MIG Welding Wire Types: ER70S-6 vs ER70S-3 vs ER70S-2 Compared

ER70S-6 is the default MIG wire for carbon steel. Buy it if you want one wire that handles everything from clean shop steel to slightly rusty farm equipment. Its high silicon and manganese content acts as a deoxidizer that burns off surface contamination and produces a smooth, wet bead with minimal spatter. About 90% of the MIG wire sold in North America is ER70S-6 for good reason.

ER70S-3 and ER70S-2 serve specific roles. ER70S-3 is a lower-deoxidizer wire for welding on very clean material, and ER70S-2 adds titanium and zirconium for the best performance on prime-coated or dirty surfaces. Knowing when to use each one saves you money and improves results.

Decoding MIG Wire Classification

AWS (American Welding Society) classifies solid MIG wires with a system that tells you exactly what you’re getting:

• ER = Electrode Rod. It’s a solid wire used as both an electrode (carries current) and filler metal.
• 70 = 70,000 psi (70 ksi) minimum tensile strength. All three wires in this comparison meet this spec.
• S = Solid wire (as opposed to tubular flux-core wire).
• -2, -3, or -6 = Chemical composition classification. The number indicates the specific alloy recipe, particularly the type and amount of deoxidizers.

All ER70S wires produce welds with 70 ksi tensile strength minimum and meet AWS A5.18 requirements. The mechanical properties of the deposited weld metal are essentially the same across classifications. The differences are in arc behavior, surface tolerance, and bead characteristics.

Chemical Composition Comparison

The practical differences between these wires come down to their deoxidizer packages. Deoxidizers (silicon, manganese, and in some cases titanium and zirconium) react with oxygen and other contaminants in the weld pool. They scavenge impurities and float them to the surface as slag islands, keeping the weld metal clean.

The key takeaway: ER70S-6 has the most manganese and silicon of the standard classifications. ER70S-2 adds titanium, zirconium, and aluminum on top of moderate Mn/Si levels. ER70S-3 has the least deoxidizer content.

ER70S-6: The Industry Standard

ER70S-6 dominates the market because it does everything reasonably well. The high silicon and manganese content gives it the strongest deoxidizing capability of the standard single-deoxidizer wires. That translates to:

• Best bead appearance. Silicon promotes wetting (the bead flows out and ties into the base metal smoothly). Beads are flat to slightly convex with smooth, even ripple patterns.
• Lowest spatter. The silicon content stabilizes the arc and reduces spatter, especially in short circuit transfer with CO2-containing gas.
• Surface tolerance. Mill scale, light surface rust, and minor contamination that would cause porosity with ER70S-3 won’t bother ER70S-6. The deoxidizers handle it.
• Works with any gas. 75/25, 100% CO2, 90/10, 85/15. ER70S-6 performs well across the board.

Downsides: The higher silicon content produces small silicon dioxide (glass) islands on the bead surface. These look like tiny, shiny spots and must be removed between passes in multi-pass welds. If you’re painting or powder coating, they can cause adhesion problems if not cleaned. The higher alloy content also makes the wire marginally more expensive than ER70S-3.

Best for: General fabrication, auto body, structural steel, repair work, farm equipment, any application where you’re welding on less-than-perfect surfaces.

ER70S-3: The Clean Metal Wire

ER70S-3 has less silicon and manganese than ER70S-6. It relies on minimal deoxidizers, which means it works best on clean, well-prepared material.

• Cleaner weld deposit. Lower silicon means fewer silicon islands on the bead. The weld metal composition is closer to the base metal, which some specs and codes require.
• Better for multi-pass welds. Less silicon in the deposit means fewer slag islands to clean between passes and less risk of silicon inclusions in multi-pass welds on thick plate.
• Lower cost. Less alloy content means slightly cheaper wire, though the difference per spool is small.
• Requires clean metal. Without the heavy deoxidizer package, ER70S-3 is less forgiving of mill scale, rust, and surface contamination. You need to grind or blast the joint area.

Downsides: More spatter than ER70S-6, especially with CO2-rich gas blends. The bead doesn’t wet out as smoothly. More sensitive to surface contamination. Not the best choice for shop work where prep time is limited.

Best for: Pre-cleaned material in production environments, code work that specifies a cleaner weld deposit, multi-pass welding on thick plate where silicon pickup is a concern, and applications where a post-weld paint or coating adhesion test is required.

ER70S-2: The Triple-Deox Specialist

ER70S-2 is sometimes called “triple deoxidized” wire because it contains titanium, zirconium, and aluminum in addition to silicon and manganese. This gives it the strongest deoxidizing capability of any standard MIG wire.

• Maximum contaminant tolerance. ER70S-2 handles dirty, rusty, and primed metal better than ER70S-6. The triple deoxidizer package aggressively scavenges oxygen, nitrogen, and other contaminants.
• Excellent for root passes. The deoxidizer package produces a cleaner root pass on open-root pipe joints. Many pipe welders use ER70S-2 for the root and switch to ER70S-6 for fill and cap passes.
• Lower carbon content. The 0.07% max carbon spec (compared to 0.15% max for S-3 and S-6) gives it slightly better ductility and crack resistance.
• Works on galvanized steel. The titanium and zirconium help manage the zinc fumes from galvanized coatings, though you should still grind off the coating from the joint area when possible.

Downsides: Higher cost per pound. The exotic alloy additions (Ti, Zr, Al) make it more expensive than ER70S-6. More silicon islands on the bead than S-3. Wire availability can be limited at smaller suppliers. Most hobby welders will never need it.

Best for: Root passes in pipe welding, welding over primer or galvanized coatings, structural work on weathered steel, and any application where surface prep is limited and contamination tolerance matters most.

Wire Diameter Selection

Wire diameter determines how much current the wire carries and how much metal it deposits per pass. Match the diameter to your material thickness and machine capability.

0.035" is the most common wire diameter and the default for most 220V MIG machines. If you weld a mix of material thicknesses from 18 gauge to 1/4", 0.035" handles the full range.

0.030" is better for 110V machines and thin material work. It runs at lower amperages and gives you more control on sheet metal without blowing through.

0.023" is a specialty size for very thin material (24-20 gauge). Few machines feed it reliably. If you need to weld material this thin regularly, TIG is usually a better process choice.

0.045" is for 220V and higher machines running spray transfer or high-deposition short circuit on thick plate. It deposits metal fast but needs more amperage to melt properly.

Wire Quality and Storage

Not all ER70S-6 is created equal. Cheap import wire can have inconsistent diameter, poor copper coating, and contaminants that cause porosity and feeding problems. The wire needs to meet AWS A5.18 specs, but budget brands sometimes cut corners.

Signs of poor-quality wire:

• Inconsistent feeding (surging, stopping)
• Excessive spatter even with proper settings
• Porosity in welds on clean material
• Rust or discoloration on the wire surface
• Wire that kinks or breaks easily

Storage matters. MIG wire absorbs moisture from the air, especially in humid environments. Moisture in the wire causes porosity. Store spools in sealed bags or containers. In a humid shop, consider a wire dryer cabinet for critical work. Don’t leave an open spool on the machine for months. If the wire shows any surface rust, replace it.

Trusted brands for MIG wire include Lincoln Electric, Hobart, ESAB, and Miller. They’re more expensive than generic imports but feed consistently and produce reliable results. For non-critical hobby work, budget wire from reputable mid-tier brands (Forney, Washington Alloy) works fine.

Copper-Coated vs Bare Wire

Most MIG wire comes with a thin copper coating. The copper serves two purposes:

1. Corrosion protection. Prevents rust during storage and shelf life.
2. Electrical conductivity. Improves current transfer at the contact tip.

Some premium wires skip the copper coating in favor of a proprietary surface treatment. These bare or “reduced copper” wires claim lower spatter and less copper buildup in the contact tip. In practice, the difference is marginal for most users. The bigger factor in contact tip life is wire quality consistency and proper tension settings.

Matching Wire to Application

Here’s a decision framework:

Grab ER70S-6 if:

• You weld carbon steel in a shop or garage
• Surface prep varies from clean to “good enough”
• You want the best bead appearance
• You’re not sure which wire to buy (this is always the safe default)

Use ER70S-3 if:

• You’re welding code work that restricts silicon content
• You always prep material to bare metal before welding
• Multi-pass welds on thick plate where silicon pickup is a concern
• A painting or coating spec requires it

Use ER70S-2 if:

• You’re welding root passes in pipe
• The material is weathered, primed, or galvanized and full prep isn’t practical
• You need maximum deoxidizer capacity for dirty environments
• The extra cost per pound is justified by reduced prep time

Other ER70S Classifications

Beyond the big three, you’ll occasionally encounter:

ER70S-4 has intermediate silicon and manganese levels between S-3 and S-6. It exists on paper but is rarely stocked. If you see it, it performs between S-3 and S-6.

ER70S-7 has very high manganese (1.50-2.00%). It’s designed for high-speed welding with CO2 gas and produces deep penetration. Used in some automated welding applications.

ER70S-G is the generic classification for wires that don’t fit the standard S-2 through S-7 categories. Some specialty and proprietary formulations use this designation. Check the manufacturer’s data sheet for specifics.

ER80S-D2 is a step up in strength (80 ksi tensile). Used for welding higher-strength steels (A514, A517) and for applications where the 70 ksi class doesn’t meet the design requirements. Not a substitute for ER70S wires on standard carbon steel.

Practical Tips for Wire Selection

Keep one spool of ER70S-6 in 0.035" loaded in your machine as the default. That covers 80%+ of general steel MIG work. Buy a second spool of 0.030" ER70S-6 if you do a lot of thin material work and switch as needed.

Don’t overthink wire selection for hobby and light fabrication. The differences between S-3 and S-6 are real but small. ER70S-6 handles everything a home shop or small fabrication business throws at it. Save the specialty wires (S-2, S-7) for the applications that actually demand them.

Buy wire in the largest spool your machine accepts. The per-pound cost drops significantly going from 2 lb. to 10 lb. to 33 lb. spools. A 33 lb. spool of ER70S-6 in 0.035" runs $35-60 and lasts months in a typical home shop.