Mechanical and microstructural stability of oxide dispersion-strengthened (ODS) steel produced by STARS® route

Oxide Dispersion Strengthened (ODS) steels are well-known for their superior high-temperature strength and irradiation resistance, primarily due to the presence of finely dispersed oxide particles within a ferritic matrix. ODS Reduced Activation Ferritic (RAF) steels were produced using the STARS® (Surface Treatment of gas Atomized powder followed by Reactive Synthesis) route, which offers controlled oxygen incorporation by oxidizing pre-alloyed, gas-atomized powders. The material was consolidated by hot isostatic pressing (HIP) and subsequently subjected to different thermomechanical treatments at 1100 °C and 1200 °C for varying times. Microstructural analyses using STEM and EBSD revealed that the post-rolling heat treatments foster grain growth, reduce dislocation density, and promote the evolution of complex Y-Ti-rich oxide precipitates, often with additional elements such as Fe, Cr, Al, or W. These precipitates were heterogeneous in size and chemistry, with a majority being sub-50 nm and showing compositional variations (Y-rich, Ti-rich, YTiO, and mixed oxides/carbides). Hardness and tensile tests demonstrated that the as-rolled state exhibits the highest strength but also displays limited ductility at low temperatures. Heat-treated samples show reduced strength—relative to the as-rolled condition—but improved uniform elongation, particularly at elevated testing temperatures, thus indicating that the STARS® route can effectively balance strength and ductility. The results confirm the feasibility of producing ODS steels with refined, stable microstructures using STARS®, while also highlighting the impact of thermomechanical parameters on both the formation and distribution of oxide dispersions and the resulting mechanical response.