Microstructure and Mechanical Properties of Fiber Laser-Metal Active Gas Hybrid Weld of X80 Pipeline Steel

Abstract

Fiber laser-metal active gas (MAG) hybrid welding process was explored to join X80 pipeline steel to improve the efficiency and performance of pipeline welding. During the hybrid welding process, five different positions are applied to simulate the practical pipe girth welding. The weldability is evaluated concerning the bead shape, hardness, tensile, impact properties, and microstructures of welded joints. The results reveal that the tensile strength is higher than that of the base metal and the weld has a good impact ductility and an excellent bend performance. At the same time, the difference in microstructure between the laser zone and arc zone of laser-MAG hybrid welding of X80 pipeline steel is observed. Compared with the arc zone, the laser zone has finer weld grains and a narrower heat affected zone (HAZ). The fusion zone microstructure of the arc zone mainly consists of columnar proeutectoid ferrite (PF) and fine acicular ferrite (AF), whereas that of laser zone comprises acicular ferrite, upper bainite (Bu), and granular bainite (BG), which verifies technical feasibility of hybrid welding in pipeline steel and lays a good foundation for practical application.