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Li et al. J Mater Inf 2024;4:27 https://dx.doi.org/10.20517/jmi.2024.44 Page 11 of 20

Table 2. The microstructural attributes and tensile properties of two designed RAFM steels in Table 1
Microstructures Tensile properties at 600 °C
No. Methods
δ-ferrite Coarsening phase V (%) V M23C6 (%) UTS (MPa) TE (%)
MX
1# ML Without Without 0.52 1.41 412 21.5
CALPHAD 0.60 1.30 - -
Experiment 0.49 1.38 404 21.0
2# ML Without Without 0.48 - 445 20.2
CALPHAD 0.50 - - -
Experiment 0.42 - 422 19.3

RAFM: Reduced activation ferritic-martensitic; UTS: ultimate tensile strength; TE: total elongation; ML: machine learning; CALPHAD: calculation
of phase diagrams.

Figure 4. The equilibrium volume fraction of phases at different temperatures calculated by the Thermo-Calc software: (A) 1# steel and
(B) 2# steel.

Similarly, the V of 2# steel predicted by ML is nearly identical to that calculated by CALPHAD (0.48% vs.
MX
0.50%). These analyses indicate that the ML predictions are in good agreement with the CALPHAD
calculations, and the microstructural model constructed in this study exhibits strong predictive ability.

Experimental validation
To further verify the practical effectiveness of the design schemes proposed by the integrated design model,
1# and 2# steels listed in Table 1 were prepared and characterized. Figure 5 shows the SEM images of the
newly designed 1# and 2# steels. It can be seen from Figure 5A(1) that the 1# steel is a fully martensitic
structure without δ-ferrite, Laves, and Z-phase. Similarly, the 2# steel has a low-carbon martensitic structure
without these phases, as shown in Figure 5A(2). Using the standard linear intercept method, the mean prior
austenite grain sizes of 1# and 2# steels are measured to be 18.8 and 9.7 m, respectively. The micrograph of
1# steel in Figure 5B(1) reveals that the PAGB and lath boundary (LB) are decorated with M C and MX
6
23
precipitates, as observed in other RAFM steels [45,46] . However, it is difficult to find M C carbides distributed
23 6
along PAGB and LB in 2# steel, as illustrated in Figure 5B(2). Some MX precipitates distributed in the
matrix can be clearly observed in 2# steel. The above SEM analyses confirm that both 1# and 2# steels
exhibit a fully martensitic structure without δ-ferrite, Laves, and Z-phase, which is consistent with the