Quantitative correlation between nano/micro-scale strucuture and high-temperature strength of 9Cr-ODS steel, 2; Relationship between high-temperature strength and nano/micro-scale strucuture

Otsuka, Satoshi   ; Kaito, Takeji ; Kim, S.-W.; Inoue, Masaki ; Asayama, Tai ; Suzuki, Junichi; Onuma, Masato*

With a view to making clear the correlation between microstructure and high-temperature strength of 9Cr-ODS ferritic/martensitic duplex steel, the correlation between matrix ferrite proportion and high-temperature strength was quantitatively evaluated. The evaluated results were compared to the nano-structure data such as oxide particle diameter and number density evaluated in the companion report. Both the decreasing excess oxygen and the increasing titanium provides for enhancement of ferrite proportion, which is accompanied by the increasing number density of nano-scale oxide particles, thus appreciably improving high-temperature creep strength. This result is consistent with the previous TEM observation results showing that nano-scale oxide particles are more densely dispersed in ferrite than in tempered-martensite. The increase of ferrite proportion is shown to certainly improve high-temperature creep strength even though the number density of nano-scale oxide particles is kept constant.