Boron Nitride cBN
Grade
also Hex Boron Nitride, White Graphite
cBN = cubic boron nitride, sintered polycrystalline
Choose only as a superhard cutting/wear material: second only to diamond in hardness and, unlike diamond, chemically stable against ferrous alloys up to ~1000 °C.
Values for the cBN condition
Other Boron Nitride tempers and conditions
Boron Nitride is listed in 8 conditions; see the grade overview at Boron Nitride.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
High-purity (>99 %) binder-free hot-pressed hBN | Choose for semiconductor, crystal-growth and vacuum-furnace parts where boron-oxide outgassing, moisture pickup or metal-ion contamination cannot be tolerated. | 25 | 60 W/m·K | |||
Grade XP | High-purity fine-grain hot-pressed hBN with low binder content — clean, low-outgassing and near-isotropic, for crucibles, insulators and semiconductor fixtures. | 30 | 40 W/m·K | |||
Pressed & SinteredDefault hot-pressed hBN with boric-oxide bond (Grade A type) | General-purpose machinable hBN block/rod for molten-metal contact, insulators and break rings; cheapest route, but the B2O3 bond is hygroscopic. | 35 | 33 W/m·K | |||
Grade BO | Hot-pressed hexagonal BN with boric-oxide (B₂O₃) bond — high strength and excellent machinability, but hygroscopic and limited to moderate air temperatures. | 35 | 27 W/m·K | |||
Grade CA | Calcium-borate bonded hot-pressed hBN — moisture-resistant version of bonded BN with higher strength and service to ~1000 °C in air. | 45 | 25 W/m·K | |||
BN-SiO₂ | Choose when strength, wear and non-hygroscopic behaviour matter more than maximum thermal conductivity — jigs, nozzles, high-humidity or load-bearing insulators. | 50 | 25 W/m·K | |||
Pyrolytic boron nitride | Choose for MBE effusion-cell crucibles, GaAs/InP growth boats and microwave-tube windows: pore-free, ultra-pure, no binder, usable to ~1800 °C in vacuum. | 100 | 60 W/m·K | |||
cBNThis page Cubic boron nitride, sintered polycrystalline | Choose only as a superhard cutting/wear material: second only to diamond in hardness and, unlike diamond, chemically stable against ferrous alloys up to ~1000 °C. | 4,000 HV | 200 W/m·K |
What is Boron Nitride cBN?
Boron Nitride cBN is Boron Nitride in the cBN grade — choose only as a superhard cutting/wear material: second only to diamond in hardness and, unlike diamond, chemically stable against ferrous alloys up to ~1000 °C. Boron Nitride cBN has a tensile strength of 35 MPa (5.08 ksi), weaker than 71% of ceramic grades. The elastic modulus is 680 GPa (98.6 Msi). Boron Nitride cBN has a density of 3.45 g/cm³ (0.125 lb/in³), lighter than 68% of ceramic grades. It melts at 2,973°C (5,383 °F). Pressed & Sintered is the default condition FabDigit quotes; cBN is available on request or by drawing note.
Advantages
- Stiff — 680 GPa (98.6 Msi), better than 99% of ceramic grades
- Conducts heat well — 200 W/m·K (115.6 BTU/hr·ft·°F), better than 96% of ceramic grades
Boron Nitride cBN properties
Typical room-temperature values for Boron Nitride cBN; 19 are specific to this condition. Other listed values are Boron Nitride reference data and may not represent this condition. Bars are the position among ceramic grades.
Physical4
Boron Nitride cBN has a density of 3.45 g/cm³ (0.125 lb/in³), lighter than 68% of ceramic grades. It melts at 2,973°C (5,383 °F).
Mechanical9
Boron Nitride cBN has a tensile strength of 35 MPa (5.08 ksi), weaker than 71% of ceramic grades. The elastic modulus is 680 GPa (98.6 Msi).
Thermal5
Boron Nitride cBN is rated for continuous service to 1,000°C (1,832 °F). It conducts heat at 200 W/m·K (115.6 BTU/hr·ft·°F), better than 96% of ceramic grades. Thermal expansion is 4.7 µm/m·K (2.61 µin/in·°F).
Electrical5
Boron Nitride cBN is an electrical insulator with a dielectric strength of 40 kV/mm (1,016 V/mil) and a resistivity of 1×10¹⁰ Ω·m.
Chemical & Environmental2
Corrosion resistance is excellent (85/100), better than 69% of ceramic grades.
Sustainability4
Producing a kilogram of Boron Nitride cBN takes about 250 MJ of energy and emits 20 kg of CO₂ — more than 67% of ceramic grades. Typical recycled content is 0%.
Manufacturability3
Boron Nitride cBN's machinability is not recommended (3/100, worse than 95% of ceramic grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Boron Nitride cBN
Is Boron Nitride easy to machine?
Machines like hard chalk — turn, mill, drill and tap dry with sharp carbide or HSS tooling at high speed and low feed; use dust extraction and avoid water coolant on B2O3-bonded grades.
Can Boron Nitride be welded?
Not weldable; join by mechanical clamping, threaded/pinned assemblies, or high-temperature BN/alumina cements and metallized-then-brazed interfaces.
Can Boron Nitride be formed, bent or molded?
Made by uniaxial hot pressing or CIP + pressureless nitridation of hBN powder into billets, then finish machined; PBN is grown as free-standing CVD shells on graphite mandrels, cBN is HP/HIP-sintered at GPa pressures.
What surface finishes work on Boron Nitride?
No plating or anodizing; surfaces are lightly ground or lapped only, remain matte and can leave a lubricious film — bake parts at 200–500 °C in vacuum/inert before high-temperature or vacuum service to drive off absorbed moisture.
Boron Nitride chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Bstoichiometric BN | 42 – 44 | 43.6 |
| B2O3boric-oxide bond phase in pressed & sintered grades; <0.5 % in high-purity and PBN grades | 0 – 6 | 3 |
| SiO2only in BN-SiO2 composite grades (borosilicate/calcium-borate bond) | 0 – 40 | 0 |
| CaOoptional calcium-borate bond addition | 0 – 5 | 0 |
| Nstoichiometric BN | balance |
Boron Nitride cBN — frequently asked
What is Boron Nitride cBN used for?
Boron Nitride cBN is typically used for crucibles for molten metal, electrical insulators and feedthroughs, break rings for horizontal continuous casting, mould release and setter plates, thermocouple protection sleeves and plasma chamber insulators. In short: machinable thermal insulator.
What is the tensile strength of Boron Nitride cBN?
Boron Nitride cBN has a typical tensile strength of 35 MPa (5.08 ksi) — weaker than 71% of ceramic grades. Strength varies by condition: see the 8 listed tempers.
Is Boron Nitride cBN easy to machine?
Not especially — machinability is rated not recommended (3/100, worse than 95% of ceramic grades). Machines like hard chalk — turn, mill, drill and tap dry with sharp carbide or HSS tooling at high speed and low feed; use dust extraction and avoid water coolant on B2O3-bonded grades.
Can Boron Nitride cBN be welded?
Not weldable; join by mechanical clamping, threaded/pinned assemblies, or high-temperature BN/alumina cements and metallized-then-brazed interfaces.
What surface finishes work on Boron Nitride cBN?
No plating or anodizing; surfaces are lightly ground or lapped only, remain matte and can leave a lubricious film — bake parts at 200–500 °C in vacuum/inert before high-temperature or vacuum service to drive off absorbed moisture.
Can Boron Nitride cBN be formed, bent or molded?
Made by uniaxial hot pressing or CIP + pressureless nitridation of hBN powder into billets, then finish machined; PBN is grown as free-standing CVD shells on graphite mandrels, cBN is HP/HIP-sintered at GPa pressures.
What is the maximum service temperature of Boron Nitride cBN?
Boron Nitride cBN is rated for continuous use to about 1,000°C (1,832 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASM Engineered Materials Handbook, Vol. 4: Ceramics and Glasses — ASM International (1991)
- Combat Boron Nitride Solids — Grades A, AX05, M, HP — Momentive Performance Materials / Saint-Gobain (2021)
- Boron Nitride Machinable Ceramics and PBN Crucibles — Kennametal / CoorsTek / Shin-Etsu (2022)
- Boron nitride (hexagonal, pyrolytic, cubic) property records — MatWeb / Ceramic Industry Materials Handbook (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.