ERW straight seam welded pipe 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. The hardness test may be performed by a Vickers hardness tester or a Rockwell or surface Rockwell hardness tester. The choice of test force (scale) is related to the effective hardened layer depth and the surface hardness of the straight seam welded pipe. There are three hardness testers involved here.
Vickers hardness tester is an important means to test the surface hardness of heat-treated straight seam welded pipe. It can test the surface hardened layer as thin as 0.05mm thick with the test force of 0.5-100kg. It has the highest precision and can distinguish the surface of heat-treated workpiece. A small difference in hardness. In addition, the effective hardened layer depth is also measured by a Vickers hardness tester. Therefore, it is necessary to equip a unit for surface heat treatment or a large number of surface heat treated straight seam welded pipes 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. Various surface hardened straight seam welded pipes with an effective hardening depth of more than 0.1 mm can be tested. Although the accuracy of the surface Rockwell hardness tester is not as high as the Vickers hardness tester, it has been able to meet the requirements as a means of quality management and inspection of the heat treatment plant. Moreover, it has the advantages of simple operation, convenient use, low price, rapid measurement, and direct reading of hardness values, etc., using the surface Rockwell hardness tester to carry out rapid and non-destructive part-by-piece inspection of batches of surface heat treated Hunan straight seam welded pipes. This is important for straight seam welded pipe processing and mechanical manufacturing plants.
When the surface heat-treated hardened layer is thick, a Rockwell hardness tester can also be used. When the thickness of the heat-treated hardened layer is 0.4 to 0.8 mm, the HRA scale can be used, and when the thickness of the hardened layer exceeds 0.8 mm, the HRC scale can be used.
Vickers, Rockwell and Surface Rockwell hardness values can be easily converted to each other and converted to standard, drawing or user-required hardness values. The corresponding conversion tables are given in the international standard ISO, the American standard ASTM and the Chinese standard GB/T.
If the local hardness of the part is high, the local quenching heat treatment can be performed by means of induction heating. Such a straight seam welded pipe is usually marked with a local quenching heat treatment position and a local hardness value on the drawing. The hardness test of the straight seam welded pipe shall be carried out in the designated area. The hardness tester can use the Rockwell hardness tester to test the HRC hardness value. If the heat treatment hardened layer is shallow, the surface hardness tester can be used to test the HRN hardness value.
