Comparison of hardness testing methods: Brinell, Vickers, Knoop and Rockwell
Not every hardness testing method is suitable for every testing task.
The material, component geometry, surface, test force and specific test task determine whether Brinell, Vickers, Rockwell or Button This overview helps in the initial classification of the most important hardness testing methods and shows when each method is appropriately used.
the essentials in brief
- The most important hardness testing methods are Brinell, Vickers, Knoop and Rockwell.
- Brinell is often suitable for softer to medium-hard materials and coarser structures.
- Rockwell is a fast method and is preferred for serial testing with high sample throughput employed.
- Vickers is very versatile and is also used for small components, thin layers and hardness gradients employed.
- Button is particularly suitable for very thin layers, brittle materials and applications where only a shallow penetration depth is permissible.
- The choice of method depends on the material, component geometry, testing standard, surface, and testing task.
Click here to access the detailed pages of the 4 procedures.
Why are there different hardness testing methods?
Materials react differently to mechanical stress. A coarse cast structure places different demands on hardness testing than a thin coating, a hardened component, or a small weld seam area. Therefore, various hardness testing methods exist, employing different test specimens, test forces, and evaluation methods.
Brinell, Vickers, and Rockwell all follow the same basic principle: A defined test specimen is pressed into the surface with a specified force. The difference lies in how the hardness value is determined. With Brinell and Vickers, the lasting indentation is measured optically. With Rockwell, the indentation depth is evaluated.
Hardness values obtained from different methods are therefore not automatically directly comparable. For a reliable decision, the method must be suitable for the testing task.
The 4 most important hardness testing methods at a glance
| Process | Measuring principle | Typical application | Strength of the procedure |
|---|---|---|---|
| Brinell | Optical measurement of the indentation diameter | Cast materials, soft to medium-hard metals, coarser microstructures | Well suited for larger test impressions and less homogeneous materials. |
| Rockwell | Measurement of penetration depth | Serial inspections, rapid incoming goods and production controls | Fast result determination without optical impression measurement |
| Vickers | Optical measurement of the impression diagonal | Small components, thin layers, hardness gradients, wide material ranges | Highly versatile and precisely positionable |
| Button | Optical measurement of the long indentation diagonal | Thin layers, brittle materials, ceramics, marginal zones and shallow penetration depths | 3x longer diagonal (vs. HV) – precise measurement of the smallest impressions |
Brinell, Vickers or Rockwell: Which hardness testing method is appropriate when?
The selection of the appropriate hardness testing method should not be based solely on familiarity or available equipment. The decisive factor is which hardness value is meaningful for the specific testing task and which standard or customer requirement must be met.
| Test task | Suitable hardness testing method |
|---|---|
| Cast materials and coarse microstructures | Brinell |
| Soft to medium-hard metals | Brinell or Rockwell, depending on the application |
| Very hard materials | Vickers or Rockwell |
| Small components and thin layers | Vickers |
| Hardness profiles and hardness depths | Vickers |
| Rapid serial testing | Rockwell |
| Different materials and processes | Universal hardness tester |
In short: Brinell hardness test
The Brinell hardness test involves a A hard metal ball was pressed into the material with a defined test force. The diameter of the permanent impression is then measured optically. The procedure is described according to ISO 6506-1 for metallic materials.
Brinell is particularly suitable for materials where a larger indentation is desirable. These include, for example, cast materials, non-ferrous metals, and softer to medium-hard metals. The method is generally less suitable for very hard materials or small test areas.
→ Go to the Brinell details page
In short: Vickers hardness test
The Vickers hardness test involves a pyramid-shaped diamond indenter It is used. After loading, the diagonals of the indentation are measured optically. ISO 6507-1 describes the Vickers hardness test for metallic materials in various test force ranges.
Vickers is one of the most versatile hardness testing methods. It is used in small components, thin areas, coatings and hardness gradients The optical evaluation allows for precise positioning of the test impression, but requires a suitable sample surface.
→ Go to the Vickers details page
In short: Rockwell hardness test
The Rockwell hardness test is The hardness is determined by the penetration depth. This makes the process particularly fast because no optical measurement of the indentation is required. ISO 6508-1 describes Rockwell and Super-Rockwell tests for various scales of metallic materials.
Rockwell is frequently used for recurring tests and serial applications. The HRC scale for hard materials is particularly well-known. A suitable test surface and stable support for the test piece are prerequisites.
In short: Knoop stress test
The Knoop hardness test uses an asymmetrical diamond indenter that produces an elongated indentation. The hardness is determined by optically measuring the long diagonal of the indentation. The Knoop hardness test is described in the DIN EN ISO 4545 series of standards.
Knoop is primarily used, when the penetration depth should be as small as possible. This method is particularly suitable for thin films, coatings, ceramics, hard metals, and microhardness testing of surface areas and metallographic specimens. The shallow penetration depth reduces the influence of the substrate material.
→ Go to the Knoop details page
What role do standards play in the choice of procedure?
Standards define how a hardness test is performed and evaluated. They specify, among other things, the test specimen, test force, test procedure, minimum distances, evaluation, and reporting of results.
The following series of standards are particularly relevant for the most important hardness testing procedures:
- DIN EN ISO 6506 for Brinell
- DIN EN ISO 6507 for Vickers
- DIN EN ISO 6508 for Rockwell
The standard should be checked early, especially if measurement results are used for test reports, customer requirements, audits or supplier verifications.
Common mistakes when selecting the hardness testing method
Errors often occur when a procedure is selected without adequately considering the material, test area, and test objective. Typical examples include:
- A procedure is chosen simply because it is already known within the company.
- Rockwell is used even though precise positioning of the test impression is required.
- Brinell is used for test areas that are too small or for materials that are too hard.
- Vickers is used without adequate sample preparation.
- Hardness values from different methods are directly compared.
- Standards or customer specifications are only checked after the device selection.
A thorough pre-selection prevents later measurement uncertainties, unnecessary re-checks and incorrect assessments.
Decision aid: Which hardness tester is suitable for the procedure?
The fitting Hardness Tester results from Procedure, testing volume and documentation requirements. For simple, individual tests, a manual device may suffice. For recurring tests, numerous measuring points, or processes requiring documentation, semi-automatic or fully automatic systems are often more practical.
With changing materials or multiple testing methods, a Universal hardness tester a suitable solution. It is important that the test force range, indenter, specimen holder, software, and standard requirements are appropriate for the application.
Frequently asked questions about hardness testing methods
What hardness testing methods are available?
The most important hardness testing methods in industrial materials testing are Brinell, Vickers, Rockwell, and Knoop. Depending on the application, other methods may also be relevant.
Which hardness testing method is the right one?
This depends on the material, component geometry, surface finish, testing standard, and test objective. Brinell is frequently used for cast materials, Vickers for hardness profiles, Rockwell for rapid serial testing, and Knoop for thin films or brittle materials.
What is the difference between Brinell, Vickers, Knoop and Rockwell?
Brinell, Vickers, Knoop and Rockwell differ primarily in the test specimen, the evaluation method and the typical area of application.
- Brinell It uses a hard metal ball. The resulting indentation is measured optically.
- Vickers It uses a pyramid-shaped diamond indenter. The diagonals of the indentation are optically evaluated.
- Button It uses an asymmetrical diamond indenter. The long indentation diagonal is optically evaluated.
- Rockwell The hardness is determined by the penetration depth. This makes the process particularly fast.
Can hardness values from different methods be compared?
Hardness values from different testing methods are not automatically directly comparable. Reclassifications are only meaningful under suitable conditions and with regard to the material, standard, and testing method.
Which method is suitable for hardness gradients?
Vickers is frequently used for hardness gradients and hardening depths, as small test indentations can be positioned precisely and evaluated optically.
