Brinell hardness test

Brinell hardness test dome impression

Origin of the Brinell hardness test

The origin of modern, industrial hardness testing was founded by the Swedish engineer Johan August Brinell. He developed the hardness testing method named after him, which was presented at the World Exhibition in Paris in 1900. The method is standardized according to DIN EN ISO 6506-1 – 6506-4. The materials listed below can be named as suitable for the Brinell test. This hardness testing method is particularly suitable for soft and medium-hard materials and for materials with an inhomogeneous or porous structure. (Cavities in cast iron).

• unalloyed Cast iron, low-alloy steel / Structural steel
• Aluminium alloys, non-ferrous metals: brass, copper…
• inhomogeneous structures (here almost all other metal hardness testing methods fail)
• sintered metal (unsintered)
• wood (ISO 3350)

Brief description of the Brinell hardness test

In this hardness testing method, a hard metal ball is pressed onto a test piece surface with a defined test force (F) and penetrates to different depths (depending on the hardness). The resulting ball impression cap is optically measured in its diameter. The hardness value can be determined using the formula below. HBW (Härte Brinell Wolefin carbide ball).

After a loading time of 10 to 15 seconds (steel and iron) or 10 to 180 seconds (non-ferrous metals and their alloys), the test force is reduced. Adhering to the loading time is important in order to take the flow behavior of the material into account. Every material has a flow behavior (soft materials have a higher flow behavior): Over time, the indenter can penetrate deeper into the material until the penetration process comes to a standstill or the material is no longer compacted.

The surface of the impression is determined by optically measuring the resulting impression diameter in the workpiece. The diameter d to be determined is calculated from the average of two measurements rotated by 90 degrees (d1+d2)/2. If the impression is not circular (oval), the diameter required to calculate the hardness is averaged from the largest d1 and smallest diameter d2.
Previously, a steel ball was used as an indenter. Since 2006, a hard metal ball (tungsten carbide) has been required. Depending on the homogeneity, material thickness and hardness, balls with different diameters are used: Ø 10 | 5 | 2,5 | 2 | 1 | 0,625 mm. Which test method (combination of ball diameter and test force) must be used depends on the different required load level (see table below). For steel, a degree of stress of HB30 (force ratio in relation to the sphere surface – formula F/D²) and for softer non-ferrous metals a load level of HB10 / HB5 / HB2,5 / HB1 should be used.

The load level is calculated from the force divided by the square of the ball diameter (F / D²) and enables the correct choice of test load or test method. If too high a load level (relative to the hardness of the material) is selected, the Brinell ball would be pressed too deeply into the material - an evaluation is no longer possible or would be incorrect (no hole should be "punched" but a dome impression should be created)

At the time the Brinell hardness test was developed, the test force was still given in kg or kp. In order to ensure that the hardness values, conversion tables and material specifications were valid, the test forces were retained - the test methods retained their names, which are based on the test force in kg (kgf). The load forces given in the table (after the slash) give the test forces in kp. Since the conversion of the test forces into Newtons results in odd values, the metrologically correct specification in Newtons is omitted in this table.