309L

Commonly employed for buffer layers and overlays on CMn, mild steel, or low alloy steels, and for joining 304L/321 clad plates, as well as in dissimilar welds. Subsequent layers are applied using a suitable filler to align with the cladding, such as 308L or 347. In dissimilar joints, the capacity to tolerate dilution is leveraged when joining stainless types 410, 304L, 321, and 316L to mild and low alloy steels, including stiffeners, brackets, and other attachments. Typically, service temperatures exceeding 400°C are avoided. This filler metal is also utilized for welding 12%Cr ‘utility ferritics’ like Cromwell 3CR12, to itself and other steels. If the service demands corrosion resistance below 400°C, it is feasible to weld wrought and cast steels of the 23Cr-12Ni type (e.g., ASTM 309 and CH8, BS 309S24, and 309C30). However, for high-temperature structural service, it is advisable to use weld metal with carefully managed higher carbon and lower ferrite. Preheat and interpass temperatures depend on the base material hardenability, with no preheat typically required for mild steels, and it can extend up to 250°C for hardenable steels.

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.