Flux-cored wire has a hollow core filled with flux, which generates its own shielding gas as it burns. This is what makes it usable outdoors where wind would blow away MIG shielding gas, and it is why flux-cored wire is the standard for field work, structural steel and heavy fabrication.
Two families exist. Self-shielded (FCAW-S) wire needs no external gas at all and tolerates wind and outdoor conditions. Gas-shielded (FCAW-G, sometimes called dual-shield) wire uses CO2 or a CO2 mix for better arc stability, deeper penetration and better mechanical properties, but must be used indoors or with wind protection.
Classification follows the same logic as stick electrodes: E70T-1 and E71T-1 are 70 ksi flux-cored wires, with the suffix describing position capability and shielding. The -1 types are generally all-position; -2 types are flat and horizontal only with higher deposition. The -9 and -11 suffixes indicate self-shielded wires with different toughness characteristics.
Polarity and gas requirements are not interchangeable. Many self-shielded wires run DC electrode negative, which requires the machine to be set accordingly; running them on the wrong polarity produces poor arc characteristics and porosity.
