Effects of Zr Addition and Addition Methods on Microstructure and Mechanical Properties of Ods-F/M Steels by Laser Additive Manufacturing

Abstract

Oxide dispersion strengthened (ODS) dual-phase steels with 3D network microarchitecture consisting of lamellar martensite/ferrite phase and equiaxed ferrite were prepared by laser additive manufacturing. The effects of Zr addition and different Zr addition methods, i.e. mechanical alloying (MA) or element powder (EP), on the 3D network microarchitecture, oxide precipitation and tensile properties were investigated. The results showed that the 3D network microarchitecture in the MA Zr-containing sample is more refined than that in the EP Zr-containing sample. A finer 3D network microarchitecture (the equiaxed ferrite size of ~ 6 μm) is presented in the MA Zr-free sample. This is related to the fact that the Ti-rich oxide particles with high melting point preferentially form and provide nucleation sites for the equiaxed ferrite during the rapid cooling process of molten pool. The large Y4Zr3O12 oxides are formed in the lamellar martensite/ferrite zone of the EP Zr-containing sample. While the nanoscale core-shell structure TiO2/Cr-rich, complex appendage Ti-rich/Y2Ti2O7, and small size Y2Ti2O7 oxides are precipitated in the equiaxed ferrite zone of the Zr-free sample. The ultimate tensile strength (UTS) of the Zr-containing samples is increased by using of MA instead of EP. The Zr-free sample shows a higher UTS than the Zr-containing samples. The UTS of the MA Zr-free sample at room temperature reaches to ~ 987 MPa, and the elongation of the EP Zr-free sample achieves ~ 16 %. The UTS of EP Zr-containing sample at 873 K reaches to 441 MPa, which is higher than that of the PM-produced ODS EUROFER.

Keywords: ODS steel, Laser additive manufacturing, 3D network microarchitecture, Nanoparticles, Zr elements