PSI - Issue 81

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

157

The use of such alloys in modern instrumentation and electronics is associated with the need to ensure strictly controlled physical properties of the metal. Therefore, increased requirements are imposed on their chemical composition, homogeneity, and cleanliness from inclusions and impurities. In precision alloy ingots produced by ESR, various forms of chemical inhomogeneity are often associated with dendritic segregation, which is determined by the nature of cast structure formation during solidification. As shown in our previous works (Protokovilov I. et al. (2019) and Protokovilov I. et al. (2021)), a promising approach to influencing metal structure formation during ESR is to conduct the process in a pulsed mode, which promotes periodic layer-by layer growth of the ingot. In this regard, it is of practical interest to investigate the patterns of cast structure formation in relation to layer-by-layer solidification parameters, such as the height of a single deposited layer, the duration of interlayer pauses, and ESR electrical parameters, which was the subject of the present study. 2. Experimental Procedure The object of the research was ingots with diameters of 85, 125, 160, and 220 mm from carbon steels (grades S235JR and C22E) and a nickel-cobalt iron-based Kovar-type alloy (54Fe-29Ni-17Co). The ingots were produced in a chamber-type ESR furnace (Fig. 1 а ). The melting space was first evacuated to a level of  5 Pa, then filled with argon to an overpressure of 25 kPa. For the steel ingots, flux grade ANF-6 (CaF 2 -28%Al 2 O 3 ) was used. For the nickel-cobalt Kovar-type alloy, a fluoride-chloride flux CaF 2 -15%SrCl 2 was employed. The ESR process was carried out in a pulsed mode according to the diagram presented in Fig. 1b. During the time period t iU , a portion of the metal (consumable electrode) was melted. After this, the voltage was reduced to the value U p , at which metal melting ceased. Simultaneously with the voltage reduction, the electrode feed was stopped. During the time period t pU , solidification of the previously melted metal portion took place, after which the voltage was again increased to the operating value U i . In this way, layer-by-layer growth of the ingot along its height was achieved. In the experiments, the durations of the melting and pause periods ( t iU , t pU ), the voltage rise time ( t tr ), and the pause voltage U p (which provided heating of the metal pool during the pauses) were varied. The parameters of the experimental heats are given in Table 1. The resulting ingots were sectioned longitudinally for macrostructural analysis.

Fig. 1. (a) schematic diagram of the ESR and (b) conventional diagram of change of voltage, electrode feed rate and current during experiments

Table 1. Parameters of Experimental Heats

Exp. No.

Alloy

d el , mm

d in , mm

t iU , s

t pU , s

t tr , s

U i , V U p , V

I i , A

I p , A

1 2 3 4 5 6 7 8 9

Fe-29Ni-17Co Fe-29Ni-17Co Fe-29Ni-17Co Fe-29Ni-17Co

50 50 50 80

85 85 85

-

-

- - - -

38 38 38 37

-

3200 – 3500 3200 – 3500 3500 – 4000 4500 – 5500 5800 – 6000 6000 – 7700 6000 – 7700 7800 – 8500 6500 – 7400

-

60 33 70 90

180 180 300 360 600 600 440 260

7.5 7.5 9.0

300 – 500 300 – 500 850 – 1000 400 – 600 500 – 900 800 – 1100 1000 – 1200 1000 – 1200

125

S235JR S235JR S235JR

120 160 150 220 150 220 140 220 140 220

0 0 0

38 – 40 32 – 38 42 – 45 41 – 43 44 – 46

7 – 8 8 – 9

180 240 200 120

8 – 10 9 – 11 9 – 11

C22E C22E

60 50