ER70S-2 is the best TIG filler rod for mild steel, especially when the base metal isn’t perfectly clean. Its triple-deoxidized chemistry contains titanium, zirconium, and aluminum on top of silicon and manganese, giving it five deoxidizers that scrub oxygen from the weld pool. The result is a cleaner, more porosity-free deposit than you’ll get from ER70S-6 or ER70S-3 under the same conditions. If you TIG weld carbon steel in a shop where every piece isn’t sandblasted to white metal, ER70S-2 should be your default rod.
The wire is classified under AWS A5.18/A5.18M and carries a minimum tensile strength of 70,000 PSI (480 MPa). It runs on DCEN (straight polarity) with pure argon shielding, which is standard for GTAW on steel.
AWS A5.18 Classification
The full designation breaks down like this:
- E = Electrode (carries current)
- R = Rod (usable as hand-fed TIG filler)
- 70 = 70,000 PSI minimum tensile strength
- S = Solid wire
- 2 = Chemical composition group (Ti, Zr, Al deoxidizers)
That “-2” suffix is the entire reason this rod exists. The titanium (0.05-0.15%), zirconium (0.02-0.12%), and aluminum (0.05-0.15%) deoxidizers react with dissolved oxygen in the molten pool before it can form gas bubbles. Silicon and manganese do similar work, but the triple-deoxidizer system catches what Si and Mn miss, particularly on steel with light rust, mill scale, or surface oxides.
Chemical Composition
| Element | Weight % | Purpose |
|---|---|---|
| Carbon (C) | 0.07 max | Strength, hardness |
| Manganese (Mn) | 0.90 - 1.40 | Deoxidizer, toughness |
| Silicon (Si) | 0.40 - 0.70 | Deoxidizer, wetting |
| Titanium (Ti) | 0.05 - 0.15 | Deoxidizer, grain refinement |
| Zirconium (Zr) | 0.02 - 0.12 | Deoxidizer, arc stability |
| Aluminum (Al) | 0.05 - 0.15 | Deoxidizer, oxygen scavenger |
| Phosphorus (P) | 0.025 max | Residual (keep low) |
| Sulfur (S) | 0.035 max | Residual (keep low) |
| Copper (Cu) | 0.50 max | Residual or coating |
Notice the lower silicon (0.40-0.70%) compared to ER70S-6 (0.80-1.15%). That’s a deliberate tradeoff. Less silicon means less tendency toward silicon islands (those glassy, hard spots on the weld surface), which makes ER70S-2 preferred for multi-pass welds and applications where post-weld machining is needed. The titanium, zirconium, and aluminum pick up the deoxidizing slack.
Mechanical Properties
| Property | AWS A5.18 Minimum | Typical Value |
|---|---|---|
| Tensile Strength | 70,000 PSI (480 MPa) | 72,000 - 80,000 PSI |
| Yield Strength | 58,000 PSI (400 MPa) | 60,000 - 68,000 PSI |
| Elongation (2") | 22% min | 26 - 30% |
| CVN Impact (-20F) | 20 ft-lbs | 50 - 80 ft-lbs |
The standout number is impact toughness. ER70S-2 consistently tests higher in Charpy V-notch values than ER70S-6, which makes it a solid pick for applications that see cold-weather service or dynamic loading. That titanium content refines the grain structure of the weld deposit, improving ductility and toughness.
ER70S-2 vs. ER70S-6 for TIG Welding
This is the comparison most welders ask about, and the answer depends on your shop conditions and what you’re welding.
Weld pool behavior: ER70S-6 produces a more fluid puddle because of its higher silicon content. It wets out to the toes better, which some welders prefer for fillet welds. ER70S-2 runs slightly stiffer, giving more control on out-of-position work and root passes.
Contamination tolerance: ER70S-2 wins here. The triple-deoxidizer system handles light surface oxides, residual oils, and mill scale that would cause porosity with a lower-deoxidized wire. If you’re doing repair work on material that hasn’t been ground to bright metal, the -2 is more forgiving.
Silicon islands: ER70S-6 deposits tend to leave glassy silicon oxide spots on the bead surface and between passes. In multi-pass welds, these silicon islands can cause inclusions if they’re not chipped off between passes. ER70S-2 produces fewer silicon residues because it has less silicon to start with.
Cost and availability: ER70S-6 is cheaper and stocked everywhere. ER70S-2 costs 15-30% more per pound and may require ordering from a welding supply distributor rather than grabbing it off the shelf at a hardware store.
Bottom line: If you TIG weld steel regularly and want the cleanest deposits with the least porosity issues, stock ER70S-2. If you’re buying one rod to share between MIG and TIG duty, ER70S-6 is the practical choice.
Diameter Selection
TIG filler rod diameter should roughly match the base metal thickness for thin material, then scale up for heavier plate. The goal is enough filler to build the weld profile without having to feed aggressively or run excessive heat.
| Rod Diameter | Base Metal Thickness | Amperage Range (DCEN) | Best Applications |
|---|---|---|---|
| 0.045" (1.2 mm) | 20 ga - 16 ga | 15 - 60A | Sheet metal, thin tubing |
| 1/16" (1.6 mm) | 16 ga - 1/8" | 40 - 110A | Light fabrication, roll cages |
| 3/32" (2.4 mm) | 1/8" - 3/16" | 80 - 180A | General fab, pipe root passes |
| 1/8" (3.2 mm) | 3/16" - 3/8"+ | 140 - 250A | Heavy plate, multi-pass fills |
A common mistake is using rod that’s too thick for the material. A 1/8" rod on 16-gauge sheet metal forces you to run higher amps just to melt the filler, which dumps excess heat into thin base metal and causes burn-through. Start with a thinner rod and step up only when you need more fill volume.
For pipe root passes, many welders use one size smaller than they’d pick for a flat plate joint. The tighter space inside a pipe joint makes it easier to control a thinner rod, and you can dab more precisely.
Applications
General steel fabrication: ER70S-2 handles A36, A500, 1018, 1020, and similar low-carbon steels. It’s the standard TIG rod for structural work, brackets, frames, and general repair.
Chromoly tubing (4130): For non-critical and thin-wall chromoly applications like aircraft tubing, bicycle frames, and light roll cages, ER70S-2 provides adequate strength and good weld quality. The weld won’t match the base metal’s heat-treated properties, but for normalized (non-heat-treated) 4130, it’s a widely accepted choice. For structural aerospace and race car chassis requiring full property matching, ER80S-D2 is the proper filler.
Root passes in pipe welding: ER70S-2’s contamination tolerance makes it popular for open-root pipe joints where back-purge conditions aren’t perfect. The extra deoxidizers help compensate for minor atmospheric contamination on the root side.
Repair welding: Maintenance and repair work often involves steel of unknown grade with surface contamination. ER70S-2 handles these conditions better than any other carbon steel TIG rod.
Shielding Gas
Pure argon (99.99%) at 15-25 CFH is the standard setup for TIG welding steel with ER70S-2. There’s no benefit to argon/CO2 blends in GTAW since the tungsten electrode would be destroyed by CO2.
For thick sections where you need more heat input without cranking amperage, some welders add 2-5% hydrogen to the argon. This increases penetration and travel speed but requires careful technique and is only appropriate for austenitic stainless and nickel alloys in specific situations. On plain carbon steel with ER70S-2, stick with pure argon.
Gas coverage matters more than flow rate. Keep the cup close to the work (3/8 to 1/2 inch), use a gas lens if you have one, and avoid drafty areas. A gas lens collet body produces a wider, more stable gas column that protects a larger area of the weld zone.
Storage and Handling
ER70S-2 TIG rod is sold in 36-inch (915 mm) cut lengths, typically in 1 lb, 5 lb, or 10 lb tubes. The rod surface should be clean and shiny with a smooth copper or bare wire finish.
Store rods in the sealed tube they come in. If you’ve opened a tube, keep it in a dry area away from moisture. Rust on TIG filler rod means porosity in your welds. Wipe each rod with a clean cloth or acetone before use if you suspect any surface contamination, especially in a dusty shop.
Don’t store TIG rod in the same drawer as stick electrodes, flux-cored wire, or other consumables. Cross-contamination with flux residue on TIG rod causes gas pockets and inclusions in the weld deposit.
Common Brands and Pricing
Most major wire manufacturers produce ER70S-2 TIG rod, but availability varies by region. Lincoln Electric, ESAB, Weldcote, and Blue Demon all stock it in common diameters. Price at time of writing runs $15-25 per pound for 36-inch cut lengths, compared to $10-18 per pound for ER70S-6 in the same format.
The price premium is worth it if you’re doing clean, critical TIG work. The reduced rework from porosity issues more than covers the extra rod cost on most jobs.
Common Mistakes with ER70S-2
Using rod that’s too thick for thin material: A 1/8" rod on 16-gauge steel forces you to crank amperage just to melt the filler, which overheats the base metal and causes burn-through. Match rod diameter to base metal thickness for thin material (see the chart above).
Contaminating the rod surface: TIG filler rod goes directly into the weld pool with no flux protection. Grease, oil, rust, or shop dust on the rod surface ends up in the weld. Wipe rods with a clean cloth or acetone before use, especially in dusty environments.
Running too much gas flow: More argon isn’t better. Excessive flow rates (above 30 CFH in most setups) create turbulence at the cup that actually draws in air instead of excluding it. Use 15-25 CFH with a gas lens, or 20-30 CFH with a standard collet body.
Pulling the rod out of the gas envelope: When you dab the rod into the puddle and then pull it back, keep the tip within the argon shielding cone. A rod tip that oxidizes in air (turns black) contaminates the next dab with oxide inclusions. If the tip oxidizes, snip off the contaminated end before the next dab.
Storing stainless and carbon steel rod together: Cross-contamination between ER70S-2 and ER308L causes problems in either direction. Carbon on stainless welds causes sensitization. Stainless contamination on carbon steel welds is less critical but still poor practice. Keep separate, labeled storage tubes.
For a complete overview of TIG filler rod types and selection, check the category guide. If you’re deciding between rod diameters for your specific application, the filler rod diameter selection guide covers thickness-to-diameter pairing in detail.