Hastelloy C-276
Introduction to Hastelloy C-276
Hastelloy C-276 is a corrosion-resistant nickel-molybdenum-chromium alloy engineered for use in the most aggressive chemical environments. It offers excellent resistance to strong oxidizers, reducing agents, and both organic and inorganic acids—especially hydrochloric acid, sulfuric acid, and wet chlorine. The alloy's low carbon content also minimizes the risk of grain boundary precipitation during welding, preserving its corrosion resistance in welded structures.
Hastelloy C-276 is widely used in CNC-machined components that operate under severe conditions, such as flue gas scrubbers, heat exchangers, and pollution control systems. Its unique thermal stability, corrosion resistance, and mechanical strength make it a top-tier material for chemical processing and marine industries.
Chemical, Physical, and Mechanical Properties of Hastelloy C-276
Hastelloy C-276 (UNS N10276 / ASTM B575 / B619 / B622 / B626) is a versatile superalloy that maintains structural and chemical stability in highly corrosive media.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Nickel (Ni) | Balance (≥57.0) | Base metal for corrosion resistance and strength |
Molybdenum (Mo) | 15.0–17.0 | Improves resistance to reducing acids and pitting |
Chromium (Cr) | 14.5–16.5 | Forms passive oxide layers to resist oxidizers |
Iron (Fe) | 4.0–7.0 | Enhances mechanical properties |
Tungsten (W) | 3.0–4.5 | Boosts localized corrosion resistance |
Cobalt (Co) | ≤2.5 | Minor alloying element |
Carbon (C) | ≤0.01 | Prevents carbide precipitation in weld zones |
Manganese (Mn) | ≤1.0 | Improves hot formability |
Silicon (Si) | ≤0.08 | Minimizes intergranular attack |
Sulfur (S) | ≤0.03 | Controlled to reduce cracking during machining |
Vanadium (V) | ≤0.35 | Enhances microstructural stability |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.89 g/cm³ | ASTM B311 |
Melting Range | 1325–1370°C | ASTM E1268 |
Thermal Conductivity | 10.5 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.20 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 11.2 µm/m·°C (20–300°C) | ASTM E228 |
Specific Heat Capacity | 420 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 205 GPa at 20°C | ASTM E111 |
Mechanical Properties (Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 760–825 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 280–355 MPa | ASTM E8/E8M |
Elongation | ≥40% (25mm gauge) | ASTM E8/E8M |
Hardness | 190–230 HB | ASTM E10 |
Impact Toughness | Excellent across sub-zero to elevated temperatures | ASTM E23 |
Key Characteristics of Hastelloy C-276
Exceptional Acid Resistance: Corrosion rates <0.02 mm/year in boiling hydrochloric acid (up to 37%), sulfuric acid, and formic acid mixtures.
Weldability: Low carbon and silicon contents prevent sensitization and intergranular attack during welding or post-weld heat treatment.
Thermal and Oxidation Stability: Withstands continuous service up to 1040°C in oxidizing and sulfur-laden atmospheres.
Precision Machinability: Maintains dimensional tolerances to ±0.01 mm and surface finishes <Ra 0.8 µm with proper tooling and coolant strategies.
CNC Machining Challenges and Solutions for Hastelloy C-276
Machining Challenges
Work Hardening
High molybdenum content promotes strain hardening during shallow cuts or interrupted machining, increasing tool wear.
Thermal Buildup
Heat retention due to low thermal conductivity causes flank wear and edge chipping in uncoated tools.
Material Stickiness
BUE (Built-Up Edge) formation can occur without high-pressure coolant and polished tool surfaces.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Carbide (K20–K30) or ceramic inserts | High-temperature wear resistance |
Coating | AlTiN or AlCrN PVD coating (3–5 µm) | Improves heat resistance and chip flow |
Geometry | Positive rake (8–12°), honed edge radius 0.02–0.05 mm | Minimizes cutting force and work hardening |
Cutting Parameters (ISO 3685)
Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 12–18 | 0.20–0.30 | 2.0–3.5 | 100–120 |
Finishing | 20–30 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Hastelloy C-276 Parts
Hot Isostatic Pressing (HIP)
HIP at 1150°C and 100–200 MPa eliminates shrinkage porosity and improves fatigue resistance by ≥20%.
Heat Treatment
Heat Treatment includes solution annealing at 1120–1175°C followed by rapid quenching to prevent secondary phase formation.
Superalloy Welding
Superalloy Welding with ERNiCrMo-4 filler ensures corrosion-resistant weld zones with low interpass temperatures (<150°C).
Thermal Barrier Coating (TBC)
TBC Coating provides insulation for parts exposed to 900–1050°C and acidic or SO₂-rich environments.
Electrical Discharge Machining (EDM)
EDM supports fine-feature profiling with tolerances of ±0.005 mm and Ra <0.6 µm.
Deep Hole Drilling
Deep Hole Drilling enables high-precision drilling at L/D ratios >30:1 for reactor tubing and chemical processing manifolds.
Material Testing and Analysis
Material Testing includes G28 and A262 corrosion testing, mechanical validation (E8, E18), and metallography.
Industry Applications of Hastelloy C-276 Components
Chemical Processing
Heat exchangers, scrubber systems, and digesters in oxidizing-reducing acid environments.
Flue Gas Desulfurization (FGD)
Ducting, fans, and absorber towers exposed to wet chlorine gas and acidic condensate at elevated temperatures.
Marine Engineering
Valve components, pump housings, and offshore riser tubes resistant to biofouling and seawater corrosion.
Waste Treatment
Pressure vessels and agitators handling nitric, hydrochloric, and sulfuric acid mixtures with organics.
FAQs
What CNC machining tolerances and finishes can be achieved on Hastelloy C-276 parts?
How does Hastelloy C-276 perform in highly acidic or mixed chemical environments?
What is the ideal post-machining heat treatment for optimizing corrosion resistance?
Can Hastelloy C-276 be used for pressure-bound parts in waste treatment or marine systems?
What certifications and test reports are provided with C-276 machined components?
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