Steel-making electric furnace capable of reducing increased nitrogen and smelting method

Abstract

The invention relates to the technical field of steelmaking, in particular to a steelmaking electric furnace capable of reducing nitrogen increase and a smelting method.The steelmaking electric furnace comprises a furnace body and a furnace cover, a protruding edge is annularly arranged on the upper surface of the furnace body, a clamping groove in sealing fit with the protruding edge is formed in the lower surface of the furnace cover, vent holes are formed in the side face of the clamping groove, and a plurality of gas nozzles and a gas analysis device are arranged in the furnace cover; an electrode hole is formed in the middle of the furnace cover, and a sliding electrode cover is arranged above the electrode hole. The steel-making electric furnace prevents molten steel from making contact with air, and air ionization and nitrogen increase can be achieved from the source. Nitrogen increase in the smelting process of the electric furnace is reduced to the maximum extent, even zero-nitrogen-increase smelting is achieved, the nitrogen content of tapping steel of the electric furnace is 0.0050%-0.007%, and equipment support is provided for production of high-grade steel grades through the electric furnace.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology, and specifically relates to a steelmaking electric furnace and smelting method that reduces nitrogen accumulation. Background Technology

[0002] The presence of nitrogen in steel has a significant impact on its performance and quality. Nitrogen is one of the main components of air. During the smelting process, the contact between molten steel and air increases the nitrogen content in the steel, negatively affecting its performance. The main hazards include: 1) Strain aging of steel. Nitrogen combines with titanium during cooling to form TiN, which leads to a decrease in the steel's plasticity and impact toughness. Studies show that when the nitrogen content in steel is 0.0010%, the steel exhibits optimal formability after continuous cold rolling and descaling, while formability gradually decreases with increasing nitrogen content. 2) Age-induced precipitation hardening or age-induced brittleness. During cold working, solute nitrogen in the steel causes the precipitation of another phase of nitrides, resulting in a sharp increase in hardness and strength, and a significant decrease in impact toughness. 3) Steel "aging". At low temperatures, the solubility of nitrogen in steel decreases, and brittle nitrides such as Fe6N2 and Fe4N precipitate at grain boundaries. Fatigue aging increases the yield strength of the steel, reduces its elongation and toughness, and makes the steel more prone to fracture. 4) Cold brittleness. Cold brittleness refers to the increased toughness and brittleness of steel at lower temperatures, making it prone to fracture during processing. The cold brittleness of steel is related to the brittle-ductile transition temperature; when the brittle-ductile transition temperature is higher than room temperature, the steel will experience cold brittleness at temperatures below room temperature. Nitrogen increases the brittle-ductile transition temperature of low-carbon steel, exacerbating cold brittleness. 5) Reduced yield. Nitrogen also affects the macrostructure of steel, causing defects such as porosity and segregation, leading to corner cracks in the slab, severely impacting the surface quality and mechanical properties of the steel, resulting in a high scrap rate during both hot and cold rolling processes.

[0003] The electric arc temperature reaches 4000–6000℃, and the molten steel temperature exceeds 2130℃. During electric arc furnace smelting, the continuous ionization of air by the electric arc causes nitrogen absorption by the molten steel. Denitrification in electric arc furnace smelting mainly relies on the bubble-carrying method of CO reaction in the molten pool. However, the carbon content of molten steel from all-scrap steel is low, and the carbon-oxygen reaction in the furnace is insufficient. Therefore, the nitrogen content of the molten steel only decreases during the decarburization stage. Furthermore, when the molten steel temperature exceeds 2130℃, the inhibitory effect of surface-active elements such as oxygen and sulfur disappears, and nitrogen absorption becomes even more severe. The nitrogen content of steel tapped from electric arc furnaces is often as high as 0.0080%–0.013%, and the denitrification capacity of vacuum refining is limited, posing significant challenges to the short-process production of high-grade steel in electric arc furnaces.

[0004] Under standard conditions, carbon dioxide has a density of 1.977 g / L, while air has a density of 1.293 g / L. Carbon dioxide is approximately 1.5 times denser than air. During electric arc furnace smelting, by sealing the furnace and utilizing the fact that carbon dioxide is heavier than air, air is expelled from the top of the furnace, ensuring that the carbon dioxide content exceeds 80%. This minimizes the amount of air inside the furnace, addressing nitrogen enrichment from ionized air at its source. A gas recovery device is installed at the top of the furnace; after multi-stage separation and filtration, the gas can be recycled, achieving the resource utilization of carbon dioxide. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a steelmaking electric furnace that reduces nitrogen addition, which can minimize nitrogen addition during the electric furnace smelting process, or even achieve zero nitrogen addition smelting, thus helping the electric furnace to produce high-grade steel.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A steelmaking electric furnace with reduced nitrogen accumulation includes a furnace body and a furnace cover. The upper surface of the furnace body is provided with a raised edge, and the lower surface of the furnace cover is provided with a groove that seals with the raised edge. The side of the groove is provided with a vent hole. The furnace cover is provided with multiple gas nozzles and a gas analysis device. The center of the furnace cover is provided with an electrode hole, and a sliding electrode cover is provided above the electrode hole.

[0008] The gas nozzles are evenly distributed circumferentially.

[0009] A steelmaking electric arc furnace smelting method for reducing nitrogen accumulation includes:

[0010] 1) Scrap steel and slag are loaded into the bottom of the furnace;

[0011] 2) Cover the furnace with the lid and close the electrode cover. The furnace body and lid are sealed by a locking groove. Carbon dioxide is introduced into the locking groove through the vent hole as a sealing gas; the gas supply pressure is 0.1–1.0 MPa, and the gas supply intensity is 0.5–2.0 m³ / min. 3 / (t·min);

[0012] 3) Carbon dioxide gas is introduced into the furnace through a gas nozzle. The initial gas supply pressure is 0.6–1.0 MPa, and the gas supply intensity is 1.0–2.0 m³ / min. 3 / (t·min), the ventilation time is 5 to 10 minutes. After the ventilation is completed, the gas composition in the furnace is measured by the gas analysis device on the furnace cover. When the carbon dioxide content in the furnace exceeds 80%, the electrode cover is opened and the electrode is lowered into the furnace to start smelting.

[0013] 4) During the smelting process, adjust the supply pressure and intensity of carbon dioxide through the gas nozzle to control the carbon dioxide content in the furnace to above 80%.

[0014] 5) After smelting, shut off the gas nozzles and tap out the steel for sampling;

[0015] 6) The steel element content was determined.

[0016] Compared with existing technologies, the beneficial effects of this invention are:

[0017] This invention relates to an electric arc furnace for steelmaking that avoids contact between molten steel and air, thus solving the problem of nitrogen addition from ionized air at its source. It minimizes nitrogen addition during the electric arc furnace smelting process, even achieving zero nitrogen addition, with nitrogen content in the tapped steel ranging from 0.0050% to 0.007%. This provides equipment support for the production of high-grade steels using electric arc furnaces. It also enables the resource utilization of carbon dioxide. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the electric furnace of the present invention.

[0019] Figure 2 This is a schematic diagram of the electric furnace used in this invention.

[0020] In the diagram: 1. Furnace body; 2. Furnace cover; 3. Rim; 4. Slot; 5. Gas nozzle; 6. Gas analyzer; 7. Electrode hole; 8. Electrode cover; 9. Electrode; 10. Vent hole. Detailed Implementation

[0021] It should be noted that, 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. The terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0022] A steelmaking electric furnace with reduced nitrogen accumulation includes a furnace body 1 and a furnace cover 2. The upper surface of the furnace body 1 is provided with a raised edge 3, and the lower surface of the furnace cover 2 is provided with a groove 4 that seals with the raised edge 3. The side of the groove 4 is provided with a vent hole 10. The furnace cover 2 is provided with multiple gas nozzles 5 and a gas analysis device 6. The middle part of the furnace cover 2 is provided with an electrode hole 7, and a sliding electrode cover 8 is provided above the electrode hole 7.

[0023] The gas nozzles are 5 and they are evenly distributed around the circumference.

[0024] A steelmaking electric arc furnace smelting method for reducing nitrogen accumulation includes:

[0025] 1) Scrap steel and slag are loaded into the bottom of furnace body 1;

[0026] 2) Cover the furnace with lid 2 and close the electrode cover 8. The furnace body 1 and furnace lid 2 are sealed by the slot 4. Carbon dioxide is introduced into the slot 4 through the vent 10 as a sealing gas; the gas supply pressure is 0.1-1.0 MPa, and the gas supply intensity is 0.5-2.0 m³ / s. 3 / (t·min);

[0027] 3) Carbon dioxide gas is introduced into the furnace through gas nozzle 5. The initial gas supply pressure is 0.6–1.0 MPa, and the gas supply intensity is 1.0–2.0 m³ / s. 3 / (t·min), the ventilation time is 5 to 10 min. After the ventilation is completed, the gas composition in the furnace is measured by the gas analysis device 6 on the furnace cover. When the carbon dioxide content in the furnace exceeds 80%, the electrode cover 8 is opened and the electrode 9 is lowered into the furnace to start smelting.

[0028] 4) During the smelting process, adjust the supply pressure and intensity of carbon dioxide introduced through gas nozzle 5 to control the carbon dioxide content in the furnace body to above 80%.

[0029] 5) After smelting is completed, shut off gas nozzle 5, tap out steel and take samples;

[0030] 6) The steel element content was determined.

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] Example 1

[0033] The smelting method using a 100t electric arc furnace with reduced nitrogen increase, for steel grade Q235, includes the following steps:

[0034] 1. 105t of scrap steel and 3t of slag are loaded into the bottom of furnace body 1;

[0035] 2. Cover the furnace with lid 2 and close the electrode cover 8. The furnace body 1 and furnace lid 2 are sealed by the slot 4. Carbon dioxide is introduced into the slot 4 through the vent 10 as a sealing gas, with a gas supply pressure of 0.5 MPa and a gas supply intensity of 1.0 m. 3 / (t·min);

[0036] 3. Carbon dioxide gas is introduced into the furnace through gas nozzle 5, with an initial supply pressure of 0.9 MPa and a supply intensity of 1.8 m³ / s. 3 / (t·min), after 7 minutes of ventilation, the gas analysis device 6 measures the gas composition in the furnace. The carbon dioxide content in the furnace is 90%. The electrode cover 8 is opened and the electrode 9 is lowered into the furnace to start smelting.

[0037] 4. During the smelting process, dynamically adjust the supply pressure and intensity of carbon dioxide introduced through gas nozzle 5 to control the carbon dioxide content in the furnace body at 86%–88%;

[0038] 5. After smelting is completed, shut off gas nozzle 5, tap out the steel and take a sample;

[0039] 6. The elemental content of the steel was determined. The chemical composition of the steel produced in this embodiment is shown in Table 1.

[0040] Table 1. Chemical composition of the steel (wt%)

[0041] element C Si Mn P S N content 0.21 0.33 1.29 0.019 0.011 0.0065

[0042] The nitrogen content of Q235 steel produced by conventional electric furnace smelting is 0.0096%. The nitrogen reduction rate of this invention is (0.0096-0.0065) / 0.0096=33.3%.

[0043] Example 2

[0044] The smelting method using a 100t electric arc furnace with reduced nitrogen increase, for steel grade H13, includes the following steps:

[0045] 1. 105 tons of scrap steel and 4 tons of slag are loaded into the bottom of furnace body 1;

[0046] 2. Cover the furnace with lid 2 and close the electrode cover 8. The furnace body 1 and furnace lid 2 are sealed by the slot 4. Carbon dioxide is introduced into the slot 4 through the vent 10 as a sealing gas, with a gas supply pressure of 0.6 MPa and a gas supply intensity of 1.2 m. 3 / (t·min);

[0047] 3. Carbon dioxide gas is introduced into the furnace body through gas nozzle 5, with an initial gas supply pressure of 0.8 MPa and a gas supply intensity of 1.5 m³ / min. 3 / (t·min), after 5 minutes of ventilation, the gas analysis device 6 measures the gas composition in the furnace. The carbon dioxide content in the furnace is 88%. The electrode cover 8 is opened and the electrode 9 is lowered into the furnace to start smelting.

[0048] 4. During the smelting process, dynamically adjust the supply pressure and intensity of carbon dioxide introduced through gas nozzle 5 to control the proportion of carbon dioxide in the furnace at 87%–90%;

[0049] 5. After smelting is completed, close gas nozzle 5 and tap out the steel for sampling.

[0050] 6. The elemental content of the steel was determined. The chemical composition of the steel produced in this embodiment is shown in Table 2.

[0051] Table 2. Composition of steel tapped from electric furnace, wt%

[0052] element C Si Mn P S N content 0.42 0.86 0.35 0.018 0.006 0.006

[0053] The nitrogen content of H13 steel produced by conventional electric furnace smelting is 0.0103%. The nitrogen reduction rate of this invention is (0.0103-0.006) / 0.0103=41.7%.

[0054] Example 3

[0055] A steelmaking method using a 100t electric arc furnace with reduced nitrogen increase, for steel grade GCr15, includes the following steps:

[0056] 1. 105t of scrap steel and 3t of slag are loaded into the bottom of furnace body 1;

[0057] 2. Cover the furnace with lid 2 and close the electrode cover 8. The furnace body 1 and furnace lid 2 are sealed by the slot 4. Carbon dioxide is introduced into the slot 4 through the vent 10 as a sealing gas, with a gas supply pressure of 0.6 MPa and a gas supply intensity of 1.2 m. 3 / (t·min);

[0058] 3. Carbon dioxide gas is introduced into the furnace through gas nozzle 5, with an initial supply pressure of 1.0 MPa and a supply intensity of 1.7 m³ / s. 3 / (t·min), after 6 minutes of ventilation, the gas analysis device 6 measures the gas composition of the furnace body. The carbon dioxide content in the furnace is 91%. The electrode cover 8 is opened and the electrode 9 is lowered into the furnace to start smelting.

[0059] 4. During the smelting process, dynamically adjust the supply pressure and intensity of carbon dioxide introduced through gas nozzle 5 to control the carbon dioxide content in the furnace body between 86% and 88%.

[0060] 5. After smelting is completed, close gas nozzle 5 and tap out the steel for sampling.

[0061] 6. The elemental content of the steel was determined. The chemical composition of the steel produced in this embodiment is shown in Table 3.

[0062] Table 3 Chemical composition of steel tapped from electric furnace, wt%

[0063] element C Si Mn P S N content 0.97 0.22 0.52 0.014 0.005 0.0056

[0064] The nitrogen content of GCr15 steel produced by conventional electric furnace smelting is 0.011%. The nitrogen reduction rate of this invention is (0.011-0.0056) / 0.011=49.1%.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A steelmaking electric furnace with reduced nitrogen increase, characterized in that, The furnace includes a furnace body and a furnace cover. The upper surface of the furnace body is provided with a raised edge, and the lower surface of the furnace cover is provided with a groove that seals with the raised edge. The side of the groove is provided with a vent hole. The furnace cover is provided with multiple gas nozzles and a gas analysis device. The center of the furnace cover is provided with an electrode hole, and a sliding electrode cover is provided above the electrode hole.

2. The steelmaking electric furnace for reducing nitrogen accumulation according to claim 1, characterized in that, The gas nozzles are evenly distributed circumferentially.

3. The smelting method of a steelmaking electric furnace with reduced nitrogen increase according to claim 1, characterized in that, include: 1) Scrap steel and slag are loaded into the bottom of the furnace; 2) Cover the furnace with the lid and close the electrode cover. The furnace body and lid are sealed by a locking groove. Carbon dioxide is introduced into the locking groove through the vent hole as a sealing gas; the gas supply pressure is 0.1–1.0 MPa, and the gas supply intensity is 0.5–2.0 m³ / min. 3 / (t·min); 3) Carbon dioxide gas is introduced into the furnace through a gas nozzle. The initial gas supply pressure is 0.6–1.0 MPa, and the gas supply intensity is 1.0–2.0 m³ / min. 3 / (t·min), the ventilation time is 5 to 10 minutes. After the ventilation is completed, the gas composition in the furnace is measured by the gas analysis device on the furnace cover. When the carbon dioxide content in the furnace exceeds 80%, the electrode cover is opened and the electrode is lowered into the furnace to start smelting. 4) During the smelting process, adjust the supply pressure and intensity of carbon dioxide through the gas nozzle to control the carbon dioxide content in the furnace to above 80%. 5) After smelting, shut off the gas nozzles and tap out the steel for sampling; 6) The steel element content was determined.

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