Two tubes can both say carbon-steel TIG rod and still contain different filler classifications. When deciding between ER70S-2 and ER70S-6, do not treat the last digit as a quality score. Start with the job requirements, then compare the actual manufacturer’s chemistry and the data that apply to TIG.
ER70S-2 uses a deoxidizer system that includes aluminum, titanium, and zirconium. ER70S-6 is associated with higher manganese and silicon levels in the comparison below. Both appear in Midalloy’s carbon-steel filler range for GMAW and GTAW. Its ER70S-2 bulletin and ER70S-6 bulletin provide a useful example of why the complete specification matters.
Compare the chemistry without turning typical values into guarantees
| Element | Midalloy ER70S-2 typical chemistry | Midalloy ER70S-6 typical chemistry |
|---|---|---|
| Manganese | 1.15% | 1.45% |
| Silicon | 0.55% | 0.98% |
| Aluminum | 0.10% | Not listed in this bulletin’s typical table |
| Titanium | 0.10% | Not listed in this bulletin’s typical table |
| Zirconium | 0.07% | Not listed in this bulletin’s typical table |
These are manufacturer-published typical values for the two products, not the complete AWS composition limits and not a certificate for the tube in your hand. “Not listed” does not mean a measured zero. Use the actual product data sheet and any required lot certificate for purchasing or procedure review. Sources: the two Midalloy bulletins linked above.
The comparison supports a narrow conclusion: these are different chemical formulations. It does not establish that the ER70S-6 product is universally stronger, that ER70S-2 is automatically approved for a critical root pass, or that either one is the correct repair rod for an unidentified material.
Keep joint cleanliness separate from deoxidizer claims
Do not use a deoxidized filler as permission to skip cleaning. Miller’s TIG welding guide identifies cleaning grease, oil, and moisture from both the base material and filler rod as part of controlling contamination. A filler change does not correct a dirty rod, an unidentified coating, or a shielding problem.
Separate the questions during troubleshooting. First ask whether the base metal is identified, the weld zone is prepared, the filler is clean, and the torch and gas system are functioning correctly. Then ask whether the selected filler matches the application. Changing rod while several other conditions remain uncontrolled makes it difficult to learn which change affected the result.
For an authorized noncritical shop trial, compare like conditions: the same identified material, joint preparation, fit-up, process setup, and inspection method. Keep the filler packages and results identifiable. A bead that looks different is an observation to evaluate, not proof of a new qualified procedure or a general strength advantage.
Read the TIG row, not the neighboring MIG gas recommendation
A single data sheet may cover both processes. In the Midalloy bulletins, the GTAW rows identify argon, while the GMAW sections show different shielding-gas combinations. Carrying a MIG gas entry into a TIG setup because it appears on the same sheet is a reading error, not a filler-metal option.
Miller’s TIG basics reference also identifies argon as a broadly usable TIG shielding gas. For the actual job, follow its applicable procedure and the correct product/process instructions. Do not copy settings from a seller’s text without checking which process those settings describe.
The same reading discipline applies to mechanical-property tables. Midalloy’s ER70S-2 bulletin describes GTAW test conditions; its ER70S-6 bulletin includes GMAW test data with specific gases and heat-treatment conditions. Comparing a number from each table without matching the conditions does not isolate the effect of the filler classification. Read the footnotes before drawing a strength or impact-toughness conclusion.
Start the selection with four job questions
What is the actual base material? Record the grade or the best reliable identification available. A shop nickname is not enough to approve filler for a pressure-containing, fatigue-sensitive, or otherwise critical component. Unknown material belongs on the verification list, not behind an assumed mild-steel label.
What must the finished weldment do? Service conditions, inspection requirements, customer specifications, and any required heat treatment belong in the decision. Do not reduce a repair question to whether the rod will melt and join the pieces.
What does the governing procedure permit? Where a WPS or other approved repair instruction applies, identify its filler requirements before ordering. Treat an apparent substitute as a question for the responsible welding or engineering authority, not an automatic purchasing substitution.
Which exact product and form are being ordered? Record the manufacturer, full classification, TIG cut-length form, diameter, length, package weight, and any certification requirement. Check the unit of sale. A classification search can return multiple forms and package sizes, so the first search result is not an approved order line.
Use the WSP lookup pages to organize—not approve—the choice
Open the exact ER70S-2 TIG rod reference and ER70S-6 TIG rod reference when comparing the classifications. Both are separate from the WSP filler-metal finder, which lets you start with the job or a known AWS grade.
The WSP pages explicitly describe their marketplace searches as starting points, not verified exact-SKU purchase buttons. Use the lookup to organize the classification and form, then verify the manufacturer’s product, diameter, package, and applicable requirements. A search result or finder recommendation does not replace the procedure review.
Make the next purchase easier to verify
Keep a short record with the approved product number, source data sheet, intended job, and any unresolved questions. Label rod storage by the complete classification rather than “steel TIG.” When a partial tube loses its identification, do not make it the default material for an important job because it looks similar to the other rods.
Unknown until the job is specified: the required filler classification, diameter, current settings, preheat or heat treatment, and acceptance criteria. Those are application decisions this comparison cannot settle. The useful outcome is a better-supported selection question—not a blanket instruction to replace every ER70S-2 tube with ER70S-6 or vice versa.
Primary references
Midalloy ER70S-2 technical bulletin; Midalloy ER70S-6 technical bulletin; Miller TIG welding basics. Documents accessed September 24, 2026; the Midalloy files are legacy bulletins still linked from its current product library. Confirm the current product revision when specifying material. This article is selection support, not a qualified welding procedure.
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