ER70S-3 vs ER70S-6: Clean Steel Wire vs All-Purpose Wire
Same wire, different deoxidizer levels. ER70S-6 handles dirty steel better and is what 90% of shops stock. ER70S-3 leaves a cleaner surface when your steel is already clean. If you are not sure, buy ER70S-6.
Side by Side
| Attribute | ER70S-3 | ER70S-6 |
|---|---|---|
| Manganese content | 0.90 - 1.40% | 1.40 - 1.85% |
| Silicon content | 0.45 - 0.75% | 0.80 - 1.15% |
| Contaminant tolerance | Requires clean base metal | Tolerates moderate rust, oil, mill scale |
| Silicon island deposits | Minimal | More common, small glassy spots on bead |
| Weld pool fluidity | Standard | More fluid, better wetting |
| Market availability | Less common, specialty orders | Universally stocked, industry standard |
Use ER70S-3 when:
Base metal is clean and properly prepared. You need minimal silicon deposits for cosmetic or coating reasons. The application specification calls for ER70S-3 specifically.
Use ER70S-6 when:
You are doing general shop welding where base metal cleanliness varies. You want a single wire that handles most mild steel applications. You are ordering from standard stock without specialty requirements.
How ER70S-3 and ER70S-6 Work Together
The real-world difference comes down to how much cleanup you want to do. ER70S-6 leaves a glassy silicon residue (called silicon islands) on the weld surface. On carbon steel that gets painted, this is not a problem. On stainless or on visible welds where surface finish matters, ER70S-3 produces a cleaner result. Most shops default to ER70S-6 because it handles light mill scale and surface contamination better, and the cleanup difference is not worth stocking two spools.
Common Mistake With ER70S-3
Specifying ER70S-3 for outdoor structural work or on steel with any surface contamination. ER70S-3 has lower deoxidizer content, which means it is less forgiving of surface impurities. If your steel has any mill scale, light rust, or oil residue, ER70S-6 is the safer choice. ER70S-3 is for clean steel in controlled environments.
Where to Buy
As an Amazon Associate, GageRef earns from qualifying purchases. These are affiliate links.
Data sourced from AWS A5.18/A5.18M.