Hastelloy C-22
Introduction to Hastelloy C-22
Hastelloy C-22 is a highly versatile corrosion-resistant alloy composed primarily of nickel, chromium, molybdenum, and tungsten. It offers superior protection against both oxidizing and reducing environments, including wet chlorine gas, ferric and cupric chlorides, nitric acid, and seawater. Its broad-spectrum corrosion resistance makes it the material of choice for critical components in chemical processing, waste treatment, and marine applications.
This alloy is particularly valuable in CNC machining for parts that must maintain high dimensional stability, mechanical integrity, and resistance to pitting, crevice attack, and stress corrosion cracking—especially in highly aggressive or mixed-media chemical environments.
Chemical, Physical, and Mechanical Properties of Hastelloy C-22
Hastelloy C-22 (UNS N06022 / ASTM B575 / B564 / B619 / B622 / B626) is a wrought nickel-base alloy known for its corrosion resistance and metallurgical stability. It offers improved performance over Hastelloy C-276 and C-4, especially in oxidizing environments.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Nickel (Ni) | Balance (≥56.0) | Provides base corrosion resistance across various chemistries |
Chromium (Cr) | 20.0–22.5 | Key to resisting oxidizing agents such as nitric acid |
Molybdenum (Mo) | 12.5–14.5 | Enhances resistance to pitting and crevice corrosion |
Iron (Fe) | 2.0–6.0 | Increases mechanical strength |
Tungsten (W) | 2.5–3.5 | Contributes to localized corrosion resistance |
Cobalt (Co) | ≤2.5 | Controlled for consistency |
Carbon (C) | ≤0.015 | Minimizes carbide precipitation during welding |
Manganese (Mn) | ≤0.5 | Aids hot forming |
Silicon (Si) | ≤0.08 | Low content for intergranular corrosion resistance |
Sulfur (S) | ≤0.02 | Controlled to prevent cracking during CNC and welding |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.69 g/cm³ | ASTM B311 |
Melting Range | 1350–1400°C | ASTM E1268 |
Thermal Conductivity | 9.7 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.20 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 12.3 µm/m·°C (20–300°C) | ASTM E228 |
Specific Heat Capacity | 390 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 | 690–760 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 275–345 MPa | ASTM E8/E8M |
Elongation | ≥45% (25mm gauge) | ASTM E8/E8M |
Hardness | 180–220 HB | ASTM E10 |
Impact Toughness | Excellent at sub-zero and ambient temperatures | ASTM E23 |
Key Characteristics of Hastelloy C-22
Broad-Spectrum Corrosion Resistance: Withstands mixed acid systems and oxidizing-reducing conditions, outperforming C-276 in environments like 70% nitric acid with chloride ions.
Resistance to Localized Attack: Pitting resistance equivalent number (PREN) >50; corrosion rates <0.02 mm/year in ferric chloride and >6% hydrochloric acid.
Thermal Stability: Resistant to sensitization and grain boundary precipitation from prolonged thermal exposure between 600–1040°C.
Precision Machining: Ideal for CNC applications requiring tolerances of ±0.01 mm and surface finishes <Ra 0.8 µm.
CNC Machining Challenges and Solutions for Hastelloy C-22
Machining Challenges
Work Hardening
High strain-hardening rate (n ≈ 0.35) necessitates deep, consistent cuts to avoid excessive surface hardness and chatter.
Low Thermal Conductivity
Results in high heat accumulation at the cutting zone (up to 600–800°C), shortening tool life under dry or flood-only coolant conditions.
Chip Control
Chips are tough and stringy, increasing the risk of tool entanglement and poor surface finish without chip breakers.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | PVD-coated carbide (K20–K30) or ceramic inserts | Maintain edge hardness at >700°C cutting temp |
Coating | AlTiN or AlCrN (3–5 µm) | Reduces thermal wear and friction |
Geometry | Positive rake (10–12°), edge honed to 0.02–0.05 mm | Balances sharpness and chip control |
Cutting Parameters (ISO 3685)
Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 10–18 | 0.20–0.30 | 2.0–3.0 | 100–120 |
Finishing | 20–35 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Hastelloy C-22 Parts
Hot Isostatic Pressing (HIP)
HIP at 100–200 MPa and 1150°C enhances fatigue strength by up to 30% and reduces microvoids in cast or additively manufactured parts.
Heat Treatment
Heat Treatment at 1120°C ±10°C followed by rapid cooling prevents intermetallic phase formation and ensures long-term corrosion resistance in HCl + HNO₃ media.
Superalloy Welding
Superalloy Welding uses GTAW with ERNiCrMo-10 filler and heat input <1.5 kJ/mm, ensuring post-weld corrosion rates remain <0.02 mm/year.
Thermal Barrier Coating (TBC)
TBC Coating up to 250 µm thick protects CNC components from acidic vapor and cyclic heat loads above 800°C.
Electrical Discharge Machining (EDM)
EDM provides tolerances down to ±0.005 mm and Ra <0.6 µm in complex internal geometries.
Deep Hole Drilling
Deep Hole Drilling enables L/D ratios of 30:1 in reactor tube sheets and scrubber components using internal coolant delivery.
Material Testing and Analysis
Material Testing includes ASTM G28 corrosion tests, intergranular attack (ASTM A262 Prac. C), tensile (ASTM E8), and hardness validation (ASTM E18).
Industry Applications of Hastelloy C-22 Components
Chemical Process Industry
Pumps, valves, and fittings exposed to chlorinated solvents, nitric-hydrofluoric acid blends, and mixed acid gas streams.
Waste Treatment and Pollution Control
Components in thermal oxidizers, incineration scrubbers, and hazardous waste reactors are exposed to both oxidizing and reducing species.
Marine and Offshore
Acid-resistant components in desalination plants, marine scrubbers, and chemical cargo handling systems.
Pharmaceutical and Food Equipment
Ultra-clean and non-contaminating flow control parts are used in aggressive sterilization and chemical clean-in-place (CIP) cycles.
FAQs
What is the typical lead time for CNC-machined Hastelloy C-22 components?
How does Hastelloy C-22 perform in multi-phase chemical environments?
What tolerances and surface finishes can be achieved for Hastelloy C-22 CNC parts?
Are there special design considerations for welding or joining Hastelloy C-22 parts?
What documentation and quality assurance is provided with Hastelloy C-22 parts?
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