Stellite 12
Introduction to Stellite 12
Stellite 12 is a cobalt-based, wear-resistant alloy engineered to perform under extreme mechanical and thermal conditions. With a unique balance of high hardness, edge retention, and moderate impact resistance, it is ideally suited for components exposed to severe abrasion, high-temperature friction, and chemical attack. Positioned between Stellite 1 (extremely hard but brittle) and Stellite 6 (ductile but less wear-resistant), Stellite 12 offers an optimal solution for applications demanding both durability and dimensional stability.
Commonly applied through casting, powder metallurgy, or hardfacing overlays, Stellite 12 is then precision-finished using advanced CNC machining processes. The alloy is frequently used in cutting tools, valve seats, hot extrusion dies, and aerospace sealing components, particularly where sliding wear and thermal fatigue are critical performance factors. Its ability to maintain structural and surface integrity at temperatures approaching 850°C makes it a top choice for engineers and procurement specialists in aerospace, oil & gas, power generation, and thermal processing sectors.
Chemical, Physical, and Mechanical Properties of Stellite 12
Stellite 12 (UNS R30012 / AMS 5387 / ISO 5832-4 family) exhibits superior dimensional stability, galling resistance, and thermal wear performance under severe service conditions.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Cobalt (Co) | Balance (≥50.0) | Provides high-temperature strength and corrosion resistance |
Chromium (Cr) | 28.0–32.0 | Enhances oxidation and aqueous corrosion resistance |
Tungsten (W) | 8.0–10.0 | Forms hard carbides for abrasion resistance |
Carbon (C) | 1.4–1.9 | Controls carbide content for improved edge wear resistance |
Nickel (Ni) | ≤3.0 | Improves fracture toughness and weldability |
Iron (Fe) | ≤3.0 | Trace residual element |
Silicon (Si) | ≤1.2 | Improves casting fluidity and metallurgical cleanliness |
Manganese (Mn) | ≤1.0 | Enhances hot ductility during solidification |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.70 g/cm³ | ASTM B311 |
Melting Range | 1275–1350°C | ASTM E1268 |
Thermal Conductivity | 12.5 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 0.96 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 12.7 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 + Heat Treated)
Property | Value (Typical) | Test Standard |
|---|---|---|
Hardness | 45–50 HRC (as-cast) / up to 52 HRC (HIP treated) | ASTM E18 |
Tensile Strength | 950–1150 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 500–650 MPa | ASTM E8/E8M |
Elongation | 1.0–2.0% | ASTM E8/E8M |
Abrasion Resistance | >3× better than 316 SS (dry sand/rubber wheel) | ASTM G65 |
Operating Temperature | Up to 850°C (intermittent) | N/A |
Key Characteristics of Stellite 12
Superior Abrasion Resistance: High tungsten carbide content (20–30% by volume) provides robust performance in abrasive slurry, sand-laden fluids, or contact wear scenarios.
Hot Hardness: Maintains structural integrity and high surface hardness at temperatures approaching 850°C, outperforming most tool steels and austenitic stainless alloys.
Corrosion Resistance: Withstands acidic and oxidizing environments; resists chloride stress corrosion cracking and pitting.
Dimensional Stability: Excellent resistance to thermal distortion, with minimal creep and expansion in cycling service conditions.
CNC Machining Challenges and Solutions for Stellite 12
Machining Challenges
High Tool Wear Rates
The abrasive carbide network accelerates flank and crater wear in conventional carbide tools. Inadequate tooling results in tolerance drift and poor surface finish.
Brittle Behavior
Limited elongation increases the risk of microchipping or edge breakout during aggressive tool engagement, especially in thin-walled sections.
Heat Management
Low thermal conductivity causes heat buildup at the tool-chip interface, increasing risk of work hardening and surface microcracks.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Ultra-fine grain carbide (K30–K40) or CBN for semi-finishing | Withstands extreme abrasion while maintaining cutting edge stability |
Coating | AlTiN or TiSiN PVD coatings (thickness: 3–5 µm) | Thermal barrier reduces heat transfer and friction |
Geometry | Neutral rake, honed cutting edge radius 0.03–0.05 mm | Resists chipping and maintains edge integrity |
Cutting Parameters (ISO 3685 Compliant)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 8–14 | 0.15–0.25 | 1.5–2.5 | 100–120 |
Finishing | 18–25 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Stellite 12 Parts
Hot Isostatic Pressing (HIP)
HIP at 1150–1200°C and 100–150 MPa eliminates porosity in cast or powder-processed components, enhancing fatigue strength and carbide distribution uniformity.
Heat Treatment
Heat Treatment optimizes hardness and relieves residual stress after rough machining or welding. Aging cycles may enhance wear performance.
Superalloy Welding
Superalloy Welding using TIG or PTA overlays with matching Stellite 12 filler metal preserves wear and oxidation resistance across joints.
Thermal Barrier Coating (TBC)
TBC Coating is recommended for parts operating above 800°C, such as valve seats, nozzle inserts, and turbine flow restrictors.
Electrical Discharge Machining (EDM)
EDM achieves sub-10 µm tolerances and mirror finishes (Ra <0.5 µm) on hardened components.
Deep Hole Drilling
Deep Hole Drilling applies to ports, throttle openings, and seat guide channels with depth-to-diameter ratios >20:1.
Material Testing and Analysis
Material Testing includes ASTM E18 hardness, ASTM G65 abrasion wear, microstructure analysis, and nondestructive inspection (UT/PT/RT).
Industry Applications of Stellite 12 Components
Rotary and Fixed Cutting Tools
Knife blades, shearing dies, and bush hog cutters benefit from long edge life and minimal distortion under heat and impact.
Valve Seats and Trims
Ideal for erosion- and galling-resistant flow control surfaces exposed to abrasive or corrosive fluids.
Hot Extrusion and Glass Molding Dies
Retains hardness and wear resistance at forming temperatures up to 850°C.
Aerospace Turbine Seal Rings and Guides
Resists fretting and erosion in hot gas path environments, ensuring tight sealing over extended cycles.
FAQs
What tooling strategies are recommended for CNC machining high-carbide Stellite 12 components?
How does Stellite 12 compare to Stellite 6 and Stellite 1 regarding hardness and wear resistance?
Can Stellite 12 be EDM machined for fine grooves, slots, and profiles?
What post-processing methods are essential for dimensional and surface control in machined Stellite 12 parts?
What test standards does Neway use to verify Stellite 12 component performance and quality?
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