EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Duplex stainless steels (SS) comprise of both ferrite and austenite phases. The combined properties of the individual phases in austenitic-ferritic stainless steel result in excellent combination of corrosion resistance and mechanical properties, and thus they are fast replacing the conventional single-phase austenitic or ferritic stainless steels. The strength of the duplex SS can be further increased by the addition of dispersoids. The most commonly used oxide (as dispersoids) in ODS steel is yttria (Y2O3). The addition of titanium to Y2O3 dispersed steel leads to the formation of Y-Ti-O clusters having a refined size of ~2-6 nm, also called nano-clusters. These nano-clusters act as obstacles to the movement of dislocations, and thus increase the strength of the alloys, especially creep resistance. Although extensive studies have been carried out with yittria as oxides in ODS steels, other rare earth oxides like lanthana (La2O3) have not been explored.
In the present study, both lanthana and yttria based ODS duplex SS have been fabricated using mechanical alloying followed by spark plasma sintering (SPS). Elemental powders with the composition of Fe-21Cr-8Ni-1Ti-0.5La2O3 (21LNT) and Fe-21Cr-8Ni-1Ti-0.5Y2O3 (21YNT) were mechanically alloyed for 35 h and then sintered at 900 oC and 1000 oC. The variation of the sintering temperatures on the density, microstructure and mechanical properties of the ODS duplex SS has also been reported. Microstructural characterization was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The quantification of mechanical properties was carried out using Vickers hardness, nano-indentation and compression testing, which indicated that 21LNT exhibit better mechanical properties than the conventional 21YNT alloy.

Keywords: ODS duplex SS, Spark plasma sintering, Nano-clusters, Mechanical alloying