Evaluation of the addition of Ti, Nb and (Ti+Nb) on the microstructure and susceptibility to sensitization of ferritic stainless steels submitted to TIG welding

In this study the microstructure and the resistance to intergranular corrosion of ferritic stainless steels with additions of Nb, Ti and (Ti+Nb) submitted to the TIG welding were investigated. The microstructure of the weld beads was characterized by optical (MO) and scanning electron (SEM) microscopies and by energy dispersive x-ray spectroscopy (EDS). The susceptibility to sensitization was assessed qualitatively by Practice W of ASTM 763 and quantitatively by the DL-EPR technique. Martensite was observed at the ferrite grain boundaries in the fusion and heat affected zones of the non-stabilized steel and a completely ferritic microstructure in the steels samples with addition of stabilizers. Practice W revealed general corrosion inside the grains of the AISI 430 steel and the presence of ditches in the AISI 430 Ti. Concomitantly, with the DL-EPR technique, it was found that the weld region of these steels was sensitized. On the other hand, the samples of the steels with Nb and (Ti + Nb) additions maintained good resistance to corrosion and presented no sensitization after welding. (author)