Smelting system and method for ultralow-carbon-nitrogen molten steel

Abstract

The invention belongs to the technical field of electric furnace steelmaking, and relates to a smelting system and method for ultralow-carbon-nitrogen molten steel, and the method comprises the following steps: step 1, placing a solid raw material in an electric furnace, then lowering an electrode for smelting, and treating the molten steel until the carbon content is less than or equal to 0.03% and the oxygen content is more than or equal to 600ppm through a waste steel melting stage, an oxidation decarburization stage and a dynamic decarburization stage in sequence; the molten steel temperature is greater than or equal to 1650 DEG C; and 2, the molten steel is tapped into a steel ladle, after tapping is finished, the molten steel is transferred into an RH vacuum refining device through the steel ladle to be subjected to deep decarburization and nitrogen removal treatment, and the ultralow-carbon-nitrogen molten steel with the carbon content smaller than or equal to 0.003% and the nitrogen content smaller than or equal to 0.003% is obtained. The method can stably control the content of carbon and nitrogen in the molten steel at a low level, and is beneficial to production of high-grade ultralow-carbon-nitrogen steel; and molten iron is not added in the electric furnace smelting process, so that carbon emission is reduced, and production and application of low-carbon green steel products such as high-grade thin plates are promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric furnace steelmaking, and relates to a smelting system and method of ultra-low carbon nitrogen molten steel, which is used for producing low-carbon green steel products such as high-grade thin plates in an electric furnace process. Background Art

[0002] In most cases, nitrogen exists as an impurity element in steel, which affects the high-temperature strength and high-temperature plasticity of steel and reduces the deep drawing performance of steel. Many high-grade thin plates or thick steel plates have stringent requirements on the carbon and nitrogen content in steel. Generally, the carbon content of the finished steel is required to be controlled below 50ppm and the nitrogen content is required to be below 40ppm; some varieties, such as high-grade automotive plates, silicon steel and other products, have lower requirements for carbon and nitrogen content, even below 30ppm. Although it is easy to produce the above-mentioned steel varieties with a converter as a roughing furnace, since the electric furnace uses scrap steel as raw material, the nitrogen content in the molten steel at the end of the smelting process is generally 70 to 120ppm due to the ionization effect of the arc during the smelting process. In the prior art, the denitrification effect is generally ensured by controlling the nitrogen content in the raw materials, increasing carbon boiling by the electric furnace to promote deep decarburization, and further increasing vacuum treatment. However, the stability is poor.

[0003] In the prior art, the patent with patent application number CN201810580268.5 discloses a method for smelting low-nitrogen steel in an electric furnace. The electric furnace + LF + VD smelting process can produce varieties with a nitrogen content below 40 ppm, but molten iron needs to be added to the inner electric furnace, and the molten iron ratio is 35-55%, which is not conducive to reducing the carbon emissions of the process; similarly, the patent with patent application number CN202110433004.9 discloses a method for reducing the nitrogen content in steel in an electric furnace steelmaking process to obtain low-nitrogen steel. This method adopts the same process route as CN201810580268.5, and molten iron is also added to the electric furnace, and the molten iron ratio is 30-40%. The patent application number CN201811132581.9 discloses a method for efficiently smelting low-nitrogen steel using an electric furnace. The method uses a double-shell electric furnace and two power supply systems. In essence, it is two electric furnaces with high investment. Although hollow electrodes are used to blow argon to avoid nitrogen in the furnace, since the electric furnace body is not a completely closed system, nitrogen will still be sucked into the molten steel from the furnace door and the four holes in the furnace cover. The patent application with the publication number CN118272719A discloses a method for smelting clean steel and clean steel. The method uses an electric furnace + LF + RH to smelt ultra-low carbon and nitrogen molten steel. The smelting process is long, and the oxygen content of the molten steel is low after LF treatment, which will increase the nitrogen content, resulting in RH refining. A large amount of oxygen blowing is required, which prolongs the refining time, making it difficult to stably produce ultra-low carbon and nitrogen molten steel. The patent application with publication number CN115927788A discloses an ultra-low carbon-nitrogen molten steel and a smelting method thereof. The process uses electric furnace spray gun powder smelting and vacuum refining for decarburization and denitrification operations. Nitrogen is easily increased during the electric furnace steelmaking process. At the same time, due to the high C content of the molten steel produced by the electric furnace, the RH treatment cycle is long.

[0004] To sum up, in order to solve the problems in the existing technology of electric furnace smelting ultra-low carbon and nitrogen molten steel, it is urgently necessary to propose a new ultra-low carbon and nitrogen molten steel smelting system and method for use in the electric furnace process to produce low-carbon green steel products such as high-grade thin plates. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a smelting system and method for ultra-low carbon nitrogen molten steel to solve the problems existing in the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for smelting ultra-low carbon nitrogen molten steel comprises the following steps:

[0008] Step 1: placing the solid raw material in an electric furnace, and then lowering the electrode for smelting, sequentially undergoing the scrap steel melting stage, the oxidation decarburization stage, and the dynamic decarburization stage to treat the molten steel to a carbon content of ≤0.03%, an oxygen content of ≥600ppm, and a molten steel temperature of ≥1650°C;

[0009] Step 2: The molten steel is then tapped into a ladle, and after tapping is completed, the molten steel is transferred to an RH vacuum refining device through the ladle for deep decarbonization and denitrification treatment to obtain ultra-low carbon and nitrogen molten steel with a carbon content of ≤0.003% and a nitrogen content of ≤0.003%.

[0010] Furthermore, during the scrap steel melting stage, oxygen is injected into the electric furnace alone, and the oxygen supply intensity is not more than 0.5 Nm 3 / min.t and is greater than zero.

[0011] Furthermore, during the oxidation decarburization stage, oxygen was blown into the electric furnace alone, and the oxygen supply intensity was 1.5 Nm 3 / min.t and is greater than zero.

[0012] Furthermore, during the dynamic decarburization stage, a mixed gas of oxygen and argon is simultaneously blown into the electric furnace, the flow ratio of oxygen to argon varies in the range of 1:1 to 1:6, and the oxygen supply intensity is no more than 1.5 Nm 3 / min.t and is greater than zero.

[0013] Furthermore, before tapping, CaCO3 powder or MgCO3 powder is spread on the bottom of the ladle.

[0014] Furthermore, the particle sizes of the CaCO3 and MgCO3 powders are both ≤0.1 mm.

[0015] The present invention also provides a smelting system for ultra-low carbon and nitrogen molten steel, comprising a gas supply device, an electric furnace, a ladle and an RH vacuum refining device, wherein the gas supply device is used to transport gas to the electric furnace body, the electric furnace is used to load solid raw materials and smelt them into molten steel, the ladle is used to transfer the molten steel in the electric furnace to the RH vacuum refining device, and the RH vacuum refining device is used to perform deep decarbonization and denitrification treatment on the molten steel.

[0016] Furthermore, the gas supply device includes a gas supply system, a gas spray gun connecting the gas supply system and the electric furnace, and a gas mixing regulation facility for adjusting the type and flow rate of gas delivered by the gas supply system, so as to deliver gas or mixed gas into the electric furnace through the gas spray gun according to the gas flow rate and proportion required by the process stage.

[0017] Furthermore, the gas spray gun has a double sleeve structure and the number is no less than 2.

[0018] Furthermore, the gas spray gun is installed in a tuyere brick on the side wall of the electric furnace at a distance of not less than 500 mm from the furnace bottom.

[0019] The beneficial effects of the present invention are:

[0020] The present invention provides a smelting system and method for ultra-low carbon and nitrogen molten steel, which adopts an electric furnace + RH vacuum refining process flow, injects gases of different flow rates and types in the scrap steel melting stage, the oxidation decarburization stage and the dynamic decarburization stage to treat the molten steel to a carbon content of ≤0.03%, an oxygen content of ≥600ppm, and a molten steel temperature of ≥1650°C, then taps the steel into a ladle, and then transfers the molten steel through the ladle to an RH vacuum refining device for deep decarburization and nitrogen treatment, thereby obtaining ultra-low carbon and nitrogen molten steel with a carbon content of ≤0.003% and a nitrogen content of ≤0.003%;

[0021] Secondly, this process method has a short flow and compact functions, and can stably control the carbon and nitrogen content in molten steel at a low level, which is conducive to the production of high-grade ultra-low carbon and nitrogen steel grades. In addition, no molten iron is added during the electric furnace smelting process, which is conducive to reducing carbon emissions and promoting the production and application of low-carbon green steel products such as high-grade thin plates.

[0022] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0024] Figure 1 It is a schematic flow chart of a method for smelting ultra-low carbon nitrogen molten steel in an embodiment. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0026] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0027] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0028] See also Figure 1 , is a smelting method of ultra-low carbon nitrogen molten steel, which specifically includes the following steps:

[0029] Step 1: Put the scrap steel and other solid raw materials into the electric furnace, lower the electrode for smelting, and sequentially process the scrap steel melting stage, oxidation decarburization stage and dynamic decarburization stage to treat the molten steel to a carbon content of ≤0.03%, an oxygen content of ≥600ppm, and a molten steel temperature of ≥1650℃;

[0030] Specifically, the definitions of the scrap steel melting stage, oxidation decarburization stage and dynamic decarburization stage are as follows:

[0031] The scrap steel melting stage: from the scrap steel feeding to more than 80% scrap steel melting; the oxidation decarburization stage: the carbon content of the molten steel is reduced to 0.06-0.1%; the dynamic decarburization stage: the carbon content of the molten steel is reduced from the actual carbon content reached in the oxidation decarburization stage to below 0.03%.

[0032] Step 2: The molten steel is then tapped into a ladle. After the tapping is completed, the molten steel is transferred to an RH vacuum refining device through the ladle for deep decarbonization and nitrogen removal (component fine adjustment) to obtain ultra-low carbon and nitrogen molten steel with a carbon content of ≤0.003% and a nitrogen content of ≤0.003%.

[0033] Specifically, before steel is tapped, CaCO3 powder is spread on the bottom of the ladle.

[0034] In another embodiment, MgCO3 powder is spread on the bottom of the ladle before tapping.

[0035] Preferably, the particle size of the CaCO3 and MgCO3 powders is ≤0.1 mm.

[0036] This embodiment also provides a smelting system for ultra-low carbon nitrogen molten steel used in the smelting method, the smelting system includes a gas supply device, an electric furnace body, a ladle and an RH vacuum refining device, and the gas supply device is used to transport gas to the electric furnace body.

[0037] Furthermore, the gas supply device includes a gas supply system, a gas spray gun connecting the gas supply system and the electric furnace body, and a gas mixing adjustment facility for adjusting the type and flow rate of gas delivered by the gas supply system, so as to deliver gas or mixed gas into the electric furnace through the gas spray gun according to the gas flow rate and proportion required by the process stage.

[0038] Preferably, during the scrap steel melting stage, oxygen is injected into the electric furnace alone, and the oxygen supply intensity is not more than 0.5 Nm 3 / min.t, and is greater than zero; during the oxidation decarburization stage, oxygen is sprayed into the electric furnace alone, and the oxygen supply intensity is 1.5Nm 3 / min.t, and is greater than zero; in the dynamic decarburization stage, a mixed gas of oxygen and argon is simultaneously blown into the electric furnace, the flow ratio of oxygen and argon varies in the range of 1:1 to 1:6, and the oxygen supply intensity does not exceed 1.5Nm 3 / min.t and is greater than zero.

[0039] Specifically, the gas spray gun has a double sleeve structure and is installed in the tuyere brick on the side wall of the electric furnace body at a distance of not less than 500mm from the furnace bottom. The number of the gas spray guns is not less than 2, and the spraying medium is one or more of oxygen, nitrogen, argon, and hydrocarbons.

[0040] Taking a 100t electric furnace as an example, the key process parameters and implementation effects involved in smelting ultra-low carbon nitrogen molten steel using the above process flow are shown in Table 1 below.

[0041] Table 1 Process parameters and implementation effects of this embodiment

[0042]

[0043] In this embodiment, an electric furnace + RH vacuum refining process is adopted, and different flow rates and types of gases are injected into the scrap steel melting stage, the oxidation decarburization stage and the dynamic decarburization stage to treat the molten steel to a carbon content of ≤0.03%, an oxygen content of ≥600ppm, and a molten steel temperature of ≥1650°C, and then the steel is tapped into a ladle. Thereafter, the molten steel is transferred to an RH vacuum refining device through the ladle for deep decarburization and nitrogen treatment to obtain ultra-low carbon and nitrogen molten steel with a carbon content of ≤0.003% and a nitrogen content of ≤0.003%. The process method has a short process flow and compact functions, and can stably control the carbon and nitrogen contents in the molten steel at a relatively low level, which is beneficial to the production of high-grade ultra-low carbon and nitrogen steel grades. In addition, no molten iron is added during the electric furnace smelting process, which is beneficial to reducing carbon emissions and promoting the production and application of low-carbon green steel products such as high-grade thin plates.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for smelting ultra-low carbon nitrogen molten steel, characterized in that: The following steps are involved: Step 1: placing the solid raw material in an electric furnace, and then lowering the electrode for smelting, sequentially undergoing the scrap steel melting stage, the oxidation decarburization stage, and the dynamic decarburization stage to treat the molten steel to a carbon content of ≤0.03%, an oxygen content of ≥600ppm, and a molten steel temperature of ≥1650°C; Step 2: The molten steel is then tapped into a ladle, and after tapping is completed, the molten steel is transferred to an RH vacuum refining device through the ladle for deep decarbonization and denitrification treatment to obtain ultra-low carbon and nitrogen molten steel with a carbon content of ≤0.003% and a nitrogen content of ≤0.003%.

2. The method for smelting ultra-low carbon nitrogen molten steel according to claim 1, characterized in that: During the scrap steel melting stage, oxygen is injected into the electric furnace alone, and the oxygen supply intensity is not more than 0.5Nm 3 / min.t.

3. The method for smelting ultra-low carbon nitrogen molten steel according to any one of claims 1 and 2, characterized in that: During the oxidation decarburization stage, oxygen was injected into the electric furnace alone, and the oxygen supply intensity was 1.5 Nm 3 / min.t.

4. The method for smelting ultra-low carbon nitrogen molten steel according to claim 3, characterized in that: In the dynamic decarburization stage, a mixed gas of oxygen and argon is simultaneously blown into the electric furnace, the flow ratio of oxygen to argon varies in the range of 1:1 to 1:6, and the oxygen supply intensity does not exceed 1.5 Nm 3 / min.t.

5. The method for smelting ultra-low carbon nitrogen molten steel according to claim 3, characterized in that: Before tapping, CaCO3 powder or MgCO3 powder is spread on the bottom of the ladle.

6. The method for smelting ultra-low carbon nitrogen molten steel according to claim 5, characterized in that: The particle sizes of the CaCO3 and MgCO3 powders are both ≤0.1 mm.

7. A smelting system for ultra-low carbon nitrogen molten steel, characterized by: It includes a gas supply device, an electric furnace, a ladle and an RH vacuum refining device. The gas supply device is used to transport gas to the electric furnace body. The electric furnace is used to load solid raw materials and smelt them into molten steel. The ladle is used to transfer the molten steel in the electric furnace to the RH vacuum refining device. The RH vacuum refining device is used to perform deep decarbonization and denitrification treatment on the molten steel.

8. The smelting system of ultra-low carbon nitrogen molten steel according to claim 7, characterized in that: The gas supply device includes a gas supply system, a gas spray gun connecting the gas supply system and the electric furnace, and a gas mixing regulating facility for adjusting the type and flow of gas delivered by the gas supply system, so as to deliver gas or mixed gas into the electric furnace through the gas spray gun according to the gas flow and proportion required by the process stage.

9. The smelting system of ultra-low carbon nitrogen molten steel according to claim 7, characterized in that: The gas spray gun has a double sleeve structure and the number is not less than 2.

10. The smelting system of ultra-low carbon nitrogen molten steel according to claim 7, characterized in that: The gas spray gun is installed in the tuyere brick on the side wall of the electric furnace and the distance from the furnace bottom is not less than 500mm.

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