The importance of the additional growth and/or transformation of the austenite phase that occurs in weld metals of super duplex stainless steel upon reheating is known. However, the effects have not been fully investigated, especially with respect to reheating induced by weaving during single-pass welding. In this work, bead-on-pipe gas tungsten arc welding (GTAW) was conducted on super duplex stainless steel to understand the effect of weaving on the microstructure of weld metal. Microstructural analysis, electron backscatter diffraction (EBSD), and focused ion beam transmission electron microscopy (FIB-TEM) were carried out to investigate the relationship between weaving and microstructural change. The weaving of GTAW produced a dynamic reheated area just before the weld bead during welding. It was revealed that extensive reheated weld existed even after one welding pass, and that the content of the austenite phase in the reheated area was higher than that in the non-reheated area, indicating the existence of a large quantity of intragranular austenite phase. In addition, the Cr 2 N content in the reheated area was lower than that in the non-reheated area. This reduction of Cr 2 N was closely related to the reheating resulting from weaving. TEM analysis revealed that Cr 2 N in the non-reheated area was dispersed following heating and transformed to secondary austenite.

Gas tungsten arc welding (GTAW) with three different heat inputs controlled by the weaving width was performed to understand their effects on the microstructural changes during bead-on-pipe welding of super duplex stainless steel. The microstructure of the weld metals was categorized into three different types of zones: non-reheated, reheated type, and reheating-free zone. Even though single-pass welding with different weaving widths was employed, a reheated microstructure was detected, which has been previously observed with multiple pass welding. This phenomenon was called "dynamic reheating", because it was produced by the weaving operation during welding regardless of the weaving width. The categorized area fraction varied with the weaving width change. Electron backscatter diffraction (EBSD) results at the edge (the area near the fusion line) of the low-heat-input condition indicated a higher austenite volume fraction and a lower Cr 2 N fraction than that of the medium heat input condition. Thus, it described an inverse relationship, because higher heat input provided a lower austenite fraction. In addition, it was observed clearly that the austenite fraction at the medium heat input condition was dramatically increased by reheating, while the Cr 2 N fraction was reduced. Regardless of the weaving width, reheating contributed to the increase of the austenite fraction, further reducing the Cr 2 N quantity. The edge areas in the map showed an inverse relationship in the reheated area fraction between low heat input and medium heat input. For this reason, the austenite fraction on the weld metal was determined not only by the heat input, but also by the amount of reheating.