Quenching technology of straight seam welded steel pipe

The surface quenching and tempering heat treatment of straight seam welded steel 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 detection can be carried out by Vickers hardness tester, Rockwell, or surface Rockwell hardness tester. When the surface heat treatment hardened layer is thicker, Rockwell hardness tester can also be used. When the thickness of the heat treatment 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.

If the local hardness requirements of the parts are high, local quenching heat treatment can be carried out by induction heating and other methods. Such straight seam welded steel pipes usually need to mark the location and local hardness value of the local quenching heat treatment on the drawings. The hardness test of straight seam welded steel pipes should be carried out in the designated area. 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.

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