TWI Industrial Member Report Summary 124/1980
By N Bailey and R J Pargeter
Earlier tests, reported in Parts 1-3, have been extended to include a wider range of Mn contents in the as-welded condition.
With multipass unalloyed submerged-arc weld metal welded at 3kJ/mm on 30-32mm plate, two major types of toughness behaviour were found. With manganese and normal calcium silicate flux types, COD and Charpy transition temperatures increased linearly as the weld metal proof stress and the weld metal carbon equivalent (CE) increased and the proportion of grain boundary ferrite in the unrefined microstructure decreased.
With alumina-rutile, alumina-basic and basic flux types, toughness improved as the proportion of fine acicular ferrite was increased by increasing the weld CE and reducing oxygen and inclusions.
These two major flux types exhibit different Charpy/COD transition temperature correlations from each other and from two welds made with low and high silica calcium silicate fluxes. These should be recognised as separate types in any flux classification.
Despite different types of behaviour, COD and Charpy transition temperatures could be estimated reasonably well for all fluxes by compositional multiple regression equations.
In two-pass single wire welds made at 5.5kJ/mm on ~30mm plate with a similar range of fluxes, strength increased and grain boundary ferrite decreased linearly with increasing CE of the weld metal.
With basic fluxes, cleavage resistance was increased if grain boundary ferrite was increased but with other flux types this behaviour was masked if P, Si and N were much above the level in basic flux welds. Crack opening displacement toughness was adequately described by a compositional equation