# Brinell number

A measure of the hardness of metals, defined in 1910 by Johann A. Brinell, a Swedish
engineer. Abbr, Bhn.

A known load is applied to a hardened steel ball resting on a
flat surface of the metal to be tested; the diameter of the dent made is measured. The
Brinell number indicating the metal's hardness is then the load on the ball in kilograms
divided by the spherical surface area of the dent in sq. millimeters. In practice workers
have standardized on a certain ball size (10 mm in diameter) and loads. For a 10-mm ball,
the Brinell number is:

A load of 3,000 kilograms is used for hard metals, 1,500 kg for those of intermediate
hardness, and 500 kg for soft metals. For very soft metals, 100 kg is sometimes used. The
length of time the load is applied also influences the size of the dent; at least 10
seconds is necessary for iron and steel and at least 30 for other metals.

Around 400 Brinell, hardened steel balls become noticeably flattened under 3,000 kg,
and workers departed from Brinell's specifications by substituting, for example, tungsten
carbide balls.

## sources

**Brinell Hardness Numeral (abbreviated B. h. n.).** — Ratio of pressure on a sphere used to indent the material to be tested to the area of the spherical indentation produced. The standard sphere used is a 10mm
diameter hardened steel ball. The pressures used are 3000 kg for steel and 500 kg for softer metals, and the time of application of pressure is 30 seconds. Values shown in the tables are based on spherical areas
computed in the main from measurements of the diameters of the spherical indentations, by the following formula:

$$\text{B}\text{.h}\text{.n}\text{.}=P+\pi tD=P+\pi D\left(\frac{D}{2}-\sqrt{\frac{{D}^{2}}{4}-\frac{{d}^{2}}{4}}\right)$$
*P* = pressure in kg, *t* = depth of indentation, *D* = diameter of ball, and
*d* = diameter of indentation, — all
lengths being expressed in mm. Brinell hardness values have a direct relation to tensile strength, and hardness
determinations may be used to define tensile strengths by employing the proper conversion factor for the material
under consideration.

Frederick E. Fowle.

*Smithsonian Physical Tables,* 7th revised edition, reprint.

Smithsonian Miscellaneous collections, vol. **71**, no. 1.

Washington, DC: Smithsonian Institution, 1921.

Page 74.

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Last revised: 22 August 2013.