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

Effect of Nano-Size Oxide Particle Dispersion and δ-Ferrite Proportion on Creep Strength of 9Cr-ODS Steel

“…This result is well consistent with the conventional qualitative data obtained by transmission electron microscope. 5,6) High number density of nano-size oxide particle dispersion would play a major part in the strength improvement produced by F/M duplex structure formation. The data of small -ferrite proportion close to 0 vol% (Hi-O, M-W(O), Hi-W, M-W) shows that number of nano-size oxide particles substantially increases only by reduction of Ex.O without increasing -ferrite proportion.…”

“…In addition, our studies revealed that -ferrite formation in tempered martensite considerably improves the creep strength of 9Cr-ODS steel. [2][3][4][5][6] As for the conventional martensitic steels, -ferrite is a detrimental phase which never acts as reinforcement phase, so that the martensite single phase matrix is preferentially chosen. However, the -ferrite in 9Cr-ODS steel is believed to be a reinforcement phase because it appears to contain higher population of nano-size oxide particles than tempered martensite.…”

“…However, the -ferrite in 9Cr-ODS steel is believed to be a reinforcement phase because it appears to contain higher population of nano-size oxide particles than tempered martensite. [2][3][4][5][6] The 9Cr-ODS steel has the complex dual-phase microstructure consisting of fine ferrite and martensite grains, in which many oxide particles are dispersed in nanometer scale. Then, it is difficult to derive trustworthy information on ferrite proportion and morphology by conventional technique such as metallographic observation.…”

Residual ferrite formation in 12CrODS steels

“…For transformable 9CrODS steels, it is known that their structure is a dual phase composed of tempered martensite and ferrite [4][5][6], although the full-tempered martensite is predicted in the equilibrium phase diagram. This ferrite is designated as a metastable residual ferrite, and it is also known that the residual ferrite significantly improves the high-temperature strength in 9CrODS steels [7][8][9][10][11][12]. The structure of martensitic base 12CrODS steels is, therefore, investigated, focusing on residual ferrite formation improving high-temperature strength.…”

Development of a Novel Melt Spinning-Based Processing Route for Oxide Dispersion-Strengthened Steels

“…[29] The additional spots in Figure 1 With encouraging results from melt spinning and internal oxidation of the MS01 ribbons, MS02 ribbons were produced with 15 times higher throughput, reduced Y concentration, and addition of Ti that is known to produce a refining effect of Y-rich oxides in mechanical alloying. [30][31][32] As shown in Figure 2(a), MS02 ribbons had a thickness of approximately 25 lm, which was comparable with the smaller-scale MS01 ribbons. However, there were now resolvable micron-sized equiaxed grains at the wheel side, and again largely featureless columnar grains growing against the 1D heat flow, and then a region of a more obvious microsegregation and dendritic structure towards the free side.…”