Microstructural changes upon annealing in ODS-strengthened ultrafine grained ferritic steel

Abstract

In this study, the stability of grain size and oxide nanoparticles in the ODS steel upon annealing at high temperature (650-1350°C) has been evaluated. The ODS Fe-Cr-W-Ti-Y 2 O 3 steel has been manufactured by powder metallurgy, consolidated by hot isostatic pressing and processed by hydrostatic extrusion. Such a processing brings about ultrafine grain structure reinforced with oxide nanoparticles (few nm in diameter) and results in superior mechanical properties. The stability of nano-oxides has been analyzed by small angle X-ray scattering together with transmission electron microscopy. The results obtained revealed excellent thermal stability of ultrafine grained ODS ferritic steel, which was attributed to the resistance of oxides against coarsening.

High-temperature oxidation resistance of ultrafine-grained 14 %Cr ODS ferritic steel

“…The mass change measured for the ODS steel after ageing for 10000 h was exceptionally low (\ 3.5 9 10 -3 g/cm -2 ). The specific weight gain (related to the surface area of the tested specimens) after 1000 h of ageing was equal to 4.1 9 10 -4 g/cm 2 . The weight gain compared with the ageing time data is shown in Fig.…”

“…Due to its unique microstructure (ultrafine grains containing oxide nanoparticles), the ODS steel has not only excellent high-temperature strength but also thermal stability. However, at a certain temperature, the grain and nanoparticle coarsening effects are expected (this problem is discussed elsewhere) [2]. On the other hand, taking into consideration the fact that the operating temperature window for the ODS ferritic steels is expected to be in the range between 600 and 800°C, the material will also be subject to the high-temperature oxidation at extended service time [3].…”

Microstructure, Grain Growth and Hardness of Nanostructured Ferritic ODS Steel Powder during Annealing

“…where f is the volume fraction of pinning particles, and r is their mean radius. It was assumed f = 0.01 , which was found by Oksiuta et al for the HIP-consolidated powders of very similar chemical composition Fe-Cr-W-Ti-Y 2 O 3 [40], while r = 6.1 nm, estimated using TEM (Fig. 11d).…”

Long-term microstructural stability of oxide-dispersion strengthened Eurofer steel annealed at 800°C

“…YTiO 5 and Y 2 Ti 2 O 7 ) undergo dissolution even at fairly low temperatures such as 600 °C. On the other hand, other authors [10,40,41] reported a great stability of Y-Ti-O in temperatures up to 1100-1300 °C. Williams et al reported that both Tibearing and Ti-free Y 2 O 3 particles displayed similar coarsening rates at 1200 °C [42].…”