Hardness indicates the ability of a material to resist the pressing of a hard object into its surface. It is one of the important performance indicators of metallic materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indexes are Brinell hardness, Rockwell hardness and Vickers hardness.

1. Brinell hardness (HB)

A certain size (usually 3000kg) of a hardened steel ball of a certain size (typically 10mm in diameter) is pressed into the surface of the material for a period of time. After the load is removed, the ratio of the load to the area of ​​the indentation is the Brinell hardness value ( HB), in kilograms force / mm ² (N / mm ² ).

2. Rockwell hardness (HR)

When HB>450 or the sample is too small, the Brinell hardness test cannot be used instead of the Rockwell hardness measurement. It uses a diamond cone with a apex angle of 120° or a steel ball with a diameter of 1.59 and 3.18 mm, and is pressed into the surface of the material to be tested under a certain load, and the hardness of the material is determined from the depth of the indentation. According to the hardness of the test material, it is represented by three different scales:

HRA: It is a hardness obtained by using a 60kg load and a diamond cone indenter for materials with extremely high hardness (such as cemented carbide).

HRB: It is a hardened steel ball with a load of 100kg and a diameter of 1.58mm. The hardness is used for materials with lower hardness (such as annealed steel, cast iron, etc.).

HRC: is the hardness obtained by using a 150kg load and a diamond cone indenter for materials with high hardness (such as hardened steel).

3. Vickers hardness (HV)

The surface of the material is pressed into the surface of the material with a load of 120 kg or less and a diamond square cone presser with a apex angle of 136°. The surface area of ​​the material indentation pit is divided by the load value, which is the Vickers hardness value (HV).

As can be seen from the above, Vickers hardness is one of the surface hardnesses. It has a conversion relationship with other hardness units.

Hardness refers to the surface hardness, and there is no hardness requirement inside the material. Only mechanical properties (tensile strength, yield strength and impact toughness).