Effect of Flux Grain Size on the Bead Appearance in Submerged Arc Welding

Research on Bead Formation in Submerged Arc Welding (Report 2)

Abstract

The effect of flux grain size on the weld bead appearance was investigated using a series of SiO₂-MnO fused type fluxes with various grain sizes. And gas permeability characteristics of model flux bed was measured in room temperature and high temperature to consider the degassing behaviour from an arc cavity.
When the finer flux was used, the finer weld bead ripples was generally obtained. And the effect of grain size on the bead appearance reduced with an increase in SiO₂/MnO. Gas permeability decreased with decrease of the grain size unless fluidized. And if fluidization occurs at room temperature due to the character of fine flux, considerable variation in permeability appears without any reduction of the permeability. When the flux was held at nearly its melting point in gas flow assuming the flux on an arc cavity, the permeability decreased considerably with holding time. But especially in case of fine flux, the fluidization was not stopped and moreover the permeability increased obviously within a short time by forming holes in the adhered flux bed.
It seems that the degassing behaviour out of the arc cavity has heavy influence on the bead ripple roughness relating pulsating state of the molten pool. And in case of coarse flux, irregular degassing which is compelled by the bonded layer of the flux grains surrounding the are cavity, result in rough bead ripples. But in case of fine flux, comparatively regular degassing which is assured by less grown layer by fluidization, result in fine ripples.