Stellite 6B
Introduction to Stellite 6B
Stellite 6B is a wrought cobalt-based alloy known for its exceptional galling resistance, high wear resistance, and toughness across a wide temperature range. Unlike most Stellite alloys that are cast or hardfaced, Stellite 6B is produced by wrought processing (hot forging and annealing), giving it superior mechanical integrity and machinability without sacrificing corrosion and thermal resistance.
CNC-machined Stellite 6B components are widely used in valve systems, pumps, industrial cutting tools, and aerospace structures. The alloy is ideal for applications involving sliding wear, impact, cavitation, and thermal cycling—making it a staple in energy, chemical, marine, and oilfield industries.
Chemical, Physical, and Mechanical Properties of Stellite 6B
Stellite 6B (UNS R30016 / AMS 5894 / ASTM F90) is a solid-solution strengthened cobalt alloy reinforced by carbides and produced through hot working to ensure improved toughness and uniform properties.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Cobalt (Co) | Balance (≥58.0) | Provides thermal stability and corrosion resistance |
Chromium (Cr) | 28.0–32.0 | Enhances oxidation and chemical resistance |
Tungsten (W) | 3.5–5.5 | Forms wear-resistant carbides |
Carbon (C) | 0.9–1.4 | Forms carbides that improve galling and abrasion resistance |
Nickel (Ni) | ≤3.0 | Contributes to toughness |
Iron (Fe) | ≤3.0 | Minor residual element |
Manganese (Mn) | ≤1.0 | Assists in hot workability |
Silicon (Si) | ≤1.2 | Improves surface finish during hot forming |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.42 g/cm³ | ASTM B311 |
Melting Range | 1320–1395°C | ASTM E1268 |
Thermal Conductivity | 13.0 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 0.95 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 13.2 µm/m·°C (20–400°C) | ASTM E228 |
Specific Heat Capacity | 420 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 205 GPa at 20°C | ASTM E111 |
Mechanical Properties (Wrought Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Hardness | 33–43 HRC (annealed) / up to 45 HRC (aged) | ASTM E18 |
Tensile Strength | 1050–1200 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 550–700 MPa | ASTM E8/E8M |
Elongation | 10–20% | ASTM E8/E8M |
Charpy Impact Toughness | >20 J (notched, room temp) | ASTM E23 |
Wear Resistance Index | >2.5× 316 stainless steel | ASTM G65 |
Key Characteristics of Stellite 6B
Unmatched Galling Resistance: Performs exceptionally in metal-to-metal sliding contact without lubrication, even against itself.
Superior Toughness: Unlike cast Stellites, 6B retains ductility, making it ideal for impact-loaded parts and cyclic service.
Corrosion and Cavitation Resistance: Resists chloride-induced pitting, seawater attack, and erosion in fluid systems.
Thermal Stability: Maintains strength and wear resistance at temperatures up to 850°C in oxidizing and thermal cycling environments.
CNC Machining Challenges and Solutions for Stellite 6B
Machining Challenges
Strain Hardening During Cutting
Surface hardness increases rapidly, requiring constant tool wear and cutting depth monitoring.
Tool Wear Due to Carbides
Even in wrought conditions, dispersed carbides degrade, cutting edges under prolonged use.
Heat Accumulation at Tool Tip
Low thermal conductivity can cause a rise in local temperature and the breakdown of coating or tool substrates.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | PVD-coated carbide (K30–K40); CBN for finishing | Provides balance of toughness and wear resistance |
Coating | TiAlN or AlCrN (3–5 µm) | Minimizes thermal diffusion and flank wear |
Geometry | Neutral rake (0°), honed cutting edge 0.03 mm | Prevents chipping and built-up edge formation |
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 6B Parts
Hot Isostatic Pressing (HIP)
HIP is typically unnecessary for wrought material but may be applied to improve microstructure in powder metallurgy variants.
Heat Treatment
Heat Treatment can enhance hardness and stress relieve after machining or welding.
Superalloy Welding
Superalloy Welding using matching filler metal preserves the alloy's wear and corrosion performance with minimal heat-affected zone degradation.
Thermal Barrier Coating (TBC)
TBC Coating is recommended for valve components and guides exposed to hot combustion gases and erosion.
Electrical Discharge Machining (EDM)
EDM is critical for small-feature finishing and tight-tolerance geometries, delivering Ra <0.5 µm.
Deep Hole Drilling
Deep Hole Drilling supports production of valve guides, wear sleeves, and orifices with L/D ratios up to 30:1.
Material Testing and Analysis
Material Testing includes microhardness, tensile testing, Charpy impact, and metallographic verification of carbide dispersion.
Industry Applications of Stellite 6B Components
Steam and Control Valves
Valve stems, seats, and cages used in power generation and marine environments.
Aerospace Actuation and Bearings
Bushings and wear rings in turbine or hydraulic assemblies where galling and fretting are concerns.
Pump Components
Sleeves, plungers, and impellers that require resistance to cavitation and erosion in high-pressure flow systems.
Downhole Oilfield Tools
Subsurface wear pads, guiding sleeves, and valve bodies exposed to sand, fluid friction, and thermal cycling.
FAQs
What CNC cutting strategies are best for maximizing tool life when machining Stellite 6B?
How does Stellite 6B compare to Stellite 6 and Stellite 3 regarding toughness and wear resistance?
Is Stellite 6B suitable for high-pressure, high-temperature valve trim applications?
Can EDM and deep-hole drilling be used on wrought Stellite 6B parts?
What quality certifications and test data are available with CNC-machined Stellite 6B components?
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