Development of Economical Nanostructured Duplex Stainless Steel Alloys for Different Industrial Applications

Stainless steels and Ni base alloys are widely used in different industrial applications due to their excellent corrosion resistance and mechanical properties. Along with Ni and Cr, many other alloying elements such as Si, Cu, Mn, Sn, Mo, and W etc. are used depending on final application requirements. Duplex stainless steels are an important class of materials, which have widespread applications because of their high strength and superior corrosion resistance. They are also less costly in some cases than austenitic stainless steels, owing to low Ni content. However most common duplex stainless steel alloys still have some amount of Ni (3~7 wt.%), which makes them still costly and they are not being used in applications, where otherwise they would have been an ideal choice. Another problem is the formation of 2ndry phases such Sigma phase, which makes the material brittle and susceptible to corrosion in many environments. There have been few efforts to develop stainless steels with and without Mo, in which Ni was replaced with Mn (up to 10%). Though such alloys overall showed higher strength and toughness, however Mn content was too high and it has been reported already that Mn content above around 6% can have a significant effect on the corrosion resistance properties. PI of this proposal has been working for last many years on the development of economical corrosion resistance stainless steel alloys and has evaluated the effect of different alloying elements independently in such alloys. Lately a special duplex stainless steel alloy [Fe-18Cr-6Mn-1%Mo-0.2%N], was developed without any Ni content. The Mn content of this alloy was also optimized in such a way, that not only the alloy showed high mechanical properties, but its corrosion resistance was also comparable to that of alloy 304. Though the corrosion resistance of this particular alloy composition was comparable to that of alloy 304, however it must be further improved to make it an effective material for different industrial applications both in acidic and chloride environments. Keeping this in mind, we are proposing here to develop a high Mn-N-x( Cu, Si, Mo/W) DSS alloy (both by wrought and sintering). Corrosion resistance properties of this alloy will be further strengthened by other minor alloying additions. Thermocalc software will be used in alloy design/development, composition optimization and for heat treatment cycles to investigate the formation of 2ndry phases. Alloys will be prepared both by vacuum arc melting and powder metallurgy (Ball milling + SPS) technique.