An arc starting method for a slab electroslag furnace

Abstract

The present invention discloses an arc starting method for a slab electroslag furnace. Low-carbon steel turnings are selected, and the chemical composition by weight percentage is C≤0.005%, P≤0.005%, S≤0.003%, T.O≤0.005%. The low-carbon steel is crushed and processed into turnings with a particle size of 5-10 mm, and the required alloy is crushed into alloy powder with a particle size of 1-3 mm. According to the composition of the steel grade to be produced and the weight of the low-carbon steel turnings for arc starting, alloy powder of corresponding types and weights is prepared. The low-carbon steel turnings for arc starting and various alloy powders are mixed evenly. The arc starting points are arranged according to the type of the mold. The arc starting points are square, horizontal with the length direction of the mold, and 3-5 points are evenly distributed along the length direction of the mold. The side length is 60%-80% of the width of the mold, and the height is 20-40 mm. Solid slag material with the same thickness as the height of the arc starting points is laid around. It realizes the safety, stability and high efficiency in the arc starting stage of the slab electroslag furnace, and solves the problems of poor arc starting effect, easy arcing, easy adhesion and easy open circuit in the prior art.

Description

Technical Field

[0001] The present invention belongs to electroslag metallurgical smelting and relates to an arc starting method for a slab electroslag furnace Background Art

[0002] Electroslag metallurgy is a process in which a metal electrode melts, molten droplets form and transition to dripping, a metal molten pool is formed, and metal crystallization occurs. During this process, heat transfer, metallurgical reactions, metal solidification and crystallization and other processes are involved. It is a new smelting technology that uses the resistance heat of molten slag to remelt a consumable electrode, so as to further purify steel and alloys to improve the crystal structure of steel ingots

[0003] An electroslag furnace is a special smelting equipment that uses a remelting current to generate heat energy to melt a consumable electrode inserted into a slag bath. After the metal molten droplets are cleaned by the slag liquid, they crystallize into an electroslag ingot in a water-cooled mold

[0004] At present, there are mainly two conventional arc starting methods for electroslag furnaces. One is liquid arc starting. Its principle is to first heat powdered slag material to melt it into liquid slag, and then inject the liquid slag into the mold before starting electroslag smelting. This method can effectively avoid disadvantages such as large fluctuations in current and voltage during the arc starting stage and can improve the quality of electroslag steel. It has been widely used, but this method requires special slag melting equipment, occupies a large area, has low production efficiency and increases the smelting cost. The other is solid arc starting. Its principle is to directly melt the slag with the electrode or add an arc starter such as graphite to start the arc. The advantage is that no slag melting treatment is required, which can improve production efficiency and save costs. The disadvantages are that this method causes large fluctuations in current and voltage during the arc starting stage, the arc starting plate and the electrode are prone to adhesion, it is easy to form an open circuit resulting in arc starting failure, and there is an easy composition deviation at the bottom of the electroslag ingot after smelting

[0005] Chinese Patent (Application No. 201520859502.X) discloses an arc starting device named "an arc starting device for an electroslag remelting furnace". The arc starting device includes an arc starting backing plate, an arc starting bottom plate and an arc starting block in contact with the electrode base material. The arc starting bottom plate is a disk radially tangent to the electrode base material and welded to the arc starting backing plate. The arc starting block is a strip-shaped block taken from the electrode base material with a length less than the radius of the arc starting bottom plate. The arc starting block is welded to the arc starting bottom plate and there are at least six pieces and they are radially evenly distributed along the edge of the arc starting bottom plate with the center of the arc starting bottom plate as the center. A space for placing pre-melted slag is formed between adjacent arc starting blocks, and an electrode rod placement plane is formed with the center of the arc starting bottom plate as the center at the top of each arc starting block. This arc starting placement can make the side of the electrode fully contact with the arc starting block, ensure the stability of current and voltage during the arc starting stage, and avoid problems such as easy arcing, easy adhesion and easy open circuit during the arc starting stage. In addition, both the arc starting bottom plate and the arc starting block are taken from the electrode base material, so there is no pollution. It is an efficient and safe arc starting device for an electroslag remelting furnace

[0006] In summary, the above electric slag furnace arc starting method controls the current and voltage smoothly during the arc starting stage by changing the shape and arrangement of the arc starting blocks, and has a certain effect on avoiding problems such as easy arcing, easy adhesion, and easy open circuit during the arc starting stage. However, arc starting blocks of the same material are required, and the arrangement of the arc starting blocks is in a circular pattern with at least six blocks evenly distributed radially along the edge of the arc starting bottom plate centered on the center of the arc starting bottom plate. This arrangement is only applicable to the arc starting of round billet electric slag furnaces and is not suitable for the arc starting operation of slab billet electric slag, having certain limitations. Summary of the Invention

[0007] The purpose of the present invention is to provide an arc starting method for a slab billet electric slag furnace, which uses low-carbon steel chips and is combined with alloy powder and solid slag material to achieve safe, stable, and efficient arc starting in the arc starting stage of the slab billet electric slag furnace, and solves the problems of poor arc starting effect, easy arcing, easy adhesion, and easy open circuit in the prior art.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows: An arc starting method for a slab billet electric slag furnace includes the following contents:

[0009] 1) Chemical composition of low-carbon steel chips: Select low-carbon steel chips, and the chemical composition weight percentage of the steel chips is: C ≤ 0.005%, P ≤ 0.005%, S ≤ 0.003%, T.O ≤ 0.005%, and the balance is Fe and unavoidable impurities;

[0010] 2) Processing of low-carbon steel chips and alloys: Crush low-carbon steel into steel chips with a particle size of 5 - 10 mm, and crush the required alloys into alloy powder with a particle size of 1 - 3 mm;

[0011] 3) Addition amount of alloy powder: Prepare alloy powder of corresponding types and weights according to the composition of the steel grade to be produced and the weight of the arc starting low-carbon steel chips;

[0012] 4) Specifications and arrangement of arc starting points: Mix the arc starting low-carbon steel chips and various alloy powders evenly, and arrange the arc starting points according to the type of the mold. The arc starting points are square, horizontal with the length direction of the mold, evenly distributed 3 - 5 points along the length direction of the mold, with a side length of 60% - 80% of the width of the mold and a height of 20 - 40 mm; solid slag material with the same thickness as the height of the arc starting points is laid around.

[0013] Further, the chemical composition weight percentage of the low-carbon steel chips is C: 0.002% - 0.004%, P: 0.002% - 0.004%, S: 0.001% - 0.002%, T.O: 0.002% - 0.004%.

[0014] Further, the particle size of the steel chips is 6 - 8 mm, and the particle size of the alloy powder is 2 - 3 mm.

[0015] Further, the side length of the square arc starting point is 65% - 75% of the width of the mold.

[0016] Furthermore, the height of the square starting arc point is 25 - 35 mm.

[0017] Furthermore, the solid slag material is a pre - melting - free slag material.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. By using low - carbon steel chips + alloy powder instead of solid conductive blocks, the present invention can be applicable to different steel grades. Without the need for conductive blocks of the same material, the starting arc of the electroslag remelting furnace can be realized.

[0020] 2. By using powder starting - arc materials instead of solid conductive blocks and, at the same time, matching with the conventional solid slag material starting - arc process, the present invention can effectively shorten the starting - arc slag - melting time. During starting arc, the current and voltage fluctuations are small and the control is stable, and the starting - arc success rate can reach 100%.

[0021] 3. The present invention can be applicable to the starting arc of electroslag remelting with electrodes of different materials, and has a wide application range.

[0022] 4. The present invention can realize the automatic separation of the bottom backing plate and the electrode without adhesion. Specific embodiments

[0023] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] In the electroslag process, first, after the consumable electrode contacts the conducting block and is energized, the fixed conducting block is melted by Joule heat. Then, an arc is generated between the electrodes to heat the melted conductive slag, causing its temperature to continuously rise and melting the electroslag material. Under continuous power supply, the melted slag gradually heats and melts the consumable electrode to complete the remelting operation. During this process, the conductivity of the conducting block and its contact degree with the consumable electrode have a great influence on the current and voltage fluctuations during the arcing stage. At the initial stage of conduction, since the contact degree between the solid conducting block and the consumable electrode cannot ensure full contact, the contacted part will melt first, while the poorly contacted part will melt slowly, which easily leads to large fluctuations in current and voltage during the arc initiation stage, causing the arcing plate to adhere to the electrode easily and forming an open circuit easily, resulting in arc initiation failure. To ensure that the arc starter can fully contact the consumable electrode, steel filings with good conductivity are selected. Since general steel grades are sensitive to carbon composition, in order to reduce the influence on the composition fluctuation of the electroslag ingot, the present invention uses low-carbon steel filings. In addition, to minimize the composition fluctuation of the steel ingot, a certain amount of alloy powder with the same composition as the remelted steel ingot is added to the steel filings. Through the above methods, it can be ensured that the consumable electrode can fully contact the arc starter and the composition fluctuation is small. Solid slag material is mixed in to achieve the premature melting of the solid slag material and accelerate the arc initiation heating speed. A safe, stable, and efficient slab electroslag furnace arc initiation method can be realized during the arc initiation stage of the slab electroslag furnace, solving the problems of poor arc initiation effect, easy arcing, easy adhesion, and easy open circuit in the prior art. The specific solutions are as follows:

[0025] 1. Chemical composition of low-carbon steel filings: Select low-carbon steel filings according to the production steel grade and limit harmful elements. The specific details are as follows: See Table 1

[0026] Table 1 Chemical composition of low-carbon steel filings, %

[0027] Chemical composition C P S T.O Content limit ≤0.005 ≤0.005 ≤0.003 ≤0.005

[0028] 2. Physical parameters of low-carbon steel filings and alloy powder: Process low-carbon steel into steel filings with a particle size of 5 - 10 mm, and crush the required alloy into alloy powder with a particle size of 1 - 3 mm.

[0029] 3. Alloy powder addition amount: Prepare the corresponding type and weight of alloy powder according to the composition of the production steel grade and the weight of the arc initiation low-carbon steel filings.

[0030] 4. Arc initiation point specifications and layout: Mix the low-carbon steel filings for arc initiation and various alloy powders evenly, and arrange the arc initiation points according to the type of the mold. The arc initiation points are square, horizontal with the length direction of the mold, evenly distributed 3 - 5 points along the length direction of the mold, with a side length of 60% - 80% of the width of the mold and a height of 20 - 40 mm; solid slag material with the same thickness as the height of the arc initiation points is laid around.

[0031] 5. In order to ensure full contact between the end face of the consumable electrode and the arc starter mixture of low-carbon steel chips and various alloy powders, after contact between the end face of the consumable electrode and the mixture, it is necessary to ensure that the consumable electrode is pressed down by 5 - 10 mm, and then the consumable electrode is energized for arc starting operation.

[0032] In a certain iron and steel enterprise, a 40t slab electroslag furnace was used, and a total of 4 furnace production tests were carried out for the arc starting method: 1 furnace was completed using the conventional process - solid-state arc starting, and 3 furnaces were completed using the present invention. The production test results are as follows:

[0033] Comparative example: (Solid-state arc starting)

[0034] Using the solid-state arc starting process, the conducting block is made of a steel plate of the same material as the electrode, with a square shape, a side length of 70% of the width of the mold, and a thickness of 30 mm. The arrangement of the conducting blocks: horizontally along the length direction of the mold, evenly distributed at 4 points along the length direction of the mold, and solid slag materials with the same thickness as the height of the arc starting point are laid around; other operations are all carried out according to the conventional solid-state arc starting process. Test results: The arc starting time is 94 min, the current fluctuation is ±30%, the voltage fluctuation is ±30%, and the bottom backing plate adheres to the electrode.

[0035] Example 1:

[0036] Using the powder arc starting process of the present invention, the low-carbon steel chip components are: [C] 0.004%, [P] 0.004%, [S] 0.001%, [T.O] 0.004%, the steel chip particle size is 5 mm, the alloy powder particle size is 1 mm, the types and addition amounts of alloy powders: according to the composition of the steel grade to be produced and the weight of the low-carbon steel chips for arc starting, the corresponding types and weights of alloy powders are formulated; the specifications and arrangements of the arc starting points: the arc starting points are arranged according to the type of the mold. The arc starting points are square, horizontally along the length direction of the mold, evenly distributed at 3 points along the length direction of the mold, with a side length of 60% of the width of the mold and a height of 20 mm, and solid slag materials with the same thickness as the height of the arc starting point are laid around; other operations are all carried out according to the conventional solid-state arc starting process. Test results: The arc starting time is 74 min, the current fluctuation is ±5%, the voltage fluctuation is ±5%, and the bottom backing plate does not adhere to the electrode.

[0037] Example 2:

[0038] Using the powder arc starting process of the present invention, the components of low-carbon steel shavings are: [C] 0.003%, [P] 0.003%, [S] 0.003%, [T.O] 0.003%. The particle size of steel shavings is 7 mm, and the particle size of alloy powder is 2 mm. The types and addition amounts of alloy powder: According to the composition of the steel grade to be produced and the weight of the low-carbon steel shavings for arc starting, alloy powder of corresponding types and weights is formulated; The specifications and layout of the arc starting points: The arc starting points are arranged according to the type of mold. The arc starting points are square, horizontal with the length direction of the mold, and 4 points are evenly distributed along the length direction of the mold. The side length is 70% of the width of the mold, and the height is 30 mm. Solid slag materials with the same thickness as the height of the arc starting points are laid around; Other operations are all carried out according to the conventional solid arc starting process. Test results: The arc starting time is 78 min, the current fluctuation is ±8%, the voltage fluctuation is ±8%, and the bottom backing plate does not stick to the electrode.

[0039] Example 3:

[0040] Using the powder arc starting process of the present invention, the components of low-carbon steel shavings are: [C] 0.002%, [P] 0.002%, [S] 0.002%, [T.O] 0.002%. The particle size of steel shavings is 10 mm, and the particle size of alloy powder is 3 mm. The types and addition amounts of alloy powder: According to the composition of the steel grade to be produced and the weight of the low-carbon steel shavings for arc starting, alloy powder of corresponding types and weights is formulated; The specifications and layout of the arc starting points: The arc starting points are arranged according to the type of mold. The arc starting points are square, horizontal with the length direction of the mold, and 5 points are evenly distributed along the length direction of the mold. The side length is 80% of the width of the mold, and the height is 40 mm. Pre-melting-free slag materials with the same thickness as the height of the arc starting points are laid around; Other operations are all carried out according to the conventional solid arc starting process. Test results: The arc starting time is 80 min, the current fluctuation is ±10%, the voltage fluctuation is ±10%, and the bottom backing plate does not stick to the electrode.

[0041] It can be seen from the above production test results that using the present invention for starting the arc of the slab electroslag furnace can effectively shorten the arc starting time by 14 - 20 min, the current and voltage are controlled stably, and the fluctuation range ≤ 10%, which is 20% lower than the conventional process (solid arc starting). At the same time, the arc starting success rate reaches 100%, and the bottom backing plate does not stick to the electrode.

[0042] 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 foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An arc starting method for a slab electroslag furnace, characterized in that, It includes the following contents: 1) Chemical composition of low-carbon steel turnings: Low-carbon steel turnings are selected, and the chemical composition of the steel turnings is in weight percentage: C ≤ 0.005%, P ≤ 0.005%, S ≤ 0.003%, T.O ≤ 0.005%, and the balance is Fe and inevitable impurities; 2) Processing of low-carbon steel turnings and alloys: The low-carbon steel is crushed into steel turnings with a particle size of 5 - 10 mm, and the required alloy is crushed into alloy powder with a particle size of 1 - 3 mm; 3) The types of alloy powder are the same as the components of the remelted steel ingot formed by the consumable electrode remelting operation; 4) Specifications and layout of the arc starting points: Low-carbon steel turnings + alloy powder are used to replace the solid conductive block. The low-carbon steel turnings and various alloy powders for arc starting are mixed evenly. According to the type of the mold, the arc starting points are arranged. The arc starting points are square, horizontal with the length direction of the mold, evenly distributed 3 - 5 points along the length direction of the mold, the side length is 60% - 80% of the width of the mold, and the height is 20 - 40 mm; Solid slag materials with the same thickness as the height of the arc starting points are laid around.

2. The starting arc method for a slab electroslag furnace according to claim 1, characterized in that, The weight percentage of the chemical composition of the low-carbon steel turnings is C: 0.002% - 0.004%, P: 0.002% - 0.004%, S: 0.001% - 0.002%, T.O: 0.002% - 0.004%.

3. A method for initiating an arc in a slab electroslag furnace according to claim 1, characterized in that, The particle size of the steel turnings is 6 - 8 mm, and the particle size of the alloy powder is 2 - 3 mm.

4. A method for initiating an arc in a slab electroslag furnace according to claim 1, characterized in that The side length of the square arc starting point is 65% - 75% of the width of the mold.

5. A method for initiating an arc in a slab electroslag furnace according to claim 1, characterized in that, The height of the square arc starting point is 25 - 35 mm.

6. A method for initiating an arc in a slab electroslag furnace according to claim 1, characterized in that, The solid slag material is a pre-melting-free slag material.