Heat treatment classification and hardness testing method of cylindrical roller bearings

The hardness of heat treated workpieces is tested using a hardness tester. The PHR series portable surface Rockwell hardness tester is very suitable for testing the hardness of surface heat treatment workpieces, and can test various surface heat treatment workpieces with an effective depth exceeding 0.1mm. It is simple to operate, easy to use, low in price, and can directly read the hardness value.

Surface heat treatment is divided into two categories, one is surface quenching and tempering heat treatment, and the other is chemical heat treatment. The hardness testing method is as follows:

Chemical heat treatment is to infiltrate atoms of one or several chemical elements into the surface of the workpiece, thereby changing the chemical composition, structure and properties of the surface of the workpiece. After quenching and low-temperature tempering, the surface of the workpiece has high hardness, wear resistance and contact fatigue strength, while the core of the workpiece has high strength and toughness.

The main technical parameters of chemical heat treatment workpieces are hardened layer depth and surface hardness. The depth of the hardened layer still needs to be tested with a Vickers hardness tester. Detect the distance from the surface of the workpiece to the point where the hardness drops to 50HRC. This is that the surface hardness detection of chemical heat treatment workpieces with effective hardening depth is similar to the hardness detection of surface quenching heat treatment workpieces. They can be detected by Vickers hardness tester, surface Rockwell hardness tester or Rockwell hardness tester, but the nitriding thickness is longer. Thin, generally not larger than 0.7mm, then the Rockwell hardness tester can no longer be used.

If the parts require high local hardness, local quenching heat treatment can be carried out by induction heating. Such parts usually need to mark the location of the local quenching heat treatment and the local hardness value on the drawing. Hardness testing of parts should be carried out in designated areas. The hardness testing instrument can use a Rockwell hardness tester to test the HRC hardness value. If the heat treatment hardened layer is shallow, a surface Rockwell hardness tester can be used to test the HRN hardness value.

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 be done with a Vickers hardness tester, a Rockwell or a surface Rockwell hardness tester. The selection of test force (scale) is related to the depth of the effective hardened layer and the surface hardness of the workpiece. There are three types of hardness testers involved.

The Vickers hardness tester is an important means of testing the surface hardness of heat-treated workpieces. It can use a test force of 0.5 to 100kg to test surface hardened layers as thin as 0.05mm thick. Its accuracy is the highest and can distinguish the smallest surface hardness of the workpiece. difference. In addition, the depth of the effective hardened layer must 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 processing or use a large number of surface heat treatment workpieces.

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 with effective hardening depth exceeding 0.1mm. Although the surface Rockwell hardness tester is not as accurate as the Vickers hardness tester, it can already meet the requirements as a testing method for quality management and qualification inspection in heat treatment plants. Moreover, it also has the characteristics of simple operation, convenient use, low price, rapid measurement, and the ability to directly read the hardness value. The surface Rockwell hardness tester can be used to quickly and non-destructively inspect batches of surface heat treatment workpieces one by one. This is of great significance for metal processing and machine building plants.

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

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