WeldMaster Which filler rod: stainless to mild steel, 4043 vs 5356, chromoly and more
Stainless to mild steel needs 309L: ER309L wire or rod for MIG and TIG, E309L-16 for stick. It is worth double-checking every time: grabbing 308L off the shelf out of habit is an easy way to crack a dissimilar joint. On 6061 aluminum, ER4043 flows better and resists cracking, while ER5356 is stronger and matches the color after anodizing. WeldMaster's Filler Selector (Pro) lists the filler per process for six base metals.
What is the filler chart by base metal?
| Base metal | Process | Filler | Why |
|---|---|---|---|
| Mild steel (A36, 1018, hot-rolled) | MIG | ER70S-6 | Extra deoxidizers handle mill scale and rust |
| Mild steel | TIG | ER70S-2 | Clean, triple-deoxidized rod for carbon steel |
| Mild steel | Flux-core | E71T-1 / E71T-11 | Dual-shield for deposition, self-shielded for field work |
| Mild steel | Stick | E7018 | Low-hydrogen structural rod; E6010/6011 for dirty roots |
| Stainless 304 / 304L | MIG, TIG / Stick | ER308L / E308L-16 | Matches 304; low carbon resists carbide precipitation |
| Stainless 316 / 316L | MIG, TIG / Stick | ER316L / E316L-16 | Keeps the molybdenum for corrosion resistance |
| Aluminum 6061 | MIG / TIG | ER4043 or ER5356 | Crack resistance and flow, or strength and color match |
| Chromoly 4130 | TIG, MIG | ER80S-D2 | Matching low-alloy filler; ER70S-2 for non-critical joints |
| Carbon steel to stainless | MIG / TIG, Stick | ER309L, E309L-16 | Bridges the dilution between the two metals |
Why use 309 filler for welding stainless to mild steel?
When you join stainless to carbon steel, the weld pool mixes both base metals with the filler. A 308L filler would be diluted by the carbon steel and can end up with a crack-prone structure. 309L carries more chromium and nickel, so after mixing the weld still lands in a sound stainless composition. That is why the app calls it the standard dissimilar-joint filler.
In the Filler Selector, pick Dissimilar: Carbon → Stainless as the base metal: ER309L for MIG and TIG, E309L-16 for stick. The 309 filler rod works with any of those processes; what changes is the form, wire, cut length or coated electrode.
4043 vs 5356: which filler for 6061 aluminum?
| ER4043 | ER5356 | |
|---|---|---|
| Alloying element | Silicon | Magnesium |
| Strengths | Better fluidity and crack resistance on 6061 | Higher strength, better color match after anodizing |
| Trade-off | Slightly duller finish | Avoid for sustained service over about 150 °F |
| Pick it when | The joint is crack-sensitive or you want an easy puddle | Strength or appearance matters |
What filler rod for chromoly?
For structural 4130 tube, such as roll cages, the app suggests ER80S-D2, a matching low-alloy filler, for both TIG and MIG. ER70S-2 is acceptable for non-critical, lower-strength joints. If a rulebook or drawing names a filler, follow it.
What filler rod for mild steel and stainless?
- Mild steel: ER70S-6 wire for MIG, ER70S-2 rod for TIG, E71T-1 or E71T-11 for flux-core and E7018 for stick.
- 304 / 304L: ER308L for MIG and TIG, E308L-16 for stick.
- 316 / 316L: ER316L for MIG and TIG, E316L-16 for stick. Do not substitute 308L, or you lose the molybdenum that gives 316 its corrosion resistance.
How do you use the Filler Selector?
- Open Filler Selector under Reference (Pro).
- Under Base Metal, pick one of the six options, for example Mild Steel or Dissimilar: Carbon → Stainless.
- Read the list: each line shows the process, the filler classification and a one-line reason.
- For the current and tungsten size, go on to TIG or MIG with the same material and thickness.
What are the limits and common mistakes?
- The list covers six base metals. Cast iron, cast aluminum, 5xxx aluminum and duplex stainless are not in the app.
- Using 308L on a stainless-to-carbon joint because it is on the shelf. Use 309L.
- Choosing 5356 for parts that run hot for long periods. The app flags sustained service over about 150 °F.
- Skipping the filler maker's data sheet because the app's one-liner sounded complete enough. It's a summary, not a full specification, and should be treated as such.
Questions and answers
What filler rod for stainless to mild steel?
Can I use 308 to weld stainless to mild steel?
What filler rod for 6061 aluminum?
Is the Filler Selector free?
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