Brinell Hardness Test

Brinell hardness test is widely used for testing hardness of metals and nonmetals of low to medium hardness. It is named after the Swedish engineer who developed it in the 19th century. In the test, a hardened steel (or cemented carbide) ball of 10-mm diameter is pressed into the surface of a specimen using a load of 500, 1500, or 3000 kg. The amount is then divided into the indentation area to obtain the Brinell Hardness Number (BHN).

Brinell hardness equation form
Brinell Hardness equation
Where,
‘BHN’ is Brinell Hardness Number,
‘P’ is applied load in kg,
‘D’ is diameter of ball in mm,
‘d’ is diameter of indentation in mm,
‘t’ is depth of the impression in mm,

Brinell hardness testing method

Figure 1: Brinell hardness testing method

Brinell hardness number (BHN) has units of kg/mm2, but the units are usually omitted in expressing the number. For harder materials (above 500 BHN), the cemented carbide ball is used because the steel ball experiences elastic deformation that compromises the accuracy of the reading. Also, higher loads (1500 and 3000 kg) are usually used for harder materials. Because of differences in BHN results under different loads, it is considered a good practice to indicate the load used in the test when reporting BHN readings.

 
Advantages and disadvantages of Brinell hardness test:

  • Large indentation averages out local heterogeneities of the microstructure.
  • Different loads are used to cover a broad range of the hardness of commercial metals.
  • Brinell hardness test is less influenced by surface scratches and roughness than other hardness tests.
  • The test has limitations on small specimens or in critically stressed parts where indentation could be a possible site of failure.
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