Character evaluation of strength in dispersion strengthened ferritic steel (3)

Yoshida, Fuyuki*; not registered; not registered; Nakashima, Hideharu*; not registered

In order to clarify the origin of strength anisotropy in ODS ferritic steel with YO particles at high temperatures, a threshold stress measured by stress abruptly loading test (SAL test) were compared with the Orowan and the void-hardening stresses calculated from dispersion parameters and subjected to the high-temperature compression test at temperature from 600 to 700 C and at strain rates from 110 to 110s, and the effect of grain-boundary sliding on the high-temperature strength was clarified. The results are summarized as follows. (1) The Orowan stress and the void-hardening stress calculated from dispersion parameters approximately agreed with the threshold stress obtained by SAL test. In addition, as the time under load elapsed, the transition of the threshold stress obtained by SAL test was observed, it is concluded that the originating mechanism of the threshold stress in ODS ferritic steel is the Srolovitz's one (2) The grain-boundary sliding was clearly observed for grain boundaries inclined by 45 to the stress axis. The flow stress was changed significantly by aspect ratio of grain size. Therefore, it is concluded that the strength anisotropy in ODS ferritic steel induces the grain-boundary sliding behaviour.