AWS A5.9/A5.9M · Stainless Steel
ER309L Welding Electrode
ER309L is the bare filler for welding stainless to carbon steel — over-alloyed at 23Cr-12Ni so the joint stays crack-free after dilution.
- 75 ksi tensile
- Polarity DCEP (GMAW), DCEN (GTAW)
- 4 positions
- Medium penetration
- TIG (GTAW) / MIG (GMAW)
What ER309L means
| Part | Meaning |
|---|---|
| ER | Electrode or rod — usable for MIG or TIG |
| 309 | Nominal 23–25% chromium, 12–14% nickel — over-alloyed to survive dilution |
| L | Low carbon, 0.03% maximum |
ER309L specifications
| AWS specification | AWS A5.9/A5.9M |
|---|---|
| Process | TIG (GTAW) / MIG (GMAW) |
| Form | Solid wire / rod |
| Polarity | DCEP (GMAW), DCEN (GTAW) |
| Welding positions | Flat, Horizontal, Vertical, Overhead |
| Tensile strength (min) | 75 ksi (515 MPa) |
| Yield strength (min) | 45 ksi (310 MPa) |
| Elongation (min) | 30% |
| Impact toughness | Not required by the specification |
| Coating / core | None — bare wire or rod |
| Penetration | Medium |
| Deposition rate | Medium to high depending on process |
| Slag | None; light oxide film to be cleaned |
| Arc character | Stable with a fluid puddle |
| Shielding gas | 100% argon for TIG; tri-mix or 98/2 for MIG |
ER309L amperage by diameter
Typical operating ranges. Start near the middle of the range, then adjust by sound and bead profile. Reduce 10–15% for vertical and overhead work.
| Diameter | Amperage range | Typical start |
|---|---|---|
| 0.030 in (0.8 mm) MIG | 50–150 A | 100 A |
| 0.035 in (0.9 mm) MIG | 70–180 A | 125 A |
| 0.045 in (1.2 mm) MIG | 100–250 A | 175 A |
| 1/16 in (1.6 mm) TIG | 40–90 A | 65 A |
| 3/32 in (2.4 mm) TIG | 70–130 A | 100 A |
| 1/8 in (3.2 mm) TIG | 100–180 A | 140 A |
Polarity: MIG DCEP, TIG DCEN.
Shielding gas for ER309L
| Gas | Notes |
|---|---|
| 100% argon | Standard for TIG and pulsed MIG. |
| 90% He / 7.5% Ar / 2.5% CO2 | Short-circuit MIG tri-mix with good wetting. |
| 98% Ar / 2% CO2 | Spray transfer on plate and overlay work. |
Flow rate: 15–20 CFH for TIG, 25–35 CFH for MIG; purge the root side of pipe joints
What ER309L is used for
- Stainless-to-carbon-steel transition joints
- Buffer layer on carbon steel before an ER308L or ER316L overlay
- Cladding on pressure vessels and process equipment
- Repair of unknown or difficult-to-weld steels
- Joining stainless to low-alloy steel in piping systems
Base metals
- 304/304L to carbon steel
- 316 to carbon steel (with the appropriate WPS)
- Type 309 and 309S
- Carbon steel requiring a stainless buffer layer
Characteristics
- The extra chromium and nickel are consumed by dilution from the carbon steel side, landing the deposit in a safe austenitic-ferritic range
- Retains ferrite after dilution, which is what prevents solidification cracking
- Widely used as a general repair filler on unknown steels for the same reason
- Oxidation resistant to about 1900 °F (1040 °C)
- Costs more than ER308L, so it is reserved for dissimilar and overlay work
Storage and handling
Clean, dry, isolated from carbon steel contamination.
- Sealed tubes for TIG rod; desiccant bag for MIG spools.
- Do not lay stainless filler on carbon steel benches.
- Wipe with acetone before use if the rods have been handled without gloves.
Welding tips
- Keep heat input and dilution low — stringer beads, low amperage, and no weaving.
- For overlay, one layer of ER309L then subsequent layers of ER308L or ER316L is the standard sequence.
- On a dissimilar butt joint, center the arc and avoid excessive penetration into the carbon side.
- Verify with a ferrite gauge on critical work; the deposit should retain measurable ferrite after dilution.
ER309L frequently asked questions
What is ER309L used for?
Joining stainless steel to carbon steel, laying the buffer layer under a stainless overlay, welding 309 base metal, and repairing steels of unknown composition.
Why not use ER308L for stainless to carbon steel?
Carbon steel melting into the puddle dilutes the chromium and nickel. ER308L diluted that way turns martensitic and cracks. ER309L starts over-alloyed, so the diluted deposit still contains crack-resisting ferrite.
What gas for ER309L MIG?
A helium-rich tri-mix (90% He / 7.5% Ar / 2.5% CO2) for short circuit, or 98% argon / 2% CO2 for spray. Pure argon for TIG.
Can ER309L be used on 316 to carbon steel?
Commonly yes, though some specifications call for ER309LMo to keep molybdenum in the transition weld. Follow the governing WPS.
What amperage for 3/32 in ER309L TIG rod?
Roughly 70–130 A DCEN, with the lower end for sheet and the upper end for 1/4 in material.
Compare ER309L with
Related electrodes
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