RU2232669C1 - Method for electroslag surfacing of small-size ends - Google Patents

Abstract

FIELD: manufacture of parts of machines and tools with use of surfacing operation.

SUBSTANCE: method comprises step of creating slag bath in volume restricted by surfaced face and sectional crystallizing pan; keeping temperature of surface of crystallizing pan higher than temperature of sharp raising of viscosity of used slag; realizing electroslag surfacing at introducing to rotating slag bath non-consumable hollow electrode connected with autonomous power source and having cone working portion; submerging electrode into slag bath by depth equal to height of electrode cone; providing high temperature region with size 2 - 2.5 diameters of electrode in slag bath; feeding surfacing material into high-temperature region through cavity of non-consumable electrode; selecting ratio of welding electric current and electric current applied to non-consumable electrode in range 1.3 - 2.0. High heating temperature and intensified agitation provide uniform melting of surfacing materials containing refractory components.

EFFECT: enhanced quality of surfaced ends.

3 cl, 4 dwg, 1 tbl, 4 ex

Description

The invention relates to metalworking, metallurgy and can be used in the manufacture of surfacing parts of machines and tools.

There is a method of electroslag surfacing (ESH) of the ends of products with a wire electrode (Bondarchuk N. A., Patoka A. I., Markin Yu. V. Application of wire of type EP-567 for surfacing the mandrels of a piercing mill. - In collection of scientific works: Theoretical and technological foundations of surfacing. Surfacing materials. - Kiev: EO Paton Electric Welding Institute, 1978, pp. 104-106) small-sized cylinders with an end area of 3-5 cm ² , in which the electrode melting material supplied to the slag bath, melts in a limited volume of slag adjacent to its surface, the temperature in which attains its 1900-2300 ° C.

The disadvantage of such a deposition scheme is that when filing material containing components with a high melting point is fed into the slag bath (for example, W, T _pl = 3450 ° C; Ta, T _pl = 2996 ° C; Mo, T _pl = 2625 ° C; Nb, T _pl = 2415 ° C) their melting is uneven, which does not allow to obtain a weld metal of a given chemical composition.

A known method of electroslag surfacing (ESH) and metal welding (see USSR author's certificate, No. 184337, 21H, 32/01, (H 05 b), publ. 1967), in which the heating and melting of the metal is carried out by heat, released in the molten slag by passing an electric current, and the heating of the slag is produced by a non-consumable electrode.

When surfacing according to this scheme, a non-consumable electrode only maintains the temperature of the slag within the required limits, as a result of which it is impossible to achieve uniform melting of the surfacing material containing refractory components. Another negative point is that it is difficult to feed the surfacing material exactly into the thermal center of the slag bath.

Closest to the invention is a method of electroslag surfacing of cast iron rolling rolls (see patent of the Russian Federation, No. 2139155, 23 K 25/00, publ. 1999). According to this method, the slag bath is induced in the volume limited by the weld surface and the sectional crystallizer containing the current supply and forming sections, the surface temperature of the mold is maintained above the temperature of a sharp increase in the viscosity of the slag used, the slag bath is rotated, the bottom level of the slag bath is maintained at a distance of no more than the thickness of the deposited layer from the lower edge of the current-supplying section and the magnitude of the welding current in the sectional mold.

The ESH process in a sectional crystallizer (SC) allows to exclude the influence of the electrode material on the formation of the metal structure, since the surfacing materials in this case are electrically neutral. But with such a process, the melting rate of the surfacing material is determined by the temperature of the slag, which in this case does not exceed 1800 ° C. This does not allow the use of surfacing materials in the form of composite rods containing thin wires, metal powders and other components (shot, shavings) containing refractory (T _pl > 2000 ° C) elements (W; Ta; Mo, etc.), since their uniform melting is not ensured.

Therefore, the objective of the proposed technical solution is to create such a method of ESH, which would ensure uniform melting of surfacing materials containing refractory components.

The technical result consists in achieving the effect of uniform melting of composite surfacing materials containing refractory components due to the formation in the slag, in the immersion zone of the non-consumable hollow electrode of a high-temperature region in which the slag is heated to boiling point and intensively mixed.

The technical result is achieved by the fact that the slag bath is induced in the volume limited by the weld surface and the sectional mold containing the current supply and molding sections, the mold surface temperature is maintained above the temperature of a sharp increase in the viscosity of the slag used, the slag bath is rotated, the bottom level of the slag bath is maintained at a distance not more than the thickness of the deposited layer from the lower edge of the current-supplying section and a given value of the welding current. In this case, electroslag surfacing is carried out by introducing into the slag bath a non-consumable hollow electrode connected to an independent power source, made with a cone on the working part, to a depth equal to the height of the cone, with the formation of a high-temperature region in the slag bath, the size of which is limited to 2-2.5 the diameters of the said electrode, while through the cavity of the non-consumable electrode, surfacing material is fed into the formed high-temperature region, and the ratio of the welding current and the current supplied to The current electrode is selected in the range of 1.3-2.0. The rotation of the slag bath is carried out at a speed of 60-150 rpm The value of the welding current is maintained in the range of 0.8-1.2 from J _nom , where J _nom is the nominal value of the welding current.

The nominal welding current is selected from the interval 200-350 A. Outside the boundaries of the specified interval, ESH stability is violated, which is explained by the design features of the SC and the composition of the surfacing materials.

A distinctive feature of the proposed method is that the melting of the surfacing material occurs due to the introduction of a non-consumable hollow electrode energized from an independent power source into the slag bath, in the immersion zone of which a high-temperature region is formed in the slag, where it is heated to boiling point and intensively mixed. The formation of such a high-temperature region in a slag bath makes it possible to uniformly melt composite filler materials containing components with a low and high melting point up to 3500 ° C.

The resulting high-temperature region in the slag bath is limited to 2-2.5 diameters of the electrode and has a temperature at which the slag is heated to a boiling point. This circumstance is due to a number of factors: the immersion depth of the non-consumable hollow electrode, the geometric shape of its working part, the ratio of the welding current and the current from the non-consumable hollow electrode and the slag electrical resistance. An increase in the size of the high-temperature region above 2.5 D leads to boiling and splashing of the slag bath, and a decrease below 2.0 D does not allow uniform melting of the surfacing material.

The immersion value of the non-consumable hollow electrode h _n in the slag bath is maintained constant and equal to the height of the cone on its working part.

With the conical shape of the electrode end, the area of its active surface decreases, which allows an increased current density to be obtained, and leads to an increase in the slag temperature to the boiling point in the electrode immersion zone, affects the temperature gradient of the slag bath and determines the dimensions of the high-temperature region in which the slag is heated to boiling point (about 3500 ° С for ANF-6 slag).

The ratio of the welding current J _nom in the SC and the current from the non-consumable hollow electrode J _AD -k ₁ is in the range 1.3-2.0 and is kept constant, which leads to the formation of a high-temperature region in the immersion zone of the electrode. The increase in this ratio of more than 2.0 does not allow to obtain a high temperature region in the slag bath. The decrease in the ratio of k ₁ less than 1.3 leads to overheating of the slag bath and splashes.

The welding current during surfacing is maintained within k ₂ = 0.8-1.2 from J _nom . An increase in k _{2 of} more than 1.2 impairs the stability of the ESH process and leads to slag outbursts, and a decrease of less than 0.8 causes an increase in the skull at the SC walls, leads to overcooling of the slag and termination of the surfacing process.

Finding the ratio of k ₁ and k ₂ within the specified limits ensures reliable mixing of the slag bath and the stable existence of the high-temperature region.

The rotation of the slag bath during surfacing is carried out at a speed of 60-150 rpm Such a rotation speed will increase the lifetime of liquid metal droplets in the slag bath, due to which metallurgical processing of the metal is carried out more fully. With a decrease in the speed of rotation of the slag bath of less than 60 rpm, the residence time of the droplets in the slag decreases, as a result of which the duration of heat transfer at the drop-slag interface decreases and the effect of slag on the process of melting of the surfacing material decreases. An increase in the speed of rotation of the slag bath of more than 150 rpm leads to a transformation of the shape of its surface, partial exposure of the mirror of the metal bath and a violation of the stability of the electroslag process due to changes in the ratios k ₁ and k ₂ .

When filler material is fed into the hole of the non-consumable electrode into the formed high-temperature region of the slag bath, it melts uniformly, accompanied by the formation of droplets and their uniform distribution over its volume with subsequent transfer to the weld pool.

The invention is illustrated by drawings. Figure 1 shows a diagram of electroslag surfacing; figure 2 - arrangement of the current lead in the SC; figure 3 - the microstructure of the weld metal obtained by the present method; figure 4 - the microstructure of the weld metal obtained at the transcendental for the proposed method modes.

The method is implemented as follows. Water cooling of the current-supplying 1 and molding 2 sections of the SC, isolated by a gasket 3, is included to maintain the temperature of the mold surface above the temperature of a sharp increase in the viscosity of the slag used. To start ESHN, slag is poured into the cavity between the product 4 and SK and the initial voltage is increased in comparison with the nominal voltage between the current supply section 1 and product 4 from the main power source 5. The amount of slag depends on the diameter of the deposited product, and the upper level of the slag bath must be higher than the lower edge of the current-carrying section by 15-20 mm. Due to the flow of the welding current J _nom through the current-supplying section 1, which functions as a non-consumable electrode, the slag temperature is kept constant, and since it has a process connector 6, the slag starts to rotate at a speed of 60-150 rpm, thereby ensuring uniform temperature distribution by its volume. The rotation of the slag bath is affected by the location of the current lead relative to the process connector 6, determined by the angle α (figure 2), and with increasing angle α, the speed of rotation of the slag increases. With the beginning of the rotation of the slag in the cavity of the current-carrying section 1, a hollow non-consumable electrode 8 is introduced into the center of the surface of the slag bath 7 with a cone on the working part to a depth equal to the height of the cone h _p . The immersion value h _{p is} kept constant, and if it decreases, the slag is added to the initial level. Non-consumable hollow electrode 8 is powered from an independent DC power supply of reverse polarity 9, at which the erosion of the electrode is reduced. Moreover, the ratio of the welding current J _nom and the current from the non-consumable electrode J _AD are in the range 1.3-2.0. In the immersion zone of the non-consumable hollow electrode 8, a high-temperature region is formed, limited by 2-2.5 diameters of the electrode, in which the slag is heated to boiling point. Then, surfacing material 10 (composite rods, wires, rods, shot, shavings, etc.) is fed into the hole of the hollow non-consumable electrode 8 into the formed high-temperature region of the slag bath. Thanks to the processing by overheated and intensively mixed slag, the components of the surfacing material 10 with a different, including elevated, melting temperature are evenly melted in it. The melting process of the surfacing material 10 is accompanied by the formation of droplets and their uniform distribution throughout the volume of the slag bath 7 with subsequent transfer to the weld pool 11. In the process of surfacing, the lower level of the slag bath is maintained at a distance of h _n (not more than the thickness of the deposited layer) from the lower edge of the current-carrying section . With a decrease in the value of h _n , a short circuit occurs in the current-carrying section of the SC with deposited metal 12. This leads to a sharp increase in the welding current J _nom , violation of the ratio k ₂ and termination of the electroslag process. In this case, the movement of the deposited product is accelerated (speed V _n increases) in order to stabilize the value of h _n . With an increase in h _n, the current density at the SC walls decreases, which leads to a decrease in the welding current J _nom and the formation of a skull at the walls of the current-supply section. The k ₂ ratio is also violated, which leads to unsatisfactory formation of the weld metal. In this case, the speed V _{n is} slowed down to restore the nominal deposition mode.

Example 1

Electroslag surfacing of the ends of a cylindrical shape in SC was carried out. For the experiment, blanks with a diameter of 25 mm made of steel 20 were used. A composite rod with a diameter of 5 mm, consisting of a nickel shell, into the cavity of which powders and wires of metals with different melting points were used, was used as surfacing material: powders: A1, T _pl = 660 ° C; Zr, T _pl = 1750 ° C; wire: W, T _PL = 3450 ° C; Ta, T _pl = 2996 ° C; Mo, T _pl = 2625 ° C; X20H80 T _mp = 1850 ° C.

For direct current ESH, an ANF-6 flux was used (since it is non-oxidizing, which prevents the loss of components of the melting composite rod as a result of oxidation), which were previously melted and poured into the cavity between the product and SC. To protect the slag bath from the atmosphere, its surface was blown with argon. At the start of the ESH, an initial increased voltage (~ 50 V) was applied to the current supply section. Slag was poured into the mold so that the upper level of the slag bath was 15-20 mm higher than the lower edge of the current-carrying section. Due to the flow of the welding current (I _nom = 300 A) through the current-supplying section, which functions as a non-consumable electrode, a constant slag temperature of 1900 ° C was maintained at a nominal voltage of 36 V. The maximum slag rotation speed was 150 rpm. With the beginning of slag rotation in the cavity of the current-carrying section, a hollow non-consumable electrode with an outer D = 15 mm and an inner d = 6 mm diameter with a cone on the working part to a depth equal to the cone height h _p = 15 mm was introduced into the center of the surface of the slag bath. The value of immersion h _p = 15 mm was kept constant, and with decreasing height of the slag bath, the slag was added to the initial level. The non-consumable hollow electrode was powered by a direct current of reverse polarity from an independent power source, while the current value J _{N.E. was} set equal (~ 190 A) to satisfy the ratio k ₁ = J _nom / J _N.E. = 1.6. This current ratio led to the formation of a high-temperature region in which the slag is heated to a boiling point (about 3500 ° C for ANF-6 slag). Then, a composite rod was fed into the hole of the hollow non-consumable electrode into the formed high-temperature region of the slag bath with a velocity V _p close to its melting rate. Due to overheated and intensively mixing slag, the components of the surfacing material with different, including elevated, melting points melt evenly with a speed of V _n = 5 mm / s (see table). The nature of the structure of the weld metal is homogeneous, with a solid solution content with hardening phases (figure 3).

Example 2

Under experimental conditions similar to example 1, ESN was performed at values of k ₁ and k ₂ corresponding to the lower and upper boundaries of the claimed ratios. The data obtained indicate that the ESH process is stable, and, as can be seen from the table of melting rates of the components of the composite rod, slightly differ from each other, and at values of k ₁ = 1.3, k ₂ = 0.8, the melting rate of tungsten and X20H80 wires higher than the optimal V _p , causing the production of high-quality deposited metal (W, V _p = 5, l mm / s; X20H80, V _p = 6.5 mm / s), and with values of k ₁ = 2.0, k ₂ = 1 , 2 - below the optimal V _p (W, V _p = 4.8 mm / s; X20H80, V _p = 4.9 mm / s). The structure of the deposited metal corresponds to the structure obtained in example 1 (figure 3).

Example 3

Under experimental conditions similar to example 1, ESN was performed at values of k ₁ and k ₂ that are outside the boundaries of the claimed ratios. The data obtained indicate that the ESH process is stable, and, as can be seen from the table of the melting rate of the components of the composite rod, significantly differ from each other, and with values of k ₁ = 1.0, k ₂ = 0.7, the melting rate of all wires is higher than the optimal V _p (W, V _p = 6.8 mm / s; Ta, V _p = 7.4 mm / s; Mo, V _p = 7.8 mm / s; X20H80, V _p = 8.5 mm / s) and with values of k ₁ = 3.0, k ₂ = 1.3 below the optimal V _p (W, V _p = 3.5 mm / s; Ta, V _p = 4.1 mm / s; Mo, V _p = 4.5 mm / s; X20H80, V _p = 4.7 mm / s). The structure of the weld metal contains not melted components of the composite rod (figure 4).

Example 4

ESN was performed according to the method described in the prototype. Surfacing material was fed into the slag bath and the melting rate of the components was determined. The experimental results show that the electroslag process is stable and with a ratio of k ₂ = 0.9-1.1, uneven melting of the components of the composite rod is observed (W, V _p = 2.6 mm / s; Ta, V _p = 3.2 mm / s; Mo, V _p = 3.7 mm / s; X20H80, V _p = 4.6 mm / s). In this case, the melting rate is much lower than the optimal V _p (see table), and the structure of the deposited metal corresponds to the structure obtained in example 3 (figure 4).

The uniformity of melting of the components of the composite rod was controlled by the nature and sequence of melting of the components of the rod visually and by the nature of the structure of the deposited metal.

Comparative data of the proposed method for electroslag surfacing of small-sized ends in comparison with the prototype are shown in the table, from which it follows that the inventive ESH method is characterized by uniform melting of the components of the composite rod with different, including elevated, melting points, a homogeneous structure containing a solid solution with hardening phases .

Using the proposed method of electroslag surfacing of small-sized ends gives in comparison with the known methods of electroslag surfacing the following technical result:

1. The ability to apply filler composite filler materials for refractory materials containing refractory components.

2. Achieving uniform melting of composite surfacing materials containing refractory components due to the formation in the slag, in the immersion zone of the electrode, of a high-temperature region in which the slag is heated to a boiling point and intensively mixed.

3. The ability to obtain a highly homogeneous, well metallurgically processed deposited metal on the surface of small-sized ends by increasing the residence time of metal droplets in superheated rotating slag.

Claims (3)

1. The method of electroslag surfacing of small-sized ends of products in a vertical position, including pointing the slag bath in a volume limited by the surfaced surface and a sectional mold containing current-supplying and molding sections, maintaining the temperature of the mold surface above the temperature of a sharp increase in the viscosity of the slag used, rotating the slag bath, maintaining the lower the level of the slag bath at a distance of not more than the thickness of the deposited layer from the lower edge of the current-supplying section and rear welding current, characterized in that the electroslag surfacing is carried out by introducing into the slag bath connected to an independent power source a non-consumable hollow electrode made with a cone on the working part to a depth equal to the height of the cone, with the formation of a high-temperature region in the slag bath, size which is limited to 2 ÷ 2.5 diameters of the said electrode, while through the cavity of the non-consumable electrode in the formed high-temperature region serves surfacing material, and the ratio cooking current to the current supplied to the non-consumable electrode is selected within 1.3 ÷ 2.0. 2. The method of electroslag surfacing according to claim 1, characterized in that the rotation of the slag bath is carried out at a speed of 60 ÷ 150 rpm 3. The method of electroslag surfacing according to claim 1, characterized in that the value of the welding current is maintained in the range of 0.8 ÷ 1.2 from J _nom .

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