Probing the interplay among elevated-temperature mechanical properties, microstructural evolution, and dynamic strain aging in reduced activation ferritic/martensitic steels

The effects of temperature (room temperature, 350 °C, 550 °C) on the microstructure evolution and mechanical properties of reduced activation ferritic/martensite steel (RAFM) were investigated using tensile experiments and theoretical calculations. The contribution of each strengthening factor to the yield strength at room temperature was calculated and then compared with the experimentally measured yield strength. The calculated results showed that the theoretical yield strength was coincide with the experimental yield strength, and the strengthening effect at room temperature was dominated by dislocation strengthening, followed by grain refinement strengthening and precipitation strengthening. The stress-strain curves at elevated temperatures were plotted, and then could be fitted well according to the two-stage Ramberg-Osgood model. The effect of microstructure evolution at elevated temperatures on RAFM strength was then analyzed according to the improved Crussar-Jaoul method and transmission electron microscope (TEM). It was found that in the medium-temperature region (350 °C), the effect of dynamic strain aging (DSA) allowed the dislocations to be uniformly distributed within the lath, improving the pinning effect of the dislocations, so the yield strength increased as well as the elongation decreased. In the high-temperature region (550 °C), dislocations accumulated at the grain boundaries. Then, the pinning effect was weakened, and the yield strength decreased substantially.