The authors carried out a large volume of experimental studies on the influence of electro-impulse current in the process of crystallization of the casting during the study of steel grade 35GL.

Table 1 – Routines of electro-impulse current influence

Current parameters

Routine 1

Routine 2

Routine 3

Routine 4

Current strength

20, 40, 60, 80

Squelching

2

5

15

24

Frequency

5

10

33

33

The treatment of the melt with an  electro-impulse current was carried out from the beginning of the casting of the metal in the form to the end of the encryption, with the parameters of the current strength varying from 20 to 80 A, squelching from 1 to 24, and also the frequency from 5 to 33 Hz. To conduct research, 4 modifications were selected (Table 1).

All four routines of modification have an effect on the morphology of crystallite of the metal base (Fig. 1).

Fig. 1. Influence on the size of the crystallite of the metal base of different routines of electro-impulse processing of manganiferous steel 35GL

Modification routines 3 and 4 are the most appropriate since the smaller the austenitic crystallite the larger the total area between the crystallites and consequently the less specific content of harmful impurities located on the boundaries of the crystallites.

With a current of 40 A (routine 3) in 35GL steel samples, the crystallite size of man-ganese carbides is the smallest: crystallites are 10 times smaller than unmodified specimens and 2 times smaller than when treated under routine 4. Thus, the smallest structure is obtained in samples at modulating the  electro-impulse current of variable polarity with the following parameters: duration of impulses more than 10…3 s, frequency 5…33 Hz, strength 30…40 A, squareness 5…24, with voltage in the power line 180…240 V (routine 3).

The electro-impulse current passing through liquid steel run away of formation of critical nucleus. This leads to active volumetric crystallization. The dendritical crys-tallization is discontinued much earlier than the unmodified casting. Metal in the volumetric crystallization zone has a finer structure and a higher density. In the modified casting the internal shrinkage is insignificant.

Electric discharge machining of a liquid-alloy steel 35GL with a current of variable polarity with an impulse time of more than 10…3 s, a frequency of 5…33 Hz, a strength of 30…40 A, a squareness of 5…24, at a voltage in the power line 180…240 V during crys-tallization in the casting-form contributes reduction of physical discontinuity: reduction of structural discontinuity: the size of the crystallite of the metal base decreases from 280 to 82…85 microns, and the size of manganese carbides – from 6,7 to 0,3…0,5 microns; significant increase in the basic mechanical properties of cast structural steel 35GL: the strength is increased by 9%, the impact hardness – by 21%, the hardness (HB) – by 6%.