What Does Brinell Hardness Mean?
Brinell hardness indicates the ability of a metal to resist permanent indentation deformation. The hardness shows the material's resistance to penetration by a spherical indenter under standardized conditions. Since Brinell hardness is a mechanical property, it also relates to the material's resistance to wear as well as plastic or permanent deformation, and the material's ability to indent or abrade another material.
Brinell hardness is named after Johan A. Brinell, a Swedish engineer.
Corrosionpedia Explains Brinell Hardness
The Brinell hardness test is used to determine hardness and is done by forcing a hard steel or carbide ball indenter of a specified diameter onto the test metal surface under a specified load. This is followed by measuring the diameter of the impression made on the metal surface. The hardness is expressed as Brinell hardness number, and is obtained by dividing the load in kilograms, by the surface area of the indention in square millimeters.
Brinell numbers for commonly used metals range from HB 15 to 750. Typical values include:
- Pure aluminum = 15
- Mild steel = 120
- Hardened tool steel = 650–700
- Hard chromium plate = 1000
- Diamond = 8000
The hardness of a material is dependent on treatment that the material has been subjected to. It is much easier to test hardness through simple and non-destructive tests as compared to bending, torsion or tensile tests.
Brinell hardness is more important in materials with heterogeneous structures, and in particular those used in heavy trucks and bulldozers, forgings and castings, engine blocks and heads, rear-end housings, springs as well as various large and coarse surface parts. This is due to the fact that it is easiest and most reliable to determine hardness for these bulk or macro-hardness materials.
Metal hardness is one of the factors that contributes to sulfide stress cracking (SSC), and harder metals are more susceptible when used in sour or corrosive environments. International standards have therefore put a limit of 200HBW as the maximum allowable Brinell hardness of weld joints. This is particularly observed when the materials are used in the oil and gas industry in corrosive environments.
Brinell hardness provides useful information which may correlate to tensile strength, ductility, wear resistance and other physical characteristics of metallic materials and is thus used in material selection and quality control.