Rockwell hardness of carbon steel is determined by the plastic deformation depth of indentation, and 0.002mm is used as the hardness unit. The use of different indenters and different testing forces in Rockwell hardness testing results in different combinations corresponding to different scales with Rockwell hardness. Three kinds of rulers are usually used, and their applications cover almost all common metal materials.


Rockwell hardness (HR) test of carbon steel is carried out when the sample is too small or the Brinell hardness (HB) is greater than 450. The test method is to use a diamond cone with a top angle of 120 degrees or a steel ball with a diameter of 1.5875mm/3.175mm/6.35mm/12.7mm and press it under the surface of the material to be measured. Certain loads are applied and materials are obtained from the depth of indentation. Hardness. The three most commonly used scales are A, B and C, namely HRA, HRB and HRC. According to the hardness of the experimental material, the scales of different hardness ranges are used to indicate:


HRA is a diamond conical indenter with hardness obtained at 60kg load and used for higher hardness materials. For example: steel plate, cemented carbide.
HRB is the hardness obtained by using 100kg load and 1.5875mm hardened steel balls for materials with lower hardness. For example: low carbon steel, non-ferrous metals, annealed steel and so on.
HRC is a diamond conical indenter with hardness obtained by 150 kg load and used for higher hardness materials. For example: hardened steel, cast iron, etc.


Rockwell hardness test of carbon steel requires sample, whose thickness can not be less than 10 times the depth of residual indentation, and there will be no obvious deformation marks on the back of the sample. Therefore, the thickness of the sample determines the choice of load, and the load must make the deformation caused by the load smaller than the minimum thickness of the sample. For each hardness test, there is a measurable minimum thickness.