Scales and Values
There are several alternative scales, the most commonly used being the "B" and "C" scales. Both express hardness as an arbitrary dimensionless number.
| Scale | Abbreviation | Load | Indenter | Use |
|---|---|---|---|---|
| A | HRA | 60 kgf | 120° diamond cone† | Tungsten carbide |
| B | HRB | 100 kgf | 1⁄16-inch-diameter (1.588 mm) steel sphere | Aluminum, brass, and soft steels |
| C | HRC | 150 kgf | 120° diamond cone | Harder steels >B100 |
| D | HRD | 100 kgf | 120° diamond cone | |
| E | HRE | 100 kgf | 1⁄8-inch-diameter (3.175 mm) steel sphere | |
| F | HRF | 60 kgf | 1⁄16-inch-diameter (1.588 mm) steel sphere | |
| G | HRG | 150 kgf | 1⁄16-inch-diameter (1.588 mm) steel sphere | |
| †Also called a brale indenter | ||||
- Except for testing thin materials In accordance with A623 & A623M the steel indenter balls have been replaced by tungsten carbide balls of the varying diameters. When a ball indenter is used, the letter "W is used to indicate a tungsten/carbide ball was used, and the letter "S" indicates the use of a steel ball. Eg: 70 HRCW indicates the reading was 70 in the Rockwell C scale using a Tungsten/Carbide indenter.
The superficial Rockwell scales use lower loads and shallower impressions on brittle and very thin materials. The 45N scale employs a 45-kgf load on a diamond cone-shaped Brale indenter, and can be used on dense ceramics. The 15T scale employs a 15-kgf load on a 1⁄16-inch-diameter (1.588 mm) hardened steel ball, and can be used on sheet metal.
Readings below HRC 20 are generally considered unreliable, as are readings much above HRB 100.
Read more about this topic: Rockwell Scale
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