Huahao Sealing · Carbon Graphite Components
Silicon carbide conducts 120–150 W/(m·K); tungsten carbide conducts 80–100 W/(m·K). This article compares hardness, thermal conductivity, corrosion resistance, PV limit, and cost to guide mechanical seal mating-face material selection.
The mating faces of a mechanical seal rotating and stationary rings determine seal life and reliability. Silicon carbide (SiC) and tungsten carbide (WC) are the two mainstream hard-face materials, commonly paired with carbon graphite. SiC offers higher thermal conductivity, higher hardness, and broader corrosion resistance; WC offers better toughness and impact resistance. This comparison quantifies 8 parameters and explains the best pairing for each.
| Property | Silicon Carbide (SiC) | Tungsten Carbide (WC) |
|---|---|---|
| Thermal conductivity | 120–150 W/(m·K) | 80–100 W/(m·K) |
| Hardness (Vickers) | 2500–2800 HV | 1500–1800 HV |
| Strong acid/alkali resistance | ✓（除 HF） | ◐ |
| Impact toughness | ◐ | ✓ |
| PV limit (vs carbon graphite) | ×1.5–2.0 | ×1.0 |
| Density | 3.1 g/cm³ | 14.5 g/cm³ |
| Dry-running capability | ✓（短时） | ◐ |
| Relative cost | ×1.3 | ×1.0 |
Prefer silicon carbide (SiC) for: high-speed, high-temperature, strongly corrosive (except HF), short-term dry-running, or high heat-dissipation seals — its thermal conductivity is 30–50% higher than WC, hardness 60%+ higher, and PV limit 1.5–2× higher. Prefer tungsten carbide (WC) for: seals with solid-particle impact, risk of mechanical collision, or high toughness requirements — WC impact toughness is significantly better than SiC, resisting chipping. Both are commonly paired with carbon graphite, leveraging graphite self-lubrication to reduce friction and wear.
SiC is a covalent crystal with efficient phonon heat transfer, giving 120–150 W/(m·K). WC has mixed metallic/covalent bonding and a cobalt binder phase that scatters phonons, giving 80–100 W/(m·K). Higher conductivity lets SiC dissipate frictional heat faster, suiting high-speed seals.
SiC is more corrosion-resistant, withstanding virtually all acids and alkalis (except hydrofluoric acid). WC contains a cobalt binder that leaches out in strong acids, degrading the material, so its corrosion resistance is inferior to SiC.
WC cobalt binder gives a fracture toughness KIc of about 10–15 MPa·m½, 3–4× that of SiC (~3–4 MPa·m½). In particulate media or assembly impact, SiC chips easily while WC resists mechanical shock.
They are usually paired with carbon graphite. Carbon graphite serves as the self-lubricating soft face, while the hard face (SiC or WC) is the wear-resistant counterface. This soft-hard pairing balances low friction with long life — the classic mechanical seal friction pair.
