TWI Industrial Member Report Summary 186/1982
By H Terashima and P H M Hart
To study the effect of Al in C-Mn-Nb steels on weld metal toughness, single-pass, bead-in-groove, tandem submerged-arc welds have been made at 4.9kJ/mm. The work was based on a 1.5%Mn-0.5%Mo (S3Mo) wire, with two types of basic agglomerated fluxes (Lincoln 11 and OP121TT) and a calcium-silicate fused flux (Linde 851). Semikilled, Si-killed and Si-killed, Al-treated plates of 25mm thickness were employed.
The preliminary findings presented in the report show that relatively small changes in Si and Al levels, produced by changes in plate deoxidation practice and Al level, can produce pronounced changes in weld metal microstructure and Charpy toughness (up to l00degC shift in 35J temperature) when using some basic fluxes. With a calcium-silicate flux, giving a higher weld oxygen level, no detrimental effect of up to ~0.05%Al in the weld metal was observed. The results indicate that achievement of high weld metal toughness with some basic fluxes may be difficult in high dilution welds in Si-killed, Al-treated steels having more than ~0.035-0.045%Al, and in steels of low Si (less than ~0.15%) and low Al (less than ~0.01%) contents.
The data obtained indicate that the changes in microstructure arise from the influence of the change in Si and Al on the weld pool deoxidation behaviour, soluble Al contents and resultant inclusion contents. It is also possible that increases in the soluble Al contents alter the microstructure in part by directly raising the austenite transformation temperature and in part by reducing the extent of formation of Ti oxides.