A method for controlling the cleanliness of molten steel in RH residual cold steel stabilization

Abstract

This invention belongs to the field of steelmaking process technology and relates to a method for controlling the cleanliness of molten steel by controlling the residual cold steel in the RH furnace. This method uses the trend of CO concentration change in the RH furnace flue gas to determine the melting status of the cold steel in the RH furnace. During the initial melting of the cold steel, the RH furnace is degassed and restored to atmospheric pressure. At this point, the cold steel has already pre-melted under the heat from the RH molten steel circulation. An oxygen lance is used to quickly purge the cold steel, causing it to drip into the cold steel collection tank. Then, the vacuum is quickly restored to the predetermined vacuum level, and RH vacuum treatment continues. The time taken from the start of degaussing to re-evacuation to the target vacuum level (i.e., the cold steel treatment time) is ≤120s. This method ensures that the O content in the molten steel during the RH process steadily decreases to the ideal O content level within the RH treatment cycle, thereby stabilizing the cleanliness of the molten steel and preventing sudden abnormal increases in O content caused by cold steel contamination of the molten steel.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking process technology, and specifically relates to a method for controlling the cleanliness of stabilizing molten steel by controlling residual cold steel in RH. Background Technology

[0002] Purity has a significant impact on the fatigue life of steel, with the control of oxygen content being particularly important. The smaller the size of inclusions in the steel, the easier it is to obtain bearing steel and gear steel with a long service life. High-end clean steel smelting often employs a production process of BOF / EAF→LF→RH→CCM. During the RH process, the cold steel remaining from the previous heats in the RH furnace can contaminate the molten steel, causing a sudden and abnormal increase in the oxygen content of the current heat. This abnormal increase in oxygen content is difficult to reduce to an ideal level during subsequent RH treatments, thus worsening the cleanliness of the molten steel. Therefore, how to effectively remove cold steel from the RH furnace and ensure continuous operation of the RH furnace to obtain stable ultra-high clean steel smelting has become a key issue in the metallurgical industry.

[0003] A search revealed that many researchers, both domestically and internationally, have conducted studies on the control of cold steelmaking in RH furnaces.

[0004] Patent CN109423537A, "A Method for Rapidly Removing Cold Steel from an RH Vacuum Chamber," describes a method for rapidly removing cold steel from an RH vacuum chamber. The method involves changing the energy medium for baking the RH vacuum chamber offline to oxygen. Baking begins within 30 minutes after the last heat of molten steel is processed during the RH vacuum chamber's operation. Following the jacking method used during steel processing, the slag-holding ladle receiving the molten slag from the vacuum chamber is immersed and reset. The total oxygen blowing volume, ignition oxygen flow rate, and oxygen lance position are set for the RH top lance. Oxygen blowing begins, and when the oxygen lance reaches the set position and the flow rate reaches the set value, the oxygen flow rate is adjusted. After liquid slag flows out of the insertion pipe, the RH oxygen lance position is adjusted 2-5 times during oxygen blowing, each time for 5-20 minutes. After slag removal, nitrogen protective gas is used to purge the vacuum chamber, reducing the oxygen concentration. This achieves rapid baking of the molten cold steel, enabling the RH top lance to perform oxygen baking during non-molten steel processing. By changing the vacuum chamber offline baking process, the baking time is shortened by 1.5 hours. The opposing patent emphasizes the conventional cold steel operation after RH use, which cannot solve the problem of cold steel formation during continuous use. At the same time, since the cold steel is already in a relatively cold RH furnace, the low temperature of the cold steel necessitates the use of natural gas or other methods to reheat and melt it, resulting in a longer overall cold steel cycle.

[0005] Patent CN102851456A, "A Method for Online Removal of Cold Steel in an RH Vacuum Chamber," relates to a method for online removal of cold steel in an RH vacuum chamber. Its key feature is the use of a top-lance oxygen blowing method to remove cold steel online during RH treatment of molten steel. The operational steps are as follows: 1) Before treating the molten steel in the vacuum chamber, the temperature of the inner wall of the vacuum chamber must be ≥1350℃; 2) During the treatment of boiling steel, the lance position and oxygen flow rate are controlled, utilizing the secondary combustion effect of CO generated during the decarburization of the molten steel to heat the inner wall of the vacuum chamber, reducing splashing and adhesion of molten steel. Alternatively, the top-lance oxygen blowing method can be used immediately after the RH treatment of the molten steel to remove cold steel online. Compared with existing technologies, the advantages are: 1) Rapid removal of cold steel from the vacuum chamber, with the fastest removal time being within 30 minutes, effectively avoiding blockage by molten steel slag inside the insertion tube. 2) Ensuring that the refractory material of the vacuum chamber is not damaged during the removal of cold steel. 3) Reducing production costs, alleviating labor intensity, and improving occupational safety. The opposing patent involves a process of melting and cooling steel during RH treatment. This is because the steel being treated is rimmed steel with a high oxygen content, and the cooled steel is entirely reintroduced into the molten steel. While this increases the oxygen content of the molten steel, the presence of rimmed steel prevents any negative impact. However, this patent deals with high-end clean steel, and therefore prohibits cooled steel from dripping into the molten steel. Furthermore, the treatment cycle is 30 minutes, whereas for high-end clean steel, the RH treatment cycle can sometimes be less than 30 minutes.

[0006] Patent CN107828938A, "A Method for Preventing Cold Steel Adhesion in Vacuum Tank During RH Vacuum Cyclic Degassing Process," provides a method for preventing cold steel adhesion in vacuum tanks during RH vacuum cyclic degassing process. The methods include: (1) using a normal turnover ladle with a turnover time of less than 60 minutes; (2) controlling the temperature of the deoxidized molten steel entering the RH furnace to be greater than 1620℃ and the temperature of the non-deoxidized molten steel to be greater than 1600℃; (3) when the OB heating or OB forced decarburization of the RH refining furnace is carried out, the vacuum degree in the tank is 5-15 kPa and the circulating gas flow rate is 1400 NL / min; (4) controlling the circulating gas flow rate of the RH refining furnace to 1600 NL / min for 5 minutes before decarburization and 2000 NL / min for 5 minutes until the end of decarburization; (5) adding aluminum to the molten steel for deoxidation for 3 minutes and then adding other alloys; (6) adding 200 kg of desulfurizing agent after the molten steel is alloyed; (7) using top lance heating to increase the temperature of the upper tank and hot bending pipe, with the top lance position at 8.5 m and the gas flow rate at 200 Nm. 3 / h, oxygen flow rate 220Nm 3 / h; (8) The pure degassing circulation time of molten steel is greater than 8 minutes, and the treatment is completed. It can effectively prevent cold steel from sticking in the vacuum tank and improve the operating rate of RH furnace. The other party's patent puts forward many strict parameter requirements for RH furnace and has high requirements for the overall cost of RH furnace, such as the need to configure top gun heating, require RH furnace to have a large circulation flow facility, and have vacuum alloying facility, etc., which are not suitable for general RH furnace equipment. Moreover, in actual process, it is impossible for there to be no residual cold steel in RH furnace.

[0007] To address the issue of cold steel in the RH furnace during the production of clean steel using the RH process, this invention provides a method for controlling the residual cold steel in the RH furnace to stabilize the cleanliness of molten steel. Instead of the traditional separate cooling and recooling operation after the RH furnace is offline, this patent achieves a continuous, monitorable, and rapid cooling and recooling process for conventional RH furnaces, thus achieving the goal of smelting high-cleanliness steel using the RH process. Summary of the Invention

[0008] The purpose of this invention is to develop a method for controlling the cleanliness of molten steel with residual cold steel after RH treatment. This method can replace the traditional method of refining cold steel after RH treatment or adding expensive RH equipment. It can easily remove RH cold steel and obtain a stable high-cleanliness steel grade.

[0009] The steel grade mentioned belongs to the category of steel grades with ultra-high cleanliness requirements, such as ultra-high cleanliness bearing steel, gear steel, wheel hub steel, and other products.

[0010] A method for controlling the cleanliness of stabilizing molten steel with residual cold steel in RH, comprising the following steps:

[0011] (1) Determine whether cold steel melting occurs in the RH furnace based on the trend of CO concentration change in the flue gas. If the CO concentration decreases naturally after reaching its peak, there is no problem with residual cold steel in the RH furnace, and the conventional RH vacuum treatment continues. If the CO concentration decreases after reaching its peak, but then rises again, the moment when it starts to rise again indicates that the residual cold steel in the RH furnace begins to melt under the heat brought by the circulation of RH molten steel during the RH treatment process.

[0012] (2) At the moment when the cold steel begins to melt (i.e. when the CO concentration reaches its peak and then begins to decrease and then rises again), the RH is restored to atmospheric pressure, and the ladle is rotated or moved so that the cold steel collection tank is located directly below the RH furnace to facilitate the collection of cold steel.

[0013] (3) Use an oxygen lance to quickly blow and melt the cold steel. The oxygen blowing time should be ≤60s. The cold steel is then melted and dripped into the cold steel collection tank.

[0014] (4) After the cold steel is purged and dripped, rotate or move the ladle so that the cold steel collection tank is located at the bottom of the impregnation tube, quickly evacuate to the predetermined vacuum level, and continue the RH vacuum treatment.

[0015] Furthermore, when the RH furnace is vented to atmospheric pressure in step (2), the RH furnace temperature must be ≥ (T0+30)℃, where T0 is the corresponding liquidus temperature of molten steel (i.e., the temperature at which molten steel is completely melted into liquid), and the measurement point is the temperature of the inner wall of the refractory material at the lower end of the RH furnace.

[0016] Furthermore, the oxygen flow rate of the oxygen lance mentioned in step (3) is 1600-2000 Nm³. 3 / h.

[0017] Furthermore, the predetermined vacuum level described in step (4) is ≤67 Pa.

[0018] Furthermore, the time taken from the start of vacuuming to the return to the predetermined vacuum level, i.e., the removal time of cold steel, is ≤120s.

[0019] To determine whether cold steel melting occurs in the RH furnace by using the trend of CO concentration changes in the flue gas: if the CO concentration decreases naturally after reaching its peak, there is no residual cold steel in the RH furnace, and conventional RH vacuum treatment continues; if the CO concentration decreases after reaching its peak but then rises again, the moment it begins to rise again indicates that, during the RH treatment process, the residual cold steel in the RH furnace begins to melt under the heat brought by the circulation of RH molten steel.

[0020] Because conventional RH furnaces are equipped with flue gas analysis capabilities to determine the progress of the carbon-oxygen reaction in molten steel, the standard analytical component includes CO. Changes in CO concentration characterize the C-O reaction occurring in the molten steel. Typically, the reaction [C] + [O] → {CO} occurs at the start of vacuuming and upon reaching the target vacuum. According to thermodynamics, this reaction reaches equilibrium after a certain point, at which point C and O in the molten steel cease to react. The CO concentration in the flue gas will, based on this principle, initially increase, approach equilibrium, and then decrease. If other abnormal factors exist in this process, such as the presence of cold steel, the equilibrium state will be disrupted. For example, after the CO concentration reaches equilibrium and begins to decrease, it will increase again. Since the main component of cold steel is metallic Fe and its oxides (Fe... x O y When iron oxides in cold steel enter the molten steel, they transfer oxygen (O) to the molten steel, causing the O content in the molten steel to rise again. This promotes the carbon-oxygen reaction ([C] + [O] → {CO}) to continue, leading to a further increase in CO concentration in the flue gas. Therefore, the unconventional changes in CO concentration in the flue gas can characterize whether cold steel melts and enters the molten steel. If the residual cold steel in the RH furnace is not removed and participates in the molten steel circulation reaction, it will lead to an abnormally high O content in the molten steel, and subsequent RH circulation treatment will find it difficult to reduce it to a reasonable level within the RH treatment cycle.

[0021] To address the requirement of restoring the RH furnace to atmospheric pressure at the moment when cold steel begins to melt (i.e., when the CO concentration reaches its peak, begins to decline, and then rises again), the ladle should be rotated or moved so that the cold steel collection trough is located directly below the RH furnace to facilitate the collection of cold steel.

[0022] Since CO concentration can characterize the behavior of residual cold steel entering the molten steel in the RH furnace, the residual cold steel must be removed from the RH furnace to ensure that it does not enter the molten steel. Since it is impossible to guarantee that the molten cold steel will not drip into the ladle during online RH annealing, the RH furnace must be ventilated, that is, restored to atmospheric pressure, and the ladle or RH furnace must be rotated to ensure that the subsequent molten cold steel drips into a special cold steel collection device.

[0023] When the RH furnace is vented to atmospheric pressure, the RH furnace temperature must meet the requirement of ≥(T0+30)℃, where T0 is the corresponding liquidus temperature of molten steel, and the measurement point is the temperature of the inner wall of the refractory material at the lower end of the RH furnace.

[0024] After the RH furnace is vented, the molten cold steel is melted and dripped. A higher temperature of the cold steel at this stage facilitates rapid melting and dripping. Since measuring the temperature of the cold steel is very difficult, the temperature of the RH furnace is used to characterize the temperature of the cold steel inside the furnace. A higher RH temperature indicates a higher temperature of the cold steel. Furthermore, a higher RH furnace temperature facilitates the smooth flow of the cold steel into the cold steel collection tank as it drips along the furnace wall, preventing secondary condensation on the furnace wall due to low furnace temperature during dripping, which would hinder its removal. Production practice has shown that an RH furnace temperature ≥ (T0 + 30)℃ is sufficient to ensure the removal of molten cold steel.

[0025] The requirement is to use an oxygen lance to quickly purge and melt cold steel, with an oxygen blowing time of ≤60s, so that the molten cold steel drips into the cold steel collection tank.

[0026] Since the cold steel will lose its heat source after the RH is broken, it will begin to solidify. Therefore, it is necessary to rapidly blow oxygen into the already molten cold steel to continue melting and promote its dripping. The shorter the oxygen blowing time, the better the temperature can be maintained, thus ensuring the rapid removal of the cold steel. Production practice has proven that an oxygen blowing time of ≤60s can ensure the rapid melting and dripping of the molten cold steel.

[0027] The requirement is that the time taken from the start of vacuuming to the return to the predetermined vacuum level after the cold steel has been purged and dripped is ≤120s.

[0028] The reason is that the RH process itself is an intermediate process connecting LF and CCM. It is necessary to ensure that the time of the entire cooling process is as short as possible so as not to affect the temperature or subsequent CCM process. On the other hand, the RH treatment process is responsible for removing inclusions and reducing the O content. It is necessary to ensure that the cooling time is very short to meet the normal RH treatment time, thereby ensuring that the O content of the molten steel meets the requirements.

[0029] This invention provides a method for controlling the cleanliness of molten steel with residual cold steel after RH treatment. This method can replace the traditional method of remelting cold steel after RH treatment or adding expensive RH equipment, easily achieving the removal of RH cold steel while obtaining a stable high-cleanliness steel grade. Production practice has verified that implementing this method can ensure that the oxygen content of the molten steel is stably controlled to an ideal level after RH treatment.

[0030] The advantages of this invention are:

[0031] By analyzing the CO flue gas trends of the RH furnace itself, it is determined whether cold steel is involved in the molten steel circulation, i.e., whether cold steel affects the O content of the molten steel. If it is determined that there is an impact, upon receiving a CO concentration change signal, the RH pressure is restored to atmospheric pressure. At this point, the cold steel has already been pre-melted by the heat from the RH molten steel circulation. Oxygen blowing is then used to continue melting the pre-melted cold steel, causing it to drip into the cold steel collection tank. The pressure is then quickly restored to the normal RH treatment requirements, and RH treatment continues. This achieves a continuous, monitorable, and rapid cold steeling process in a conventional RH furnace, ensuring that the O content of the molten steel is stably controlled to an ideal level upon RH termination. Attached image description:

[0032] Figure 1 This is a graph showing the CO concentration variation in the RH furnace of Example 1. Figure 2 This is a graph showing the change in O content in molten steel in Example 1;

[0033] Figure 3 This is a graph showing the CO concentration variation in the RH furnace in Example 2. Figure 4 This is a graph showing the change in O content in molten steel in Example 2;

[0034] Figure 5 This is a graph showing the CO concentration variation in the RH furnace of Comparative Example 1. Figure 6 This is a graph showing the change in O content in molten steel for Comparative Example 1.

[0035] Figure 7 This is a graph showing the CO concentration variation in the RH furnace of Comparative Example 2; Figure 8 This is a graph showing the change in O content in molten steel for Comparative Example 2;

[0036] Figure 9 This is a graph showing the CO concentration variation in the 3RH furnace (compare example). Figure 10 This is a graph showing the change in O content in molten steel for Comparative Example 3;

[0037] Figure 11 This is a graph showing the CO concentration variation in the RH furnace (Comparative Example 4). Figure 12 This is a graph showing the change in O content in molten steel for Comparative Example 4;

[0038] Figure 13 This is a graph showing the CO concentration variation in the 5RH furnace as a comparative example. Figure 14 This is a graph showing the change in O content in molten steel, Comparative Example 5.

[0039] Figure 15 This is a graph showing the CO concentration variation in the 6RH furnace as a comparative example. Figure 16 The graph shows the change in O content in the molten steel for Comparative Example 6. Detailed Implementation

[0040] The steel smelting process adopts BOF / EAF→LF→RH→CCM, and the bearing steel is produced by a 120-ton top and bottom blown converter → 120-ton LF refining furnace → 120-ton RH refining furnace → 300*325 section continuous casting machine.

[0041] The BOF / EAF process uses a 120-ton top-and-bottom combined blowing converter and adopts conventional blowing methods. The final converter temperature is controlled at approximately 1625℃, and the final carbon content (C) is controlled at approximately 0.15%. When tapping steel from the converter, 200 kg of aluminum cake, 280 kg of low-aluminum, low-titanium ferrosilicon, 300 kg of high-carbon ferromanganese, 2200 kg of low-titanium, high-carbon ferrochrome, and 900 kg of carbon raiser are added first, followed by 400 kg of lime and 1000 kg / furnace of refining slag.

[0042] The LF process uses a 120-ton LF refining furnace. The molten steel is sampled after being heated to 1550℃. The composition of the sample is fed back to the main control room. Then, 140 kg of silicon carbide is added for slag surface deoxidation. Low-titanium high-carbon ferrochrome, high-carbon ferromanganese, low-aluminum low-titanium ferrosilicon, and low-nitrogen carbonizer are added to adjust the composition.

[0043] The RH process uses a 120-ton RH refining furnace, vacuum treatment for 35 minutes, and soft blowing for 20 minutes after the RH process.

[0044] The CCM process uses a 300*325 section continuous casting machine and adopts full-process protective casting to produce bearing steel.

[0045] Example 1: (The RH furnace is a brand new furnace body)

[0046] The RH furnace is brand new. After the RH boiler arrives at the station, a vacuum operation is performed, with a target vacuum pressure of ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 1 As shown, the total RH treatment time was 34 minutes. From the start of RH treatment, samples were taken every 2 minutes to monitor the change trend of O content in the molten steel. The results are as follows: Figure 2As shown. Because a brand-new RH furnace is used for smelting, there is no problem of residual cold steel in the RH furnace. Therefore, the O content of the molten steel after RH treatment can be stably controlled at ≤4.5ppm.

[0047] Example 2: (Executed according to the scheme of this patent)

[0048] The RH furnace is not a completely new furnace. After the RH furnace arrives at the station, a vacuuming operation is performed, with a target vacuum pressure of ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 3 As shown, the process of purging to atmospheric pressure was immediately executed when the CO concentration began to rise a second time. The ladle car was moved to align the RH furnace with the cold steel collection tank, and the temperature of the inner wall of the RH impregnation tube was measured at 1518℃ (the liquidus temperature of the bearing steel is 1453℃, and the temperature of the molten steel at the time of purging is 1542℃). The cold steel was rapidly purged using an oxygen lance, causing it to drip into the cold steel collection tank. The total oxygen blowing time was 52 seconds, and the oxygen flow rate was 1800 Nm³. 3 After the purging and dripping process is completed, the ladle is rotated or moved to position the cold steel collection tank below the impregnation tube. The process of breaking the vacuum until re-vacuuming to ≤67Pa takes 110 seconds, with a total RH treatment time of 35 minutes. At the start of the RH treatment, samples are taken every 2 minutes to monitor the change trend of O content in the molten steel. The results are as follows: Figure 4 As shown in the figure. According to this scheme, the O content of molten steel after RH treatment can be stably controlled to ≤4.5ppm.

[0049] Comparative Example 1: (Refrigerated steel without RH treatment)

[0050] The RH furnace is not a completely new furnace. After the RH furnace arrives at the station, a vacuuming operation is performed, with a target vacuum pressure of ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 5 As shown, when the CO concentration begins to rise a second time, the process of breaking the air pressure to atmospheric pressure is not performed; the routine RH treatment continues. The total RH treatment time is 35 minutes. From the start of RH treatment, samples are taken every 2 minutes to monitor the change in O content in the molten steel. The results are shown below. Figure 6 As shown. Because all the RH-treated cold steel was introduced into the molten steel, the oxygen content was high, and the final O content of the molten steel after RH treatment was 6.7 ppm.

[0051] Comparative Example 2: (Chilled steel before a second increase in CO concentration)

[0052] The RH furnace is not a completely new furnace. After the RH furnace arrives at the station, a vacuuming operation is performed, with a target vacuum pressure of ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 7As shown, when the CO concentration first reached its highest point, the process of purging to atmospheric pressure was performed. The ladle car was moved to align the RH furnace with the cold steel collection tank, and the temperature of the inner wall of the RH impregnation tube was measured at 1523℃ (the liquidus temperature of the bearing steel was 1453℃, and the temperature of the molten steel at the time of purging was 1548℃). The cold steel was rapidly purged using an oxygen lance, causing it to drip into the cold steel collection tank. The total oxygen blowing time was 60 seconds, and the oxygen flow rate was 1800 Nm³. 3 After the purging and dripping process is completed, the ladle is rotated or moved to position the cold steel collection tank below the impregnation tube. The process of breaking the vacuum until re-vacuuming to ≤67Pa takes 120 seconds, with a total RH treatment time of 36 minutes. At the start of the RH treatment, samples are taken every 2 minutes to monitor the change trend of O content in the molten steel. The results are as follows: Figure 8 As shown, since the CO concentration has not yet increased a second time, it indicates that the cold steel in the RH furnace has not yet begun to melt. At this time, the temperature of the cold steel is also low, and the effect of using an oxygen lance to melt the cold steel is poor. Therefore, the O content of the molten steel after RH treatment is 6.8 ppm.

[0053] Comparative Example 3: (Delayed cooling of steel after a second increase in CO concentration)

[0054] The RH furnace is not a completely new furnace. After the RH furnace arrives at the station, a vacuuming operation is performed, with a target vacuum pressure of ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 9 As shown, after the CO concentration reached its second peak, the process of purging to atmospheric pressure was performed with a 5-minute delay. The ladle car was moved to align the RH furnace with the cold steel collection tank, and the temperature of the inner wall of the RH impregnation tube was measured at 1510℃ (the liquidus temperature of the bearing steel was 1453℃, and the temperature of the molten steel at the time of purging was 1521℃). The cold steel was rapidly purged using an oxygen lance, causing it to drip into the cold steel collection tank. The total oxygen blowing time was 29 seconds, and the oxygen flow rate was 1800 Nm³. 3 After the purging and dripping process is completed, the ladle is rotated or moved to position the cold steel collection tank below the impregnation tube. The process of breaking the vacuum until re-vacuuming to ≤67Pa takes 88 seconds, with a total RH treatment time of 34 minutes. At the start of the RH treatment, samples are taken every 2 minutes to monitor the change in O content in the molten steel. The results are as follows: Figure 10 As shown, because the CO concentration was increased twice before the cold steel treatment, the oxides in the cold steel had already entered the molten steel, and the oxygen content of the molten steel had increased. Therefore, the effect of the cold steel treatment was poor. Finally, the O content of the molten steel after RH treatment was 6.7 ppm.

[0055] Comparative Example 4: (Reducing furnace body temperature during RH furnace cavitation)

[0056] The RH furnace is not a completely new furnace; lowering the molten steel temperature upon RH entry reduces the temperature during RH cavitation. After RH enters the furnace, a vacuum operation is performed, with a target vacuum pressure ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 11As shown, the process of purging to atmospheric pressure was immediately executed when the CO concentration began to rise a second time. The ladle car was moved to align the RH furnace with the cold steel collection tank, and the temperature of the inner wall of the RH impregnation tube was measured at 1471℃ (the liquidus temperature of the bearing steel was 1453℃, and the temperature of the molten steel at the time of purging was 1491℃). The cold steel was rapidly purged using an oxygen lance, causing it to drip into the cold steel collection tank. The total oxygen blowing time was 58 seconds, and the oxygen flow rate was 1800 Nm³. 3 After the purging and dripping process is completed, the ladle is rotated or moved to position the cold steel collection tank below the impregnation tube. The time from initial vacuuming to re-vacuuming to ≤67Pa is 117s, with a total RH treatment time of 35min. At the start of the RH treatment, samples are taken every 2 minutes to monitor the change in O content in the molten steel. The results are as follows: Figure 12 As shown. Due to the poor pre-melting effect of the cold steel after the temperature of the molten steel decreases, the effect of oxygen lance cooling of the cold steel is also poor. In addition, the temperature of the RH immersion tube is also low, which causes condensation of the molten steel as it flows down the RH furnace, which also leads to a poor cooling effect. Finally, the O content of the molten steel after RH treatment is 6.5 ppm.

[0057] Comparative Example 5: (Delaying oxygen blowing time)

[0058] The RH furnace is not a completely new furnace. After the RH furnace arrives at the station, a vacuuming operation is performed, with a target vacuum pressure of ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 13 As shown, the process of breaking the vent to atmospheric pressure was immediately executed when the CO concentration began to rise a second time. The ladle car was moved to align the RH furnace with the cold steel collection tank, and the temperature of the inner wall of the RH impregnation tube was measured at 1516℃ (the liquidus temperature of the bearing steel is 1453℃, and the temperature of the molten steel at the time of breaking the vent was 1541℃). The cold steel was then annealed using an oxygen lance, employing an intermittent annealing process with a 5-second pause, followed by 10 seconds of oxygen blowing, and then another 5-second pause, to prolong the oxygen blowing time. The oxygen flow rate was 1800 Nm³. 3 / h, cold steel drips into the cold steel collection tank. The total oxygen blowing time is 93s. After the purging and dripping are completed, the ladle is rotated or moved so that the cold steel collection tank is located below the immersion tube. The time from the start of venting to the re-vacuuming to ≤67Pa is 152s, and the total RH treatment time is 36min. At the start of RH treatment, samples are taken every 2 minutes to detect the changing trend of O content in the molten steel. The results are as follows: Figure 14 As shown. Due to the slowed pace of the oxidation cooling process, both the cold steel and the refractory material may experience temperature drops, resulting in a poor cooling effect. Ultimately, the O content in the molten steel after RH treatment was 6.2 ppm.

[0059] Comparative Example 6: (Delaying the re-vacuuming time)

[0060] The RH furnace is not a completely new furnace. After the RH furnace arrives at the station, a vacuuming operation is performed, with a target vacuum pressure of ≤67 Pa. Changes in flue gas CO concentration are monitored. Figure 15As shown, the process of purging to atmospheric pressure was immediately initiated when the CO concentration began to rise a second time. The ladle car was moved to align the RH furnace with the cold steel collection tank, and the temperature of the inner wall of the RH impregnation tube was measured at 1517℃ (the liquidus temperature of the bearing steel is 1453℃, and the temperature of the molten steel at the time of purging is 1543℃). The cold steel was rapidly purged using an oxygen lance, causing it to drip into the cold steel collection tank. The total oxygen blowing time was 51 seconds, and the oxygen flow rate was 1800 Nm³. 3 After the purging and dripping process is completed, the ladle is rotated or moved so that the cold steel collection tank is located at the bottom of the impregnation tube. When the vacuum is re-evacuated to ≤67Pa, the number of vacuum pumps is reduced, and the re-evacuation time is extended. The time from the start of vacuum breaking to re-evacuation to ≤67Pa is 336 seconds, and the total RH treatment time is 34 minutes. At the start of RH treatment, samples are taken every 2 minutes to detect the changing trend of O content in the molten steel. The results are as follows: Figure 16 As shown, the extended RH re-extraction time after quenching and cooling resulted in a shorter overall RH treatment time, leading to a decrease in the overall cleanliness of the molten steel. Ultimately, the O content of the molten steel after RH treatment was 5.5 ppm.

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling the cleanliness of stabilizing molten steel with residual cold steel in RH, characterized in that: Includes the following steps: (1) Determine whether cold steel melting occurs in the RH furnace based on the trend of CO concentration change in the flue gas of the RH furnace: If the CO concentration decreases naturally after reaching the peak, there is no problem of residual cold steel in the RH furnace, and the conventional RH vacuum treatment continues. If the CO concentration starts to decrease after reaching its peak, but then rises again, the moment it starts to rise again indicates that during the RH process, the remaining cold steel in the RH furnace begins to melt under the heat generated by the RH molten steel circulation. (2) When the cold steel begins to melt, the pressure in the RH furnace is reduced to atmospheric pressure, and the ladle is rotated or moved so that the cold steel collection trough is located directly below the RH furnace to facilitate the collection of cold steel; (3) Use an oxygen lance to quickly purge and melt the cold steel, and drip the molten cold steel into the cold steel collection tank. The purging time is ≤60s. (4) After the cold steel is purged and dripped, rotate or move the ladle so that the cold steel collection tank is located at the bottom of the impregnation tube, quickly evacuate to the predetermined vacuum level, and continue to carry out RH vacuum treatment. The RH furnace temperature must be ≥ (T0+30)℃, where T0 is the corresponding liquidus temperature of molten steel, and the measurement point is the temperature of the inner wall of the refractory material at the bottom of the RH furnace. The time taken from the start of vacuum breaking to the re-vacuuming to the predetermined vacuum level is ≤120s; After RH treatment, the O content in molten steel can be stably controlled to ≤4.5ppm.

2. The method for controlling the cleanliness of stabilizing molten steel with residual cold steel in RH according to claim 1, characterized in that: The oxygen flow rate of the oxygen lance in step (3) is 1600~2000 Nm. 3 / h.

3. The method for controlling the cleanliness of stabilizing molten steel with residual cold steel in RH according to claim 1, characterized in that: The predetermined vacuum level mentioned in step (4) is ≤67Pa.

Images