The authors investigated the change of penetration shape with time of wide range, and the influence of atmospheric condition and slag addition to the molten pool upon the penetration by fixed TIG arc hitting the mild steel plate.
After discussing the result obtained, we have come to the following conclusion.
1) The shape of penetration, in general, changes in the undermentioned series with the time lapse ; a) central type b) peripheral type and c) simple type.
Such a change can be explained by the change of convectional mode in the molten metal corresponding to the distribution of arc current on the surface of the molten pool.
2) Conical or saucepan-like penetration obtained in Nitrogen atmosphere seems to be a modified central type caused by the characteristic turbulent state of molten pool.
3) Deep penetration of simple type in the hydrogen rich atmosphere or under the very viscous slag such as silica shows the effect of concentrated arc.
4) If the molten metal is added to the molten pool, the central part of penetration surface is re-solidified leaving the peripheral penetration of ring-shape. This fact proves the existence of radial surface flow caused by the differrence in surface tension.