The Rockwell hardness test uses three test forces and three indenters, resulting in nine combinations corresponding to nine Rockwell hardness scales: HRA, HRB, HRC, HRD, HRE, HRF, HRG, HRH, and HRK. These nine scales cover almost all commonly used metallic materials. HRA: 60kg load diamond cone indenter; HRB: 100kg load 1/16" diameter steel ball indenter; HRC: ... A 150kg load diamond cone indenter; the most commonly used scales are HRC, HRB, and HRF. The HRC scale is used to test quenched steel, tempered steel, quenched and tempered steel, and some stainless steels. This is the most widely used hardness testing method in the metalworking industry. The HRB scale is used to test various annealed steels, normalized steels, mild steels, some stainless steels, and harder copper alloys. The HRF scale is used to test pure copper, softer copper alloys, and hard aluminum alloys. Although the HRA scale can also be used for most ferrous metals, its practical application is generally limited to testing hard alloys and thin hard steel strips.
The surface Rockwell hardness test uses three test forces and two indenters, resulting in six combinations, corresponding to the six scales of surface Rockwell hardness. The surface Rockwell hardness test is a supplement to the Rockwell hardness test. When using the Rockwell hardness test, when… When encountering thin materials, small specimens, shallow surface hardening layers, or coated surfaces, a surface Rockwell hardness test should be used instead. In this case, using the same indenter as the Rockwell hardness test but with only a fraction of the test force, effective hardness test results can be obtained on the specimen. The N-scale of surface Rockwell hardness is suitable for materials similar to those tested with Rockwell hardness (HRC, HRA, and HRD); the T-scale is suitable for materials similar to those tested with Rockwell hardness (HRB, HRF, and HRG).
Practice has shown that there is an approximate correlation between the hardness value and the strength value of metallic materials. This is because the hardness value is determined by the resistance to initial plastic deformation and the resistance to continued plastic deformation; the higher the strength of the material, the higher the resistance to plastic deformation, and thus the higher the hardness value. However, the conversion relationships are not consistent across different materials.
