A method for producing ultra-high cleanliness steel by using horizontal ladle electromagnetic stirring

Abstract

The present invention belongs to the technical field of steelmaking process, and specifically relates to a method for producing ultra-high clean steel by utilizing electromagnetic stirring of a horizontal ladle, and adopts the "BOF-LF (ladle with horizontal electromagnetic stirring)-RH (ladle with horizontal electromagnetic stirring)-CC" process route. BOF is responsible for decarburization, dephosphorization and ensuring a certain tapping temperature, LF adjusts the composition, temperature and inclusion removal of the molten steel, and RH and the ladle with electromagnetic stirring are responsible for degassing, inclusion removal and other tasks. During LF refining, by controlling the horizontal electromagnetic stirring (forward and reverse) of the ladle + bottom argon blowing vertical system, the traditional simple large-flow vertical bottom argon blowing stirring system is replaced to better suppress the slag rolling during ladle refining, and then the RH is combined with the electromagnetic stirring of the ladle + bottom argon blowing to improve the RH stirring effect, so as to achieve efficient removal of inclusions in this process, and finally achieve the purpose of ultra-high clean steel smelting.

Description

Technical Field

[0001] The present invention belongs to the technical field of steelmaking processes, and particularly relates to a method for producing ultra-high cleanliness steel by using horizontal ladle electromagnetic stirring. Background Art

[0002] Purity has a great influence on the fatigue life of steel. Among them, the control of inclusions is particularly important. The smaller the size of inclusions in steel, the easier it is to obtain bearing steel and gear steel with high life. Therefore, how to achieve the smelting of ultra-high cleanliness steel has become a key issue in the smelting industry.

[0003] At present, a large number of studies have been carried out on ultra-high cleanliness steel at home and abroad. For example, when continuously casting steel in Patent CN114025897A, an oxygen-free atmosphere is created in the tundish before pouring molten steel into the tundish to prevent the reoxidation of molten steel, and the secondary oxidation of the tundish is controlled to reduce inclusions. However, this control method requires equipment modification, increasing production costs. Patent CN107746907A discloses a method for producing ultra-low carbon clean steel by the process of "vanadium extraction converter dephosphorization - desulfurization - steelmaking converter dephosphorization, decarburization - LF refining furnace deep dephosphorization - desulfurization station dephosphorization and slag skimming - LF furnace refining - RH furnace refining", and this production process is complex and requires the additional addition of a large amount of deoxidizers, slag formers, slag modifiers, etc. -6 Summary of the Invention

[0004] Therefore, aiming at the production of clean steel by the "BOF - LF - RH - CC" process, the object of the present invention is to provide a method for smelting ultra-high cleanliness steel by combining horizontal ladle electromagnetic stirring with vertical argon blowing stirring. This method can replace the traditional vertical argon blowing large stirring smelting method, inhibit the occurrence of slag entrainment in the refining process, realize the production of ultra-high cleanliness steel, and further uniform the molten steel temperature and composition while improving product quality.

[0005] The steel grades belong to steel grades with ultra-high cleanliness requirements, such as products like ultra-high cleanliness bearing steel, gear steel, cord steel, etc.

[0006] A method for smelting ultra-high cleanliness steel by combining horizontal ladle electromagnetic stirring with vertical argon blowing stirring, and this process includes the following key points:

[0007] (1) The converter adopts a conventional blowing method, and the end-point temperature and end-point carbon of the converter are controlled within a reasonable range;

[0008] (2) When tapping from the converter, first add aluminum for deoxidation, then add alloys for alloying, and after adding the alloys, add lime and refining slag materials for slag making;

[0009] (3) During the LF process, silicon carbide is added for deoxidation on the slag surface. The content of (TFe + MnO) in the slag is controlled below 1.00%, and the basicity of the refining slag is controlled between 3.0 and 8.0. No Ca-containing alloys such as calcium carbide, calcium-containing ferrosilicon, and calcium-containing ferroaluminum are added during the LF process;

[0010] Controlling the content of (TFe + MnO) in the slag below 1.00% and the basicity of the refining slag between 3.0 and 8.0 aims to control the oxygen content in the steel from being too high. Since the oxygen content is a key indicator of steel cleanliness, being too high will lead to excessive amounts and sizes of inclusions, affecting the cleanliness and performance indicators of the steel. Controlling to meet this indicator can ensure that the O content ≤ 0.0015%. Combining with RH, ladle electromagnetic stirring, etc. can further reduce the T.O content.

[0011] Controlling the LF process to use silicon carbide for deoxidation and not adding Ca-containing alloys such as calcium carbide, calcium-containing ferrosilicon, and calcium-containing ferroaluminum during the LF process aims to control the inclusions in the steel to be high-melting-point inclusions such as Al2O3 and MgO·Al2O3. Al deoxidation easily reduces CaO in the slag, and the addition of Ca-containing alloys will directly increase the Ca content in the molten steel. The increase in the Ca content in the molten steel will promote the transformation of inclusions from Al2O3 to liquid CaO-Al2O3. The wetting angle between liquid CaO-Al2O3 and the molten steel is small, and it is easy to adhere to the molten steel and is not easily separated and removed. Controlling this indicator can ensure that the Ca content in the molten steel ≤ 5 ppm and the proportion of solid inclusions in the steel ≥ 85%.

[0012] (4) The ladle horizontal electromagnetic stirring can be started as soon as the LF furnace is charged. The stirring force generated is a horizontal force, with a stirring current of 340 A and a frequency of 2 Hz. It is required that the ladle horizontal electromagnetic stirring has a forward and reverse function, that is, the cycle period is forward working time t1 - stop time t0 - reverse working time t1 - stop time t0. At the same time, the ladle bottom argon blowing system is started, and the bottom argon blowing flow rate is 1 / 10 of the low argon blowing flow rate when the ladle electromagnetic stirring is not started, about 30 NL / min.

[0013] During the LF smelting process, it is necessary to ensure the fluidity of the molten steel to meet the uniformity of the molten steel composition and temperature while removing inclusions in the steel. Conventional LF ladle smelting uses separate bottom argon blowing. To ensure the flow of molten steel during the LF smelting process, a relatively large argon blowing flow rate is required. While stirring the molten steel, it is easy to blow through the slag surface of the molten steel, causing the entrainment of refining slag and affecting the cleanliness. Combining ladle horizontal electromagnetic stirring with weak bottom argon blowing can achieve a better stirring effect. Compared with the conventional bottom argon blowing intensity, the combined bottom argon blowing intensity is only 1 / 10, which can ensure that the slag surface will not be blown through, and at the same time, the molten steel can also obtain a better stirring effect. On the other hand, if the stirring current is too large, it will disturb the molten steel surface and entrain the steel slag into the molten steel; if the stirring current is too small, it will not achieve the stirring effect. Therefore, the best current intensity is 340 A. Since continuous ladle horizontal electromagnetic stirring in the same direction will cause a "vortex" flow similar to that on the molten steel surface, it is required that after combining the ladle horizontal electromagnetic stirring with the bottom argon blowing system, the forward and reverse functions need to be turned on to reduce the generation of vortices, ensure the flow of molten steel, and prevent the entrainment of refining slag.

[0014] (5) RH vacuum treatment. During the RH treatment process, it is required to turn on the horizontal ladle electromagnetic stirring. The stirring force is a horizontal force, the stirring current is 200 A, and the frequency is 2 Hz; it is required that the horizontal ladle electromagnetic stirring turns on the forward and reverse functions, that is, the cycle period is: forward working for t1 time - stop for t0 time - reverse working for t1 time - stop for t0 time. At the same time, turn on the ladle bottom argon blowing system. The argon flow rate of the bottom argon blowing system is 1 / 15 of the low argon blowing flow rate when the ladle electromagnetic stirring is not turned on, about 20 NL / min; no alloys and slag materials are added during the RH process, and no calcium treatment is carried out after the RH ends; after the RH smelting ends, soft blowing is carried out, and the forward and reverse functions of the ladle horizontal electromagnetic stirring and the bottom argon blowing flow rate are kept unchanged, and the electromagnetic stirring current is reduced to 150 A;

[0015] Conventional RH treatment does not turn on bottom argon blowing and ladle electromagnetic stirring. However, the key control point during the RH process is the circulation flow frequency of the molten steel in the RH vessel and the LF vessel. That is, the more the number of circulation flows, the better the degassing and inclusion removal effects of the molten steel. Therefore, the present invention requires that the RH process needs to turn on the horizontal ladle electromagnetic stirring (forward and reverse) and bottom argon blowing. However, since the molten steel mainly circulates in the RH vessel during the RH process, there is no need for excessive circulation flow in the LF vessel. Therefore, compared with the LF process, the ladle electromagnetic stirring current during the RH process is reduced to 200 A, and the bottom argon blowing flow rate is reduced to 20 NL / min.

[0016] During the soft blowing process, the ladle electromagnetic stirring and bottom argon blowing are started. The stirring direction of the ladle electromagnetic stirring is horizontal and cannot be vertical. The intensity is reduced to 150 A (forward and reverse) compared with that in LF. The bottom argon blowing stirring system stirs in the vertical direction, and the bottom argon blowing flow rate needs to be controlled at 20 NL / min. The main purpose of soft blowing is to adjust the production rhythm and further remove the residual inclusions in the steel. Therefore, too high stirring intensity is not required. Thus, the electromagnetic stirring intensity is set at 150 A (forward and reverse), and the bottom argon blowing is controlled at 20 NL / min.

[0017] For the forward and reverse cycle of the ladle horizontal electromagnetic stirring: t1 lasts for 4 - 6 seconds, and t0 lasts for 1 - 3 seconds. If the forward or reverse time lasts too long, it will easily cause vortices similar to those on the steel liquid surface and entrain the slag into the molten steel. Therefore, the time needs to be controlled preferably at 4 - 6 seconds. The stop time is to ensure a certain electrical buffer time for the equipment. If the stop time is too short, the equipment is easily damaged. If the stop time is too long, the stirring effect will be affected. Therefore, the time needs to be controlled at 1 - 3 seconds.

[0018] For the ladle electromagnetic stirring equipment, it is required to be installed at about 2 / 3 of the ladle height. If the electromagnetic stirring equipment is installed too high, it will have a flowing effect on the refining slag and is easily entrained into the molten steel, deteriorating the cleanliness. If the installation height is too low, it cannot achieve the stirring effect on the overall molten steel and weakens the stirring ability. Therefore, it is set at about 2 / 3 of the ladle height.

[0019] (6) During the continuous casting process, full protection casting is adopted.

[0020] A method for producing ultra-high cleanliness steel by using horizontal ladle electromagnetic stirring combined with argon bottom blowing stirring according to the present invention. By adjusting the conventional argon blowing stirring in the vertical direction to the horizontal direction mainly, while reducing the slag entrainment in LF refining, a vertical + horizontal combination method is developed during the RH process to promote the molten steel flow and efficiently remove inclusions. Through production practice verification, by implementing the method of the present invention, the extreme size of the finished product inclusions can be controlled at ≤18 μm, and T.O ≤ 4.3 ppm.

[0021] The progressive effect of the present invention is: by controlling the ladle horizontal electromagnetic stirring + bottom argon vertical system to replace the traditional simple large-flow vertical bottom argon blowing stirring system, the slag entrainment in the ladle refining process is better inhibited. Then, by means of RH combined with ladle electromagnetic stirring + bottom argon blowing, the stirring efficiency of RH is improved, achieving the efficient removal of inclusions in this process, and finally realizing the purpose of ultra-high cleanliness steel smelting. Description of the Drawings

[0022] Figure 1 Schematic diagram of the molten steel flow in the LF ladle for Example 1;

[0023] Figure 2 Schematic diagram of the molten steel flow in the LF ladle for Comparative Example 1;

[0024] Figure 3 It is a schematic diagram for sampling and testing rolled materials. Specific implementation method

[0025] Use a 120-ton top and bottom combined blowing converter → 120-ton LF refining furnace → 120-ton RH refining furnace → 300*325 section continuous casting machine to produce bearing steel.

[0026] For the 120-ton top and bottom combined blowing converter, the conventional blowing method is adopted. The end-point temperature of the converter is controlled at about 1620°C, and the end-point C is controlled at about 0.15%. When tapping from the converter, first add 200 kg of aluminum cakes, 280 kg of low-aluminum and low-titanium ferrosilicon, 300 kg of high-carbon ferromanganese, 2200 kg of low-titanium and high-carbon ferrochromium, 900 kg of carburizer, and then add 400 kg of lime and 1000 kg / furnace of refining slag materials.

[0027] For the 120-ton LF refining furnace, when the temperature is raised to 1550°C, take a sample of the molten steel. After the sampling, the composition is fed back to the main control room, and then add 140 kg of silicon carbide for deoxidation on the slag surface, and add 700 kg of low-titanium and high-carbon ferrochromium, 2350 kg of high-carbon ferromanganese, 70 kg of low-aluminum and low-titanium ferrosilicon, and 300 kg of low-nitrogen carburizer.

[0028] For the 120-ton RH vacuum treatment, the treatment time is about 35 min, and after the RH is finished, soft blowing is carried out for about 20 minutes.

[0029] For continuous casting, full-process protected casting is adopted.

[0030] After smelting, it is sent to the rolling mill for rolling, and the rolling specification is φ55 mm.

[0031] Example 1

[0032] LF process: After the ladle enters the station, start the horizontal ladle electromagnetic stirring and vertical argon stirring. The electromagnetic stirring current of the ladle is 340 A, the frequency is 2 Hz, and the positive and negative rotation periods t1: 5 seconds, t0: 2 seconds. The vertical argon stirring flow rate is 30 NL / min. The schematic diagram of molten steel stirring during the LF process is as Figure 1 . The total treatment time of horizontal electromagnetic stirring of the ladle is 45 min.

[0033] RH process: During the treatment process, the horizontal ladle electromagnetic stirring current is 200 A, the frequency is 2 Hz; the positive and negative rotation periods t1: 5 seconds, t0: 2 seconds. At the same time, start the bottom argon blowing system of the ladle, and the argon flow rate of the bottom argon blowing system is 20 NL / min. The total treatment time of horizontal electromagnetic stirring of the ladle is 35 min.

[0034] Soft blowing process: The electromagnetic stirring current of the ladle is 150 A, and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The bottom blowing argon flow rate is 20 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 20 min. The sampled molten steel composition is: C: 0.957%, Si: 0.224%, Mn: 0.294%, P: 0.010%, S: 0.0046%, Cr: 1.467%, Al: 0.0186%.

[0035] Comparative example 1 (LF, RH, soft blowing, ladle electromagnetic stirring turned off)

[0036] LF process: After the ladle enters the station, the horizontal ladle electromagnetic stirring is not turned on, only the vertical argon stirring is turned on, and the vertical argon stirring flow rate is 300 NL / min. The schematic diagram of molten steel stirring during the LF process is as Figure 2 .

[0037] RH process: During the treatment process, the horizontal ladle electromagnetic stirring is not turned on, and the ladle bottom blowing argon system is not turned on either.

[0038] Soft blowing process: The ladle electromagnetic stirring is not turned on, and the bottom blowing argon flow rate is 20 NL / min. The sampled molten steel composition is: C: 0.966%, Si: 0.231%, Mn: 0.289%, P: 0.011%, S: 0.0052%, Cr: 1.398%, Al: 0.0190%.

[0039] Comparative example 2 (LF, RH, soft blowing, ladle electromagnetic stirring forward and reverse turned off)

[0040] LF process: After the ladle enters the station, the horizontal ladle electromagnetic stirring and the vertical argon stirring are turned on. The electromagnetic stirring current of the ladle is 340 A, the frequency is 2 Hz, and the forward and reverse are turned off. The vertical argon stirring flow rate is 30 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 46 min.

[0041] RH process: During the treatment process, the horizontal ladle electromagnetic stirring current is 200 A, the frequency is 2 Hz, and the forward and reverse are turned off. At the same time, the ladle bottom blowing argon system is turned on, and the argon flow rate of the bottom blowing argon system is 20 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 33 min.

[0042] Soft blowing process: The ladle electromagnetic stirring current is 150 A, the frequency is 2 Hz, and the forward and reverse are turned off. The bottom blowing argon flow rate is 20 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 22 min. The sampled molten steel composition is: C: 0.981%, Si: 0.237%, Mn: 0.295%, P: 0.010%, S: 0.0061%, Cr: 1.481%, Al: 0.0183%.

[0043] Comparative example 3 (LF, ladle electromagnetic stirring turned off)

[0044] LF process: After the ladle enters the station, the horizontal ladle electromagnetic stirring is not turned on, only the vertical argon stirring is turned on, and the vertical argon stirring flow rate is 300 NL / min.

[0045] RH process: During the treatment process, the horizontal ladle electromagnetic stirring current is 200 A and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. At the same time, the bottom argon blowing system of the ladle is turned on, and the argon flow rate of the bottom argon blowing system is 20 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 34 min.

[0046] Soft blowing process: The ladle electromagnetic stirring current is 150 A and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The bottom argon blowing flow rate is 20 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 21 min. The sampled molten steel composition is: C: 0.993%, Si: 0.241%, Mn: 0.301%, P: 0.011%, S: 0.0039%, Cr: 1.399%, Al: 0.0179%.

[0047] Comparative example 4 (RH, ladle electromagnetic stirring turned off)

[0048] LF process: After the ladle enters the station, the horizontal ladle electromagnetic stirring and the vertical argon stirring are turned on. The ladle electromagnetic stirring current is 340 A, the frequency is 2 Hz, and the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The vertical argon stirring flow rate is 30 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 43 min.

[0049] RH process: During the treatment process, the horizontal ladle electromagnetic stirring is turned off and the ladle bottom argon blowing system is not turned on.

[0050] Soft blowing process: The ladle electromagnetic stirring current is 150 A and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The bottom argon blowing flow rate is 20 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 20 min. The sampled molten steel composition is: C: 0.961%, Si: 0.264%, Mn: 0.294%, P: 0.011%, S: 0.0049%, Cr: 1.329%, Al: 0.0177%.

[0051] Comparative example 5 (soft blowing, ladle electromagnetic stirring turned off)

[0052] LF process: After the ladle enters the station, the horizontal ladle electromagnetic stirring and the vertical argon stirring are turned on. The ladle electromagnetic stirring current is 340 A, the frequency is 2 Hz, and the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The vertical argon stirring flow rate is 30 NL / min. The total treatment time of the ladle horizontal electromagnetic stirring is 45 min.

[0053] RH process: During the treatment process, the electromagnetic stirring current of the horizontal ladle is 200 A and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. At the same time, the bottom argon blowing system of the ladle is turned on, and the argon gas flow rate of the bottom argon blowing system is 20 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 36 min.

[0054] Soft blowing process: Turn off the electromagnetic stirring of the ladle, and the bottom argon blowing flow rate is 20 NL / min. The chemical composition of the molten steel is sampled and detected as follows: C: 0.985%, Si: 0.247%, Mn: 0.291%, P: 0.010%, S: 0.0054%, Cr: 1.349%, Al: 0.0193%.

[0055] Comparative example 6 (LF, turn off the forward and reverse of the electromagnetic stirring of the ladle)

[0056] LF process: After the ladle enters the station, turn on the horizontal electromagnetic stirring of the ladle and the vertical argon stirring. The electromagnetic stirring current of the ladle is 340 A, the frequency is 2 Hz, and the forward and reverse are turned off. The vertical argon stirring flow rate is 30 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 44 min.

[0057] RH process: During the treatment process, the electromagnetic stirring current of the horizontal ladle is 200 A and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. At the same time, the bottom argon blowing system of the ladle is turned on, and the argon gas flow rate of the bottom argon blowing system is 20 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 35 min.

[0058] Soft blowing process: The electromagnetic stirring current of the ladle is 150 A and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The bottom argon blowing flow rate is 20 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 21 min. The chemical composition of the molten steel is sampled and detected as follows: C: 0.969%, Si: 0.294%, Mn: 0.289%, P: 0.011%, S: 0.0059%, Cr: 1.399%, Al: 0.0186%.

[0059] Comparative example 7 (RH, turn off the forward and reverse of the electromagnetic stirring of the ladle)

[0060] LF process: After the ladle enters the station, turn on the horizontal electromagnetic stirring of the ladle and the vertical argon stirring. The electromagnetic stirring current of the ladle is 340 A, the frequency is 2 Hz, and the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The vertical argon stirring flow rate is 30 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 46 min.

[0061] RH process: During the treatment process, the electromagnetic stirring current of the horizontal ladle is 200 A and the frequency is 2 Hz; the forward and reverse are turned off. At the same time, the bottom argon blowing system of the ladle is turned on, and the argon gas flow rate of the bottom argon blowing system is 20 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 33 min.

[0062] Soft blowing process: The electromagnetic stirring current of the ladle is 150 A, and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The flow rate of bottom blowing argon is 20 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 23 min. The chemical composition of the molten steel detected by sampling is: C: 0.991%, Si: 0.268%, Mn: 0.291%, P: 0.010%, S: 0.0062%, Cr: 1.349%, Al: 0.0179%.

[0063] Comparative Example 8 (soft blowing, turning off the forward and reverse of the ladle electromagnetic stirring)

[0064] LF process: After the ladle enters the station, the horizontal ladle electromagnetic stirring and vertical argon stirring are started. The electromagnetic stirring current of the ladle is 340 A, the frequency is 2 Hz, the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. The flow rate of vertical argon stirring is 30 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 45 min.

[0065] RH process: During the treatment process, the electromagnetic stirring current of the horizontal ladle is 200 A, and the frequency is 2 Hz; the forward and reverse cycle t1: 5 seconds, t0: 2 seconds. At the same time, the bottom blowing argon system of the ladle is started, and the argon flow rate of the bottom blowing argon system is 20 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 37 min.

[0066] Soft blowing process: The electromagnetic stirring current of the ladle is 150 A, the frequency is 2 Hz, and the forward and reverse are turned off. The flow rate of bottom blowing argon is 20 NL / min. The total treatment time of the horizontal electromagnetic stirring of the ladle is 19 min. The chemical composition of the molten steel detected by sampling is: C: 0.993%, Si: 0.286%, Mn: 0.286%, P: 0.010%, S: 0.0056%, Cr: 1.366%, Al: 0.0186%.

[0067] Samples are taken at the 1 / 2 radius of the rolled material, and the sample size is 15 mm * 15 mm (the sampling schematic diagram is as Figure 3 ), after grinding and polishing, the maximum inclusions in the cross-sectional direction are detected by an optical microscope and their sizes are recorded. 24 samples are detected in both the comparative examples and the examples, and each sample is detected for 200 mm 2 , and the corresponding inclusion sizes are extrapolated by the extreme value statistical method for 30000 mm 2 . After calculation, the T.O content and the extreme value characteristic sizes of the inclusions corresponding to the examples and the comparative examples are shown in Table 1.

[0068] Table 1 T.O content and extreme value characteristic sizes of inclusions

[0069] Example T.O / ppm Extreme characteristic size X of inclusions / μm Example 1 4.3 16.92 Comparative Example 1 6.1 36.86 Comparative Example 2 6.5 48.24 Comparative Example 3 5.1 29.58 Comparative Example 4 6.3 35.74 Comparative Example 5 4.8 27.98 Comparative Example 6 6.3 39.76 Comparative Example 7 5.8 39.98 Comparative Example 8 6.2 42.87

Claims

1. A method for producing ultra-high purity steel by using horizontal ladle electromagnetic stirring, characterized in that, The smelting steps of the ultra-high cleanliness steel are as follows: (1) In the converter, the conventional blowing method is adopted, and the reasonable ranges of the converter end temperature and end carbon are controlled; (2) When tapping from the converter, aluminum is first added for deoxidation, and then alloys are added for alloying. After the alloys are added, lime and refining slag materials are added for slag making; (3) During the LF process, silicon carbide is added for slag surface deoxidation. The content of (TFe + MnO) in the slag is controlled below 1.00%, and the basicity of the refining slag is controlled between 3.0 and 8.

0. No calcium-containing alloys are added during the LF process; (4) When the LF station is in operation, the ladle horizontal electromagnetic stirring and the forward and reverse rotation functions are turned on. The stirring current is 340 A and the frequency is 2 Hz; at the same time, the ladle bottom argon blowing system is turned on, and the flow rate of the bottom argon blowing is 1 / 10 of the flow rate of the bottom argon blowing when the ladle electromagnetic stirring is not turned on; (5) RH vacuum treatment, the ladle horizontal electromagnetic stirring and the forward and reverse rotation functions are turned on. The stirring current is 200 A and the frequency is 2 Hz; at the same time, the ladle bottom argon blowing system is turned on, and the flow rate of the bottom argon blowing system is 1 / 15 of the flow rate of the bottom argon blowing when the ladle electromagnetic stirring is not turned on; No alloys and slag materials are added during the RH process, and no calcium treatment is carried out after the RH is completed; After the RH smelting is completed, soft blowing is carried out, and the forward and reverse rotation functions of the ladle horizontal electromagnetic stirring and the flow rate of the bottom argon blowing are kept unchanged, and the electromagnetic stirring current is reduced to 150 A; (6) During the continuous casting process, full protection casting is adopted.

2. The method for producing ultra-high purity steel by using horizontal ladle electromagnetic stirring according to claim 1, characterized in that: The forward and reverse cycle period of the ladle horizontal electromagnetic stirring is that after working in the forward direction for a time t1, stopping for a time t0, working in the reverse direction for a time t1, and stopping for a time t0.

3. The method for producing ultra-high purity steel by using horizontal ladle electromagnetic stirring according to claim 1, characterized in that: t1 is 4 - 6 s, and t0 is 1 - 3 s.

4. The method for producing ultra-high purity steel by using horizontal ladle electromagnetic stirring according to claim 1, characterized in that: The ladle electromagnetic stirring equipment is installed at the ladle position and does not move with the ladle. After the ladle is moved into the LF or RH position, it approaches the ladle by rotating or moving, and the height is 2 / 3 of the ladle height.

5. An ultra-high purity steel prepared by the method according to any one of claims 1 to 4, characterized in that: The T.O of the ultra-high cleanliness steel is ≤ 4.3 ppm; the extreme value statistical method is used to calculate 30000 mm 2 The corresponding extreme inclusion size is ≤ 18 μm.

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