2000 Volume 40 Issue Suppl Pages S174-S178
Microstructures and mechanical properties were investigated in ultra fine-grained oxide-dispersion steels with 24 mass% Cr ferrite matrix fabricated from mechanical milled powders. Powder mixtures of Fe, Cr and Y2O3 were mechanically milled in an argon gas atmosphere and then consolidated at around 1100K. After 720 ks mechanical milling (MM), nanocrystalline ferrite grain structures were formed within powder particles. As for Y2O3 particles. It was observed that they were not only crushed to several nanometers but also decomposed during MM, and then oxides like Y2O3 and YCrO3 finely precipitated in ultra fine grained structure on annealing at around 1200K. Such ultra fine oxide particles effectively retarded the growth of matrix grains. The sample with 1 vol.% Y2O3 addition maintained ultra fine ferrite grains of 0.4 μm even after the annealing of 1573 K-3.6 ks by the Zener pinning effect of the oxide particles of about 10 nm in diameter. Tensile strength of the bulk samples markedly rose as the ferrite grain size became smaller in the grain size range below 1 μm and reached 1.93 GPa for the bulk sample with 1 vol.% Y2O3 addition and with the smallest mean grain size of 0.16 μm.
