Microstructures and corrosion properties of submerged arc welded joint for X80 pipeline steel

The X80 pipeline steel was welded using the submerged-arc welding procedure.The microstructure of the welded joint was observed by scanning electron microscope(SEM),the corrosion behavior of the welded joint of X80 pipeline steel was investigated by method of potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The results show that the welded joint has good pitting corrosion resistance generally.However in solution of 0.5 mol/L NaHCO₃+0.02 mol/L NaCl,the base metal of X80 pipeline steel showed the best resistance to pitting corrosion because of the differences in microstructure.Though it can keep the same level as the base metal at first,the pitting corrosion resistance of weld metal will get worse after longtime immersion.The pitting corrosion resistance of heat-affected zone was always the worst and had a large gap with the base metal and weld metal.