Rockwell Hardness
May 12, 2021| Rockwell Hardness
The diamond cone with the top Angle of 120° or Ø1.588mm and the quenched steel ball with 3.176mm are used as the indenter and the load is used together. Under the action of the initial load of 10kgf and the total load of 60, 100 or 150kgf (that is, the initial load plus the main load), the sample is pressed into the sample. After the action of the total load, The hardness is expressed by the difference between the pressing depth when the main load is removed but the main load is retained and the pressing depth under the action of the initial load.
Rockwell hardness test uses three test forces, three pressure heads, they have a total of nine combinations, corresponding to the Rockwell hardness of nine scales. The applications of these nine scales cover almost all commonly used metal materials. HRA, HRB and HRC are commonly used, and HRC is the most widely used.
Common Rockwell hardness test specification
hardness | Head type | total test force F/N（kgf） | Hardness range
| Applications
|
HRA | 120°Diamond cone | 588.4(60) | 20~88 | Cemented carbide, carbide, |
HRB | Ø1.588mm Quenching steel ball | 980.7(100) | 20~100 | Annealed, normalized steel, aluminum |
HRC | 120°Diamond cone | 1471(150) | 20~70 | Hardened steel, tempered steel, deep surface hardening steel |
The HRC scale can be used in the range of 20 to 70HRC. When the hardness value is less than 20HRC, because the cone part of the head is pressed too much, the sensitivity decreases, then HRB scale should be used; When the sample hardness is greater than 67HRC, the pressure at the tip of the indenter is too large, the diamond is easy to be damaged, and the indenter life will be greatly shortened. Therefore, HRA scale should be used generally.
Rockwell hardness test is easy to operate, rapid, small indentation, can test the surface of finished products and harder, thinner workpiece. Because of the small indentation, the hardness value fluctuates greatly for the material with uneven structure and hardness, and the accuracy is not as high as Brinell hardness. Rockwell hardness is used to determine the hardness of iron and steel, non-ferrous metals, cemented carbide, etc.
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