What Is Rockwell Hardness (HR)
Use a diamond cone or quenched steel ball with a cone apex angle of 120 ° as the indenter and load, and press the specimen under an initial load of 10kgf and a total force of 60, 100, or 150 (i.e. initial load plus main load). After the total load is applied, the hardness is expressed by the difference between the depth of pressing when the main load is removed and the depth of pressing under the initial load.
The Rockwell hardness test uses three test forces and three types of indenters, with a total of nine combinations corresponding to the nine scales of Rockwell hardness. These 9 scales cover almost all commonly used metal materials. There are three commonly used types: HRA, HRB, and HRC, with HRC being the most widely used.
|
Item |
Press Head |
Test Force F/N(kg) |
Scope |
Applications |
|
HRA |
120 ° Diamond |
588.4(60) |
20~88 |
Tungsten Carbide, surface hardening steel, etc. |
|
HRB |
Ø1.588mm, Quenched steel ball |
980.7(100) |
20~100 |
annealed, normalized steel, aluminum alloy Gold, copper alloy, cast iron. |
|
HRC |
120 ° Diamond Cone |
1471(150) |
20~70 |
quenched and tempered steel, quenched and tempered steel, deep Layer surface hardening steel. |
The range of the HRC is 20~70HRC. When the hardness is less than 20HRC, the sensitivity decreases due to excessive pressure on the conical part of the indenter. In this case, an HRB ruler should be used instead; When the hardness of the sample is greater than 67HRC, the pressure on the tip of the indenter is too high, and the diamond is easily damaged, which greatly shortens the life of the indenter. Therefore, an HRA should generally be used instead.
The Rockwell hardness test is easy to operate, fast, and has a small indentation. It can test the surface of finished products and harder and thinner workpieces. Due to the small indentation, for materials with uneven organization and hardness, the hardness value fluctuates greatly, and the accuracy is not as high as Brinell hardness. Rockwell hardness is used to determine the hardness of steel, non-ferrous metals, hard alloys, etc.
