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Solid MIG Wire Classifications (ER70S-x)

Solid carbon steel MIG wires are classified under AWS A5.18 as ER70S-x, with low-alloy wires under AWS A5.28. This sheet explains how to read the designation and how the common classifications differ.

Ref WG-0103AWS A5.18AWS A5.28

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

AWS A5.18 classifies carbon steel solid wires and rods for GMAW, GTAW and plasma arc welding, plus composite (metal-cored) electrodes. AWS A5.28 covers low-alloy steel solid wires, such as those with molybdenum, nickel or chromium-molybdenum. The classification tells you the minimum tensile strength of the weld metal, that the wire is solid, and the chemistry group, mainly how much deoxidizer (manganese and silicon, and in some grades titanium, zirconium and aluminum) it contains.

How to read it

ER70S-6: E = electrode (for MIG), R = rod (for TIG), 70 = minimum tensile strength of the weld deposit in ksi (70,000 psi), S = solid, 6 = chemistry. Low-alloy A5.28 wires add a chemistry suffix of letters and numbers, such as ER80S-D2 or ER80S-Ni1, and are often higher strength. Some labels add a diffusible hydrogen designator, such as H4 or H8.

Common classifications

Classification	Spec	Chemistry note	Typical use
ER70S-2	A5.18	Triple deoxidized (titanium, zirconium, aluminum)	TIG root passes, welding over light rust or contamination
ER70S-3	A5.18	Moderate manganese and silicon	Clean steel, general fabrication
ER70S-6	A5.18	Higher manganese and silicon	Most common MIG wire; better on mill scale and light rust; wets well
ER70S-G	A5.18	Chemistry agreed by maker	Special-purpose wires; read the maker's data
ER80S-D2	A5.28	Molybdenum bearing	Higher strength steels, some pressure work
ER80S-Ni1	A5.28	Nickel bearing	Low-temperature toughness
ER80S-B2	A5.28	Chromium-molybdenum	Cr-Mo steels such as 1-1/4Cr-1/2Mo, per WPS
E70C-6M	A5.18	Metal-cored composite, argon mix gas	Higher deposition production work

Key points

ER70S-6 is the default stock wire for most shops. ER70S-3 is used where a lower silicon deposit or a cleaner bead is wanted on clean steel.
Solid carbon steel wire runs on 100% CO2 or argon-CO2 mixes. Gas choice changes penetration, spatter and bead shape. Check the maker's recommended gases.
Low-alloy wires must match the base metal and the WPS. Do not substitute ER70S-6 for a specified A5.28 wire.
Wire diameter must match the contact tip and drive rolls. See the contact tip and wire size matching chart.
Keep spools dry and covered. Rusty wire feeds poorly and adds porosity.

Common mistakes

Treating ER70S-3 and ER70S-6 as identical on dirty or mill-scale steel.
Using ER70S-6 on Cr-Mo or other alloy steel that needs an A5.28 wire.
Reading 70 as the yield strength. It is the minimum tensile strength.
Running a metal-cored wire on gas it was not classified for.

Governing standards: AWS A5.18 (carbon steel electrodes and rods for gas shielded arc welding); AWS A5.28 (low-alloy steel electrodes and rods for gas shielded arc welding).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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