Welding stainless steel: which filler and gas, and how to stop rust spots and warping

Stainless welds with the same machines as mild steel, and most of the gear carries over. What changes is the filler, the gas, how much heat the metal will take, and how easily a stray steel brush ruins it.

Use 308L filler on 304 stainless, 316L on 316, and 309L when joining stainless to mild steel. For mig, use a gas with under 5 percent CO2, not 75/25; tig uses argon. Weld with less heat than steel, and keep brushes and grinding wheels only for stainless, or it will rust.

Which filler for which job

From Lincoln, Harris and Hobart filler data, checked 2026-10-15:

Job	Filler	What the makers say
304 or 304L to itself	308L	Lincoln: ideal for welding 304L; Harris: for 301, 302, 304, 305 and 308
316 or 316L to itself	316L	Harris: for similar alloys with about 2 percent molybdenum
Stainless to mild or low alloy steel	309L	Lincoln: designed for joining stainless steel to mild or low alloy steel

The L means low carbon. Hobart gives 0.03 percent maximum for L-grade bare wire and 0.04 percent for coated rods, low enough that welding heat does not cause carbide precipitation next to the weld. That matters for corrosion resistance.

Do not use 308 on the stainless to mild steel joint. Hobart says it sometimes works, but dilution can leave a weld composition that cracks. Hobart names 309L and 312 as the fillers for dissimilar joints.

The gas, by process

Process	Gas the makers specify
Mig, solid wire, short circuit	Tri-mix of about 90 percent helium, 7.5 argon, 2.5 CO2 (Hobart, Lincoln), or 98 percent argon, 2 percent CO2 (Miller)
Mig, solid wire, spray	98 percent argon, 2 percent oxygen (Lincoln)
Flux cored stainless, gas shielded	75/25 or 100 percent CO2 (Hobart, Lincoln, Miller)
Tig	100 percent argon (Miller), 15 to 20 cubic feet per hour

Miller’s rule for solid wire is under 5 percent CO2, to avoid adding carbon to the weld. Hobart’s Handler 210i manual pairs 308L wire with 98/2. No maker document we read approves 75/25 for solid stainless wire, so the mig cylinder you use for steel is not the right one. Hobart also warns not to use argon-oxygen blends with flux cored stainless wire. Lincoln’s two tri-mix sheets differ slightly, one listing oxygen and one CO2 as the small component; buy what your supplier sells as stainless tri-mix.

Gas suppliers and cylinders are covered in mig welding gas.

Will your machine do it?

Most mig welders that run gas can run solid stainless wire. Hobart lists .023 to .030 inch stainless on the Handler 140EZ, and .023 to .035 on the 210MVP. Miller’s 211 lists .024 to .035 stainless in its Auto-Set. Miller also recommends drive rolls and a gun liner kept only for stainless.

Flux cored stainless wire exists, but the common E308LT1 and E309LT1 wires are gas shielded and run on DC electrode positive. Self-shielded stainless flux core is a separate class; we found no maker document offering it for small home machines, so a flux-core-only machine is not a stainless route.

Stick works too: Lincoln’s 309L-16 rod runs on DC positive or AC, and its 308L-16 rod is sold in 3/32 to 3/16 inch. Tig on stainless is DC, so any DC tig or multiprocess machine covers it, with 2 percent lanthanated or similar tungsten from tungsten electrodes.

Starting settings: Hobart’s stainless guide gives .030 wire at 50 to 150 amps and 18 to 22 volts on tri-mix with 3/8 to 1/2 inch stickout. Your machine’s door chart is the better start if it has a stainless row; see mig welder settings chart.

Why stainless warps and discolors

Hobart explains that stainless conducts heat at about a third the rate of carbon steel and expands up to 50 percent more. Heat stays near the weld, and thin parts warp. Hobart’s advice is less current and more clamping.

Too much heat for too long has a second cost. Miller says it causes carbide precipitation, which costs the metal its corrosion resistance, and oxidation on the back of the joint. Miller’s fixes: move faster rather than slower, avoid weaving, shorten the arc, and use pulse if your machine has it. Hobart, for plain 304, gives an interpass limit of 350 F, so let the part cool between passes.

The colors around a weld are heat tint. Miller says overheating changes the color and reduces corrosion resistance, and cannot be reversed. Hobart says removing the tint matters most in aggressive environments, by pickling paste, acid, glass bead blasting or electropolishing. On the back of a tig weld, a grainy black crust called sugaring means the root oxidized; Miller says to back purge with argon or reduce amperage.

Rust spots: keep the tools separate

Hobart: only stainless brushes used on stainless alone should touch the weld, because carbon steel brushes introduce contamination that causes surface rusting. It lists grinding wheels, steel tools, fixtures and shop dust as sources of iron. Miller adds files and grinders that never touch carbon steel or aluminum.

In a shared garage: one brush and one grinding wheel marked for stainless, a clean bench surface, and grind your steel projects somewhere else.

Fume: hexavalent chromium

Hobart’s safety bulletin says welding stainless can expose you to hexavalent chromium, and that OSHA limits workplace exposure to 5 micrograms per cubic meter averaged over eight hours. OSHA names welding on stainless steel as a major source of exposure. Weld with ventilation that carries fume away from your face; respirators are compared in welding respirators.

Sources: Hobart stainless steel welding guide; Miller, mig welding stainless; Miller, tig problems; Lincoln 308LSi and 309LSi data sheets; OSHA hexavalent chromium.

Exhaust parts, food equipment and anything holding pressure or a load belong to a certified welder if failure matters. For the other metal that needs a different setup, see welding aluminum.