Stellite 20
Introduction to Stellite 20
Stellite 20 is a cobalt-based, high-alloy material engineered for severe service conditions involving elevated temperatures, corrosive environments, and mechanical wear. Distinguished by its enhanced chromium and tungsten content, along with added nickel and molybdenum, Stellite 20 offers superior corrosion resistance, especially in oxidizing and sulfidizing atmospheres. It is also known for maintaining structural stability and hardness up to 1000°C.
Stellite 20 is typically cast or applied via hard facing and then finished through precision CNC machining. It is widely used in industrial valves, hot gas seals, pump components, and furnace parts operating in chemically aggressive or thermally unstable environments. The combination of high wear resistance, excellent corrosion tolerance, and elevated temperature strength makes it a top choice for energy, aerospace, and chemical processing sectors.
Chemical, Physical, and Mechanical Properties of Stellite 20
Stellite 20 (UNS R30605 / AMS 5382) is a corrosion-resistant cobalt alloy offering high-performance wear characteristics across a broad thermal range. Its chemical balance delivers both solid solution strengthening and carbide dispersion for durability under load and attack.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Cobalt (Co) | Balance (≥50.0) | Base element for corrosion and thermal stability |
Chromium (Cr) | 30.0–33.0 | Oxidation resistance and passive layer formation |
Tungsten (W) | 4.0–6.0 | Forms hard carbides for wear resistance |
Nickel (Ni) | 2.0–5.0 | Enhances corrosion resistance and ductility |
Molybdenum (Mo) | 2.0–4.0 | Improves resistance to pitting and crevice corrosion |
Carbon (C) | 1.0–1.4 | Contributes to hardness via carbide network |
Iron (Fe) | ≤3.0 | Residual element |
Silicon (Si) | ≤1.2 | Enhances casting fluidity |
Manganese (Mn) | ≤1.0 | Stabilizes austenitic structure |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.50 g/cm³ | ASTM B311 |
Melting Range | 1300–1380°C | ASTM E1268 |
Thermal Conductivity | 12.8 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 0.90 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 13.1 µm/m·°C (20–400°C) | ASTM E228 |
Specific Heat Capacity | 430 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 215 GPa at 20°C | ASTM E111 |
Mechanical Properties (As-Cast or HIP + Heat Treated)
Property | Value (Typical) | Test Standard |
|---|---|---|
Hardness | 42–50 HRC (as-cast) / up to 53 HRC (HIP-treated) | ASTM E18 |
Tensile Strength | 950–1100 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 450–600 MPa | ASTM E8/E8M |
Elongation | 2.0–3.5% | ASTM E8/E8M |
Oxidation Resistance | Stable up to 1000°C | ASTM G111 |
Sulfidation Resistance | Excellent | NACE TM0177 |
Key Characteristics of Stellite 20
Exceptional Oxidation and Sulfidation Resistance: Chromium, nickel, and molybdenum enable Stellite 20 to retain corrosion integrity in aggressive chemical atmospheres, particularly sulfur-rich or chlorine-laden environments.
Thermal Strength and Stability: Maintains wear resistance and mechanical integrity up to 1000°C, making it suitable for furnace and turbine-related applications.
High Hardness with Ductility: Offers superior abrasion resistance with moderate toughness, reducing cracking risk under cyclic thermal loads or impact.
Corrosion Resistance in Acids and Chlorides: Effective in resisting hydrochloric acid, sulfur dioxide, and seawater exposure, ensuring longevity in chemical and marine applications.
CNC Machining Challenges and Solutions for Stellite 20
Machining Challenges
Abrasive Carbide Structures
Tungsten-carbide formations are highly abrasive, rapidly degrading, uncoated, or low-grade tools.
Work Hardening
As with most cobalt-based alloys, Stellite 20 exhibits strain hardening, increasing the surface hardness during machining and causing chatter or tool deflection.
Heat Accumulation
The alloy’s low thermal conductivity results in tool overheating, leading to coating delamination or microcracking at the cutting edge.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Fine-grain carbide (K30–K40) or PCD/CBN inserts | Resists wear from carbides and maintains edge stability |
Coating | TiAlN or AlCrN, PVD-applied (3–5 µm) | Minimizes thermal diffusion and friction |
Geometry | Negative rake with 0.05 mm edge honing | Balances tool strength and reduces notching |
Cutting Parameters (ISO 3685 Compliance)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 10–16 | 0.20–0.25 | 1.5–2.5 | 100–120 |
Finishing | 18–24 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Stellite 20 Parts
Hot Isostatic Pressing (HIP)
HIP improves mechanical properties by removing internal voids, enhancing fatigue strength and hardness uniformity.
Heat Treatment
Heat Treatment optimizes microstructure and improves resistance to thermal cracking and dimensional drift post-machining.
Superalloy Welding
Superalloy Welding using Stellite 20-compatible filler metals preserves wear and corrosion performance in assemblies.
Thermal Barrier Coating (TBC)
TBC Coating protects exposed surfaces in hot gas or combustion environments, extending part life at >950°C.
Electrical Discharge Machining (EDM)
EDM is ideal for precise geometry and surface integrity control in hard-wear structures.
Deep Hole Drilling
Deep Hole Drilling allows accurate guide bores and nozzle orifices machining with length-to-diameter ratios >20:1.
Material Testing and Analysis
Material Testing includes G65 wear testing, corrosion analysis, hardness validation, and ultrasonic defect inspection.
Industry Applications of Stellite 20 Components
Chemical Process Equipment
Valve trims, pump sleeves, and agitator shafts are resistant to acidic and oxidizing chemicals.
High-Temperature Industrial Furnaces
Burner nozzles, shields, and guide tubes require stability in high-thermal cycling environments.
Marine and Offshore
Components exposed to seawater, chloride-rich vapors, or corrosive brines in energy or desalinization systems.
Oil & Gas
Downhole tools, blowout preventer inserts, and drilling hardware subjected to sand erosion and sour gas.
FAQs
What are the best cutting tools and parameters for CNC machining Stellite 20?
How does Stellite 20 compare to Stellite 12 and 6B in corrosion resistance and hardness?
Can Stellite 20 be EDM machined for complex geometries or thin-walled parts?
What post-machining heat treatments are recommended for dimensional stability and hardness enhancement?
What certifications and tests are performed to ensure quality and performance of CNC-machined Stellite 20 components?
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