A method for feeding steelmaking in a vacuum consumable furnace

Abstract

The present invention provides a method for feeding shrinkage in a vacuum consumable furnace steelmaking process, comprising the following steps: preparing a vacuum consumable furnace melting electrode, placing the electrode into a copper crucible, and evacuating the vacuum consumable furnace; starting smelting when the vacuum degree and leakage rate respectively meet certain requirements, entering a normal smelting stage after the arc starting stage, and smelting steel; determining the weight and time of the feeding electrode; performing a feeding operation when the smelting time and the remaining electrode weight meet the requirements; stopping smelting, cooling the outer wall of the crucible at a certain vacuum degree, and demolding after cooling. This method solves the problem of shrinkage defects in ingots in vacuum consumable furnace steelmaking, improves product quality, can effectively solve the problem of shrinkage defects in ingots in vacuum consumable furnace steelmaking, significantly improves the internal quality of the ingots, and lays a solid foundation for the smelting and development of special steels.

Description

Technical Field

[0001] The invention belongs to the field of iron and steel metallurgy and relates to a method for feeding steelmaking shrinkage in a vacuum consumable furnace. Background Art

[0002] Special steel plays a crucial role in economic development and the national defense industry. This is particularly true in cutting-edge technologies such as aerospace, aviation, marine development, energy, electronics, and defense, all of which require high-quality special steel. Due to its excellent and diverse properties, special steel is widely used in numerous sectors, including automotive manufacturing, transportation, electromechanical manufacturing, petrochemicals, light industry and textiles, food, medicine, information technology, energy, and defense. It holds an irreplaceable position and is a key indicator of a country's or region's scientific and technological development and economic strength. Currently, special steel production both domestically and internationally primarily utilizes vacuum consumable furnace smelting. However, ingots smelted using this process are prone to internal defects such as shrinkage cavities and segregation. This is due to the failure to promptly vent gases in the late stages of smelting, and the ineffective replenishment of shrinkage cavities caused by the solidified steel volume by the upper molten steel. This formation of shrinkage cavities within the ingot not only affects the internal crystal structure, but also reduces the cleanliness and yield of the ingot. Therefore, ingot feeding is a crucial step in vacuum consumable furnace steelmaking.

[0003] For a long time, many metallurgists have been engaged in research on special steel smelting. There are also many patents and literature on vacuum consumable furnace steelmaking, but most of them are about melting processes and product development. There is little literature on feeding in vacuum consumable furnace steelmaking. The article "Vacuum Consumable Remelting of 30CrMnSiMoV Steel" published in the fourth issue of "Special Steel" in 1998 pointed out that Yao Changgui et al. used a vacuum consumable furnace to melt 30CrMnSiMoV steel with a diameter of 660mm and carried out experimental research on the feeding process. The feeding weight was 250 kg, and the current was reduced from 13,000 amperes to 8,500 amperes, and finally to 6,000-6,500 amperes. The mid-feeding time was 15-25 minutes. At the end of the feeding, the current was increased to melt the molten edge. The shrinkage cavity depth after ingot head cutting was 130 mm. The feeding method has the following problems: first, the feeding weight is too small, and the changes in current, voltage and metal pool temperature have a certain reaction time. If the feeding weight is too small, the feeding will be insufficient and the effect will be unsatisfactory. Second, the current drop gradient in the early stage of feeding is too large, reaching 35% of the normal smelting current, which will cause a sharp drop in the molten pool temperature and a significant reduction in the molten pool stirring intensity, which will aggravate the segregation of elements and reduce the internal quality of the ingot. Third, the current in the later stage of feeding is too large, reaching 50% of the normal smelting current, which will cause the molten steel pool to be too deep, and the solidification interval between the upper and lower molten steel is too short. The upper molten steel cannot fill the shrinkage cavity generated in the lower part in time, resulting in poor feeding effect. Fourth, increasing the current in the later stage of feeding will affect the uniformity of the crystal structure of the ingot head tissue, which is not conducive to subsequent processing and use. Fifth, the time before and after feeding is not clearly defined. The feeding time is a key parameter of the feeding process and will greatly affect the feeding effect. Sixth, after using this method for feeding, the shrinkage cavity depth of the ingot reached 130 mm, and the feeding effect was unsatisfactory. Summary of the Invention

[0004] In order to solve the problem of shrinkage defects in ingots during steelmaking in a vacuum consumable furnace, the present invention adopts a technical solution: a method for feeding shrinkage in vacuum consumable furnace steelmaking, comprising the following steps:

[0005] Prepare a vacuum consumable furnace to melt the electrode and place the electrode into a copper crucible;

[0006] Evacuate the vacuum consumable furnace;

[0007] When the vacuum degree and leakage rate reach certain requirements, smelting begins. After the arc starting stage, it enters the normal smelting stage to melt the steel.

[0008] Determine the feeding electrode weight and feeding time;

[0009] When the melting time and the remaining electrode weight meet the requirements, the ingot feeding operation is carried out;

[0010] Stop smelting, cool the outer wall of the crucible under a certain vacuum degree, and demould after cooling.

[0011] Furthermore, the weight of the feeding electrode is 10% to 25% of the total weight of the smelting electrode.

[0012] Furthermore: the ingot feeding time is 25% to 35% of the total smelting time

[0013] Furthermore, the ingot feeding operation includes: in the early stage of feeding, the current decrease gradient is 5% to 20% of the normal melting current, and the time is 10% to 20% of the total feeding time; in the middle stage of feeding, the current decrease gradient is 3% to 10% of the normal melting current; in the late stage of feeding, the current is 20% to 30% of the normal melting current, and the time is 30% to 40% of the total feeding time.

[0014] Furthermore, the ingot feeding operation includes: the voltage drop gradient in the early feeding stage is 0.5% to 1.5% of the normal melting voltage; the voltage drop gradient in the middle and late feeding stages is 0.5% to 1.0% of the normal melting voltage.

[0015] Furthermore, the outer wall of the crucible is cooled, the vacuum degree is controlled below 1 Pa, and the cooling time is 3 to 6 hours.

[0016] Furthermore, the cooling is carried out in a copper crucible under vacuum, and the cooling method is to cool the outer wall of the copper crucible through circulating water.

[0017] Furthermore, the vacuum consumable furnace is evacuated by starting a mechanical pump, starting a Roots pump when the vacuum degree reaches 700 Pa, and starting a booster pump when the vacuum degree reaches 5 Pa.

[0018] Furthermore, the vacuum degree and the leakage rate reaching certain requirements respectively refer to the vacuum degree reaching below 0.1 Pa and the leakage rate reaching below 1 Pa / min.

[0019] The present invention provides a method for feeding shrinkage in a vacuum consumable furnace steelmaking process. In the later stage of smelting, sufficient weight of feeding electrodes is reserved to fully feed the ingot. The amplitude of current and voltage drop in the early stage of feeding is controlled to avoid affecting the internal quality of the ingot due to a significant drop in current. In the later stage of feeding, the current is as low as possible and the duration of low current is appropriately extended to ensure that the upper molten steel remains in liquid state when the lower molten steel solidifies, allowing the gas in the ingot to completely escape, and the shrinkage cavity produced by the solidification and shrinkage of the lower molten steel can be effectively filled by the upper molten steel, thereby completing the feeding of the ingot. The method provided by the present invention can completely solve the problem of shrinkage cavity defects in steelmaking ingots, and the operation is simple and easy to implement without any safety hazards. It has the following advantages:

[0020] This method solves the problem of shrinkage defects in ingots produced during steelmaking in a vacuum consumable furnace, significantly improving the internal quality of the ingots and laying a solid foundation for the smelting and development of special steels. The invention can be widely applied in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 is a flow chart of the method; DETAILED DESCRIPTION

[0023] It should be noted that, unless there is any conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0027] In the description of the present invention, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0028] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0029] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0030] Figure 1is a flow chart of the method;

[0031] A method for feeding steelmaking in a vacuum consumable furnace comprises the following steps:

[0032] S1: Prepare a vacuum consumable furnace to melt the electrode and place the electrode into a copper crucible;

[0033] S2: evacuate the vacuum consumable furnace;

[0034] S3: When the vacuum degree and leakage rate reach certain requirements, smelting begins, and the normal smelting stage begins after the arc starting stage;

[0035] S4: Determine the feeding electrode weight and time;

[0036] S5: When the melting time and the remaining electrode weight reach the requirement, the feeding operation is performed;

[0037] S6: The power is turned off to stop smelting, and the outer wall of the crucible is cooled under a certain vacuum degree, and then demolded to obtain an ingot with no shrinkage cavities and good internal quality.

[0038] Furthermore, the feeding current and voltage are based on the normal melting current and voltage, and are gradually reduced according to a certain proportion. The normal melting current and voltage are different for different furnace types. For example, the normal melting current of a 150 kg furnace is 6000-6200 amperes, and the normal melting voltage is 24-26 V. That is, the current drop gradient in the early feeding period is 5% to 20% of the normal melting current; the current drop gradient in the middle feeding period is 3% to 10% of the normal melting current; the current in the late feeding period is 20% to 30% of the normal melting current, the voltage drop gradient in the early feeding period is 0.5% to 1.5% of the normal melting voltage; and the voltage drop gradient in the middle and late feeding period is 0.5% to 1.0% of the normal melting voltage.

[0039] Furthermore, the cooling is carried out in a copper crucible under vacuum, and the cooling method is to cool the outer wall of the copper crucible through circulating water.

[0040] Furthermore, the vacuum consumable furnace is evacuated by starting a mechanical pump, starting a Roots pump when the vacuum degree reaches 700Pa, and starting a booster pump when the vacuum degree reaches 5Pa.

[0041] Furthermore, the vacuum degree and the leakage rate reaching certain requirements respectively refer to the vacuum degree reaching below 0.1 Pa and the leakage rate reaching below 1 Pa / min.

[0042] The steel is smelted by using the steel ingot to be smelted as a consumable electrode and melting it in a copper crucible by applying electricity. The steel smelting is carried out under vacuum;

[0043] The weight of the feeding electrode refers to the weight of the electrode that needs to be melted and consumed during the feeding process in the later stage of smelting.

[0044] Example 1: Co3W3 is smelted using the method of the present invention;

[0045] The specific steps are as follows:

[0046] (1) Raw material preparation

[0047] A vacuum consumable furnace with a capacity of 150 kg was used for melting. The Co3W3 electrode to be melted was prepared, weighing 112 kg, and placed in a copper crucible with a diameter of 250 mm.

[0048] (2) Vacuuming

[0049] Start the mechanical pump, start the Roots pump when the vacuum degree reaches 700Pa, and start the booster pump when the vacuum degree reaches 5Pa.

[0050] (3) Melting

[0051] When the vacuum degree reaches below 0.1Pa and the leakage rate reaches below 1Pa / min, melting begins. After the arc starting stage, it enters the normal melting stage. The normal melting current is 6000A and the voltage is 25V.

[0052] (4) Determine the weight and time of the feeding electrode

[0053] According to the needs of steel ingot feeding, the weight of the feeding electrode is determined to be 25 kg and the feeding time is 26 minutes.

[0054] (5) Ingot feeding

[0055] After 54 minutes of smelting, feeding began when the remaining electrode weight reached 25 kg. In the early stages of feeding, the current decreased by a gradient of 400 A, with an interval of 1 minute, for a total of 5 minutes. In the middle stages of feeding, the current decreased by a gradient of 200-300 A, with intervals of 1.5-2 minutes, for a total of 11 minutes. In the late stages of feeding, the current decreased to 1600 A for 10 minutes. The feeding voltage decreased by a gradient of 0.2 V in the early stages and 0.18 V in the middle and late stages.

[0056] (6) Cooling

[0057] After the feeding is completed, the smelting is stopped, the vacuum degree is maintained below 1 Pa, the outer wall of the crucible is kept cooled by circulating water, and the mold is demoulded after cooling for 240 minutes.

[0058] Ten furnaces of Co3W3 ingots were smelted using the method of the present invention, and no shrinkage defects were found in any of the ingots after inspection.

[0059] Example 2: Smelting GH4169 using the method of the present invention

[0060] The specific steps are as follows:

[0061] (1) Raw material preparation

[0062] A vacuum consumable furnace with a capacity of 150 kg is used for melting. The GH4169 electrode weighing 120 kg is prepared and placed in a copper crucible with a diameter of 250 mm.

[0063] (2) Vacuuming

[0064] Start the mechanical pump, start the Roots pump when the vacuum degree reaches 700Pa, and start the booster pump when the vacuum degree reaches 5Pa.

[0065] (3) Melting

[0066] When the vacuum degree reaches below 0.1Pa and the leakage rate reaches below 1Pa / min, melting begins. After the arc starting stage, it enters the normal melting stage. The normal melting current is 6200A and the voltage is 25.5V.

[0067] (4) Determine the weight and time of the feeding electrode

[0068] According to the needs of steel ingot feeding, the weight of the feeding electrode is determined to be 27 kg and the feeding time is 28 minutes.

[0069] (5) Ingot feeding

[0070] After 53 minutes of smelting, feeding began when the remaining electrode weight reached 27 kg. In the early stages of feeding, the current decreased by a gradient of 400 A, with a 1-minute interval, for a total of 5 minutes. In the middle stages of feeding, the current decreased by a gradient of 200 to 300 A, with a 1.5-minute interval, for a total of 12 minutes. In the late stages of feeding, the current decreased to 1600 A, lasting 11 minutes. The feeding voltage decreased by a gradient of 0.25 V in the early stages and 0.18 V in the middle and late stages.

[0071] (6) Cooling

[0072] After the shrinkage is completed, the smelting is stopped, the vacuum degree is maintained below 1 Pa, the outer wall of the crucible is kept cooled by circulating water, and the mold is demoulded after cooling for 300 minutes.

[0073] Eleven furnaces of GH4169 ingots were smelted using the method of the present invention, and no shrinkage defects were found in any of the ingots after inspection.

[0074] Example 3: GH4065 is smelted using the method of the present invention;

[0075] The specific steps are as follows:

[0076] (1) Raw material preparation

[0077] A vacuum consumable furnace with a capacity of 150 kg is used for melting. The GH4065 electrode weighing 118 kg is prepared and placed in a copper crucible with a diameter of 250 mm.

[0078] (2) Vacuuming

[0079] Start the mechanical pump, start the Roots pump when the vacuum degree reaches 700Pa, and start the booster pump when the vacuum degree reaches 5Pa.

[0080] (3) Melting

[0081] When the vacuum degree reaches below 0.1Pa and the leakage rate reaches below 1Pa / min, melting begins. After the arc starting stage, it enters the normal melting stage. The normal melting current is 6100A and the voltage is 25V.

[0082] (4) Determine the weight and time of the feeding electrode

[0083] According to the needs of steel ingot feeding, the weight of the feeding electrode is determined to be 26 kg and the feeding time is 28 minutes.

[0084] (5) Ingot feeding

[0085] After 54 minutes of smelting, feeding began when the remaining electrode weight reached 26 kg. In the early stages of feeding, the current decreased by a gradient of 400 A, with a 1-minute interval, for a total of 6 minutes. In the middle stages of feeding, the current decreased by a gradient of 200 to 300 A, with a 1.5-minute interval, for a total of 12 minutes. In the late stages of feeding, the current decreased to 1500 A for 10 minutes. The feeding voltage decreased by a gradient of 0.2 V in the early stages and 0.18 V in the middle and late stages.

[0086] (6) Cooling

[0087] After the shrinkage is completed, the smelting is stopped, the vacuum degree is maintained below 1 Pa, the outer wall of the crucible is kept cooled by circulating water, and the mold is demoulded after cooling for 280 minutes.

[0088] Eleven furnaces of GH4065 ingots were smelted using the method of the present invention, and no shrinkage defects were found in any of the ingots after inspection.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for feeding steelmaking in a vacuum consumable furnace, characterized in that: The following steps are involved: Prepare a vacuum consumable furnace to melt the electrode and place the electrode into a copper crucible; Evacuate the vacuum consumable furnace; When the vacuum degree and leakage rate reach certain requirements, smelting begins. After the arc starting stage, it enters the normal smelting stage to melt the steel. Determine the feeding electrode weight and feeding time; When the melting time and the remaining electrode weight meet the requirements, the ingot feeding operation is carried out; Stop smelting, cool the outer wall of the crucible under a certain vacuum degree, and demould after cooling; The weight of the feeding electrode is 10% to 25% of the total weight of the smelting electrode; The feeding time is 25% to 35% of the total smelting time; In the early stage of feeding, the current drop gradient is 5% to 20% of the normal melting current, and the time is 10% to 20% of the total feeding time; in the middle stage of feeding, the current drop gradient is 3% to 10% of the normal melting current; in the late stage of feeding, the current is 20% to 30% of the normal melting current, and the time is 30% to 40% of the total feeding time; The voltage drop gradient in the early stage of feeding is 0.5% to 1.5% of the normal melting voltage; the voltage drop gradient in the middle and late stages of feeding is 0.5% to 1.0% of the normal melting voltage.

2. The method for feeding steelmaking in a vacuum consumable furnace according to claim 1, wherein: The outer wall of the crucible is cooled, the vacuum degree is controlled below 1 Pa, and the cooling time is 3 to 6 hours.

3. The method for feeding steelmaking in a vacuum consumable furnace according to claim 1, wherein: The cooling method is to cool the outer wall of the copper crucible through circulating water.

4. The method for feeding steelmaking in a vacuum consumable furnace according to claim 1, wherein: The vacuum consumable furnace is evacuated by starting a mechanical pump, starting a Roots pump when the vacuum degree reaches 700 Pa, and starting a booster pump when the vacuum degree reaches 5 Pa.

5. The method for feeding steelmaking in a vacuum consumable furnace according to claim 1, wherein: The vacuum degree and the leakage rate reaching certain requirements respectively refer to the vacuum degree reaching below 0.1 Pa and the leakage rate reaching below 1 Pa / min.

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