No-Nb wires of 550 MPa and 650 MPa grades were employed to carry out dual submerged arc welding test on economic Nb-bearing X70 steel. The mechanical properties of the welded joint met the technical requirements, and the HAZ had toughness with large margin and little fluctuation; the properties are uniform indicating a good mixture of the two wires in melting pool. The microstructure of GCHAZ is granular bainite with granular ferrite and plate ferrite. In spite of the Nb dilution from X70 parent metal to weld metal, the precipitates in welds of either as welded or reheated are still mainly oxides of Ti, Al, Mn and Si, but without Nb, sizing from 200 nm to 1.5 μm, and singly 80 nm by TEM observation, which is much different with that in X70 steel.