Laser welding applications for low-carbon commercial X80 steel

The study investigates the structure and mechanical properties of laser welded X80 pipeline steel. It is found that the fusion zone has a dendritic martensite structure, and the heat affected zone exhibits ferrite-bainite structures. The fine-grained heat affected zone has a small fraction of granular bainite and regions of degenerate upper bainite consisting of parallel bainitic ferrite laths separated by martensitic-austenitic constituents and twinned martensite plates. The laser welded joint is shown to have the strength and ductility characteristics at the level of the base material. Despite an ≈2-fold decrease in the impact toughness KCV of the welded samples in comparison with the base material, the weld material demonstrates high KCV values (KCV–70°C = 170 J/cm2).