Improvement of the welded joints properties of P460NH steel with AC-assisted GTAW arc

Abstract

Aiming at the problems of small grain size and difficult welding of P460 NH steel, an efficient and high-quality welding method of AC assisted arc welding is proposed. In this AC-assisted arc welding process, the alternating current was added to the filling wire to form an additional electromagnetic field. The alternating electromagnetic force generated by the interaction of the main arc and other electromagnetic fields can stir the molten pool during the welding process. The feasibility of improving the grain size and mechanical properties of microstructures with AC power in 0-30A was confirmed. The experiment proved that the arc oscillation caused by the alternating electromagnetic force can alleviate the root stay of the traditional GTAW process. When the AC strength doesn't exceed 20A, the average grain size decreases while the content of acicular ferrite and granular bainite increases. The average grain size is 3.258 μm refined to 2.960 μm. Moreover, the tensile strength and hardness of welded joints first increase with the addition of current and then decrease with the rise of current to 30A. Finally, the mechanism of AC on microstructure and solidification of molten pool was discussed.