# ER309L filler metal

ER309L stainless solid filler selection for dissimilar joints and overlays, with dilution, process and service limitations.

Reviewed: 2026-11-01

Tags: consumables, welding, stainless-steel, filler-metals

In Hobart's example of **309L overlay on 1030 carbon steel**, **25% dilution** approaches 308 chemistry but exceeds the cited carbon maximum. At **40%**, carbon, chromium and nickel are unsuitable in the example. Qualify deposit chemistry and ferrite using the actual joint, pass sequence and dilution. [Hobart Brothers, *Overlay and clad steel welding: a few guidelines*](https://www.hobartbrothers.com/resources/technical-guides/stainless-steel-technical-guide/overlay-and-clad-steel-welding-a-few-guidelines/)

Hobart's 309/309L TIG rod is dual-classified AWS A5.9 ER309 and ER309L. It covers similar alloys or selected 300-series stainless to carbon or low-alloy steel. Qualify the exact alloy pair and filler form. [Hobart Brothers, *309/309L TIG product details*](https://www.hobartbrothers.com/product/product-details/309-309l-tig/)

## Classification, composition and product form

Hobart's linked **309/309L datasheet, revision `160923` replacing `150629`**, distinguishes typical wire analysis from specification limits:

| Element, mass percent | ER309L limit shown | Product's typical analysis |
| --- | --- | --- |
| Carbon | 0.03 maximum | 0.02 |
| Chromium | 23.0–25.0 | 24.00 |
| Nickel | 12.0–14.0 | 13.50 |
| Silicon | 0.20–0.65 | 0.40 |

“L” identifies the lower-carbon grade; the same sheet permits 0.12% carbon for ER309. Verify classification against the required AWS edition and current lot documentation; this sheet does not identify an edition year. [Hobart Brothers, *309/309L datasheet*](https://www.hobartbrothers.com/wp-content/uploads/hobart-catalog/datasheets/309_309L.pdf)

ER309LSi is a distinct higher-silicon choice. Exocor describes its **Executive 309Si/LSi** as improving GMAW usability, but warns that dilution producing low-ferrite or fully austenitic weld metal can make the higher-silicon deposit more crack-sensitive than a lower-silicon one. Improved wetting is therefore not sufficient reason to substitute LSi into a procedure requiring L. Keep the complete classification on the purchase order and WPS. [Exocor, *Executive 309Si/LSi*](https://exocor.com/executive-309si-lsi.html)

Also distinguish solid filler from covered E309L electrodes and flux-cored 309-type wires. Hobart treats tubular and solid stainless wires separately and publishes different process arrangements for them. Similar alloy-family names do not transfer shielding gas, polarity, wire-feeding requirements or operating ranges between consumable forms. [Hobart Brothers, *Tubular and solid stainless steel wires*](https://www.hobartbrothers.com/resources/technical-guides/stainless-steel-technical-guide/tubular-and-solid-stainless-steel-wires/)

## Why dissimilar joints need dilution control

The fused weld contains filler plus melted base material. When carbon steel mixes into stainless filler, it changes carbon, chromium, nickel and the resulting microstructure. Kobelco explains that 309-type consumables carry more chromium and nickel than 308-type consumables to accommodate this dilution; using 308-type material can leave a brittle martensitic structure after sufficient carbon-steel dilution. That rationale does not establish that any amount of penetration or dilution is acceptable with ER309L. [Kobelco, *Welding of stainless steel: dissimilar-metal selection*](https://www.kobelco-welding.jp/education-center/stainless/stainless02.html)

For MIG/TIG dissimilar-metal joints, Kobelco recommends limiting penetration into the carbon-steel member. Its procedure guidance separately warns that excessive base-metal dilution with a 309-type consumable can cause cracking. Control fusion and dilution together through the qualified joint preparation, heat input, travel and filler addition; reducing fusion indiscriminately is not an acceptable substitute for sound joining. [Kobelco, *Dissimilar-metal selection*](https://www.kobelco-welding.jp/education-center/stainless/stainless02.html); [Kobelco, *Stainless welding procedures*](https://www.kobelco-welding.jp/education-center/stainless/stainless03.html)

Hobart’s 1030 steel example models one overlay pass. A subsequent layer changes the chemistry again. Qualify chemistry at the required layer and depth. [Hobart Brothers, *Overlay and clad steel welding: a few guidelines*](https://www.hobartbrothers.com/resources/technical-guides/stainless-steel-technical-guide/overlay-and-clad-steel-welding-a-few-guidelines/)

## Ferrite and properties are not guaranteed joint results

Hobart reports typical as-welded tensile strength of **87,000 psi**, elongation of **40%**, and diagram-related ferrite-number ranges of **8–14** for its 309/309L product. These typical rows have no listed AWS requirement. They do not establish diluted-joint properties. Preserve the method and conditions with ferrite results. [Hobart Brothers, *309/309L datasheet*](https://www.hobartbrothers.com/wp-content/uploads/hobart-catalog/datasheets/309_309L.pdf)

For overlay work, Hobart explicitly recommends chemical analysis during procedure qualification because parameter changes alter dilution. A visually sound bead does not establish the required surface composition, and a first layer cannot be assumed to have the chemistry of undiluted ER309L. The required number of layers and final surface condition belong to the particular overlay specification. [Hobart Brothers, *Overlay and clad steel welding*](https://www.hobartbrothers.com/resources/technical-guides/stainless-steel-technical-guide/overlay-and-clad-steel-welding-a-few-guidelines/)

## Process setup and service boundaries

The cited Hobart sheet separates GTAW cut-length guidance using **DCEN with argon shielding** from GMAW spray-transfer and short-circuit tables. Use the process-specific data with the machine and WPS; classification alone does not specify amperage or gas flow. [Hobart Brothers, *309/309L datasheet*, p. 2](https://www.hobartbrothers.com/wp-content/uploads/hobart-catalog/datasheets/309_309L.pdf)

Selection must also address the assembled joint's service. Kobelco warns that carbon steel and austenitic stainless have different thermal-expansion behavior and identifies high-nickel consumables as alternatives for intense thermal cycling. Low-carbon fillers also require review where creep strength matters. Assess hot service, heat treatment and corrosion for the complete alloy pair and thermal history. [Kobelco, *Welding of stainless steel: consumable selection and heat treatment*](https://www.kobelco-welding.jp/education-center/stainless/stainless02.html)

## Identification, storage and exposure

Maintain filler identity through issue and use. Hobart supplies its TIG product in identified tubes and lists AWS classification and agency approvals separately. Confirm required documentation for the actual diameter and process; a product-family page does not certify an unknown loose rod or the completed joint. Keep unused filler protected from contamination and retain its package identification. [Hobart Brothers, *309/309L TIG*](https://www.hobartbrothers.com/product/product-details/309-309l-tig/)

The linked North American **309/309L/309HiSil MIG and TIG SDS**, covering product codes **S5208/S5108/S5275**, is **version 1.0, revised January 8, 2026**. It calls for dry, closed storage and appropriate handling protection. Its as-shipped classification does not remove welding hazards: fumes, arc radiation and electric shock require controls. Fume composition depends on the consumable, base metal, coatings and process; the SDS addresses chromium, nickel, manganese and hexavalent-chromium exposure considerations. Use ventilation/local exhaust and exposure assessment appropriate to the operation rather than assuming a stainless filler is harmless because it is solid wire. [Hobart Brothers, *309/309L/309HiSil SDS*](https://www.hobartbrothers.com/wp-content/uploads/hobart-catalog/msds/309-309L-309HiSil_S5208_S5108_S5275_V1_NA_EN.pdf)

## Related references

[Gas tungsten arc welding](../../processes/welding-methods/gas-tungsten-arc-welding.md) · [Gas metal arc welding](../../processes/welding-methods/gas-metal-arc-welding.md)