Special steels are very important for accurate hardness testing due to their excellent mechanical properties and wide range of applications (such as cutting tools, molds, aerospace components, etc.). When measuring the hardness of parts, everyone is familiar with three commonly used hardness expressions, namely Brinell hardness (HB), Rockwell hardness (HR) and Vickers hardness (HV). However, for the first two hardnesses, you sometimes see other ways of writing, such as Brinell hardness has HBS and HBW, Rockwell hardness has HRA, HRB, HRC, etc. What are the differences between these different writing methods? Different hardness test methods are based on different principles and applicable conditions. What are the specific differences? With the above questions, find the answers from the following article.
What is the testing principle of Brinell hardness?
The measurement principle is to use a hardened steel ball or carbide ball with a diameter of D to press into the surface of the material with the corresponding test force F. After maintaining the test force for a specified time, the test force is removed and the average diameter d of the residual indentation is measured with a reading microscope. The hardness value is expressed by the pressure on the unit surface area of the spherical crown indentation. The actual measurement can be obtained by measuring the d value and then looking up the table to obtain the hardness value.
What is the difference between Brinell hardness HBS and HBW?
The difference between HBS and HBW lies in the different ball head materials used. HBS represents the Brinell hardness value measured by a hardened steel ball indenter, which is often used to measure materials with a hardness value less than 450HBS. HBW represents the Brinell hardness value measured by a carbide indenter, which is used to measure materials with a hardness value of 450~650HBW. For materials of different hardness, a suitable ball head should be selected, otherwise the measurement result may be inaccurate due to the deformation of the indenter ball.
However, in the latest standards, it has been stipulated that only carbide ball indenters are allowed, and the Brinell hardness symbol is HBW. Both HB and HBS are outdated.
Is there a relationship between Brinell hardness and tensile strength?
There is a certain relationship between Brinell hardness and tensile strength, so the strength value of the material can be estimated based on its value. If you need a specific relationship comparison, please contact us.
What are the advantages and disadvantages of Brinell hardness measurement?
Brinell hardness measurement can be used to measure materials with large or uneven structures (such as cast iron) because of the large residual indentation area.
Due to the large indentation of Brinell hardness measurement, it is not suitable for measuring the hardness of finished products or thin metal sheets.
Which materials are suitable for Brinell hardness measurement?
Brinell hardness is mainly used for hardness measurement of raw materials or semi-finished products, such as cast iron, non-ferrous metals (non-ferrous metals), and steel with low hardness (such as annealed, normalized, and quenched & tempered steel).
What is the testing principle of Rockwell hardness?
Rockwell hardness measurement uses a diamond cone or a hardened steel ball as an indenter. Under the action of the test pressure F, the indenter is pressed into the material surface. After maintaining the specified time, the main test force is removed, the initial test force is maintained, and the hardness value is calculated using the residual indentation depth increment. During actual measurement, the Rockwell hardness value can be directly read from the dial of the test machine.
The difference between HRA, HRB and HRC lies in the difference in the indenter and test force used. For details, please refer to the table below.
| Hardness symbol | Indenter Type | Total test force F/N（kgf） | Hardness range | Application Examples |
| HRA | 120° Diamond Cone | 588.4(60) | 20-88 | Cemented carbide, carbide, shallow surface hardened steel, etc. |
| HRB | Φ1.588mm hardened steel ball | 980.7(100) | 20-100 | Annealed steel, normalized steel, aluminum alloy, copper alloy, cast iron |
| HRC | 120° Diamond Cone | 1 471(150) | 20-70 | Quenched steel, quenched and tempered steel, deep case hardened steel |
In fact, the Rockwell hardness scale is not only divided into A, B, and C, but also from D to K. There are many other scales, which can be selected according to different material types, hardness, and thickness. You can refer to the standards for details.
What are the advantages and disadvantages of Rockwell hardness measurement?
Rockwell hardness measurement has the advantages of being quick, simple, with small indentation, and a large hardness measurement range. It can be used to measure finished products or thinner workpieces. However, the data accuracy, stability, and repeatability are not as good as Brinell hardness. It is usually necessary to test three points on different parts of the sample surface, and take the average value as the Rockwell hardness value of the material. To ensure the accuracy of hardness measurement, Rockwell hardness is generally not suitable for measuring materials with uneven structure.
What is the testing principle of Vickers hardness?
- Principle: Use a diamond regular tetrahedron indenter to calculate the hardness based on the diagonal length of the indentation, with a wide load adjustment range.
- Applicable scenarios: Suitable for testing extremely thin materials (such as nitriding layers, coatings) or small areas, with high accuracy and can test high-hardness materials.
- Limitations: Complex operation, requires a microscope to measure the indentation, and takes a long time
Which hardness testing methods are commonly used in special steels?
We will conduct hardness tests on special steels according to customer requirements, among which Rockwell hardness (HRC) and Brinell hardness (HBW) are often used.For example, for low alloy steels such as 4140, 4340, and 34CrNiMo6, when it comes to quenching and tempering heat treatment, customers generally give hardness requirements of Rockwell hardness 28-34HRC and Brinell hardness 280-320HBW. After the heat treatment, we will conduct corresponding tests according to the requirements.
Can Rockwell hardness and Brinell hardness be converted to each other?
Rockwell hardness and Brinell hardness can be converted to each other. For example, the commonly used Rockwell hardness of 28-32HRC is converted to Brinell hardness between 269-302HBW. If other numerical conversions are required, please refer to the standard or contact us for it.
Summary
The hardness test methods for special steels each have their own scientific principles and application boundaries. When choosing, it is necessary to comprehensively consider material properties, workpiece size, test accuracy requirements and actual scenario conditions. From traditional Brinell and Rockwell methods to modern Vickers and Leeb technologies, these methods together constitute the cornerstone of material performance evaluation and provide a reliable basis for the research and development, production and quality control of special steels. In the future, with the popularization of intelligent testing equipment and the development of new hardness characterization technologies, hardness testing of special steels will continue to evolve in the direction of higher efficiency and higher precision, further promoting the deep integration of materials science and industrial applications.
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