Grain Coarsening Kinetics and Strength Modeling of Fe–15Cr–2W Oxide Dispersion Strengthened Steels with Varying Yttria Contents

Abstract

15 Cr ferritic oxide dispersion strengthened (ODS) steels are considered prime fuel cladding materials in nuclear reactors due to their excellent creep, swelling, and oxidation resistance. In the present study, the nominal compositions Fe–15Cr–2W–xY₂O₃ (x = 0, 0.3, 0.7, and 1.0) of ferritic ODS steels were prepared by mechanical alloying followed by spark plasma sintering. The sintered samples were annealed at different temperatures of 950, 1100, and 1250°C with a holding time of 60 min at respective temperatures. Further, the samples were also annealed at 1100°C for various durations of 0, 60, and 120 min. The role of varying yttria dispersoids and annealing temperatures on the grain growth kinetics, as well as their mechanical properties (hardness and compressive strength), were analyzed. The compressive strength of the sintered samples with varying yttria contents and at elevated temperatures of 600 and 700°C was determined. Modeling of compressive yield strength at room and elevated temperatures, as well as a correlation with the experimental values, were established for all the compositions. The grain growth exponent (n) and activation energy (Q) rose with the increase in yttria content and were estimated to be 11.52 and 612.91 kJ/mol, respectively, with 1.0 wt.% yttria. The grain size was nearly stable at the annealing temperature of 1100°C. A significant rise in compressive strength at room temperature and elevated temperatures was observed with a yttria reinforcement content of 0.7 wt.%. According to the strength model at different conditions, the role of ultrafine grains and dispersoids seemed to be predominant at room temperature and high temperatures, respectively.