Technical Paper
430LNb - A New Ferritic Wire for Automotive Exhaust Applications
2000-03-06
2000-01-0314
The increasing use of ferritic stainless steels (AISI 409, 439, 436 and 441) in automotive exhaust systems, especially for manifolds and catalytic converter canning, has led the authors to develop a new ferritic welding wire, designated 430LNb. This new material is recommended for the GMAW and GTAW processes and provides better metallurgical compatibility with the ferritic base metals, in terms of both thermal expansion and microstructure. The composition of the new welding wire has been adjusted in order to guarantee an entirely ferritic structure in the welds of ferritic sheet materials, together with good resistance of the welds to both wet corrosion and high temperature oxidation, corresponding to the conditions encountered respectively in the colder and hotter parts of the exhaust line. This is achieved by limitation of the C (<0.02%) and N (<0.02%) contents, stabilisation with Nb, such that Nb > 0.05 + 7 (C + N) and Nb < 0.5%, and a Cr content of 17.8-18.8%.