RU2701698C1 - Method of billet alloying by means of melting electrode with coating in process of electroslag remelting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to electrometallurgy, namely, to billet surface alloying by means of melting electrode with coating in process of electroslag remelting at electroslag installation, equipped with electrode rotation mechanism with speed determined from expression, at that, prior to remelting, a coating is applied on a remelted electrode in the form of a liquid mixture comprising a metal powder which consists of 80 wt% of refractory metal particles with size of up to 9 mcm and 20 wt% of a water-based anti-stick paint, coating is dried, the electrode is fixed at the plant; the process is carried out at current intensity of 1.5 kA; at that, transfer of alloying elements from the coating takes place along the billet surface.

EFFECT: invention allows improving mechanical properties of ingot due to increased degree of predictability of particles delivery to bath of liquid metal and ensuring preservation of their chemical composition due to short time of interaction with working flux.

1 cl, 2 ex, 3 dwg

Description

The invention relates to the field of electrometallurgy, and in particular to special processes of electric melting.

A known method of alloying electroslag metal in the process of remelting, in which to increase the degree of assimilation of alloying materials, together with their oxides, carbon is supplied. In this case, the assimilation of alloying elements increases from 5-6 to 40-60% (RU 1585339, IPC С22В 9/18, 08/15/90).

The disadvantage of this method is that despite the increase in the absorption of alloying elements, a significant part of the alloying elements remains in the bath of liquid slag due to their prolonged contact. The second disadvantage is that this method does not provide the supply of alloying elements to a specific zone, alloying occurs randomly, as a result of which a defect such as segregation occurs.

A known method of introducing alloying elements in the process of electroslag remelting (ESR) (RU 2355790, IPC С22В 9/18, 05/20/2009).

The method includes supplying part of the alloying materials to the mold of the furnace together with the flux before the remelting and the rest during the remelting process, while supplying the alloying materials before the remelting in the amount of 1-2% by weight of the flux is carried out in a mixture with flux. Alloying materials are crushed to a fraction of 2-3 mm. EFFECT: invention makes it possible to evenly distribute alloying elements over the ingot and reduce the trimmings of the lower part of the ingot.

The disadvantage of this method (introduction) is the long interaction of alloying elements with a working flux, which entails not only the predictability of the amount of alloying materials introduced into the melt, but also the impossibility of a uniform distribution of the input phase.

A known method of electroslag remelting, adopted for the prototype, including the rotation of the consumable electrode, in which the consumable electrode at the initial moment of remelting is rotated around its axis with a linear speed determined from the expression

(1)

(one)

where g is the acceleration of gravity, m / s ² ;

σ _me-sh - interfacial tension at the metal-slag interface, J / m ² ;

Δr - the difference in the densities of metal and slag, kg / m ³ ;

r is the radius of the electrode, m,

in the process of remelting, this linear velocity is reduced in direct proportion to the drop in resistance at the electrode and slag bath.

(RU 2241050, IPC С22B 9/18 11/27/2004)

The disadvantage of this method is that it does not provide alloying of the surface of the workpiece.

The technical task of the invention is the hardening of the surface layer of the metal of the workpiece during the ESR process with solid refractory particles from the coating of the molten electrode with their uniform distribution over the surface of the formed workpiece.

The technical problem is solved in that the method of alloying the surface of the workpiece using a melting electrode with a coating in the process of electroslag remelting on electroslag installation equipped with a mechanism for rotating the electrode with a speed determined from the expression

where g is the acceleration of gravity, m / s ² ;

σ _me-sh - interfacial tension at the metal-slag interface, J / m ² ;

Δr - the difference in the densities of metal and slag, kg / m ³ ;

r is the radius of the electrode, m,

according to the invention, before starting the remelting, a coating is applied to the remelted electrode by coloring in the form of a liquid mixture comprising a metal powder, which consists of 80 mass% particles of refractory metals with a particle size of up to 9 microns and 20 mass% of non-stick water-based paint, the coating is dried, the electrode the coating is fixed on the installation, the process is carried out at a current strength of 1.5 kA, while the transfer of alloying elements from the coating occurs on the surface of the workpiece.

The essence of the method lies in the fact that prior to the start of electroslag remelting with the rotation of the electrode, the surface of the consumable electrode is uniformly coated with solid dispersed refractory particles, for example, such as titanium carbide, tungsten carbide, and others. Then, the electrode with a hard refractory coating is dried , set in the furnace for electroslag remelting and begin the process. In this case, the linear speed of rotation of the electrode is determined by the formula (1) depending on the diameter of the remelted electrode, since it should provide a full radial flow of metal at the reflowable end, in which case a drop is formed and its separation occurs from the perimeter of the electrode. Solid refractory particles from the surface of the electrode, as the electrode melts, fall into the formed metal droplets and are transported through the liquid flux layer to the minimum temperature zone of the liquid metal bath, having minimal contact with the working flux.

An essential feature of the proposed method is that the reinforcing particles are fed into a liquid metal bath, not by directly feeding the liquid flux into the bath, but by transferring drops of liquid metal from the surface of the coated electrode under the influence of radial flow arising at a certain linear speed of rotation of the electrode for the corresponding diameters of the electrode and the mold, the rotation speed is determined by the formula (1). In this case, the predicted transportation of metal drops is achieved, which in turn capture particles of alloying elements from the surface of the remelted coated electrode. There is a predicted distribution over the surface of the resulting workpiece including alloying particles, since drops of liquid metal with a captured phase have a minimum contact time with the liquid flux bath, and are fed directly to the edge of the liquid metal bath in the cold zone, where, in turn, the particles are captured by the crystallizing metal formed in the resulting workpiece due to a flat crystallization front (a flat front is also formed due to rotation) of the hardening metal and an increased crystallization rate compared to the classical electroslag method remelting. [Thesis on the topic: Management of the processes of melting, transportation and crystallization of metal in ESR. Chumanov, Ilya Valerevich. 1996, specialty of the Higher Attestation Commission of the Russian Federation 05.16.03].

The method is illustrated in FIG. 1, 2, 3. In FIG. 1 shows a setup diagram for an ESR. In FIG. 2 shows the surface microstructure of the preform of Example 1. FIG. 3 shows the microstructure of the surface of the workpiece in example 2

In FIG. 1 shows a diagram of a device for implementing the method of semi-industrial electroslag furnace A-550, which was used to implement the proposed method for remelting an electrode coated with a mixture of reinforcing particles. This device (Fig. 1) consists of a mold 1 with a pan 2, a melting electrode 3 with an alloying coating 4.

During the ESR process, the liquid metal bath is cooled by a tray 2 and a mold 1, as in the classical ESR technology [Latash Yu.V., Medovar B.I. Electroslag remelting. - M.: Metallurgy, 2011 - p. 240]

In the process of remelting from the surface of the electrode 3 rotating around its axis around the perimeter of its fused end, pre-applied reinforcing particles are captured by drops of liquid metal 4 and they are transferred through the working flux layer 5 to the low temperature zone of the liquid metal bath 6.

The method is as follows (Fig. 1)

Before starting the ESR process, a liquid mixture is prepared from refractory alloying elements for applying to the surface 4 of the melting electrode 3. The mixture contains 80 wt% refractory elements in the form of a metal powder with a dispersion of not more than 9 μm (such as titanium carbide, tungsten carbide), and 20 wt% non-stick water-based paints CP-2 GOST 10772-78. A mixture containing more than 80 mass% of refractory elements loses its fluidity and the coating of the electrode by coloring method becomes impossible, in turn, using less than 80 mass% of refractory particles in the content does not allow to achieve a paste-like state of the mixture and when applied, the mixture spreads without forming a uniformly covering layer . The use of a powder of greater dispersion, in turn, does not lead to hardening of the surface layer, but to the creation of stress concentrators, which will sharply reduce the quality of the resulting workpiece. Then, by brushing, the mixture is applied to the surface 4 of electrode 3.

After drying of the coating 4, the electrode 3 is installed on the installation for ESR. The remelting process is carried out on an A-550 semi-industrial furnace, at a current strength of 1.5 kA, and the electrode rotation speed is calculated by the formula (1), depending on the diameter of the electrode 3. After the process is complete and the metal solidifies in the mold, the workpiece is removed from the mold one.

Example 1

Before the start of electroslag remelting, a melting electrode was prepared, for this a liquid mixture was prepared for application by painting the surface of the molten electrode of the following composition: titanium carbide in an amount of 400 g., A non-stick water-based paint CP-2 GOST 10772- was used as a binder. 78 - in an amount of 100 g. Then, on the melted electrode from st.20, diameter 40 mm., Length 1500 mm, the prepared mixture was applied by the uniform method of coloring with a uniform layer. After drying the applied mixture, the remelted electrode was installed on the installation of electroslag remelting A-550. Remelting was carried out on a semi-industrial furnace A-550 under a layer of flux ANF-6. The current strength during remelting was 1.5 kA. The electrode rotation speed was 100 rpm. After complete solidification of the metal and the liquid flux bath, the preform was removed.

Studies of the surface quality of the obtained workpiece showed a dense surface structure without shrinkage defects. A study of the microstructure in the longitudinal section of the billet showed that the alloying elements, titanium carbide, are evenly spaced on the surface of the billet, without being washed in the middle, a photo of the microstructure is shown in FIG. 2.

Example 2

To confirm the operability of the method on electrodes of various diameters, it was decided to conduct an experiment with remelting the electrode 60 mm. Before the start of electroslag remelting, a melting electrode was prepared, a liquid mixture was prepared for painting the surface of the molten electrode, the composition for the purity of the experiment was similar to the first experimental experiment: titanium carbide in an amount of 400 g was used as a binder, a non-stick paint based on water-based CP-2 GOST 10772-78 in an amount of 100 g. Then to a melt electrode from st. 20, diameter 60 mm., Length 1500 mm. manually using a brush, the prepared mixture was applied in an even layer. After drying the applied mixture, the remelted electrode was installed on the installation of electroslag remelting A-550. Remelting was carried out on a semi-industrial furnace A-550 under a layer of flux ANF-6. The current strength during remelting was 1.5 kA. The rotation speed of the electrode due to changes in the diameter of the remelted electrode was recounted and for these diameters was 92 rpm After complete solidification of the metal and the liquid flux bath, the preform was removed.

Studies of the surface quality of the obtained workpiece showed a dense surface structure without shrinkage defects. A study of the microstructure in the longitudinal section of the workpiece showed that the alloying elements, titanium carbide, are evenly spaced on the surface of the workpiece, without being washed in the middle, a photo of the microstructure is shown in FIG. 3.

From the studies (example 1, 2) it follows that the proposed method allows to achieve hardening of the surface layer of the metal of the workpiece in the process of ESR with solid refractory particles from the coating of the molten electrode with their uniform distribution over the surface of the formed workpiece.

Claims (7)

The method of alloying the surface of the workpiece using a melting electrode with a coating in the process of electroslag remelting on electroslag installation, equipped with an electrode rotation mechanism with a speed determined from the expression

where g is the acceleration of gravity, m / s ² ; σ _me-sh - interfacial tension at the metal-slag interface, J / m ² ; Δr - the difference in the densities of metal and slag, kg / m ³ ; r is the radius of the electrode, m, characterized in that before the start of remelting, a coating is applied to the remelted electrode by a liquid mixture, including a metal powder, which consists of 80 wt.% particles of refractory metals with a particle size of up to 9 microns and 20 wt.% non-stick water-based paint, the coating is dried , the electrode is fixed on the installation, the process is conducted at a current strength of 1.5 kA, while the transfer of alloying elements from the coating occurs on the surface of the workpiece.

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