Development of Wire for Large Current Double Side Submerged Arc Welding of Pipe Steel

In this paper, the characteristics of wire for submerged arc welding of oil and gas pipe line and the principles for the design of chemical compositions of high toughness welding wire are discussed. Steels of wire are smelted in high frequency induction furnace, medium frequency induction furnace, and top oxygen blown converter respectively. Matching the agglomerated flux SJ101, these wires are used for double side submerged arc welding.The chemical compositions, impact toughness, microstructure of weld metal and hardness and tensile strength of welded joint are investigated. The fractured surfaces of impact specimens are analyzed by scanning electron microscope, the microstructures of weld metal are analyzed by transmission electron microscope,and the distributions of B, Ti, N are examined by Auger spectrum analysis. It is indicated that B segregates in the boundary of original austenite grains, that is beneficial for the restriction proeutectoid ferrite. Uniformly distributed particles are helpful for the produce of acicular ferrite. These factors, combined with low content of S, P, gas elements and impurity, result in high toughness of weld metal. The hardness of weld metal is between HV185 and Hv214, which is in the same level with the average hardness, HV190, of base metal. The transverse tensile strength of weld metal is higher than that of base metal.