Investigation on the weldability of a Zr-Ti microalloyed X120 linepipe

Three-wire submerged arc welding was utilized to weld a newly developed Zr-Ti microalloyed X120 linepipe with heat input of 21 kJ/cm.The microstructure in the heat-affected zone（HAZ）,predominantly consisted of bainite,was examined by means of optical and scanning electron microscope.The average Vickers hardness of grain coarsening heataffected zone（GCHAZ） is about 290 HVO.2.The lowest Vickers hardness in HAZ is about 265 HVO.2.No obvious softening occurred in HAZ.The average impact toughness at-30℃ in HAZ was 186-191 J.The tested results indicated that HAZ of newly developed Zr^Ti microalloyed X120 linepipe steel had high strength and excellent low temperature toughness which met the requirements of API 5L standard.