Stellite F
Introduction to Stellite F
Stellite F is a cast cobalt-based alloy specifically designed for high-strength, high-temperature applications requiring galling resistance, thermal fatigue stability, and corrosion performance. It is commonly used for high-speed components like valve rotors, seals, and steam turbine parts where exposure to thermal cycling, frictional wear, and aggressive process media is continuous and severe.
Stellite F exhibits excellent workability and mechanical uniformity as a cast-wrought hybrid material, making it ideal for post-processing using advanced CNC machining. It retains hardness up to 1000°C and performs exceptionally well under metal-to-metal sliding contact, particularly in rotating or sealing applications.
Chemical, Physical, and Mechanical Properties of Stellite F
Stellite F (UNS R30665) is characterized by a moderate carbon content with a well-balanced chromium and tungsten matrix, offering high resistance to galling, oxidation, and impact under heat.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Cobalt (Co) | Balance (≥50.0) | Matrix for high-temperature strength and corrosion resistance |
Chromium (Cr) | 25.0–28.0 | Enhances oxidation resistance and forms protective surface scales |
Tungsten (W) | 4.5–6.5 | Forms hard carbide phases for wear protection |
Carbon (C) | 0.9–1.2 | Controls carbide volume for strength and hardness |
Iron (Fe) | ≤3.0 | Residual element |
Nickel (Ni) | ≤2.5 | Improves ductility and casting properties |
Silicon (Si) | ≤1.2 | Aids in oxidation resistance and casting flow |
Manganese (Mn) | ≤1.0 | Improves hot ductility and microstructure integrity |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.7 g/cm³ | ASTM B311 |
Melting Range | 1300–1385°C | ASTM E1268 |
Thermal Conductivity | 13.0 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 0.96 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 12.8 µm/m·°C (20–400°C) | ASTM E228 |
Specific Heat Capacity | 420 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 210 GPa at 20°C | ASTM E111 |
Mechanical Properties (As-Cast or HIP-Treated)
Property | Value (Typical) | Test Standard |
|---|---|---|
Hardness | 40–47 HRC (as-cast) / up to 50 HRC (HIP) | ASTM E18 |
Tensile Strength | 980–1100 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 520–640 MPa | ASTM E8/E8M |
Elongation | 3.0–4.0% | ASTM E8/E8M |
Galling Resistance | Excellent | ASTM G98 |
Operating Temperature | Up to 1000°C | N/A |
Key Characteristics of Stellite F
High Galling and Wear Resistance: Designed for sliding contact under pressure, Stellite F resists adhesion and material transfer in dry and lubricated conditions.
Thermal Fatigue Strength: Performs well under repeated heating and cooling cycles with minimal dimensional drift or surface damage.
Corrosion and Oxidation Resistance: Effective in resisting acidic and oxidizing process environments, including high-pressure steam and combustion gases.
Impact and Cavitation Resistance: Withstands cyclic stress and cavitation forces in high-speed rotating systems such as pumps and turbines.
CNC Machining Challenges and Solutions for Stellite F
Machining Challenges
Galling During Tool Engagement
Due to its adhesive resistance properties, cutting tools can experience rubbing instead of shearing, leading to chatter or built-up edge formation.
Low Thermal Conductivity
Heat generated during cutting accumulates at the tool tip, increasing the risk of microcracks or thermal degradation of carbide inserts.
Abrasive Carbide Network
Moderate carbide content wears tooling aggressively, particularly during roughing or interrupted cuts.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | K30-grade carbide or CBN inserts | Offers balance between hardness and fracture toughness |
Coating | AlCrN or TiSiN (PVD 3–5 µm) | Provides thermal protection and reduces friction |
Geometry | Neutral rake with 0.05 mm edge hone | Supports cutting integrity and mitigates edge chipping |
Cutting Parameters (ISO 3685 Compliant)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 10–14 | 0.20–0.30 | 1.5–2.0 | 100–120 |
Finishing | 18–22 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Stellite F Parts
Hot Isostatic Pressing (HIP)
HIP enhances fatigue and creep resistance while eliminating internal porosity in as-cast parts.
Heat Treatment
Heat Treatment stabilizes the carbide structure, relieves stress, and improves hardness uniformity across machined zones.
Superalloy Welding
Superalloy Welding using filler materials with matching chemistry ensures joint integrity in high-wear or corrosive systems.
Thermal Barrier Coating (TBC)
TBC Coating provides added insulation for surfaces operating in hot gas flows above 950°C.
Electrical Discharge Machining (EDM)
EDM is ideal for achieving ±0.01 mm tolerance in valve features, orifices, and complex contours.
Deep Hole Drilling
Deep Hole Drilling enables manufacturing of deep-seated bores or cooling channels without compromising structural stability.
Material Testing and Analysis
Material Testing includes hardness testing, microstructure validation, galling resistance trials, and non-destructive testing (UT, PT).
Industry Applications of Stellite F Components
Turbine and Steam Plant Hardware
Valve rotors, deflector rings, and seat faces operating in extreme temperatures and rotational speeds.
High-Pressure Sealing Components
Sliding seals, pump sleeves, and rotary joints in chemical, power generation, and aerospace sectors.
Marine & Desalination Equipment
Pump housings, shaft sleeves, and wear plates exposed to brine, cavitation, and thermal fluctuation.
Oil & Gas
Valve internals, guide rings, and cutting tools subject to sand erosion, chemical attack, and pressure cycling.
FAQs
What are the best tooling materials and parameters for CNC machining Stellite F components?
How does Stellite F compare to Stellite 6 and Stellite 21 in thermal fatigue and galling resistance?
Is EDM suitable for finishing Stellite F parts with tight tolerances?
What heat treatment processes are recommended for machined Stellite F parts used in thermal environments?
What industrial certifications and material testing standards does Neway use for Stellite F components?
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