Method for desulfurizing molten steel in RH furnace and desulfurized steel product

Abstract

The invention provides a method for desulfurizing molten steel in an RH furnace and a desulfurized steel product, and the method comprises the following steps: transporting the molten steel to an operation position of the RH furnace, carrying out bottom blowing on a steel ladle, and maintaining until the work of the RH furnace is finished; the steel ladle is jacked up or falls down from a vacuum chamber of the RH furnace, and the RH furnace is vacuumized, so that the liquid level height of molten steel in the vacuum chamber of the RH furnace is smaller than or equal to 250 mm; adding a desulfurizing agent into the vacuum chamber of the RH furnace; and the molten steel is subjected to alloying treatment, and the molten steel subjected to alloying treatment is conveyed out for casting forming. According to the method for desulfurizing the molten steel in the RH furnace, the desulfurization efficiency of the RH furnace can be improved.

Description

Technical Field

[0001] This application relates to the technical field of steel smelting, and particularly to a method for desulfurizing molten steel in an RH furnace and a desulfurized steel product. Background Art

[0002] The RH furnace is a very effective molten steel vacuum degassing treatment device. The cleanliness of the molten steel in the RH furnace is also the best in large-scale steelmaking production. However, compared with other molten steel refining equipment such as the LF furnace, the desulfurization efficiency of the RH furnace is quite limited. In view of this, it is necessary to design a new desulfurization process in the RH furnace according to the flow characteristics in the RH furnace to improve the desulfurization efficiency of the RH furnace. Summary of the Invention

[0003] Based on this, this application provides a method for desulfurizing molten steel in an RH furnace and a desulfurized steel product, which can improve the desulfurization efficiency of the RH furnace.

[0004] The first aspect of this application provides a method for desulfurizing molten steel in an RH furnace, including:

[0005] Transport the molten steel to the operating position of the RH furnace, perform bottom blowing on the ladle and maintain it until the end of the operation of the RH furnace;

[0006] Lift the ladle or lower the vacuum chamber of the RH furnace, and perform a vacuum pumping operation on the RH furnace so that the liquid level height of the molten steel in the vacuum chamber of the RH furnace is less than or equal to 250 mm;

[0007] Add a desulfurizing agent into the vacuum chamber of the RH furnace;

[0008] Perform alloying treatment on the molten steel, and transport the alloyed molten steel out for casting and forming.

[0009] In some embodiments of this application, the liquid level height of the molten steel in the vacuum chamber of the RH furnace is 100 mm to 200 mm.

[0010] In some embodiments of this application, before adding the desulfurizing agent into the vacuum chamber of the RH furnace, it further includes:

[0011] Adjust the flow rate of the lifting gas of the RH furnace to be higher than the flow rate in the standby state of the vacuum chamber of the RH furnace;

[0012] Optionally, the flow rate of the lifting gas of the RH furnace is 60 Nm 3 / h to 140 Nm 3 / h, and the flow rate in the standby state of the vacuum chamber of the RH furnace is 45 Nm 3 / h to 60 Nm 3 / h;

[0013] Optionally, the lifting gas includes nitrogen and / or argon.

[0014] In some embodiments of the present application, one or more of the following conditions are satisfied:

[0015] (1) The average particle size of the desulfurizer is less than or equal to 50 mm, and may be optionally 3 mm to 50 mm;

[0016] (2) The mass ratio of the desulfurizer to the molten steel is 1:1000 to 15:1000;

[0017] (3) The desulfurizer includes 12CaO·7Al2O3 phase and 11CaO·7Al2O3·CaF2 phase. In the desulfurizer, the sum of the mass percentage contents of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is more than 30%;

[0018] Optionally, in the desulfurizer, the sum of the mass percentage contents of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is 30% to 80%.

[0019] In some embodiments of the present application, the desulfurizer includes the following components by mass percentage: CaO, 35% to 50%; CaF2, 5% to 35%; Al2O3, 20% to 38%; SiO2, 1% to 8%; MgO ≤ 8%; TiO2 ≤ 0.1%; C ≤ 0.15%; S ≤ 0.1%.

[0020] In some embodiments of the present application, the desulfurizer is added to the vacuum chamber of the RH furnace in 2 to 3 batches.

[0021] In some embodiments of the present application, one or more of the following conditions are satisfied:

[0022] (1) The vacuum degree of the evacuation operation is 0 kPa to 10 kPa;

[0023] (2) The nominal capacity of the ladle is 120 tons to 350 tons.

[0024] In some embodiments of the present application, alloying treatment of the molten steel is performed, including:

[0025] Performing an oxygen blowing heating operation according to the target temperature of the RH furnace;

[0026] According to the target chemical composition requirements of the molten steel in the RH furnace, ferroalloys are added to the molten steel for smelting treatment to alloy the molten steel;

[0027] Optionally, the time of the smelting treatment is 15 min to 60 min.

[0028] In some embodiments of the present application, one or more of the following conditions are satisfied:

[0029] (1) During the alloying treatment, the vacuum degree of the RH furnace is controlled to be 0 - 10 kPa and maintained for more than 3 minutes;

[0030] (2) During the alloying treatment, the flow rate of the lifting gas of the RH furnace is controlled to be 140 Nm 3 / h - 240 Nm 3 / h and maintained for more than 3 minutes;

[0031] (3) The alloying treatment is completed before the addition of the desulfurizer, and / or is carried out within 6 min - 20 min after the addition of the desulfurizer.

[0032] The second aspect of the present application provides a desulfurized steel product obtained by the method described in the first aspect of the present application.

[0033] The above method provided by the present application can reduce the flow rate of the molten steel, reduce the formation of vortices and weaken the kinetic energy of the vortices by reducing the liquid level height of the molten steel in the vacuum chamber of the RH furnace to be less than or equal to 250 mm, and reduce the relative velocity between the molten steel and the desulfurization slag, thereby effectively slowing down the roll-out effect of the desulfurization slag, further increasing the reaction time between the steel and the slag, and improving the desulfurization effect. Specific Embodiments

[0034] To facilitate the understanding of the present application, the present application will be described more comprehensively below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0035] For simplicity, the present application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, although not explicitly recorded, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower limit or upper limit and combined with any other point or single value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be noted that unless otherwise specified, the term "and / or" used herein includes any and all combinations of one or more of the related listed items, "above" and "below" include the recited number, and "one or more" means two or more for "more than one".

[0037] In this document, when referring to a numerical interval (i.e., a numerical range), unless otherwise specifically stated, the distribution of the selectable numerical values within this numerical interval is considered continuous and includes the two numerical endpoints of this numerical interval (i.e., the minimum value and the maximum value), as well as each numerical value between these two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within this numerical interval, it includes the two endpoint integers of this numerical range, as well as each integer between the two endpoints, which is equivalent to directly listing each integer. When providing multiple numerical ranges to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. The "numerical interval" allows for a broad inclusion of numerical interval types such as percentage intervals, ratio intervals, and ratio value intervals.

[0038] In this document, for a method process involving multiple steps, unless there are clear different descriptions in this document, the execution of these steps is not strictly limited in order, and they can be executed in an order other than the described one. Moreover, any step can include multiple sub-steps or multiple stages. These sub-steps or stages do not necessarily need to be completed at the same moment but can be executed at different moments, and their execution order is not necessarily sequential but can be executed alternately or simultaneously with other steps or a part of the sub-steps or stages of other steps.

[0039] The above application content of this application does not intend to describe every disclosed embodiment or every implementation mode in this application. The following description more specifically gives examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. In each instance, the listing is only a representative group and should not be construed as exhaustive.

[0040] In the research process, the inventor found that, compared with other molten steel refining equipment such as LF furnaces, the desulfurization efficiency of RH furnaces is very limited. The main reason is that the stirring in the vacuum chamber of the RH furnace is very strong, and the flow rate of the molten steel is very high, which will quickly roll the desulfurization slag out of the vacuum chamber and into the ladle top slag, thus losing the driving force for desulfurization.

[0041] In view of this, in order to weaken the "rolling out" effect of the slag in the RH furnace, increase the residence time of the desulfurization slag in the RH furnace to improve the desulfurization effect in the RH furnace, and at the same time not overly weaken the mixing effect of the molten steel and slag in the vacuum chamber, the present application proposes the following technical solutions.

[0042] In a first aspect, the present application provides a method for desulfurizing molten steel in an RH furnace, which may include the following steps:

[0043] Transport the molten steel to the operating position of the RH furnace, perform bottom blowing on the ladle and maintain it until the end of the operation of the RH furnace;

[0044] Lift the ladle or lower the vacuum chamber of the RH furnace, and perform a vacuum pumping operation on the RH furnace so that the liquid level height of the molten steel in the vacuum chamber of the RH furnace is less than or equal to 250 mm;

[0045] Add desulfurizing agent into the vacuum chamber of the RH furnace;

[0046] Perform alloying treatment on the molten steel, and transport the alloyed molten steel out for casting and forming.

[0047] In the above method provided by the present application, by reducing the liquid level height of the molten steel in the vacuum chamber of the RH furnace and making it less than or equal to 250 mm, the flow rate of the molten steel can be reduced, the formation of vortices can be reduced and the kinetic energy of the vortices can be weakened (i.e., reduce the vortices), and the relative velocity between the molten steel and the desulfurization slag can be reduced. Thus, the rolling out effect of the desulfurization slag can be effectively slowed down, and further the reaction time of the molten steel and slag can be increased, improving the desulfurization effect. Accordingly, using the above method during steelmaking can effectively improve the desulfurization rate of the RH furnace process, thereby reducing the sulfur content of the prepared molten steel and steel products, improving the purity of the molten steel and steel products, and at the same time relieving the production pressure of the LF furnace.

[0048] At the same time, when the liquid level height of the molten steel in the vacuum chamber of the RH furnace is less than or equal to 250 mm, a small circulation can be formed in the surface layer area near the liquid level of the molten steel, but the molten steel at the bottom of the ladle is difficult to participate in the circulation process, resulting in uneven flow of the molten steel and easy segregation of the molten steel composition. In view of this, cooperating with the operation of bottom blowing on the ladle can make the molten steel at the bottom of the ladle flow upward to participate in the circulation, thus facilitating the promotion of the uniformity of the molten steel flow and solving the problem of uneven circulation of the molten steel in the ladle easily caused by the lower liquid level height of the molten steel. In this way, by combining the operation of reducing the liquid level height of the molten steel with bottom blowing of the ladle, while achieving the improvement of the desulfurization effect, the homogenization of the molten steel can also be achieved.

[0049] It can be understood that the "liquid level height of molten steel in the vacuum chamber" described in this application refers to the height difference between the surface of the molten steel liquid level in the vacuum chamber and the surface of the refractory material at the bottom of the vacuum chamber.

[0050] In some embodiments, making the liquid level height of molten steel in the vacuum chamber of the RH furnace less than or equal to 250 mm can be achieved by increasing the vacuum degree in the vacuum chamber (i.e., reducing the vacuum pressure); for example, for every 1 kPa reduction in the pressure in the vacuum chamber, the liquid level height of the molten steel can rise by approximately 14.5 mm (related to the density of the molten steel, calculated with reference to the reference value of the molten steel density of 7.0 g / cm 3 ). In some other embodiments, making the liquid level height of molten steel in the vacuum chamber of the RH furnace less than or equal to 250 mm can also be achieved by reducing the height of the ladle relative to the vacuum chamber.

[0051] It should be noted that for "bottom blowing the ladle" in this application, it is only necessary to blow until the molten steel liquid level fluctuates slightly or bulges slightly.

[0052] It should be noted that while performing the vacuum pumping operation on the RH furnace, the ladle can be slowly raised or the vacuum chamber can be lowered to prevent slag suction.

[0053] In some embodiments, the liquid level height of molten steel in the vacuum chamber of the RH furnace can be 250 mm, 249 mm, 238 mm, 227 mm, 216 mm, 205 mm, 194 mm, 183 mm, 172 mm, 161 mm, 150 mm, 141 mm, 132 mm, 123 mm, 114 mm, 105 mm, 96 mm, 87 mm, 78 mm, 69 mm, 50 mm, etc. Optionally, the liquid level height of molten steel in the vacuum chamber of the RH furnace is 100 mm to 200 mm. In this way, it is beneficial to improve the desulfurization effect and also beneficial to achieve the homogenization of the molten steel.

[0054] In some embodiments, before adding the desulfurizing agent into the vacuum chamber of the RH furnace, it may further include:

[0055] Adjusting the flow rate of the lifting gas of the RH furnace to be higher than the flow rate in the standby state of the vacuum chamber of the RH furnace.

[0056] In some embodiments, the flow rate of the lifting gas of the RH furnace is 60 Nm 3 / h to 140 Nm 3 / h, and the flow rate in the standby state of the vacuum chamber of the RH furnace is 45 Nm 3 / h to 60 Nm 3 / h (this flow rate corresponds to an RH furnace with a nominal capacity of 180 tons to 300 tons).

[0057] In some embodiments, the lifting gas includes nitrogen and / or argon.

[0058] In some embodiments, the average particle size of the desulfurizer is less than or equal to 50 mm, and may be optionally 3 mm to 50 mm. For example, the average particle size of the desulfurizer may be 3 mm, 5 mm, 8 mm, 10 mm, 14 mm, 25 mm, 36 mm, 47 mm, 50 mm or within the range composed of any of the above values. Thus, it is beneficial to form a cooperation with the flow control agent, further weaken the "rolling out" effect, increase the residence time of the desulfurized slag in the RH furnace, and improve the desulfurization effect in the RH furnace.

[0059] In some embodiments, the mass ratio of the desulfurizer to the molten steel is 1:1000 to 15:1000.

[0060] In some embodiments, the desulfurizer includes 12CaO·7Al2O3 phase and 11CaO·7Al2O3·CaF2 phase. In the desulfurizer, the sum of the mass percentage contents of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is more than 30%. Thus, the melting point of the desulfurizer is relatively low, its melting speed in the vacuum chamber is relatively fast, the interaction between the desulfurizer and the molten steel can be accelerated, so as to accelerate the desulfurization rate and improve the desulfurization efficiency.

[0061] In some embodiments, in the desulfurizer, the sum of the mass percentage contents of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is 30% to 80%.

[0062] In some embodiments, the desulfurizer includes the following components by mass percentage: CaO, 35% to 50%; CaF2, 5% to 35%; Al2O3, 20% to 38%; SiO2, 1% to 8%; MgO ≤ 8%; TiO2 ≤ 0.1%; C ≤ 0.15%; S ≤ 0.1%.

[0063] In some embodiments, the desulfurizer is added to the vacuum chamber of the RH furnace in 2 to 3 batches.

[0064] It can be understood that the addition amount of the desulfurizer can be adjusted according to different steel grades and desulfurization rates, etc., and no limitation is made here. For example, for low-carbon low-silicon aluminum-killed steel (w[C]<0.15%, w[Si]<0.10%, w[Al]=0.02%~0.1%), for every 2.5%~5.0% increase in the desulfurization rate, 1 kg / ton of steel of the desulfurizer is added; for high-silicon steel grades (w[Si]>0.30%, w[Al]=0.02%~0.1%), for every 3.5%~8.0% increase in the desulfurization rate, 1 kg / ton of steel of the desulfurizer is added; for high-silicon high-aluminum steel grades (w[Al]>0.1%, w[Si]>1.0%), for every 5.0%~12.0% increase in the desulfurization rate, 1 kg / ton of steel of the desulfurizer is added.

[0065] In some embodiments, the vacuum degree of the vacuum pumping operation is 0 kPa~10 kPa.

[0066] It should be noted that except during the alloying treatment, the steel desulfurization process can maintain the lifting gas flow rate in the RH furnace at 60 Nm 3 / h~140 Nm 3 / h.

[0067] In some embodiments, the lifting gas is an inert gas, including nitrogen and / or argon.

[0068] In some embodiments, the nominal capacity of the ladle is 120 tons~350 tons.

[0069] In some embodiments, the alloying treatment of the molten steel may include the following steps:

[0070] According to the target temperature of the RH furnace, an oxygen blowing heating operation is performed;

[0071] According to the target molten steel chemical composition requirements of the RH furnace, ferroalloys are put into the molten steel for smelting treatment to alloy the molten steel.

[0072] It can be understood that the "target temperature of the RH furnace" described in this application refers to the temperature required to achieve all necessary subsequent treatments (including but not limited to alloying, casting, etc.) of the molten steel; the "target molten steel chemical composition requirements of the RH furnace" refer to the target chemical composition required for the molten steel prepared by the RH furnace.

[0073] In some embodiments, the time of the smelting treatment is 15 min~60 min.

[0074] In some embodiments, the ferroalloys include but are not limited to ferrosilicon alloy, ferromanganese alloy, etc.

[0075] In some embodiments, during the alloying treatment, the vacuum degree of the RH furnace is controlled to be 0 - 10 kPa and maintained for more than 3 minutes. Thus, it is beneficial to increase the liquid level height of the molten steel in the vacuum chamber to more than 200 mm to strengthen the homogenization of ferroalloys.

[0076] In some embodiments, during the alloying treatment, the lifting gas flow rate of the RH furnace is controlled to be 140 Nm 3 / h - 240 Nm 3 / h and maintained for more than 3 minutes. For example, the lifting gas flow rate of the RH furnace can be 140 Nm 3 / h, 160 Nm 3 / h, 180 Nm 3 / h, 200 Nm 3 / h, 210 Nm 3 / h, 230 Nm 3 / h, 240 Nm 3 / h. Thus, it is beneficial to increase the stirring intensity and promote the melting and homogenization of ferroalloys during the smelting process.

[0077] In some embodiments, the alloying treatment is completed before the addition of the desulfurizer, or is carried out within 6 min - 20 min after the addition of the desulfurizer. Conducting the alloying treatment after the addition of the desulfurizer is beneficial to obtaining a better desulfurization effect.

[0078] In some embodiments, the vacuum chamber system may include a vacuum chamber, immersion tubes (riser tube and downcomer), hot bend pipe, alloy feeding port, etc. Each part can be connected by steel structure welding and is attached with refractory materials for heat preservation and isolation of molten steel.

[0079] In a second aspect, the present application provides a desulfurized steel product prepared by the method described in the first aspect of the present application.

[0080] Examples

[0081] The following are specific examples. The following examples more specifically describe the content disclosed in the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0082] Example 1

[0083] The method for desulfurizing molten steel in an RH furnace in this example includes the following steps:

[0084] Transport the ladle containing approximately 300 tons of molten steel to the treatment position of the RH furnace;

[0085] Open the bottom blowing of the ladle, adjust the argon gas flow rate to 50 - 400 NL / min, and observe the phenomenon of bulging on the molten steel surface;

[0086] Lift the ladle to the immersion tube so that the immersion tube is immersed in the ladle, and make the liquid level height of the molten steel in the vacuum chamber 150 mm;

[0087] Start the vacuum pumping operation. As the vacuum pressure drops, gradually increase the lifting height so that the vacuum degree of the vacuum pumping operation is controlled at 30 kPa, and adjust the lifting gas flow rate to 120 Nm 3 / h, take a molten steel sample to test the full composition (including sulfur content);

[0088] Add 1200 kg of desulfurizer into the vacuum chamber in two batches (with an interval of 6 min). Among them, the desulfurizer includes the following components by mass percentage: CaO, 50%; CaF2, 8%; Al2O3, 33%; SiO2, 2%; MgO, 5%; TiO2, 0.03%; C, 0.08%; the sum of the mass percentages of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is 46%; the average particle size of the desulfurizer is 43 mm;

[0089] After treatment for 15 min, add ferromanganese alloy to carry out alloying treatment on the molten steel;

[0090] After adding the alloy, adjust the vacuum degree to 4 kPa, and increase the lifting gas flow rate to 150 Nm 3 / h. After treatment for 4 min, take a molten steel sample to test the full composition (including sulfur content);

[0091] Vent the RH furnace and transport the qualified molten steel to continuous casting for shaping.

[0092] Example 2

[0093] Similar to the preparation method of Example 1, the main difference is: regulate the height of the ladle relative to the vacuum chamber so that the liquid level height of the molten steel in the vacuum chamber is 100 mm.

[0094] Example 3

[0095] Similar to the preparation method of Example 1, the main difference is: regulate the height of the ladle relative to the vacuum chamber so that the liquid level height of the molten steel in the vacuum chamber is 200 mm.

[0096] Example 4

[0097] Similar to the preparation method of Example 1, the main difference is that: the height of the ladle relative to the vacuum chamber is adjusted so that the liquid level height of the molten steel in the vacuum chamber is 250 mm.

[0098] Comparative Example 1

[0099] Similar to the preparation method of Example 1, the main difference is that: the height of the ladle relative to the vacuum chamber is adjusted so that the liquid level height of the molten steel in the vacuum chamber exceeds 300 mm. The specific steps are as follows:

[0100] Transport the ladle containing about 300 tons of molten steel to the treatment position of the RH furnace;

[0101] Open the bottom blowing of the ladle, adjust the argon flow rate to 400 NL / min, and observe that there is a bulging phenomenon on the molten steel surface;

[0102] Lift the ladle to the immersion tube so that the immersion tube is immersed in the ladle, and adjust the height of the ladle relative to the vacuum chamber so that the liquid level height of the molten steel in the vacuum chamber exceeds 300 mm;

[0103] Start the vacuum pumping operation. As the vacuum pressure drops, gradually increase the lifting height so that the vacuum degree of the vacuum pumping operation is controlled at 30 kPa, and adjust the lifting gas flow rate to 120 Nm 3 / h, take a molten steel sample to test the full composition (including sulfur content);

[0104] Add 1800 kg of desulfurizer into the vacuum chamber in two batches (with an interval of 3 min). Among them, the desulfurizer includes the following components by mass percentage: CaO, 50%; CaF2, 8%; Al2O3, 33%; SiO2, 2%; MgO, 5%; TiO2, 0.03%; C, 0.08%; the sum of the mass percentages of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is 46%; the average particle size of the desulfurizer is 43 mm;

[0105] After treatment for 15 min, add ferromanganese alloy to carry out alloying treatment on the molten steel;

[0106] After the alloy is added, adjust the vacuum degree to 4 kPa, and increase the lifting gas flow rate to 150 Nm 3 / h. After treatment for 4 min, take a molten steel sample to test the full composition (including sulfur content);

[0107] The RH furnace breaks the vacuum, and transport the qualified molten steel to continuous casting for pouring and forming.

[0108] Among them, the test conditions or test standards for each performance test item are as follows:

[0109] (1) Detection of sulfur content in molten steel

[0110] The carbon and sulfur contents of molten steel are determined by the carbon-sulfur method 《Combustion-infrared absorption method in GB / T 12497-2014 Chemical analysis methods for iron, steel and alloys》.

[0111] 《GB / T 4336-2002 Carbon steels and medium and low alloy steels - Spark source atomic emission spectrometric analysis method (conventional method)》 and 《GB / T 11170-2008 Stainless steels - Determination of multi-elements content - Spark discharge atomic emission spectrometric method (conventional method)》 are used to test the composition of molten steel (carbon and sulfur elements can also be included according to the accuracy requirements).

[0112] Desulfurization rate = 100% × (1 - w[S] after RH furnace treatment ÷ w[S] before RH furnace treatment).

[0113] Table 1

[0114]

[0115] As can be seen from Table 1 above, although the addition amount of desulfurizer in Comparative Example 1 is much higher than that in Examples 1 to 4, the desulfurization rate is much lower than that in Examples 1 to 4, indicating that controlling the liquid level height of molten steel in the vacuum chamber below 250 mm can effectively improve the desulfurization efficiency.

[0116] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0117] The above-described embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for desulfurizing molten steel in an RH furnace, characterized in that: include: Transport the molten steel to the RH furnace operation position, perform bottom blowing on the ladle and maintain it until the RH furnace operation is completed; Lifting the ladle or lowering the vacuum chamber of the RH furnace, and evacuating the RH furnace so that the liquid level of the molten steel in the vacuum chamber of the RH furnace is less than or equal to 250 mm; Adding a desulfurizing agent into the vacuum chamber of the RH furnace; The molten steel is alloyed and then transported out for casting.

2. The method according to claim 1, characterized in that The liquid level of the molten steel in the vacuum chamber of the RH furnace is 100 mm to 200 mm.

3. The method according to claim 1 or 2, characterized in that: Before adding the desulfurizing agent into the vacuum chamber of the RH furnace, the method further comprises: adjusting the flow rate of the lifting gas of the RH furnace to be higher than the flow rate of the vacuum chamber of the RH furnace in the standby state; Optionally, the flow rate of the lifting gas of the RH furnace is 60Nm 3 / h~140Nm 3 / h, the flow rate of the RH furnace vacuum chamber in standby state is 45Nm 3 / h~60Nm 3 / h; Optionally, the lifting gas comprises nitrogen and / or argon.

4. The method according to claim 1 or 2, characterized in that: One or more of the following conditions are met: (1) The average particle size of the desulfurizer is less than or equal to 50 mm, and can be selected from 3 mm to 50 mm; (2) The mass ratio of the desulfurizer to the molten steel is 1:1000 to 15:1000; (3) The desulfurizer includes a 12CaO·7Al2O3 phase and a 11CaO·7Al2O3·CaF2 phase, and in the desulfurizer, the sum of the mass percentages of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is greater than 30%; Optionally, in the desulfurizer, the sum of the mass percentages of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is 30% to 80%.

5. The method according to claim 4, characterized in that The desulfurizer includes the following components by mass percentage: CaO, 35% to 50%; CaF2, 5% to 35%; Al2O3, 20% to 38%; SiO2, 1% to 8%; MgO≤8%; TiO2≤0.1%; C≤0.15%; S≤0.1%。 6. The method according to claim 1 or 2, characterized in that: The desulfurizing agent is added into the vacuum chamber of the RH furnace in 2 to 3 batches.

7. The method according to claim 1 or 2, characterized in that: One or more of the following conditions are met: (1) The vacuum degree of the vacuum pumping operation is 0 kPa to 10 kPa; (2) The nominal capacity of the ladle is 120 tons to 350 tons.

8. The method according to claim 1 or 2, characterized in that: The molten steel is alloyed, comprising: According to the target temperature of the RH furnace, an oxygen blowing and heating operation is performed; According to the target chemical composition requirements of the molten steel in the RH furnace, adding ferroalloy into the molten steel for smelting treatment to alloy the molten steel; Optionally, the smelting treatment time is 15min~60min.

9. The method according to claim 1 or 2, characterized in that: One or more of the following conditions are met: (1) During the alloying treatment, the vacuum degree of the RH furnace is controlled to be 0-10 kPa and maintained for more than 3 minutes; (2) During the alloying treatment, the lifting gas flow rate of the RH furnace was controlled to 140 Nm 3 / h~240Nm 3 / h and maintain for more than 3 minutes; (3) The alloying treatment is completed before the desulfurization agent is added, and / or is carried out within 6 minutes to 20 minutes after the desulfurization agent is added.

10. A desulfurized steel product, characterized in that: It is prepared by the method according to any one of claims 1 to 9.

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