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What is the difference between HBS and HBW, HRA, HRB and HRC?

The hardness of materials is a very important performance parameter, which plays an important role in the wear, fatigue resistance, and compression resistance during use. Therefore, we need to measure the hardness to meet our design requirements and ensure the normal operation of the equipment,

Some are the hardness of the material itself, while others are obtained through heat treatment or other treatments. There are different hardness testing methods for different materials.

When measuring the hardness of parts, everyone is familiar with three commonly used hardness measurement methods, namely Brinell hardness (HB), Rockwell hardness (HR), and Vickers hardness (HV). However, when it comes to the first two types of hardness, people sometimes see other ways of writing them, such as Brinell hardness divided into HBS and HBW, Rockwell hardness divided into HRA, HRB, HRC, and so on. What are the differences between these different writing styles?

Let's first take a look at Brinell hardness. Its measurement principle is to use quenched steel balls or hard alloy balls with a diameter of D, press them into the surface of the material with the corresponding test force F, and after holding for a specified time, remove the test force. Use a reading microscope to measure the average diameter d of the residual indentation, and use the pressure on the surface area of the spherical indentation unit to represent the hardness value. The actual measurement can obtain the hardness value by checking the table after measuring the d value.

The difference between HBS and HBW lies in the use of different ball head materials. HBS represents the Brinell hardness value measured with a quenched steel ball indenter and is commonly used to measure materials with hardness values less than 450HBS. HBW represents the Brinell hardness value measured using a hard alloy indenter, used to measure materials with hardness values ranging from 450 to 650 HBW. Suitable ball heads should be selected for materials with different hardness, otherwise the measurement results may be inaccurate due to deformation of the ball head.

However, in the latest standard GB/T 231, it has been stipulated that only hard alloy ball indenters are allowed, and the Brinell hardness symbol is HBW. Both HB and HBS are outdated writing methods.

Using Brinell hardness measurement, due to the large residual indentation area, it can accurately reflect the average hardness of the material, and the measurement data is stable. Therefore, it can be used to measure materials with large or uneven microstructure (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 magnitude. Due to the large indentation of Brinell hardness measurement, it is not suitable to measure the hardness of finished or thin sheet metals. It is mainly used for hardness measurement of raw materials or semi-finished products, such as measuring cast iron, non-ferrous metals (non-ferrous metals), and steel with lower hardness (such as annealed, normalized, quenched and tempered steel). Let's take a look at Rockwell hardness again. Rockwell hardness measurement uses a diamond cone or quenched steel ball as the indenter. Under the test pressure F, the indenter is pressed into the surface of the material, held for a specified time, the main test force is removed, and the initial test force is maintained. The hardness value is calculated using the increment of residual indentation depth. In actual measurement, the Rockwell hardness value can be directly read out through the dial of the testing machine.

The difference between HRA, HRB, and HRC lies in the difference in the pressure head and test force used. Please refer to the table below for details.

In fact, the Rockwell hardness scale is not only divided into A, B, and C, but also has many others ranging from D to K. It can be selected according to different material types, hardness, and thickness. For details, please refer to GB/T 230 standard.

Rockwell hardness measurement has the advantages of speed, simplicity, small indentation, and large hardness measurement range, and can be used for measuring finished products or thinner workpieces. However, the accuracy, stability, and repeatability of the data are not as good as Brinell hardness. Usually, three points need to be tested on different parts of the sample surface, and the average value is taken 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 tissue.