P/M 18Cr ODS steels produced by mechanical alloying and hot powder forging

Abstract

Mechanical alloying in attritor mill and powder consolidation through hot forging were employed to produce 18Cr ODS steels. Elemental powders were mechanically alloyed with nano-size yttria powder for up to 12 h. The effect of milling time on powder morphology, crystallite size and lattice strain were studied. Optimum milling time of mechanical alloying was determined for dissolution of constituents in the ferrite matrix. Further milling led to peak broadening. TEM confirmed the presence of fine crystallites in milled powders. HRTEM fringes were taken on the oxide particles. Their FFT confirmed that Y2O3 and TiO2 particles were present in the milled powders. The milled powders were consolidated through hot powder forging. Addition of Ti and Y2O3 significantly reduce the grain size in forged alloys. It also leads to formation of fine complex Y-Ti-O oxides. The powder forged alloys exhibited fine grained recrystallized microstructure. Reasons for this are discussed.