The most widely used in production is the hardness of press-in method, such as Brinell hardness, Rockwell hardness, Vickers hardness and micro hardness. The obtained hardness value essentially represents the resistance of the metal surface to the plastic deformation caused by the intrusion of foreign objects.
The following is a brief introduction to the various hardness units:
1. Brinell hardness (HB)
Press a hardened steel ball of a certain size (usually 10mm in diameter) into the surface of the material with a certain load (generally 3000kg) and keep it for a period of time. After the load is removed, the ratio of the load to the indentation area is the Brinell hardness value ( HB), in kilogram force/mm2 (N/mm2).
2. Rockwell hardness (HR)
When HB>450 or the sample is too small, Brinell hardness test cannot be used and Rockwell hardness measurement should be used instead. It uses a diamond cone with a vertex angle of 120° or a steel ball with a diameter of 1.59mm and 3.18mm to press into the surface of the material to be tested under a certain load, and the hardness of the material is obtained from the depth of the indentation. According to the hardness of the test material, it can be expressed in three different scales:
HRA: It is the hardness obtained by using a 60kg load and a diamond cone indenter, and is used for materials with extremely high hardness (such as cemented carbide, etc.).
HRB: It is the hardness obtained by using a 100kg load and a hardened steel ball with a diameter of 1.58mm. It is used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC: It is the hardness obtained by using a 150kg load and a diamond cone indenter, and is used for materials with high hardness (such as hardened steel, etc.).
3 Vickers hardness (HV)
Use a diamond square cone indenter with a load of less than 120kg and a vertex angle of 136° to press into the material surface, and divide the surface area of the material indentation pit by the load value, which is the Vickers hardness HV value (kgf/mm2).
Compared with Brinell and Rockwell hardness tests, Vickers hardness test has many advantages. It does not have the constraints of the specified conditions of load P and indenter diameter D like Brinell, and the problem of deformation of the indenter; nor does it have the problem that the hardness value of Rockwell cannot be unified. And it can test any soft and hard materials like Rockwell, and it can test the hardness of extremely thin parts (or thin layers) better than Rockwell, which can only be done by Rockwell surface hardness. But even under such conditions, it can only be compared within the Rockwell scale, and cannot be unified with other hardness levels. In addition, because Rockwell uses the indentation depth as the measurement index, and the indentation depth is always smaller than the indentation width, so its relative error is also larger. Therefore, the Rockwell hardness data is not as stable as Brinell and Vickers, and of course not as stable as Vickers precision.
There is a certain conversion relationship between Brinell, Rockwell and Vickers, and there is a conversion relationship table that can be queried.
Post time: Mar-16-2023
