Method for testing the hardness of heat-treated workpieces

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:

一 Surface quenching and tempering heat treatment

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 hardening layer depth. Hardness testing can use Vickers hardness tester or Rockwell hardness machine The choice of experimental force is related to the depth of the effective hardened layer and the surface hardness of the workpiece. Three hardness machines are involved here.

Vickers hardness tester is an important method to test the surface hardness of heat-treated workpieces. It can use 0.5-100KG of experimental force to test the surface hardening layer as thin as 0.05mm. Its accuracy is the highest and can distinguish heat-treated workpieces. Small differences in surface hardness, in addition, the effective hardened layer depth must also be tested by a Vickers hardness tester. Therefore, for units that perform surface heat treatment or use a large number of surface heat treatment workpieces, it is necessary to equip a Vickers hardness tester.

Surface Rockwell hardness tester is also very suitable for testing the hardness of surface quenched workpieces. There are three types of scales to choose from.

It can test various surface hardened workpieces with an effective hardening layer depth of more than 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 used as a means of quality management and qualification inspection for heat treatment plants. It can meet the requirements. Moreover, it 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 be used to quickly and non-destructively test batches of surface heat treatment workpieces. This is of great significance to metal processing and machinery manufacturing plants.

When the surface heat treatment hardened layer is thick, Rockwell hardness tester can also be used. When the thickness of the heat-treated hardness layer is 0.4-0.8mm, the HRA scale can be used. When the depth of the hardened layer exceeds 0.8mm, the HRC scale can be used. (Guide: What is the inherent difference between electro-galvanizing and hot-dip galvanizing (hot-dip galvanizing)?)

The three hardness standard values u200bu200bof Vickers. Rockwell and Surface Rockwell can be easily converted to each other and converted into standards, drawings or hardness values u200bu200brequired by users. The corresponding conversion tables are in the international standard ISO. American standards ASTM and China It has been given in the standard GB/T.

Second chemical heat treatment

Chemical heat treatment is to make the surface of the workpiece infiltrate the atoms of one or several chemical elements, thereby changing the chemical composition, structure and performance 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, and the core of the workpiece has high strength and toughness.

The main technical parameters of the chemical heat treatment workpiece are the depth of the hardened layer and the surface hardness. The depth of the hardened layer is still to be tested with a Vickers hardness tester to detect the distance from the surface of the workpiece to the point where the hardness drops to 50HRC, which is the effective hardened layer depth.

The surface hardness detection of chemical heat treatment workpieces is similar to the hardness detection of surface quenching heat treatment workpieces. Both can be tested with Vickers hardness tester, surface Rockwell hardness tester or Rockwell hardness tester, only the thickness of the nitriding thickness is thinner , Generally not greater than 0.7mm, at this time Rockwell hardness tester cannot be used

The third 　　 local heat treatment

　　 If the parts have high local hardness requirements, they can be locally quenched and heat treated by induction heating. Such parts usually need to be marked on the drawing for the location of the local quenching heat treatment and the local hardness value. The hardness of the parts should be tested in the designated area. To proceed, the hardness testing instrument can use Rockwell hardness tester to test the HRC hardness value. If the heat treatment hardened layer is shallow, the surface Rockwell hardness tester can be used to test the HRN hardness value.

More related heat treatment processing industry news: