Effects of Y4Zr3O12 addition on the microstructure and mechanical properties of Fe–15Cr–2W-0.35Ti ODS steels

Abstract

The addition of Zr can hardly transform all Y2O3 into fine Y–Zr–O dispersoids in the ODS steels, and the residual large Y2O3 and ZrO2 deteriorate the mechanical properties. Hereof, Y4Zr3O12 nanoparticles (NPs) were successfully prepared by stearic acid sol-gel method and directly added in the Fe–15Cr–2W-0.35Ti ODS steels. The effects of Y4Zr3O12 addition on the microstructure and mechanical properties of the ODS steels were systematically characterized. The mean particle size and number density of oxide NPs in the Fe–15Cr–2W-0.35Ti-0.6Y4Zr3O12 steel were 7.9 ± 2.9 nm and 1.4 × 1023 m−3, showing a narrower size distribution than the Fe–15Cr–2W-0.5Ti-0.35Y2O3 steel. Both Y2Ti2O7 in Fe–15Cr–2W-0.5Ti-0.35Y2O3 and Y4Zr3O12 in Fe–15Cr–2W-0.35Ti-0.6Y4Zr3O12 shared the coherent interface with the ferrite matrix, (151‾)Y2Ti2O7//(1‾1‾0)α-Fe and (303)Y4Zr3O12//(110)α-Fe, with lattice misfit of 3.99% and 1.66%. As respect to the mechanical properties, substituting Y2O3 with Y4Zr3O12 did not apparently vary the strength of the ODS steel, but did effectively improve the uniform elongation from 12.2% to 15.5%. The improvement of ductility was attributable not only to the formation of homogeneous oxide NPs but also to the strong bonding force of the coherent interface in the Fe–15Cr–2W-0.35Ti-0.6Y4Zr3O12 steel. With the increasing Y4Zr3O12 content from 0.6 to 1.8 wt%, the tensile strength of the ODS steels increased from 1006 MPa to 1168 MPa, and the plastic deformation capacity still maintained a relatively high uniform elongation of 7.2%. Our work demonstrates a new way to obtain homogeneous oxide dispersoids in the ODS steels and improve the mechanical properties.