1. Why Diamond Fails When Grinding Hardened Steels
Diamond is the hardest known material on earth (Knoop hardness ~7000 kg/mm²), making it the primary abrasive for non-ferrous materials like tungsten carbide, ceramics, glass, and stone. However, when diamond is used to grind ferrous alloys (hardened steel, cast iron, HSS) at high speeds, friction generates localized temperatures exceeding 700°C. At these temperatures, the carbon atoms in diamond react chemically with the iron atoms in steel, causing rapid carbon diffusion, graphitization, and premature wheel breakdown.
2. The Solution: Cubic Boron Nitride (CBN) Superhard Chemistry
Cubic Boron Nitride (CBN) is second only to diamond in hardness (Knoop hardness ~4700 kg/mm²), but possesses two decisive thermal and chemical advantages:
- Chemical Inertness to Iron: CBN consists of boron and nitrogen atoms, which do not react with iron or dissolve into steel matrix alloys under high grinding heat.
- High Thermal Stability: CBN withstands oxidation up to 1400°C in air, compared to diamond which oxidizes rapidly above 750°C.
3. Comparing GDM CBN R (Black) and CBN A (Amber) Grades
GDM CBN R — Black Monocrystalline Superhard Abrasive
Dark black monocrystalline grains with high thermal stability and sharp cutting edges. Engineered for electroplated CBN grinding wheels, resin bond tools, and precision internal grinding of hardened bearing steel, tool steel (HRC 45-68), and automotive crankshafts.
GDM CBN A — Amber High-Toughness Semi-Blocky Superhard
Translucent amber crystals exhibiting semi-blocky irregular structure and superior impact toughness. Designed for heavy-duty vitrified bond CBN wheels, nickel-based aerospace superalloys (Inconel, René), and cobalt-chrome machining.
4. Material Application Matrix
| Workpiece Material | Recommended Abrasive | Optimal Tool Bond |
|---|---|---|
| Hardened Steel (HRC 45-68) | CBN R (Black) / CBN A | Resin Bond / Vitrified Bond |
| High-Speed Tool Steel (HSS) | CBN R (Black) | Electroplated / Vitrified |
| Nickel Aerospace Alloys (Inconel) | CBN A (Amber) | Vitrified Bond Wheels |
| Tungsten Carbide / Non-Ferrous | Synthetic Diamond Powder | Resin / Metal Bond |