Research On Key Welding Technology Of Low Alloy High Strength UHV Tower

In recent years, as ultra-high volt (UHV) power transmission technique developing rapidly, UHV towers start to be applied in the nationwide. For the reason of economic and carrying capacity, high strength low alloy (HSLA) steels are applied in UHV tower manufacturing. However, because of HSLA steels' material properties, after welding, trend of weld crack in the weld joints is greater than that of other steels, and performance of weld joints is declining. All these flaws are hindered the HSLA steels to be used in the UHV towers.According to the actual demand of UHV towers, this paper analyzes the weldability and weld technology of HSLA steels. Weld alloying theory is also discussed in this paper. The weldability of GR.65 steels, representative of HSLA steels used in the UHV towers, is studied in theory and practice, and their weld technology is also discussed. In order to improve the toughness and decrease the cracks of weld, Ni alloying technique is proposed. The influence of Ni, which is the key element of special welding formula, on the weld's structure and performance is researched by method of weld experiment, tensile and impact toughness experiment, chemical composition analysis experiment and metallographic observation.Conclusions are as follows: on the basis of research on GR.65 steels' weldability, preventing cracks by method of weld technology is proposed. The weld technology proposed in the research is checked by the practice and applied in large scope. Ni is the key element which is good for improving the toughness and decreasing the cracks.Within a certain range of Ni, as the content of Ni increasing, the weld structure refines and content of acicular ferrite increases while that of pro-eutectoid ferrite decreases. The proportion of volume content between acicular ferrite and pro-eutectoid ferrite raises, carbide segregation reduces and the toughness of weld increases largely. The research also provides a theoretical basis and practical experience on exploring special welding consumables by adding Ni element.