Hot deformation behavior and microstructural evolution of a novel ODS ferrite steel reinforced with ultra-fine Y2(Zr0.6, Ti0.4)2O7 particles

Oxide dispersion strengthened (ODS) ferritic steels are widely recognized as leading contenders for structural materials in the demanding environment of Generation IV fission reactors. However, the attainment of a homogeneous grain structure alongside ultra-fine oxide precipitates presents a significant challenge. In this study, a novel ODS ferritic steel strengthened by ultra-fine Y 2 (Zr 0.6 , Ti 0.4 ) 2 O 7 particles was synthesized via powder metallurgy. To investigate microstructural evolution and optimize processing parameters, hot compression experiments were performed across a range of strain rates (0.01 - 10 s -1 ) and temperatures (1100 - 1250 °C). The results reveal that the flow stress of the novel ODS steel is remarkably high. The optimal processing window is determined to be 1178 - 1200 °C with a strain rate greater than 0.01 s -1 . The size, number density and crystal structure of the Y 2 (Zr 0.6 , Ti 0.4 ) 2 O 7 particles remained stable within the investigated hot deformation conditions. The primitively coarse grains could be eliminated completely through continuous dynamic recrystallization (CDRX) during hot deformation. Such CDRX mediated hot deformation behavior of the novel ODS ferrite steel can be accurately described by building the deformation constitutive model. On the contrary, some undesirable microstructures such as retaining of the primitively coarse grains or coarsening of the recrystallized grains occurred at unsuited deformation parameters, especially at low temperature with high strain rate or at high temperature with low strain rate, which should be avoided during thermal-mechanical processing. The findings are helpful for controlling the microstructures and optimizing the performance of novel ODS ferrite steel.