Effect Of Process Gas Composition On The Characteristics Of Atomised UNS S32760 Duplex Stainless Steels Powders

Super duplex stainless steels (SDSS) combine the advantages of ferritic and austenitic steels and reach an excellent combination of mechanical and corrosion properties. In addition, high-level mass fractions of chromium, molybdenum, and intermediate nitrogen mass fractions have enabled the higher Pitting Resistance Equivalent Number of SDSS. One of the main goals of the research activity is to evaluate the possible nitrogen variation into the UNS S32760 (X2CrNiMoCuWN25-7-4, AISI F55, 1.4501) super duplex stainless steel powders produced by Vacuum induction melting Inert Gas Atomization (VIGA) (starting from metals scraps and wastes) with two different melt chamber gas atmospheres, Ar or N2. Another study objective concerns the influence of different atomisation gas, Ar or N2 (in combination with the two different melt chamber atmospheres), on powder properties. The identification of the optimal gas process parameters necessary to obtain AISI F55 powders with the correct chemistry composition, especially in terms of nitrogen content, is essential for any subsequent process techniques (L-PBF, 3D printing, MIM, …) to get the best pitting resistance and a good balance in the α ferrite/austenite phase, crucial for the mechanical properties. Therefore, after sieving, the effect of the different gas process parameters on the characteristics of the final powder, in terms of granulometry, morphology, microstructure, chemical composition (also taking into account light elements such as N, O, H, C, and S) and rheology, was investigated.