Abstract:
This review is focused on the thermochemical behaviour of fluxes in submerged arc welding
(SAW). The English-language literature from the 1970s onwards is reviewed. It was recognised early
on that the thermochemical behaviour of fluxes sets the weld metal total ppm O and the element
transfer extent from the molten flux (slag) to the weld pool. Despite the establishment of this link
between the flux-induced oxygen potential and element transfer, it is also well accepted that the
slag–metal equilibrium does not control SAW process metallurgy. Instead, the gas phase must be
taken into account to better describe SAW process metallurgy equilibrium calculations. This is
illustrated in the gas–slag–metal equilibrium simulation model developed by Coetsee. This model
provides improved accuracy in predicting the weld metal total ppm O values as compared to the
empirical trend of Tuliani et al. Recent works on the application of Al metal powder with alloying
metal powders provide new insights into the likely gas phase reactions in the SAW process and
the modification of the flux oxygen behaviour via Al additions. Aluminium may lower the partial
oxygen pressure in the arc cavity, and aluminium also lowers the partial oxygen pressure at the weld
pool–slag interface. The weld metal total ppm O is lowered with the addition of aluminium in SAW,
but not to the same extent as would be expected from steelmaking ladle metallurgy de-oxidation
practice when using Al as de-oxidiser. This difference indicates that slag–metal equilibrium is not
maintained in the SAW process.
