Evaluation of Ductile-to-Brittle Transition Temperature by Reference Temperature (T-O) Approach at Higher Loading Rates for a Mod. 9Cr-1Mo Steel

To evaluate the ductile-to-brittle transition temperature of ferritic-martensitic steels, the ASTM E1921-based reference temperature (T-O) approach has now been widely recognized; however, until now, the standard restricts itself to static/quasi-static loading rates. It is well recognized that the flow stress of rate-sensitive material increases with the strain rate, and thus it is imperative that the increase in loading rate would lead to limited plasticity-induced brittleness, reflected in higher T-O. There have been efforts in the literature for developing empirical correlations to derive T-O at higher loading rates from T-O at quasi-static loading rates or vice versa. However, there is a need to experimentally evaluate the T-O at higher loading rates, especially for the 9Cr-1Mo family of steels, proposed to be used as wrapper material in the upcoming commercial liquid-sodium-cooled fast breeder reactors in India. The present study is directed toward determining T-O for Mod. 9Cr-1Mo steel at loading rates of 1.12, 3, and 5 m/s.