Er70S 2 Filler Rod – The Secret To Cleaner Tig Welds On Mild Steel

ByJim Boslice Metalworking & Fabrication

The er70s 2 filler rod is a premium, triple-deoxidized TIG welding wire designed for high-quality results on mild steel. It contains added zirconium, titanium, and aluminum to eliminate porosity and produce X-ray quality welds even on slightly oxidized surfaces.

This rod is the industry standard for critical applications like chromoly tubing, pipe welding, and automotive fabrication where strength and bead clarity are non-negotiable.

Most DIYers and hobbyist welders start their journey thinking all steel rods are created equal. You grab a handful of wire, strike an arc, and suddenly find yourself fighting “pepper” or tiny bubbles in your puddle.

When you pick up an er70s 2 filler rod, you are holding a specialized tool designed to solve those exact frustrations. It is the “old reliable” in many professional shops because it handles the realities of real-world metal better than most.

In this guide, we will break down exactly why this rod belongs on your welding cart and how to master its use for your next garage project. We will look at the chemistry, the technique, and the specific scenarios where this filler shines.

Understanding the er70s 2 filler rod Classification

To use a tool effectively, you have to understand what the labels actually mean. The American Welding Society (AWS) uses a specific coding system that tells you everything about the metal’s properties.

The “ER” stands for Electric Rod or Electrode, indicating it can be used as a filler or a current carrier. The “70” represents the minimum tensile strength, which is 70,000 pounds per square inch (PSI).

The “S” tells you it is a solid wire, not a flux-cored or tubular variety. Finally, the “2” refers to the chemical composition, specifically the triple deoxidizers that make this rod so unique in the welding world.

The Power of Triple Deoxidizers

What sets this rod apart from cheaper alternatives is the addition of aluminum, titanium, and zirconium. These elements act like a cleaning crew for your weld puddle while you work.

As you melt the steel, these deoxidizers react with oxygen and impurities. They pull those contaminants to the surface, preventing internal porosity that can weaken your joint.

This makes the rod particularly forgiving if the steel isn’t perfectly polished. While you should always aim for “bright and shiny” metal, this filler provides a safety net for those hard-to-reach corners.

Tensile Strength and Ductility

At 70,000 PSI, this rod matches or exceeds the strength of standard A36 mild steel. This ensures that the weld is not the weakest point of your fabrication.

Beyond just strength, it offers excellent ductility, meaning the weld can withstand some flex without cracking. This is why it is a favorite for structural frames and roll cages.

Mastering the er70s 2 filler rod for Precision Projects

Using the er70s 2 filler rod effectively requires a mix of proper machine settings and manual dexterity. Because it is a TIG-specific rod, your control over the heat is paramount.

Start by ensuring your TIG welder is set to DCEN (Direct Current Electrode Negative). This focuses the heat on the workpiece while keeping your tungsten sharp and cool.

For most mild steel projects, an argon shielding gas flow rate of 15 to 20 cubic feet per hour (CFH) is ideal. This protects the deoxidizers in the rod so they can do their job in the puddle.

Pre-Weld Preparation Steps

Even though this rod is deoxidized, you should still prep your material. Use a flap disc or a dedicated grinding wheel to remove all mill scale until the steel is silver.

Wipe the area down with acetone to remove oils or fingerprints. Contaminants on the base metal can overwhelm even the best filler rod if they are heavy enough.

Don’t forget to wipe the filler rod itself. Manufacturing oils can linger on the wire, so a quick pass with an acetone-soaked rag ensures a contaminant-free start.

Feeding the Puddle

The technique for feeding this rod is standard for TIG, but consistency is key. You want to dip the rod into the leading edge of the puddle, not directly under the tungsten.

If you get the rod too close to the arc, it will melt before it hits the puddle. This often leads to large “blobs” and poor penetration, which ruins the aesthetics and strength of the bead.

Maintain a 15-degree angle with your rod. This allows you to “dab” smoothly while keeping the end of the rod within the gas shield envelope at all times.

Comparing ER70S-2 vs. ER70S-6

A common question in the workshop is whether to use the S-2 or the S-6 variety of filler. Both are incredibly popular, but they behave very differently under the torch.

The ER70S-6 rod contains higher levels of silicon and manganese. These elements make the puddle more fluid, which many beginners find easier to manage when trying to get a “wet” look.

However, that extra fluidity can be a downside. On thin-wall tubing or overhead welds, the S-6 puddle can become difficult to control because it wants to run or sag.

When to Choose S-2

The er70s 2 filler rod produces a “stiffer” puddle that stays exactly where you put it. This makes it the superior choice for out-of-position welding or intricate joints.

If you are welding 4130 chromoly tubing, the S-2 is often the preferred specification. It provides a clean, predictable result that passes visual and X-ray inspections more consistently.

Professional pipe welders almost exclusively reach for the S-2 for root passes. Its ability to bridge gaps without blowing through is a massive advantage in critical fabrication.

When to Choose S-6

If you are working on heavy plate steel with stubborn mill scale, the S-6 might be the better choice. Its high silicon content helps “float” heavy impurities better than the S-2.

For general “farm-grade” repairs where the metal isn’t perfectly clean, the S-6 offers a bit more chemical cleaning power. But for the Jim BoSlice workshop standard, S-2 is the king of quality.

Essential Tools and Material Selection

To get the most out of your filler rod, you need to match it with the right supporting cast. This starts with your tungsten electrode and ends with your gas lens.

I recommend using a 2% lanthanated tungsten (blue tip). It handles high heat well and maintains a sharp point, which is vital for the focused arc needed for TIG steel.

A gas lens is also a game-changer. It provides a more stable, laminar flow of argon, ensuring your S-2 rod stays protected even when you have a slightly longer stick-out.

Choosing the Right Rod Diameter

Filler rods come in various sizes, typically ranging from 1/16″ to 1/8″. Matching the rod diameter to your material thickness is a fundamental skill.

  • 1/16″ Rod: Best for thin sheet metal and tubing (up to 1/8″ thick).
  • 3/32″ Rod: The “all-purpose” size for 1/8″ to 1/4″ plate.
  • 1/8″ Rod: Reserved for heavy plate and multi-pass structural welds.

Using a rod that is too thick will chill the puddle too much, leading to a lumpy bead. Using one that is too thin will require you to feed wire like a madman to keep up.

Storage and Maintenance

Steel filler rods will rust if left out in a humid garage. Once rust starts, the rod is essentially ruined for high-quality work because that oxide will go straight into your weld.

Store your rods in airtight plastic tubes. You can buy dedicated rod canisters, or even make your own out of PVC pipe with capped ends to keep the moisture out.

If you notice any discoloration or “fuzz” on the rod, don’t use it for anything critical. Toss it in the scrap bin or use it for practice pieces where strength doesn’t matter.

Common Pitfalls and Troubleshooting

Even with the best er70s 2 filler rod, things can go wrong. The most common issue is porosity, which looks like tiny pinholes in your finished weld.

This is usually caused by a lack of shielding gas or a contaminated rod. Check your flow meter and ensure there are no drafts in your shop blowing the argon away.

Another issue is “black soot” around the weld. This is often a sign that you are pulling the rod out of the gas shield between dabs, allowing the hot tip to oxidize.

Managing Heat Sink

Mild steel is a great conductor of heat. If you linger too long in one spot, the base metal will heat up, causing the puddle to sink or widen uncontrollably.

To prevent this, use a “tack and move” strategy for long seams. Place small tacks every few inches to keep the parts aligned and to act as heat sinks.

If the metal starts glowing bright orange far away from the arc, stop and let it cool. Overheating steel can lead to grain growth, which makes the metal brittle.

The “Dipping” Rhythm

Beginners often struggle with the rhythm of the dip. They either dip too fast, creating a mountain of metal, or too slow, causing the puddle to undercut the base metal.

Watch the “toes” of the weld—the edges where the puddle meets the base metal. You want the filler to fill that area completely before moving the torch forward.

Practice on scrap plate by drawing a straight line. Try to make every “dime” look identical in size and spacing to build the muscle memory required for pro-level results.

Frequently Asked Questions About er70s 2 filler rod

Can I use ER70S-2 for MIG welding?

While the chemical composition is the same, TIG rods come in 36-inch straight lengths. For MIG, you need a continuous spool of wire. You can find “S-2” MIG wire, but it is much less common than the standard S-6 wire used in most feeders.

Is this rod suitable for welding cast iron?

No, the er70s 2 filler rod is designed for mild steel and low-alloy steels. Cast iron requires high-nickel filler rods to handle the carbon content and prevent cracking during the cooling process.

Do I need to back-purge when using this rod?

Back-purging is usually reserved for stainless steel to prevent “sugar” or oxidation on the back side. For mild steel using S-2, it is generally not required unless you are doing high-pressure code piping or aerospace work.

What is the shelf life of these rods?

As long as they are kept dry and free of rust, they last indefinitely. If they have a light film of oil from the factory, just wipe them with acetone before use to ensure the best arc stability.

Final Thoughts on Mastering Mild Steel TIG

The journey to becoming a proficient welder is paved with practice and the right materials. Choosing the er70s 2 filler rod is a conscious decision to prioritize quality over convenience.

By understanding how the triple deoxidizers work and mastering the rhythm of the puddle, you can produce welds that are as strong as they are beautiful. Remember to keep your metal clean, your tungsten sharp, and your gas flowing.

Don’t be afraid to experiment with different rod diameters and travel speeds on scrap metal before moving to your final project. Consistency is the hallmark of a craftsman, and this rod is the perfect partner for that pursuit.

Now, head out to the garage, fire up the machine, and start laying some beads. There is no substitute for “hood time” when it comes to perfecting your craft!

Jim Boslice
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