Brinell hardness test simply explained (introduction to hardness testing)

The hardness of a material describes its resistance to indentation by a standardized object. In many applications where components come into contact, both high strength and wear resistance are critical. Hardness tests follow the principle of pressing an indenter into the material with a defined force. The most common methods are the Brinell, Vickers, and Rockwell tests. This text focuses on the Brinell hardness test.

In the Brinell method, a carbide ball (e.g., tungsten carbide) serves as the indenter. The ball is pressed into the surface with increasing force until the maximum load is reached, which is then maintained for 10 to 25 seconds to ensure reproducibility. The indentation is examined under a microscope, and two perpendicular diameters are measured and averaged to determine the hardness.

The Brinell hardness value (HBW) is the ratio of the applied force to the indentation surface. Force is measured in newtons, and diameters are in millimeters. Accurate measurements require indentations to be sufficiently far from edges and each other. The diameter of the impression should be between 24% and 60% of the indenter diameter.

To ensure comparable hardness values using different indenter diameters, the load factor, defined as the ratio of force to the square of the indenter diameter, must be constant. Load factors are standardized, influencing the choice of test force.

Indenter balls ranging from 1 to 10 mm in diameter are used depending on material thickness and microstructure. Larger balls are better for coarse-grained materials like cast iron, as they provide representative hardness values for the overall structure.

Brinell hardness is expressed without units as a combination of hardness value, ball diameter, and test force. The abbreviation "HBW" indicates the use of a tungsten carbide indenter. For unalloyed and low-alloy steels, there is an empirical correlation between HBW and tensile strength.

The Brinell test is unsuitable for very hard materials or thin layers due to insufficient indentation depth. Alternative methods like the Vickers test provide more reliable results in such cases.

00:00 What is indentation hardness? Definition!
02:10 How is the Brinell hardness test carried out?
03:42 How is Brinell hardness calculated?
05:11 Minimum edge and indentation distance, and sample thickness
06:56 Load factor
09:40 Test balls (spherical indenters)
10:48 Standard-compliant specification of Brinell hardness
11:48 Disadvantage of the Brinell hardness test