The surface quenching and tempering heat treatment of ERW pipe
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 surface hardness of the straight seam welded pipe
. Three types of hardness testers are involved here.
The Vickers hardness tester is an important method for testing the surface hardness of heat-treated straight seam welded pipes. It can use a test force of 0.5 to 100 kg to test the surface hardened layer as thin as 0.05 mm. Its accuracy is the highest and can distinguish the surface of the heat-treated workpiece. Small difference in hardness. In addition, the effective depth of the hardened layer must also be tested by the Vickers hardness tester. Therefore, it is necessary to provide a Vickers hardness tester for units that perform surface heat treatment or use a large number of surface heat treatment of Hunan straight seam welded pipes.
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. It can test all kinds of surface hardened straight seam welded pipes 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 fast and non-destructive piece-by-piece inspection of batches of surface heat-treated Hunan straight seam welded pipes . This is of great significance to the processing of straight seam welded pipes 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 hardened layer is 0.4-0.8mm, the HRA ruler can be used, and when the thickness of the hardened layer exceeds 0.8mm, the HRC ruler 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.
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 a straight seam welded pipe is usually marked with the location of local quenching heat treatment and local hardness value on the drawing. Straight seam welded pipe hardness testing 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.