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CBN vs PCD Superabrasive Cutting Inserts: Hard Steels & Non-Ferrous

CBN (Cubic Boron Nitride) and PCD (Polycrystalline Diamond) superabrasives provide extreme hardness second only to diamond, enabling high-speed machining of hardened steels (65 HRC) and abrasive composites.

Engineering Specifications & Parameters

CBN Hardness 4,500 HV (Extreme Hot Hardness for Steels)
PCD Hardness 8,000 HV (Maximum Wear Resistance for Non-Ferrous)
Surface Finish Capability Ra 0.2 - 0.4 microns (Grinding Quality)
PCD Cutting Speed (Aluminum) 500 - 2500 m/min
CBN Cutting Speed (Hard Steel) 120 - 220 m/min (at 60 HRC)

CBN vs PCD Material Selection Guide

  1. CBN (Cubic Boron Nitride):
    • Hardness: ~4500 HV.
    • Thermal Stability: Chemically inert to iron up to 1200°C.
    • Target Materials: Hardened alloy steels (50–65 HRC), chilled cast iron, high-nickel superalloys.
    • Replaces traditional cylindrical/surface grinding operations on hardened shafts.
  2. PCD (Polycrystalline Diamond):
    • Hardness: ~8000 HV (Hardest known tooling material).
    • Thermal Limitation: Reacts with ferrous carbon at >600°C (Do NOT use on steel).
    • Target Materials: High-silicon aluminum (A380/A390), carbon fiber (CFRP), PEEK-CF30, ceramics.

Surface Finishes & Productivity

CBN hard turning achieves Ra 0.2 to 0.4 micron finishes directly on the lathe, eliminating secondary cylindrical grinding cycles.

Frequently Asked Questions

Why cannot PCD diamond inserts be used to cut steel?

At cutting temperatures above 600°C, diamond (pure carbon) dissolves into iron via chemical affinity, causing rapid crater failure.

How does CBN hard turning replace secondary cylindrical grinding?

CBN inserts maintain sharp geometry under high cutting pressure in 60 HRC steel, achieving cylindrical tolerances within 0.005mm and Ra 0.2 surface finishes.