Introduction to surface quenching and tempering heat treatment of straight seam welded pipes

Introduction to surface quenching and tempering heat treatment of straight seam welded pipes

The surface quenching and tempering heat treatment of straight seam welded pipes 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 be done with a Vickers hardness tester, a Rockwell or a surface Rockwell hardness tester. The selection of test force (scale) is related to the depth of the effective hardened layer and the surface hardness of the straight seam welded pipe. There are three types of hardness testers involved.
The Vickers hardness tester is an important means of testing the surface hardness of heat-treated Hunan straight seam welded pipes. It can use a test force of 0.5 to 100kg to test surface hardened layers as thin as 0.05mm thick. Its accuracy is the highest and can distinguish heat-treated workpieces. Small differences in surface hardness. In addition, the depth of the effective hardened layer must also be detected by a Vickers hardness tester. Therefore, it is necessary for units that perform surface heat treatment or use a large number of surface heat treatment Hunan straight seam welded pipes to be equipped with a Vickers hardness tester.

The surface Rockwell hardness tester is also very suitable for testing the hardness of surface quenched workpieces. The surface Rockwell hardness tester has three scales to choose from. It can test various surface-hardened Hunan straight seam welded pipes with effective hardening depth exceeding 0.1mm. Although the surface Rockwell hardness tester is not as accurate as the Vickers hardness tester, it can already meet the requirements as a testing method for quality management and qualification inspection in heat treatment plants. Moreover, it also has the characteristics of simple operation, convenient use, low price, rapid measurement, and the ability to directly read the hardness value. The surface Rockwell hardness tester can be used to quickly and non-destructively inspect batches of surface heat-treated Hunan straight seam welded pipes one by one. . This is of great significance to Hunan straight seam welded pipe processing and machinery manufacturing plants.

When the surface heat treatment hardened layer is thick, the Rockwell hardness tester can also be used. When the thickness of the heat treatment hardened layer is between 0.4 and 0.8mm, the HRA scale can be used. When the thickness of the hardened layer exceeds 0.8mm, the HRC scale can be used.

Vickers, Rockwell and superficial Rockwell hardness values can be easily converted to each other and converted into hardness values required by standards, drawings or users. The corresponding conversion tables have been given in the international standard ISO, the American standard ASTM and the Chinese standard GB/T.

If the parts require high local hardness, local quenching heat treatment can be carried out by induction heating. Such Hunan straight seam welded pipes usually have to mark the location of local quenching heat treatment and the local hardness value on the drawing. The hardness testing of Hunan straight seam welded pipes must be carried out in designated areas. The hardness testing instrument can use a Rockwell hardness tester to test the HRC hardness value. If the heat treatment hardened layer is shallow, a surface Rockwell hardness tester can be used to test the HRN hardness value.