JPS602141B2 - Manufacturing method of clad steel ingot - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a clad steel ingot using electroslag welding.

Clad steel sheets, which are made by laminating ordinary steel sheets with different metal plates such as stainless steel and nickel alloys, are suitable for use in reaction vessels, high-pressure cookers, etc., because the ordinary steel sheets have the strength as a structural base material, and the stainless steel sheets have corrosion resistance. It is widely used in various fields such as heavy chemical industry, food, civil engineering, shipbuilding, and nuclear power, which use heat exchangers.

As a method for manufacturing a steel core used in manufacturing this clad steel plate, for example, a method schematically shown in FIG. 4 is known. That is, inside the mold 11 of the bottom pouring ingot saddle, a cladding plate 10 of stainless steel is suspended along the side wall, and the arm 22 of the electrode lifting device 20 installed on the coin deck is suspended. An electrode plate 21 supported by the cladding plate 10 is vertically inserted from the upper entrance of the mold 11 at an appropriate distance from the cladding plate 10, and is lifted and lowered by two electrode lifting devices. 1 and the electrode 21 are connected to a welding power source (not shown).The molten steel 1 (
When the steel (ordinary steel) is fed into the mold 11 from its lower opening,
Powdered welding flux charged in advance into the mold is melted by the heat of molten steel and becomes molten slag 2, and molten slag 2, which has a lighter specific gravity than molten 1, forms a slag layer with a depth of about 40 to 6 ribs. It floats on the molten steel surface and rises as the molten steel surface rises.

When an electric current is applied between the electrode plate 21 and the clad plate 10 immersed in this slag bath to cause the current to flow through the molten slag 2, the electrical resistance value is reduced to 0, which is extremely large compared to the molten steel 1.
The molten slag 2 shown in FIG.
Customer loan. Next, when the moat surface of the molten steel 1 rises and the surface of the clad plate 10 whose surface layer part is softened and melted is covered with the molten steel 1, the surface layer part of the clad plate 10 and the molten steel 1 are mixed, and the molten steel 1
In the steel ingot obtained by solidification, the boundary between the part occupied by the injected molten steel and the clad plate 1 inserted into the mold in advance is sharp, and therefore the adhesion between the stainless steel part and the ordinary steel part is extremely poor. A clad steel ingot with good quality is obtained. By the way, while the slag rating is rising, electricity is stably passed between the electrode plate 21 and the cladding plate 10 to obtain a substantially constant amount of resistance heat generation, and uniformly good welding is achieved from the bottom to the top of the cladding plate 10. In order to achieve this condition, it is necessary that the electrode plate 21 do not penetrate into the lacquered steel, and that the depth of the electrode plate 21 immersed in the slag must be maintained stably.

For this reason, in the conventional method, the electrode plate 21 is lifted up from the river of the electrode lifting device 2 in accordance with the rise of the slag margin or the molten steel flaw surface, and in accordance with the melting and consumption of the electrode plate 21 itself due to the resistance heat of the molten slag 2. However, the molten steel surface position was detected by visually observing the position of the molten slag scratch surface, or by inserting a Takafuji point metal rod into the slag gap from the upper part of the mold and checking the electrical conductivity between the metal rod and the mold. It is difficult to maintain a constant slag immersion depth of the electrode plate 21, and when the electrode plate 21 moves upward, the gap between the electrode plate 21 and the cladding plate 10 changes, making the energization state unstable. Therefore, in some cases, it may come into contact with the cladding plate 10, causing inconveniences such as the inability to generate heat. Furthermore, it is practically impossible to install a large-scale device such as the electrode lifting device 20 for each mold on the key deck due to the installation layout and economical reasons. For ingot-making equipment that distributes and injects molten steel into four molds, it is only possible to install this for two molds due to the installation space, so the other two molds are used to manufacture ordinary steel ingots. Productivity was extremely poor as they had no choice but to do the same. The present invention has been made in view of the above circumstances, and does not require an electrode lifting device when performing electroslag welding, allows electricity to be passed between the electrode plate and the cladding plate in a stable state, and provides high quality welding. It is an object of the present invention to provide a method for manufacturing clad steel ingots with high production efficiency and without requiring large-scale equipment.

The method for manufacturing a clad steel soul according to the present invention is to manufacture a clad steel ingot by applying electricity through molten slag suspended on molten steel between a clad plate placed in a mold using a bottom pouring method and an electrode. In the method of It is characterized by controlling the money transfer speed and/or the energizing current.

The method of the present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing the implementation state of the method of the present invention. An injection pipe 14 is installed vertically in the center of the upper surface of a base plate 13 installed on the floor, and four surface plates 12 (see Fig. (Only the base is shown) are arranged in 4 equal intervals, and each surface plate 1
Square tube-shaped molds 11 are placed on each of the molds 2 (only two molds are shown in the figure). The sprue 12a and injection pipe 14 provided in the center of each surface plate 12 are connected to the base plate 1.
The molten steel in the ladle 15 is connected to the sliding nozzle 1 by a runner 13a which is installed approximately at the center in the thickness direction of the ladle 15 and extends radially in four directions from directly below the injection pipe installation position.
It is injected into the injection pipe 14 while controlling the injection amount by adjusting the ratio in step 6, and is supplied to the four molds 11 through the runner 13a.
Inside each mold, a clad plate 3 whose upper end is supported by the upper edge of the mold 11 is vertically installed along the side wall of the mold. The plate 4 (only one is shown in the drawing) is arranged to leave an appropriate gap between the cladding plate 3 and the electrode plate 4,
They are arranged in parallel in the width direction of the clad plate 3 and fixed at several locations in the longitudinal and axial directions with a heat-resistant adhesive 5 mixed with welding flux.

In this way, the cladding plate 3 and the electrode plate 4 are installed vertically inside each of the four molds 11, and above one of the molds 11 is placed the antenna 18 of a microwave range finder. The microwave emitted vertically downward from the antenna 18 is reflected by the flawed surface of the molten steel in the mold 11, and the echo is captured by the antenna 18, which is input into the main body 17 of the microwave range finder to determine the location of the flawed surface of the molten steel. Detect.

This data regarding the molten steel surface position is transferred to a minicomputer (not shown) (hereinafter abbreviated as minicomputer), and the minicomputer compares the measurement result of the rising speed of the molten steel surface with a predetermined rising speed pattern set in advance. Then, a control signal is output to the sliding nozzle 16 in order to make the measured value of the rising speed of the wound surface match a predetermined pattern. Therefore, the antenna 18 and main body 17 of the microwave rangefinder, the minicomputer, and the sliding nozzle 16 constitute an automatic molten steel coin control system. Casting control is performed. Furthermore, the minicomputer has
In order to select the one that corresponds to the required electrode consumption rate, mirroring conditions, steel type, molten steel temperature, etc., which will be described later, 10q
A speed pattern for increasing the wound surface is set. Then, injection of molten steel from the ladle 15 to the injection pipe 14 is started, and this molten steel flows through the flaw 13a and is supplied to the mold 11, and the pouring of the molten steel into the mold 11 is started. The welding flux, which had been previously charged into the mold in powder form, is melted by the heat of the molten steel, forms a slag layer, floats on the flawed surface of the molten steel, and gradually rises as the surface of the molten bath rises.

In the method of the present invention, when electricity is applied between the electrode plate 4 immersed in the molten slag and the cladding plate 3, the electrode plate itself melts due to the resistance heat generation of the molten slag 2. Then, in order to raise the flawed surface of the molten steel by an amount commensurate with the wear length of the electrode, the rate of rise of the flawed surface is controlled and/or the applied current is controlled.

For this reason, the relationship between the value of the current flowing between the electrode plate and the clad plate and the rate of electrode consumption is determined in advance. Table 1 shows an electrode slope with a thickness of 1 shipboard and a width of 140 ships in a molten slag bath with a depth of 50m, and the lower end of the electrode plate and the molten steel surface (the interface between the steel and the molten slag).
The relationship between each energization condition and the electrode consumption rate is shown by taking as an example the case where the electrode is immersed so that the separation distance from the electrode becomes the value described in the "evening" column. The current supplied in Table 1 is the value per one electrode plate.

As is clear from Table 1, if a current of 3000A is passed through the molten slag between a pair of electrode plates and the cladding slope, the electrode plate itself will be heated by the resistance heat generated by the molten slag, and Melts at the rate of consumption. Further, when the applied current value is 3750 A and 560 M, the lower end of the electrode plate melts at a consumption rate of low board/min and 12 board/min, respectively. Therefore, for example, when the energizing current value is set to 375 ships, by setting the hot water level rising speed pattern so that the moat level rising speed is 100 pigs/min and performing coin control,
Even if the molten steel surface moves upward in the mold, there is a nearly constant gap between the lower end of the electrode slope and the molten steel surface (with a constant electrode penetration depth in the slag), and the electrode Stable current can be passed between the plate and the clad slope, and a clad steel ingot with good welding from the bottom to the top of the steel core can be produced.

As the electrode plate 4 melts, the heat-resistant adhesive 5 mixed with welding flux that fixed the electrode plate 4 to the cladding plate 3 is removed.
is separated from the clad plate 3, but after it is separated, it floats in the slag or is melted by the heat of the molten slag and mixed into the slag, so it does not remain in the steel ingot. Furthermore, even if the current value is set and the mirror control is performed based on the electrode wear rate at this set value as described above, the final value may be zero or
That is, when the electrode plate 4 is about to come into contact with the molten steel 1,
Before the electrode plate 4 becomes immersed in the molten steel 1, the applied current increases and the applied voltage decreases instantaneously.

When this is detected, the current applied may be increased to accelerate the consumption rate of the electrode plate 4. Furthermore, if the flaw surface rising speed has to be changed from the initial setting value for some reason during pouring of twill steel, or if such a keying pattern is used, the energizing current should be adjusted according to the change in the surface rising speed. change.

In Figure 2, the axis shows the elapsed time after the molten steel 1 starts to be deposited in the mold, and the vertical axis shows the rate of rise in the molten metal level and the value of current flowing between the cladding plate 3 and the electrode plate 4 (per electrode). This represents the change in the rising speed of the scratch surface (indicated by the solid line) during the molten steel coin purse, and the accompanying change pattern in the applied current (indicated by the broken line). The set value of the energizing current at the beginning of mirror insertion is 3750 A, and the hot water level rising speed is 10 m/min, so the hot water level rising speed is gradually increased from point A at the beginning of the change to a predetermined speed (10 m/min). After reaching point B (point B), control is performed to maintain this value, and the current value is also maintained after increasing from point A' to point B' (375 ships).
Normally, the initial energizing current value and hot water level rising speed are maintained until the final point (G, ○) is reached, but by changing the mirror setting conditions, for example, the hot water level rising speed can be changed to 12 If the current is to be increased to 5,600 A per minute (points C to D), the current value is changed accordingly to 5600 A, which corresponds to an electrode consumption rate of 120 bars/minute, based on Table 1 (points C' to ○). This also applies to the same machine when the hot water level rise speed decreases from 120 m/min to 8 m/min (point E→F), and in this case, the current value is set to 56 m/min.
Change from 0 ships to 300 ships (point E'→F'). In this way, when changing the rate of rise in the hot water level during pouring of twill steel, the applied current may be controlled so as to melt the electrode plate 4 at a corresponding consumption rate. Next, the results of producing a clad steel core using the method of the present invention will be described. Each manufacturing condition is as follows. Ladle capacity: 250T Ingot making equipment: 2 injection pipes, 8 molds Therefore, molten steel is distributed and supplied from one injection pipe to 4 molds.

Ingot weight: 27.5T Steel ingot dimensions (average dimensions inside the mold): Thickness 85 mould, width 170 sails, height 280 sails Clad plate: High carbon steel, width 160 ribs, embossed inside each mold.

Electrode plate: 1 inch thick, 14 inch wide. Four electrode plates are placed in parallel on each clad plate at intervals of 26 mm in the width direction.

Molten slab composition: Ca○...20%, Si02...
-40%, Mn〇...20%, CaF2...2%, A〆2〇3...4%, Mg0...4%, Ti02...4%, Fe0
…1%, Ba○…2.5%, Others…2.5% Welding flux: Sumiflux #103 (trade name) Molten slag tolerance temperature: 1700-1800 qo Molten slag depth: 5 items Rise in the molten metal surface Control of speed and current: Control pattern shown in Figure 2 As a result, current can be stably passed between the electrode plate and the cladding slope, and the boundary between the cladding plate and the injected molten steel in the steel ingot is also sour, and the cladding We were able to produce a clad steel ingot with extremely good plate adhesion.

Figure 3 is a photograph taken after the boundary between the cladding plate and the injected molten steel has been corroded by etching.The upper half of the figure is the area occupied by the injected molten steel, and the lower half is the cladding plate. The white portion extending substantially horizontally from the vertical center of the figure is the boundary (welding surface) between the two. In this way, FIG. 3 demonstrates that the weldability of the clad plate is extremely excellent. As described above, in the method of the present invention, the wear rate of the electrode and the molten steel level are measured, and based on the measurement results, the molten steel is adjusted so that the electrode tip position is at a predetermined height from the molten steel level. Since the control is carried out to raise the surface of the slag, and the current is controlled as necessary, the depth of the haze in the slag can be maintained constant while the slag is rising, and the contact with the clad plate can be maintained. It is possible to produce a clad steel ingot with good adhesion and stable current flow between the two.

In addition, since there is no need to move the electrode as the molten steel level rises, stable current can be passed by ensuring a gap between the electrode plate and the cladding plate. Furthermore, since this gap can be maintained at a constant value, current can be passed between the electrode plate and the cladding plate. Not only is the current stable, but there is no need to install large-scale equipment such as an electrode lifting device, and all ingots cast in one charge can be made by installing clad plates and electrode plates in all molds (as described above). In the example of 8
) can be made into clad steel ingots, and productivity is extremely high. As detailed above, when using the method of the present invention, electricity can always be applied in a stable state, and clad steel ingots with excellent welding quality can be manufactured with high efficiency, and the present invention has greatly improved the manufacturing technology of clad steel ingots. It has the effect of

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the implementation state of the method of the present invention, Fig. 2 is a graph showing an example of the relationship between the rate of rise in the melt level and the current value, and Fig. 3 is a clad steel manufactured by the method of the present invention. FIG. 4 is a metallurgical microscope photograph showing the welded portion of the clad plate of the lump, and is a schematic diagram of the conventional method. DESCRIPTION OF SYMBOLS 1... Molten steel, 2... Molten slag, 3... Clad plate, 4... Electrode plate, 11... Mold, 16... Sliding nozzle, 17... Main body, 18... Antenna. Figure 1 Figure 3 Figure 2 Figure 4

Claims (1)

[Claims] 1 Measuring the molten steel surface level in a method of producing a molten steel ingot by applying electricity through molten slag suspended on molten steel between a clad plate placed in a mold and an electrode using the bottom pouring method. At the same time, the consumption rate of the electrode is measured from the applied current, and based on the measurement result, the casting speed and/or the applied current are controlled so that the electrode tip position is at a predetermined height from the molten steel surface. Characteristic method for manufacturing clad steel ingots.