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What is surface hardening?

What is surface hardening?

The surface quenching and tempering heat treatment is usually carried out by induction heating or flame heating. The main technical parameters are surface hardness, local hardness and effective hardened layer depth. Hardness testing can use Vickers hardness tester, Rockwell or surface Rockwell hardness tester can also be used. The choice of test force (scale) is related to the effective hardened layer depth and the surface hardness of the workpiece. There are three types of hardness testers involved here.

1. The Vickers hardness tester is an important method to test the surface hardness of heat-treated workpieces. It can choose a test force of 0.5-100kg to test the surface hardened layer as thin as 0.05mm. Its accuracy is the highest and can distinguish the surface of the heat-treated workpiece. Minor differences in hardness. In addition, the effective hardened layer depth should also be detected by a Vickers hardness tester. Therefore, it is necessary to equip a Vickers hardness tester for units that perform surface heat treatment or use a large number of surface heat treatment workpieces.

2. The surface Rockwell hardness tester is also very suitable for testing the hardness of surface quenched workpieces. The surface Rockwell hardness tester has three scales to choose from. It can test various surface hardened workpieces whose effective hardening depth exceeds 0.1mm. Although the accuracy of the surface Rockwell hardness tester is not as high as that of the Vickers hardness tester, it has been able to meet the requirements as a means of quality management and qualification inspection for heat treatment plants. Moreover, it also has the characteristics of simple operation, convenient use, low price, rapid measurement, and direct reading of the hardness value. The surface Rockwell hardness tester can quickly and non-destructively test the batches of surface heat-treated workpieces. This is of great significance to metal processing and machinery manufacturing plants.

3. When the surface heat treatment hardened layer is thick, Rockwell hardness tester can also be used. When the thickness of the heat-treated hardened layer is between 0.4 and 0.8mm, the HRA scale can be used, and when the thickness of the hardened layer exceeds 0.8mm, the HRC scale can be used.

The three hardness values ​​of Vickers, Rockwell and Surface Rockwell can be easily converted into each other and converted into the hardness values ​​required by standards, drawings or users. The corresponding conversion table has been given in the international standard ISO, the American standard ASTM and the Chinese standard GB/T.