Hardness testing method for heat treatment of pit furnace

There are three types of hardness testing standards for pit furnaces, namely three hardness values ​​of Vickers, Rockwell and surface Rockwell. According to the same heat treatment method, the hardness testing method of surface quenching and tempering heat treatment furnace and chemical heat treatment furnace is also different.

Heat treatment pit furnace

The main technical parameters of the chemically heat treated workpiece are the depth of the hardened layer and the surface hardness. The depth of the hardened layer must still be tested with a Vickers hardness tester. Measure the distance from the workpiece surface to the point where the hardness drops to 50HRC. This is the effective hardening depth

Chemical heat treatment is to infiltrate the surface of the workpiece with atoms of one or several chemical elements, thereby changing the chemical composition, organization and performance of the workpiece surface. 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 surface hardness testing of chemically heat-treated workpieces is similar to the hardness testing of surface-quenched heat-treated workpieces. They can be tested with Vickers hardness tester, surface Rockwell hardness tester or Rockwell hardness tester, but the thickness of nitriding is thinner, generally not greater 0.7MM, then Rockwell hardness tester can no longer be used.

If the local hardness of parts is required to be high, induction quenching and other methods can be used for local quenching heat treatment. Such parts are usually marked on the drawing with the location of local quenching heat treatment and local hardness value. The hardness test of the parts should be carried out in the designated area. The hardness testing instrument can use Rockwell hardness tester to test HRC hardness value. If the heat treatment hardened layer is shallow, surface Rockwell hardness tester can be used to test HRN hardness value.

Pit furnace 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 depth of the effective hardened layer and the hardness of the workpiece surface. Three types of hardness testers are involved here.

Vickers hardness tester is an important method for testing the surface hardness of heat-treated workpieces. It can use a test force of 0.5 to 100KG to test the surface hardened layer as thin as 0.05MM. Its accuracy is the highest, which can distinguish the small surface hardness of the workpiece. difference. In addition, the effective depth of the hardened layer must also be detected by a Vickers hardness tester. Therefore, it is necessary to equip a unit that performs surface heat treatment or a large number of surface heat treatment workpieces with a Vickers hardness tester.

The surface Rockwell hardness tester is also very suitable for testing the hardness of surface-hardened workpieces. The surface Rockwell hardness tester has three scales to choose from. Can test all kinds of surface hardened workpieces with effective hardening depth exceeding 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 test method for quality management and qualification inspection of 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 be used for rapid non-destructive piece-by-piece inspection of batches of surface heat-treated workpieces. This is of great significance to metal processing and machinery manufacturing plants.

When the heat treatment hardening layer on the surface of the pit furnace is thick, Rockwell hardness tester can also be used. When the thickness of the hardened layer is 0.4-0.8MM, 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 to each other and converted into hardness values ​​required by standards, drawings or users. Corresponding conversion tables are given in the international standard ISO, American standard ASTM and Chinese standard GB / T.

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