Influence of Induction and furnace Postweld Heat Treatment on Corrosion Properties of SAF 2205 (UNS 31803)

The duplex stainless steels are well known for their excellent combination of strength and corrosion resistance, which is strictly related to control of the composition and the microstructural balance. When duplex stainless steels are welded, the thermal cycles and rapid cooling caused by the welding process may alter the original microstrucure, thereby affecting the above-mentioned properties of the base material. However, if welding is accomplished by using specific filler metals for duplex steels, the application of a postweld heat treatment on duplex stainless steels is usually not needed. Nevertheless, for certain applications it is prescribed by technical standards to submit the workpiece to solution heat treatment or stress-relieving annealing before use. The heat treatment of duplex stainless steels requires very accurate control of both time and temperature. In this work, the influence of postweld heat treatments on the corrosion resistance of a duplex stainless steel (SAF 2205, alias UNS 31803) has been analyzed. Different results may be obtained if furnace heat treatment is used instead of an induction one. Thus, the study was specifically aimed at a detailed investigation of the corrosion behavior of welded compo- nents after induction postweld heat treatment and furnace postweld heat treatment. It was found that pitting corrosion resistance is affected by the presence of secondary austenite and its morphology. Such morphology depends on time and temperature parameters so that if post-weld induction heat treatment is used, the temperature gradient across the thickness of the joint has to be taken into account.