KR100333074B1 - Large steel ingot casting by hot top heating method - Google Patents

Abstract

The present invention relates to a method of casting a healthy large ingot by preventing the occurrence of solidification defects caused by inappropriate solidification conditions in the mold, such as shrinkage holes, solidification cracks, pores caused by casting defects in the process of casting large ingots The induction heating coil 2 having an insulated surface of fire resistant tape and powder is applied to the upper hot water part 1 or the hot top of the large ingot mold, and the molten steel temperature of the hot water part 1 is provided. The induction heating coil 2 is heated to a superheating temperature ΔT above the melting point so as to remain in the molten state until the end of the solidification of the ingot, and the heating and holding time of the induction heating coil 2 is managed as the ingot solidifies. The steel ingot is formed by casting the large ingot by interlocking heating by the induction heating coil 2 according to the temperature of the molten steel measured by the thermocouple 3 installed at the upper center of the hot water part 1. To prevent casting defects, such as the elimination of injury and the gas separation effect of the non-metallic inclusions, shrinkage and internal pores occurs in the solidification shrinkage that may exist will be in the advantage of being able to cast a sound ingot.

Description

Large steel ingot casting by hot top heating method

The present invention relates to a method of casting a healthy large ingot by preventing the occurrence of solidification defects caused by inappropriate solidification conditions in the mold, such as shrinkage holes, solidification cracks, pores caused by casting defects in the process of casting large ingots In particular, during the process of injecting molten steel into a large ingot mold and solidifying with heat dissipation as time passes in the mold to form a steel ingot, the hot top of the mold is intermittently heated by an induction heating method. By adjusting the progress of solidification of molten steel by suppressing the occurrence of internal shrinkage holes, solidification cracks, and pores generated during solidification of large steel ingots, the large size by the induction heating method to cast the ingot under the hot top to form a sound casting structure. It relates to a steel ingot casting method.

In general, casting technology in which molten steel is injected into a specific shape and solidified to manufacture a product in a desired shape and size is manufactured using a fluidity of molten steel to produce a complicated shape at a low process cost, and to repeatedly manufacture a product of the same shape and size. Although it has an advantage, there is a disadvantage that the internal defect of the cast product is easy to occur irrespective of the intention of the operator, compared to the process such as machining, heat treatment, etc., there has been a problem that there are few artificially controlled manufacturing parameters during the solidification of molten steel. In particular, ingots with a size of more than a few tens of tonnes have long solidification time and are affected by small variables for a long time. Actual casting results show that unpredictable shrinkage holes, pores, and segregation problems occur in light weight castings less than 2 tons. This often leads to large product losses.

Therefore, in recent years, before manufacturing a product by an actual casting process, casting is attempted by setting mold design and casting process conditions to predict defects through computer simulation and to minimize defects that can actually occur in simulation casting conditions. Efforts have been made to artificially control the parameters of the casting process, including the use of heating elements in the hot water section, the arc heating method, and the bottom surface cooling method.

In large ingots, various casting defects, such as ingot segregation, incorporation and retention of non-metallic inclusions, solidification shrinkage, solidification cracking, and porosity, which occur in the casting process, are frequently generated and the losses are large. In addition, when casting defects occur, it is not easy to inspect and determine the defects inherent in large ingots, which adds a lot of process cost loss such as cracking during the forging process and defect detection in the final product.

Since the internal defects of large ingots are mostly due to inadequate casting conditions, that is, inadequate solidification models, the molten steel temperature and molten steel conditions when the molten steel is filled into the mold and the molten steel is filled in the mold, The quality of the ingot depends on the solidification conditions.

Therefore, as a conventional method for minimizing the internal defects of the steel in the casting process of the large steel ingots, as shown in US Patent No. 4,134,433, graphite electrode rods are installed in the hot water ingots to control the solidification of the ingot after the molten steel is filled in the mold. To this end, while molten steel is solidifying, there is a method of intermittently supplying a current to the graphite electrode and generating an arc at the surface of the hot water part to make the hot water temperature higher than the ingot temperature of the other part and finally manage the solidification. As a result, it seeks to prevent the floating separation of non-metallic inclusions, gas removal, shrinkage hole and solidification crack which may exist in the large ingot molten steel.

In addition to the above method, a cover is installed in the hot water unit to minimize heat dissipation to maintain the high temperature of the hot water unit, and at the time when the molten steel is filled, a heating material powder or a heating plate material is added to the surface of the hot water to supply an additional heat source. Methods are being used as in situ techniques in the large ingot casting process.

However, among these methods, a method of heating graphite rods by heating them in the ingot of large ingots, such as US Patent No. 4,134,433, is easy to artificially manage the temperature of the large ingots ingot by controlling the current and time supplied to the electrodes. One advantage is that the graphite electrode is eroded and consumed by the molten steel surface during prolonged arc generation by the graphite electrode, and the consumed graphite is mixed in the steel ingot, so that unwanted carbon and other impurities (oxides) are mixed. There is this. In addition, due to securing the installation space of the graphite electrode, there is a problem that a high facility cost, such as high space consumption and a cradle of the graphite electrode rod is required.

On the other hand, the method of applying the heating element powder and the heating plate on the surface of the hot water part is expected to increase the molten steel temperature of the hot water part normally, but the degree of actual contribution to the temperature of the hot water part depending on the amount of the heat generating agent, the application time and the surface area of the hot water part. Since there is a difficulty in accumulating many skills and application data, there is a problem that it is practically impossible to control the temperature of the fine hot water by continuously adjusting the calorie while the molten steel of the mold solidifies.

The present invention has been invented to solve various problems caused by the conventional large ingot casting method in view of the above situation, by installing an induction heating coil in the large ingot mold quenching part to supply the current intermittently in accordance with the progress of solidification of the ingot It is an object of the present invention to provide a large ingot casting method by a hot-dip heating method that improves the casting quality of large ingots by precisely controlling the temperature of the ingot without incorporation of impurities.

1 is a view showing a mold shape for induction casting and induction heating apparatus according to the present invention.

<Explanation of symbols for main parts of drawing>

1: hot water unit 2: induction heating coil

3: thermocouple 4: ingot

5: surface plate and pouring part

In order to achieve the above object, the large-scale ingot casting method according to the present invention of the induction heating method induces the surface of the large ingot mold by applying a fire-resistant tape and powder to the upper inlet part 1 or a hot top portion of the large ingot mold. The heating coil 2 is installed, and heated by the induction heating coil 2 to the superheating temperature ΔT above the melting point so that the molten steel temperature of the hot water portion 1 is in a molten state until the solidification of the ingot is completed. As the coagulation progresses, the induction heating coil (2) is characterized in that the intermittent heating.

In addition, the superheating temperature (ΔT) of the molten steel of the large ingot molten steel part 1 is managed in the range of 20 to 50 ° C, and the heating and holding time of the induction heating coil 2 according to the solidification progress of the steel ingot is 0.3 to 0.6 hours / ton. It is characterized by managing.

Hereinafter, with reference to the accompanying drawings will be described in detail a large ingot casting method according to the present invention hot water heating method.

1 is a view showing a mold shape and induction heating apparatus for large ingot casting according to the present invention, reference numeral 1 is a hot water part, 2 is an induction heating coil, 3 is a thermocouple, 4 is an ingot, 5 is a surface plate and a pouring part, respectively. Indicates. The induction heating coil (2) having an insulated surface of fire resistant tape and powder is applied to the upper hot water portion (1) or the hot top portion of the large ingot mold, and after the molten steel is completely filled in the mold, Induction heating is performed so that the molten steel temperature of the inlet portion 1 is in a molten state until the ingot is solidified. The overall induction heating time and intermittent time control vary depending on the size of steel ingot, the type of molten steel, and the mold condition, so that the heating conditions are based on the solidification time of steel ingot obtained in actual casting or steel ingot casting time and progress in simulation casting using computer. Set up and run. For example, when casting molten steel at a temperature of 45 ° C higher than the melting point in an 8-ton mold made of FC20 of AISI 1045 (JIS S45C) and casting it naturally, the solidification is completed to the upper part of the ingot (4). It takes Based on this initial basis, the initial heating conditions are set, and during induction heating, the actual temperature of the hot water part is measured with a thermocouple (3) installed in the state of being deposited on the molten steel surface above the hot water part (1) to precisely manage the desired temperature. . During the induction heating of the induction heating coil 2, a large error occurs in the measurement temperature under the influence of the magnetic field, so that the temperature measurement value in the state in which the induction heating coil 2 is turned off is read. Intermittent induction heating It is possible to realize more accurate temperature management of the hot water part by measuring the actual temperature of the hot water part and reflecting the induction heating condition according to the solidification progress of the molten steel.

Next, a method of manufacturing a sound ingot with less casting defects in the ingot by controlling the solidification progress by controlling the solidification progress by controlling the temperature of the hot water part 1 by induction heating after the molten steel is filled in the mold in the casting process of a large ingot. .

First, set the solidification time according to the size and type of the ingot to be cast and the induction heating capacity and time according to the size of the inlet unit 1, and adopt it as the initial heating condition, as shown in FIG. Install the induction heating coil (2) and the power supply control device in the. In the casting process, in general, FC20 mold is used, and when the molten steel is applied to steel grades such as S45C, SUS304, SCM440, etc. according to JIS standards, the natural solidification time of the steel ingot is set to 0.5 to 0.6 hours / ton, and induction heating capacity. According to the size of the hot water is determined by the capacity of 10 ~ 100kWh / 100kg and the intermittent hot water induction (1) induction heating according to the solidification progress.

If the capacity of induction heating is less than 10kWh / 100kg, the heating effect is weak, so continuous heating time is required to satisfy the sufficient heat supply of the hot water unit 1, and it is not suitable because the temperature is difficult to control. If it exceeds 100 kWh / 100 kg, the mold may be partially melted and damaged due to high heat supply and unnecessarily high equipment investment is not suitable. Therefore, it is appropriate that the capacity range of induction heating capacity is 40 to 70 kWh / 100 kg. The induction heating operation cycle and the heating time for each cycle are operated in an on-off type according to the temperature of the molten steel measured in the thermocouple 3 deposited on the upper center of the hot water unit 1. The molten steel temperature management time of the hot water unit 1 is managed at 0.2 to 1 hour / ton from the start of injection of the molten steel or the end of injection. When the temperature control time of induction heating (1) by induction heating is less than 0.2 hours / ton, the effect of reducing internal defects is weak in the large ingots where the solidification time is several hours or more, and the temperature management of the induction heating (1) by induction heating If it exceeds 1 hour / ton, it is not suitable because the solidification time of the steel ingot becomes longer and the productivity decreases accordingly, which is more than necessary. Therefore, the induction heating time range of a more suitable hot water part is 0.3-0.6 hours / ton.

On the other hand, the molten steel temperature of the large ingot sintering unit (1) should be maintained 10 ~ 50 ℃ higher than the melting point within the induction heating time range. That is, superheating part (DELTA) T of a hot water part is managed in 5-100 degreeC range. If ΔT is less than 5 ° C., the viscosity of the molten steel is increased, so that the injuries of non-metallic inclusions and gases, which float in the molten steel, are suppressed and remain at the bottom of the hot water part, thereby causing defects in the casting. And if ΔT is over 100 ℃, the temperature of molten steel is high, so if it is maintained for more than a few hours, erosion of the hot water refractories is severe, it causes thermal damage to the mold itself, and it is not suitable condition because it consumes more power than necessary in terms of economy. . Therefore, more suitable hot water part (DELTA) T is 20-50 degreeC. As described above, when the hot water unit 1 is subjected to temperature control by an induction heating method in a large ingot casting process, a sound cast product having less internal defects may be manufactured.

Example 1

Hereinafter, the large-size ingot casting method by the present invention hot water heating method will be described.

The induction heating coil is intermittently installed in the molten steel part 1 by injecting molten steel super alloyed at 45 ° C. higher than the melting point into the mold as shown in FIG. 1.

Induction heating coil (2) with a high frequency (1000 Hz) induction heating device of 50 to 200 kWh capacity in order to control the temperature of the molten steel to maintain the temperature range of 5 to 100 ℃ higher than the melting point by heating (2). Heated.

At this time, the ingot's melt ratio [P = (melt cross section area / (melt cross section area + ingot cross section)) × 100] is set to 15, and the shape ratio (height / diameter) is set to 2, and each other induction heating as described above. Table 1 shows the results obtained by qualitatively comparing and evaluating the casting defects and the quality of the steel ingots obtained by heating and maintaining the holding temperature of the hot water unit 1 at 0.1 to 1.5 hours / ton.

From Table 1, the molten steel superheating temperature (ΔT) of the large ingot molten part 1 was managed in the range of 20 to 50 ° C., and the heating holding time of the induction heating coil 2 according to the solidification progress of the steel ingot was 0.3 to 0.6 hours / It can be seen that managing in tonnes can cast sound ingots without casting defects.

Ingot Quality Evaluation Table According to Superheating Temperature (ΔT) Retention time (hours / tons) ΔT (℃) Shrinkage (%) Coagulation crack Crack location Ingot Quality 0.1 5 8 plenty Ingot × 10 8 plenty Ingot × 30 5 slightly Ingot top ↓ 50 4 slightly Ingot top △ 70 3 slightly Pressure △ 100 3 slightly Pressure △ 0.25 5 7 plenty Ingot top × 20 5 slightly Ingot top ↓ 30 4 slightly Pressure △ 50 2 Less Pressure ○ 70 2 Less Pressure ○ 0.5 10 4 slightly Ingot top △ 30 2 Less Pressure △ 40 One Less Pressure ○ 50 0.5 none Pressure ○ 60 0.1 none Pressure ◎ 0.7 10 2 slightly Ingot top △ 20 One Less Pressure ○ 30 0.5 none Pressure ○ 40 0.1 none Pressure ◎ 50 0.1 none Pressure ◎ One 5 2 slightly Ingot top △ 10 One none Pressure ○ 20 0.2 none Pressure ○ 30 0.1 none Pressure ◎ 40 0.1 none Pressure ◎ 1.5 5 2 slightly Ingot top △ 15 0.5 none Pressure ○ 20 0.2 none Pressure ◎ 30 0.1 none Pressure ◎

Excellent ※: ◎, good: ○, under: ↓, bad: ×

As described above, the large ingot casting method by the induction heating method of the present invention may be present in the molten steel of the steel ingot by controlling the solidification process during the solidification process by superheating the hot water over the melting point of the alloy by induction heating in the casting process of the large ingot. Preventing casting defects such as floating separation effect of non-metallic inclusions and gas removal, shrinkage holes and internal pores generated in solidification shrinkage, has the advantage of casting sound ingots.

Claims (3)

delete In the casting method for reducing the casting defect of large ingots, Install the induction heating coil 2 insulated by applying a refractory tape and powder on the surface of the upper hot water unit 1 or the hot top of the large ingot mold, and the molten steel temperature of the hot water unit 1 The induction heating coil 2 is heated to a superheating temperature ΔT above the melting point so as to remain in the molten state until the end of the solidification of the ingot, and the heating and holding time of the induction heating coil 2 is managed as the ingot solidifies. The large ingot casting method according to the hot water heating method, characterized in that the heating by the induction heating coil (2) in accordance with the temperature of the molten steel measured by the thermocouple (3) installed in the upper center of the hot water. The method of claim 2, wherein the superheating temperature (ΔT) is controlled in a range of 20 to 50 ° C., and the heating holding time is 0.3 to 0.6 hours / ton.