Cause of Low Impact Toughness on Friction Welding Seam Zone of S135 Drill Pipe

In order to find out the reason why the impact toughness of S135 drill pipe welding seam is low and does not meet the requirements, the impact test, mechanical property test, metallographic examination, chemical composition analysis and non-metallic inclusion examination were carried out on the welding seam, and the macro and micro analysis were carried out on the fracture of impact sample. The results show that the high content of sulfur element in drill pipe joint material and the high level and high content of class A non-metallic inclusions result in the formation of more class A non-metallic inclusions in the welding seam zone during friction welding, which affects the continuity of microstructure. Under the impact force, cracks first appear at the weak joint surface of defects, the cracks expand rapidly and finally fracture, resulting in the low impact toughness and disqualification of welding seam sample.