There are three different standards of Rockwell hardness: HRA, HRB and A, B and C in HRC. It is called Grade A, Grade B and Grade C. HRA is the hardness measured by a diamond cone press with a load of 60Kg and 120, which is used for materials with higher hardness. For example: cemented carbide.
Extended data:
The measurement method is to press the steel ball or diamond indenter vertically into the surface of the measured material under the specified external load, resulting in dents. According to the depth of the dent after the load is released, the Rockwell hardness can be calculated by the formula HR = (k-h)/c, and the Rockwell hardness value is displayed on the dial of the hardness tester and can be directly read out.
In the above formula, k is a constant, the diamond indenter K=0.2MM, and the hardened steel ball indenter k = 0.26 mm; H is the indentation depth of the sample after releasing the main load;
C is also a constant, generally c = 0.002 mm It can be seen that the shallower the indentation, the greater the HR value and the higher the hardness of the material. For cutting materials with high hardness, HRC is often used to express the hardness of the blade in the cutting field, such as 60HRC, which means that when the test load is 147 1. 1N and a diamond cone indenter with the top angle of120 is used, the indentation depth of the tested material is 0.08 mm ..
Generally speaking, the higher the hardness, the higher the wear resistance, but the greater the brittleness. The hardness of general high-speed steel is 62~66HRC, that of high-performance high-speed steel is 63~70HRC, and that of cemented carbide tool is 70~75HRC.
Baidu encyclopedia -HRC