Flux-Cored Arc Welding (FCAW) is a welding process that uses a tubular wire filled with flux instead of a solid wire. The flux protects the weld pool from contamination and may eliminate the need for an external shielding gas, depending on the wire type. Flux-cored welding offers high deposition rates, deep penetration and excellent productivity, making it ideal for structural steel, heavy fabrication, shipbuilding and outdoor construction.
This guide explains how flux-cored welding works, how to choose the right wire for your application, the difference between gas-shielded and self-shielded wire, and how to get the settings right. Each section links to a focused in-depth page so you can go straight to what you need.
What is flux-cored welding?
Flux-cored welding uses a continuously fed tubular wire that contains flux in its core. As the wire melts, the flux produces shielding gases and forms a protective slag over the weld. Some flux-cored wires require an external shielding gas, while self-shielded wires generate their own protection. The process is valued for its speed, penetration and ability to weld thicker materials efficiently.
FCAW stands for Flux-Cored Arc Welding. It is a semi-automatic or automatic process that uses tubular flux-filled wire to create high-quality welds, and it is widely used wherever productivity, penetration and welding speed matter more than weld appearance alone.
There is no separate “flux-cored welder” — flux-cored wire runs on a MIG/wire-feed machine, so if you are picking equipment for the process see our guide to choosing a welding machine.
For a fuller explanation of the mechanics, the advantages and how fast the process really is, see our guide to how flux-cored welding works.
Why choose flux-cored welding?
Flux-cored welding offers faster deposition rates than solid MIG wire, excellent penetration and high productivity. It performs well on thicker materials and is less sensitive to mill scale and surface contamination than some other processes. Because of this, it is widely used in structural steel, heavy engineering, shipbuilding and outdoor applications where productivity is important.
Its main strengths are:
- High deposition rates — among the fastest manual welding processes available.
- Deep penetration — well suited to thicker sections.
- Tolerance of less-than-perfect surfaces — less sensitive to mill scale and surface contamination.
- Outdoor capability — self-shielded wire welds reliably in windy conditions.
Gas-shielded vs self-shielded flux-cored wire
There are two families of flux-cored wire, and choosing between them is the single most important decision in the process.
Self-shielded flux-cored wire generates its own shielding gases from the flux inside the wire, eliminating the need for an external gas supply. This makes it ideal for outdoor welding, where wind cannot easily disperse the shielding gas.
Gas-shielded flux-cored wire requires an external shielding gas — usually Argon/CO₂ or CO₂ — in addition to the flux contained within the wire. It generally produces smoother welds with better mechanical properties, which is why it is preferred in workshop fabrication.
The right choice depends on your working environment and application. Our guide to gas-shielded vs self-shielded flux-cored wire covers the trade-offs in full, including which shielding gas to use.
Choosing the right flux-cored wire
The best flux-cored wire depends on the material, the welding position, the required strength, and whether welding will take place indoors or outdoors. You should consider the wire classification, shielding gas requirements and compliance with relevant welding standards before selecting a consumable.
In brief:
- Mild steel fabrication — E71T-1 gas-shielded flux-cored wire is widely used for its deposition rates, mechanical properties and positional welding characteristics.
- Structural steel — low-hydrogen gas-shielded wires meeting BS EN ISO or AWS standards.
- Outdoor welding — self-shielded flux-cored wire.
- Heavy fabrication — gas-shielded flux-cored wire for high deposition and deep penetration.
Flux-cored wire can also weld stainless steel and galvanised steel. Wire diameter selection matters too, as it affects both productivity and weld quality. Our full guide to choosing the right flux-cored wire walks through every application.
Flux-cored welding outdoors
Yes — flux-cored welding can be used outdoors. Self-shielded flux-cored wire is specifically designed for outdoor welding because it does not rely on external shielding gas, so windy conditions that would disrupt MIG welding do not affect it. This makes it ideal for construction sites, structural steel and repair work. See our page on flux-cored welding outdoors and on site.
Flux-cored vs MIG welding
Flux-cored welding provides deeper penetration and higher deposition rates than conventional MIG welding, and it performs better outdoors — particularly with self-shielded wire. MIG welding generally produces cleaner welds with less slag and is often preferred for thinner materials and workshop fabrication. We compare the two processes in detail in flux-cored vs MIG welding. For more on MIG, see our MIG welding hub.
Settings, slag and troubleshooting
Getting flux-cored welds right depends on correct machine setup. Polarity matters: most gas-shielded wires use DC Electrode Positive (DCEP), while many self-shielded wires require DC Electrode Negative (DCEN) — always follow the manufacturer’s recommendations. Flux-cored welding also produces a protective slag that must be removed after welding, and common faults such as porosity, worm tracks and excessive spatter usually trace back to settings or material condition.
Our flux-cored welding settings and troubleshooting page covers polarity, slag removal and how to fix the most common defects. For wider fault-finding, see the welding defects and troubleshooting hub.