Brinell hardness test
Brinell
Hardness Test :- The Brinell hardness test 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.