The welding process of ERW pipe is to heat the edge of hot rolled coil to the melting state by using the skin receiving principle generated by high frequency current, and then weld it by mechanical extrusion. The steel pipe produced by this method has a white fusion line at the center of the weld, and the heat affected zone on both sides of the fusion line will have a metal flow line extending from the middle to the inner surface and the outer surface. Because ERW pipe is made of base material as welding material, the performance of weld seam is closely related to the performance of base material. In common materials, the ductile-brittle transition temperature curves of welds and base metals. In general materials, the difference of energy absorption between weld and base metal is very small in Charpy impact test. On the contrary, the impact toughness of high toughness materials is much lower than that of base metal, but much better than that of common materials. It can be seen that the impact toughness of the welding center of high frequency steel pipe is usually lower than that of the base metal. Even with the use of tough materials, although the toughness of the weld has been improved, the impact toughness of the welding center can not be completely improved.


Factors Influencing Impact Toughness of Welds
The main factors affecting the impact toughness of welds are: (1) physical and chemical properties of raw materials; (2) raw materials of crystal materials and non-metallic inclusions; (3) heat treatment conditions of welds; (4) forming conditions; (5) welding conditions.