Microstructure and mechanical properties of welded joints of a novel Cr3MoNb pipeline steel

Gas tungsten arc welding (GTAW) of novel Cr3MoNb pipeline was conducted with TGS-2CML wire. The hardness,impact toughness and tensile properties of welded joints were measured,and the microstructure characteristics were examined. The results show that the welded joints can achieve good mechanical properties without preheating and PWHT. Elongation after thermal refining increased by one hundred percent, which fulfilled the DNV-OS-F101 standard. For low carbon or super low carbon pipeline steels,the calculation formula modified with A(c) was reasonable for predicting the maximum hardness on heat affected zone. The microstructure of weld metal mainly consisted of fine granular bainite with some dispersive MA islands in the ferrite matrix. The grain size in weld zone was quite small while subtle regional differences existed and a few large columnar crystals formed. Polygonal ferrite and granular bainite were distributed within the fusion zone,and no sharp boundary was observed between WM and HAZ.