Welding Mild Steel

Mild steel is the most forgiving metal you’ll weld. Carbon content below 0.25% means it doesn’t harden in the heat-affected zone, it doesn’t crack easily, and it works with every welding process on the market. A36 structural plate, 1018 bar stock, and ERW tubing all fall in this category.

MIG welding mild steel is the fastest process for most shop work. Run .030 ER70S-6 wire with 75/25 argon/CO2 shielding gas on a 220V machine and you can weld everything from 16-gauge sheet to 3/8 inch plate. Voltage in the 18-22 range, wire feed speed between 250-400 IPM depending on thickness. Short-circuit transfer handles thin material and out-of-position work. Spray transfer at higher voltage and wire speed speeds up flat-position runs on thicker plate.

TIG on mild steel uses ER70S-2 filler rod with 100% argon at 15-20 CFH. It’s slower than MIG, but the bead quality is superior for visible joints, roll cages, and furniture. Run DCEN at 80-150 amps depending on thickness, with a 3/32 2% lanthanated tungsten for most work.

Stick welding mild steel works with 6013 (easy arc, all-position, beginner-friendly), 7018 (structural quality, low-hydrogen, smooth arc), or 6011 (deep penetration, runs on AC, handles dirty material). Rod diameter and amperage follow the material thickness, with 1/8 inch 7018 at 110-130 amps covering the most common range.

Flux-cored wire (E71T-11 self-shielded or E71T-1 gas-shielded) gives the highest deposition rates on mild steel and works in wind that would blow away MIG shielding gas.

Joint prep on mild steel is straightforward. Grind off mill scale and rust in the weld zone, degrease with acetone if needed, and maintain proper fit-up. Mild steel tolerates moderate gaps better than most alloys, but tight fit-up still produces stronger welds with less filler consumption.