TWI Industrial Member Report Summary 213/1983
By H Terashima and P H M Hart
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. The effects of Al introduced via the wire as well as the plate were also examined. Significant improvements in toughness of high Al (~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. The effect of Al on microstructure and toughness was found to be independent of its source (wire or plate). A schematic diagram describing the different effects of Al, Ti, Si, oxygen and flux TiO2 content on acicular ferrite formation is proposed.