TIG Welding Steel Settings: Amperage Chart, Filler Rod & Gas Setup

TIG welding mild steel uses DCEN polarity, 100% argon at 15-20 CFH, a 2% lanthanated or ceriated tungsten, and ER70S-2 filler rod. Set amperage to roughly 1 amp per thousandth of inch of material thickness, using a foot pedal for real-time control.

Steel is the easiest metal to TIG weld. It’s forgiving on heat input, tolerates a wider range of settings than aluminum or stainless, and gives clear visual feedback through puddle color and fluidity. If you’re learning TIG, start on mild steel. The skills transfer directly to stainless, chromoly, and other DC metals.

Amperage Settings by Thickness

Steel TIG settings follow the same “1 amp per thou” rule as most metals, with adjustments for joint type and position. The chart below covers A36 mild steel and similar low-carbon steels (1018, 1020) in flat position butt joints.

T-joints and fillets use the lower end of the amperage range because heat concentrates in the corner. Lap joints can run mid-range. Outside corners dissipate heat fast, so they sit at the upper end.

Beyond 1/4", TIG becomes impractical for fill passes. Most shops use TIG for the root pass on thick steel, then switch to MIG or stick for fill and cap. The root pass amperage for a 1/4" V-groove butt joint runs 90-120A with a 3/32" tungsten and 3/32" filler.

DCEN Polarity Setup

Every TIG weld on steel uses DCEN (DC Electrode Negative), sometimes labeled “straight polarity” on older machines. The torch is negative, the workpiece is positive.

In DCEN, electrons flow from the tungsten to the workpiece. This concentrates approximately 70% of the arc heat into the base metal and only 30% into the tungsten. The result is good penetration with a long tungsten life. DCEN produces a narrow, deep weld profile on steel.

Don’t use AC for steel. AC is for aluminum and magnesium where oxide cleaning is needed. On steel, AC would overheat the tungsten and produce a wide, shallow puddle with poor penetration.

For a full explanation of when to use AC vs. DC, see AC vs. DC TIG welding.

Tungsten Selection and Preparation

2% lanthanated (blue band) is the best all-around tungsten for DC steel work. It starts easy, holds a point well, and handles high amperage without splitting.

2% ceriated (gray band) is a close second. Slightly better at low amperages (under 50A), making it useful for thin sheet metal work.

2% thoriated (red band) was the old standard for DC welding. It works fine but is mildly radioactive. Grinding thoriated tungsten creates radioactive dust. Most shops have moved to lanthanated or ceriated as safer alternatives with equal performance.

Grinding the Tungsten

Grind the tungsten to a point on a dedicated grinding wheel (diamond or silicon carbide). Grind lengthwise, not across the tip, so the grind lines run parallel to the electrode. Grinding across the tip creates an unstable arc that wanders.

A sharper point concentrates the arc into a smaller area, giving more precise control and deeper penetration on thin material. A blunter point spreads the arc wider and handles higher amperages without eroding.

For complete details on every tungsten type and color code, see the tungsten electrode guide.

Filler Rod Selection

ER70S-2

The preferred filler for TIG welding mild steel. The “70” means 70,000 psi tensile strength. The “-2” designation includes triple deoxidizers (aluminum, titanium, and zirconium) on top of the silicon and manganese in all 70S wires.

This extra deoxidizer package makes ER70S-2 tolerant of slightly dirty or mill-scaled base metal. It produces clean welds with minimal porosity even when conditions aren’t perfect. The rod feeds smoothly into the puddle and produces a convex, well-shaped bead.

ER70S-6

Higher silicon content (0.8-1.15%) than ER70S-2. This extra silicon acts as a deoxidizer and improves puddle fluidity. ER70S-6 is the standard wire for MIG welding and it works for TIG, but the higher silicon can make the weld slightly more brittle. For TIG-specific work, ER70S-2 is the better choice.

ER70S-3

Minimal deoxidizers. Only use this on perfectly clean, freshly ground base metal. Any mill scale, rust, or contamination causes porosity. Rarely used for TIG in shop settings.

Filler Rod Diameter Selection

Match filler diameter to tungsten diameter and material thickness. Using filler that’s too thick absorbs too much heat and creates cold, humped beads. Filler that’s too thin melts before it reaches the puddle.

Shielding Gas

100% argon is the standard and only gas most shops need for TIG welding steel. Don’t confuse TIG gas requirements with MIG. MIG needs CO2 or argon/CO2 mixes for proper arc transfer. TIG works perfectly with pure argon on all steels.

Flow rates: 15-20 CFH for most work. Use 12-15 CFH with small cups (#5-#6) on thin material. Increase to 20-25 CFH with larger cups (#8-#10) or in drafty conditions.

Argon/helium mixes (25% He / 75% Ar) increase arc voltage and heat input. This helps on thick steel sections where you need more penetration without increasing amperage. Helium mixes cost more and require higher flow rates because helium is lighter than argon and disperses faster.

Torch and Travel Technique

Torch Angle

Hold the torch at 15-20 degrees from vertical, tilted in the direction of travel (push angle). This gives you a clear view of the puddle’s leading edge and keeps shielding gas over the solidifying weld.

On fillet welds, split the angle between the two pieces. For a 90-degree T-joint, hold the torch at 45 degrees to each plate, tilted 15 degrees in the travel direction.

Travel Speed

Steel is forgiving on travel speed compared to aluminum. Move fast enough that the puddle stays small and controlled, but slow enough to achieve full fusion. A good visual indicator: the puddle should be about 2-3 times the width of the filler rod.

If the puddle gets too large, you’re moving too slowly or running too much amperage. Speed up or back off the pedal. If you see the edges of the puddle solidifying before the bead forms properly, you’re moving too fast.

Arc Length

Keep the tungsten tip 1/8" to 3/16" from the workpiece. This distance is called arc length. Too long an arc (more than 1/4") spreads the heat zone, reduces penetration, and increases the chance of contamination. Too short an arc (under 1/16") risks dipping the tungsten into the puddle.

Filler Addition

Feed filler into the leading edge of the puddle with a steady dip-and-withdraw rhythm. The rod should enter the puddle at a shallow angle (15-30 degrees from horizontal). Don’t dip straight down into the center of the puddle. Keep the filler rod tip within the gas shield at all times to prevent oxidation. Pull the rod back about 1/2" between dips, but don’t pull it out of the gas envelope.

For detailed filler rod manipulation techniques, see the TIG dip technique guide.

Autogenous Welding (No Filler)

On thin steel sheet metal (22 ga to 16 ga), you can fusion weld without adding filler. This is called autogenous welding. The arc melts the edges of the joint together without additional material.

Autogenous welds work best on butt joints with tight fit-up (no gap) and flanged edges. The flanged edges provide extra material that acts as built-in filler. Without a flange, the joint may be slightly concave, which is acceptable for non-structural applications but not for code work.

Reduce amperage by about 20% from the filler settings above when welding autogenous. The heat doesn’t have to melt filler rod, so less energy is needed. Travel speed increases since you’re not pausing to dip.

Common Problems and Fixes

Gray or Oxidized Welds

The weld surface should be bright and shiny with a golden or straw-colored heat tint at the edges. Gray, black, or scaly welds indicate insufficient gas coverage. Check gas flow, cup condition, and post-flow time. Also check for drafts. Post-flow should be at least 5-8 seconds to protect the cooling weld.

Porosity

Pinhole clusters in the weld come from contamination or gas issues. Common causes in order of likelihood:

1. Oil, paint, or rust on the base metal (grind to bright metal)
2. Moisture in the gas line (purge the line before welding)
3. Gas flow too high, causing turbulence (reduce to 15-20 CFH)
4. Contaminated filler rod (wipe with acetone)
5. Leaking gas connections at the torch or regulator

Undercut

Grooves along the toes of the weld mean too much heat or too slow a travel speed at the edges. Reduce amperage slightly or increase travel speed. On fillet welds, undercut on the vertical leg usually means the torch angle is favoring the horizontal plate too much. Redirect the arc toward the vertical member.

Lack of Penetration

If the weld sits on top of the joint without fusing into the base metal, amperage is too low or travel speed is too fast. Increase amperage by 10-15% and slow down slightly. On butt joints, check your root opening. A tight root on thick material prevents full penetration regardless of amperage.

Tungsten Inclusions

If bits of tungsten end up in the weld, you’re dipping the electrode into the puddle. This happens when arc length is too short or when you lose focus during a long bead. Maintain at least 1/8" arc gap. If you do dip, stop, break off the contaminated tungsten tip, regrind, and restart.

When TIG Is and Isn’t the Right Choice for Steel

Use TIG on steel for:

• Thin sheet metal (22 ga to 14 ga) where MIG can blow through
• Root passes on pipe and structural joints
• Visible welds where appearance matters
• Small, precise joints and tight spaces
• Repair work on thin sections

Use MIG or stick instead for:

• Fill and cap passes on thick material
• Long runs on 3/16" and thicker plate
• Production work where speed matters
• Outdoor work where gas coverage is difficult to maintain

TIG on steel produces beautiful, precise welds, but at about one-third the deposition rate of MIG. For a direct comparison of when each process makes sense, see TIG vs. MIG: when to use each.