Both ER312 and ER309L are used for stainless-to-carbon-steel dissimilar welding. So when should you choose which? Here is the direct answer engineers need.
Chemistry
- ER309L: ~23 % Cr, ~13 % Ni, low carbon, ~8–15 FN
- ER312: ~29 % Cr, ~9 % Ni, ~40–80 FN
Weld Metal Behavior
- ER309L: designed for moderate-dilution dissimilar joints; balanced austenite-ferrite deposit, good corrosion resistance
- ER312: designed for high-dilution, high-restraint, or unknown base metal scenarios; heavily ferritic, crack-resistant, harder
When to Use ER309L
- Standard stainless-to-carbon-steel joints in production fabrication
- Corrosion-service dissimilar joints
- When color match with 300-series is desirable
When to Use ER312
- Welding unknown or mixed base metals
- Welding onto tool, spring, manganese, or high-carbon steel
- Repair welding of cast steel or cracked components with high restraint
- Buttering layers where downstream welds must survive high dilution
Cost and Availability
ER309L is more widely stocked and generally cheaper per kg. ER312 is a specialty product priced higher, but it eliminates cracking risk in scenarios where 309L would fail. Choosing the cheaper wire on the wrong application is almost always more expensive than buying the right wire the first time.
Rule of Thumb
Routine stainless-to-carbon-steel → ER309L.
Repair, unknown, or hardenable base metal → ER312.
Dayang Welding stocks both ER309L and ER312 to AWS A5.9 with full test documentation.
