Surface hardness test of workpiece after heat treatment
Hardness testing after surface heat treatment
1. Surface quenching and tempering heat treatment
Surface quenching and tempering heat treatment is usually performed by induction heating or flame heating. The main technical parameters are surface hardness, local hardness and effective depth of hardened layer.
Surface hardness testing can be done by using a rockwell hardness tester (HR). The selection of test force (scale) is related to effective hardening depth and workpiece surface hardness. HRA scale can be used when the workpiece's heat treatment hardened layer thickness is between 0.4 and 0.8mm, and HRC scale can be used when the hardened layer thickness exceeds 0.8mm.
The vickers hardness tester is another important means to detect the surface hardness of the heat-treated workpiece. It can choose the test force of 0.5~100kg to test the surface hardening layer of the workpiece thin to 0.05mm thick. It has the highest accuracy and can distinguish the slight difference of the surface hardness of the heat-treated workpiece. In addition, vickers hardness tester can be used to test the effective hardened layer if desired.
The surface rockwell hardness tester is also very suitable for testing surface hardened workpiece. Various surface hardened workpieces whose effective hardening depth exceeds 0.1mm can be tested. Although the precision 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 qualified inspection in the heat treatment plant. In addition, it is easy to operate, easy to use, low price, rapid measurement and direct reading of hardness values. By using the surface rockwell hardness tester, it can be used to quickly and nondestructive testing of the surface heat treatment workpieces. This is of great significance to metal processing and machinery manufacturing plants.
2. Chemical heat treatment
After chemical heat treatment, the surface of the workpiece has high hardness, wear resistance and contact fatigue strength, and the core of the workpiece has high strength and toughness. The main technical parameters of chemical heat treatment workpiece are the depth of hardened layer and surface hardness.
The depth of the hardened layer is still determined by a vickers hardness tester. Detect the distance from the surface of the workpiece to the point where the hardness is reduced to 50HRC. This is the effective hardening depth.
The surface hardness test of the workpiece of chemical heat treatment is similar to that of the workpiece of surface quenching heat treatment. If the nitridation thickness is relatively thin, generally no more than 0.7mm, then the rockwell hardness tester can no longer be used.
3. Local heat treatment
For parts with high local hardness requirements, local quenching heat treatment can be carried out by induction heating, etc. Such parts usually need to indicate the location of local quenching heat treatment and local hardness value on the drawing. The hardness test of the part should be carried out in the designated area. The hardness tester can use the rockwell hardness tester to test the HRC hardness value. For example, the surface rockwell hardness tester can be used to test the HRN hardness value if the hardening layer of heat treatment is shallow.