Microstructure and property tailoring of castable nanostructured alloys through thermomechanical treatments

Irradiation damage concurrent challenges with RAFM and ODS steels for fusion reactor first-wall/blanket: a review

“…The chemical compositions of the 'carbide-CNAs' include Ti, in the range 0.11-0.16 wt.%, and the N content is restricted to less than 40 ppm, which promotes the formation of (Ti, Ta)C carbides, while avoiding the formation of coarse TiN particles or the conversion of MN nitrides to Z-phase nitrides with a high coarsening rate during long-term service at high temperature, a phenomenon known to induce significant loss of precipitation strengthening [356]. The calculated equilibrium MX volume fractions in the CNAs are up to 0.5%, significantly higher than the MX volume fractions in Eurofer97 and F82H (<0.2%) [3,354]. The CNAs were fabricated at laboratory scale (in batches of 0.7-23 kg), and their microstructures and mechanical properties were characterised in detail.…”

“…The presence of fine coherent or semi-coherent MX particles is known to play a key role in the long-term creep resistance at high temperatures of FM steels due to their slow coarsening rate Ostwald ripening [353]. Therefore, the strategy followed by alloy designers for certain advanced RAFM steels such as the CNAs [3,354,355] is to increase the amount of MX compared to the volume fractions present in Eurofer97 or F82H. CNAs strengthened by MX carbonitrides or MX carbides were developed, with a focus on strengthening by carbides [355].…”

Design of Reduced Activation Ferritic/Martensitic Steels by Multiphase Optimization during the Entire Processing

“…Most related studies reported that an improved balance of the mechanical properties of RAFM steels could be obtained by controlling the matrix and precipitates during thermomechanical treatment. 20) Thermomechanical treatment could provide a high density of defects, especially dislocations, which provide potential nucleation sites for precipitation 21,22) and hence refine MX particles during the hot-rolling stage. In work by Tan, a series of hot rolling steps above the tempering temperature were applied to Grade 92 and two prototype steels, and the results showed a large positive influence of the modified hot rolling treatment on the refinement of MX and mechanical properties.…”

“…24) In addition, based on the fixed composition and rolling process, many researchers also attempted to optimize the heat treatment process to refine the microstructure. 25,26) It was demonstrated that the mixed microstructure of martensite and ferrite with coarse M 23 C 6 at ferrite grain boundaries in RAFM steels could decrease the Charpy impact properties in the normalized and tempered conditions. 27) Moreover, intercritical heating was introduced to RAFM steels because it could help decrease the size of prior austenite grains and improve both the tensile strength and ductility.…”

“…These results are also basically consistent with calculation results by Thermo-Calc and previous studies. 19,20) Figure 7 shows the tensile and impact properties of M-RAFM, EUROFER97 and CNA1 steels at room temperature, including the yield strength (YS), ultimate tensile strength (UTS), total elongation (TE) and impact toughness (IT). The error bars for M-RAFM steel represent the standard deviation from the average value of 5 tensile and 5 Charpy impact specimens, and the data for EUROFER97 and CNA1 steels were obtained from the literature.…”