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. Vickers hardness tester can be used for hardness testing, Rockwell hardness tester or surface Rockwell hardness tester can also be used. 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 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 of the parts is high, the local quenching heat treatment can be carried out using induction heating. Such a
straight seam welded pipe usually needs to mark the location and local hardness value of the local quenching heat treatment on the drawing. The hardness test of the
straight seam welded pipe shall be carried out in the area. The hardness testing instrument can use the Rockwell hardness tester to test the HRC hardness value. If the heat treatment hardened layer is shallow, the surface Rockwell hardness tester can be used to test the HRN hardness value.
The three hardness values of Vickers, Rockwell, and superficial Rockwell can be easily converted to each other and converted into standard, drawings or hardness values required by users. The corresponding conversion table has been given in the international standard ISO, American standard ASTM, and Chinese standard GB/T.
