The Brinell hardness testing method consists of indenting the test
material with a 10 mm diameter hardened steel or carbide ball subjected
to a load of 3000 kg. For softer materials the load can be reduced to
1500 kg or 500 kg to avoid excessive indentation. The full load is
normally applied for 10 to 15 seconds in the case of iron and steel and
for at least 30 seconds in the case of other metals. The diameter of
the indentation left in the test material is measured with a low
powered microscope. The Brinell harness number is calculated by
dividing the load applied by the surface area of the indentation.
The diameter of the impression is the average of two readings at right
angles and the use of a Brinell hardness number table can simplify the
determination of the Brinell hardness. A well structured Brinell
hardness number reveals the test conditions, and looks like this, "75
HB 10/500/30" which means that a Brinell Hardness of 75 was obtained
using a 10mm diameter hardened steel with a 500 kilogram load applied
for a period of 30 seconds. On tests of extremely hard metals a
tungsten carbide ball is substituted for the steel ball. Compared to
the other hardness test methods, the Brinell ball makes the deepest and
widest indentation, so the test averages the hardness over a wider
amount of material, which will more accurately account for multiple
grain structures and any irregularities in the uniformity of the
material. This method is the best for achieving the bulk or
macro-hardness of a material, particularly those materials with
heterogeneous structures.
