Stellite 3
Introduction to Stellite 3
Stellite 3 is a cobalt-based alloy engineered for applications demanding extreme wear resistance, hardness, and corrosion stability, especially at elevated temperatures. It contains higher carbon and tungsten than Stellite 1, giving it a more abrasion-resistant carbide-rich structure. Stellite 3 offers outstanding protection against galling, sliding wear, and erosion—especially under high pressure and thermal load.
Due to its brittleness and hardness, Stellite 3 is typically used for CNC-machined components where dimensional precision, thermal stability, and long service life under severe mechanical contact are critical. Common applications include hard valve trim, orifice plates, cutting blades, and dies exposed to intense abrasion or impact.
Chemical, Physical, and Mechanical Properties of Stellite 3
Stellite 3 (UNS R30003 / AMS 5382 / ISO 5832-4 family) is one of the hardest cobalt alloys commercially available and is typically produced via casting, powder metallurgy, or hard-facing processes followed by CNC machining.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Cobalt (Co) | Balance (≥50.0) | Base matrix providing hot hardness and oxidation resistance |
Chromium (Cr) | 27.0–32.0 | Improves corrosion resistance, especially in oxidizing environments |
Tungsten (W) | 13.0–16.0 | Boosts abrasion resistance via hard tungsten carbides |
Carbon (C) | 2.4–3.3 | Increases carbide volume for wear protection |
Nickel (Ni) | ≤3.0 | Toughens matrix phase |
Iron (Fe) | ≤3.0 | Residual element |
Silicon (Si) | ≤1.2 | Enhances castability and surface finish |
Manganese (Mn) | ≤1.0 | Microstructural stability during solidification |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.75 g/cm³ | ASTM B311 |
Melting Range | 1265–1355°C | ASTM E1268 |
Thermal Conductivity | 11.0 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 0.98 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 12.5 µm/m·°C (20–400°C) | ASTM E228 |
Specific Heat Capacity | 410 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 210 GPa at 20°C | ASTM E111 |
Mechanical Properties (As-Cast or HIP + Heat Treated)
Property | Value (Typical) | Test Standard |
|---|---|---|
Hardness | 50–55 HRC (as-cast) / up to 58 HRC (HIP treated) | ASTM E18 |
Tensile Strength | 1100–1250 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 600–750 MPa | ASTM E8/E8M |
Elongation | 0.5–1.5% (very low) | ASTM E8/E8M |
Wear Resistance Index | >3× that of 316 stainless steel | ASTM G65 |
Key Characteristics of Stellite 3
Extreme Abrasion Resistance: High volume of hard carbides makes it ideal for applications involving heavy particulate or metal-to-metal wear.
Exceptional Hot Hardness: Retains >50 HRC at temperatures up to 800°C, providing long-term wear protection in thermal cycling conditions.
Corrosion and Erosion Stability: Performs well in acidic, chloride-laden, and oxidizing environments—ideal for flow control and chemical process equipment.
Low Ductility: Excellent for fixed-position components, not recommended for dynamic bending or high-impact cyclic loading.
CNC Machining Challenges and Solutions for Stellite 3
Machining Challenges
Carbide-Induced Tool Wear
The high carbide content causes abrasive wear on tool flanks and edges, even at low cutting speeds.
Brittleness
The material has limited ductility, so improper feeds or interrupted cuts can induce cracking or chipping.
Thermal Damage Risk
Low thermal conductivity concentrates heat at the cutting zone, degrading tool coatings and dimensional accuracy.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | CBN or ceramic; PVD-coated carbide for finishing | Handles extreme hardness and abrasion |
Coating | AlTiN or TiSiN (3–5 µm) | Reduces thermal stress and flank wear |
Geometry | Neutral or slightly negative rake (0° to -5°), honed edge 0.03–0.05 mm | Increases tool stability and avoids microchipping |
Cutting Parameters (ISO 3685)
Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 8–12 | 0.15–0.25 | 1.5–2.5 | 80–100 |
Finishing | 15–22 | 0.05–0.10 | 0.3–1.0 | 100–120 |
Surface Treatment for Machined Stellite 3 Parts
Hot Isostatic Pressing (HIP)
HIP at 1150°C and 150 MPa enhances microstructure uniformity and improves wear resistance in cast or additive parts.
Heat Treatment
Heat Treatment post-machining can relieve residual stress and enhance carbide distribution for long-term hardness retention.
Superalloy Welding
Superalloy Welding using TIG with preheated substrate and low dilution ensures crack-free joints and consistent wear zones.
Thermal Barrier Coating (TBC)
TBC Coating improves heat resistance for components facing 850–1050°C thermal loads with abrasion risk.
Electrical Discharge Machining (EDM)
EDM is essential for complex profiles or hardened parts requiring ±0.005 mm tolerances and Ra <0.6 µm.
Deep Hole Drilling
Deep Hole Drilling supports long, straight features in Stellite bushings and wear sleeves, especially for abrasive fluids.
Material Testing and Analysis
Material Testing includes microhardness mapping, ASTM G65 wear evaluation, and cross-sectional metallography.
Industry Applications of Stellite 3 Components
Valve Trim and Seats
Excellent wear and galling resistance for steam valves, throttle plates, and high-pressure sealing components.
Mining and Slurry Systems
Pump liners, impellers, and orifices where abrasive minerals degrade conventional alloys.
Aerospace and Turbine
Burner tips, shrouds, and nozzle inserts are exposed to erosion and high thermal gradients.
Cutting and Forming Tools
Knives, shears, and dies are hard-to-cut materials where edge retention and heat resistance are essential.
FAQs
What are the optimal CNC cutting speeds and tooling for Stellite 3?
How does Stellite 3 compare to Stellite 1 regarding wear resistance and brittleness?
Can Stellite 3 be used for dynamic load-bearing applications?
What heat treatment is recommended after CNC machining Stellite 3?
What are the standard QA procedures for CNC-machined Stellite 3 components?
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