This study shows the time variation of temperature distribution and concentration distribution of metal vapor during gas tungsten arc welding. In this study, stationary gas tungsten arc welding of pure iron was conducted in helium as shielding gas. We investigated the influence of iron vapor on arc plasma and mechanism of iron vapor transportation from the weld pool into the arc plasma. We observed the arc plasma two-dimensionally with spectrometric method. We captured three different monochromatic images simultaneously by three monochromators with high speed video cameras. Thus, two inherence spectra of iron and also one inherence spectrum of helium in arc plasma were obtained. Using these spectra, plasma temperature distribution was obtained. In addition, concentration distribution of iron vapor was obtained by measuring electron density. It was concluded that plasma temperature decreased with increase of iron vapor concentration. Especially, the metal vapor concentration indicated the highest value near the base metal and the temperature around the weld pool decreased rapidly.
