1. Flux Cored Arc Welding (FCAW)
Flux Cored Arc Welding (FCAW) uses a tubular wire that is filled with a flux. The arc is initiated between the continuous wire electrode and the workpiece. The flux, which is contained within the core of the tubular electrode, melts during welding and shields the weld pool from the atmosphere. Direct current, electrode positive (DCEP) is commonly employed as in the FCAW process.

2. There are two basic process variants; self shielded FCAW (without shielding gas) and gas shielded FCAW (with shielding gas). The difference in the two is due to different fluxing agents in the consumables, which provide different benefits to the user. Usually, self-shielded FCAW is used in outdoor conditions where wind would blow away a shielding gas. The fluxing agents in self shielded FCAW are designed to not only deoxidize the weld pool but also to allow for shielding of the weld pool and metal droplets from the atmosphere.
The flux in gas-shielded FCAW provides for deoxidation of the weld pool and, to a smaller degree than in self-shielded FCAW, provides secondary shielding from the atmosphere. The flux is designed to support the weld pool for out-of position welds. This variation of the process is used for increasing productivity of out-of-position welds and for deeper penetration.
Linnert, Welding Metallurgy,
AWS, 1994

3. FCAW Electrode Classification
Flux-Cored Arc Welding
E70 T - 1
Electrode
Type Gas, Usability
and Performance
Minimum UTS
70,000 psi
Classification for FCAW wire is designed to tell the user the ultimate tensile strength of the as welded weld metal, the position(s) it can be used in, and its usability characteristics.
In the example above, The ultimate tensile strength of the weld metal is specified as 70 ksi. Positions the electrode can be used in are specified by the third item in the specification, 0- for flat and 1 for all positions. The “T” designates that this is a flux cored wire. The usability and performance of the consumable is specified after the dash. In the example above the 1 stands for a general purpose electrode using DCEP and for multi-pass welding.
Flux Cored /Tubular
Electrode
Position
American Welding Society Specification
AWS A5.20 and AWS A5.29.

4. This slide lists a couple of flux cored electrodes and the elements present within the flux material. Note that there are both gas shielded and self-Shielded electrode types represented (limestone giving the self-shielding gas).
Linnert, Welding Metallurgy
AWS, 1994

5. Flux-Cored Arc Welding
Advantages
Flux-Cored Arc Welding
High deposition rates
Deeper penetration than SMAW
High-quality
Less pre-cleaning than GMAW
Slag covering helps with larger out-of-position welds
Self-shielded FCAW is draft tolerant.
The FCAW process combines the best characteristics of SMAW and GMAW. It uses a flux to shield the weld pool, although a supplemental shielding gas can be used. A continuous wire electrode provides high deposition rates.
The flux for FCAW consumables can be designed to support larger weld pools out of position and provide higher penetration compared to using a solid wire (GMAW). Larger welds can be made in a single pass with larger diameter electrodes where GMAW and SMAW would need multiple passes for equivalent weld sizes. This improves productivity and reduces distortion of a weldment.

6. Flux-Cored Arc Welding
Limitations
Flux-Cored Arc Welding
Slag must be removed
More smoke and fumes than GMAW and SAW
Spatter
FCAW wire is more expensive
Equipment is more expensive and complex than for SMAW
As with SMAW, the slag must be removed between passes on multipass welds. This can slow down the productivity of the application and result in possible slag inclusion discontinuities. For gas shielded FCAW, porosity can occur as a result of insufficient gas coverage.
Large amounts of fume are produced by the FCAW process due to the high currents, voltages, and the flux inherent with the process. Increased costs could be incurred through the need for ventilation equipment for proper health and safety.
FCAW is more complex and more expensive than SMAW because it requires a wire feeder and welding gun. The complexity of the equipment also makes the process less portable than SMAW.