The influence of W on Sigma Phase in δ-$\gamma$ duplex stainless steels have been studied with the impact test and microstructures. The degree of embrittlement was evaluated by impact tests after the embrittling heat treatments. In order to compare the properties of embrittling behavior, conventional duplex stainless steels containing 3 wt% Mo was also prepared and heat treated as applied to those of the W-containing alloys. The result of impact test, W-containing alloys were immune to sigma phase embrittlement even after holding at 850℃ for 10 hrs, while the conventional duplex stainless steel was embrittled only after 20min, holding at 850℃. On the other hand 475℃ embrittling heat treatments, there was no significant difference between this W-bearing duplex stainless steels and the conventional Mo-bearing duplex stainless steels. There was significant difference between the microstructures of two alloys in 850℃ annealing condition. Precipitation of Sigma phase didn't occur after holding at 850℃ for 10 hrs in W-containing alloys, while precipitation of Sigma phase occur after holding at 850℃ for conventional duplex stainless steel for only 20min. As a result of this work, it is found that tungsten does not significantly promote the sigma phase precipitation, compare with that caused by molybdenum.
