When measuring the hardness of parts, everyone is familiar with three commonly used hardness representation methods, namely Brinell hardness (HB), Rockwell hardness (HR) and Vickers hardness (HV). However, for the first two hardnesses, you will sometimes see other ways of writing, such as Brinell hardness is divided into HBS and HBW, Rockwell hardness is divided into HRA, HRB, HRC, etc. What are the differences between these different writing methods?
Let's first look at 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.
The difference between HBS and HBW lies in the different ball head materials used. HBS represents the Brinell hardness value measured with 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, and is used to measure materials with a hardness value of 450~650HBW. For materials of different hardness, a suitable ball head must be selected, otherwise the measurement result may be inaccurate due to the deformation of the indenter ball.
However, in the latest standard GB/T 231, it has been stipulated that only carbide ball indenters are allowed to be used, and the Brinell hardness symbol is HBW. Both HB and HBS are outdated.
Using Brinell hardness measurement, due to the large residual indentation area, it can more truly reflect the average hardness of the material, and the measurement data is stable, so it can be used to measure materials with large or uneven structures (such as cast iron). 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. Due to the large indentation of Brinell hardness measurement, it is not suitable for measuring the hardness of finished products or thin metal sheets. It 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 lower hardness (such as annealed, normalized, and tempered steel).
Let's look at 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 through 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.
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. For details, please refer to GB/T 230 standard.(BISHEN is a top cnc precision parts processing company in China. The company has sophisticated equipment, professional processing of high precision difficulty level parts. Good at a variety of medical, aviation, robotics and other industries processing, and has a wealth of experience.)
Rockwell hardness measurement has the advantages of rapidity, simplicity, small indentation, and 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 at 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.(文章来源：iMechanics机械)
