Shielding gas selection
Which mixture suits the material, the process and the thickness — with the EN ISO 14175 designation, so you can order it by name rather than by nickname.
Carbon steel
Argon with 8–25 % CO₂ covers nearly everything. More CO₂ means a hotter, deeper-penetrating arc and more spatter; less means a cleaner bead face and a steadier arc, and it is what spray transfer needs — above about 20 % CO₂ spray transfer stops working at all. Pure CO₂ is cheap and penetrates well, but it only gives globular transfer and it spatters.
Stainless and aluminium
Austenitic stainless takes argon with a small active addition — 2 % CO₂ or 2 % oxygen — kept small on purpose: carbon picked up from CO₂ reduces corrosion resistance. Aluminium takes pure argon, or argon with helium once the section is thick enough that argon alone will not carry the heat.
TIG
Inert gas without exception. Any active component destroys the tungsten within minutes. Argon-hydrogen mixtures are used on austenitic stainless to raise the heat and clean the surface, and on nothing else — hydrogen in ferritic or duplex steel causes exactly the cracking that preheat is meant to prevent.
Reading the gas designation
| Group | What it is | Examples |
|---|---|---|
| I | Inert | I1 — Ar, I2 — He, I3 |
| M1, M2, M3 | Mixtures with an oxidising addition, in rising order | M12, M13, M21 |
| C | Strongly oxidising | C1 — CO₂ |
| R | Reducing, with hydrogen | R1 — Ar + H₂ |
| N, O, Z | Nitrogen, oxygen, other compositions | — |
Frequently asked questions
What does the CO₂ content change?
Penetration and arc stability, in opposite directions. More CO₂ gives deeper, wider penetration and more spatter; less gives a cleaner bead face and a steadier spray arc. M21 with 18 % is the usual compromise for carbon steel.
Can I weld stainless with M21?
Better not. Carbon from the CO₂ enters the weld and lowers the corrosion resistance — the very property the material was bought for. For stainless the cylinder should hold no more than 2 to 3 % active component.
Why pure argon for TIG and for MIG on aluminium?
Because any active component burns the tungsten away in TIG, and on aluminium it thickens the oxide film instead of removing it. Aluminium also gets helium in the mix to carry heat into thick material — which is why it is argon-helium and never anything with CO₂.
Updated: