ESAB has introduced Exaton 19.9.Nb HF, classified as an AWS A5.9: ER347 as well as an EN ISO 14343-A S 19 9 Nb, is a 300 series austenitic steel submerged arc welding wire with niobium and high ferrite to further increase weld deposit mechanical properties at elevated temperature. It is ideal for stainless steel applications on pressure vessels (e.g. for components requiring cladding restoration) and other thick plate applications requiring multiple passes (e.g. at pipe mills performing longitudinal welds).
“As phosphorus and sulfur levels or other impurities increase, increasing the ferrite content helps resist weld cracking, especially in multi-pass welds,” says Paolo Torchiana, Global Product Manager, ESAB.
The lack of ductility at high temperatures causing hot cracking is usually due to the formation of an intergranular liquid film of an impurity, usually sulfur and phosphorous in the metal. These impurities combine with the elements to form low-melting-point compounds, thereby reducing cohesion. The lack of cohesion between grain boundaries, in turn, initiates cracks aided by tensile stresses resulting from the contraction of the weld. Wires with higher ferrite combat this situation. Ferrite has the body centered cubic crystal structure as opposed to the face centered cubic crystal structure of austenite. The bcc structure allows more rapid diffusion of impurity elements in stainless steels. By basically absorbing it, the ferrite provides a reduction in the volume of liquid films, therefore limiting the cracks. Also, the addition of niobium to stainless steel filler metals generally forms carbide precipitates, which create a beneficial dispersion hardening effect – strengthening the weld metal at higher temperatures.
“By adding niobium and a high ferrite level, we’ve created a filler metal that will save our customers time and money on rework due to faulty welds,” continues Torchiana. “Our Exaton 19.9.Nb HF wire’s chemical composition is designed for tough applications when a post weld heat treatment might also be required.”
Hot cracking can also be prevented by using lower heat input (such as with ESAB’s Integrated Cold Electrode, or ICE process), using joints with a larger groove radius, avoid concave beads and using ferrite controlled filler metals.
“When your application requires higher heat input and a smaller groove radius, using filler metals with high ferrite in the austenitic matrix will be beneficial,” says Torchiana. Exaton 19.9.Nb HF has a FN deLong of 13 percent, a FN as per WRC-92 of 12 and a nominal niobium composition of 0.7 percent.
Exaton 19.9 Nb HF is available in 2.4 mm and 3.2 mm diameters, in 25 kg spools and 280 kg drums. Its recommended flux is Exaton 15W, however Exaton 19.9.Nb HF can also be used in combination with other fluxes.
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