Welding Stainless Steel

Stainless steel welds clean and looks great, but it punishes sloppy technique harder than mild steel. Too much heat causes warping, sensitization (chromium carbide precipitation), and loss of corrosion resistance. The right combination of filler metal, shielding gas, and heat management produces joints that maintain the properties you’re paying for.

The austenitic grades (304, 316, 321) make up most stainless welding in the shop. 304 is the workhorse, found in food equipment, handrails, and general fabrication. 316 adds molybdenum for better chemical and saltwater resistance. Filler metals match the base: ER308L for 304, ER316L for 316, ER347 for 321. Always use the “L” (low carbon) version to prevent sensitization in the HAZ.

TIG (GTAW) is the preferred process for stainless under 1/4 inch. Run DCEN with 100% argon shielding at 15-20 CFH. Keep amperage just high enough to maintain the puddle and move quickly. Stainless holds heat longer than steel, so interpass temperatures need monitoring. Stay under 350F between passes on austenitic grades.

MIG on stainless works well for production and thicker sections. The traditional shielding gas is a helium-rich tri-mix (90% He / 7.5% Ar / 2.5% CO2), though 98% argon / 2% CO2 has become popular for simpler setup and good results. Use a pulsed MIG program if your machine supports it to reduce heat input.

Back purging with argon protects the root side of the weld from oxidation. Without purge, the backside develops heavy oxidation (sugaring) that destroys corrosion resistance and creates a rough, weak root. For pipe and tubing, seal the ends with tape or silicone plugs, fill with argon at 10-15 CFH, and purge until oxygen levels drop below 100 PPM.

Cleanup after welding stainless requires stainless-only tools. Carbon steel brushes, grinding wheels, and clamps contaminate the surface and cause rust spots. Dedicated stainless brushes, clean gloves, and proper pickling paste restore full corrosion resistance.