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hardness of steel

January 11, 2020

Hardness refers to 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 metal materials. Generally, the higher the hardness, the better the abrasion resistance. Common hardness indicators are Brinell hardness, Rockwell hardness, and Vickers hardness.

Brinell hardness (HB)

A certain load (generally 3000kg) is used to press a hardened steel ball of a certain size (generally 10mm in diameter) into the surface of the material for a period of time. After unloading, the ratio of the load to the indentation area is the Brinell hardness value ( HB).

Rockwell hardness (HR)

When HB> 450 or the sample is too small, the Brinell hardness test cannot be adopted and the Rockwell hardness measurement is used instead. It is a diamond cone with a vertex angle of 120 ° or a steel ball with a diameter of 1.59 / 3.18mm. It is pressed into the surface of the material 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 is expressed in three different scales:

HRA: It is a hardness obtained by using a 60kg load and a diamond cone indenter. It is used for extremely hard materials (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 determined for materials with lower hardness (such as annealed steel and cast iron).

HRC: It is a hardness obtained with a 150kg load and a diamond cone indenter. It is used for very hard materials (such as quenched steel).

Vickers hardness (HV)

The diamond square cone indenter with a load within 120kg and a vertex angle of 136 ° is pressed into the surface of the material. The surface area of the material indentation pit is divided by the load value to obtain the Vickers hardness value (HV).