Influence of post-weld heat treatments on the formation of the sigma phase and the corrosion resistance of S32001 steel

Due to their good resistance to corrosion, duplex stainless steels are often used in more demanding environments. S32001 duplex stainless steels are of recent development, so there is practically no information on how welding processes affect them or which are the best post-weld heat treatments to maintain their corrosion resistance without alterations. This article analyses several welded coupons made with the GMAW process, which have subsequently undergone three different post-weld heat treatments, to evaluate their influence on corrosion resistance. The study has made it possible to determine the influence of heat treatments on the phase balance of ferrite and austenite and on the appearance of the sigma phase. The heat treatments that favour a more balanced phase and, consequently, an improvement in the mechanical properties, could favour the formation of the sigma phase. Therefore, the corrosion resistance would be impaired. The study has made it possible to determine the range of temperatures for the formation of the sigma phase for this duplex (forming mainly between 450 and 850 degrees C), which differs from the temperature range for duplex stainless steels with other compositions.