RU2337158C2 - Method of production of bimetallic ingots - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method suggests to re-melt consumable electrodes out of metal of interior layer into shell out of metal of exterior layer; at that immediately prior to melt shell is subject to non-oxidation heating to temperature of 0.3-0.8 of metal solidus of exterior layer, at that height of a heated lower portion of shell is equal to 1-6 of thickness of shell wall.

EFFECT: invention ensures reliable welding of layers; dense macrostructure and reduction of bottom trimming.

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Description

The invention relates to the field of production of bimetals and can be used in ferrous and non-ferrous metallurgy, as well as in special branches of mechanical engineering.

A known method of producing bimetallic ingots by the method of electroslag remelting, comprising placing a metal billet, which is the main layer of a bimetallic ingot, in a mold with a gap from the wall and melting this gap with corrosion-resistant steel [1].

The disadvantage of this method is the lack of guarantee of weldability of the ingot layers due to the constant presence of hot flux, the ingress of which into the welding zone of the layers is not excluded. In addition, layers may not be welded in the lower part of the ingot due to poor heating of the metal billet inserted into the mold.

A known method of producing bimetallic ingots, comprising melting the metal of the base layer into a hollow shell made of clad metal by vacuum arc remelting of a sacrificial electrode on the direct polarity of the arc [2].

The disadvantage of this method is the lack of penetration of the lower part of the ingot of the main layer with the shell to a height of 1-6 thickness of the shell. Remelting at the right polarity of the arc leads to contamination of the boundary of the base metal with the shell. At the beginning of remelting, when melting of the electrode begins, the shell is still cold and the heat from the deposited metal is not enough to weld it with the shell in the lower part of the ingot.

The closest in technical essence to the proposed is a method for producing bimetallic ingots, including a vacuum arc remelting of consumable electrodes from the metal of the main inner layer into the hollow shell of the cladding outer layer on the reverse polarity of the arc by welding the base metal into the shell to a height equal to its thickness, followed by exposure without melting to warm the shell [3].

The use of remelting on the reverse polarity of the arc allows us to obtain clean boundaries of the main layer with the shell.

The disadvantage of this method is the uneven welding of the base layer with the shell along the height of the ingot - in the lower part of the ingot, lack of fusion is observed and it goes into technological trim.

The objective of the invention is to improve the weldability of the layers in the lower part of the ingot, the quality of the metal of the inner layer and the reduction of bottom trim.

The problem is solved due to the fact that the shell immediately before melting is subjected to non-oxidative heating to a temperature equal to 0.3-0.8 of the solidus temperature of the metal of the outer layer, with a height of the heated lower part of the shell equal to 1-6 of the shell wall thickness.

The shell is heated in a non-oxidizing environment, which prevents the formation of an oxide film containing slag inclusions, and does not provide reliable welding of the layers.

The interval of heating the shell to 0.3-0.8 is the solidus temperature of the metal of the outer layer due to different melting points of the articulated pairs of metals of the inner and outer layers.

When the shell is heated below the solidus temperature, the desired effect is not achieved, because in the initial melting period, the necessary conditions for welding in the lower part of the ingot are not created. If the shell is heated above 0.8 solidus temperature, the outer layer is melted and the inner and outer layers are mixed, which leads to a large rejection of the metal.

As a result of the experiments with various metal vapors (steel 30 + 95X18), (10GN2MFA + 08Kh18N10T), (KVK55 + KVK37) and others, it was found that the height of the heated lower part of the shell within 1-6 of the shell wall thickness is that necessary start the beginning of the process, which ensures uniform welding of the seam in the lower part of the ingot, improves the quality of the bimetal and minimizes the bottom trim.

If the shell is heated to a height of less than one shell wall thickness, the bottom part does not warm up to the required temperature, since heat dissipation prevails over the shell accumulation, and as a result reliable welding is not achieved in the lower part.

When the shell is heated to a height exceeding 6 shell wall thicknesses, the main melting process is destabilized due to the presence of excessive heat in the outer layer (shell), which leads to layer melting and geometry disruption, i.e. to marriage.

An example of a specific implementation.

Vacuum arc remelting was carried out in a shell made of 10GN2MFA steel with an outer diameter of 600 mm and an inner diameter of 320 mm. If shell heating was not used, poor weldability of the layers, poor macrostructure, and bottom trim were approximately 300 mm or 180 kg / t (see table).

Table Shell heating temperature The height of the heated part of the shell The height to which the surfaced ingot is not welded to the shell, mm Bottom trim, kg / t prototype 300 180 0.2 t solidus 0.8 200 150 0.3 t solidus 1,0 fifty thirty 0.6 t solidus 4.0 45 25 0.8 t solidus 6.0 40 23 0.9 t solidus 7.0 300 * 180 * due to melting of the shell

When using the proposed method, the shell was heated using an inductor in a non-oxidizing environment - vacuum for 20 minutes to a temperature of 750 ° C (0.5 solidus temperature for 10GN2MFA steel) and a height of 280 mm (2 shell wall thicknesses). At the same time, reliable welding of the layers, a dense macrostructure and a reduction of the bottom trim to 25 kg / t by 6 times were ensured.

Information sources

1. USSR copyright certificate No. 2193071, class. C22C 9/20, 2000.

2. US patent No. 3109235, CL. 29, 1973

3. Copyright certificate of the USSR No. 435288, cl. C21C 5/56, 1974.

Claims (1)

A method of producing bimetallic ingots by vacuum arc remelting, comprising remelting consumable electrodes from the metal of the inner layer into a shell of metal of the outer layer, characterized in that immediately before melting the shell is subjected to oxidative heating to a temperature of 0.3-0.8 solidus temperature of the metal of the outer layer , with a height of the heated lower part of the shell equal to 1-6 of the shell wall thickness.