Surface treatment of welded duplex stainless steels by diode laser

The good mechanical properties and the high corrosion resistance are some of the most appreciated characteristics of duplex stainless steels, which are now widely used in several application fields. One limit in the duplex stainless steel diffusion derives from their complex structure: The optimal 50%-50% austenite to ferrite ratio is lost after welding and measures must be taken to improve the as welded structure. The joint can be postweld heat treated or a filler wire having a tailored composition can be selected. As a further option, the present paper discusses the possibility of adopting a diode laser for a postweld superficial heat treatment process, aimed at recovering the balanced microstructure of the welded joint. It has been shown that the laser treatment process can lead to a ratio of austenite to ferrite close to 50%-50%. Moreover, the process has been optimized in order to increase the rate of treatment at levels acceptable for the industrial treatments (10 mm/s). Finally, the corrosion resistance of the laser treated joints were experimentally evaluated and compared to as welded and to postweld furnace heat treated specimens. The results showed that the corrosion resistance of the laser treated joints is very close to that of the furnace treated samples.