Tension fracture behaviors of welded joints in X70 steel pipeline

Abstract

The surface of welded joints in X70 steel pipeline was processed by laser shock wave, its mechanical behaviors of tension fracture were analyzed with tension test, and the fracture morphologies and the distributions of chemical element were observed with scanning electron microscope and energy dispersive spectrum, respectively. The experimental results show that the phenomenon of grain refinement occurs in the surface of welded joints in X70 steel pipeline after the laser shock processing, and compressive residual stress is formed in its surface strengthened layer. There is no yield stage but a continuous yield behavior in the welded joints in X70 steel pipeline after the laser shock processing, and its extensibility has decreased by 20 %. The welded joints in X70 steel pipeline in primitive state exhibits brittle fracture with less tearing edges, while the fracture of welded joints in X70 steel pipeline processed by laser shock is ductile fracture with a lot of tearing edges.