The formulation of stainless steel welding consumables is meticulously tailored to harmonize with the underlying or parent material. The chemical analyses (composition) of the utilized consumables are typically fine-tuned to optimize the welding process and mitigate the risk of hot cracking.
Austenitic Stainless Steels
To diminish the susceptibility to intergranular (intercrystalline) corrosion after cooling through temperatures ranging from approximately 850 to 450°C post-weld solidification, low carbon levels are conventionally employed. Refer to Corrosion Mechanisms in Stainless Steel for further insights. Consumables like 19 9 and 19 12 2, featuring elevated carbon levels, are designed to yield welds with increased strength, making them better suited for applications at elevated service temperatures.
Titanium-stabilized steels, namely 1.4541 (321) and 1.4571 (316Ti), are welded using consumables containing niobium rather than titanium. This choice is informed by the fact that the exceedingly high melting point titanium carbides present in titanium-containing consumables are unlikely to liquefy during welding. In contrast, niobium carbo-nitrides in niobium-type consumables boast lower melting points, rendering them a superior selection.
Ferrite levels in austenitic consumables are typically calibrated within the 4% to 12% range to mitigate the risk of hot cracking just below the solidification point of the weld metal. For welding special low/zero ferrite grades designed for specific corrosion-resistant, cryogenic temperature, or low magnetic permeability service conditions, it is advisable to employ matching low/zero ferrite consumables, such as 18 15 3 L.
Ferritic, Martensitic, and Precipitation Hardening Stainless Steels
In general, one can opt for either matching consumables or an austenitic filler with corresponding chromium and molybdenum contents. While austenitic fillers are indispensable for applications where superior weld toughness is paramount, they may not be the most prudent choice when aligning with the parent material necessitates consideration of weld appearance (color), mechanical strength (particularly in the case of welds involving martensitic and precipitation-hardening parent material), and physical properties (thermal expansion).
Duplex Stainless Steels
In contradistinction to austenitic consumables, duplex fillers like 22 9 3 N L are calibrated to generate more austenite in the weld than in the parent metal. This meticulous balance aims to optimize weld mechanical properties and corrosion resistance, achieved by incorporating more nickel and typically nitrogen into the consumable than what is present in the matched base metal.
Compositions of Consumables
Consumable alloy symbols adhere to common standards in European codes. However, it is imperative to note that compositions can diverge for various consumable types between BS EN 1600, BS EN 12072, and BS EN 12073, even when utilizing the same ‘Alloy symbol’ in each standard. Consultation of the specific standard for each consumable type is recommended.