Microstructure and Mechanical Properties of the FeCrW Series ODS Steel Produced by A High-throughput Preparation Method

Jinru Luo*, Pei He^*, Changhao Wang, Pengcheng Zhang

Institute of Material, China Academy of Engineering Physics, Mianyang, 621908

ABSTRACT: The new generation advanced nuclear reactor and controlled fusion have been considered as the one of the most important components of the future energy. Obtaining higher thermal efficiency with more secure guarantee is the main development objective of the new generation nuclear energy. Therefore, the structural material has been to facing the tough challenge that must be working under the extreme conditions of high temperature, irradiation, corrosion and the coupled stress, which makes the structural material designed for the coming nuclear reactor has to have perfect comprehensive performance. Oxide dispersion strengthened (ODS) ferritic steel has been considered as one of the most promising candidates of the fuel cladding materials for the fission reactors and structural blanket materials for the fusion reactors of the coming new generation because of its outstanding performance under the neutron exposure, helium atmosphere, and reactor coolant. A FeCrW series ODS-steel has been developed in the present study on the base of Fe13.5CrWAl and Fe13.5CrWY alloys adding Y2O3 or Y2O3 and Ti. Sheet samples of multi-component on gradient deformation strain level have been prepared by synchronous hot isostatic sintering (HIP) and wedge hot rolling. The distribution of Y-rich dispersed phase in the samples is uniform and the density of the HIPed initial sheet is close to 100% measuring by Archimedes method. The characterization technique of XRD, ECC, EBSD and SANS have been applied to analyze the phase composition, sub-structure of the matrix alloy, and the chemical composition, structure, size and density distribution of the ODS phase. Uni-axial tensile tests at the ambient and high temperature of 700 °C have been carried on to discuss the mechanical properties of rolled samples. The results indicate that the addition of Al element can coarsen both the matrix grains and ODS phase. And the formability of the sheet in this series is higher. All the samples on different strain level are ferrite. The Y addition pre-alloying samples have smaller ODS particles which successfully obtained by means of internal oxidation, and leads to a higher room temperature and high temperature mechanical properties of the sheet. Y added samples are more likely to undergo martensitic transformation during deformation. Therefore the matrix grains suffered martensitic transformation at a certain strain level and makes the rolled sheets have duplex structure of ferrite and martensite. Comparing with the samples without ODS particles, the mechanical properties of samples can be significantly improved by nearly 100 MPa. The hot rolling deformation at the strain of 70% can effectively break the carbide inclusions in, and the matrix grain refinement effect is remarkable without obvious coarsening of the ODS phase. Finally, a ODS-steel sheet sample with the strength as high as 1.5 GPa at room temperature and the high temperature strength nearly 250 MPa at 700 ℃ can be obtained without significant plasticity lose.

 Figure 1.  Formability of hot rolling and the microstructural and mechanical evolution for the developed FeCrW series steel

Keywords: ODS steel; hot isostatic pressing; wedge rolling; microstructure; high temperature strength