Principle of Rockwell Hardness Test

The general principle of the Rockwell indentation hardness test is illustrated in Fig. 1. The test is divided into three steps of force application and removal.

Step 1—The indenter is brought into contact with the test specimen, and the preliminary test force F0 is applied. After holding the preliminary test force for a specified dwell time, the baseline depth of indentation is measured.

Step 2—The force on the indenter is increased at a controlled rate by the additional test force F1 to achieve the total test force F. The total test force is held for a specified dwell time.

Step 3—The additional test force is removed, returning to the preliminary test force. After holding the preliminary test force for a specified dwell time, the final depth of indentation is measured. The Rockwell hardness value is derived from the difference h in the final and baseline indentation depths while under the preliminary test force. The preliminary test force is removed and the indenter is removed from the test specimen.

There are two general classifications of the Rockwell test: the Rockwell hardness test and the Rockwell superficial hardness test. The significant difference between the two test classifications is in the test forces that are used. For the Rockwell hardness test, the preliminary test force is 10 kgf (98 N) and the total test forces are 60 kgf (589 N), 100 kgf (981 N), and 150 kgf (1471 N). For the Rockwell superficial hardness test, the preliminary test force is 3 kgf (29 N) and the total test forces are 15 kgf (147 N), 30 kgf (294 N), and 45 kgf (441 N). Indenters for the Rockwell hardness test include a diamond conical indenter and tungsten carbide ball indenters of specified diameters.