RU2247787C1 - Method for vacuum arc remelting of ingots - Google Patents

Abstract

FIELD: special branches of metallurgy, in particular, vacuum arc remelting of high-reactivity metals and alloys, may be used for manufacture of second-remelting ingots from titanium alloys.

SUBSTANCE: method involves preparing consumable electrode for melting process; providing melting process; before beginning of melting process, locating consumable electrode into furnace chamber and lowering until short circuiting occurs; setting value of arc gap of 10-25 mm and melting electrode at arc current value of 25-37 kA until electrode is melted out by length equal to 0.5-1.0 of diameter of electrode; setting working arc gap between lower end of electrode and liquid metal tank of ingot to be fused-on in the range of 25-65 mm and continuing melting process.

EFFECT: increased yield of metal of melted ingots due to reduced casting and liquor defects by providing fixed melting of lower part of electrode by predetermined length before proceeding to working melting mode and obtaining of flat end of electrode.

3 cl, 2 dwg, 1 ex

Description

The invention relates to the field of special electrometallurgy, namely to a vacuum arc remelting of highly reactive metals and alloys, and can be used to obtain second remelting ingots from titanium alloys.

The choice of a technological scheme for producing ingots depends on their purpose and quality requirements for semi-finished products. For the bulk of the ingots, the main requirement is the purity of the metal from internal defects, as well as the uniformity of the chemical composition and the efficiency of the ingot production process.

A known method of vacuum arc remelting of ingots of titanium alloys with a diameter of 650-850 mm, including the preparation of consumable electrodes (ingots of the first remelting) for melting and the melting process (Titanium alloys. Melting and casting of titanium alloys. Ed. Editor V.V.Dobatkin, M .: Metallurgy, 1978, p.295-306) [1] - the prototype.

The preparation of ingots of the first remelting involves trimming the crown, chamfering from the bottom of the ingot, grooving or trimming of the oxidized sections, and removal of chloride from the side surface of the ingot.

The ingot melting process includes the initial melting period, which consists in diluting the molten metal bath with a smooth increase in the arc current from 5 kA to 25-37 kA for 25-30 minutes; the main melting period with an arc current of 25-37 kA and an arc voltage of 46-50 V; the final melting period is the removal of the shrink shell, which is carried out with a decrease in the arc current for a long time from 10 kA to 1.0 kA.

The disadvantage of this method is the lack of control of the magnitude of the arc gap between the end of the electrode and the molten metal bath when breeding a molten metal bath on a pallet. Due to the presence of casting defects in the ingot of the first remelting, which is used as a consumable electrode in the second remelting, an error accumulates in the initial melting period when determining the real arc gap by the voltage on the arc. Melting at high arc currents with an arc gap of more than 60 mm leads to advanced melting of the central part of the consumable electrode (see [1], p. 298, Fig. 117, 118). The concavity in the central part of the electrode reaches a depth of 80-120 mm and more and it not only does not decrease during the melting process, but concentrates on the end of the electrode at the end of the melting and melts the remainder of the electrode in the area of welding of the electrode to the cinder or the welding zone, which leads to an increase in marriage ingot and reduced metal yield.

The problem to which this invention is directed is to increase the yield of smelted ingots metal by reducing casting and segregation defects by providing a fixed fusion of the lower part of the electrode to a certain length before entering the working mode of melting and obtaining a flat end of the electrode.

The problem is solved in that in the method of vacuum arc remelting of the ingots, including the preparation of the consumable electrode and the process of melting it, according to the invention, before the start of the melting process, the consumable electrode is placed in the furnace chamber and lowered down to a short circuit, then the arc gap is set to 10-25 mm and the electrode is melted at an arc current of 25-37 kA until the length of 0.5-1.0 electrode diameter is fused, after which a working arc gap is established between the lower end of the electrode and the liquid metal bath All the deposited ingot is within 25-65 mm and continue the melting process, lowering the electrode down at a constant speed. In addition, before the start of the melting process, the magnitude of the working arc gap is determined for each alloy to be smelted, and after the installation of the working arc gap, the voltage drop across the electric arc is measured and it is maintained automatically during the entire melting by the ARDP regulator.

The difference of the proposed method of vacuum arc remelting of ingots in comparison with the prototype is that before entering the working mode of melting at the fused end of the electrode form a flat end. It is formed when the arc gap is reduced to 10-25 mm, as a result of which all kinds of shells and irregularities are intensively fused due to the close proximity of the electrode end to the molten pool of the deposited ingot.

In addition, the formation of a flat end of the electrode is carried out with a shallow depth of the molten metal bath and when the electrode is fused to a length of not more than 0.5-1.0 of the electrode diameter, which allows the arc gap to be adjusted even with an arc current of more than 25-30 kA. During the main melting of the electrode, a flat end cannot be created due to strong vibration of the molten metal bath.

The essence of the proposed method of vacuum arc remelting of ingots is illustrated by graphic materials, where in FIG. Figure 1 shows the dependence of the arc voltage on the length of the arc gap, recorded during experimental melting and used to determine the optimal arc gap during the smelting of the ingot, which sets the minimum arc gap (10-15 mm) to form a flat electrode end.

In FIG. 2 shows photographs of the annular gap between the wall of the mold and the side surface of the fused electrode

a) when the length of the arc gap is 10-15 mm (the beginning of melting);

b) with an arc gap of 45-50 mm (main melting period).

Example. The ingot was melted in a DTV-8.7-G10 vacuum electric arc furnace from a consumable electrode (first remelting ingot) of a W6 titanium alloy with a diameter of 670 mm and a length of 2100 mm. On the lateral surface of the electrode, a 120 mm long mark was made by the milling cutter to fix the beginning of the removal of the shrink shell. The current-voltage characteristics of electric arc burning were determined from the experimental melting of the W6 alloy (see Fig. 1). The electrode was loaded into a mold with a diameter of 770 mm, centered, welded to the electrode holder (cinder) and the furnace was evacuated. After the electric arc was excited at an arc current of 5 kA and the lower end of the electrode was heated for 30 minutes, the operating mode was smoothly set: arc current 25 kA, arc voltage 36.5 V. The gap between the tray and the end of the consumable electrode was 27 mm. After diluting the molten metal bath, the voltage on the arc was 32 V, and the arc gap was 15 mm and melted for 30 minutes. Additionally, to maintain the established arc gap, an adjustment was made according to the color of the liquid metal on the pallet (Fig. 2, a). This technological operation made it possible to form a flat end of the electrode in the initial period of melting (the depth of the molten metal bath is 330 mm, which corresponds to 0.5 of the diameter of the alloyed electrode). After the flat end of the electrode was formed, the arc gap length was set to 45 mm by raising the rod up by 30 mm and correcting the color of the liquid bath (Fig. 2, b) and increased the arc voltage to 38 V (Fig. 1). The melting process was continued at an electrode downward speed of 2.8 mm / min until a mark appeared, after which the arc current was smoothly reduced to 1 kA for 120 minutes. At the end of the removal of the shrink shell, after 1 hour, the arc gap between the remainder of the electrode and the melted ingot, which was 8 mm, was measured. Then, after cooling the ingot in vacuum for three hours, the furnace was opened and the ingot was unloaded.

The obtained ingot was of good quality, the yield increased by 1% due to the reduction of casting defects.

The proposed method of vacuum arc remelting of ingots in comparison with the known ones allows for fixed fusion of the lower part of the electrode, which makes it possible to obtain a flat end of the electrode in the initial melting period, reduce the formation of casting defects and, in general, increase the yield of smelted ingots. In addition, the flat end of the electrode allows you to maintain a quasi-stationary mode of combustion of the electric arc by reducing the temperature gradient from the center to the periphery.

Claims (3)

1. The method of vacuum arc remelting of ingots of titanium alloys, including preparing the consumable electrode for melting and the melting process, characterized in that before the start of the melting process, the consumable electrode is placed in the furnace chamber and lowered down to a short circuit, then the arc gap is set to 10-25 mm and the electrode is melted at an arc current of 25-37 kA until the length of 0.5-1.0 electrode diameter is fused, after which a working arc gap is established between the lower end of the electrode and the weld metal of the weld metal the ingot within 25-65 mm and continue the process of melting of the electrode, lowering it down at a constant speed. 2. The method according to claim 1, characterized in that before the start of the melting process, the magnitude of the working arc gap for each smelted alloy is determined. 3. The method according to any one of claims 1 and 2, characterized in that after installing the working arc gap, measure the voltage drop across the electric arc and maintain it throughout the entire melting process in automatic mode.

Images