Development of gas metal arc welding wire for X80 pipeline steel

The developed wires are used for gas metal arc welding. The chemical composition,microstructure,impact toughness,strength,hardness and tensile strength of welded joint are investigated. The microstructure is composed of acicular ferrite and a little proeutectoid ferrite and a little granular bainite. The fractured surfaces of impact specimen are analyzed by scanning electron microscope, and the microstructures of weld metal are analyzed by transmission electron microscope. Experiment results indicated that it was effective to resist proeutectoid ferrite and make fine homogeneous acicular formation by adding microcontent Ti-B elements in the wire. It had been found that alloy element in weld metal could be the nucleating-centers of acicular ferrite as long as they formed fine disperse inclusion. It is effective to prevent crack propagation and improve impact toughness because there are lots of dislocation agglomerating in acicular ferrite.