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Page 12 of 20 Li et al. J Mater Inf 2024;4:27 https://dx.doi.org/10.20517/jmi.2024.44

Figure 5. SEM micrographs of the designed RAFM steels: [A(1) and B(1)] 1# steel and [A(2) and B(2)] 2# steel. SEM: Scanning electron
microscopy; RAFM: reduced activation ferritic-martensitic.

predictions from ML and CALPHAD.

The typical TEM micrographs of 1# and 2# steels are shown in Figure 6. As seen in Figure 6A(1) and B(1),
the martensitic lath structures in both steels are decorated by dislocations and small precipitates. The lath
width and dislocation density of 1# steel were measured to be around 334 nm and 2 × 10 m , respectively,
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whereas 2# exhibits a narrower lath width of 317 nm and a higher dislocation density of 3 × 10 m . As in
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conventional RAFM steels [47,48] , the main precipitates observed in 1# steel are M C and MX, as shown in
23
6
Figure 6A(2) and (3). M C precipitates have an average size of 48.4 nm and a number density of 2.32 ×
6
23
-3
10 m , primarily forming along PAGBs, sub-grain boundaries, and within martensitic laths. MX
20
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20
precipitates with an average size of 24.2 nm and a number density of 6.57 × 10 m are randomly
distributed in the matrix. In 2# steel [Figure 6B(2) and (3)], only a large amount of MX precipitates
randomly distributed in the matrix are observed, measuring 22.5 nm and 7.04 × 10 m in average size and
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number density, respectively.
The experimental measurement value for V M23C6 in 1# steel is about 1.38%, nearly matching the CALPHAD
calculation of 1.30% and the ML prediction of 1.41%. Based on the experimental analysis results, the
statistical V of 1# steel is around 0.49%, which is less than the 0.6% calculated by CALPHAD and the
MX