PSI - Issue 81

Anatolii Babinets et al. / Procedia Structural Integrity 81 (2026) 353–359

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Fig. 4. Microstructure of the metal near the fusion line of the deposited (top) and base (bottom) metal at B content, (magnification ×300): 1 – without additives; 2 and 5 – 0.01%; 3 – 0.02%; 4 – 0.05%.Powder granulometry: 1 – 4 – 50 –300 µm; 5 – 50 –100 µm.

The structure of the upper zone of the deposited metal of the specimens is shown in Fig. 5. The crystallite width in the specimens is as follows: No. 1 – 40 –45 µm; No. 2 – 20 –22 µm; No. 3 – 18 –20 µm; No. 4 – 15 –20 µm; No. 5 – 15 –18 µm. Thus, the introduction of boron micro-additives in amounts from 0.01 to 0.05% promotes refinement of the microstructure and a reduction in grain size by 2.2 – 2.5 times. At the same time, in specimen No. 5 (0.01% B, MPW core granulometry 50 –100 µm), a synergistic effect is observed from the optimization of the content of modifying additives and the granulometric composition of the core – the grain size in this specimen is the same as in specimen No. 4, which contains 0.05% B and uses powder of standard granulometry.

Fig. 5. Microstructure of the central part of the deposited metal at B content (magnification ×300): 1 – without additives; 2, 5 – 0.01%; 3 – 0.02%; 4 – 0.05%. Powder granulometry: 1 – 4 – 50 –300 µm; 5 – 50 –100 µm.

The matrix of the deposited metal is characterized by fine acicular martensite. Along the crystallite boundaries, light-colored inclusions, likely corresponding to alloyed austenite, are observed. Increasing the boron content from 0.01 to 0.05% raises the microhardness of the deposited metal from HV1 5820 – 5930 MPa to HV1 7130 – 7240 MPa. For specimens with the same boron content (0.01%), the microhardness is HV1 6260 – 6390 MPa (No. 2, particle size 50 –300 µm) and HV1 6420– 6540 MPa (No. 5, particle size 50 –100 µm). Additionally, it was found that in specimens Nos. 1 – 4 (granulometric composition 50 –300 µm), microdefects in the form of non-metallic inclusions are present both near the fusion line and within the volume of the deposited metal (Fig. 6a). The size of