Strengthening Effect of Multiscale Second Phases in Reduced Activation Ferrite/Martensitic Steel

Reduced activation ferrite/martensitic steels containing yttrium (Y), titanium (Ti), and zirconia (Zr) are melted using vacuum induction melting–electroslag remelting (ESR) to study the effects of second phases on the microstructure, tensile properties, and impact toughness of the alloys. In addition, two heat treatment processes are used to obtain the dispersed distribution of fine M23C6 carbides in reduced activation steel. The results show that ESR not only refined micron inclusions but also increase the number of submicron inclusions in the alloys. The number of submicron inclusions per unit volume of the ESR ingots is 1.11–1.43 × 1019 m−3. These inclusions not only reduced the austenite grain size through pinning but also effectively pinned dislocations to improve the mechanical properties of the steel. MX carbonitrides rather than M23C6 precipitated first in the steel with A–A–T heat treatment at 920 °C, decreasing the mean size of M23C6. The refined grain size, martensitic laths, and M23C6 are beneficial to the mechanical properties of the alloys. The yield strengths of the E–Y–Ti and E–Y–Zr alloys are 659 and 657 MPa, and their ductile–brittle transition temperatures are −93 and −86 °C, respectively. Effects of multiscale second phases on microstructures and properties of reduced activation ferritic martensitic (RAFM) steel were evaluated. Submicron inclusions not only reduced grain size by pinning but also effectively pinned dislocations. MX rather than M23C6 precipitated first in the A–A–T steel, decreasing the size of M23C6. Fine‐grain size, inclusion, and M23C6 lead to a balance of strength and impact toughness.