The Brinell Hardness Test, commonly used for metallic materials, determines hardness by applying a known load (3000, 1500, or 500 kgf) to the surface of the test specimen via a hardened steel or diamond ball of prescribed size (10 mm in diameter).
The size of the permanent impression on the specimen surface is converted into a Brinell Hardness Number (HB) according to the formula:
A measurement is considered valid if the diameter of the permanent impression is in the range of 2.5 to 4.75 mm (slightly exceeding this limit is tolerated). As a result, the 3000 kgf load yields HB measures between 160 and 600; the 1500 kgf load, HB 80 to 300; and the 500 kgf load, HB 26 to 100. Smaller loads (e.g., 250, 125, 100 kgf) can be used for softer metals.
According to the ASTM (American Society for Testing and Materials) Standard E10-66, a steel ball may be used up to HB 450, and carbide may be used up to HB 630. It is NOT recommended to use the Brinell test on materials harder than HB 630. These limits were set to avoid errors introduced by the deformation of the ball indenter itself.