Stellite 4
Introduction to Stellite 4
Stellite 4 is a cobalt-chromium-tungsten alloy developed for applications requiring excellent wear resistance, galling resistance, and corrosion resistance under high loads and moderate thermal conditions. Positioned between Stellite 1 and Stellite 6 regarding hardness and toughness, it balances machinability and durability.
Stellite 4 is widely utilized in CNC-machined parts exposed to metal-to-metal sliding, fretting wear, and moderate-impact environments. Its microstructure consists of a tough cobalt matrix reinforced with hard carbide phases, making it suitable for both as-cast and post-machining service in aerospace, energy, marine, and oil & gas sectors.
Chemical, Physical, and Mechanical Properties of Stellite 4
Stellite 4 (UNS R30004 / AMS 5387 / ISO 5832-4 group) is a medium-carbon cobalt alloy designed to resist wear and corrosion in high-pressure, corrosive, and mildly thermal environments.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Cobalt (Co) | Balance (≥50.0) | Base element for hot hardness and corrosion resistance |
Chromium (Cr) | 28.0–32.0 | Provides oxidation and chemical resistance |
Tungsten (W) | 12.0–15.0 | Enhances wear and abrasion resistance |
Carbon (C) | 1.5–2.0 | Forms carbides to improve hardness |
Nickel (Ni) | ≤3.0 | Increases ductility |
Iron (Fe) | ≤3.0 | Minor residual element |
Silicon (Si) | ≤1.2 | Enhances casting characteristics |
Manganese (Mn) | ≤1.0 | Aids in hot workability |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.75 g/cm³ | ASTM B311 |
Melting Range | 1260–1345°C | ASTM E1268 |
Thermal Conductivity | 12.0 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 0.95 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 12.6 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 | 43–48 HRC (as-cast) / up to 50 HRC (HIP treated) | ASTM E18 |
Tensile Strength | 950–1150 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 550–700 MPa | ASTM E8/E8M |
Elongation | 1.5–3.5% | ASTM E8/E8M |
Wear Resistance Index | >2× 316 stainless steel | ASTM G65 |
Key Characteristics of Stellite 4
Balanced Wear Resistance and Toughness: Offers high wear protection without the brittleness of harder Stellite grades, making it ideal for sliding contact and impact-prone components.
Moderate Hardness with Good Machinability: Easier to machine than Stellite 1 or 3 while maintaining superior surface durability.
Corrosion Resistance: Resistant to acid, saline, and oxidizing environments up to 900°C, making it suitable for valve and pump internals.
Dimensional Stability: Maintains structural integrity and tight tolerances in parts exposed to pressure, friction, and moderate heat.
CNC Machining Challenges and Solutions for Stellite 4
Machining Challenges
Abrasive Wear on Tools
Moderate carbide volume still leads to flank wear on uncoated or improperly selected tools.
Built-Up Edge and Smearing
Insufficient coolant or improper rake angle can cause adhesion, reducing surface finish and tolerance control.
Heat Generation
Poor thermal conductivity concentrates heat at the cutting interface, leading to tool edge degradation.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | PVD-coated carbide (K20–K30), or CBN for finishing | Handles abrasive wear and maintains edge integrity |
Coating | TiAlN or AlCrN (3–5 µm) | Reduces heat and friction |
Geometry | Positive to neutral rake (5° to 0°), honed edge 0.03 mm | Controls cutting force and prevents chipping |
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 | 20–28 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Stellite 4 Parts
Hot Isostatic Pressing (HIP)
HIP at 1150°C and 150 MPa refines microstructure, reducing porosity and improving fatigue and wear resistance.
Heat Treatment
Heat Treatment can be used post-machining to relieve residual stresses and stabilize carbides.
Superalloy Welding
Superalloy Welding allows for crack-free overlaying using TIG or PTA methods with preheat and controlled interpass temperature.
Thermal Barrier Coating (TBC)
TBC Coating protects parts exposed to hot gas erosion in high-speed, high-temperature systems.
Electrical Discharge Machining (EDM)
EDM is recommended for finishing hardened Stellite 4 parts with tolerances ±0.005 mm and Ra <0.6 µm.
Deep Hole Drilling
Deep Hole Drilling is ideal for manufacturing wear-resistant bore features in valve cages and sleeves.
Material Testing and Analysis
Material Testing includes hardness testing, wear simulation (ASTM G65), and metallographic carbide mapping.
Industry Applications of Stellite 4 Components
Valve Seats and Stems
CNC-machined parts for high-pressure valve internals operating in corrosive and erosive service.
Oil and Gas
Orifices, sleeves, and choke valve trim exposed to slurry flow, sand-laden fluids, or gas throttling.
Marine Engineering
Shaft sleeves, pump components, and bushings resistant to biofouling and saltwater erosion.
Energy and Power
Sliding pads and wear rings in steam turbines and thermal cycling systems.
FAQs
What tooling and speeds are optimal for machining Stellite 4?
How does Stellite 4 compare to Stellite 1 or Stellite 6 in wear resistance and toughness?
Is HIP necessary for cast or additively manufactured Stellite 4 components?
Can Stellite 4 be used for steam valves and turbine wear pads under thermal cycling?
What inspection and quality reports are provided with CNC-machined Stellite 4 parts?
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