Advanced Welding Processes: Technologies and Process Control

Filler materials for arc welding 51
Alloying addition
The range of compositions of solid GMAW wires is limited by the technical
and commercial difficulties involved in producing relatively small quantities
of special compositions. Flux-cored wires can, however, be modified by
minor adjustments in the flux formulation to produce a range of weld metal
compositions and operating characteristics. The range of compositions currently
available for plain carbon and alloy steels (the Australian, UK and US
specifications for flux-cored welding consumables are summarized in Appendix
4) is similar to that for MMA electrodes; with rutile (TiO2) based formulations
for ease of operation, basic (CaO) high-toughness, hydrogen-controlled
formulations and metal powder cores for high recovery and low slag formation.
It is also possible to extend this technique to produce low-cost austenitic
stainless steel or highly alloyed hardfacing deposits from wires with a plain
carbon steel sheath.
Slag shielding and support
The solidification characteristics of the slag may be designed to enhance the
performance of the process. For example, a fast freezing rutile slag may be
used to support the weld pool in vertical or overhead welding enabling
higher operating currents, improved productivity and better fusion
characteristics to be obtained. Alternatively, the slag characteristics may be
adjusted to provide additional shielding and control of bead shape. This is
particularly important in the case of the stainless-steel consumables discussed
below.
Arc stabilization and shielding
The decomposition of the flux constituents may be used to generate shielding
gases as in MMA welding, for example CO2 may be produced by the
decomposition of calcium carbonate
CaCO3 + CaO + CO2 (4.2)
Arc ionizers may also be added to the flux to obtain improved running
characteristics and arc stability. It is possible using these techniques to produce
electrodes that operate with alternating current or DC electrode negative and
this may have beneficial effects on the melting rate and weld bead properties.
4.4.3 Modes of operation
Flux-cored wires may be operated successfully with or without an additional
gas shield.