Effect of Alloying Elements on Corrosion, Microstructure and Mechanical Properties for Casted Free-Nickel Duplex Stainless Steels

Free nickel Duplex stainless steels containing two different levels of 6–13 wt% manganese contents have been studied and analysed. The alloys, made up of appropriate mixtures of the alloying elements, Ferro-alloys and Ferro-alloys bearing nitrogen were melted in an induction furnace under nitrogen pressure. Even though the resistance to the pitting attack was controlled and enhanced by the nitrogen addition as well as, chromium, molybdenum contents. Also, the cast experimental alloy that contained high manganese was found to offer some advantages over the 2205-type duplex stainless steel in combination of mechanical properties and corrosion resistance. The microstructure development due to increasing manganese contents from 6 to 13 wt% revealed the decrease of the ferrite volume fraction from 82 to 75 %, respectively. Mechanical testing results showed that the free nickel alloys containing 0.14–0.23 wt% carbon with manganese contents ranging from 6.44 to 13.45 wt% have moderate mechanical properties whereas U.T.S. ranging from (691–815) MPa, Y.S. (585–738) MPa, elongation (19–21 %), and a corrosion rate of 0.044–6.0 mm/year, respectively. Manganese is therefore an effective element of duplex microstructures. As an economical development, it is concluded that manganese is a useful replacement element for nickel in duplex alloys, but further work is required before the present alloys, or variations of them, could be commercially viable.