TheBrinell hardness test (pronounced /brəˈnɛl/) measures the indentation hardness of materials. It determines hardness through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science. The hardness scale is expressed in terms of a Brinell hardness value, sometimes referred to as the Brinell hardness number but formally expressed as HBW (Hardness Brinell Wolfram – Wolfram being an alternative name for the tungsten carbide ball indenter used during the test).
The test was named after Johan August Brinell (1849-1925) who developed the method at the end of the 19th century.
Premiered bySwedishengineerJohan August Brinell at the 1900 Paris Exposition, it was the first widely used and standardised hardness test inengineering andmetallurgy. The large size of indentation and thus possible damage to test-pieces limits its usefulness. However, it also had the useful feature that the hardness value divided by two gave the approximateUTS inksi for steels. This feature contributed to its early adoption over competing hardness tests.
The test uses a Tungsten Carbide ball indenter and a precisely controlled force, the ratio of ball size to test force being a function of the material being tested. Most commonly the test is used for ferrous metals and uses a 10mm ball and a 3000 Kgf test force, although it can go as low as 1mm and 1 Kgf (HBW 1/1).
Although the maximum test force is 3000 kgf, there are hand-pumped, hydraulic, portable Brinell testers less than 58 cm / 23 inches in height that can develop this force and hold it for sufficient time to perform a Brinell test. One such is pictured.
As there are numerous situations where the failure of a metal component due to it being of the wrong hardness could have catastrophic consequences, Brinell testing is governed by International Standards Organisation (ISO) and American Society for Testing and Materials (ASTM) rules. Brinell testing machines must be calibrated regularly and in many industries daily checks are carried out using calibration blocks of a precise, known hardness, against which the machine measurements of such blocks are compared. A block of this type is pictured.
The advantage of the Brinell test over other measurement systems is that the indentation diameters usually range between 2.4mm and 6mm. This means that the indentation is unaffected by the grain structure of the metal under test, so Brinell testing is especially useful in testing materials such as rough castings with coarse grains. However, measurement of the indentation is normally carried out by a technician using a low-powered microscope, and it can be difficult to judge exactly where an indentation begins and ends. Three experienced technicians could obtain three slightly different readings using the same microscope - and an error of 0.2mm can equal 20 hardness points. The problem of operator interpretation errors was overcome in the 1980s in a collaboration between Birmingham University and the British company Foundrax Engineering Products. They developed a system which harnessed an optical microscope to a computer and which was able to measure indentations across multiple axes in under a second. Automatic measurement systems are now used in many production environments where accuracy is critical.
Brinell hardness is sometimes quoted in megapascals; the Brinell hardness value (expressed as HBW (see above)) is multiplied by the acceleration due to gravity, 9.80665 m/s2, to convert it to megapascals.
The Brinell hardness value can be correlated with theultimate tensile strength (UTS), although the relationship is dependent on the material, and therefore determined empirically. The relationship is based on Meyer's index (n) fromMeyer's law. If Meyer's index is less than 2.2 then the ratio of UTS to HBW is 0.36. If Meyer's index is greater than 2.2, then the ratio increases.[1]
The Brinell hardness is designated by the most commonly used test standards (ASTM E10-14[2] and ISO 6506–1:2005) asHBW (H from hardness,B from brinell andW from the material of the indenter, tungsten (wolfram) carbide). In former standards HB or HBS were used to refer to measurements made with steel indenters.
HBW is calculated in both standards using the SI units as
where:
When quoting a Brinell hardness value (HBW), the conditions of the test used to obtain the number must be specified. The standard format for specifying tests can be seen in the example "HBW 10/3000". "HBW" means that a tungsten carbide (from the chemical symbol for tungsten or from the Spanish/Swedish/German name for tungsten, "Wolfram") ball indenter was used, as opposed to "HBS", which (formerly) meant a hardened steel ball (these are no longer in use). The "10" is the ball diameter in millimeters. The "3000" is the force in kilograms force.
The hardness may also be shown as XXX HB YYD2. The XXX is the force to apply (in kgf) on a material of type YY (5 for aluminum alloys, 10 for copper alloys, 30 for steels). Thus a typical steel hardness could be written: 250 HB 30D2. It could be a maximum or a minimum.
| Hardness symbol | Diameter of Indenter mm | F/D2 | Test force N/kgf |
|---|---|---|---|
| HBW 10/3000 | 10 | 30 | 29420(3000) |
| HBW 10/1500 | 10 | 15 | 14710(1500) |
| HBW 10/1000 | 10 | 10 | 9807(1000) |
| Material | Hardness |
|---|---|
| Softwood (e.g.,pine) | 1.6 HBS 10/100 |
| Hardwood | 2.6–7.0 HBS 10/100 |
| Lead | 5.0 HB (pure lead; alloyed lead typically can range from 5.0 HB to values in excess of 22.0 HB) |
| PureAluminium | 15 HB |
| Copper | 35 HB |
| Hardened AW-6060Aluminium | 75 HB |
| Mild steel | 120 HB |
| 18–8 (304)stainless steel annealed | 200 HB[3] |
| Quenched and tempered steel wear plate | 400-700 HB |
| Hardenedtool steel | 600–900 HB (HBW 10/3000) |
| Glass | 1550 HB |
| Rhenium diboride | 4600 HB |
| Note: Standard test conditions unless otherwise stated | |
