Behaviour of the Solidification Variables in Welding

Solidification Process of Submerged Arc Weld Metals (Report 1)

Abstract

To achieve the latest stringent requirements for the mechanical properties and the bead shape of submerged arc welds (SAW) such as the longitudinal welds of large diameter pipe, the solidification process has been fundamentally studied using 25Cr-20Ni welds obtained by the one-sided SAW process at two heat input levels.
The basic solidification variables have been measured by immersing W·3Re-W·25Re thermocouples and the correlation with weld puddle shapes has been discussed in relation to welding heat transfer.
In the liquid-solid region of tear-drop shaped weld puddles observed commonly in SAW process, cooling rate and temperature gradient decreased toward the weld center and consequently the length of liquid-solid region increased. These results are similar to those in casting. Solidification rate, however, showed a maximum value at the inflection point of hammer decanted weld puddle contour, which was approximately agree with the measured isotherm of liquidus temperature.
Formation of the tear-drop shaped weld puddle can be explained by considering a substantial decrease in heat flow dimension in the vicinity of inflection point. This proposed mechanism provides interpretations that the shape transit of weld puddle from the ellipse to the tear-drop occurs with increasing in heat input or welding velocity and the solidification process of the latter is significantly influenced by the latent heat of fusion.