An arc-starting method for a billet electroslag furnace

Abstract

This invention discloses an arc-starting method for a billet electroslag furnace, using low-carbon steel scrap with the following chemical composition: C≤0.008%, P≤0.008%, S≤0.005%, T0≤0.005%. The low-carbon steel is processed into 5-10mm particles, and the required alloy is crushed into 1-3mm particles. Based on the steel grade composition and the weight of the low-carbon steel scrap used for arc starting, alloy powder of the appropriate type and weight is prepared. The steel scrap and alloy powder are mixed evenly. The arc-starting point has a circular or square cross-section, similar to the cross-sectional shape of the crystallizer, with its center point coinciding with the center point of the crystallizer. The arc-starting point is a single point with an area of ​​50%-70% of the cross-sectional area of ​​the crystallizer's shape and a height of 40-60mm. A baffle of the same material as the steel scrap is provided around the arc-starting point, with a thickness of 0.5-1mm and a height consistent with the arc-starting point. Solid slag is laid around the baffle, with a height consistent with the arc-starting point. To achieve safe, stable, and efficient arc initiation in the electroslag furnace for billets, and to solve problems such as poor arc initiation effect, easy arc breaking, easy adhesion, and easy circuit opening in existing technologies.

Description

Technical Field

[0001] This invention pertains to electroslag metallurgical smelting and relates to an arc-starting method for a billet electroslag furnace. Background Technology

[0002] Electroslag remelting (ESR) is a process in which metal electrodes melt, droplets form, and then drip, forming a molten metal pool and crystallizing. This process involves heat transfer, metallurgical reactions, and metal solidification and crystallization. It is a novel smelting technology that uses the resistance heat of slag to remelt consumable electrodes, thereby further purifying steel and alloys to improve the crystalline structure of steel ingots.

[0003] An electroslag furnace is a special smelting device that uses remelting current to generate heat to melt consumable electrodes inserted into a slag pool. The molten metal droplets are then washed by the slag liquid and crystallized into electroslag ingots in a water-cooled crystallizer. Based on the shape of the crystallizer and the electroslag ingot, it can be divided into slab electroslag furnaces and billet (square billet, round billet) electroslag furnaces.

[0004] Currently, there are two main conventional arc initiation methods for electroslag remelting furnaces. One is liquid arc initiation, which involves first heating powdered slag to melt it into liquid slag, then injecting the liquid slag into the crystallizer to begin electroslag smelting. This method can effectively avoid the disadvantages of large current and voltage fluctuations during the arc initiation stage and can improve the quality of electroslag steel. It has been widely used, but this method requires dedicated slag-forming equipment, which occupies space, has low production efficiency, and increases smelting costs. The other is solid arc initiation, which involves directly slag-forming the electrodes or adding arc-initiating agents such as graphite to initiate the arc. The advantage is that no slag-forming treatment is required, which can improve production efficiency and save costs. The disadvantage is that this method causes large current and voltage fluctuations during the arc initiation stage, the arc-initiating plate and the electrode are prone to sticking, and open circuits are easily formed, leading to arc initiation failure. In addition, the bottom of the electroslag furnace is prone to compositional deviations after smelting.

[0005] Chinese patent (application number CN201220522868.4) discloses a device entitled "An Arc-Initiating Device for an Electroslag Furnace." This utility model relates to an arc-initiating device for an electroslag furnace, belonging to auxiliary facilities of the electroslag furnace. It consists of two steel plates, one circular and the other annular, with the circular plate positioned within the annular plate. This utility model offers smooth demolding and low costs. While it achieves smooth demolding and low costs, it requires an arc-initiating block of the same material, limiting its applicability. Furthermore, using a solid steel plate as the arc-initiating block is problematic because poor or uneven contact between the steel plate and the electrode end face can lead to unstable current and voltage, making arc initiation relatively difficult.

[0006] Chinese Patent (Application No. 201520859502.X) discloses an arc-starting device entitled "An arc-starting device for an electroslag remelting furnace". This utility model relates to an arc-starting device for an electroslag remelting furnace, including an arc-starting pad, an arc-starting base plate, and an arc-starting block in contact with the electrode base material. The arc-starting base plate is a disc radially tangent to the electrode base material and welded to the arc-starting pad. The arc-starting block is a strip-shaped block taken from the electrode base material with a length smaller than the radius of the arc-starting base plate. The arc-starting block is welded to the arc-starting base plate, and there are at least six blocks, which are radially evenly distributed along the edge of the arc-starting base plate with the center as the center. A space for placing pre-melted slag is formed between each adjacent arc-starting block. The top of each arc-starting block forms an electrode rod placement plane with the center of the arc-starting base plate as the center. This placement method ensures full contact between the sides of the electrode and the arc-starting block, guaranteeing stable current and voltage during the arc-starting stage and avoiding problems such as easy arcing, sticking, and open circuits. However, since consumable electrodes are usually forged after die casting, their dimensions are generally quite large, weighing several tons or even tens of tons, making it extremely difficult to manufacture arc-starting blocks of the same material from them. Furthermore, the arrangement of the arc-starting blocks—at least six in a circle evenly distributed radially along the edge of the arc-starting base plate with its center as the center—is only suitable for arc-starting in round billet electroslag furnaces and is unsuitable for square electric arc furnaces, thus having certain limitations. Summary of the Invention

[0007] The purpose of this invention is to provide an arc-starting method for a billet electroslag furnace, which addresses the limitations of current arc-starting methods, such as the arc-starting block arrangement being applicable only to slabs or round billets, large fluctuations in current and voltage during the arc-starting stage, easy adhesion between the arc-starting plate and the electrode, easy formation of open circuits leading to arc-starting failure, easy compositional deviation at the bottom of the electroslag ingot after melting, and the limitations of the arc-starting block.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows: an arc-starting method for a billet electroslag furnace, comprising the following:

[0009] 1) Chemical composition of low carbon steel scrap: Low carbon steel scrap is selected, and the chemical composition of the scrap by weight percentage is: C≤0.008%, P≤0.008%, S≤0.005%, TO≤0.005%, with the balance being Fe and unavoidable impurities;

[0010] 2) Low carbon steel chips and alloy processing: Process low carbon steel into steel chips with a particle size of 5-10mm, and crush the required alloy into alloy powder with a particle size of 1-3mm.

[0011] 3) Alloy powder addition amount: Prepare the corresponding type and weight of alloy powder according to the composition of the steel grade produced and the weight of the low carbon steel scrap for arc initiation;

[0012] 4) Arc-starting point specifications and layout: The low-carbon steel scrap and various alloy powders for arc starting are mixed evenly. The cross-section of the arc-starting point is circular or square, similar to the cross-sectional shape of the crystallizer, with its center point coinciding with the center point of the crystallizer. There is one arc-starting point, with an area of ​​50%-70% of the cross-sectional area of ​​the crystallizer's shape and a height of 40-60mm. Simultaneously, a baffle of the same material as the low-carbon steel scrap is installed around the arc-starting point, with a thickness of 0.5-1mm and a height consistent with the arc-starting point. Solid slag is laid around it, with a height consistent with the arc-starting point.

[0013] Furthermore, in order to ensure that the end face of the consumable electrode is in full contact with the arc ignition agent mixed with low-carbon steel shavings and various alloy powders, the electrode is pressed down by 5-10 mm after the end face of the consumable electrode is in contact with the arc ignition agent mixed with low-carbon steel shavings and various alloy powders, and then the consumable electrode is energized to start the arc.

[0014] Furthermore, the chemical composition of the low-carbon steel scrap, by weight percentage, is C: 0.005%–0.007%, P: 0.005%–0.007%, S: 0.002%–0.004%, and TO: 0.002%–0.004%.

[0015] Furthermore, the steel shavings have a particle size of 6–8 mm, and the alloy powder has a particle size of 2–3 mm.

[0016] Furthermore, the area of ​​the arc initiation point is 55%-65% of the cross-sectional area of ​​the shape enclosed by the crystallizer.

[0017] Furthermore, the height of the arc initiation point is 45-55mm.

[0018] Furthermore, the solid slag is a pre-melting slag.

[0019] Furthermore, after the self-consuming electrode end face comes into contact with the arc-initiating agent, which is a mixture of low-carbon steel shavings and various alloy powders, it is pressed down by 8-10mm.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. This invention uses low-carbon steel scrap and alloy powder instead of solid conductive blocks, making it applicable to different steel grades and eliminating the need for conductive blocks of the same material to achieve arc initiation in an electroslag furnace for billets. It has the advantages of strong applicability, simple process, safety and reliability, and the elimination of the need for conductive blocks of the same material.

[0022] 2. This invention, by using powdered arc-initiating material instead of solid conductive blocks, and combined with a conventional solid slag arc-initiating process, can effectively shorten the arc-initiating and slag-forming time, resulting in small and stable current and voltage fluctuations during arc initiation, and achieving a 100% arc-initiating success rate.

[0023] 3. This invention is applicable to the electroslag remelting arc initiation of electrodes made of different materials, and has a wide range of applications.

[0024] 4. This invention enables the automatic separation of the base plate and the electrode without adhesion. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0026] In the electroslag remelting process, the consumable electrode and the conductive block first come into contact, and electricity is applied to melt the fixed conductive block using Joule heating. Then, an electric arc is generated by the electrode to heat the molten conductive slag, continuously increasing its temperature and melting the electroslag material. The molten slag, under continuous energization, gradually heats and melts the consumable electrode, completing the remelting process. During this process, the conductivity of the conductive block and the degree of contact with the consumable electrode significantly affect the current and voltage fluctuations during the arc initiation stage. In the initial stage of conduction, because the contact between the solid conductive block and the consumable electrode cannot be guaranteed to be sufficient, the contact points will melt first, while areas with poor contact will melt slowly. This easily leads to large fluctuations in current and voltage during the arc initiation stage, causing the arc-starting plate to easily stick to the electrode and easily forming an open circuit, resulting in arc initiation failure. To ensure sufficient contact between the arc-starting agent and the consumable electrode, highly conductive steel scrap is selected. Since most steel grades are sensitive to carbon content, to reduce the impact of fluctuations in the composition of the electroslag ingot, this invention utilizes low-carbon steel scrap. In addition, to minimize compositional fluctuations in the steel ingot, a certain amount of alloy powder with the same composition as the remelted steel ingot is added to the steel scrap. This ensures that the consumable electrode can fully contact the arc-initiating agent while minimizing compositional fluctuations. Adding solid slag allows for pre-melting of the solid slag, accelerating the arc-starting heating process. This enables a safe, stable, and efficient arc-starting method for slab electroslag furnaces, solving problems such as poor arc-starting performance, easy arc breaking, easy sticking, and easy open circuits in existing technologies. Furthermore, to adapt to the arc-starting requirements of round or square irregularly shaped billets, the arc-starting area can be arranged according to the billet shape structure, as detailed below:

[0027] 1. Chemical composition of low-carbon steel scrap: Low-carbon steel scrap is selected according to the steel grade being produced, and harmful elements are limited, as detailed in Table 1.

[0028] Table 1 Chemical composition of low carbon steel scrap, %

[0029] chemical composition C P S TO Content Limit ≤0.008 ≤0.008 ≤0.005 ≤0.005

[0030] 2. Physical parameters of low carbon steel chips and alloy powder: Low carbon steel is processed into steel chips with a particle size of 5-10mm, and the required alloy is crushed into alloy powder with a particle size of 1-3mm.

[0031] 3. Alloy powder addition amount: Prepare the appropriate type and weight of alloy powder according to the composition of the steel grade produced and the weight of the low carbon steel scrap for arc initiation.

[0032] 4. Arc-starting point specifications and layout: The low-carbon steel scrap and various alloy powders used for arc starting are mixed evenly. The cross-section of the arc-starting point is circular or square, with a shape consistent with the shape of the crystallizer. The center point coincides with the center point of the crystallizer. There is one arc-starting point, with an area of ​​50%-70% of the cross-sectional area of ​​the crystallizer's shape and a height of 40-60mm. Simultaneously, a baffle of the same material as the low-carbon steel scrap is installed around the arc-starting point, with a thickness of 0.5-1mm and a height consistent with the arc-starting point. Solid slag is laid around the baffle, with a height consistent with the arc-starting point.

[0033] 5. In order to ensure that the end face of the consumable electrode is in full contact with the arc-starting agent mixed with low-carbon steel shavings and various alloy powders, after contact with the end face of the consumable electrode, the consumable electrode should be pressed down by 5-10mm before energizing the consumable electrode to start the arc.

[0034] In a steel company using a 15t billet electroslag furnace, a total of 8 production trials were conducted on the arc-starting method: 2 heats were completed using the conventional process with solid-state arc starting, and 6 heats were completed using the present invention. The specific results of the production trials are as follows:

[0035] Comparative Example 1: (Solid-state arc initiation)

[0036] Solid-state arc initiation was employed. The conductive block was made of steel plate of the same material as the electrode, circular in shape, with an area of ​​60% of the cross-sectional area of ​​the crystallizer and a thickness of 50 mm. Solid slag of the same thickness as the arc initiation point was laid around it. All other operations followed the conventional solid-state arc initiation process. Test results: Arc initiation time 86 min, current fluctuation ±20%, voltage fluctuation ±20%, and adhesion between the bottom plate and the electrode.

[0037] Comparative Example 2: (Solid-state arc initiation)

[0038] Solid-state arc initiation was employed. The conductive block was made of steel plate of the same material as the electrode, square in shape, with an area of ​​60% of the cross-sectional area of ​​the crystallizer and a thickness of 50 mm. Solid slag of the same thickness as the arc initiation point was laid around it. Other operations followed the conventional solid-state arc initiation process. Test results: Arc initiation time 94 min, current fluctuation ±30%, voltage fluctuation ±30%, and adhesion between the bottom plate and the electrode.

[0039] Example 1:

[0040] The powder arc-starting process of this invention uses the following low-carbon steel chip composition: [C] 0.007%, [P] 0.007%, [S] 0.004%, [TO] 0.004%, with a steel chip particle size of 1mm and an alloy powder particle size of 1mm. The type and amount of alloy powder are determined based on the composition of the steel grade being produced and the total weight of the low-carbon steel chips and baffle used for arc starting. The arc-starting point is circular, similar to the cross-sectional shape of the crystallizer, with its center point coinciding with the crystallizer's center point. There is one arc-starting point, with an area of ​​50% of the cross-sectional area of ​​the crystallizer's shape and a height of 40mm. Simultaneously, a baffle of the same material as the low-carbon steel chips is provided around the arc-starting point, with a thickness of 0.5mm and a height matching the arc-starting point. Solid slag of the same thickness as the arc-starting point is laid around the baffle. All other operations follow the conventional solid-state arc-starting process. Test results: Arc start time 72 min, current fluctuation ±10%, voltage fluctuation ±10%, base plate and electrode do not stick.

[0041] Example 2:

[0042] The powder arc-starting process of this invention uses the following low-carbon steel chip composition: [C] 0.006%, [P] 0.006%, [S] 0.003%, [TO] 0.003%, with a steel chip particle size of 2mm and an alloy powder particle size of 2mm. The type and amount of alloy powder added are determined based on the composition of the steel grade being produced and the total weight of the low-carbon steel chips and baffle used for arc starting. The arc-starting point is circular, similar to the cross-sectional shape of the crystallizer, with its center point coinciding with the crystallizer's center point. There is one arc-starting point, with an area of ​​60% of the cross-sectional area of ​​the crystallizer's shape and a height of 50mm. Simultaneously, a baffle of the same material as the low-carbon steel chips is placed around the arc-starting point, with a thickness of 0.7mm and a height matching the arc-starting point. Solid slag of the same thickness as the arc-starting point is laid around the baffle. All other operations follow the conventional solid-state arc-starting process. Test results: Arc start time 71 min, current fluctuation ±9%, voltage fluctuation ±9%, and the base plate did not stick to the electrode.

[0043] Example 3:

[0044] The powder arc-starting process of this invention uses the following low-carbon steel chip composition: [C] 0.005%, [P] 0.005%, [S] 0.002%, [TO] 0.002%, with a steel chip particle size of 3mm and an alloy powder particle size of 3mm. The type and amount of alloy powder added are determined based on the composition of the steel grade being produced and the total weight of the low-carbon steel chips and baffle used for arc starting. The arc-starting point is uniformly mixed with the low-carbon steel chips and various alloy powders. The arc-starting point is circular, similar to the cross-sectional shape of the crystallizer, with its center point coinciding with the center point of the crystallizer. There is one arc-starting point, with an area of ​​70% of the cross-sectional area of ​​the crystallizer's shape and a height of 60mm. Simultaneously, a baffle of the same material as the low-carbon steel chips is provided around the arc-starting point, with a thickness of 1mm and a height consistent with the arc-starting point. Solid slag of the same thickness as the arc-starting point is laid around the baffle. All other operations follow the conventional solid-state arc-starting process. Test results: Arc start time 74 min, current fluctuation ±10%, voltage fluctuation ±10%, base plate and electrode do not stick.

[0045] Example 4:

[0046] The powder arc-starting process of this invention uses the following low-carbon steel chip composition: [C] 0.007%, [P] 0.007%, [S] 0.004%, [TO] 0.004%, with a steel chip particle size of 1mm and an alloy powder particle size of 1mm. The type and amount of alloy powder added are determined based on the composition of the steel grade being produced and the total weight of the low-carbon steel chips and baffle used for arc starting. The arc-starting point is a square, similar in shape to the cross-section of the crystallizer, with its center point coinciding with the crystallizer's center point. There is one arc-starting point, with an area of ​​50% of the cross-sectional area of ​​the crystallizer's shape and a height of 40mm. Simultaneously, a baffle of the same material as the low-carbon steel chips is placed around the arc-starting point, with a thickness of 0.5mm and a height matching the arc-starting point. Solid slag of the same thickness as the arc-starting point is laid around the baffle. All other operations follow the conventional solid-state arc-starting process. Test results: Arc start time 72 min, current fluctuation ±12%, voltage fluctuation ±12%, base plate and electrode do not stick.

[0047] Example 5:

[0048] The powder arc-starting process of this invention uses the following low-carbon steel chip composition: [C] 0.006%, [P] 0.006%, [S] 0.003%, [TO] 0.003%, with a steel chip particle size of 2mm and an alloy powder particle size of 2mm. The type and amount of alloy powder added are determined according to the composition of the steel grade being produced and the total weight of the low-carbon steel chips and baffle used for arc starting. The arc-starting point is specified and arranged as follows: the low-carbon steel chips and various alloy powders are mixed evenly, and the arc-starting point is a square, similar to the cross-sectional shape of the crystallizer, with the center point coinciding with the center point of the crystallizer. There is one arc-starting point, with an area of ​​60% of the cross-sectional area of ​​the crystallizer and a height of 50mm. Simultaneously, a baffle made of the same material as the low-carbon steel shavings is installed around the arc-starting point. The baffle is 0.7 mm thick and its height is the same as the arc-starting point height. Solid slag of the same thickness as the arc-starting point height is laid around the baffle. After the consumable electrode's end face comes into contact with the arc-starting agent, a mixture of low-carbon steel shavings and various alloy powders, it is pressed down by 6 mm, and then the arc-starting operation is performed by energizing the consumable electrode. Other operations follow the conventional solid-state arc-starting process. Test results: Arc-starting time 68 min, current fluctuation ±8%, voltage fluctuation ±8%, and the base plate does not stick to the electrode.

[0049] Example 6:

[0050] The powder arc-starting process of this invention uses the following low-carbon steel chip composition: [C] 0.005%, [P] 0.005%, [S] 0.002%, [TO] 0.002%, with a steel chip particle size of 3mm and an alloy powder particle size of 3mm. The type and amount of alloy powder added are determined according to the composition of the steel grade being produced and the total weight of the low-carbon steel chips and baffles used for arc starting. The arc-starting point is specified and arranged as follows: the low-carbon steel chips and various alloy powders are mixed evenly, and the arc-starting point is a square, similar to the cross-sectional shape of the crystallizer, with the center point coinciding with the center point of the crystallizer. There is one arc-starting point, with an area of ​​70% of the cross-sectional area of ​​the crystallizer and a height of 60mm. Simultaneously, a baffle made of the same material as the low-carbon steel shavings is installed around the arc-starting point. The baffle is 1mm thick and its height is the same as the arc-starting point height. Solid slag of the same thickness as the arc-starting point height is laid around the baffle. After the consumable electrode's end face comes into contact with the arc-starting agent, a mixture of low-carbon steel shavings and various alloy powders, it is pressed down 8mm, and then the arc-starting operation is performed by energizing the consumable electrode. Other operations follow the conventional solid-state arc-starting process. Test results: Arc-starting time 62 minutes, current fluctuation ±6%, voltage fluctuation ±6%, and the base plate does not stick to the electrode.

[0051] The above production test results show that using the present invention for arc starting in a billet electroslag furnace can effectively shorten the arc starting time by 15-18 minutes, stabilize the current and voltage control with a fluctuation range of ≤12%, reduce the time by more than 10% compared with the conventional process (solid arc starting), and achieve an arc starting success rate of 100%, with the bottom plate and electrode not sticking together.

[0052] 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 arc initiation in a billet electroslag furnace, characterized in that, Includes the following: 1) Chemical composition of low carbon steel scrap: Low carbon steel scrap is selected, and the chemical composition of the scrap by weight percentage is: C≤0.008%, P≤0.008%, S≤0.005%, TO≤0.005%, with the balance being Fe and unavoidable impurities; 2) Low carbon steel chips and alloy processing: Process low carbon steel into steel chips with a particle size of 5-10mm, and crush the required alloy into alloy powder with a particle size of 1-3mm. 3) The alloy powder is the same type as the composition of the remelted steel ingot formed by the consumable electrode remelting process; 4) Specifications and arrangement of the arc initiation point: Low-carbon steel scrap + alloy powder is used to replace the solid conductive block. The low-carbon steel scrap and various alloy powders are mixed evenly. The cross-section of the arc initiation point is circular or square, similar to the cross-sectional shape of the crystallizer. The center point coincides with the center point of the crystallizer. There is one arc initiation point. The area is 50%-70% of the cross-sectional area of ​​the shape enclosed by the crystallizer and the height is 40-60mm. At the same time, a baffle of the same material as the low-carbon steel scrap is provided around the arc initiation point. The thickness of the baffle is 0.5-1mm and the height is the same as the height of the arc initiation point. Solid slag material is laid around the arc, with the same height as the arc initiation point.

2. The arc-starting method for a billet electroslag furnace according to claim 1, characterized in that, After the consumable electrode end face comes into contact with an arc-initiating agent mixed with low-carbon steel chips and various alloy powders, it is pressed down 5-10mm, and then the consumable electrode is energized to start the arc.

3. The arc-starting method for a billet electroslag furnace according to claim 1, characterized in that, The chemical composition of low-carbon steel scrap, by weight percentage, is C: 0.005%–0.007%, P: 0.005%–0.007%, S: 0.002%–0.004%, and TO: 0.002%–0.004%.

4. The arc-starting method for a billet electroslag furnace according to claim 1, characterized in that, The steel shavings have a particle size of 6–8 mm, and the alloy powder has a particle size of 2–3 mm.

5. The arc-starting method for a billet electroslag furnace according to claim 1, characterized in that, The area of ​​the arc initiation point is 55%-65% of the cross-sectional area of ​​the shape enclosed by the crystallizer.

6. The arc-starting method for a billet electroslag furnace according to claim 1, characterized in that, The height of the arc starting point is 45-55mm.

7. The arc-starting method for a billet electroslag furnace according to claim 1, characterized in that, The solid slag material is a pre-melting slag material.

8. The arc-starting method for a billet electroslag furnace according to claim 1, characterized in that, After the self-consuming electrode end face comes into contact with the arc-initiating agent, which is a mixture of low-carbon steel shavings and various alloy powders, it is pressed down by 8-10mm.