Effects of SSAW Techniques on the Microstructures of Welded Parts in Steel

This study investigated the effects of self-shielded arc welding on the microstructures of welded parts in laminar-cooled-thermo-mechanical-controlled-process (LC-TMCP), titanium nitride (TiN), and B grade steels. The microstructure of the fusion zone was the same in all three samples, consisting of ferrite (grain boundary ferrite (GBF)+acicular ferrite+ferrite side plate) and pearlite phases, and the LC-TMCP and TiN steels had a higher volume fraction of ferrite and smaller grain sizes than those of the B grade steel. In all three samples, the microstructure near the fusion line consisted of ferrite and pearlite phases with a small amount of bainite, and the grain sizes of the LC-TMCP and TiN steels were smaller than those of the B grade steel. In addition, the TiN steel was smaller than the TMCP steel, and the volume fraction of ferrite (GBF, etc.) was the highest in the B grade steel and lowest in the TiN steel. The microstructure of the heat-affected zone included a phase in which a small amount of bainite was present in the ferrite and pearlite phases near the fusion line (1 mm) in all three samples. However, the shape was different from that of the base material, and the grain size was the largest in the B grade steel and smallest in the TiN steel. The volume fraction of ferrite (GBF, etc.) was the highest in the B grade steel and lowest in the TiN steel. All three samples had the same shape as the base metal phase at 5 mm from the fusion line. However, grain was growth.