Influence of austenitizing temperature on the mechanical properties and microstructure of reduced activation ferritic/martensitic steel

The mechanical properties and microstructure of reduced activation ferritic/martensitic (RAFM) steel after austenitizing at 930–1080 °C for 30 min and tempering at 760 °C for 90 min were investigated using field emission scanning electron microscopy, field emission transmission electron microscopy, electron back-scattered diffraction, X-ray diffraction, tensile, and impact tests. The results showed that the size of the M₂₃C₆ particles decreased from 930 to 1030 °C and then increased from 1030 to 1080 °C, whereas their number densities showed the opposite trend with increasing austenitizing temperature. After austenitizing at 930 and 980 °C, the largest proportion consisted of the sub-grain structure, and when the austenitizing temperature was raised to 1030 and 1080 °C, the major component consisted of bundle martensite laths. The tensile strength increased gradually with increasing austenitizing temperature, and dislocation strengthening accounted for the largest proportion among the various strengthening mechanisms. Finally, fitting analysis showed that among the various hierarchical structural units in RAFM martensitic steel, the packets served as the effective "grain" that governed the increase in yield strength.