Rockwell Hardness Test is the most commonly used hardness tests after Brinell Hardness Test, named after the metallurgists Stanley P. Rockwell and Hugh M. Rockwell who developed it in the early 1920s. It is convenient to use and several enhancements over the years have made the test adaptable to a variety of materials.
Rockwell hardness test
In the Rockwell Hardness Test, a cone-shaped indenter or small-diameter ball, with diameter 1.6 or 3.2 mm (1/16 or 1/8 inch) is pressed into the specimen using a minor load of 10 kg, thus seating the indenter in the material. Then, a significant load of 150 kg (or other value) is applied, causing the indenter to penetrate the specimen a certain distance beyond its initial position. This additional penetration distance (d) is converted into a Rockwell hardness reading by the testing machine. The sequence is shown in the above figure. Differences in load and indenter geometry provide various Rockwell scales for different materials.
The most common scales are shown in the below table.
Common Rockwell hardness scales:
| Rockwell Scale | Hardness Symbol | Indenter | Load (kg) | Typical Materials Tested |
|---|---|---|---|---|
| A | HRA | Cone | 60 | Carbides, Ceramics |
| B | HRB | 1.6 mm ball | 100 | Nonferrous metals |
| C | HRC | Cone | 150 | Ferrous metals, tool steels |
