Mechanism of formation of solute bands in resistance seam welds of mild steel

Abstract

Metallographic examination of resistance seam welds in mild steel sheet made at welding speeds in the range 2–16 m min⁻¹ indicated that solute bands were formed as a direct result of differences in growth rate of the solid/liquid interface during the solidification process. The frequency of the bands in the longitudinal direction was equal to that of the waveform of the welding current used. It is considered that bands seen in the transverse direction represent discrete sections of the solidification front in the longitudinal section. The associated bands of solute segregation in the substructure were formed as a result of the sinusoidal phase shifted current waveform which was shunted back through the solidifying weld seam, thereby arresting the movement of the solid/liquid interface. The extent of these bands can be related to welding current, welding speed, and sheet thickness.

MST/3371