamless pipes, welded pipes, forged fittings, and round bars with full mill certification and ASTM G28 intergranular corrosion testing.
Nickel (Ni)
65 – Balance
Base element — Ni-Mo matrix
Molybdenum (Mo)
26 – 30%
Primary corrosion driver
Chromium (Cr)
≤ 1.0%
Deliberately excluded
Iron (Fe)
≤ 2.0%
Residual, tightly controlled
Tensile Strength (min)
≥760 MPa
110 ksi
Yield Strength (min)
≥350 MPa
51 ksi
Elongation (min)
≥40%
Highly ductile
Hardness (max)
≤100 HRB
Solution-annealed condition
Density
9.22 g/cm³
0.334 lb/in³
Melting Range
1330–1380°C
2430–2510°F
What is Hastelloy B-2?
Hastelloy B-2 (UNS N10665 / WNr 2.4617) is a solid-solution nickel-molybdenum alloy engineered for one purpose: surviving hydrochloric acid at any concentration and any temperature, right up to the boiling point. The alloy achieves this through a high-molybdenum matrix (26–30% Mo) that forms a protective MoO₂ surface film in reducing environments, while chromium is deliberately restricted to ≤1.0% to prevent the formation of deleterious intermetallic phases that would compromise both corrosion resistance and ductility. In boiling 20% HCl — a condition that dissolves 316L stainless steel in hours — B-2 corrodes at less than 0.1 mm/yr, a rate so low that equipment designed for 20-year service lives easily meets their targets.
The Ni-Mo matrix delivers a tensile strength of ≥760 MPa and elongation ≥40% in the solution-annealed condition, making B-2 both strong and fabricable. However, this alloy has a critical limitation: the β-Ni₄Mo intermetallic phase precipitates rapidly in the 550–800°C range, causing severe embrittlement in heat-affected zones after welding. For this reason, Hastelloy B-3 (UNS N10675) was developed as an improved version with modified Mo content and thermal stability that eliminates β-phase formation in weld HAZs. B-3 is now strongly preferred for welded fabrications, though B-2 remains available and is still specified for applications where full post-weld solution annealing can be reliably performed.
Chemical Composition of Hastelloy B-2 (ASTM B333)
| Element |
Min (%) |
Max (%) |
Role |
| Nickel (Ni) |
Balance |
— |
Base element — austenitic Ni-Mo matrix |
| ⭐ Molybdenum (Mo) |
26.0 |
30.0 |
Primary HCl resistance driver — forms protective MoO₂ film |
| ⭐ Iron (Fe) |
— |
2.0 |
Tightly limited — excess Fe promotes β-phase precipitation |
| ⭐ Chromium (Cr) |
— |
1.0 |
Deliberately excluded — Cr degrades reducing-acid performance |
| ⭐ Silicon (Si) |
— |
0.10 |
Ultra-low to prevent weld decay and intergranular corrosion |
| Carbon (C) |
— |
0.02 |
Ultra-low carbon — minimizes carbide precipitation in HAZ |
| Cobalt (Co) |
— |
1.0 |
Residual impurity — no functional role |
| Manganese (Mn) |
— |
1.0 |
Deoxidizer — improves hot workability |
⭐ Elements that define B-2's HCl performance — note the deliberate absence of Cr. The ultra-low Si and C limits (0.10% and 0.02% respectively) further protect against intergranular corrosion in the weld heat-affected zone, though β-Ni₄Mo embrittlement remains a separate concern addressed by Hastelloy B-3.
Mechanical Properties of Hastelloy B-2 (Solution Annealed)
| Property |
Value |
Unit / Note |
| Ultimate Tensile Strength (UTS) |
≥760 |
MPa (110 ksi) |
| Yield Strength (0.2% offset) |
≥350 |
MPa (51 ksi) |
| Elongation (in 50 mm) |
≥40 |
% — highly ductile |
| Hardness (Rockwell B) |
≤100 |
HRB — solution-annealed |
Elastic Properties
| Property |
Value |
Unit |
| Elastic Modulus (E) |
217 |
GPa |
| Shear Modulus (G) |
84 |
GPa |
| Poisson's Ratio (ν) |
0.30 |
— |
Physical Properties of Hastelloy B-2
| Property |
Value |
Unit |
| Density |
9.22 |
g/cm³ (0.334 lb/in³) |
| Melting Range |
1330 – 1380 |
°C (2430 – 2510°F) |
| Thermal Conductivity (20°C) |
11.1 |
W/m·K |
| Specific Heat (20°C) |
373 |
J/kg·K |
| Electrical Resistivity (20°C) |
1.37 |
µΩ·m |
| Coefficient of Thermal Expansion (20–100°C) |
10.3 |
µm/m·°C |
| Magnetic Permeability |
<1.001 |
Non-magnetic at room temperature |
Heat Treatment of Hastelloy B-2
Step 1
Solution Anneal
1065–1095°C, hold 1 hour per 25 mm of thickness, rapid water quench. This dissolves all secondary phases and restores full ductility.
⚠ Critical: Inadequate quench rate → β-Ni₄Mo embrittlement within seconds at intermediate temperatures.
Step 2
Avoid 550–800°C — The Danger Zone
This is the precipitation range for β-Ni₄Mo and Ni₃Mo intermetallic phases. Even brief exposure (minutes) causes measurable embrittlement and loss of ductility. No intermediate thermal treatments are safe.
Step 3
Stress Relief — 400°C Safe Zone
For moderate stress relief, 400°C for 1–2 hours is safe. This temperature is well below the β-phase precipitation range and will not cause embrittlement. Full solution annealing remains the preferred post-weld treatment.
⚠ B-2 Critical Limitation Never dwell at 550–800°C. The β-Ni₄Mo phase precipitates within minutes in this range, causing severe loss of ductility and toughness. For welded fabrications where rapid post-weld quenching cannot be guaranteed,
Hastelloy B-3 is strongly preferred — it eliminates β-phase formation entirely through modified Mo and Fe chemistry.
Corrosion Resistance of Hastelloy B-2
Hydrochloric Acid (HCl) — Primary Design Environment
Hastelloy B-2's defining capability is resistance to HCl at all concentrations and all temperatures up to the boiling point. In boiling 20% HCl, B-2 corrodes at less than 0.1 mm/yr — a rate virtually negligible for engineering design. This performance stems from the high Mo content forming a stable MoO₂ passive film in the reducing acid environment. At room temperature, even concentrated (37%) commercial-grade HCl produces corrosion rates below 0.05 mm/yr. No stainless steel, and few other nickel alloys, can approach this level of performance in HCl.
Sulfuric Acid (H₂SO₄) — Air-Free Conditions
B-2 shows excellent resistance to sulfuric acid in air-free (reducing) conditions at concentrations up to 60% at the boiling point. In moderate concentrations (10–50%) at temperatures below 80°C, corrosion rates are typically below 0.1 mm/yr. However, the presence of dissolved oxygen or oxidizing contaminants (Fe³⁺, Cu²⁺ ions) dramatically accelerates corrosion, just as in HCl service.
Oxidizing Environments — The Limitation
B-2 performs poorly in oxidizing environments. With Cr ≤1.0%, the alloy lacks the chromium oxide passive film that protects Ni-Cr-Mo alloys like C-276. Even trace oxidizing contaminants (dissolved oxygen, Fe³⁺, Cu²⁺, nitric acid) in reducing media can cause corrosion rates to spike by 10–100×. For environments with any oxidizing component — including most real-world chemical process streams —
Hastelloy C-276 or
C-22 is the correct selection.
Hastelloy Grade Selection Guide
| Grade |
Strength |
HCl Resistance |
Oxidizing Resistance |
Weldability |
Cost |
| B-2 |
★★★ |
★★★★★ |
★ |
★★ |
$$$ |
| B-3 |
★★★ |
★★★★★ |
★ |
★★★★ |
$$$ |
| C-276 |
★★★ |
★★★ |
★★★★★ |
★★★★★ |
$$$$ |
| C-22 |
★★★ |
★★★ |
★★★★★ |
★★★★★ |
$$$$$ |
Key insight: B-2 and B-3 dominate in pure reducing (HCl/H₂SO₄) environments. C-276 and C-22 dominate in mixed oxidizing/reducing environments. If your process stream contains any oxidizing species, choose C-276 or C-22.
Typical Applications of Hastelloy B-2
Chemical Processing
HCl distillation columns, acid recovery and regeneration plants, HCl storage tanks and piping, reactor vessels handling pure reducing media, heat exchangers in acid service.
Pharmaceutical
Organic acid synthesis reactors, catalyst recovery systems, process piping for acid-based drug intermediates where contamination from corrosion products must be avoided.
Petrochemical
Alkylation unit acid regeneration, sulfuric acid alkylation process equipment, HF acid service (where B-2 provides resistance comparable to Monel at lower cost).
Nuclear
Fuel reprocessing equipment handling reducing acid streams, waste treatment systems, and specialized components where ultra-low corrosion rates are mandatory.
Applicable Standards for Hastelloy B-2
| Standard |
Product Form |
| ASTM B333 |
Plate, Sheet, Strip |
| ASTM B335 |
Seamless Pipe & Tube |
| ASTM B366 |
Welded Fittings |
| ASTM B619 / B622 / B626 |
Welded Pipe & Tube (ERW / SAW / EFW) |
| DIN 2.4617 |
European designation (Werkstoffnummer) |
HT PIPE Supply Forms — Hastelloy B-2
Welded Pipes
ASTM B619/B622
Forged Fittings
ASTM B366
Round Bars
ASTM B335 / B573
HT PIPE Project Reference
HT PIPE supplied 3.8 tons of Hastelloy B-2 seamless pipe (ASTM B335, sizes DN50–DN150) to a Southeast Asian HCl regeneration plant in 2022. The specification required ASTM G28 Method A intergranular corrosion testing on every heat, full solution-anneal documentation with quench-rate verification, and EN 10204 3.1 mill test certificates including chemical analysis, mechanical testing, and PMI (Positive Material Identification) confirmation. All 12 heats passed G28 Method A with corrosion rates below 1.1 g/m² per 24-hour cycle. The project completed on schedule with zero rejection rate, and the plant has reported no corrosion incidents after 3+ years of continuous service in boiling 22% HCl.
Hastelloy B-2 Frequently Asked Questions
Q1: What is the difference between Hastelloy B-2 and B-3?
Hastelloy B-3 (UNS N10675) is the improved successor to B-2 with the same HCl resistance but vastly superior thermal stability. B-3's modified Mo content (27–32%) and adjusted Fe/Cr limits eliminate the β-Ni₄Mo intermetallic phase that causes HAZ embrittlement in B-2 welds. In practical terms: B-3 can be welded without mandatory full post-weld solution annealing, while B-2 requires it. B-3 also has a wider safe working temperature range. For any welded fabrication, B-3 is now the recommended choice.
Q2: What acids can Hastelloy B-2 handle that stainless steel cannot?
Hastelloy B-2 handles hydrochloric acid at all concentrations and temperatures up to boiling — a environment where 316L corrodes at 50+ mm/yr. It also handles air-free sulfuric acid up to 60% at boiling, and organic acids (acetic, formic) at concentrations and temperatures that destroy stainless steel. The key limitation: B-2 only works in reducing (oxygen-free) environments. Any dissolved oxygen or oxidizing ions invalidate its corrosion advantage.
Q3: Can Hastelloy B-2 be welded?
Yes, Hastelloy B-2 can be welded using GTAW (TIG) with matching filler metal (ERNiMo-7 / AWS A5.14). However, the weld HAZ passes through the 550–800°C β-phase precipitation range during cooling, causing embrittlement unless a full post-weld solution anneal (1065–1095°C + rapid water quench) is performed. For welded fabrications where full PWHT is impractical,
Hastelloy B-3 is the better choice — it resists β-phase formation in the HAZ without requiring post-weld annealing.
Q4: Is Hastelloy B-2 magnetic?
No. Hastelloy B-2 is non-magnetic with a permeability below 1.001. The high-nickel Ni-Mo matrix is fully austenitic at all temperatures, making B-2 suitable for applications where magnetic interference must be avoided.
Q5: What is the maximum service temperature for Hastelloy B-2 in HCl?
In hydrochloric acid, B-2 resists all concentrations up to the boiling point — which varies by concentration (roughly 108°C for 20% HCl). From a mechanical standpoint, the practical upper limit is approximately 540°C for pressure-bearing components. Above this temperature, creep and oxidation become limiting factors. The β-phase danger zone (550–800°C) must never be entered for sustained service.
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