PSI - Issue 81

Igor Protokovilov et al. / Procedia Structural Integrity 81 (2026) 156–161

159

Figure 4 shows the as-cast structure of large-diameter ingots (160 and 220 mm) made of carbon steel. In all cases, a distinct layering of the metal structure is observed. The boundaries between layers appear as light bands that follow the shape of the molten metal pool. This boundary is predominantly flat with a slight depression along the ingot axis (Fig. 4b). In Experiments No. 6 and 7, defects in the form of microporosity were found along the interlayer boundaries (Fig. 4a, No. 6, 7). The location of these defects slightly below the interlayer boundary indicates their shrinkage nature. This may be caused by the formation of a solidified metal crust on the surface of the molten pool due to insufficient heating power during electrode melting pauses. The formation of defects along the interlayer boundaries could also result from a sharp increase in voltage after the pause, causing droplets of electrode metal to fall onto the relatively cold surface of the molten pool. In Experiments No. 8 and 9, the heating power of the molten pool was increased, and the voltage after the pause was raised not stepwise but gradually over a period of t tr = 50 – 60 s (Table 1). Analysis of the structure of the resulting ingots revealed no defects in the interlayer zones. Within each deposited layer, the structure is mixed and consists of small columnar crystals oriented perpendicular to the solidification front, as well as fine equiaxed crystals. The parameters of the с ast structure of the obtained ingots are presented in Table 2. Analysis of the data indicates that the refinement of the metal structure is significantly higher than in ingots produced by conventional ESR. The structure of ingots No. 8 and 9 is uniform across the entire ingot cross-section, with no pores, slag inclusions, or other defects present (Fig. 4, No. 8, 9). Furthermore, with increasing height of the deposited layer, the average crystal size also increases (Fig. 5). When the layer height exceeds the ingot radius, the effectiveness of structure refinement decreases substantially, and the crystal size becomes comparable to that observed in conventional ESR.

Fig. 4. (a) cast structure and (b) scheme of cast structure of carbon steel ingots (numbers indicate the experiments No.)

Table 2. Characteristics of the ingots cast structure

Exp. No.

Grain size, mm (percentage of cross-sectional area of the ingot)

Layer height, mm Defects

peripheral columnar 2.5  36.3 (78%) 1.9  12.4 (37%) 1.7  8.5 (33%) 2.2  14.8 (44%) 3.2  13.5 (13%) 3.6  16.2 (18%) 4.6  22.0 (21%) 4.5  20.0 (27%)

internal columnar 2.4  17.5 (12%) 2.6  17.7 (59%) 1.5  7.9 (40%) 2.0  12.3 (45%) 3.2  14.7 (84%) 3.8  17.8 (49%) 3.8  18.0 (42%) 3.5  13.8 (52%)

fine equiaxed 1.8  2.1 (10%) 2.1  2.8 (4%) 0.5  0.6 (27%) 2.0  2.5 (11%) 2.4  2.4 (3%) 2.5  4.0 (33%) 4.0  6.0 (37%) 3.5  5.0 (21%)

1 2 3 4 6 7 8 9

-

Yes No

33 20 35 24 50 55 30

No No

Yes Yes No

No