Method for reducing shrinkage cavity depth of electroslag remelting steel ingot

Abstract

The invention discloses a method for reducing the shrinkage cavity depth of an electroslag remelting steel ingot. The method comprises the following steps: preparing a special-shaped consumable electrode with a thick lower part and a thin upper part; selecting slag charge with alkalinity of more than or equal to 5 and viscosity of less than or equal to 0.08 Pa.s; welding the thin end of the consumable electrode with the dummy electrode; lowering the consumable electrode until the thick end of the consumable electrode reaches the bottom in the crystallizer, and adding slag into the crystallizer for slagging after arcing; smelting is started after the slag is cleared; the feeding amount is 4-6% of the weight of the steel ingot, the feeding current is reduced to 40-60% of the normal smelting current, and the feeding time accounts for 15% of the total smelting time. According to the method, the novel special-shaped consumable electrode with the thick lower part and the thin upper part is used, the high-alkalinity and low-viscosity slag charge is selected, and the current is reasonably reduced in the feeding process, so that the head shrinkage cavity is fully filled with the molten liquid, the effect of reducing the shrinkage cavity depth is achieved, the shrinkage cavity depth is reduced by more than 20mm, and the yield of the electroslag remelting steel ingot is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for reducing the shrinkage depth of electroslag remelted steel ingots. Background Technology

[0002] The core of electroslag remelting feeding is to form a "hot cap" on the top of the ingot to compensate for solidification shrinkage by precisely controlling the metallurgical reaction and solidification process. During the feeding stage, the melting rate of the metal is reduced and the high temperature of the slag pool (1700~1800℃) is maintained, thereby prolonging the existence time of the molten metal at the top and causing the shrinkage cavities to concentrate in the removable parts of the ingot head.

[0003] Currently, the electroslag remelting process uses automatic constant melting rate smelting. The consumable electrode generally uses cylindrical mold casting billets or continuous casting billets of uniform diameter. As electroslag remelting proceeds, the radial cooling intensity of the electroslag ingot decreases with the increase of the steel ingot height, while the filling ratio remains unchanged or increases (the size of the electroslag crystallizer is larger at the bottom and smaller at the top). This leads to an increase in the heat of the molten pool and a deeper molten pool. After entering the feeding stage, even if the input power is reduced, the melting rate does not decrease significantly, resulting in a shortened effective feeding time and a deeper shrinkage cavity. This is especially true for products such as tool steel with large solidification shrinkage. For example, the shrinkage cavity depth of 5~12t electroslag ingots can reach 120~160mm, which affects the yield of electroslag ingots. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, the present invention provides a method for reducing the shrinkage depth of electroslag remelted steel ingots, comprising: Step S1: Fabricate an irregular consumable electrode, wherein the consumable electrode is fabricated as an irregular structure with a thicker bottom and a thinner top, and the diameter of the lower section of the consumable electrode is D. x =0.8×D j The diameter of the upper section of the consumable electrode is D. s =0.7×D j , where D x D is the diameter of the lower section of the consumable electrode, in mm. s D is the diameter of the upper section of the consumable electrode, in mm. j D is the average diameter of the crystallizer. j =(lower diameter of crystallizer + upper diameter of crystallizer) / 2, unit: mm; Step S2: Select slag material with basicity ≥ 5 and viscosity ≤ 0.08 Pa·s; Step S3: Weld the thin end of the consumable electrode to the dummy electrode; Step S4: Control the consumable electrode to descend until the thick end of the consumable electrode reaches the bottom of the crystallizer. After arcing, add slag material evenly into the crystallizer to slag. Step S5: After the slag is cleared, smelting begins; Step S6: Perform feeding, with the feeding amount controlled at 4%~6% of the ingot weight, the feeding current reduced to 40~60% of the normal smelting current, and the feeding time controlled to be greater than 15% of the total smelting time; Step S7: Cool and demold the electroslag remelted steel ingot.

[0005] Furthermore, in step S1 above, the irregular consumable electrode is prepared such that the length of the lower section of the consumable electrode accounts for 2 / 3 of the total length of the consumable electrode, and the length of the upper section of the consumable electrode accounts for 1 / 3 of the total length of the consumable electrode.

[0006] Furthermore, in step S2 above, the chemical composition of the slag material by weight percentage is: Al2O3=20~25%, CaO=10~20%, SiO2=1~2%, and the remainder is CaF2.

[0007] Furthermore, in step S2 above, each component in the slag is pre-melted before use.

[0008] Furthermore, in step S5 above, the melting rate is calculated according to 0.72 D. j ~0.78D j The value is controlled, and the unit is kg / h.

[0009] Preferably, in the above method for reducing the shrinkage depth of electroslag remelted steel ingots, one electrode remelts one steel ingot during the electroslag remelting process, without exchanging electrodes.

[0010] The method for reducing the shrinkage depth of electroslag remelted steel ingots of the present invention has the following advantages and beneficial effects: This invention utilizes a novel, non-circular consumable electrode with a coarser bottom and a thinner top, which reduces the filling ratio of the upper section of the electrode, thereby enhancing the axial heat flow of the molten metal. When the power is reduced during the feeding stage, the heat input to the molten pool by the small-diameter electrode decreases rapidly, making the molten pool shallower and flatter. This allows the shrinkage cavity to rise to the ingot head. Furthermore, by selecting slag with a basicity ≥5 and viscosity ≤0.08 Pa·s, the heating efficiency of the slag pool is improved, the ability to remove inclusions is enhanced, and the viscosity of the slag system is reduced to shorten the metal solidification time. Simultaneously, by reasonably reducing the current during the feeding process, the heat input to the molten pool is reduced, the hot zone is moved upward, and the feeding time is controlled to exceed 15% of the total smelting time, allowing the molten metal to fully fill the head shrinkage cavity. This achieves the effect of reducing the shrinkage cavity depth, decreasing the shrinkage cavity depth of 5~12t electroslag ingots from the existing 120~160mm to 80~100mm, significantly improving the yield of electroslag ingots. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of the present invention and constitute a part of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the consumable electrode used in the method for reducing the shrinkage depth of electroslag remelted steel ingots according to the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0013] The method for reducing the shrinkage depth of electroslag remelted steel ingots provided by this invention includes: Step S1: Fabrication of irregular consumable electrode, see [link to documentation]. Figure 1 The consumable electrode, for example, is prepared by forging into an irregular structure that is thicker at the bottom and thinner at the top. The length of the lower section accounts for 2 / 3 of the total length of the consumable electrode, and the diameter is D. x =0.8×D j The upper section accounts for 1 / 3 of the total length of the consumable electrode, and its diameter is D. s =0.7×D j , where D x D is the diameter of the lower section of the consumable electrode, in mm. s D is the diameter of the upper section of the consumable electrode, in mm. j D is the average diameter of the crystallizer. j =(lower diameter of crystallizer + upper diameter of crystallizer) / 2, unit: mm; Compared with the consumable electrode of uniform diameter in the prior art, the present invention adopts an irregular consumable electrode with a thicker bottom and a thinner top. The cross-sectional area of ​​the upper section of the consumable electrode is smaller than that of the lower section, so the filling ratio of the upper section of the consumable electrode is reduced accordingly. This can enhance the axial heat flow of the melt. When the power is reduced during the feeding stage, the heat input to the molten pool by the small diameter electrode will decrease rapidly, making the molten pool shallow and flat, thereby causing the shrinkage cavity to float to the ingot head.

[0014] It should be noted that the filling ratio refers to the proportion of the consumable electrode within the crystallizer, i.e.: Filling ratio = Electrode cross-sectional area / Crystallizer cross-sectional area. For the irregularly shaped consumable electrode of this invention, since the lower segment length and upper segment length account for 2 / 3 and 1 / 3 of the total length of the consumable electrode, respectively, and the lower segment diameter and upper segment diameter are respectively D... x =0.8×D j and D s =0.7×D j Therefore, the filling ratio of the top 1 / 3 of the consumable electrode is 0.7, and the filling ratio of the remaining 2 / 3 of the consumable electrode is 0.8.

[0015] Step S2: Select slag with basicity (CaO / SiO2) ≥ 5 and viscosity ≤ 0.08 Pa·s. The chemical composition of the slag by weight percentage is: Al2O3 = 20~25%, CaO = 10~20%, SiO2 = 1~2%, and the remainder is CaF2. The components in the slag are pre-melted according to the above proportions before use. By selecting high-basicity slag with a basicity ≥5, the heating efficiency of the slag pool can be improved, and the ability to remove inclusions can be enhanced. The CaF2 and 1-2% SiO2 in the slag can reduce the viscosity of the slag system, ensuring its fluidity. A high-fluidity slag system allows for more flexible step-down current regulation strategies, and precise control of the hot spot location can effectively reduce the depth of shrinkage cavities. Simultaneously, by limiting the slag viscosity to ≤0.08 Pa·s, a low-viscosity slag system can shorten the metal solidification time.

[0016] Step S3: Weld the thin end of the consumable electrode to the dummy electrode, ensuring the weld is straight and strong; Step S4: Control the consumable electrode to descend until the thick end of the consumable electrode reaches the bottom of the crystallizer. After arcing, add slag material evenly into the crystallizer to slag. Step S5: After the slag is cleared, smelting begins, with a melting rate of 0.72D. j ~0.78D j The value of D is controlled, and the unit is kg / h, where D j It is the average diameter of the crystallizer, expressed in mm; Step S6: Perform feeding, with the feeding amount controlled at 4%~6% of the ingot weight, the feeding current reduced to 40~60% of the normal smelting current, and the feeding time controlled to be greater than 15% of the total smelting time; The amount of feeding is calculated based on the solidification shrinkage rate of the steel grade and set to 4-6% of the ingot weight. The feeding process mainly involves reducing the current, lowering it to 40-60% of the normal smelting current to reduce heat input to the molten pool and shift the hot zone upwards, which helps to reduce the depth of the shrinkage cavity. In addition, controlling the feeding time to exceed 15% of the total smelting time ensures that the molten liquid fully fills the head shrinkage cavity.

[0017] Step S7: Cool and demold the electroslag remelted steel ingot.

[0018] Furthermore, in the method for reducing the shrinkage depth of electroslag remelted steel ingots of the present invention, one electrode remelts one steel ingot during the electroslag remelting process without exchanging electrodes.

[0019] The method for reducing the shrinkage depth of electroslag remelted steel ingots according to the present invention is further illustrated below with reference to specific embodiments.

[0020] Example 1 The electroslag remelted steel ingot involved in Example 1 of this invention uses H13 steel, and its main chemical composition by weight percentage is: C=0.39%, Si=1.05%, Mn=0.38%, Cr=5.21%, Ni=0.51%, Mo=1.55%, V=0.97%. The diameter of the crystallizer is... 970mm / 1030mm (i.e., the large diameter of the lower part of the crystallizer is...) 1030mm, the smaller diameter of the upper part of the crystallizer is 970mm, average diameter D of crystallizer j The ingot is 1000mm thick and weighs 12t. The specific process of Example 1 includes: Step S1: Forge a non-circular consumable electrode with a coarser lower section and a finer upper section. The lower section of the consumable electrode accounts for 2 / 3 of the total length of the consumable electrode and has a diameter of Dx = 0.8 × Dj = 800 mm. The upper section of the consumable electrode accounts for 1 / 3 of the total length of the consumable electrode and has a diameter of Ds = 0.7 × Dj = 700 mm. Step S2: Select slag material with basicity ≥ 5 and viscosity ≤ 0.08 Pa·s. The chemical composition of the slag material by weight percentage is: CaF2=62%, Al2O3=23%, CaO=14%, SiO2=1.0%, and the amount of slag is 480 kg. Step S3: Weld the thin end of the consumable electrode to the dummy electrode, ensuring the weld is straight and strong; Step S4: Lower the consumable electrode until its coarse end reaches the bottom of the crystallizer. After arcing, add slag material evenly into the crystallizer to slag. Step S5: After the slag is cleared, smelting begins. The melting rate is 750 kg / h, the total smelting time is 16 hours, the smelting current is 15500~16500A, and the smelting voltage is 45~50V. Step S6: Perform compensation feeding, with a compensation amount of 600 kg, a compensation current of 7500~8500 A, and a compensation time of 150~170 min; Step S7: Cool and demold the electroslag remelted steel ingot.

[0021] Ultrasonic testing was performed on the head of the H13 steel ingot obtained from smelting, and the shrinkage cavity depth was 90 mm. However, using existing electroslag remelting technology, the shrinkage cavity depth at the head of the resulting ingot was 115 mm. Therefore, compared to existing technology, this invention can reduce the shrinkage cavity depth of the electroslag remelted steel ingot by more than 20 mm, significantly improving the yield of the electroslag remelted steel ingot.

[0022] Example 2 The electroslag remelting steel ingot involved in Example 2 of this invention uses S136 (4Cr13) steel, and its main chemical composition by weight percentage is: C=0.38%, Si=0.91%, Mn=0.50%, Cr=13.61%, Ni=0.95%, Mo=0.22%. The diameter of the crystallizer is... 790mm / 830 (i.e., the large diameter of the lower part of the crystallizer is...) 830mm, the smaller diameter of the upper part of the crystallizer is 790mm, average diameter D of crystallizer j The ingot is 810mm thick and weighs 7.6t. The specific process of Example 2 includes: Step S1: Forge an irregularly shaped consumable electrode with a coarser lower section and a finer upper section. The lower section of the consumable electrode accounts for 2 / 3 of the total length of the consumable electrode, and its diameter is D. x =0.8×D j =648mm, the upper section of the consumable electrode accounts for 1 / 3 of the total length of the consumable electrode, and the diameter is D. s =0.7×D j =567mm; Step S2: Select slag material with basicity ≥5 and viscosity ≤0.08Pa·s. The chemical composition of the slag material by weight percentage is: CaF2=60%, Al2O3=23%, CaO=15.5%, SiO2=1.5%, and the amount of slag is 260kg. Step S3: Weld the thin end of the consumable electrode to the dummy electrode, ensuring the weld is straight and strong; Step S4: Lower the consumable electrode until its coarse end reaches the bottom of the crystallizer. After arcing, add slag material evenly into the crystallizer to slag. Step S5: After the slag is cleared, smelting begins. The melting rate is 610 kg / h, the total smelting time is 12 hours, the smelting current is 13500~14500A, and the smelting voltage is 45~50V. Step S6: Perform compensation feeding, with a compensation amount of 380 kg, a compensation current of 7000~8000 A, and a compensation time of 110~130 min; Step S7: Cool and demold the electroslag remelted steel ingot.

[0023] Ultrasonic testing was performed on the head of the S136 steel ingot obtained from smelting, and the shrinkage cavity depth was 85 mm. However, using existing electroslag remelting technology for S136 steel ingots, the shrinkage cavity depth at the head of the resulting ingot is 110 mm. Therefore, compared to existing technology, this invention can reduce the shrinkage cavity depth of electroslag remelted steel ingots by more than 20 mm, significantly improving the yield of electroslag remelted steel ingots.

[0024] In summary, this invention utilizes a novel consumable electrode with a coarser bottom and a finer top, which reduces the filling ratio of the upper section of the electrode, thereby enhancing the axial heat flow of the molten metal. When the power is reduced during the feeding stage, the heat input to the molten pool by the small-diameter electrode decreases rapidly, making the molten pool shallower and flatter. This allows the shrinkage cavity to rise to the ingot head. Furthermore, by selecting slag with a basicity ≥5 and viscosity ≤0.08 Pa·s, the heating efficiency of the slag pool is improved, the ability to remove inclusions is enhanced, and the viscosity of the slag system is reduced to shorten the metal solidification time. Simultaneously, by reasonably reducing the current during the feeding process, the heat input to the molten pool is reduced, the hot zone is moved upward, and the feeding time is controlled to exceed 15% of the total smelting time, allowing the molten metal to fully fill the head shrinkage cavity. This achieves the effect of reducing the shrinkage cavity depth, decreasing the shrinkage cavity depth of 5~12t electroslag ingots from the existing 120~160mm to 80~100mm, significantly improving the yield of electroslag ingots.

[0025] It should be noted that, unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, when a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum. Further, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe features, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] It should also be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method of reducing the depth of shrinkage cavity in an electroslag remelted ingot, characterized by, The application relates to a method for producing a steel ingot by using an electric-shock remelting process. Step S1: preparing a profiled consumable electrode, the consumable electrode is prepared as a profiled structure of thick bottom and thin top, the diameter of the lower section of the consumable electrode is D x =0.8×D j , the diameter of the upper section of the consumable electrode is D s =0.7×D j , wherein D x is the diameter of the lower section of the consumable electrode, in mm, D s is the diameter of the upper section of the consumable electrode, in mm, D j is the average diameter of the crystallizer, D j =(the large diameter of the lower section of the crystallizer+the small diameter of the upper section of the crystallizer) / 2, in mm; Step S2: selecting slag with alkalinity greater than or equal to 5 and viscosity less than or equal to 0.08 Pa.s; Step S3: welding the thin end of the consumable electrode and the dummy electrode together; Step S4: controlling the consumable electrode to descend until the thick end of the consumable electrode reaches the bottom of the crystallizer, and then adding the slag into the crystallizer to perform slagging after starting the arc; Step S5: starting smelting after the slagging is completed; Step S6: performing feeding, and the feeding amount is controlled to be 4%-6% of the weight of the steel ingot, the feeding current is reduced to 40-60% of the normal smelting current, and the feeding time accounts for more than 15% of the total smelting time; Step S7: performing mold cooling and demolding on the electric-shock remelted steel ingot.

2. The method of reducing the depth of a cavity in an electroslag remelted ingot as defined in claim 1, wherein, In step S1, the special-shaped consumable electrode is prepared as follows: the length of the lower section of the consumable electrode accounts for 2 / 3 of the total length of the consumable electrode, and the length of the upper section of the consumable electrode accounts for 1 / 3 of the total length of the consumable electrode.

3. The method of reducing the depth of a cavity in an electroslag remelted ingot as claimed in claim 1, wherein, In step S2, the chemical components of the slag are as follows in percentage by weight: Al2O3=20-25%, CaO=10-20%, SiO2=1-2%, and the rest is CaF2.

4. The method of reducing the depth of a cavity in an electroslag remelted ingot as defined in claim 3, wherein, In step S2, each component in the slag is pre-melted and then used.

5. The method of reducing the depth of a cavity in an electroslag remelted ingot as claimed in claim 1, wherein, In step S5, the melting rate is controlled to a value of 0.72 D j 0.78 D j kg / h.

6. The method of reducing the depth of a cavity in an electroslag remelted ingot as defined in claim 1, wherein, In the electric-shock remelting process, one electrode is used to remelt one steel ingot, and the electrodes are not exchanged.

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