Optical and spectroscopic study of a submerged arc welding cavern

For the first time, a combination of high-speed imaging and spatially resolved spectroscopy at 5000 fps was performed on a submerged arc welding process. This was achieved by inserting a thin-gauge steel tunnel into the flux and aligning the diagnostics accordingly. Four processes were observed; both direct current electrode positive (DCEP) and direct current electrode negative (DCEN), as well as alternating current (AC) at 600 A and DCEP with a higher current at 1000 A. The videos show an erratic droplet transfer with a lot of spatter that was caught by the cavern walls and directed into the weld pool. Additionally, flux was molten at the top of the cavern close to the electrode and merged into the droplet that was still attached to the wire. The cavern walls were a mixture of solid flux that was partially falling into the weld pool and molten flux, which created a smooth wall. The surface properties of the cavern wall behind the process was mostly smooth and merged wi th the weld pool, which created a solidifying layer of slag on top of the slowly cooling weld joint. The observed processes showed only a slight change in chemical composition of main alloying elements in the solidified weld joint, while the oxygen content varied significantly in the droplet stage and weld joint between the processes. The high-speed images indicated a correlation between droplet-flux interaction and oxygen content. The spatially resolved spectra showed intense self-reversed lines of Na, Ca, and Mn. Fe lines suggested that the arc was also dominated by metal vapor. Especially during the AC process, a fluctuating emission of Mn lines was observed, which correlated with the frequency of the shifting polarity.