Improvement of 9Cr-ODS martensitic steel properties by controlling excess oxygen and titanium contents

The effects of different percentages of oxygen and titanium on the mechanical properties and microstructure of 9Cr-ODS steel were investigated. It was shown that the high-temperature strength was drastically improved by controlling the atomic ratio between excess oxygen and titanium (x in TiOx) around 1.0. When x is around 1.0, the elongated alpha-grains containing the ultra-fine and close oxide particle dispersion were generated in addition to equiaxed martensite grains. Furthermore, the number density of oxide particle in the martensite grains increased. The control of phase transformation and oxide particle dispersion by adjusting oxygen and titanium contents should be a key technology to achieve superior high-temperature strength.