Effects of fabrication processing on the microstructure and mechanical properties of oxide dispersion strengthening steels

Two types of oxide dispersion strengthening (ODS) steels (i.e. 12Cr-ODS-NIFS and 12Cr-ODS-IMR) with similar chemical compositions were produced through different fabrication processing. A systematic comparison was performed to investigate the effects of different fabrication processing on microstructure and mechanical properties of ODS steels. Compared to 12Cr-ODS-NIFS, the 12Cr-ODS-IMR steel exhibited significantly enhanced mechanical properties, such as higher Vickers hardness, tensile strength and creep strength. To understand the microstructural reasons for the excellent mechanical properties of ODS steels, systematic microstructure characterizations were carried out through a combined study of X-ray diffraction, electron backscattered diffraction, and transmission electron microscopy. It was found that both steels had similar grain structures comprising fine and heavily deformed grains smaller than ~1 μm and elongated coarse grains larger than ~10 μm, both of which possessed similar precipitates including coarse TiC_xO_1−x particles and homogenously distributed Y₂TiO₅ nanoparticles with diameters of several nanometers. 12Cr-ODS-IMR had a finer grain size, larger aspect ratio of grain length to width, and higher density of dislocations, which should be derived from the additional cold rolling and responsible for its better mechanical properties compared with 12Cr-ODS-NIFS.