Smelting method and application of ultra-low carbon steel

Abstract

The invention provides an ultra-low carbon steel smelting method and application. The ultra-low carbon steel smelting method comprises the following steps that S1, an oxygen-containing material is added along with steel flow in the molten steel tapping process; s2, in the process of waiting for the molten steel to reach the LF furnace, argon is blown to the bottom of a steel ladle to stir the molten steel; and S3, the molten steel is hoisted to an LF furnace for refining treatment. The oxygen content in the molten steel is increased by adding the oxygen-containing material into the molten steel, and then the argon is blown to the bottom of the steel ladle, so that the molten steel generates a stirring effect, inclusions in the molten steel float upwards, meanwhile, the reaction of oxygen and carbon in the molten steel is promoted, and the effect of reducing the carbon content in the molten steel is achieved. The method is a brand-new method for reducing the carbon content in the molten steel, can directly reduce the process of decarburization of the molten steel through an RH furnace, does not depend on RH furnace equipment any more, reduces the molten steel treatment process and smelting time, and greatly reduces the production cost.

Description

Technical Field

[0001] This application relates to the technical field of steelmaking, and particularly relates to a smelting method and application of ultra-low carbon steel. Background Art

[0002] Carbon plays a crucial role in the hardness, toughness, and wear resistance of steel. Increasing the carbon content is beneficial to improving the strength, hardness, and wear resistance of steel, but it will also have a negative impact on the toughness of steel. Therefore, the steel composition design of acid-resistant pipelines and nickel-based containers often adopts ultra-low carbon components. If the carbon component cannot reach the predetermined target, the rejudgment loss is extremely large.

[0003] The method for smelting ultra-low carbon steel disclosed in the related art is as follows: The molten steel passes through the RH vacuum circulation device, and oxygen is blown into the molten steel for forced decarburization. This method can control the carbon in the steel to the required predetermined target. However, the defect in the related art is that the molten steel must go through the process of blowing oxygen and decarburizing in the RH vacuum furnace, which is equipment-dependent, has a long treatment time, and high costs.

[0004] LF furnace refining is a commonly used secondary refining device in steelmaking, which can perform argon stirring, desulfurization with white slag, arc heating, and composition adjustment on molten steel. Since it uses electrode heating, compared with aluminum-oxygen heating, it can reduce the generation of foreign inclusions in the molten steel, so it is widely used.

[0005] The existing LF refining process has the following disadvantages: The adjustment of the molten steel composition is mainly carried out after the first sample. During the process of heating the molten steel by electricity, the high-temperature electric arc (about 4000 °C) accelerates the reaction between the graphite electrode and the slag or molten steel, and part of the carbon element in the graphite electrode is absorbed by the molten steel. The carbon increase amount of low-carbon steel is often ≥0.02%. In addition, the molten steel is stirred with a large amount of argon for a long time, which inevitably causes the molten steel to come into contact with air, resulting in nitrogen and oxygen absorption of the molten steel, which has an adverse impact on the quality of the molten steel. Patent CN113088628A discloses an LF refining method for low-carbon steel. After the molten steel reaches the refining position, power is supplied, silicon carbide and carburizer are added for diffusion deoxidation, and argon is blown at the bottom of the ladle. The argon flow rate is the soft argon blowing flow rate + (10 - 30) NL / min, and the power supply time is ≥20 min. It can be seen that there are problems of low stirring efficiency and long time consumption in the use of LF furnace refining in this technology. Summary of the Invention

[0006] This application is made in view of the above problems, and its purpose is to provide a smelting method and application of ultra-low carbon steel.

[0007] Specifically, the first aspect of this application provides a smelting method of ultra-low carbon steel, including the following steps:

[0008] S1: Add oxygen-containing materials along with the molten steel flow during the tapping process of the molten steel;

[0009] S2: While waiting for the molten steel to reach the LF furnace, argon gas is blown into the bottom of the ladle to stir the molten steel. After the oxygen-containing material melts, the oxygen content in the molten steel is increased.

[0010] S3: The molten steel is lifted to the LF furnace for refining treatment.

[0011] Furthermore, the mass ratio of the oxygen-containing material to the molten steel in step S1 is 3 kg - 6 kg: 1 t.

[0012] Furthermore, the oxygen-containing material is at least one of scale, iron ore, and billet cutting slag.

[0013] Furthermore, the flow rate of the argon gas blown in step S2 is 500 NL / min - 600 NL / min.

[0014] Furthermore, the time for blowing the argon gas is 8 - 15 min.

[0015] Furthermore, the mass fraction of carbon in the molten steel in step S1 is below 0.07%.

[0016] Furthermore, the mass fraction of oxygen in the molten steel in step S1 is 0.05% - 0.06%.

[0017] Furthermore, the molten steel in step S1 is smelted by a converter. The converter smelting process includes an oxygen-blowing step, and the time for blowing oxygen is 12 min - 14 min.

[0018] Furthermore, during the converter smelting process, slag-making materials are added to the molten steel. The slag-making materials include lime and dolomite.

[0019] The mass ratio of the lime to the hot metal is 18.5 kg - 44.5 kg: 1 t.

[0020] The mass ratio of the dolomite to the hot metal is 7.4 kg - 22.2 kg: 1 t.

[0021] Furthermore, the tapping temperature of the molten steel in step S1 is 1580°C - 1600°C.

[0022] The second aspect of the present invention provides an application of the above-mentioned method for smelting ultra-low carbon steel in the preparation of low-carbon series steel grades.

[0023] Furthermore, the LF refining also includes refining treatments such as slag-making and composition adjustment of the molten steel. After the refining is completed, the molten steel is subjected to vacuum treatment in a VD furnace. The molten steel after the vacuum treatment is used for continuous casting of low-carbon steel, and the low-carbon steel can be all low-carbon series steel grades, such as X65MS pipeline steel or low-temperature nickel-based steel.

[0024] The present invention has the following beneficial effects:

[0025] The present invention increases the oxygen content in the molten steel by adding oxygen-containing materials to the molten steel, blows argon gas at the bottom of the ladle while waiting to go to the LF furnace for refining to produce a stirring effect, makes the inclusions in the molten steel float, and at the same time promotes the reaction of oxygen and carbon in the molten steel to achieve the effect of reducing the carbon content in the molten steel. The present invention is a brand-new method for reducing the carbon content in molten steel. This method can directly reduce the process of decarburizing molten steel by the RH furnace, no longer rely on the RH furnace equipment, reduce the molten steel treatment process and smelting time, and greatly reduce the production cost. Specific Embodiments

[0026] In order to make the purpose, technical solution and advantages of the present application clearer, the following describes and explains the present application in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Based on the embodiments provided by the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0027] Obviously, the following description is only some examples or embodiments of the present application. For those of ordinary skill in the art, without creative efforts, the present application can also be applied to other similar scenarios. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some designs, manufacturing or production changes based on the technical content disclosed in the present application are only conventional technical means and should not be understood as the content disclosed in the present application being insufficient.

[0028] If there is no special indication, the "including" and "comprising" mentioned in the present application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or only the components listed can be included or comprised.

[0029] If there is no special indication, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0030] An embodiment of the first aspect of the present application provides a method for smelting ultra-low carbon steel, including the following steps:

[0031] S1: Add oxygen-containing materials along with the molten steel flow during the process of tapping the molten steel;

[0032] S2: While waiting for the molten steel to reach the LF furnace, argon gas is blown into the bottom of the ladle to stir the molten steel. After the oxygen-containing material melts, the oxygen content in the molten steel is increased.

[0033] S3: The molten steel is lifted to the LF furnace for refining treatment.

[0034] The molten steel is made from hot metal through oxygen blowing and carbon reduction smelting in a converter, and the carbon content of the hot metal is 3.5%-5.5%. In the present invention, by adding an oxygen-containing material to the molten steel, after the oxygen-containing material melts, the oxygen content in the molten steel is increased. When waiting for refining in the LF furnace, argon gas is blown into the bottom of the ladle to stir the molten steel, causing inclusions in the molten steel to float up. At the same time, it promotes the reaction between oxygen and carbon in the molten steel, achieving the effect of reducing the carbon content in the molten steel. And when waiting for refining in the LF furnace, argon gas is blown into the bottom of the ladle, saving the time for decarbonization in the LF furnace, thereby shortening the entire molten steel smelting time. The present invention is a brand-new method for reducing the carbon content in molten steel. This method can directly reduce the process of decarbonizing the molten steel through the RH furnace, no longer relying on the RH furnace equipment, reducing the molten steel treatment process and smelting time, and greatly reducing the production cost.

[0035] In the embodiment of the present application, the mass ratio of the oxygen-containing material to the molten steel in step S1 is 3 kg - 6 kg: 1 t. Preferably, the mass ratio of the oxygen-containing material to the molten steel is 4 kg - 5 kg: 1 t. Specifically, the mass ratio of the oxygen-containing material to the molten steel is any one of 3 kg: 1 t, 4 kg: 1 t, 5 kg: 1 t, 6 kg: 1 t. The addition amount of the oxygen-containing material is calculated according to the target carbon content. After decarbonization of the molten steel using the oxygen-containing material in the present invention, the carbon content in the molten steel is 0.02% - 0.04%.

[0036] In the embodiment of the present application, the oxygen-containing material is at least one of mill scale, iron ore, and billet cutting slag. The main functions of adding mill scale, iron ore, and billet cutting slag to the molten steel include maintaining the temperature of the molten steel and acting as an oxidant to increase the oxygen content in the molten steel.

[0037] In the embodiment of the present application, the flow rate of the argon gas blown in step S2 is 500 NL / min - 600 NL / min. The time for blowing argon gas is 8 - 15 min, specifically any one of 8 min, 10 min, 12 min, 13 min, 14 min, 15 min. In the present application, the time for blowing argon gas can be set according to the size of the ladle.

[0038] During the process of waiting for the molten steel to reach the LF furnace, argon gas is blown into the bottom of the ladle in the present invention, which has the following effects: Argon stirring causes the molten steel to circulate. By controlling the gas flow rate to adjust the stirring intensity, the composition segregation and temperature gradient of the molten steel in the ladle can be quickly eliminated, ensuring the stability of the subsequent refining process. Moreover, during the rising process of argon bubbles, non-metallic inclusions (such as oxides and sulfides) are adhered to and brought to the surface of the molten steel to be absorbed by the slag layer, reducing the inclusion content. In addition, argon stirring expands the contact area between the molten steel and the molten slag, promoting the mass transfer efficiency of reactions such as deoxidation and desulfurization, and at the same time accelerating the dissolution and uniform distribution of alloying elements. Further, by adjusting the argon blowing intensity and time, the temperature of the molten steel can be adjusted to the target range. In addition, argon covers the surface of the molten steel to form an inert protective layer, reducing the contact between the molten steel and air and avoiding composition fluctuations caused by oxidation.

[0039] In the embodiment of the present application, the mass fraction of carbon in the molten steel in step S1 is 0.07% or less. Preferably, the mass fraction of carbon in the molten steel is 0.05% or less.

[0040] In the embodiment of the present application, the mass fraction of oxygen in the molten steel in step S1 is 0.05% - 0.06%. Preferably, the mass fraction of oxygen in the molten steel in step S1 is 0.06%.

[0041] In the embodiment of the present application, the molten steel in step S1 is smelted in a converter. The converter smelting process includes an oxygen blowing step, and the time of oxygen blowing is 12 min - 14 min. The oxygen blowing flow rate ≥ 400 Nm 3 / min. By means of short-time oxygen blowing combined with high oxygen supply intensity in the present invention, the rate of the carbon-oxygen reaction can be accelerated, enabling rapid completion of decarburization and dephosphorization, shortening the smelting cycle of a single heat, and improving the converter turnover rate.

[0042] In the embodiment of the present application, during the converter smelting process, slag-making materials are also added to the molten steel. The slag-making materials include lime and dolomite,

[0043] The mass ratio of the lime to the hot metal is 18.5 kg - 44.5 kg: 1 t;

[0044] The mass ratio of the dolomite to the hot metal is 7.4 kg - 22.2 kg: 1 t.

[0045] In the embodiment of the present application, the tapping temperature of the molten steel in step S1 is 1580 °C - 1600 °C.

[0046] In the embodiment of the present application, the LF refining also includes refining treatments such as slag-making and composition adjustment of the molten steel; the molten steel after refining is subjected to vacuum treatment in a VD furnace, and the molten steel after vacuum treatment is used for continuous casting of low-carbon steel, such as X65MS pipeline steel or low-temperature nickel-based steel.

[0047] Example 1

[0048] A smelting method for ultra-low carbon steel, the steps of which are as follows:

[0049] A. Oxygen is blown into the hot metal in a converter to smelt the hot metal into molten steel. The oxygen-blowing time is 13 minutes. During the converter smelting process, slag-making materials are added to the molten steel. When the weight fraction of carbon in the molten steel in the converter ≤ 0.07% and the weight fraction of oxygen ≥ 0.06%, and the temperature of the molten steel in the converter reaches 1600 °C, the molten steel is tapped into a ladle, and a slag blocking process is adopted during the tapping process;

[0050] B. Add a calculated amount of iron oxide scale into the ladle to increase the oxygen content in the molten steel;

[0051] C. During the waiting process for the molten steel to reach the LF furnace, argon gas is blown at the bottom of the ladle to stir the molten steel. The argon gas flow rate is 600 NL / min, and the argon gas blowing time is 8 minutes. Carbon in the molten steel reacts with oxygen to generate decarburization product carbon monoxide.

[0052] Example 2

[0053] A smelting method for ultra-low carbon steel, the steps of which are as follows:

[0054] A. Oxygen is blown into the hot metal in a converter to smelt the hot metal into molten steel. The oxygen-blowing time is 12 minutes. During the converter smelting process, slag-making materials are added to the molten steel. When the weight fraction of carbon in the molten steel in the converter ≤ 0.05% and the weight fraction of oxygen ≥ 0.05%, and the temperature of the molten steel in the converter reaches 1590 °C, the molten steel is tapped into a ladle, and a slag blocking process is adopted during the tapping process;

[0055] B. Add a calculated amount of iron ore into the ladle to increase the oxygen content in the molten steel;

[0056] C. During the waiting process for the molten steel to reach the LF furnace, argon gas is blown at the bottom of the ladle to stir the molten steel. The argon gas flow rate is 500 NL / min, and the argon gas blowing time is 10 minutes. Carbon in the molten steel reacts with oxygen to generate decarburization product carbon monoxide.

[0057] Example 3

[0058] A smelting method for ultra-low carbon steel, the steps of which are as follows:

[0059] A. Oxygen is blown into the hot metal in a converter to smelt the hot metal into molten steel. The oxygen-blowing time is 14 minutes. During the converter smelting process, slag-making materials are added to the molten steel. When the weight fraction of carbon in the molten steel in the converter ≤ 0.05% and the weight fraction of oxygen ≥ 0.07%, and the temperature of the molten steel in the converter reaches 1580 °C, the molten steel is tapped into a ladle, and a slag blocking process is adopted during the tapping process;

[0060] B. Add the calculated amount of billet cutting slag into the ladle to increase the oxygen content in the molten steel;

[0061] C. During the waiting process for the molten steel to reach the LF furnace, blow argon gas at the bottom of the ladle to stir the molten steel. The argon gas flow rate is 600 NL / min, and the argon gas blowing time is 14 min. After the carbon and oxygen in the molten steel react, decarburization product carbon monoxide is generated.

[0062] Example 4

[0063] A smelting method for extra-low carbon steel, the steps are as follows:

[0064] A. Blow oxygen in the converter to smelt the hot metal into molten steel. The oxygen blowing time is 13 min. Add slag-making materials into the molten steel during the converter smelting process. When the weight fraction of carbon in the molten steel in the converter ≤ 0.05% and the weight fraction of oxygen ≥ 0.06%, and the temperature of the molten steel in the converter reaches 1580 °C, tap the steel into the ladle, and use a slag blocking process during the tapping process;

[0065] B. Add the calculated amount of scale into the ladle to increase the oxygen content in the molten steel;

[0066] C. During the waiting process for the molten steel to reach the LF furnace, blow argon gas at the bottom of the ladle to stir the molten steel. The argon gas flow rate is 500 NL / min, and the argon gas blowing time is 12 min. After the carbon and oxygen in the molten steel react, decarburization product carbon monoxide is generated.

[0067] Experimental case

[0068] The smelting is organized and produced by the converter-LF furnace-VD furnace-slab continuous casting process (taking 120 t of molten steel as an example). The steel grade to be smelted is acid-resistant pipeline X65MS, and the furnace numbers are A516051-A516066. The specific composition requirements are as follows:

[0069] Element C Si Mn P S Al Standard ≤0.05％ ≤0.30％ ≤1.35％ ≤0.012％ ≤0.0015％ ≤0.060％

[0070] The specific technical operation steps are as follows:

[0071] S1: Pretreat 120 t of molten steel according to the method of step A in Example 1, and add 360 kg of scale along with the steel flow during the tapping process;

[0072] The specific calculation method is as follows:

[0073] M = ((X c0 %-X c %) / 0.01%)*m 0 ;

[0074] Among them, M is the scale addition amount; m 0 is the conversion coefficient; X c0X is the mass percentage of carbon in the molten steel in Step 1; c X is the mass percentage of carbon in the target molten steel; c0 %-X c % is the decarburization amount.

[0075] In the present invention, the target carbon content of the molten steel is 0.03%, so

[0076] Target decarburization amount = Endpoint carbon content - Target carbon content = 0.06% - 0.03% = 0.03%;

[0077] Calculate the addition amount of scale according to the target decarburization amount. The calculation formula is as follows:

[0078] M = (0.03% / 0.01%) * 120 = 360 kg;

[0079] S2: During the process of waiting for the molten steel to reach the LF furnace, argon gas is blown into the bottom of the ladle to stir the molten steel. The argon gas flow rate is 600 NL / min, and the argon gas blowing time is 8 min. Carbon in the molten steel reacts with oxygen to generate decarburization product carbon monoxide;

[0080] S3: Then lift the molten steel to the LF furnace for refining treatments such as heating, slag making, and composition adjustment;

[0081] S4: The molten steel after refining is subjected to vacuum treatment in the VD furnace;

[0082] S5: The molten steel after vacuum treatment is used for continuous casting of X65MS pipeline steel;

[0083] S6: Take steel samples from the 5# BOF at the converter station, the 4# LF at the LF refining station, the 1# VD at the VD vacuum treatment station, and the 10# CC at the continuous casting station for composition inspection.

[0084] Mark them as Steel Sample 1, Steel Sample 2, Steel Sample 3, Steel Sample 4, Steel Sample 5, Steel Sample 6, Steel Sample 7, Steel Sample 8, and Steel Sample 9 in the sampling order. The test results are shown in Table 1.

[0085] Table 1 Element Contents of Steel Samples at Different Stations

[0086]

[0087]

[0088] Among them, Steel Sample 2 is taken from the incoming sample of the LF furnace, and Steel Sample 6 is taken from the outgoing sample of the LF furnace.

[0089] As can be seen from Table 1, the carbon content of Steel Sample 2 is 0.0121%, and the carbon content of Steel Sample 6 is 0.0191%, meeting the carbon content standard of pipeline steel.

[0090] It should be noted that this application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same constitution and achieving the same effects as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A method for smelting ultra-low carbon steel, characterized in that: The following steps are involved: S1: oxygen-containing materials are added along with the steel flow during the process of molten steel tapping; S2: While waiting for the molten steel to arrive at the LF furnace, argon gas is blown into the bottom of the ladle to stir the molten steel; S3: The molten steel is hoisted to the LF furnace for refining.

2. The smelting method of ultra-low carbon steel according to claim 1, characterized in that: The mass ratio of the oxygen-containing material to the molten steel in step S1 is 3kg-6kg:1t.

3. The smelting method of ultra-low carbon steel according to claim 1, characterized in that: The oxygen-containing material is at least one of iron oxide scale, iron ore and ingot cutting slag.

4. The smelting method of ultra-low carbon steel according to claim 1, characterized in that: The flow rate of the argon gas blown in step S2 is 500NL / min to 600NL / min.

5. The method for smelting ultra-low carbon steel according to claim 4, characterized in that: The argon blowing time is 8-15 minutes.

6. The smelting method of ultra-low carbon steel according to claim 1, characterized in that: The mass fraction of carbon in the molten steel in step S1 is less than 0.07%.

7. The smelting method of ultra-low carbon steel according to claim 1, characterized in that: The mass fraction of oxygen in the molten steel in step S1 is 0.05% to 0.06%.

8. The method for smelting ultra-low carbon steel according to claim 1, characterized in that: The molten steel in step S1 is smelted in a converter, and the converter smelting process includes an oxygen blowing step, and the oxygen blowing time is 12 minutes to 14 minutes.

9. The method for smelting ultra-low carbon steel according to claim 8, characterized in that: The converter smelting process also includes adding slag-making materials to the molten steel, wherein the slag-making materials include lime and dolomite. The mass ratio of lime to molten iron is 18.5kg-44.5kg:1t; The mass ratio of dolomite to molten iron is 7.4kg-22.2kg:1t.

10. Use of the smelting method of ultra-low carbon steel according to any one of claims 1 to 9 in preparing low carbon series steel grades.

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