ER70S-6 Welding Wire: Specs, Settings & Buying Guide

Chromium, nickel, molybdenum and vanadium are not on that list because they improve the weld. They are capped low precisely so they do not. Those elements raise hardenability, and a hardened, brittle heat-affected zone next to a sound deposit is a worse defect than a mediocre bead. If you want them in quantity, you are no longer looking at mild steel wire. That logic runs in reverse for alloy steel welding electrodes, where the point is a deliberate shift in deposit chemistry.

Manganese and Silicon: The Deoxidizer Engine

Weld metal picks up dissolved oxygen from the base metal, mill scale, rust and oil. Oxygen in the pool promotes porosity, embrittles the deposit and fights the filler as it tries to fuse. A deoxidizer solves this by tying up the oxygen as an oxide that floats out as slag. Manganese and silicon are the workhorses in ER70S-6, and their surplus is why this wire tolerates steel left out in the rain.

ER70S-6 carries roughly 50 percent more manganese and nearly twice the silicon of ER70S-3. That extra deoxidizing power turns a pool loaded with oxide into slag instead of porosity. The upshot: ER70S-6 runs over light rust, mill scale and a thin film of oil without spitting holes through the bead, where ER70S-3 leaves you chasing them.

Silicon does a second job. Once enough silicon is present to satisfy the oxygen, the surplus improves wetting out: the molten filler spreads into the joint instead of sitting on top of it. That produces a flat to slightly convex bead with good edge fusion and little reinforcement to grind off, which is why ER70S-6 turns up on visible structural and trailer work where the bead is left as-is.

Requirement Versus Typical Result

The spec is a floor, not a prediction. Two mills report the following for ER70S-6 deposits.

These typical values come from published manufacturer certificates, including the Lincoln Electric ER70S-6 certificate of conformance and the Washington Alloy ER70S-6 deposit chemistry. Notice how tight phosphorus and sulphur run against their limits, and how manganese sits mid-range rather than pinned to the maximum. The spool in your hand is still the authority, so read its certificate rather than assuming.

The ASME Section IX “A-No. 1” Option

AWS A5.18:2021 permits an optional supplemental designator showing that an ER70S-6 electrode or R70S-6 rod also meets ASME Boiler and Pressure Vessel Code Section IX “A-No. 1” chemistry, which caps manganese at 1.60% maximum and silicon at 1.00% maximum. Wire meeting those tighter limits carries the marking on the label and the certificate.

Why does that matter? For multi-pass code welds only the top layer of a fillet, or the reinforcement of a groove weld, is subject to the chemistry limits, because earlier layers get remelted. In a single-pass weld the whole deposit is final, so every bit of filler chemistry must satisfy the limits on its own. Qualifying a single-pass procedure under Section IX with a wire at 1.70% manganese, inside the A5.18 window but above the 1.60% A-No. 1 limit? Not a candidate. The supplemental designator tells an inspector you did not guess.

The takeaway is simple. ER70S-6 chemistry is deliberately generous in manganese and silicon because that surplus buys tolerance for the steel you actually get handed, not the steel on a clean bench. Check the certificate for the chemistry you need, and you will know how forgiving the wire in your gun will be.

Mechanical Properties, Impact Testing and What the Spec Actually Guarantees

Spec sheets blur together in a hurry. The values printed in AWS A5.18/A5.18M:2021 are floors, legal minimums a weld must clear to be classified ER70S-6. The values a manufacturer publishes are typicals from their own test welds, usually better than the floor. The standard says at minimum, this is what you get; the data sheet says here is what we usually achieve. A weld that misses the typical is still perfectly good ER70S-6.

The impact requirement is the one most often misquoted. A Charpy test pendulum-strikes a notched specimen and measures the energy it swallows: a tough deposit absorbs a lot before it cracks, a brittle one very little before it snaps. That 27 J figure at minus 30 °C keeps a weld from shattering in cold weather, which is why ER70S-6 is the cold-weather default for outdoor structural work while ER70S-3, tested only to 0 °F, trails it.

The Five Qualification Tests

AWS A5.18 Table 5 spells out what a manufacturer must do before it can stamp a spool ER70S-6. Five tests, each catching a different failure mode:

1. Chemical analysis confirms the deposit landed inside the specified ranges for manganese, silicon and residual elements, catching a mis-melt.
2. Radiographic test looks inside the bead for porosity, lack of fusion and inclusions, the only test that sees inside.
3. Tension test pulls the deposit apart to confirm the minimums and that the weld metal, not the base metal, carries the load.
4. Bend test bends the weld to see if it bends rather than cracks, showing the deposit fused into the base metal.
5. Impact test runs the notched specimen through Charpy at the specified temperature to confirm toughness.

Those five are why the classification carries weight: a wire that passes them all gives consistent results lot after lot, and the filler metal certification behind that claim is what a code weld relies on.

What the Data Sheets Actually Show

Now the typicals. Washington Alloy’s ER70S-6 data shows a mill publishing real test results rather than the bare minimum:

• Yield strength: 66,587 psi
• Tensile strength: 80,380 psi
• Elongation: 25%
• Reduction of area: 60%
• Charpy impact: 28 ft·lb at 0 °F
• Average Brinell hardness: 160

Against the floor: 58 ksi yield versus 66.6 ksi actual, 70 ksi tensile versus 80.4 ksi actual. The deposit runs roughly 15% above the minimum on both strength numbers, and that headroom is deliberate: it lets a fabricator weld slightly off the ideal feed speed or voltage and still land inside the classification. Set expectations against the typicals, but qualify against the minimums.

Brinell hardness around 160 sits in a predictable band, because carbon steel weld metal is not a hardenable grade. A reading well above 160 usually means excessive deoxidizer carry-through or dirty base metal contaminating the pool.

How Shielding Gas Changes the Deposit

Here the spec numbers start behaving like a floor: same wire, base metal, amps and volts, different shielding gas, measurably different weld metal. Gas sets oxidation level and transfer mode: a leaner argon mix burns hotter and cleaner for a finer, better-wetted deposit, while carbon dioxide adds depth and heat but oxidizes the pool more, costing toughness. The wire’s deoxidizer budget only covers what the gas leaves open. Published Charpy results by gas from Harris Products Group show the spread:

Even the weakest combination, 100% CO2, clears the 20 ft·lb minimum the standard demands, but with almost no margin. On a cold-weather code job with a toughness requirement, gas choice is about margin, not passing or failing the label.

One number that rarely appears on a spool label but shows up in calculations: the density of ER70S-6 wire is 0.283 lb per cubic inch, roughly 7,850 kg/m³. Feedability calculations, deposition rate math and spool weight checks all use it, and sound velocity checks stay marginally sensitive to filler metal.

Bottom line: the classification guarantees a chemistry band, a strength floor, a ductility floor and a toughness floor at cold temperature. It does not guarantee a bead shape, a penetration profile or a surface finish; those depend on your gas, parameters and technique, and they matter more than the number on the box.

Where ER70S-6 Wins: Base Metals, Joints and Transfer Modes

ER70S-6 sits in a sweet spot: carbon and low-alloy steel around the 70 ksi tensile class and below, in structural, pressure-vessel, plate, pipe and sheet form. Inside that window the wire is at its most forgiving. Step outside it and you are asking a short-circuit MIG wire to do spray-grade work.

Base metals it was designed for

The classic list, the one that appears on manufacturer data sheets and in filler metal selection tables such as Pinnacle Alloys’ ER70S-6 data sheet, covers:

• ASTM A36 structural plate and shapes (UNS K02600)
• ASTM A285-C pressure vessel steel (UNS K02801)
• ASTM A515-55 and A516-70 for boilers and pressure vessels (UNS K02001 and K02700)
• ASTM A123 hot-dip galvanised sheet and structural shapes
• ASTM A179 seamless and welded pipe
• ASTM A181 Gr. 60 forgings, valves and fittings
• ASTM A266 Gr. 1 seamless pipe fittings

That is the “designed for” list. AWS A5.18/A5.18M:2021 governs the filler metal classification and the base metals it is approved against, but it does not hand you a welding procedure. It sets the chemistry, mechanical properties and impact requirements for the wire; joint design, preheat and procedure still live in a qualified WPS.

Where the wire shows up every week

Talk to any fabricator and ER70S-6 turns up in the same handful of places: truck and trailer bodies, farm implements, buckets and frames, tanks, hoppers and skip bodies, pipe spooling and general structural steel, steel castings and forgings, and shaft build-ups and hardfacing underlayers where the extra deoxidisers help. Then there is sheet metal, where a smooth, well-wetted cosmetic bead matters more than penetration. That is why ER70S-6 has outsold plainer wires in general shop work: the silicon wets out the puddle quickly and lays a flatter, slightly convex bead needing very little cleanup.

Single-pass, multi-pass and all-position work

ER70S-6 is suitable for single-pass and multi-pass welding, one of the reasons it is so broadly approved. Single-pass fillets on thin to medium plate and multi-pass groove joints on anything heavier sit within its comfort zone, and it is approved for all positions.

One caveat from the manufacturers: the 3/16 in diameter version is recommended for flat and horizontal positions only. The larger diameters carry a heavier droplet and a bigger pool, and holding that stable overhead or vertically takes heat control and confidence many shops do not need.

The three transfer modes

The same spool behaves very differently depending on how you run it, and the shielding gas largely decides which mode you get. Air gas welding explained covers the gas options in detail, but the shop summary is this:

In short-circuit mode the wire touches the puddle, the arc shorts, and the transfer repeats hundreds of times a second. It is the default because it puts the least heat into thin material. Spray mode is the opposite: droplets are thrown across the gap by arc force, which needs high current, a machine that will hold it and a cleaner gas mix. That is why Washington Alloy’s ER70S-6 guidance frames the gas choice as a decision about transfer mode, not just about bead appearance.

Why the bead shape changes: the Marangoni effect

Two solid wires of the same tensile class, fed at the same settings, can produce visibly different beads. The reason is surface tension and how it changes with temperature across the weld pool. That gradient, known as the Marangoni effect, pushes molten metal either toward the centre of the pool (deep, narrow penetration) or outward toward the edges (wide, shallow, well-wetted bead).

Deoxidisers steer that gradient. ESAB’s guide to ER70S wire selection puts it plainly: ER70S-6 carries more deoxidiser, producing a more stable pool with lower oxygen levels and therefore wider beads with less penetration than ER70S-3, while the extra silicon improves wetting and bead shaping. Low-deoxidiser ER70S-3 drives the metal the other way, deeper penetration and a narrower bead.

So the “narrow, deep” look people associate with quality MIG work is not automatically better. On dirty steel a deeper, narrower bead is a less forgiving result, because the wider ER70S-6 bead ties into the base metal and grinds off clean. The comparison is broken down further in this guide to the differences between ER70S-2, -3, -4, -6 and -7.

Welding out of position

Vertical and overhead welds run hot and the pool hangs. The manufacturer rule of thumb: decrease amperage by about 15% out of position. That pulls heat input back, keeps the puddle tighter and stops the bead sagging into a teardrop. Watch wire feed speed and voltage relationships rather than dropping the amps alone, or the arc will hunt and crackle.

For heavy structural work that is mostly out of position, sometimes a different process fits better. Self-shielded or gas-shielded flux-cored wire handles vertical and overhead structural joints more comfortably, and the case for why stick welding still wins is worth reading before you commit a whole job to solid wire.

The rule most shops settle on: keep .035 in as your everyday size, add .045 in for plate over half an inch, and keep .030 in the cabinet for anything that warps easily. ESAB’s guide to ER70S wire selection works through the same logic with matching settings. One caveat from the position guidance: 3/16 in wire suits flat and horizontal positions only, because the puddle is too heavy to control out of position.

Spool and Packaging Formats

ER70S-6 ships in enough formats to cover a weekend hobbyist and a full production line.

• 2 lb and 11 lb spools for hobbyists and repair shops; 11 lb is the common retail format for home and light work.
• 33 lb and 44 lb spools for shops and contract welders wanting fewer changeovers. Weldwire’s ER70S-6 data sheet reflects the same range.
• 550 lb pails for high-volume production and automated cells; Washington Alloy lists .035 in ER70S-6 in a 550 lb pail.
• 10 lb plastic tubes for pull-through feeders and automated systems that prefer a coil-free format.
• 30 lb and 50 lb master cartons for distributors and production shops; Lincoln Electric lists these in its literature.

McMaster-Carr lists spool weights of 1, 2, 5, 11, 33 and 44 lb, with a 4 in spool diameter and 0.63 in arbor hole. Check the arbor size before buying: a spool that will not mount is an expensive paperweight. Cartons and pails make price per pound work for volume users, but they need rotation, since rust and lubricant contamination spreads through a whole carton.

Copper-Coated, Copper-Free and Bronze Finishes

Pinnacle Alloys offers ER70S-6 in three surface finishes, and the difference changes contact tip life, feedability and what else you can weld with one spool.

• Copper-coated is the industry standard. The copper layer gives excellent conductivity at the contact tip, extending tip life and reducing the wear debris that clogs a liner, and it improves feedability over long setups.
• Copper-free (bare) wire skips the copper. It is cheaper per pound and useful where copper contamination is a concern, such as stainless or aluminium work, but it needs more tip maintenance.
• Bronze-finish wire sits in the middle, chosen most often when one spool is used for aluminium MIG alongside carbon steel. It resists corrosion better than bare wire while reducing copper pickup.

That point is one most shops overlook. A bronze-finish spool saves cross-contamination headaches on aluminium work. Our aluminum MIG welding guide covers wire and gas choices, and how to prep aluminum right covers the cleaning step.

Storage Discipline Decides Whether You Waste It

Wire storage is where good ER70S-6 quietly goes bad. A rust bloom under the copper coating changes the surface chemistry of the wire as it melts, and oil or grease on the coating produces porosity and undercut that no parameter tweaking will fix.

Store sealed, dry and off the floor. A plastic bin with a tight lid in a conditioned storage room suits a small shop. Never leave spools on damp concrete or an open spool on the bench over the weekend. Rotate stock first-in, first-out, and never mix a half-used spool with a fresh one without cleaning the tip and liner.

If a spool has been wet, rusty or contaminated with oil, set it aside. Do not weld through it and do not grind the rust off; a ruined spool costs a fraction of a ruined part or a lost certification. When a new spool arrives, check the finish before you wire the feeder: clean copper, no kinks, no bird-nesting, consistent winding, readable label.

Shielding Gas, Polarity and the Parameters That Actually Work

Get the gas and polarity wrong and no amount of good wire saves the job. Get them right and ER70S-6 behaves like a different, far more capable material.

Polarity: DCEP, and Only DCEP

ER70S-6 solid wire is a DCEP wire: torch positive, work clamp negative. Run it DCEN and the arc will not behave. You get a stubby, unstable arc that spits, poor penetration, and a bead nobody would sign off on. ESAB’s guide to ER70S wire selection puts it plainly: solid steel MIG wire is designed for positive polarity, and running it backwards wastes wire and gas.

Many machines are factory-locked to DCEP for MIG and DCEN for GTAW, so a lot of people never think about it. Others carry a polarity switch, and that switch is among the most abused knobs in the shop. Check it before you start, not after the first bad pass.

The Three Gas Choices, Honestly Compared

• 100% CO2. Cheapest shielding per unit, deepest penetration, highest deposition rate. Expect more spatter and a rougher, more convex bead that takes more cleanup. For structural work on thick plate where throughput matters more than cosmetics, CO2 is hard to beat on cost per pound of weld metal.
• 75% argon / 25% CO2. The shop default. The argon fraction stabilises the arc and makes short-circuiting easier to control, giving thinner, cleaner beads and easy striking even on a small machine that struggles to hold spray-mode amperage. Most forgiving of the three for a fabricator moving between 3/16 in plate and 16 gauge sheet, and the most expensive per cubic foot, which is why shops buy it in bulk.
• 98% argon / 2% oxygen. The spray-transfer gas. The small oxygen fraction holds a spray pattern at higher amperage than pure argon can, giving the smoothest bead profile and fastest travel speed of the three. Your machine must hold high current and stay stable, and the gas must be clean: a contaminated or damp mix shows up immediately as erratic arc behaviour and heavy spatter.

On gas supply, sizing and cylinder handling, see our background on welding gas services and supply before you set up a new station.

Flow Rate: 30 to 50 CFH

AWS A5.18 ER70S-6 product sheets specify a minimum of 30 CFH, and shops typically run 30 to 50 CFH, roughly 850 to 1,400 litres per hour. The setting scales with nozzle size and with wind: a 5/8 in nozzle wants more flow than a 1/4 in nozzle, and outdoors you increase flow because wind strips shielding gas off the puddle faster than the nozzle can replace it. Shielding gas is not a place to economise.

Short-Circuit Parameters

Short-circuit transfer covers thin material, out-of-position work and general fab shop welding, and it is the mode you will use most. Weldwire’s published ER70S-6 data gives this starting point with 75/25 Ar/CO2:

These figures come from the Weldwire ER70S-6 mild steel data sheet, and they are starting points, not gospel. What matters is the relationship between the three settings: wire feed speed drives amperage, and voltage tracks feed speed to hold arc length stable. Raise feed speed without adding voltage and the arc goes stubby and starts crackling. Add voltage without feed speed and you get spatter.

Spray Parameters and Wire Sizes

Spray transfer is where the wire earns its keep. Harris Products Group publishes spray settings using an Ar/1.5% O2 blend, right next to the common 98/2 mix:

Note how gas flow climbs with nozzle size. Bigger nozzles sit further from the work and spread gas over a wider area, so they need more volume to keep the puddle protected.

Every machine has its own voltage-to-wire-feed relationship, which is why the control on a modern unit is called a voltage adjust or, on some machines, an arc length adjust. If yours has a separate arc length control, set it mid position, lock in amperage and feed speed from the chart, and let the machine’s calibration dial in the voltage. Lincoln Electric, which lists ER70S-6 as conforming to AWS ER70S-6, CWB/CSA B-G 49A 3 C1 S6 and ISO W 49 6, publishes the same guidance: start at the chart, then correct in small steps by watching the bead.

Reading the Result

Once gas and polarity are right, the bead tells you everything. A slight convex profile, tight edges and minimal spatter means good gas coverage and voltage matched to feed speed. A wide, flat, soapy-looking bead usually means too much voltage for your mix. A narrow, tall bead with sharp edges and heavy spatter points to low voltage or a feed speed set too high for the current.

ER70S-6 as a GTAW Rod

The same ER70S-6 classification is widely sold as a GTAW rod, run with 100% argon on DCEN. Plenty of shops buy one product and use it in both processes, which is convenient but worth flagging in your procedure: the filler metal designation is the same, but the process, parameters and qualification are entirely different animals. Qualify a TIG procedure as a TIG procedure.

For a quick sanity check on whether the metal you are about to weld is even a candidate for this wire, read up on alloy steel welding electrode selection before you fire up the torch.

Common Mistakes and a Troubleshooting Playbook

ER70S-6 is forgiving, and that is the whole marketing pitch. It runs on scaled steel, hot-rolled plate, or a trailer frame built at 6 p.m. on a Friday. But forgiving is not self-correcting: most bad ER70S-6 welds are parameter defects wearing a wire disguise.

Start at the symptom, not at the spool. Find the symptom, identify the cause, apply the fix.

The Big One: Porosity

Porosity shows up as gas pockets, wormholes, or a bead that looks eaten from the inside. It is the most common defect in gas-shielded MIG and the usual reason people blame the wire. In most cases the shielding gas never did its job: the arc is protected only while gas flows and the nozzle is aimed right. Flux core welding forgives far more, but gas-shielded MIG demands discipline.

• Dirty or oily base metal. Cutting oil, hydraulic fluid, grease and drawing compound carry hydrogen and hydrocarbons that gas off at the pool. Degrease, then wire-wheel to bright metal.
• Not enough gas flow. Flow set for a small nozzle, then swapped to a larger one without adjusting. Bigger nozzle, more flow.
• Too much gas flow. Over 40 CFH on a small nozzle creates turbulence that pulls room air in through the back. High flow on a large nozzle in a draught does the same.
• Wind above roughly 5 mph. Cross drafts, open bay doors and a shop fan aimed at the welder strip the cover. Hang a curtain if you cannot shut the wind off.
• Wet or contaminated shielding gas. A cylinder in a cold shed can pick up moisture, and a botched install can introduce oil to the regulator. A full-looking cylinder is not proof.
• Aluminium contamination. A wheel used on stainless or aluminium and then taken to carbon steel leaves an aluminium film. The arc burns it off and traps gas. Keep dedicated wheels for carbon steel.
• Incorrect polarity. ER70S-6 runs DCEP. DCEN gives a stubby, unstable arc, poor penetration and heavy spatter that mimics a shielding problem.

The Symptom-to-Cause-to-Fix Playbook

Reading the Arc: Sound and Shape

Listen first. A healthy ER70S-6 arc on 75/25 has a smooth, steady crackle, like frying bacon. Harsh, rapid popping means voltage is low for your feed speed. A smooth but wandering arc means the feed is not keeping up with the current. A convex, domed bead standing proud of the plate is normal and easy to grind. A narrow finger-like bead points to a low-deoxidizer wire, while flat or slightly concave means too much voltage or too little speed.

The Groove Weld Problem: Oxidation and Slag

ESAB’s guidance is clear: for groove welds made without purging gas, ER70S-3 is the better choice, because it has less deoxidizer in the deposit. Both ER70S-2 and ER70S-6 benefit from root purging to prevent oxidation and trapped slag. ER70S-2 carries the highest deoxidant content, including zirconium, aluminium and titanium, which makes it tolerant of rusty single-pass work but also creates slag risk. ER70S-6 sits between the two, inheriting a moderate version of that issue.

The mechanism is the Marangoni effect. High deoxidizer concentration shifts the surface tension of the molten pool so flow is driven toward the pool edges. On a flat surface that gives you the wide, well-wetted bead you want; in an unpurged groove, the same flow carries floating oxide and slag to the sides, trapping them in the root. Higher-manganese wires also show the silicon-island problem, where silicon-rich oxide clusters can act as crack initiation sites in restrained joints.

When the Wire Is Not the Problem

If the defect follows the machine rather than the material, you have a machine problem. Check the gun liner for a kink and the contact tip for wear: a constricted liner makes the wire wander and creates stubby arcs and spatter that look like a parameter fault. Check the drive rolls for correct knurl and tension.

On a windy day with a gas-shielded wire, no setting will save you. Self-shielded flux-cored wire such as E71T-11 or E71T-GS removes the wind sensitivity entirely. As ESAB points out, all four common carbon steel classifications, ER70S-6, E71T-1, E71T-11 and E71T-GS, carry a 70,000 psi minimum tensile strength, so the choice is about shielding, position and deposition rate rather than raw strength. On a windy structural job, reach for a rod or flux-cored alternative and keep moving.

Before you condemn a spool, clean the joint, reset the parameters to the manufacturer’s data sheet values and run a test coupon on the same plate you are welding. If the coupon is sound, the spool is fine and the problem is in your setup. Only then is it worth looking at chemistry. The published ER70S-6 data sheets give you the voltage, amperage and feed speed combinations to reset to.

ER70S-6 Compared With the Alternatives

ER70S-6 is the safe pick for most shops, but the wrong pick in a few specific cases. Knowing exactly how it differs from its siblings in the AWS A5.18 family, and from the flux-cored wires that look superficially similar, saves you from buying the wrong spool for a dirty structural job or from discovering a paperwork problem during a code inspection. The differences are real, and they are documented in the AWS A5.18/A5.18M:2021 classification system.

The ER70S solid wire family side by side

The practical differences are easier to feel than to read. ER70S-2 carries more deoxidizer than ER70S-6, so it will happily lay a pass over light rust and mill scale, but it also tends to generate more slag that has to be chipped and ground before the next layer. ER70S-3 is the clean-metal specialist: less deoxidizing power means it will not tolerate contamination well and is more prone to porosity on dirty steel, but it drives deeper penetration and produces a narrower, more concentrated bead. A shop that only ever welds shot-blasted plate and structural shapes will get excellent results with ER70S-3.

ER70S-4 sits between them, offering more deoxidation than ER70S-3 but carrying no impact testing obligation, which keeps it inexpensive for non-critical work. ER70S-7 takes a different route entirely. Its higher manganese and lower silicon content, at 1.5–2.0% Mn and 0.5–0.8% Si, produces superior wetting and bead shape and allows noticeably faster welding travel speeds than ER70S-3. If you run a lot of long fillet welds on a production line and want a smooth, well-shaped bead at speed, ER70S-7 is worth a look. This side-by-side comparison of the ER70S classes breaks down the chemistry differences further.

Solid wire versus flux cored

Sometimes the right move is not a different AWS classification but a different process. Gas-shielded flux-cored E71T-1 runs DCEP with CO2 or a 75/25 Ar/CO2 blend and delivers very high deposition rates for structural steel, shipbuilding and heavy plate. Its deposit is faster to lay down and easier to position in the field, at the cost of more spatter, more fume and a rougher bead that needs cleanup. Self-shielded flux-cored E71T-11 and E71T-GS run DCEN and need no gas bottle at all, which makes them the standard for field repairs and remote site work. E71T-GS is a single-pass product aimed at thin gauge, roughly 18 gauge up to 1/4 inch.

Solid ER70S-6 remains the right answer when appearance matters, cleanup time is the real cost driver, and the work happens indoors with gas available. That is the short version of the ESAB guide to ER70S wire selection: match the process to the job conditions, not to habit.

The wrong material traps

• Stainless steel: ER70S-6 is a carbon steel wire and will not weld stainless. Use an austenitic filler such as ER308L, which also matches the higher thermal expansion and corrosion behaviour of stainless.
• Aluminium: Carbon steel wire on aluminium produces a brittle, unusable joint. Use ER4043 or ER5356 as covered in the aluminium MIG welding guide, and note that aluminium often prefers flux-cored wire for heavier sections, as explained in the aluminium flux core welding breakdown.
• Code substitutions: Do not swap ER70S-6 for E71T-1, or the reverse, in a code weld without requalifying the procedure. Different processes, different filler designators and different strength requirements mean the WPS has to be written and tested for what you are actually running.

The short version: if the base metal is clean carbon steel and the bead has to look good, stay with ER70S-6. If the steel is rusty and single-pass, or the job demands deposition speed and out-of-position capability, move to flux-cored. If the base metal is not carbon steel, stop and change filler entirely.

Safety: Welding Fume, Hexavalent Chromium and Ventilation

Most safety advice for MIG welding arrives as a footnote nobody reads. The hazard is not abstract, and it does not care which wire you loaded.

Fume is a respiratory hazard whether you run ER70S-6, ER70S-3 or a self-shielded flux-cored wire. Classification changes deposit character and travel speed, not the toxicology of the arc. OSHA’s welding, brazing and cutting standard is the reference.

What Is Actually in the Plume

The plume off a MIG arc on carbon steel is a mixture that shifts with base material, consumable and gas.

• Metal fume particulates: fine base and filler metal particles, including iron oxide, the brown dust on every surface, fine enough to reach deep into the lungs.
• Zinc oxide: produced on galvanised work, and the cause of the flu-like reaction below.
• Manganese: part of ER70S-6, which carries 1.40–1.85% Mn as a deoxidiser. Manganese fume is linked to parkinsonism-like effects after heavy exposure.
• Carbon monoxide: formed when shielding gas (CO₂, or a CO₂/argon blend) reacts with the hot arc. It builds up in poorly ventilated spaces and has no smell or taste.

Carbon monoxide is odourless, so a welder can be overcome before noticing. Fume settles fast, so grinding after the arc turns the airborne fraction into contaminated dust that passers-by stir up.

Hexavalent Chromium: The One That Deserves Respect

Hexavalent chromium, Cr(VI), turns a routine welding job into a regulated exposure. It arises from stainless steels, chrome plating, and galvanised or chromate-bearing material. OSHA regulates it in general industry under 1910.1026, construction under 1926.1126, and shipyards under 1915.1026. OSHA’s dedicated Cr(VI) resource explains the health effects.

Small numbers, deliberately. Cr(VI) fume is highly toxic, damaging eyes, skin, nose, throat and lungs, and it is a confirmed carcinogen linked to lung and nasal cancer. The standard requires labelling of Cr(VI) areas, respiratory protection where engineering controls cannot hold exposure below the PEL, and that affected employees be informed and medically monitored.

The Ventilation Rule, In Plain English

Under 29 CFR 1910.252(c)(2)(i)(A), welding in a space of less than 10,000 cubic feet (284 m³) per welder requires mechanical ventilation of at least 2,000 cubic feet per minute (57 m³/min) per welder. Local exhaust hoods and airline respirators are recognised alternatives where general ventilation will not keep exposure acceptable.

That 10,000 cubic foot figure is where the rule stops applying, not a safe harbour. A booth with one high-flow extractor is compliant; a large open shop with no capture is not.

ANSI Z49.1, Safety in Welding and Cutting, from the American Welding Society, is the standard OSHA points to under 1910.252(c)(1)(v)(A): the practical reference for ventilation design, cylinder storage and PPE selection.

Confined Spaces and the Asphyxiation Risk

Carbon dioxide shielding gas and the argon blends used for MIG on carbon steel are denser than air. In a confined space they pool low and displace breathable air without warning: colourless, odourless. Test and ventilate before striking the arc. A gas monitor on the entrant is the sensible control; buddy system plus retrieval winch is non-negotiable in a tank or vessel.

A related hazard is metal fume fever, also called Monday morning fever or welder’s flu. It appears hours after exposure to zinc oxide from galvanised steel, with flu-like symptoms: throat irritation, chills, fever, nausea and chest tightness. It clears within a day or two, and it means fume control was inadequate, not a rite of passage.

Cylinder Storage and Gas Handling

• Store cylinders upright, secured against tipping, with caps on.
• Keep shielding gas away from heat, sparks and open flame; gas supplier guides cover labelling and handling.
• Never purge a line with oxygen, and never exceed a hose’s pressure rating.
• Keep full and empty cylinders in separate, clearly marked areas.
• Check hoses, regulators and connections for leaks before every shift; soap and water beats a torch and a bang.

PPE That Actually Does Something

• Helmet or goggles with the right shade for the process and amperage. Shade 10-13 covers most MIG work on carbon steel; check the manufacturer’s shade chart. Add eye and face protection for chipping, grinding and slag breakout.
• Respiratory protection when ventilation cannot hold exposure below limits. An N95 or P100 facepiece handles particulates but not gases; carbon monoxide and Cr(VI) need a cartridge or supplied air. OSHA’s welding safety fact sheet maps the options.
• Leather or leather-cotton gloves for heat and abrasion, plus flame-resistant clothing and a leather apron for grinding. Keep oil-soaked gear away from an arc.

Finally, keep the ground clamp on the workpiece, not a random piece of structure: a wandering ground path is a shock risk and a stray arc hazard to bystanders. For the plume chemistry, including the manganese and silicon ER70S-6 carries as deoxidisers, see the AWS A5.18 specification preview.

A Practical Buying Checklist — and What to Do Next

Spool shelves make poor decisions easy: two spools, similar price, similar label, wildly different behaviour in the tank. This checklist closes the loop between knowing the spec and buying the right wire.

What to read on the spool itself

Turn the spool over and read the label line by line.

• AWS A5.18 (often ASME SFA 5.18). “AWS A5.18 ER70S-6” confirms the wire was made and tested to that specification, the same document summarised in the AWS A5.18/A5.18M:2021 standard. A spool marked only “MIG wire”, with no standard named, deserves a certification request before you buy.
• UNS K11140. The unified number that maps the wire to global equivalents. Pinnacle Alloys publishes ER70S-6 classification data as AWS A5.18 / ASME SFA 5.18 with UNS K11140, and that triple appears on other makers’ data sheets too. It is the fastest way to confirm you are holding the wire you think you are.
• Manufacturer, size and weight. A 33 lb spool with the label half torn off is one you cannot date, and undated wire cannot be certified.
• Lot number. The number that pulls a certificate. No lot number, no traceability.
• The optional “A-No. 1” designator. AWS A5.18/A5.18M:2021 permits this marking to show that an ER70S-6 electrode or R70S-6 rod meets ASME BPVC Section IX chemistry requirements. On a single-pass procedure where the whole deposit must sit inside those limits, it saves an argument with the inspector.
• Third-party certification marks your contract names. CWB/CSA, ISO 14341, ABS, DNV, Lloyd’s Register. Only the ones your project requires matter: a wire certified to a standard you do not need is marketing, and one missing the mark you do need is a problem.

What a mill test report actually gives you

A mill test report, or heat and lot certificate, is the manufacturer’s record of what a specific lot did in the laboratory: heat chemistry, as-welded mechanical results, lot identity. Lincoln Electric offers Q2 lot certificates showing actual wire chemistry and mechanical properties online, searchable by lot, plus coil identification markings on both ends of each rod for traceability. On pressure work, the certificate is how you demonstrate the deposit came from material with a known chemical analysis and known strength. Pull it before the wire goes into the tank, not after the inspector asks.

Physical inspection before it goes on the machine

Open the box and look at the wire itself. A spool in good order passes these checks:

• No kinks or bird-nesting. Crushed or tangled wire feeds in surges, spits, and jams the liner even when everything else is perfect.
• No oil or grease on the copper coating. The most common cause of feed problems. Handle spools by the rim, never the wire.
• No rust. White or orange speckling means the wire was wet. It will spit and pore.
• Consistent winding. Even layers, no crossover, no loose outer wrap that unwinds on the floor.
• Correct spool weight and diameter. A “33 lb” spool weighing 29 lb is not a deal, it is a shortage. Check hub size and flange diameter against your feeder.
• Intact packaging. Sealed, dry, off the floor, stored first in first out.

Wire is easy to buy in quantity. ER70S-6 stock is widely available in 1, 2, 5, 11, 33 and 44 lb weights and from .023 up to 5/32 in diameter, so there is no good reason to accept a bad spool. Availability is not a constraint, which makes rejecting an off-spec spool entirely reasonable.

Two warnings worth repeating

Relabelled or off-spec wire. If the print on the flange is smeared, hand-written, or from another standard, assume it is not what it claims. The real risk is believing you have deoxidised, impact-qualified wire when you do not. Check the classification data sheet, and an all position welding rod guide comparison, before swapping anything in.

The ER70S-8 myth. ER70S-8 is not an AWS A5.18 classification. It appears on retail packaging and even bargain-brand spools, but “8” is not one of the A5.18 classes. It is not a superior ER70S-6 and not a different standard, just a label with no specification behind it. Judge the spool by AWS A5.18, the UNS number and the lot certificate.

Cost per weld, not cost per pound

Price per pound is the wrong metric. Count what a cheap spool really costs: wire consumed per pound of finished weld, spatter cleanup, grinding to fix a bead profile that misses your cosmetic spec, labour lost to porosity and rework, and the risk of rejecting a weld on a code job. ER70S-6’s surplus manganese and silicon mean fewer rejects and far less cleanup, so buy on total deposited cost, then buy on the certificate.

Where this leaves you

ER70S-6 is the wire that does the most jobs: carbon steel, plate, sheet, pipe, tanks, truck bodies, farm implements, castings and forgings. Its rich deoxidiser content makes it forgiving of mildly dirty, scaled or oily steel, and its wetting behaviour produces a flat, well-filled bead that needs little finishing. The settings that make it behave are ordinary MIG parameters with DCEP polarity and a shielding gas matched to your transfer mode. None of that is guesswork: it is on the label, in the data sheet and on the lot certificate. Read them before you strike an arc and most bad days never happen.

Frequently Asked Questions

What does the designation ER70S-6 actually mean?

It is a classification from AWS A5.18/A5.18M:2021 for carbon steel filler metal for gas-shielded arc welding. ‘E’ means electrode (AWS uses ‘R’ for rod), ’70’ means a minimum as-welded tensile strength of 70,000 psi (480 MPa), ‘S’ means a solid wire, and the trailing ‘6’ identifies a specific chemistry family. It is not a quality ranking — ER70S-6 is simply the class with the richest manganese and silicon deoxidizer content among the common solid wires.

What is the difference between ER70S-6 and ER70S-3?

ER70S-6 carries far more deoxidizer: 1.40–1.85% manganese and 0.80–1.15% silicon versus 0.9–1.4% Mn and 0.45–0.75% Si for ER70S-3. That surplus is why ER70S-6 tolerates moderate rust, mill scale and oil and produces smoother, better-wetted beads, while ER70S-3 is preferred on clean steel and unpurged groove welds because it gives deeper penetration and narrower beads.

Can I use ER70S-6 instead of E71T-1 flux-cored wire?

Not as a like-for-like swap in a qualified procedure. Both have 70,000 psi minimum tensile strength, but E71T-1 is a tubular flux-cored wire with higher deposition rates, all-position capability including vertical-up, and better tolerance of wind and rust. Solid ER70S-6 requires external shielding gas, produces little slag, and gives the better cosmetic finish. Changing filler metal or process requires requalification of the WPS and, on code work, a new PQR.

Which shielding gas should I use with ER70S-6 wire?

For short-circuit and general shop work, 75% argon/25% CO2 is the standard choice because it strikes easily, limits spatter and suits thin material. Use 100% CO2 for deeper penetration and lower gas cost on thicker plate, and 98% argon/2% oxygen for spray transfer and the smoothest beads at high travel speeds. Set flow at roughly 30–50 CFH, and never run 100% argon in a MIG gun with solid wire.

Is ER70S-6 allowed for ASME pressure vessel and boiler work?

Yes, when the wire carries the ASME Section IX ‘A-No. 1’ supplemental designator, which confirms it also meets the 1.60% manganese maximum and 1.00% silicon maximum chemistry limits that AWS A5.18:2021 allows to be added to ER70S-6. Your WPS must still be qualified, and for a single-pass weld the entire deposit must satisfy the chemistry limits rather than just the top layer.

What wire diameter should I use for my project?

Use .030 in for material under 3/16 in, .035 in for 3/16 in and heavier, and .045 in for heavy plate, long-bevel groove welds and high-deposition work. The .023 in size is a specialty option for very light sheet. Remember that thicker wire feeds faster and carries more heat, so it needs a machine that will hold the current and voltage you are running.

Does ER70S-6 need DC+ (DCEP) or DC- (DCEN) polarity?

DC electrode positive, DCEP. ER70S-6 solid wire is a DCEP consumable. Running it on DCEN produces a stubby, unstable arc with poor penetration and erratic wire feeding, and it will also give an erratic bead that looks like a machine fault rather than a settings fault.

Why is my ER70S-6 weld full of porosity?

The usual culprits are dirty or oily base metal, shielding gas flow that is too low (or too high, which creates turbulence that pulls air in), wind or a draught on the job, moisture or contamination in the gas, aluminium contamination from grinding stainless with the same wheel, and occasionally the wrong polarity. Work through the symptom list in the troubleshooting section — start with gas flow and cleanliness before touching the machine settings.

Can I weld stainless steel or aluminium with ER70S-6?

No. ER70S-6 is a carbon steel wire with a70 ksi tensile class, and welding stainless with it will produce a weak, brittle and corrosion-prone deposit. Use ER308L or ER309L for stainless and ER4043 or ER5356 for aluminium, and match the filler metal to the base metal group before you think about settings.

Is ‘ER70S-8’ a real AWS classification, and is it better than ER70S-6?

ER70S-8 does not appear in the solid-wire classification table of AWS A5.18/A5.18M, which lists ER70S-2, ER70S-3, ER70S-4, ER70S-6, ER70S-7 and ER70S-G. The label appears on some retail packaging and is used loosely by sellers for low-spatter, high-deoxidizer solid wire, but if a product matters to a code weld, verify the actual AWS A5.18 classification and certification rather than the marketing description.