Hastelloy B-2
Introduction to Hastelloy B-2
Hastelloy B-2 is a wrought, nickel-molybdenum alloy engineered to resist strong reducing agents, particularly hydrochloric acid. As an improved version of Hastelloy B, it offers greater thermal stability, better weldability, and reduced susceptibility to stress corrosion cracking and knife-line attack in heat-affected zones.
The alloy’s optimized composition, with minimized iron and carbon content, ensures superior corrosion resistance in chemical processing environments. Hastelloy B-2 is frequently CNC machined into components such as heat exchanger parts, pump housings, and acid handling equipment where structural integrity and chemical compatibility are essential.
Chemical, Physical, and Mechanical Properties of Hastelloy B-2
Hastelloy B-2 (UNS N10665 / ASTM B333 / B335) is a solid-solution strengthened nickel-molybdenum alloy with refined impurity control. It maintains structural stability across a wide temperature range and is typically used in the annealed condition for optimal performance.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Nickel (Ni) | Balance (≥65.0) | Base element; ensures corrosion resistance in reducing media |
Molybdenum (Mo) | 26.0–30.0 | Improves pitting and crevice corrosion resistance |
Iron (Fe) | ≤2.0 | Controlled to enhance corrosion resistance and stability |
Carbon (C) | ≤0.01 | Prevents carbide precipitation in heat-affected zones |
Manganese (Mn) | ≤1.0 | Improves hot workability |
Silicon (Si) | ≤0.1 | Reduced to mitigate intergranular corrosion |
Cobalt (Co) | ≤1.0 | Limited as an impurity |
Chromium (Cr) | ≤1.0 | Kept low to avoid compromising performance in reducing environments |
Sulfur (S) | ≤0.02 | Minimized to prevent hot cracking during processing |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 9.22 g/cm³ | ASTM B311 |
Melting Range | 1330–1380°C | ASTM E1268 |
Thermal Conductivity | 10.5 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.25 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 12.2 µm/m·°C (20–300°C) | ASTM E228 |
Specific Heat Capacity | 395 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 200 GPa at 20°C | ASTM E111 |
Mechanical Properties (Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 690–760 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 275–345 MPa | ASTM E8/E8M |
Elongation | ≥40% (25mm gauge) | ASTM E8/E8M |
Hardness | 180–220 HB | ASTM E10 |
Impact Toughness | Excellent at cryogenic and ambient conditions | ASTM E23 |
Key Characteristics of Hastelloy B-2
Superior Acid Resistance: Offers corrosion rates <0.01 mm/year in boiling 20% hydrochloric acid, outperforming many high-nickel alloys in reducing environments.
Weldability Improvements: Unlike Hastelloy B, Hastelloy B-2 is less prone to weld-related intergranular attack due to reduced C, Si, and Fe content.
Thermal Stability: Resists phase separation and maintains corrosion resistance after thermal cycling between 425–870°C.
CNC-Friendly Annealed Structure: Consistent grain size and ductility aid in achieving fine finishes and tight tolerances (<±0.01 mm) in machined parts.
CNC Machining Challenges and Solutions for Hastelloy B-2
Machining Challenges
Work Hardening
Surface hardness may increase by 30–40% during cutting if feed rates are too low, leading to excessive tool wear.
Heat Generation
Low thermal conductivity causes cutting zone temperatures to exceed 600°C, necessitating coolant optimization.
Tool Adhesion
High nickel content promotes chip adhesion and built-up edge formation on standard inserts.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | PVD-coated carbide (ISO K20–K30) or ceramic inserts | High wear resistance under thermal loads |
Coating | AlTiN or AlCrN (3–5 µm) | Reduces heat absorption and chip adhesion |
Geometry | Positive rake (10–15°), honed edges (0.02–0.04 mm radius) | Enhances chip flow and surface finish |
Cutting Parameters (ISO 3685)
Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 10–20 | 0.20–0.30 | 2.0–3.0 | 90–120 |
Finishing | 20–35 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Hastelloy B-2 Parts
Hot Isostatic Pressing (HIP)
HIP improves fatigue life and eliminates porosity in critical cast or additive parts.
Heat Treatment
Heat Treatment involves annealing at 1065°C ±10°C followed by rapid quenching to retain corrosion resistance.
Superalloy Welding
Superalloy Welding utilizes GTAW with ERNiMo-7 filler to minimize phase segregation and ensure corrosion resistance in the weld zone.
Thermal Barrier Coating (TBC)
TBC Coating can be applied to extend component life in mixed-phase or acid vapor environments.
Electrical Discharge Machining (EDM)
EDM enables non-contact machining of tight-tolerance geometries in heat exchanger plates or fittings.
Deep Hole Drilling
Deep Hole Drilling supports L/D up to 30:1 for reactor tubing, acid distributor ports, and internal channeling.
Material Testing and Analysis
Material Testing includes corrosion testing (ASTM G28 Method A), metallographic evaluation (ASTM E3), and mechanical validation (ASTM E8, E18).
Industry Applications of Hastelloy B-2 Components
Chemical Processing
Pump bodies, impellers, and acid nozzles for HCl-rich environments.
Maintains <0.05 mm/year corrosion rates even at 90°C in reducing acid flows.
Pharmaceutical Reactors
Mixing shafts, liners, and vessels exposed to high-purity reducing agents.
Prevents contamination and pitting from chlorides and sulfides.
Pickling and Acid Regeneration
Components in HF, HCl, and sulfuric acid recovery lines.
Withstands multi-phase flows and rapid thermal cycling.
Metal Finishing
Heater elements and anodes exposed to strong acid baths.
Maintains mechanical integrity under long-term immersion.
FAQs
What improvements does Hastelloy B-2 offer over Hastelloy B in chemical environments?
What are the best CNC tool materials and coatings for Hastelloy B-2?
Can Hastelloy B-2 be safely welded for use in pressure-rated acid systems?
What surface treatments improve the longevity of Hastelloy B-2 parts?
How is corrosion performance verified in Hastelloy B-2 components for chemical plants?
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