Computational model of submerged arc welding (SAW) was developed to clarify the arc phenomena and the heat source characteristics. Furthermore, the weld part during SAW was observed using an X-ray transmission system. To investigate the effect of the closed space on arc phenomena, the heat flux and current density distributions on a base metal surface during closed gas tungsten arc welding were measured by split anode method. Computational results showed that the metal vapor concentration in arc space during SAW became higher because the arc was generated in the closed space. However, its heat input to the base metal was almost the same as that of gas metal arc welding. Meanwhile, the welding current and arc voltage which largely affect characteristics of arc plasma agreed with the experiment results. The slag thickness obtained from the computation was also the same as that of the experiment, which supports the validity of this computational model. Moreover, comparative experiments with gas tungsten arc and closed gas tungsten arc showed that the closed space environment around the weld part in SAW did not affect heat characteristics of arc plasma. It was clarified that heat transfer and radiation energy of arc play different roles in SAW. Penetration of a base metal was formed by the heating from arc. Flux was melted by the radiative heating from arc, and it formed slag. It was suggested that the high heat efficiency from 90 to 99% during SAW was obtained since the radiation energy was given to a base metal indirectly through the slag.
