Effect of flux TiO2 and wire Ti content on tolerance to high Al content welds - Effect of Al in C-Mn steels on microstructure and toughness of submerged-arc welds (Report 2)

In an earlier report an initial investigation into the influence of parent plate steel deoxidation practice, and in particular Al level, on the microstructure and toughness of submerged-arc welds had shown that even small changes in weld metal Si and Al levels (e.g. 0.02 to 0.03% Al) could produce drastic deterioration in Charpy toughness when using some basic fluxes.In the present report the results are presented of further work, primarily aimed at improving the tolerance to high weld metal Al levels, by using TiO2 additions to fluxes or Ti additions to wires.Significant improvements in toughness of high Al (0.03-0.04%) weld metals were observed by increasing flux TiO2 contents and weld metal oxygen levels. Titanium introduced from the wire was much less effective than that introduced from TiO2 in the flux. A schematic diagram describing the different effects of Al, Ti, Si, oxygen and flux TiO2 content on acicular ferrite formation is proposed.