Alloy 309LMo MIG & TIG
Stainless Steel ER309LMo Welding Wire Supplier in Mumbai, India
Nicorex Alloys is an ISO 9001:2015 and ISO 14001:2015 certified stockist and distributor of ER309LMo stainless steel welding wire, designated AWS A5.9 / ASME SFA-5.9, UNS S30986.
ER309LMo is a low-carbon austenitic stainless steel wire with 2.0-3.0% molybdenum for GTAW (TIG), GMAW (MIG), SAW and PAW welding of dissimilar joints between carbon or low-alloy steel and austenitic stainless steels. The “L” means carbon is limited to 0.03% to avoid intergranular corrosion, and “Mo” means extra molybdenum is added to improve corrosion resistance. Higher chromium (23-25%) offsets dilution from the carbon-steel side, so the weld stays fully austenitic. ER309LMo is the required first buffer layer under 316L or 317L overlays on carbon steel to maintain pitting resistance. The weld metal typically has a tensile strength of 586 MPa (85 ksi) with 36% elongation in the as-welded state. The wire is supplied as TIG rods (1.6-3.2 mm), MIG spools (0.8-1.6 mm) and SAW wire (2.4-4.8 mm). This molybdenum-alloy filler metal is available for dissimilar joints in the form of TIG rods, MIG spools and SAW coils,
The weld deposit is austenitic with controlled delta ferrite to resist hot cracking. ER309LMo is widely used in petrochemical, chemical processing, power generation, pulp and paper, food, pharmaceutical and clad-vessel fabrication industries. Every shipment from Nicorex Alloys includes EN 10204/3.1B mill test certificates with full heat and lot traceability for quality assurance.
ER309LMo Welding Wire Specifications
Below are the key ER309LMo welding wire specifications, including AWS classification, welding processes, polarity, shielding gases, and wire diameters.
| AWS Classification | ER309LMo |
|---|---|
| UNS Number | S30986 |
| Welding Processes | GTAW (TIG), GMAW (MIG), SAW, PAW |
| Polarity (GTAW / GMAW) | DCEN / DCEP |
| Shielding Gas (TIG / MIG) | 100% Argon; Ar + 2% O₂ |
| TIG Rod Diameters | 1.6, 2.0, 2.4, 3.2 mm |
| MIG Wire Diameters | 0.8, 0.9, 1.0, 1.2, 1.6 mm |
| SAW Wire Diameters | 2.4, 3.2, 4.0, 4.8 mm |
AWS Classification Explained: What Does ER309LMo Mean?
Each part of the AWS designation carries metallurgical meaning.
| Designation Element | Meaning |
|---|---|
| ER | Electrode/Rod: bare solid wire for GTAW, GMAW, SAW, and PAW |
| 309 | 23% Cr, 12% Ni composition type: over-alloyed to compensate for dilution in dissimilar joints |
| L | Low carbon (0.03% max): prevents sensitisation and intergranular corrosion |
| Mo | Molybdenum addition (2.0–3.0%): higher pitting and crevice corrosion resistance than plain ER309L |
The 309 composition is designed so that even with 20-30% dilution from carbon steel, the weld metal still stays austenitic.
Chemical Composition of ER309LMo Weld Deposit (%)
ER309LMo weld metal has extra chromium and nickel to make up for dilution from the carbon-steel side of dissimilar joints.
| Material | Carbon (C) | Chromium (Cr) | Nickel (Ni) | Molybdenum (Mo) | Manganese (Mn) | Silicon (Si) | Phosphorus (P) | Sulphur (S) | Copper (Cu) |
|---|---|---|---|---|---|---|---|---|---|
| AWS A5.9 Requirement | 0.03% max | 23.0–25.0% | 12.0–14.0% | 2.0–3.0% | 1.0–2.5% | 0.30–0.85% | 0.03% max | 0.03% max | 0.75% max |
| Typical (WeldWire) | 0.02% | 23.75% | 13.10% | 2.40% | 1.75% | 0.40% | 0.012% | 0.010% | – |
On dissimilar joints, the first weld pass absorbs about 20-40% iron from the base plate. Use at least two overlay layers to achieve the required surface alloy composition and corrosion resistance.
All-Weld-Metal Mechanical Properties of ER309LMo Stainless Steel
The table below lists the typical properties of ER309LMo weld metal in the as-welded state.
| Material | Tensile Strength | Yield Strength (0.2%) | Elongation | Reduction of Area |
|---|---|---|---|---|
| Typical (WeldWire, Ar+2%O₂) | 550 MPa (80,000 psi) | 400 MPa (58,000 psi) | 36% | 55% |
| Typical (Weldtool) | 580 MPa (84,100 psi) | 450 MPa (65,250 psi) | 28% | – |
Base Metal Compatibility and Dissimilar Joint Applications for Alloy ER309LMo
ER309LMo is made for dissimilar metals. It joins alloy types that you cannot weld using standard matching fillers.
| Joint Configuration | P-No. (Steel Side) | P-No. (SS Side) |
|---|---|---|
| Carbon steel to 304/304L SS | P-1 | P-8 |
| Carbon steel to 316/316L SS | P-1 | P-8 |
| Low-alloy CrMo steel to austenitic SS | P-3 / P-4 / P-5A | P-8 |
| Ferritic SS (409/430) to austenitic SS | P-6 / P-7 | P-8 |
In overlay welding, use ER309LMo as a buffer layer before ER316L or ER317L caps. It handles dilution and avoids the molybdenum gap that low‑Mo ER309L would leave.
Recommended Welding Parameters for ER309LMo MIG & TIG Filler Metal & Wire
On dissimilar joints, use stringer beads to limit dilution and back-purge pipe roots with argon for protection.
GMAW (MIG) Spray Arc Parameters
| Diameter | Wire Feed (ipm) | Amps | Volts | Gas Flow |
|---|---|---|---|---|
| 0.035″ (0.9 mm) | 20–39 | 140–220 | 24–29 | 38 CFH |
| 0.045″ (1.2 mm) | 16–30 | 160–260 | 25–30 | 38 CFH |
| 1/16″ (1.6 mm) | 10–16 | 230–350 | 27–31 | 38 CFH |
GTAW (TIG) Parameters
| Diameter | Amps | Volts | Gas |
|---|---|---|---|
| 1.6 mm (1/16″) | 50–100 | 10–14 | 100% Argon |
| 2.4 mm (3/32″) | 80–150 | 11–15 | 100% Argon |
| 3.2 mm (1/8″) | 120–200 | 12–16 | 100% Argon |
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Industrial Welding Applications of ER309LMo Filler Wire
ER309LMo filler wire joins dissimilar metals and provides corrosion-resistant cladding in harsh industrial environments, serving key sectors that require reliable transition welds.
- Petrochemical and oil refining: ER309LMo filler wire connects carbon steel vessels to stainless steel components and is also used to clad reactor shells and apply buffer layers in hydroprocessing piping.
- Chemical processing: It is used for transition joints in sulphuric acid, phosphoric acid and chlor-alkali plants. The 2-3% molybdenum content improves resistance in chloride-rich environments.
- Power generation: ER309LMo is used for dissimilar welds in boiler economiser and superheater tubes where ferritic steels connect to austenitic stainless steels, including HRSG tube-to-header joints.
- Food, beverage, and pharmaceutical processing: The wire is used for transition joints where carbon steel jacketing connects to 316L stainless steel product-contact surfaces and for vessel cladding that must meet hygiene standards.
- Pulp and paper industry: ER309LMo is used for dissimilar joints in digesters, bleach plant equipment and recovery boilers where carbon steel structures connect to stainless steel linings.
- Clad vessel and plate fabrication: The filler metal welds explosion-bonded, roll-bonded, and weld-overlaid clad plates at plate edges, nozzle cut-outs and manways.
Storage and Handling of ER309LMo Welding Filler Wire
Stainless steel filler wire storage focuses on preventing carbon contamination and surface oxidation.
- Keep the product in its original, sealed packaging in a clean, dry area.
- Maintain storage temperature between 15-30 °C with humidity under 60%.
- Keep stainless steel wire away from carbon steel. Even small amounts of carbon steel dust can cause pitting, so always use separate stainless-steel-only storage racks.
- Do not handle wire with carbon steel tools, gloves contaminated with carbon steel grinding dust or carbon steel wire brushes
- Clean TIG rods with acetone before use
- Partially used MIG spools: return to sealed packaging
- Shelf life: Indefinite if stored correctly in original sealed packaging
- For the SMAW electrode equivalent (E309LMo-16): store in heated ovens, re-bake if exposed to the atmosphere.
Available Forms, Diameters and Packaging of ER309LMo Filler Wire
ER309LMo filler wire is available as TIG rods, MIG wire, SAW wire and in drum packs.
| Form | Diameters | Packaging |
|---|---|---|
| TIG Rod (GTAW) | 1.6, 2.0, 2.4, 3.2 mm | 5 kg tubes, 1000 mm lengths |
| MIG Spool (GMAW) | 0.8, 0.9, 1.0, 1.2, 1.6 mm | 12.5 kg (D200), 15 kg (D300), 25–33 lb spools |
| SAW Wire | 2.4, 3.2, 4.0, 4.8 mm | 60 lb coils, mill coils |
| Drum Pack (GMAW) | 1.2, 1.6 mm | For high-volume automated welding |
How to Order ER309LMo TIG Filler Rod & MIG Wire from Nicorex Alloys
When ordering ER309LMo welding wire from Nicorex Alloys, specify the following in your RFQ:
- Product Form - TIG Rod / MIG Spool / SAW Wire
- AWS Classification - ER309LMo per AWS A5.9
- Diameter - Specify in mm or inches
- Quantity - In kg
- Spool Type / Size Preference - Specify
- Welding Position - Specify
- Third-Party Approvals - ABS / DNV / Lloyds / Bureau Veritas / TUV
- Test Certificate Requirements - EN 10204 3.1 / 3.2
- Delivery Destination - Domestic, India / Export
Nicorex Alloys can supply matching consumables across welding processes: ER309LMo TIG rod + MIG wire + E309LMo-16 SMAW electrode + E309LMoT1-1/4 flux-cored wire for the same dissimilar joint project. Complete 316L overlay kits (ER309LMo buffer + ER316L cap) are also available.
Frequently Asked Questions
Why is ER309LMo required as a buffer layer under ER316L overlay instead of plain ER309L?
The first overlay layer on carbon steel picks up 20-40% iron. ER309LMo, with 2-3% Mo, keeps this layer resistant to pitting. Plain ER309L has little Mo and creates a weak, corrosion-prone zone in chlorides.
What shielding gas should be used for MIG welding with ER309LMo?
Use Ar + 2% O₂ as the main shielding gas. You can also use Ar + 1-2% CO₂ or Ar/He/CO₂ tri-mix. Keep CO₂ below 5% to avoid raising carbon above 0.03%.
What Spool sizes and TIG rod lengths are available for ER309LMo from Nicorex Alloys?
TIG rods come in 1000 mm (39 in.) lengths packed in 5 kg tubes. MIG wire is supplied on 12.5 kg and 15 kg spools. SAW wire comes on 60 lb coils. Drum packs are available on request.
When not to use ER309LMo welding wire
Don’t use ER309LMo for similar stainless joints like 316L to 316L (use ER316L), for continuous service above 300 °C (use nickel-based fillers), or for duplex stainless steel (use ER2209).
Can ER309LMo be used for welding clad plate (Carbon Steel + Stainless Steel Cladding)?
Yes. ER309LMo is the standard filler for carbon-steel-to-stainless clad plate joints. First, seal-weld the carbon steel with ER70S-6, then add an ER309LMo buffer layer, and finish with an ER316L cap on the clad side.