Effect of Solubilization and Stabilization Heat Treatment on Microstructure of a 347 Stainless Steel Welded Joint

ABSTRACT

This paper makes the study of the microstructure formed in the heat affected zone (HAZ) and the melted zone (MZ) of a joint welded by automatic TIG process in the root bead and plasma in the filling and finish beads in a single V groove joint, using austenitic stainless steel AISI 347. In addition to study the as welded condition, the welded joint was submitted to thermal treatment of solubilization at 1060°C and stabilization at 900°C. The results show that, in the as welded condition, there was grain grow in the HAZ, the formation of ( ferrite with different morphologies and the precipitation of Nb and Cr carbides. The MZ showed 13% of ( ferrite. After solubulization heat treatment, a significant reduction of ( ferrite content was observed in the HAZ and MZ, with Nb carbides been observed, distributed in a more spread form and with smaller sizes. After solubilization followed by stabilization heat treatment, a greater reduction in the size of Nb carbides was observed, showing the efficiency of this heat treatment to spread these particles which contribute to minimize the possibility to occur the sensitization phenomena. The results allow to conclude that both heat treatments are effective to solubilization of ( ferrite, in the formation of Nb carbides and to reduce the microstructure changes resulting to the weld thermal cycles.

Keywords:
Stainless steel 347; welding; solubilization; stabilization; microstructure.