Stellite 1
Introduction to Stellite 1
Stellite 1 is a cobalt-chromium-tungsten alloy known for its outstanding wear resistance, high hardness, and excellent corrosion and oxidation resistance at elevated temperatures. It is part of the Stellite alloy family and is designed for severe service environments with critical mechanical wear and thermal stability. Stellite 1 stands out due to its superior resistance to metal-to-metal contact, galling, erosion, and thermal fatigue. It is highly suitable for hard-facing and CNC-machined components exposed to extreme wear.
This alloy is widely used in industries requiring high-performance surfaces, including aerospace, oil & gas, power generation, and valve manufacturing. CNC-machined parts made from Stellite 1 typically include valve seats, pump plungers, cutting tools, and bearings for corrosive and abrasive environments.
Chemical, Physical, and Mechanical Properties of Stellite 1
Stellite 1 (UNS R30001 / AMS 5385 / ASTM F75 base family) is a cast or wrought cobalt alloy with exceptional wear resistance and mechanical strength, even at temperatures exceeding 800°C.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Cobalt (Co) | Balance (≥55.0) | Matrix element providing high-temperature strength |
Chromium (Cr) | 28.0–32.0 | Improves corrosion and oxidation resistance |
Tungsten (W) | 11.0–14.0 | Enhances hot hardness and wear resistance |
Carbon (C) | 2.4–3.0 | Forms carbides for extreme abrasion resistance |
Nickel (Ni) | ≤3.0 | Enhances toughness |
Iron (Fe) | ≤3.0 | Impurity control |
Silicon (Si) | ≤1.2 | Improves castability |
Manganese (Mn) | ≤1.0 | Stabilizes the structure during solidification |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.70 g/cm³ | ASTM B311 |
Melting Range | 1260–1350°C | ASTM E1268 |
Thermal Conductivity | 13.0 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 0.94 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 | 47–53 HRC (as-cast) / up to 55 HRC (HIP treated) | ASTM E18 |
Tensile Strength | 1000–1200 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 580–720 MPa | ASTM E8/E8M |
Elongation | 1–3% (low ductility typical) | ASTM E8/E8M |
Wear Resistance Index | >2.5× 316 stainless steel | ASTM G65 |
Key Characteristics of Stellite 1
Outstanding Wear and Galling Resistance: Excellent in metal-to-metal contact, erosion, and abrasive wear environments—ideal for components like valve trim and pump bushings.
High Hardness: Retains ≥47 HRC even at elevated temperatures (up to 800°C), maintaining dimensional stability under thermal cycling.
Oxidation and Corrosion Resistance: Excellent performance in acidic and chloride-rich media; withstands oxidation up to 1100°C in air.
Thermal Shock Tolerance: Suitable for applications with repeated heating and cooling cycles, such as steam valves and high-speed cutting tools.
CNC Machining Challenges and Solutions for Stellite 1
Machining Challenges
High Hardness and Carbide Content
Abrasive carbides (e.g., Cr₇C₃, W₆C) in the matrix reduce tool life and cause rapid flank wear.
Low Ductility
It tends to chip or crack during machining if cutting forces are not carefully controlled.
Built-Up Edge (BUE)
The tendency for material to adhere to cutting tools under insufficient lubrication or incorrect tool geometry.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | CBN or PVD-coated carbide (K30–K40) inserts | Withstands abrasion from carbides |
Coating | TiAlN or AlCrN (3–5 µm) | Reduces heat buildup and wear |
Geometry | Neutral to slightly negative rake (-5° to 5°), honed edge (0.02–0.05 mm) | Prevents chipping and tool fracture |
Cutting Parameters (ISO 3685)
Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 10–15 | 0.15–0.25 | 1.5–2.5 | 80–100 |
Finishing | 20–25 | 0.05–0.10 | 0.5–1.0 | 100–120 |
Surface Treatment for Machined Stellite 1 Parts
Hot Isostatic Pressing (HIP)
HIP at 1150°C and 100–200 MPa improves the density and wear life of cast or additively manufactured Stellite 1 parts.
Heat Treatment
Heat Treatment optimizes carbide distribution for uniform hardness and wear resistance.
Superalloy Welding
Superalloy Welding using low-heat input GTAW techniques allows for Stellite overlays and joining without cracking or loss of hardness.
Thermal Barrier Coating (TBC)
TBC Coating increases service life in parts exposed to thermal fatigue in turbines, valves, and cutting tools.
Electrical Discharge Machining (EDM)
EDM is essential for tight tolerances in hardened parts, offering precision up to ±0.005 mm and Ra <0.5 µm.
Deep Hole Drilling
Deep Hole Drilling ensures straight bore alignment and smooth walls in wear-critical parts like sleeves and orifices.
Material Testing and Analysis
Material Testing includes metallographic carbide analysis, ASTM E18 hardness testing, and wear performance validation.
Industry Applications of Stellite 1 Components
Valve and Flow Control
Seats, stems, and cages for steam, petrochemical, and nuclear valves subject to high wear and erosion.
Oil and Gas
Drill bit components, flow restrictors, and erosion-resistant nozzles exposed to slurry and sand-laden media.
Aerospace
Turbine shrouds, vanes, and wear pads for jet engines operating at 800–1000°C with high-speed airflow erosion.
Industrial Cutting Tools
Hardfacing overlays and cutting inserts where thermal fatigue and metal-to-metal contact degrade softer alloys.
FAQs
What tolerances and finishes can be achieved in CNC machining of Stellite 1?
What are the best strategies to extend tool life when machining Stellite 1?
Is post-machining heat treatment necessary for achieving optimal hardness in Stellite 1 parts?
Can Stellite 1 be used in high-pressure steam valve components with thermal cycling?
What documentation and inspection reports are available for precision machined Stellite 1 components?
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