Production method of 20Mn23AlV large flat steel ingot

Abstract

The invention discloses a production method of a 20Mn23AlV large flat steel ingot. The production method comprises the working procedures of EAF furnace primary smelting, LF furnace refining, VD furnace vacuum treatment and die casting pouring. In the die casting pouring process, low-carbon low-melting-point casting powder is used, and the use amount of the casting powder is 2.5-3 kg / t; the casting speed is 12-16 minutes for the body and 3-5 minutes for the cap opening. The weight of the 20Mn23AlV large flat steel ingot produced by the method is 10-30 t, the surface quality of the steel ingot is good, few inclusions exist, and the flaw detection qualification rate is high and reaches 98.5% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a production method of a 20Mn23AlV large flat steel ingot. Background Art

[0002] 20Mn23AlV is a high-manganese, low-magnetic steel with extremely low magnetic permeability, good mechanical properties and easy processing performance. It can replace low-magnetic austenitic stainless steel and non-ferrous alloys for the manufacture of non-magnetic components in electrical equipment such as transformers, magnetic separators and motors. It is a high-quality carbon structural steel. The production difficulties are as follows: (1) The liquidus temperature of 20Mn23AlV steel is low, and the surface quality of the steel ingot is difficult to control. The surface of the steel ingot forms a corrugated shape, or the surface is drawn into the protective slag to form a large number of slag pits; after the rolled steel plate is mechanically ground, the surface presents a large area of ​​fish-scale-like subcutaneous cracks with a depth of about 5-6mm. The grinding cost is extremely high, and the utilization rate of the steel plate is greatly reduced. (2) After the steel ingot is rolled, the inclusions inside the steel plate are likely to exceed the standard, resulting in unqualified flaw detection. The Al content in 20Mn23AlV steel is 1.50-2.50%, while the Al content in general steel grades is less than 0.06%. The molten steel is easily aspirated and secondary oxidized to form Al 2 O 3 Inclusions, large amounts of Al 2 O 3 Inclusions cause the flaw detection to be unqualified due to excessive inclusions. The flaw detection pass rate of wide and thick steel plates is often only 86% to 92%. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a production method of 20Mn23AlV large flat steel ingots. The produced 20Mn23AlV steel ingots have good surface quality, few inclusions and high flaw detection pass rate, reaching more than 98.5%.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: A production method of 20Mn23AlV large flat steel ingot comprises EAF furnace primary smelting, LF furnace refining, VD furnace vacuum treatment and mold casting pouring process.

[0005] Furthermore, in the EAF furnace primary smelting process of the present invention, the molten steel before tapping is controlled to have 0.06%≤C≤0.10%, P≤0.010%, and lime 2.0-3.0kg / t and silicon manganese 10-12kg / t are added with the steel flow. The tapping composition and the materials added during tapping are controlled so that the molten steel is not over-oxidized during tapping, and an appropriate amount of slag is initially formed to reduce secondary oxidation of the molten steel when it contacts the air.

[0006] Furthermore, the LF furnace refining process of the present invention firstly slags, deoxidizes and desulfurizes, adds 4-6 kg / t of refined pre-melted slag, 0.5-1.0 kg / t of calcium carbide, and 3-5 kg / t of lime, and rapidly slags and submerges the arc to raise the temperature; when the temperature reaches 1570-1590°C, 2.0-2.5 kg / t of strong deoxidizer aluminum wire is fed, and 0.5-0.8 kg / t of aluminum particles are added to produce white slag with higher basicity; electrolytic manganese is used to adjust the Mn element to 23.5-24.2%; when the temperature reaches 1590-1610°C, strong stirring (argon flow rate 400-600 NL / m in) for 3-5 minutes, take samples, and continue to adjust the composition to C: 0.13-0.15%, Si: 0.10-0.18%, Mn: 23.50-24.50%, V: 0.05-0.08%; stir with argon (argon flow rate 200-300NL / min) for 1.5-2.5 minutes, take samples, then slag, pour out 55-65% of the slag, feed 22-25kg / t of aluminum wire (the previous Al was mainly deoxidation, and the Al at this time is mainly alloying), add 2-4kg / t of refined pre-melted slag, and 2-4kg / t of fluorite. When the temperature reaches 1610-1620℃, take samples, and the LF refining is completed, and directly enter the VD furnace vacuum treatment process.

[0007] Quickly make a slag with good arc absorption and strong inclusion absorption ability. After the temperature reaches 1600℃, the slag is fully contacted with the inclusions in the steel through strong stirring, and most of the inclusions such as sulfides and oxides are absorbed into the slag. After stirring evenly, about 60% of the slag is removed, and re-adding refined pre-melted slag and fluorite can reduce the melting point of the slag, preparing for the later stage of the VD process to maintain good fluidity of the slag. The liquidus of this steel is only about 1415℃, which is 100℃ lower than ordinary low-alloy steel, and the pouring temperature is more than 60℃ lower than ordinary low-alloy steel. If the slag melting point is not reduced, the slag becomes viscous and has poor fluidity in the later stage of vacuum treatment due to the low temperature of the molten steel and the lower temperature of the slag, and the ability to absorb inclusions is greatly weakened; by reducing the melting point of the slag, the fluidity of the slag is improved, and the ability of the slag to absorb inclusions is improved, which can effectively reduce inclusions in the molten steel.

[0008] Furthermore, in the VD vacuum treatment process of the present invention, the component contents are fine-tuned to C: 0.16-0.17%, Si: 0.15-0.22%, Mn: 23.50-24.50%, Al: 2.00-2.50%, V: 0.05-0.08%, so that all components meet the target requirements; wherein Mn has a large fluctuation in the vacuum process and needs to be higher than the target value. Since the Mn element in the molten steel is as high as about 24%, Mn is easy to volatilize under vacuum conditions. Under the condition of ensuring the degassing effect, the vacuum time can be appropriately shortened to reduce the loss of Mn. Mn is adjusted to 1.0-1.5% higher than the target value; the vacuum degree is ≤66.7Pa and the treatment is carried out for 12-14 minutes, the argon flow rate is 100-150NL / min in the first 9-10 minutes, and the argon flow rate is 20-50NL / min in the last 2-3 minutes.

[0009] Furthermore, in the die casting pouring process of the present invention, the ladle pouring superheat of molten steel is 65-70°C, which is about 20°C higher than that of general alloy steel. This is mainly because the Al content in 20Mn23AlV steel is high and the fluidity of molten steel is greatly reduced. In order to ensure smooth pouring, the superheat is increased.

[0010] Furthermore, in the mold casting pouring process of the present invention, low-carbon and low-melting-point protective slag is used, and the amount of protective slag is 2.5-3kg / t; when the protective slag is used, 8-10kg / t of the steel ingot mold is hung, and the protective slag is 200-300mm away from the bottom of the mold. The rest is poured into the mold after breaking the protective slag bag after pouring, and the addition is completed within 2 minutes; the main performance parameters of the protective slag are: C: 5.0-7.0%, melting point: 800-900℃, and basicity 0.8-1.0. When 20Mn23AlV is poured, not only the temperature is low but also the fluidity of the molten steel is poor. The melting point of ordinary mold casting protective slag is 1100-1250℃. If ordinary protective slag is used, the protective slag will not have time to melt, and the solid protective slag will easily be drawn into the surface of the steel ingot, resulting in large areas of fish-scale subcutaneous cracks on the rolled steel plate. After using low-carbon and low-melting-point protective slag, the protective slag can be melted quickly by hanging it and then adding it in a scattered manner. The liquid slag is in contact with the molten steel, and the surface of the ingot is hardly involved in the protective slag, so the surface quality of the ingot is significantly improved.

[0011] Furthermore, in the mold casting process of the present invention, the pouring speed is: 12 to 16 minutes for the main body and 3 to 5 minutes for the cap. The purpose of pouring at a faster speed is to keep the molten steel in the ingot mold at a higher temperature during pouring, keep the protective slag in contact with the molten steel in a liquid state, and avoid slag rolling.

[0012] Furthermore, in the mold casting process of the present invention, argon is used between the nozzle and the center pouring pipe for protection. A fully enclosed protective cover is used to isolate the steel flow from the air during the casting process. 20Mn23AlV has a high Al content and is easily oxidized to form Al 2 O 3Inclusions, which are easy to gather and form large inclusions, causing the inclusions to exceed the standard and the flaw detection to fail.

[0013] Furthermore, the chemical composition and mass percentage of the 20Mn23AlV steel described in the present invention are: C: 0.14-0.20%, Si≤0.50%, Mn: 21.50-25.00%, P≤0.03%, S≤0.030%, Al: 1.50-2.50%, V: 0.04-0.10%, and the rest are Fe and unavoidable impurity elements.

[0014] The steel ingot produced by the method of the present invention has a weight of 10 to 30 t, the thickness of the rolled 20Mn23AlV steel plate is 10 to 80 mm, and the flaw detection qualified rate is ≥98.5%.

[0015] The 20Mn23AlV steel product standard and performance testing standard described in the present invention refer to GB / T 2975 "Steel and Steel Product Mechanical Properties Test Sampling Location and Sample Preparation", GJB 937 "Measurement Method of Magnetic Permeability of Weak Magnetic Materials"; ultrasonic flaw detection is performed on the steel plate according to GB / T2970-2016 standard, and the flaw detection level is Level II.

[0016] In the present invention, the unit kg / t refers to per ton of steel.

[0017] The performance indicators of the refined pre-melted slag of the present invention are as follows: melting point 1280-1350°C, refined slag composition H 2 O≤0.5%, CaO: 35~50%, Al 2 O 3 :35~45%,SiO 2 :2.0~5.0%,Fe 2 O 3 ≤1.5%, MgO: 2.0~5.0%, Na 2 O: 1.0~3.0%.

[0018] The beneficial effects of adopting the above technical solution are: 1. The present invention controls the steel composition and the addition of steel materials from the EAF primary furnace, so that the molten steel is not over-oxidized during steel tapping, and a proper amount of slag is initially formed to reduce secondary oxidation caused by the contact between the molten steel and the air.

[0019] 2. The LF furnace refining process of the present invention first produces slag with strong deoxidation ability, adds alloy, quickly removes most of the inclusions by stirring with large argon gas, and then removes 55-65% of the slag by slagging. On the one hand, it reduces the total amount of slag and facilitates vacuum operation, and on the other hand, it is convenient to reduce the melting point of slag by adding refined pre-melted slag and fluorite. The slag in the late vacuum stage has strong fluidity, improves the slag's ability to absorb inclusions, and has a significant effect on reducing inclusions in molten steel.

[0020] 3. In the VD vacuum treatment process of the present invention, the treatment is carried out for 12 to 14 minutes at a vacuum degree of ≤66.7Pa, which reduces the Mn loss by about 25 to 35% compared with the vacuum treatment for 20 minutes; the Mn element is easier to control, and the addition of Mn in the final stage can be avoided to bring in inclusions and affect the internal quality of the steel ingot.

[0021] 4. The mold casting process of the present invention reasonably uses low-carbon and low-melting-point protective slag and reasonably controls the injection speed, which greatly improves the surface quality of the steel ingot and almost eliminates subcutaneous cracks.

[0022] 5. The 20Mn23AlV steel produced by the method of the present invention has less inclusions, and the qualified rate of steel plate flaw detection reaches more than 98.5%, with significant benefits. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific embodiments. Example 1

[0024] In this embodiment, the electric furnace produces 22t*4 large flat ingots of 20Mn23AlV steel, and the production method includes EAF furnace primary refining, LF furnace refining, VD furnace vacuum treatment and mold casting. The specific process steps are as follows: (1) EAF furnace primary refining: planned steel production is 70 tons, C in molten steel before refining is 0.10%, P is 0.010%; according to the total molten steel volume of 92 tons at the end of refining, lime 3.0 kg / t and silicon manganese 12 kg / t are added.

[0025] (2) LF furnace refining: first slag deoxidation and desulfurization, add 5.5kg / t of refined pre-melted slag, 1.0kg / t of calcium carbide, and 5kg / t of lime; when the temperature reaches 1590℃, feed 2.5kg / t of strong deoxidizer aluminum wire and add 0.8kg / t of aluminum particles. Use electrolytic manganese to adjust the Mn element to 24%. When the temperature reaches 1600℃, strong stirring (argon flow rate 450NL / min) for 4 minutes, take samples, and continue to adjust the composition content to C: 0.13%, Si: 0.14%, Mn: 23.504%, V: 0.054%, argon stirring (argon flow rate 250NL / min) for 2 minutes to take samples, then skim off the slag, pour out about 62% of the slag, feed 24kg / t of aluminum wire, add 3kg / t of refined pre-melted slag and 3kg / t of fluorite. When the temperature reaches 1620℃, take samples, LF refining is completed, and directly enter the VD furnace vacuum treatment process.

[0026] (3) VD vacuum treatment: Before vacuum treatment, the composition content was fine-tuned to C: 0.17%, Si: 0.22%, V: 0.065%, Mn: 24.3%, Al: 2.05%. The treatment was carried out for 13 minutes at a vacuum degree of ≤ 66.7 Pa, with an argon flow rate of 150 NL / min in the first 10 minutes and 30 NL / min in the last 3 minutes.

[0027] (4) In the mold casting process, the overheating temperature of the molten steel ladle pouring is 67℃. Low-carbon and low-melting-point protective slag is used, and the amount of protective slag is 3kg / t. When the protective slag is used, 9.5kg / ingot mold is hung. The protective slag is 250mm away from the bottom of the mold. The rest is poured into the mold after the protective slag bag is opened after pouring. It should be added within 2 minutes. The main performance parameters of the protective slag are: C: 5.8%, melting point: 840℃, basicity 0.88. Argon protection is used for pouring, and the pouring speed is 14 minutes for the main body and 4 minutes for the cap.

[0028] The chemical composition of the 20Mn23AlV steel in this embodiment is: C: 0.17%, Si: 0.24%, Mn: 23.01%, P: 0.011%, S: 0.0022%, Al: 1.778%, V: 0.065%, and the rest are Fe and unavoidable impurity elements.

[0029] The finished steel plate of 20Mn23AlV steel in this embodiment has a thickness of 20 mm, has no subcutaneous cracks, and the flaw detection meets the standard GB / T2970-2016 Level II, with a flaw detection pass rate of 98.9%. Example 2

[0030] In this embodiment, the electric furnace produces 26t*4 large flat steel ingots of 20Mn23AlV steel. The production method includes EAF furnace primary refining, LF furnace refining, VD furnace vacuum treatment and mold casting. The specific process steps are as follows: (1) EAF furnace primary refining: planned steel production is 81 tons, C in molten steel before refining is 0.06%, P is 0.009%; according to the total molten steel volume of 107 tons at the end of refining, lime 2.0 kg / t and silicon manganese 10 kg / t are added.

[0031] (2) LF furnace refining: First, slag deoxidation and desulfurization, add 4kg / t of refined pre-melted slag, 0.5kg / t of calcium carbide, and 5kg / t of lime. When the temperature reaches 1570℃, feed 2.0kg / t of strong deoxidizer aluminum wire and add 0.5kg / t of aluminum particles. Use electrolytic manganese to adjust the Mn element to 24%. When the temperature reaches 1610℃, stir strongly (argon flow rate 600NL / min) for 3 minutes, take samples, and continue to adjust the composition content to C: 0.15%, Si: 0.15%, Mn: 24.50%, V: 0.08%. Stir with argon (argon flow rate 300NL / min) for 1.5 minutes and take samples, then skim off the slag, pour out about 65% of the slag, feed 22kg / t of aluminum wire, add 2.5kg / t of refined pre-melted slag and 3kg / t of fluorite. When the temperature reaches 1610℃, take samples, LF refining is completed, and directly enter the VD furnace vacuum treatment process.

[0032] (3) VD vacuum treatment: Before vacuum treatment, the composition content was fine-tuned to C: 0.16%, Si: 0.22%, V: 0.058%, Mn: 24.0%, Al: 2.00%. The treatment was carried out for 12 minutes at a vacuum degree of ≤ 66.7 Pa, with an argon flow rate of 120 NL / min in the first 10 minutes and 20 NL / min in the last 3 minutes.

[0033] (4) Mold casting: The overheating temperature of the molten steel ladle pouring is 65℃. Use low-carbon and low-melting-point protective slag, the amount of protective slag is 3kg / t, and the protective slag is hung on 8-10kg / ingot mold when using it. The protective slag is 290mm away from the bottom of the mold. The rest is poured into the mold after the protective slag bag is opened after pouring, and it should be added within 2 minutes; the main performance parameters of the protective slag are: C: 6.5%, melting point: 880℃, basicity 0.96. Use argon protection for pouring, and the pouring speed is 16 minutes for the main body and 5 minutes for the cap.

[0034] The chemical composition of the 20Mn23AlV steel in this embodiment is: C: 0.18%, Si: 0.35%, Mn: 23.12%, P: 0.015%, S: 0.0031%, Al: 1.732%, V: 0.059%, and the rest are Fe and unavoidable impurity elements.

[0035] The finished steel plate of 20Mn23AlV steel in this embodiment has a thickness of 65 mm, has no subcutaneous cracks, and the flaw detection meets the standard GB / T2970-2016 Level II, with a flaw detection pass rate of 98.5%. Example 3

[0036] In this embodiment, the electric furnace produces 30t*3 20Mn23AlV steel large flat ingots. The production method includes EAF furnace primary refining, LF furnace refining, VD furnace vacuum treatment and mold casting. The specific process steps are as follows: (1) EAF furnace primary refining: planned steel production is 71 tons, C in molten steel before refining is 0.07%, P is 0.006%; according to the total molten steel volume of 93 tons at the end of refining, lime 3.0 kg / t and silicon manganese 11 kg / t are added.

[0037] (2) LF furnace refining: First, slag deoxidation and desulfurization, add 4kg / t of refined pre-melted slag, 0.8kg / t of calcium carbide, and 5kg / t of lime. When the temperature reaches 1580℃, feed 2.5kg / t of strong deoxidizer aluminum wire and add 0.5kg / t of aluminum particles. Use electrolytic manganese to adjust the Mn element to 24%. When the temperature reaches 1600℃, stir strongly (argon flow rate 600NL / min) for 3.5 minutes, take samples, and continue to adjust the composition content to C: 0.15%, Si: 0.18%, Mn: 23.50%, V: 0.07%. Stir with argon (argon flow rate 280NL / min) for 2.5 minutes and take samples, then skim off the slag, pour out about 60% of the slag, feed 24kg / t of aluminum wire, add 3.8kg / t of refined pre-melted slag and 2kg / t of fluorite. When the temperature reaches 1618℃, take samples, LF refining is completed, and directly enter the VD furnace vacuum treatment process.

[0038] (3) VD vacuum treatment: Before vacuum treatment, the composition content was fine-tuned to C: 0.16%, Si: 0.21%, V: 0.068%, Mn: 24.5%, Al: 2.10%. The treatment was carried out for 14 minutes at a vacuum degree of ≤ 66.7 Pa, with an argon flow rate of 150 NL / min in the first 10 minutes and an argon flow rate of 50 NL / min in the last 3 minutes.

[0039] (4) Mold casting: The overheating temperature of the molten steel ladle pouring is 70℃. Use low-carbon and low-melting point protective slag, the amount of protective slag is 2.5kg / t, and the protective slag is hung on the steel ingot mold with 8-10kg / t. The protective slag is 220mm away from the bottom of the mold. The rest is poured into the mold after the protective slag bag is opened after pouring, and it should be added within 2 minutes; the main performance parameters of the protective slag are: C: 5.8%, melting point: 850℃, basicity 0.9. Use argon protection for pouring, and the pouring speed is 16 minutes for the main body and 4 minutes for the cap.

[0040] The chemical composition of the 20Mn23AlV steel in this embodiment is: C: 0.16%, Si: 0.44%, Mn: 22.86%, P: 0.016%, S: 0.0018%, Al: 1.84%, V: 0.068%, and the rest are Fe and unavoidable impurity elements.

[0041] The finished steel plate of 20Mn23AlV steel in this embodiment has a thickness of 50 mm, has no subcutaneous cracks, and the flaw detection meets the standard GB / T2970-2016 Level II, with a flaw detection pass rate of 98.9%. Example 4

[0042] In this embodiment, the electric furnace produces 11t*8 20Mn23AlV steel large flat ingots, and the production method includes EAF furnace primary refining, LF furnace refining, VD furnace vacuum treatment and mold casting. The specific process steps are as follows: (1) EAF furnace primary refining: planned steel production is 70 tons, C in molten steel before refining is 0.08%, P is 0.009%; according to the total molten steel volume of 92 tons at the end of refining, lime 2.5 kg / t and silicon manganese 11 kg / t are added.

[0043] (2) LF furnace refining: first slag deoxidation and desulfurization, add refined pre-melted slag 5.5kg / t, calcium carbide 0.7kg / t, lime 4.5kg / t, temperature reaches 1585℃, feed strong deoxidizer aluminum wire 2.3kg / t, add aluminum particles 0.55 / t. Use electrolytic manganese to adjust the Mn element to 24%. The temperature reaches 1600℃, strong stirring (argon flow rate 550NL / min) for 5 minutes, sampling, and continue to adjust the composition content to C: 0.15%, Si: 0.17%, Mn: 724.50%, V: 0.08%, argon (argon flow rate 300NL / min) stirring for 2.2 minutes to take samples, then slag, pour out about 58% of the slag, feed aluminum wire 23.5kg / t, add refined pre-melted slag 2.5kg / t, fluorite 3.5kg / t. When the temperature reaches 1609℃, sampling is taken, LF refining is completed, and the product directly enters the vacuum treatment process in the VD furnace.

[0044] (3) VD vacuum treatment: Before vacuum treatment, the composition content was fine-tuned to C: 0.17%, Si: 0.21%, V: 0.071%, Mn: 23.5%, Al: 2.45%. The treatment was carried out for 12.5 minutes at a vacuum degree of ≤ 66.7 Pa, with an argon flow rate of 145 NL / min in the first 10 minutes and 35 NL / min in the last 3 minutes.

[0045] (4) Mold casting: The overheating temperature of the molten steel ladle pouring is 70℃. Use low-carbon and low-melting-point protective slag, the amount of protective slag is 2.8kg / t, and the protective slag is hung on 8kg / ingot mold when using it. The protective slag is 200mm away from the bottom of the mold. The rest is poured into the mold after the protective slag bag is opened after pouring, and it should be added within 2 minutes; the main performance parameters of the protective slag are: C: 5.0%, melting point: 900℃, basicity 0.8. Use argon protection for pouring, and the pouring speed is 12 minutes for the main body and 3 minutes for the cap.

[0046] The chemical composition of the 20Mn23AlV steel in this embodiment is: C: 0.19%, Si: 0.34%, Mn: 22.6%, P: 0.018%, S: 0.0025%, Al: 1.962%, V: 0.071%, and the rest are Fe and unavoidable impurity elements.

[0047] The finished steel plate of 20Mn23AlV steel in this embodiment has a thickness of 20 mm, has no subcutaneous cracks, and the flaw detection meets the standard GB / T2970-2016 Level II, with a flaw detection pass rate of 99.5%. Example 5

[0048] In this embodiment, the electric furnace produces 20t*5 20Mn23AlV steel large flat ingots. The production method includes EAF furnace primary refining, LF furnace refining, VD furnace vacuum treatment and mold casting. The specific process steps are as follows: (1) EAF furnace primary refining: planned steel production is 79 tons, C in molten steel before refining is 0.07%, P is 0.004%; according to the total molten steel volume at the end of refining is 104 tons, lime 2.5 kg / t, silicon manganese 10.5 kg / t are added.

[0049] (2) LF furnace refining: first slag deoxidation and desulfurization, add refined pre-melted slag 4.5kg / t, calcium carbide 1.0kg / t, lime 4.53~5kg / t, temperature reaches 1578℃, feed strong deoxidizer aluminum wire 2.3kg / t, add aluminum particles 0.59kg / t. Use electrolytic manganese to adjust the Mn element to 24%. The temperature reaches 1600℃, strong stirring (argon flow rate 480NL / min) for 4.5 minutes, sampling, and continue to adjust the composition content to C: 0.145%, Si: 0.13%, Mn: 23.85%, V: 0.07%, argon stirring (argon flow rate 260NL / min) for 1.8 minutes to take samples, then slag, pour out about 65% of the slag, feed aluminum wire 23kg / t, add refined pre-melted slag 2.5kg / t, fluorite 3.5kg / t. When the temperature reaches 1615℃, sampling is taken, LF refining is completed, and the product directly enters the vacuum treatment process in the VD furnace.

[0050] (3) VD vacuum treatment: Mn: 23.5%, Al: 2.35% before vacuum treatment. Treatment for 13.5 min at a vacuum degree of ≤66.7 Pa, with an argon flow rate of 140 NL / min in the first 10 minutes and 40 NL / min in the last 3 minutes.

[0051] (4) Mold casting: The overheating temperature of the molten steel ladle pouring is 68℃. Use low-carbon and low-melting point protective slag, the amount of protective slag is 2.5kg / t, and the protective slag is hung on 10kg / ingot mold when using it. The protective slag is 300mm away from the bottom of the mold. The rest is poured into the mold after the protective slag bag is opened after pouring, and it should be added within 2 minutes; the main performance parameters of the protective slag are: C: 7.0%, melting point: 800℃, basicity 1.0. Use argon protection for pouring, and the pouring speed is 13 minutes for the main body and 4.5 minutes for the cap.

[0052] The chemical composition of the 20Mn23AlV steel in this embodiment is: C: 0.16%, Si: 0.35%, Mn: 23.25%, P: 0.014%, S: 0.0023%, Al: 1.863%, V: 0.061%, and the rest are Fe and unavoidable impurity elements.

[0053] The finished steel plate of 20Mn23AlV steel in this embodiment has a thickness of 20 mm, has no subcutaneous cracks, and the flaw detection meets the standard GB / T2970-2016 Level II, with a flaw detection pass rate of 98.8%.

[0054] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for producing a large 20Mn23AlV flat steel ingot, comprising the steps of primary smelting in an EAF furnace, refining in an LF furnace, vacuum treatment in a VD furnace and mold casting; in the mold casting step, low-carbon and low-melting-point protective slag is used, and the amount of protective slag is 2.5-3kg / t; the casting speed is: 12-16 minutes for the main body and 3-5 minutes for the cap.

2. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: In the EAF furnace primary smelting process, the molten steel before tapping is controlled to have 0.06%≤C≤0.10%, P≤0.010%, and 2.0-3.0 kg / t of lime and 10-12 kg / t of silicon manganese are added along with the steel flow.

3. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: The LF furnace refining process comprises the following steps: firstly slagging, deoxidation and desulfurization, adding 4-6 kg / t of refined pre-melted slag, 0.5-1.0 kg / t of calcium carbide and 3-5 kg / t of lime, and rapidly slagging and submerging arc heating; when the temperature reaches 1570-1590°C, 2.0-2.5 kg / t of strong deoxidizer aluminum wire is fed, and 0.5-0.8 kg / t of aluminum particles are added; electrolytic manganese is used to adjust the Mn element to 23.5-24.2%; when the temperature reaches 1590-1610°C, argon gas flow rate of 400-600 NL / min is used for strong stirring for 3-5 minutes, sampling is performed, and further adjustment is performed. The composition content is C: 0.13-0.15%, Si: 0.10-0.18%, Mn: 23.50-24.50%, V: 0.05-0.08%; use argon flow rate of 200-300NL / min to stir for 1.5-2.5 minutes, take samples, then skim the slag, pour out 55-65% of the slag, feed 22-25kg / t of aluminum wire, add 2-4kg / t of refined pre-melted slag and 2-4kg / t of fluorite; take samples when the temperature reaches 1610-1620℃, LF refining is completed, and directly enters the VD furnace vacuum treatment process.

4. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: The VD vacuum treatment process fine-tunes the component content to C: 0.16-0.17%, Si: 0.15-0.22%, Mn: 23.50-24.50%, Al: 2.00-2.50%, V: 0.05-0.08%; the treatment is carried out for 12-14 minutes at a vacuum degree of ≤66.7Pa, the argon gas flow rate is 100-150NL / min in the first 9-10 minutes, and the argon gas flow rate is 20-50NL / min in the last 2-3 minutes.

5. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: In the mold casting process, the molten steel ladle pouring overheats to 65-70°C.

6. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: In the mold casting process, the main performance parameters of the low-carbon and low-melting-point protective slag are: C: 5.0-7.0%, melting point: 800-900°C, and basicity 0.8-1.

0.

7. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: In the mold casting pouring process, the low-carbon and low-melting-point protective slag is used to hang 8-10kg / ingot mold, the protective slag is 200-300mm away from the bottom of the mold, and the rest is poured into the mold after the protective slag bag is opened after pouring, and the addition is completed within 2 minutes.

8. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: In the mold casting process, argon gas is used to protect the casting between the nozzle and the center injection pipe.

9. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: The weight of the flat steel ingot is 10 to 30 tons.

10. The method for producing a 20Mn23AlV large flat steel ingot according to claim 1, characterized in that: The chemical composition and mass percentage of the 20Mn23AlV steel are: C: 0.14-0.20%, Si≤0.50%, Mn: 21.50-25.00%, P≤0.03%, S≤0.030%, Al: 1.50-2.50%, V: 0.04-0.10%, and the rest are Fe and unavoidable impurity elements.