This is part 3 of David Pye's blog series on hardness testing.
Categorization of Hardness Test Methods
Microhardness test methods are generally conducted with a load application beginning at 10 grams up to 1,000 grams. Once again, the principle of the test is load divided by area.
Brinell Hardness Testing
The Brinell test method can be used on forgings, castings, hot-rolled bar, cold-rolled bar, low-alloy steels and high-alloy steels. Dr. J.A Brinell of Sweden primarily developed the Brinell hardness-test procedure.
Principle of Indentation and Calculation Method for Brinell Hardness
The Brinell test is a simple indentation test. As with any metallurgical hardness testing method, the steel surface must be prepared in an appropriate manner. This will necessitate the grinding of the surface to go below any surface decarburization and surface oxidation. The golden rule with hardness testing is to prepare the steel surface to get into virgin steel; that is, steel that is not influenced by surface oxidation and decarburization.
The method of Brinell testing consists of forcing a hardened steel ball, under a predetermined pressure, into the test material. The Brinell hardness number is obtained by dividing the pressure in kilograms spherical surface of the impression, which is expressed in square millimeters.
The test machine will be fitted with a 10-mm-diameter tungsten steel ball as the indenter. The load selection is made based on the thickness of the steel sample being tested. The load is either 500 kg or 3,000 kg. Therefore, do not use the Brinell method of hardness testing for thin-gauge materials. A false reading will be obtained.