Microstructural comparison of Oxide Dispersion Strengthened Fe-14Cr steels produced by HIP and SPS

Once the feasibility of the STARS route (Surface Treatment of gas Atomized powder followed by Reactive Synthesis) has been demonstrated to produce ODS ferritic steels by internal oxidation avoiding mechanical alloying, two strategies are proposed in this work to enhance precipitation of oxide nanoparticles. Firstly, consolidation by Spark Plasma Sintering (SPS) is used to produce finer microstructures compared to HIP consolidation. SPS parameters like temperature, heating rate, pressure and time of exposure under pressure were explored, and dense samples (up to 99,5%RD) were obtained. Secondly, precipitation of nanoparticles is achieved through a combination of HIP consolidation at low temperature (700-900 degrees C) followed by hot deformation under the presence of metastable oxides, to increase the density of dislocations, preferential nucleation sites for the precipitation of nanometric Y-Ti-O oxides. Deformation dilatometry and plane strain compression tests were performed to simulate hot deformation under different hot rolling schedules. Total deformation, number of passes, time between passes or initial and final rolling temperatures are some of the parameters explored. Microstructural characterization by Scanning Electron Microscopy (SEM) of consolidated materials is presented.