309L

Bearing layers and claddings on steels: Ideal for overlays on carbon-manganese steels, mild or low alloy steels, and for joining cladded plates in 304L/321. Successive layers are applied with electrodes selected to match the cladding, such as 308L or 347.
Dissimilar connections: Thanks to its tolerance to dilution, it is used to join stainless steels like 410, 304L, 321, and 316L with mild and low alloy steels for reinforcements, brackets, and other accessories. Not suitable for service temperatures above 400 °C. It is also suitable for welding 12% Cr ferritic steels, such as Cromwell 3CR12, both among themselves and with other steels.
Similar metal joints: Wrought and cast steels, type 23Cr-12Ni (e.g., ASTM 309 and CH8, BS 309S24 and 309C30), can be welded when corrosion resistance below 400 °C is required. For high-temperature structural applications, a welding metal with a higher carbon content and reduced ferrite is necessary. Preheating and interpass temperatures depend on the hardenability of the base material. As a guide, no preheating is necessary for mild steels; on hardenable ones, the temperature can reach up to 250 °C.

24%Cr-13%Ni (309L) austenitic stainless for dissimilar joint buffer layers etc.

Austenite with ferrite in the range 8-20FN. GMAW tends to have lower ferrite (8-15 FN) than the MMA and FCW consumables.

Mainly used under high dilution conditions, particularly dissimilar welds between stainless and CMn steels.