Basic knowledge of hardness of metal materials
1. Brinell hardness HB
The Brinell hardness is obtained by pressing the hardened steel ball indenter into the surface of the material to be tested with a certain load P, and then unloading after a certain period of time, according to the indentation area A of the diameter d of the press-in.
HB is mainly used for steel, cast iron, non-ferrous metals and some special non-metallic materials in annealed state. It is suitable for metal materials with HB<450.
For example, the Brinell hardness is recorded as 200HB10/1000/30. This means that the steel ball having a diameter of 10 mm has a hardness of 200 measured after being held for 30 s under the action of 1000 kgf.
2. Rockwell hardness HR
Rockwell hardness is measured by pressing the diamond cone indenter into the surface of the material with a specified pressure and measuring the indentation depth h:
HR = (K-h) / 0.002
According to the size of the indenter and the load, the Rockwell hardness is divided into three types: HRC, HRB, and HRA.
Rockwell hardness can be read directly, easy to operate, and widely used to measure metal materials with low hardness and high hardness. However, the Rockwell hardness load is large and the scale is not uniform. It is not suitable for measuring hard and brittle thin layers. Thin layer materials are generally measured using Vickers hardness.
3. Vickers hardness HV
The Vickers hardness is determined by a diamond tetrahedral diamond indenter with two pairs of opposite faces at an angle of 136°. It is calculated by measuring the diagonal length of the indented portion of the indenter.
HV=1.8544P/d2
The three hardness methods of Brinell, Rockwell and Vickers have a large load and a large area, so they are generally suitable for the determination of the hardness values of various metal materials.
Moreover, since the indenter load is large and the area is large, generally, the average hardness value of the microstructure of the metal material can be measured, and it is not suitable for measuring the hardness of the material in the local region.
The Brinell hardness is obtained by pressing the hardened steel ball indenter into the surface of the material to be tested with a certain load P, and then unloading after a certain period of time, according to the indentation area A of the diameter d of the press-in.
HB is mainly used for steel, cast iron, non-ferrous metals and some special non-metallic materials in annealed state. It is suitable for metal materials with HB<450.
For example, the Brinell hardness is recorded as 200HB10/1000/30. This means that the steel ball having a diameter of 10 mm has a hardness of 200 measured after being held for 30 s under the action of 1000 kgf.
2. Rockwell hardness HR
Rockwell hardness is measured by pressing the diamond cone indenter into the surface of the material with a specified pressure and measuring the indentation depth h:
HR = (K-h) / 0.002
According to the size of the indenter and the load, the Rockwell hardness is divided into three types: HRC, HRB, and HRA.
Rockwell hardness can be read directly, easy to operate, and widely used to measure metal materials with low hardness and high hardness. However, the Rockwell hardness load is large and the scale is not uniform. It is not suitable for measuring hard and brittle thin layers. Thin layer materials are generally measured using Vickers hardness.
3. Vickers hardness HV
The Vickers hardness is determined by a diamond tetrahedral diamond indenter with two pairs of opposite faces at an angle of 136°. It is calculated by measuring the diagonal length of the indented portion of the indenter.
HV=1.8544P/d2
The three hardness methods of Brinell, Rockwell and Vickers have a large load and a large area, so they are generally suitable for the determination of the hardness values of various metal materials.
Moreover, since the indenter load is large and the area is large, generally, the average hardness value of the microstructure of the metal material can be measured, and it is not suitable for measuring the hardness of the material in the local region.
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