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 (Ruhrstahl Heraeus) furnace and a desulfurized steel product. The method comprises the following steps: transporting the molten steel to an operation position of the RH furnace, jacking a steel ladle or falling off a vacuum chamber of the RH furnace, and vacuumizing the RH furnace; adding a flow control agent into a vacuum chamber of the RH furnace, and adding a desulfurizing agent; 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 device for vacuum degassing molten steel. 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] Transporting the molten steel to the operating position of the RH furnace, lifting the ladle or lowering the vacuum chamber of the RH furnace, and performing a vacuum pumping operation on the RH furnace;

[0006] Adding a flow control agent and a desulfurizing agent into the vacuum chamber of the RH furnace;

[0007] Performing alloying treatment on the molten steel, and transporting the alloyed molten steel out for casting and forming.

[0008] In some embodiments of this application, based on the mass of the molten steel, the addition amount of the flow control agent is 0.1 kg / ton to 1.0 kg / ton.

[0009] In some embodiments of this application, one or more of the following conditions are satisfied:

[0010] (1) The melting point of the flow control agent is greater than or equal to 1700 °C;

[0011] (2) The flow control agent includes one or more of alumina-based materials, aluminum-magnesium spinel-based materials, and magnesia-chrome-based materials;

[0012] (3) The average particle size of the flow control agent is 30 mm to 300 mm, and can be selected as 80 mm to 300 mm.

[0013] In some embodiments of this application, one or more of the following conditions are satisfied:

[0014] (1) The average particle size of the desulfurizing agent is less than or equal to 50 mm, and can be selected as 3 mm to 50 mm;

[0015] (2) The mass ratio of the desulfurizer to the molten steel is 1:1000 to 15:1000.

[0016] (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%;

[0017] 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%.

[0018] 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%.

[0019] In some embodiments of the present application, the desulfurizer is added to the vacuum chamber of the RH furnace in 2 to 3 batches.

[0020] In some embodiments of the present application, one or more of the following conditions are satisfied:

[0021] (1) The vacuum degree of the evacuation operation is 0 kPa to 10 kPa;

[0022] (2) The lifting gas flow rate of the evacuation operation is 100 Nm 3 / h to 210 Nm 3 / h;

[0023] Optionally, the lifting gas includes nitrogen and / or argon;

[0024] (3) The nominal capacity of the ladle is 120 tons to 350 tons.

[0025] In some embodiments of the present application, alloying treatment of the molten steel includes:

[0026] According to the target temperature of the RH furnace, an oxygen blowing and temperature raising operation is performed;

[0027] According to the target chemical composition requirements of the molten steel in the RH furnace, ferroalloys are put into the molten steel for smelting treatment to alloy the molten steel;

[0028] Optionally, the time of the smelting treatment is 15 min to 60 min.

[0029] In some embodiments of the present application, one or more of the following conditions are satisfied:

[0030] (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;

[0031] (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;

[0032] (3) The alloying treatment is completed before the addition of the desulfurizing agent, or is carried out within 6 min - 20 min after the addition of the desulfurizing agent.

[0033] A second aspect of the present application provides a desulfurized steel product obtained by the method described in the first aspect of the present application.

[0034] The above method provided by the present application can, to a certain extent, prevent the formation of vortices caused by the rapid flow of molten steel by adding a flow control agent to the vacuum chamber of the RH furnace, and can dissipate the kinetic energy of the vortices, block the entry of desulfurization slag into the vortices to a certain extent, and finally effectively slow down the rolling-out effect of the desulfurization slag, thereby increasing the reaction time between the steel and the slag and improving the desulfurization effect. Specific Embodiments

[0035] 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, these embodiments are provided to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0036] 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 the range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recorded.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. It should be noted that unless otherwise stated, 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".

[0038] In this document, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the selectable numerical values within the numerical interval is considered continuous and includes the two numerical endpoints of the 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 integers within the numerical interval, it includes the two endpoint integers of the 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 the 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.

[0039] In this document, for a method process involving multiple steps, unless there are clear different descriptions in this document, the execution of these steps has no strict order limit, 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 does not necessarily need to be sequential, but can be executed alternately or simultaneously with other steps or a part of the sub-steps or stages of other steps.

[0040] The above application content of this application does not intend to describe every disclosed embodiment or every implementation manner in this application. The following description more specifically gives examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, and these embodiments can be used in various combinations. In each instance, the listing is only a representative group and should not be construed as exhaustive.

[0041] In the research process, the inventors 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.

[0042] 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.

[0043] In a first aspect, the present application provides a method for desulfurizing molten steel in an RH furnace, which may include the following steps:

[0044] Transport the molten steel to the operating position of the RH furnace, lift the ladle or lower the vacuum chamber of the RH furnace, and perform a vacuum pumping operation on the RH furnace;

[0045] Add a flow control agent and a 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 method provided by the present application, by adding a flow control agent into the vacuum chamber of the RH furnace, the formation of vortices caused by the rapid flow of the molten steel can be blocked to a certain extent, and the kinetic energy of the vortices can be dissipated, which can block the entry of the desulfurization slag into the vortices to a certain extent. Finally, the rolling out effect of the desulfurization slag can be effectively slowed down, thereby increasing the reaction time of the molten steel and slag and 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] In some embodiments, based on the mass of the molten steel, the addition amount of the flow control agent is 0.1 kg / ton to 1.0 kg / ton. For example, the addition amount of the flow control agent can be 0.1 kg / ton, 0.2 kg / ton, 0.3 kg / ton, 0.4 kg / ton, 0.5 kg / ton, 0.6 kg / ton, 0.7 kg / ton, 0.8 kg / ton, 0.9 kg / ton, 1.0 kg / ton or within the range composed of any of the above values. In this way, it can not only have a good blocking effect on the entry of the desulfurization slag into the vortices and improve the desulfurization effect, but also be beneficial to cost control.

[0049] In some embodiments, the melting point of the flow control agent is greater than or equal to 1700 °C. In this way, the flow control agent is not easily melted at the temperature in the vacuum chamber of the RH furnace, and can effectively improve the desulfurization effect.

[0050] In some embodiments, the flow control agent includes one or more of alumina-based materials, spinel-based materials, and magnesia-chrome materials. The above materials selected for the flow control agent are not easily reactive with desulfurization slag and molten steel, and can effectively improve the desulfurization effect.

[0051] In some embodiments, the average particle size of the flow control agent is 30 mm to 300 mm, and can be selected as 80 mm to 300 mm. For example, the average particle size of the flow control agent can be 30 mm, 50 mm, 80 mm, 100 mm, 130 mm, 150 mm, 170 mm, 200 mm, 230 mm, 250 mm, 270 mm, 300 mm or within the range composed of any of the above values. In this way, not only can the flow control agent itself not be easily carried out of the vacuum chamber by the vortex, but it can also easily fall into the ladle slag after the vacuum is completed.

[0052] It can be understood that when the average particle size of the flow control agent is 30 mm to 80 mm, it can be put into the RH furnace vacuum chamber through the alloy feeding system; when its average particle size is 80 mm to 300 mm, it can be manually thrown below the nozzle of the immersion tube before the ladle rises, so that it floats into the vacuum chamber during the rising process of the ladle.

[0053] In some embodiments, the average particle size of the desulfurizing agent is less than or equal to 50 mm, and can be selected as 3 mm to 50 mm. For example, the average particle size of the desulfurizing agent can 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. In this way, it is beneficial to form a cooperation with the flow control agent, further weaken the "carrying out" effect, increase the residence time of the desulfurization slag in the RH furnace, and improve the desulfurization effect in the RH furnace.

[0054] In some embodiments, the mass ratio of the desulfurizing agent to the molten steel is 1:1000 to 15:1000.

[0055] In some embodiments, the desulfurizing agent includes 12CaO·7Al2O3 phase and 11CaO·7Al2O3·CaF2 phase. In the desulfurizing agent, the sum of the mass percentages of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is more than 30%. In this way, the melting point of the desulfurizing agent is relatively low, its melting speed in the vacuum chamber is relatively fast, the interaction between the desulfurizing agent and the molten steel can be accelerated, so as to accelerate the desulfurization rate and improve the desulfurization rate.

[0056] In some embodiments, in the desulfurizing agent, the sum of the mass percentages of the 12CaO·7Al2O3 phase and the 11CaO·7Al2O3·CaF2 phase is 30% to 80%.

[0057] In some embodiments, the desulfurizer comprises the following components by mass percentage: CaO, 35% - 50%; CaF2, 5% - 35%; Al2O3, 20% - 38%; SiO2, 1% - 8%; MgO ≤ 8%; TiO2 ≤ 0.1%; C ≤ 0.15%; S ≤ 0.1%.

[0058] In some embodiments, the desulfurizer is added to the vacuum chamber of the RH furnace in 2 - 3 batches.

[0059] It can be understood that the addition amount of the desulfurizer can be adjusted according to different steel grades and desulfurization rates, etc., and is not limited herein.

[0060] In some embodiments, the vacuum degree of the evacuation operation is 0 kPa - 10 kPa.

[0061] In some embodiments, the flow rate of the lifting gas for the evacuation operation is 100 Nm 3 / h - 210 Nm 3 / h.

[0062] It should be noted that except during the alloying treatment, the flow rate of the lifting gas in the RH furnace can be maintained at 100 Nm 3 / h - 210 Nm 3 / h during the desulfurization process of the molten steel.

[0063] In some embodiments, the lifting gas is an inert gas, including nitrogen and / or argon.

[0064] In some embodiments, the nominal capacity of the ladle is 120 tons - 350 tons.

[0065] In some embodiments, the alloying treatment of the molten steel may include the following steps:

[0066] According to the target temperature of the RH furnace, an oxygen blowing and heating operation is performed;

[0067] 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.

[0068] It can be understood that the "target temperature of the RH furnace" as 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 chemical composition requirements of the molten steel in the RH furnace" refer to the target chemical composition that the molten steel prepared by the RH furnace needs to reach.

[0069] In some embodiments, the time of the smelting treatment is 15 min - 60 min.

[0070] In some embodiments, the ferroalloy includes but is not limited to ferrosilicon alloy, ferromanganese alloy, etc.

[0071] 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. In this way, 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 the ferroalloy.

[0072] It can be understood that the "liquid level height of the 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.

[0073] 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 or within the range composed of any of the above values. In this way, it is beneficial to increase the stirring intensity and promote the melting and homogenization of the ferroalloy during the smelting process.

[0074] In some embodiments, the alloying treatment is completed before the addition of the desulfurizing agent, or is carried out within 6 min - 20 min after the addition of the desulfurizing agent. Conducting the alloying treatment after the addition of the desulfurizing agent is beneficial to obtaining a better desulfurization effect.

[0075] In some embodiments, the vacuum chamber system may include a vacuum chamber, immersion tubes (riser tube and downcomer), hot bend pipes, alloy feeding ports, etc. Each part can be welded and connected through a steel structure and is attached with refractory materials for heat preservation and isolation of the molten steel.

[0076] In a second aspect, the present application provides a desulfurized steel product obtained by the method described in the first aspect of the present application.

[0077] Example

[0078] The following are specific embodiments. The following embodiments more specifically describe the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the present application disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0079] Example 1

[0080] The method for desulfurizing molten steel in an RH furnace in this embodiment includes the following steps:

[0081] Transport a ladle containing approximately 300 tons of molten steel to the RH furnace treatment position;

[0082] 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 exceed 300 mm;

[0083] 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 5 kPa, and adjust the lifting gas flow rate to 150 Nm 3 / h, take a molten steel sample to test the full composition (including sulfur content);

[0084] Add 100 kg of flow control agent into the vacuum chamber at one time. Among them, the flow control agent is an alumina-based material with an average particle size of 80 mm;

[0085] Add 1200 kg of desulfurizer (at an interval of 6 min) into the vacuum chamber in two batches. 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;

[0086] After treatment for 15 min, add ferromanganese alloy to carry out alloying treatment on the molten steel;

[0087] After the alloy is added, increase the lifting gas flow rate to 180 Nm 3 / h. After treatment for 4 min, take a molten steel sample to test the full composition (including sulfur content);

[0088] Break the vacuum of the RH furnace, and transport the qualified molten steel to continuous casting for pouring and forming.

[0089] Example 2

[0090] Similar to the preparation method of Example 1, the main difference is that: the flow control agent is made of alumina material with an average particle size of 30 mm.

[0091] Example 3

[0092] Similar to the preparation method of Example 1, the main difference is that: the flow control agent is made of alumina material with an average particle size of 300 mm.

[0093] Comparative Example 1

[0094] Similar to the preparation method of Example 1, the main difference is that: no flow control agent is added during the process. The specific steps are as follows:

[0095] Transport a ladle containing about 300 tons of molten steel to the treatment position of the RH furnace;

[0096] Lift the ladle to make the immersion tube dip into the ladle, and make the liquid level height of the molten steel in the vacuum chamber exceed 300 mm;

[0097] Start the vacuum pumping operation. As the vacuum pressure drops, gradually increase the lifting height to control the vacuum degree of the vacuum pumping operation to 5 kPa, and adjust the lifting gas flow rate to 150 Nm 3 / h, take a molten steel sample to test the full composition (including sulfur content);

[0098] Add 1800 kg of RH furnace 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;

[0099] After treatment for 15 min, add ferromanganese alloy to carry out alloying treatment on the molten steel;

[0100] After the alloy is added, increase the lifting gas flow rate to 180 Nm 3 / h. After treatment for 4 min, take a molten steel sample to test the full composition (including sulfur content);

[0101] The RH furnace breaks the vacuum, and transports the qualified molten steel to continuous casting for pouring and forming.

[0102] Among them, the test conditions or test standards for each performance test item are as follows:

[0103] (1) Detection of sulfur content in molten steel

[0104] The carbon and sulfur contents of molten steel are determined by the carbon-sulfur method, i.e., the combustion-infrared absorption method in "GB / T 12497-2014 Methods for Chemical Analysis of Iron, Steel and Alloys - Combustion-Infrared Absorption Method".

[0105] "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-Element Contents - 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).

[0106] Desulfurization rate = 100% × (1 - w[S] after RH furnace treatment ÷ w[S] before RH furnace treatment).

[0107] Table 1

[0108]

[0109] It can be seen from Table 1 that although the addition amount of desulfurizer in Comparative Example 1 is much higher than that in Examples 1 to 3, the desulfurization rate is much lower than that in Examples 1 to 3, indicating that the addition of the flow control agent can effectively improve the desulfurization efficiency.

[0110] The technical features of the above-mentioned embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-mentioned 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 described in this specification.

[0111] The above-mentioned 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: Transporting molten steel to the operating position of the RH furnace, lifting the ladle or dropping the vacuum chamber of the RH furnace, and performing a vacuum operation on the RH furnace; Adding a flow control agent and 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 Based on the mass of the molten steel, the added amount of the flow control agent is 0.1kg / ton to 1.0kg / ton.

3. The method according to claim 1 or 2, characterized in that: One or more of the following conditions are met: (1) The melting point of the flow control agent is greater than or equal to 1700°C; (2) The flow control agent includes one or more of alumina material, aluminum magnesium spinel material and magnesium chromium material; (3) The average particle size of the flow control agent is 30 mm to 300 mm, and can be optionally 80 mm to 300 mm.

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 lifting gas flow rate of the vacuum operation is 100Nm 3 / h~210Nm 3 / h; Optionally, the lifting gas includes nitrogen and / or argon; (3) 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, 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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