A method for producing an ultra-low sulfur steel

Abstract

The application discloses a preparation method of ultra-low sulfur steel and belongs to the technical field of steelmaking. The preparation method of the ultra-low sulfur steel comprises the following steps: (1) adopting semi-steel with sulfur content less than or equal to 0.005% to clean and pretreat a steelmaking equipment, and then performing steelmaking to control the tapping temperature to be 1635 DEG C-1665 DEG C, so as to obtain crude steel S1; (2) adding a slag adjusting agent to a slag surface of the S1, and then preparing the ultra-low sulfur steel through RH vacuum refining; the RH vacuum refining comprises desulfurization treatment; the desulfurization treatment is that a desulfurizing agent is added from a vacuum device of an RH vacuum refining furnace into molten steel for desulfurization; the desulfurizing agent of the desulfurization treatment comprises the following components: 73wt%-78wt% of calcium oxide, 11wt%-13wt% of calcium fluoride, and the balance of impurities. The method reduces the sulfur content of the vacuum steel through the common optimization of the desulfurization material and the condition parameters.

Description

Technical Field

[0001] This invention relates to the field of steelmaking technology, and in particular to a method for preparing ultra-low sulfur steel. Background Technology

[0002] Sulfur is one of the harmful elements in steel, often segregating in the form of MnS at grain boundaries or heterogeneous interfaces, severely reducing the processing and performance properties of steel. Except for a few steel grades such as free-cutting steel, sulfur forms sulfide inclusions in steel, reducing its ductility, toughness, and impact toughness. High sulfur content can also lead to hydrogen-induced cracking in steel. Some high-grade special steels have extremely strict requirements for sulfur content, such as requiring the finished steel to have a sulfur content ≤0.005% and a hydrogen content ≤0.0002%, or even lower. High-quality pipeline steel and corrosion-resistant steel typically require a sulfur content ≤0.005%, or even ≤0.001%, while high-grade non-oriented electrical steel also requires [S] ≤0.002%.

[0003] To meet the production demands of low-sulfur steel, the commonly used industrial process is: hot metal pretreatment – ​​converter smelting – ladle refining – continuous casting. While hot metal pre-desulfurization can reduce the sulfur content to below 0.005%, it is difficult to further desulfurize deeply desulfurized hot metal during converter smelting. Conversely, the addition of sulfur-containing scrap steel, ore, lime, and other auxiliary materials during converter smelting can sometimes increase the sulfur content in the steel. Therefore, deep desulfurization treatment of the molten steel is essential during the ladle refining stage.

[0004] External desulfurization can be carried out in refining reactors such as LF furnaces, CAS, and RH. However, when certain steel grades require both desulfurization and dehydrogenation, traditional processes often separate external desulfurization from vacuum refining processes such as RH. Specifically, desulfurization is first performed in refining equipment such as LF, followed by dehydrogenation in vacuum refining furnaces such as RH. This segmented process has drawbacks such as large heat loss, complex material flow, and difficulty in production organization. Especially when the vacuum refining furnace such as RH itself has desulfurization tasks, desulfurization cannot be performed in refining equipment such as LF first.

[0005] Vacuum refining technology provides unique process conditions for steel desulfurization. RH vacuum refining technology has evolved from a simple degassing device into a multi-functional ladle refining system encompassing vacuum degassing, decarburization, oxygen blowing decarburization, powder injection desulfurization, temperature compensation, and uniform temperature and composition. RH vacuum desulfurization offers several advantages: vacuum smelting reduces oxygen activity in molten steel; it isolates the steel from air, preventing oxidation; it has a short processing cycle, high production capacity, and excellent refining effect. RH vacuum treatment also has unique advantages: the high vacuum within the RH chamber reduces oxygen activity in the molten steel, making desulfurization more effective; the RH process avoids top slag, minimizing the impact of top slag on the ladle; and the isolation from the atmosphere prevents nitrogen absorption due to surface turbulence in the molten steel. However, using RH vacuum refining alone has drawbacks such as low and unstable desulfurization rates, short reaction times and poor kinetic conditions, and poor effectiveness for weakly deoxidized steels.

[0006] Therefore, it is urgent to research and develop a new vacuum refining method for preparing ultra-low sulfur steel, thereby solving the problem that high-sulfur molten iron cannot be used to smelt ultra-low sulfur vacuum steel and improving the ability and stability of smelting vacuum low-sulfur steel. Summary of the Invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing ultra-low sulfur steel. The method reduces the sulfur content of the vacuum steel through the joint optimization of desulfurization materials and condition parameters.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a method for preparing ultra-low sulfur steel, comprising the following steps:

[0010] (1) Use semi-steel with sulfur content ≤0.005% to clean and pre-treat the steelmaking equipment, and then carry out steelmaking, controlling the tapping temperature to 1635℃-1665℃ to obtain crude steel S1;

[0011] (2) Add slag conditioner to the slag surface in S1, and then prepare ultra-low sulfur steel by RH vacuum refining;

[0012] The RH vacuum refining includes desulfurization treatment;

[0013] The desulfurization process involves adding a desulfurizing agent from the vacuum device of the RH vacuum refining furnace into the molten steel to desulfurize it.

[0014] The desulfurizing agent used in the desulfurization process comprises the following components:

[0015] Calcium oxide: 73wt%-78wt%, calcium fluoride: 11wt%-13wt%, balance is impurities.

[0016] The semi-steel in the above preparation method refers to molten steel obtained after desulfurization and vanadium extraction of vanadium-containing molten iron. In this invention, semi-steel with a sulfur content ≤0.005% is used for cleaning pretreatment.

[0017] The present invention does not impose any special limitation on the steelmaking equipment in the above preparation method; any equipment known to those skilled in the art is acceptable.

[0018] In some specific embodiments of the present invention, a converter is preferably used.

[0019] The cleaning pretreatment can effectively remove residual sulfur-containing slag and molten steel from the converter, ladle (pot) and vacuum chamber of the RH vacuum refining furnace, avoiding sulfur pollution in the subsequent ultra-low sulfur steel smelting process.

[0020] The raw materials for steelmaking in the preparation method preferably include molten iron and scrap steel.

[0021] Preferably, the crude steel S1 is placed in a ladle.

[0022] The slag surface in S1 refers to the top surface of a layer of molten slag floating on the surface of molten steel.

[0023] Preferably, the desulfurizing agent of the present invention is composed of 75 wt% calcium oxide, 12 wt% calcium fluoride and 13 wt% impurities.

[0024] Preferably, in the desulfurization process of the present invention, the mass ratio of desulfurizing agent to molten steel is 10:(1145-1155).

[0025] Preferably, the particle size of the desulfurizing agent is 80-120 nm; more preferably, it is 100 nm.

[0026] Preferably, the desulfurization treatment time is 4-8 min; more preferably, it is 6 min.

[0027] In the above preparation method, the slag conditioner is used to adjust the oxidizability of the slag, reduce the (FeO) content in the slag, create low-oxidizability slag conditions for subsequent RH vacuum desulfurization, and reduce the desulfurization efficiency of the desulfurizer due to the consumption of oxygen in the slag.

[0028] Preferably, in step (3), the mass ratio of slag conditioner to crude steel S1 is 10:(1148-1152).

[0029] More preferably, the slag conditioner in step (3) is selected from high-alumina slag conditioners with an aluminum content of 40wt%-45wt%. Preferably, the desulfurization treatment further includes decarburization treatment, temperature compensation, and deoxidation alloying performed sequentially before the desulfurization treatment.

[0030] More preferably, the temperature range for temperature compensation is 10℃-20℃; more preferably, it is 15℃.

[0031] The above method is simple, efficient, and suitable for large-scale industrial production.

[0032] The preparation method described in this invention achieves the goal of reducing the sulfur content of molten steel after vacuum treatment through the combined effect of desulfurization materials, the method of adding desulfurization materials, and the optimization of other parameters of the preparation method. This improves the problem that high-sulfur molten iron cannot be used to smelt ultra-low sulfur vacuum steel and enhances the ability and stability of smelting vacuum low-sulfur steel.

[0033] The present invention also provides an ultra-low sulfur steel, which is prepared by the above-described preparation method;

[0034] The sulfur content of the ultra-low sulfur steel is ≤0.002wt%.

[0035] The ultra-low sulfur steel described in this invention includes, but is not limited to, electrical steel grades PW600 and above.

[0036] Compared with the prior art, the method for preparing ultra-low sulfur steel provided by the present invention includes the following steps: (1) using semi-steel with a sulfur content ≤0.005% to clean and pre-treat the steelmaking equipment, and then steelmaking is carried out, controlling the tapping temperature to 1635℃-1665℃ to obtain crude steel S1; (2) adding a slag conditioner to the slag surface of the S1, and then preparing ultra-low sulfur steel by RH vacuum refining; the RH vacuum refining includes desulfurization treatment; the desulfurization treatment is to add a desulfurizing agent from the vacuum device of the RH vacuum refining furnace into the molten steel for desulfurization; the desulfurizing agent for the desulfurization treatment includes the following components: calcium oxide: 73wt%-78wt%, calcium fluoride: 11wt%-13wt%, and the balance is impurities. The method reduces the sulfur content of the vacuum steel through the joint optimization of desulfurization materials and condition parameters. Detailed Implementation

[0037] To further illustrate the present invention, the preparation method of ultra-low sulfur steel provided by the present invention will be described in detail below with reference to embodiments.

[0038] This invention provides a method for preparing ultra-low sulfur steel, comprising the following steps:

[0039] (1) Use semi-steel with sulfur content ≤0.005% to clean and pre-treat the steelmaking equipment, and then carry out steelmaking, controlling the tapping temperature to 1635℃-1665℃ to obtain crude steel S1;

[0040] (2) Add slag conditioner to the slag surface in S1, and then prepare ultra-low sulfur steel by RH vacuum refining;

[0041] The RH vacuum refining includes desulfurization treatment;

[0042] The desulfurization process involves adding a desulfurizing agent from the vacuum device of the RH vacuum refining furnace into the molten steel to desulfurize it.

[0043] The desulfurizing agent used in the desulfurization process comprises the following components:

[0044] Calcium oxide: 73wt%-78wt%, calcium fluoride: 11wt%-13wt%, balance is impurities.

[0045] The semi-steel in the above preparation method refers to molten steel obtained after desulfurization and vanadium extraction of vanadium-containing molten iron. In this invention, semi-steel with a sulfur content ≤0.005% is used for cleaning pretreatment.

[0046] The present invention does not impose any special limitation on the steelmaking equipment in the above preparation method; any equipment known to those skilled in the art is acceptable.

[0047] In some specific embodiments of the present invention, a converter is preferably used.

[0048] The cleaning pretreatment can effectively remove residual sulfur-containing slag and molten steel from the converter, ladle (pot) and vacuum chamber of the RH vacuum refining furnace, avoiding sulfur pollution in the subsequent ultra-low sulfur steel smelting process.

[0049] The raw materials for steelmaking in the preparation method preferably include molten iron and scrap steel.

[0050] Preferably, the crude steel S1 is placed in a ladle.

[0051] The slag surface in S1 refers to the top surface of a layer of molten slag floating on the surface of molten steel.

[0052] Preferably, the desulfurizing agent of the present invention is composed of 75 wt% calcium oxide, 12 wt% calcium fluoride and 13 wt% impurities.

[0053] Preferably, in the desulfurization process of the present invention, the mass ratio of desulfurizing agent to molten steel is 10:(1145-1155).

[0054] Preferably, the particle size of the desulfurizing agent is 80-120 nm; more preferably, it is 100 nm.

[0055] Preferably, the desulfurization treatment time is 4-8 min; more preferably, it is 6 min.

[0056] In the above preparation method, the slag conditioner is used to adjust the oxidizability of the slag, reduce the (FeO) content in the slag, create low-oxidizability slag conditions for subsequent RH vacuum desulfurization, and reduce the desulfurization efficiency of the desulfurizer due to the consumption of oxygen in the slag.

[0057] Preferably, in step (3), the mass ratio of slag conditioner to crude steel S1 is 10:(1148-1152).

[0058] More preferably, the slag conditioner in step (3) of the present invention is selected from high-alumina slag conditioners with an aluminum content of 40wt%-45wt%.

[0059] Preferably, the present invention further includes decarburization treatment, temperature compensation and deoxidation alloying performed sequentially before the desulfurization treatment.

[0060] More preferably, the temperature range for temperature compensation is 10℃-20℃; more preferably, it is 15℃.

[0061] The above method is simple, efficient, and suitable for large-scale industrial production.

[0062] The preparation method described in this invention achieves the goal of reducing the sulfur content of molten steel after vacuum treatment through the combined effect of desulfurization materials, the method of adding desulfurization materials, and the optimization of other parameters of the preparation method. This improves the problem that high-sulfur molten iron cannot be used to smelt ultra-low sulfur vacuum steel and enhances the ability and stability of smelting vacuum low-sulfur steel.

[0063] The present invention also provides an ultra-low sulfur steel, which is prepared by the above-described preparation method;

[0064] The sulfur content of the ultra-low sulfur steel is ≤0.002wt%.

[0065] The ultra-low sulfur steel described in this invention includes, but is not limited to, electrical steel grades PW600 and above. Example 1

[0066] The production of high-grade electrical steel (PW600 and above) will be used as an example for explanation.

[0067] (1) Cleaning the furnace, cleaning the tank, and cleaning the vacuum chamber

[0068] Before production, two furnaces of low-sulfur semi-steel are cleaned by washing the furnace, washing the ladle, and washing the vacuum chamber, so that the sulfur content of the low-sulfur semi-steel is controlled to S≤0.005%.

[0069] (2) Converter endpoint control

[0070] After completing the aforementioned furnace cleaning, ladle cleaning, and vacuum chamber cleaning operations, molten iron and scrap steel are immediately loaded into the converter for conventional smelting. The tapping temperature at the end of the converter smelting process is controlled at 1650±15℃. Within this temperature range, the molten steel maintains good fluidity and provides suitable initial temperature conditions for subsequent RH vacuum refining, reducing the temperature compensation pressure of the RH process.

[0071] (3) Oxygen adjustment at the slag surface of the converter tapping

[0072] After the converter tapping is completed, add 450±50 kg of high-alumina slag conditioner to the slag surface of the ladle.

[0073] (4) RH vacuum refining

[0074] The molten steel obtained in step (3) is transferred to the RH vacuum refining furnace for vacuum treatment. After the RH decarburization is completed, a temperature compensation of 15°C is performed based on the temperature measurement results. The temperature drop of the RH desulfurization test is estimated to be 15°C. After the deoxidation and alloying operation is completed, 1 ton of desulfurizing agent is quantitatively added to the vacuum chamber 5 minutes after the deoxidation and alloying is completed (specifically, using the alloy feeding system provided by the RH refining furnace, the desulfurizing agent is added to the vacuum chamber under the action of gravity under vacuum conditions, just like adding alloys). The desulfurizing agent and the molten steel are mixed and reacted.

[0075] The desulfurizing agent has a particle size of 100 nm and, by mass percentage, its chemical composition is: 75% calcium oxide (CaO), 12% calcium fluoride (CaF2), with the balance being unavoidable impurities. After the desulfurizing agent is added, the system continues to circulate for 6 minutes to ensure sufficient contact and reaction between the desulfurizing agent and the molten steel.

[0076] After testing, the sulfur content in the molten steel after the above (1)-(4) treatments was 0.002%, which meets the production requirements of ultra-low sulfur steel.

[0077] Comparative Example 1

[0078] Similar to Example 1, except that the desulfurizing agent in step (4) is replaced with commercially available ordinary calcium magnesium powder desulfurizing agent to obtain molten steel with a sulfur content of 0.004%.

[0079] Comparative Example 2

[0080] Similar to Example 1, except that in step (4), the desulfurizing agent is added by spraying, and molten steel with a sulfur content of 0.004% is obtained.

[0081] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing ultra-low sulfur steel, characterized in that, Includes the following steps: (1) Use semi-steel with sulfur content ≤0.005% to clean and pre-treat the steelmaking equipment, and then carry out steelmaking, controlling the tapping temperature to 1635℃-1665℃ to obtain crude steel S1; (2) Add slag conditioner to the slag surface in S1, and then prepare ultra-low sulfur steel by RH vacuum refining; The RH vacuum refining includes desulfurization treatment; The desulfurization process involves adding a desulfurizing agent from the vacuum device of the RH vacuum refining furnace into the molten steel to desulfurize it. The desulfurizing agent used in the desulfurization process comprises the following components: Calcium oxide: 73wt%-78wt%, calcium fluoride: 11wt%-13wt%, balance is impurities.

2. The preparation method according to claim 1, characterized in that, The desulfurizing agent consists of 75 wt% calcium oxide, 12 wt% calcium fluoride and 13 wt% impurities.

3. The preparation method according to claim 1, characterized in that, The mass ratio of desulfurizing agent to molten steel in the desulfurization process is 10:(1145-1155).

4. The preparation method according to claim 1, characterized in that, The particle size of the desulfurizing agent is 80-120 nm.

5. The preparation method according to claim 1, characterized in that, The desulfurization process takes 4-8 minutes.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the slag conditioner to crude steel S1 in step (3) is 10:(1148-1152).

7. The preparation method according to claim 1 or 6, characterized in that, The slag conditioner in step (3) is selected from high-alumina slag conditioners with an aluminum content of 40wt%-45wt%.

8. The preparation method according to claim 1, characterized in that, The desulfurization process includes sequential decarburization, temperature compensation, and deoxidation alloying.

9. The preparation method according to claim 8, characterized in that, The temperature range for temperature compensation is 10℃-20℃.

10. An ultra-low sulfur steel, characterized in that, Prepared by the preparation method according to any one of claims 1-9; The sulfur content of the ultra-low sulfur steel is ≤0.002wt%.