Er70S 2 Vs Er70S 6 Which Tig Filler Rod Should You Use

ByJim Boslice Metalworking & Fabrication

Choose ER70S-2 for high-purity welds on clean, critical joints like roll cages or pressure vessels where puddle control is paramount. Opt for ER70S-6 when welding metal with light rust or mill scale, as its higher silicon content provides better deoxidation and a more fluid puddle.

Every welder eventually stands in front of the filler rod rack at the local supply shop, scratching their head over the subtle differences in labels. You know you need a mild steel rod for your TIG project, but deciding er70s 2 vs er70s 6 which tig filler rod should you use is the difference between a pristine bead and a porous mess. Choosing the wrong one won’t just make the job harder; it can compromise the structural integrity of your build.

I promise that by the end of this guide, you will understand exactly how these two rods behave under the arc. We will break down the chemistry of the metal, the flow of the puddle, and which rod belongs on your workbench for specific DIY tasks. You’ll gain the confidence to select the right consumable for everything from fine furniture to heavy-duty automotive repairs.

In the following sections, we will explore the deoxidizing power of the S-2 and the wetting capabilities of the S-6. We will also cover surface preparation, cost differences, and the common pitfalls that lead to weld failure. Let’s dive into the technical details so you can get back to the torch with total clarity.

The Basics of Mild Steel TIG Filler Rods

Before we compare the two giants of the TIG world, we need to understand what those letters and numbers actually mean. The American Welding Society (AWS) uses a standardized naming system that tells you exactly what is in your hand. Understanding this code is the first step in mastering material selection.

The “ER” stands for Electrode or Rod, meaning it can be used for both TIG and MIG welding. The “70” indicates the tensile strength of the weld metal, which is 70,000 pounds per square inch (psi). This is the standard for most mild steel projects you will encounter in a home workshop.

The “S” stands for Solid, indicating it is a solid wire rather than a flux-cored or tubular wire. Finally, the number after the dash tells us about the chemical composition and deoxidizers present in the rod. This is where the real magic happens and where our comparison truly begins.

Comparing er70s 2 vs er70s 6 which tig filler rod should you use in the Shop

When you are at the bench, the physical properties of these rods dictate how you move your torch. The er70s 2 vs er70s 6 which tig filler rod should you use debate usually centers on the cleanliness of your base material and how much control you want over the molten pool. Both are excellent, but they serve different masters.

ER70S-2 is often referred to as a “triple deoxidized” rod because it contains Aluminum, Titanium, and Zirconium. These elements act like a cleaning crew for the weld puddle, pulling out impurities and preventing porosity. It is the gold standard for critical work where the metal is perfectly clean.

ER70S-6, on the other hand, relies heavily on Silicon and Manganese for its deoxidizing properties. It contains significantly more silicon than S-2. This extra silicon makes the puddle more fluid, allowing it to “wet out” or flow better against the edges of the joint.

When to Reach for ER70S-2

If you are working on 4130 Chromoly tubing for a bicycle frame or a roll cage, ER70S-2 is likely your best friend. It produces a very clean weld with a stack-of-dimes appearance that many TIG welders crave. Because the puddle is less fluid, it stays exactly where you put it.

This rod is ideal for out-of-position welding, such as overhead or vertical joints. The stiffer puddle doesn’t want to sag or run away from you as easily as more fluid rods. However, it is very unforgiving; if your base metal has even a hint of mill scale or oil, you will see bubbles and pits in your weld.

Always use ER70S-2 when you have spent the time to grind your metal down to a bright, shiny finish. It rewards your preparation with a high-strength, aesthetically pleasing weld that requires very little post-weld cleanup. It is the precision tool of the filler rod world.

When to Reach for ER70S-6

Let’s be honest: not every project allows for surgical cleanliness. If you are repairing a lawnmower deck or building a workbench from hot-rolled angle iron, you might not get every speck of mill scale off. This is where the ER70S-6 shines.

The high silicon content in ER70S-6 helps the puddle float impurities to the surface rather than trapping them inside the weld. It also creates a wider, flatter bead. If you find that your welds with S-2 are looking “humpy” or aren’t blending into the base metal, switching to S-6 can solve the problem instantly.

For beginners, ER70S-6 is often the better choice because the fluid puddle is easier to read. You can see the edges of the puddle “wetting out” into the metal more clearly. It makes achieving a smooth transition between the weld and the workpiece much simpler for those still developing their torch hand.

Puddle Behavior and Operator Preference

While the chemistry matters, the “feel” of the rod is what determines long-term preference. When considering er70s 2 vs er70s 6 which tig filler rod should you use, you have to consider your own welding style. Some people prefer a fast-moving, watery puddle, while others want total control.

ER70S-2 has a very distinct “freeze” rate. As soon as you pull the heat away, the puddle solidifies. This is great for tack welding or thin gauge sheet metal where you want to minimize the heat-affected zone. It allows for a very rhythmic “dab-and-move” technique that produces those classic TIG ripples.

ER70S-6 stays molten just a fraction of a second longer. This extra time allows the gas to escape, which is why it is more resistant to porosity on “dirty” steel. However, if you are welding a thin edge, that extra fluidity can sometimes cause the metal to drop away or blow through if you aren’t careful with your amperage pedal.

I often suggest that hobbyists keep a tube of both in their workshop. Start with the S-2 for your high-end projects. If you notice the arc is spitting or the puddle looks like it’s boiling, swap over to the S-6. It’s a simple fix that can save a project from the scrap bin.

Surface Preparation: The TIG Welder’s Burden

Regardless of which rod you choose, TIG welding demands cleanliness. Unlike Stick or Flux-Core welding, TIG has no slag to protect the weld or consume heavy rust. You are the filter. If you don’t clean the metal, the weld will fail.

For ER70S-2, you must remove all mill scale (the dark, flaky coating on hot-rolled steel) until you see bright silver. Use a flap disc or a dedicated grinding wheel. Then, wipe the area down with acetone to remove oils and fingerprints. Even the oils from your skin can cause issues with S-2.

With ER70S-6, you still need to grind away the heavy stuff. However, if there is a slight “haze” of oxidation left in a tight corner where your grinder can’t reach, the S-6 will likely handle it. Think of S-6 as a rod with a built-in insurance policy against minor prep mistakes.

Always remember to clean your filler rods as well. Rods sitting in an open tube in a dusty garage can collect shop grime. A quick wipe with an acetone-soaked rag before you start can prevent mysterious porosity issues that frustrate even the best welders.

Cost and Availability Factors

In most cases, the price difference between these two rods is negligible for the average DIYer. You might pay a few cents more per pound for ER70S-2 because of the specialized deoxidizers like Titanium and Zirconium. However, for a 1lb or 5lb tube, the difference won’t break the bank.

ER70S-6 is arguably the most common filler rod in the world because it is used extensively in MIG welding wire. Because of this massive production scale, it is available at every hardware store and welding supply house in the country. If you run out on a Sunday afternoon, S-6 is easier to find.

When buying, check the ends of the rods. Most manufacturers stamp the alloy type on the end. If you mix them up in your storage tube, you can still identify them. If you can’t see the stamp, ER70S-6 often has a slightly more “copper” or shiny appearance due to its coating, though this varies by brand.

Step-by-Step Selection Guide

If you are still unsure about er70s 2 vs er70s 6 which tig filler rod should you use, follow this simple decision tree for your next project. It will keep you on the right track and ensure your welds are both strong and beautiful.

  1. Check the Material: Is it brand-new cold-rolled steel or 4130 Chromoly? Use ER70S-2.
  2. Check the Surface: Is there mill scale you can’t fully remove or light surface rust? Use ER70S-6.
  3. Check the Position: Are you welding overhead or on a vertical pipe? Use ER70S-2 for better puddle control.
  4. Check the Fit-up: Is there a slight gap in the joint? Use ER70S-6 because it flows better to fill the void.
  5. Check the Appearance: Do you want the “stack of dimes” look on a show piece? Use ER70S-2.

By following these steps, you eliminate the guesswork. Most professional shops keep both on hand because no single rod is perfect for every situation. As your skills grow, you will start to feel the difference the moment the arc strikes the metal.

Safety Practices for TIG Welding

Welding is a blast, but it’s also dangerous if you’re careless. Whether you’re using S-2 or S-6, the ultraviolet (UV) light from the TIG arc is intense. It will give you a “sunburn” in minutes. Always wear a long-sleeved welding jacket and high-quality gloves.

Proper ventilation is critical. While TIG doesn’t produce as much smoke as Stick welding, the cleaning chemicals (like acetone) and the ozone created by the arc can be harmful. Never weld on metal cleaned with chlorinated solvents (like some brake cleaners), as the heat can turn them into deadly phosgene gas.

Finally, protect your eyes. Use a modern auto-darkening helmet with a shade setting appropriate for your amperage. For most mild steel TIG work between 50 and 150 amps, a shade 10 or 11 is usually the sweet spot. If you feel eye strain, turn the shade up.

Frequently Asked Questions About er70s 2 vs er70s 6 which tig filler rod should you use

Can I use ER70S-6 for roll cages?

Technically, yes, as it meets the 70,000 psi tensile strength requirement. However, most chassis builders prefer ER70S-2 because it is “cleaner” and offers better control on thin-wall tubing. Always check the specific racing organization’s rulebook, as some mandate specific filler metals.

Is ER70S-2 stronger than ER70S-6?

Both rods have a minimum tensile strength of 70,000 psi. In a laboratory pull test, they are very similar. The “strength” of your weld will depend more on your penetration and the cleanliness of the joint than the choice between these two specific alloys.

Why is my ER70S-2 weld full of holes?

Porosity in S-2 welds is almost always caused by inadequate cleaning or a lack of shielding gas. Because S-2 has fewer deoxidizers than S-6, it cannot “fight off” surface contaminants. Grind your metal to a mirror finish and check your argon flow rate.

Which rod is better for a beginner?

Many instructors recommend ER70S-6 for beginners. The increased silicon makes the puddle flow more easily, which helps a new student learn how to “wet in” the toes of the weld. It is more forgiving of slight torch angle mistakes and imperfect cleaning.

Mastering Your Filler Metal Selection

Choosing between er70s 2 vs er70s 6 which tig filler rod should you use doesn’t have to be a source of stress. Think of them as two different flavors of the same high-quality tool. One is a precision scalpel for clean, critical work, and the other is a versatile workhorse for general fabrication.

As you spend more time under the hood, you’ll develop a “sixth sense” for which rod to grab. You’ll see the way the light reflects off the puddle and know exactly how much silicon you need to make that bead lay down perfectly. This expertise is what separates the weekend tinkerer from the master craftsman.

Now, go out to your workshop, clean a couple of scrap pieces of steel, and run a few beads with both rods. Pay attention to how they flow, how the puddle freezes, and how the final bead looks. There is no better teacher than the arc itself. Stay safe, keep your tungsten sharp, and happy welding!

Jim Boslice
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