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

This work studies the microstructure formed in the heat affected zone (HAZ) and the melted zone (MZ) of a joint welded by automatic TIG in the root bead, plasma in the filling and SAW in the finish beads in a single V groove joint, using austenitic stainless steel AISI 347. The following conditions were studied: as welded; after conventional heat treatment of solubilisation at 1060 °C and stabilization at 900 °C; and after alternative heat treatment, where the piece was solubilized at 1060 °C and kept in the oven which was cooled up to 900 °C for stabilization. The results show that, in the as welded condition, there was grain growth in the HAZ and the MZ shows 13% of 𝛿 ferrite with different morphologies, and the precipitation of Nb carbides and Cr carbides. After the conventional solubilisation and stabilization heat treatment, it was observed a significant reduction on 𝛿 ferrite content both in HAZ and MZ, and Nb Cr carbides have been observed dispersed and distributed more with smaller sizes, which contribute to minimize the possibility of the phenomenon of sensitization. After the alternative heat treatment of solubilisation and stabilization, the microstructure of both HAZ and MZ was similar to the obtained with the conventional heat treatment, with the δ ferrite content in MZ was further reduced to 4.5%. It was concluded that the alternative heat treatment of solubilisation and stabilization was so effective as the conventional heat treatment for adjusting the microstructure of the welded joint, with a significant advantage of the proposed heat-treatment to reduce the time and cost of the this operation.

Stainless steel 347; Welding; Heat treatment; Solubilisation; Stabilization; Microstructure