Tungsten Carbide Properties: Hardness, Density & More

This comprehensive property table captures the fundamental trade-offs in WC-Co materials. Reading from left to right (increasing cobalt), you'll notice a consistent pattern: hardness drops from 2600 HV (pure WC) to 1100-1250 HV (WC-15%Co), while toughness (TRS) increases from essentially zero for pure WC to 3500-4000 MPa for high-cobalt grades. Density decreases because cobalt (8.9 g/cm³) is much lighter than WC (15.63 g/cm³). Stiffness (elastic modulus) falls from 700 GPa to 530 GPa with more binder. Grain size adds another dimension—coarser grain increases TRS but reduces hardness at any given cobalt level. Use this table to quickly compare grades for your specific balance of wear resistance versus impact tolerance.

All commercial tungsten carbide powder is α-WC. The β-WC₂ phase can form during improper sintering—specifically at excessive temperatures or in oxidizing atmospheres—and represents a quality control failure. Its presence degrades hardness and wear resistance. When purchasing WC powder or finished parts, X-ray diffraction analysis can confirm phase purity. Reputable suppliers provide only α-WC with phase purity exceeding 99%.

This hardness comparison table spans from diamond at the top to hardened alloy steel at the bottom, providing context for where WC-Co grades fit in the overall materials hierarchy. WC-Co grades span 87-94+ HRA—a range that determines application suitability. Grades above 92 HRA are typically used for cutting tools where wear resistance is paramount. The 89-92 HRA range suits general wear parts that see some impact. Below 89 HRA, grades have enough toughness for mining and percussion drilling. The steel references at the bottom show that even the softest WC-Co grade (WC-15%Co at 87 HRA) is significantly harder than any steel, explaining why carbide outlasts steel tooling by 10-50× in abrasive conditions.

Hot hardness—the retention of hardness at elevated temperatures—explains why carbide tools can machine at higher speeds than high-speed steel (HSS). At room temperature, WC-6%Co is about twice as hard as HSS M2 (1650 vs 850 HV). But at 600°C, a temperature commonly reached at cutting edges during high-speed machining, WC-6%Co retains ~65% of its room temperature hardness (1100 HV) while HSS retains only ~40% (350 HV). This diverging performance at temperature means carbide tools can operate at cutting speeds 3-10× faster than HSS without catastrophic softening. Above 800°C, even carbide begins rapid softening, which is why extreme-speed machining often requires ceramic or CBN tooling.

Density decreases linearly with increasing cobalt content because cobalt (8.9 g/cm³) is much lighter than tungsten carbide (15.63 g/cm³). Moving from 6% to 15% cobalt reduces density by about 7%—a meaningful difference for weight-sensitive applications. High-speed rotating tools experience centrifugal stresses proportional to density × (RPM)², so lower-density grades may allow higher spindle speeds. Handheld equipment benefits from lower density to reduce operator fatigue. Conversely, for counterweights, ballast, or kinetic penetrators, the high density of low-cobalt grades provides more mass in a given volume—a feature exploited in specialty applications.

Density affects application suitability in ways that go beyond simple weight. Rotating tools develop centrifugal stresses proportional to density × radius × (angular velocity)², meaning a denser tool generates more internal stress at the same RPM. Precision balancing becomes critical to prevent vibration. For handheld equipment like pneumatic grinders with carbide burrs, dense heads contribute to operator fatigue over extended use. Shipping costs for carbide are almost always weight-based rather than volume-based, so a 1-ton shipment of WC-Co occupies only about 70 liters yet incurs the same freight as a ton of steel. These factors should be considered alongside mechanical properties when selecting grades.

The high elastic modulus of WC-Co has profound implications for precision tooling. Under the same cutting force, a carbide tool deflects only one-third as much as a steel tool of identical geometry. This translates directly to tighter dimensional tolerances on machined parts. For example, a 10 mm diameter carbide boring bar deflects about 0.003 mm under a 100N side force where a steel bar would deflect 0.009 mm—the difference between holding ±0.01 mm tolerance easily versus struggling. The empirical relationship E ≈ 695 − 11×Co% predicts modulus accurately: each 1% cobalt reduces stiffness by about 11 GPa because the softer cobalt binder contributes less to composite stiffness.

This benefit-drawback table summarizes the engineering trade-offs of WC-Co's high stiffness. In most precision machining applications, the benefits dominate—minimal deflection means consistent cut depth and surface finish. The higher natural frequency reduces chatter risk in many scenarios. However, the drawbacks become significant in interrupted cutting (milling, broaching), impact loading (mining, rock drilling), or shock conditions. High stiffness means the material stores more elastic energy before yielding, but when it does fail, it fails catastrophically rather than deforming plastically. Design mitigation strategies include using higher-cobalt grades for shock applications, increasing section thickness to reduce peak stress, and avoiding sharp internal corners that concentrate stress.

TRS is the inverse of hardness in the property trade-off spectrum. Note that TRS increases with both higher cobalt content AND coarser grain size—exactly opposite to the direction of hardness. This inverse relationship creates a fundamental design constraint: high-impact grades (WC-15-20%Co, coarse grain) necessarily have low hardness (87-89 HRA), while the hardest grades (WC-3-6%Co, ultrafine) are brittle (TRS 1800-2200 MPa). The empirical relationship TRS ≈ 1800 + 120×Co% approximates the cobalt effect—each 1% cobalt adds roughly 120 MPa of bend strength because the ductile binder provides crack-bridging capability that absorbs fracture energy.

WC-Co exhibits extraordinarily high compressive strength—2-3× higher than any steel. This property makes cemented carbide ideal for dies, punches, and any application under compressive loading. Even the highest-cobalt grades (WC-25%Co at 3500-4000 MPa) significantly outperform hardened tool steel (2000-2500 MPa). Failure under compression typically occurs by cobalt matrix flow rather than WC grain fracture—the hard WC skeleton resists crushing while the softer binder eventually yields. This is why cold heading dies and wire drawing dies, which experience extreme compressive stresses, universally use cemented carbide.

Fracture toughness increases dramatically with cobalt content and grain size—the same direction as TRS and opposite to hardness. Pure WC has K_IC of only 5-6 MPa·m^(1/2), barely better than ceramics, making it useless without a binder. Adding 6% cobalt more than doubles toughness to 9-13 MPa·m^(1/2) depending on grain size. At 15% cobalt, K_IC reaches 16-20 MPa·m^(1/2), approaching structural steel territory. The fracture mode column explains the mechanism: at low cobalt, cracks propagate through WC grains (brittle cleavage). With more binder, cracks must stretch ductile cobalt ligaments between grains, absorbing significant energy before fracture—a process called crack bridging.

This comparison table puts WC-Co toughness in perspective relative to common engineering materials. Glass, the canonical brittle material, serves as the 1× baseline. Alumina ceramics are 5× tougher—good for wear but still too brittle for impact. WC-6%Co at 10-12 MPa·m^(1/2) is tough enough for most cutting tool applications where impacts are controlled. WC-15%Co at 18-20 MPa·m^(1/2) approaches tool steel toughness, enabling rock drill bits and mining tools that experience repeated percussion loading. The table illustrates why WC-Co uniquely bridges the gap between brittle ceramics and ductile metals.

Tungsten carbide's thermal conductivity of 110 W/(m·K) is remarkably high for a ceramic material—3-4× better than high-speed steel and alumina. This property is crucial for cutting tools: heat generated at the cutting edge conducts away rapidly into the tool body rather than accumulating at the tip. Higher temperature at the cutting edge accelerates wear, so effective heat dissipation directly extends tool life. Cobalt reduces overall conductivity because Co (100 W/(m·K)) conducts slightly less than WC (110 W/(m·K)), but even WC-15%Co at 75-85 W/(m·K) significantly outperforms HSS. This thermal advantage compounds with hot hardness—carbide both stays harder at temperature AND conducts heat away faster.

WC-Co's thermal expansion coefficient is roughly half that of steel. This low expansion provides excellent dimensional stability during temperature changes—a precision gauge made from carbide holds calibration better than a steel equivalent. However, the expansion mismatch creates challenges when joining carbide to steel. Brazing a carbide tip onto a steel shank induces residual stress upon cooling because the steel contracts more than the carbide. Careful joint design with stress-relieving geometry is essential. In service, the low expansion means less thermal distortion and more consistent dimensional accuracy during machining operations that generate heat.

Unlike most carbides and ceramics, tungsten carbide is an electrical conductor—approximately 5-10% the conductivity of copper. This unusual property arises from the metallic W-W bonding component in the crystal structure. The practical implications are significant: WC-Co can be machined by electrical discharge machining (EDM), enabling complex geometries that would be impossible to grind. Carbide can serve in electrical contact wear applications where conductivity and wear resistance are both required. It can also be grounded in static-sensitive environments. Silicon carbide and aluminum oxide, by contrast, are electrical insulators and cannot be EDM machined.

Abrasive wear resistance (measured by ASTM G65 dry sand/rubber wheel test) correlates strongly with hardness. WC-6%Co removes only 0.5-1.0 mm³ per 1000 wheel revolutions, while hardened steel loses 20-40 mm³—a 30-50× difference. This explains why carbide wear parts in sand-handling, mineral processing, and agricultural equipment last decades while steel alternatives wear through in months. Within the carbide family, lower cobalt means better abrasion resistance: WC-15%Co wears 3-4× faster than WC-6%Co. For pure abrasion applications without impact, always choose the lowest cobalt content that provides adequate toughness for handling without chipping.

Erosive wear—caused by particles impacting a surface—depends strongly on impact angle. At shallow angles (15-30°), particles slide and cut the surface like micro-machining tools; high hardness resists this cutting action best. At near-perpendicular angles (75-90°), particles impact and rebound, causing plastic deformation and fatigue crack initiation; toughness matters more than hardness here. Many erosion environments involve a distribution of impact angles, requiring a balanced grade. This angle dependence explains why a single erosion-resistant grade doesn't exist—the optimal choice depends on the specific particle trajectories in the application.

Chemical resistance is often limited by the cobalt binder rather than the tungsten carbide phase. WC itself resists most environments except hydrofluoric acid (HF) and mixed HNO₃/HF (used deliberately for dissolving samples for analysis). The cobalt binder is the weak link: it dissolves in strong acids, corrodes galvanically in seawater, and limits life in aggressive chemical environments. For applications requiring acid resistance, nickel-bound grades (WC-Ni) or nickel-chromium-bound grades (WC-Ni-Cr) provide significantly better performance. The trade-off is slightly lower hardness and toughness compared to equivalent cobalt-bound grades, but the corrosion resistance improvement is dramatic.

Tungsten carbide oxidizes at elevated temperatures in air, with the rate increasing exponentially above 500°C. The oxidation reaction forms tungsten trioxide (WO₃) which grows as a porous, non-protective scale that eventually spalls off, exposing fresh surface to continued attack. This limits WC-Co use in high-temperature oxidizing environments. However, in inert atmospheres (argon, nitrogen) or reducing atmospheres (hydrogen), WC is stable to much higher temperatures—important for vacuum and controlled-atmosphere processing. Cutting tools, which can reach 800-1000°C at the chip-tool interface, survive because the cut duration is short and heat dissipates rapidly; prolonged exposure would cause oxidation failure.

This flowchart illustrates the fundamental trade-off that governs all cemented carbide design: hardness and toughness move in opposite directions. Reducing cobalt content and refining grain size increases hardness but sacrifices toughness and impact resistance. Conversely, adding cobalt and using coarser grains improves toughness but reduces hardness and wear resistance. Every WC-Co grade represents a specific compromise point on this spectrum—there is no grade that maximizes both properties simultaneously. The engineering task is matching the grade to the application's dominant failure mode: if parts fail by abrasive wear, choose higher hardness; if they fail by chipping or cracking, choose higher toughness.

Read this selection matrix from top to bottom as a spectrum from hardest to toughest grades. The top row (3-6% Co, ultrafine grain) achieves maximum hardness for applications where microscopic edge sharpness matters more than impact resistance—printed circuit board drilling with 0.1 mm bits is a perfect example. The bottom row (20-30% Co, coarse grain) maximizes toughness for applications like cold heading dies that experience millions of impact cycles. Most applications fall in the middle rows. If you're uncertain where your application fits, start with a "balanced" grade (8-12% Co, medium grain)—it's forgiving and provides a baseline to adjust from based on actual field performance.