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Brinell Hardness Test On Metals

 


The Brinell Hardness Test is the most commonly adopted test for hardness of iron and steel. In this test, a Hardened ball is impressed on a flat polished surface of the sample under a load. The load is maintained and diameter of the impression made on the test piece is subsequently measured by means of microscope the order of  accuracy being +_ 0.1 mm. The Brinell Hardness number is obtained from the equation,

BHN =  Load on Ball / area of indentation .

         = 2P / 3.14* D (D-(D^2 - d^2)^(1/2) ) 

where BHN = Brinell Hardness Number,

                 P = Load applied in kg,

                 D = Diameter of ball in mm.

                 d = Diameter of ball impression in mm. 

The harder the metal, the higher its Brinell number will be. In practice, hardness number corresponding to a particular indentation diameter is read off from a table in which load, indenter size, indentation sizes, and hardness numbers are correlated.

The Brinell test, irrespective of some limitations, does give a linear scale of hardness and is particularly useful for design work. 


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