Abstract:
Post-weld slag and weld metal analyses were used to interpret the effects of different
commercial flux compositions on element transfer between molten flux (slag) and weld
metal in Submerged Arc Welding (SAW). Selected fluoride based flux compositions cover a
wide range of basicity index (BI) values of 0.5e3.0. Thermochemical modelling in FactSage
software is used to simulate the welding process in terms of gas-slag-metal equilibria. The
importance of the gas phase in SAW element transfer is illustrated. The model provides
improved accuracy in predicted weld metal oxygen values (ppm O) compared to the
generally used empirical relationship of weld metal ppm O vs. flux BI. Model predicted
oxygen values are within 150 ppm of the analysed values, compared to the empirical
relationship values which are within 240 ppm from the analysed values. The model provides
resolution in ppm O values at BI > 1.8. This information is lacking in the empirical
relationship with constant ppm O of 250 ppm at BI > 1.8. The measured ppm O values
follow the FeeFeO equilibrium trend with a positive offset. The relative level of oxygen to
deoxidation elements (Ti, Al, Mn, Si) in the weld metal is an important factor in oxide
inclusion engineering. This model will aid in the specification of flux formulations to attain
specific weld metal compositions for maximum acicular ferrite formation. In this way the
weld metal mechanical properties can be improved. This model will reduce the number of
welding tests required to develop new flux formulations.
