Flux-Cored Wire — Selection Guide

Flux-cored wire combines the continuous-feed speed of MIG with a built-in flux that either replaces or supplements shielding gas. It’s the fastest way to put down heavy welds on mild steel, and self-shielded versions work outdoors where wind would blow away MIG shielding gas.

Two categories split the flux-core world. Self-shielded (FCAW-S) wire like E71T-11 and E71T-GS generates shielding gas from flux decomposition. No bottle, no regulator, no wind problems. This is the go-to for field work, farm repairs, and 110V machines. Gas-shielded (FCAW-G) wire like E71T-1 runs with external CO2 or 75/25 mix for cleaner welds, better impact toughness, and higher deposition rates in the shop.

Self-shielded wire tolerates dirtier conditions and gusty environments, but produces more spatter and a rougher bead profile. Gas-shielded wire gives structural-quality welds that meet AWS D1.1 requirements, with deposition rates that beat solid MIG wire by 15-25% on the same amperage.

Diameter selection works like MIG wire: .030 for thin material on 110V machines, .035 for general fabrication on 220V, and .045 for production work on 300+ amp power sources. Drive rolls should be knurled (V-knurl) type to grip the softer tubular wire without crushing it.

The guides below cover wire-by-wire comparisons, polarity settings, and starting parameters for common joint configurations.