A method for smelting low-nitrogen automotive sheet in an electric arc furnace

Abstract

The application discloses a method for smelting low-nitrogen automobile plate in an electric arc furnace, which comprises an electric arc furnace smelting process, an RH vacuum refining process and a continuous casting process. The electric arc furnace smelting process comprises the following steps: continuously adding iron skin carbon balls as carbon-rich raw materials into the furnace, specifically, adding 1-2 kg of iron skin carbon balls per ton of molten steel when electrically conducting for 3-5 minutes, adding 2-4 kg of iron skin carbon balls per ton of molten steel when electrically conducting for 15-18 minutes, and adding 2-4 kg of iron skin carbon balls per ton of molten steel when electrically conducting for 25-28 minutes; during the electrically conducting period, one oxygen lance is turned off every time interval, three oxygen lances are turned off 5-10 minutes before the smelting is completed, and the flow rates of the turned-on oxygen lances are all reduced to 1800-2000 NL / min; after the molten steel is discharged, a carbon lance is immediately turned on to spray carbon reduction and thicken the final slag, and the flow rate of the carbon lance is set to 30-50 kg / min. According to the method, the nitrogen content of the plate can be controlled to be below 0.004%.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a smelting method for ultra-low carbon, high purity automotive steel. Background Technology

[0002] For automotive panel steel, nitrogen is a harmful element. It reduces the steel's plasticity and impact toughness, and like phosphorus, it can cause brittleness during cooling. Furthermore, nitrogen can combine with elements such as titanium, aluminum, and vanadium in the steel to form nitride inclusions, leading to deterioration of the steel's surface quality and reduced yield. With increasingly stringent quality requirements for automotive panels, controlling the nitrogen content in steel to a lower level has become a key focus.

[0003] Based on the concept of low-carbon and green environmental protection, electric arc furnace (EAF) steelmaking is becoming a future development trend. However, due to the characteristics of raw materials, processes, and equipment, it is difficult to achieve low-nitrogen steel production. The EAF's limitations in the early-stage foam slag formation rate, the maintenance of foam slag during the process, and nitrogen absorption through the steel-slag interface severely restrict further reductions in nitrogen content in steel. How to take measures to control the nitrogen content in molten steel during modern EAF steelmaking processes, so that the nitrogen content of EAF process products reaches a high level that meets material usage requirements, and improves the market competitiveness of EAF process products, is a key issue currently being addressed in EAF steelmaking. Summary of the Invention

[0004] The purpose of this invention is to provide a method for smelting low-nitrogen automotive steel sheets in an electric arc furnace, which can control the nitrogen content of the steel sheets to below 0.004%.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for smelting low-NOx automotive steel sheets in an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; the electric arc furnace smelting process includes the following steps:

[0007] Iron-coated carbon balls are continuously added to the furnace as carbon-rich raw materials. Specifically, 1-2 kg of iron-coated carbon balls are added per ton of molten steel after 3-5 minutes of energization, 2-4 kg of iron-coated carbon balls are added per ton of molten steel after 15-18 minutes of energization, and 2-4 kg of iron-coated carbon balls are added per ton of molten steel after 25-28 minutes of energization.

[0008] During the power-on cycle, one oxygen lance is turned off at regular intervals. Five to ten minutes before the end of smelting, all three oxygen lances are turned off, and the flow rate of the open oxygen lances is reduced to 1800-2000 NL / min.

[0009] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 30-50 kg / min.

[0010] Furthermore, the iron-carbon ball of the present invention is made of a mixture of iron oxide scale and dust removal ash.

[0011] Furthermore, the chemical composition of the iron-coated carbon ball of the present invention is as follows: TFe 65-72%, SiO2 1.5-2.0%, CaO 0.5-0.8%, MgO 0.1-0.2%, Al2O3 0.1-0.3%, ZnO 0.2-0.5%, Cr2O3 0.1-0.2%, TiO2 ≤0.2%, S≤0.1%, P ≤0.1%, C 12.0-18.0%.

[0012] Furthermore, in the RH vacuum refining process of the present invention, the equipment sealing is checked before RH treatment, argon is used as the boosting gas, and the vacuum degree is reduced to below 67Pa with the fastest efficiency. The molten steel is then circulated cleanly for 8-20 minutes under high vacuum.

[0013] Furthermore, in the continuous casting process described in this invention, the ladle superheating temperature is 10-30°C, and the argon gas flow rate at the ladle nozzle is 3-7 m³ / h. 3 / h, operate on the black slag surface inside the crystallizer, and ensure the slag thickness is 40-60mm.

[0014] Furthermore, the low-nitrogen automotive steel sheet of the present invention has the following chemical composition and weight percentage: C≤0.005%, Si≤0.20%, Mn: 0.75~1.00%, P: 0.050~0.080%, S: ≤0.015%, Al: 0.020~0.035%, Ti: 0.010~0.030%, Nb: 0.010~0.020%, N≤0.004%, with the remainder being Fe and unavoidable impurity elements.

[0015] The inventive principle of this invention is as follows:

[0016] Using carbon balls made of sheet metal as a carbon-rich raw material in the furnace creates favorable conditions for the rapid formation of foamy slag in the early stage of smelting and for maintaining the foamy slag during the process. The foamy slag coverage reduces the exposure of the electric arc and nitrogen absorption, and nitrogen is released in large quantities along with CO bubbles. As smelting progresses, the carbon content in the molten steel continuously decreases, and the carbon-oxygen reaction also weakens. Oxygen control is carried out by using oxygen lances on the furnace wall to reduce the oxidation of a large amount of iron in the molten steel into the slag, which can keep the foamy slag stable before the end of smelting. From the end of tapping to the formation of foamy slag in the next furnace, a large amount of nitrogen will be absorbed through the steel-slag interface. The carbon lance is turned on to carry out a carbon injection process. By injecting carbon to reduce iron oxide in the slag, the final slag is thickened, which can increase the surface tension of the slag and thus significantly reduce nitrogen absorption.

[0017] The beneficial effects of adopting the above technical solution are as follows:

[0018] The method of this invention can significantly reduce the nitrogen content in molten steel, and the nitrogen content of the prepared automotive sheet metal is below 0.004%.

[0019] The smelting process involves sequentially shutting down three oxygen lances and reducing the oxygen blowing intensity of the lances, which alleviates the erosion of the furnace lining and greatly reduces the cost of refractory materials.

[0020] The self-produced iron oxide carbon balls are made from a mixture of self-circulating iron oxide scale and dust collector ash. As a carbon-rich raw material, it also recovers the iron element, greatly reducing costs. Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Example 1

[0022] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0023] (1) The electric arc furnace smelting process includes the following steps:

[0024] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 1.2 kg of iron scale carbon balls were added per ton of molten steel 3 minutes after the start of energization, 2.1 kg per ton of molten steel 15 minutes after the start of energization, and 2.7 kg per ton of molten steel 25 minutes after the start of energization, for a total of 6.0 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were made of a mixture of iron oxide scale and dust collector ash, and their chemical composition was as follows: TFe 70.2%, SiO2 1.82%, CaO 0.67%, MgO 0.13%, Al2O3 0.15%, ZnO 0.24%, Cr2O3 0.13%, TiO2 0.09%, S 0.031%, P 0.018%, C 17.4%.

[0025] The power-on cycle is 35 minutes. After 15 minutes of power-on, oxygen lance #1 is turned off, oxygen lance #3 is turned off after 23 minutes of power-on, and oxygen lance #6 is turned off after 30 minutes of power-on. At this time, the flow rates of oxygen lances #2, #4, and #5 are reduced to 1852 NL / min, 1810 NL / min, and 1835 NL / min, respectively.

[0026] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 38.6 kg / min.

[0027] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was circulated for 11 minutes under high vacuum.

[0028] (3) Continuous casting process: The ladle is superheated to 17°C, and the argon flow rate at the ladle nozzle is 4.5 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 47mm. Example 2

[0029] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0030] (1) The electric arc furnace smelting process includes the following steps:

[0031] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 1.0 kg of iron scale carbon balls were added per ton of molten steel 5 minutes after the start of energization, 4.0 kg per ton of molten steel 16 minutes after the start of energization, and 2.0 kg per ton of molten steel 27 minutes after the start of energization, for a total of 7.0 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were made of a mixture of iron oxide scale and dust collector ash, and their chemical composition was as follows: TFe 66.1%, SiO2 1.58%, CaO 0.51%, MgO 0.17%, Al2O3 0.22%, ZnO 0.46%, Cr2O3 0.18%, TiO2 0.07%, S 0.044%, P 0.025%, C 13.2%.

[0032] The power-on cycle is 35 minutes. After 15 minutes of power-on, oxygen lance #3 is turned off, oxygen lance #1 is turned off after 23 minutes of power-on, and oxygen lance #6 is turned off after 30 minutes of power-on. At this time, the flow rates of oxygen lances #2, #4, and #5 are reduced to 1879 NL / min, 1904 NL / min, and 1846 NL / min, respectively.

[0033] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 41.2 kg / min.

[0034] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 66Pa as quickly as possible. The molten steel was circulated for 9 minutes under high vacuum.

[0035] (3) Continuous casting process: During continuous casting, the ladle is superheated to 21°C, and the argon flow rate at the ladle nozzle is 3.5 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 51mm. Example 3

[0036] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0037] (1) The electric arc furnace smelting process includes the following steps:

[0038] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 1.6 kg of iron scale carbon balls were added per ton of molten steel 4 minutes after the start of energization, 2.2 kg per ton of molten steel 17 minutes after the start of energization, and 2.4 kg per ton of molten steel 28 minutes after the start of energization, for a total of 6.2 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were made of a mixture of iron oxide scale and dust collector ash, and their chemical composition was as follows: TFe 69.4%, SiO2 1.91%, CaO 0.74%, MgO 0.15%, Al2O3 0.26%, ZnO 0.43%, Cr2O3 0.17%, TiO2 0.11%, S 0.016%, P 0.027%, C 15.8%.

[0039] The power-on cycle is 35 minutes. After 15 minutes of power-on, oxygen lance #1 is turned off, oxygen lance #6 is turned off after 23 minutes of power-on, and oxygen lance #3 is turned off after 30 minutes of power-on. At this time, the flow rates of oxygen lances #2, #4, and #5 are reduced to 1805 NL / min, 1886 NL / min, and 1867 NL / min, respectively.

[0040] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 38.1 kg / min.

[0041] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was then circulated for 8 minutes under high vacuum.

[0042] (3) Continuous casting process: During continuous casting, the ladle is superheated to 24°C, and the argon flow rate at the ladle nozzle is 5.5 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 49mm. Example 4

[0043] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0044] (1) The electric arc furnace smelting process includes the following steps:

[0045] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 2.0 kg of iron scale carbon balls were added per ton of molten steel 5 minutes after the start of energization, 2.3 kg per ton of molten steel 18 minutes after the start of energization, and 2.2 kg per ton of molten steel 26 minutes after the start of energization, for a total of 5.5 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were composed of iron oxide scale and dust, and their chemical composition was as follows: TFe 67.8%, SiO2 1.64%, CaO 0.69%, MgO 0.11%, Al2O3 0.18%, ZnO 0.31%, Cr2O3 0.14%, TiO2 0.06%, S 0.039%, P 0.022%, C 14.6%.

[0046] The power-on cycle is 35 minutes. After 15 minutes of power-on, oxygen gun #3 is turned off. After 23 minutes of power-on, oxygen gun #6 is turned off. After 30 minutes of power-on, oxygen gun #1 is turned off. At this time, the flow rates of oxygen guns #2, #4, and #5 are reduced to 1901 NL / min, 1837 NL / min, and 1891 NL / min, respectively.

[0047] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 44.6 kg / min.

[0048] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was circulated for 12 minutes under high vacuum.

[0049] (3) Continuous casting process: The ladle is superheated to 16°C, and the argon flow rate at the ladle nozzle is 3.2 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 43mm. Example 5

[0050] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0051] (1) The electric arc furnace smelting process includes the following steps:

[0052] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 1.7 kg of iron scale carbon balls were added per ton of molten steel 3 minutes after the start of energization, 2.8 kg per ton of molten steel 17 minutes after the start of energization, and 2.8 kg per ton of molten steel 27 minutes after the start of energization, for a total of 7.3 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were made of a mixture of iron oxide scale and dust collector ash, and their chemical composition was as follows: TFe 71.6%, SiO2 1.77%, CaO 0.56%, MgO 0.18%, Al2O3 0.12%, ZnO 0.36%, Cr2O3 0.17%, TiO2 0.12%, S 0.036%, P 0.019%, C 16.7%.

[0053] The power-on cycle is 35 minutes. After 15 minutes of power-on, oxygen lance #6 is turned off. After 23 minutes of power-on, oxygen lance #1 is turned off. After 30 minutes of power-on, oxygen lance #3 is turned off. At this time, the flow rates of oxygen lances #2, #4, and #5 are reduced to 1856 NL / min, 1897 NL / min, and 1912 NL / min, respectively.

[0054] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 30.8 kg / min.

[0055] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was circulated for 14 minutes under high vacuum.

[0056] (3) Continuous casting process: During continuous casting, the ladle is superheated to 21°C, and the argon flow rate at the ladle nozzle is 3.9 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 54mm. Example 6

[0057] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0058] (1) The electric arc furnace smelting process includes the following steps:

[0059] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 1.9 kg of iron scale carbon balls were added per ton of molten steel 4 minutes after the start of energization, 3.1 kg per ton of molten steel 16 minutes after the start of energization, and 3.6 kg per ton of molten steel 28 minutes after the start of energization, for a total of 8.6 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were made of a mixture of iron oxide scale and dust collector ash, and their chemical composition was as follows: TFe 65.8%, SiO2 1.57%, CaO 0.61%, MgO 0.17%, Al2O3 0.22%, ZnO 0.27%, Cr2O3 0.18%, TiO2 0.15%, S 0.027%, P 0.016%, C 12.6%.

[0060] The power-on cycle is generally 35 minutes. After 15 minutes of power-on, oxygen lance #6 is turned off, oxygen lance #3 is turned off after 23 minutes of power-on, and oxygen lance #1 is turned off after 30 minutes of power-on. At this time, the flow rates of oxygen lances #2, #4, and #5 are reduced to 1944 NL / min, 1872 NL / min, and 1849 NL / min, respectively.

[0061] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 37.6 kg / min.

[0062] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was then circulated for 18 minutes under high vacuum.

[0063] (3) Continuous casting process: During continuous casting, the ladle is superheated to 27°C, and the argon flow rate at the ladle nozzle is 3.4 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 40mm. Example 7

[0064] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0065] (1) The electric arc furnace smelting process includes the following steps:

[0066] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 1.4 kg of iron scale carbon balls were added per ton of molten steel 5 minutes after the start of energization, 2.3 kg / t per ton of molten steel 15 minutes after the start of energization, and 2.1 kg / t per ton of molten steel 27 minutes after the start of energization, for a total of 5.8 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were composed of iron oxide scale and dust, and their chemical composition was as follows: TFe 70.8%, SiO2 1.65%, CaO 0.74%, MgO 0.16%, Al2O3 0.17%, ZnO 0.21%, Cr2O3 0.14%, TiO2 0.06%, S 0.033%, P 0.014%, C 13.5%.

[0067] The power-on cycle is 35 minutes. After 15 minutes of power-on, oxygen gun #1 is turned off. After 23 minutes of power-on, oxygen gun #6 is turned off. After 30 minutes of power-on, oxygen gun #3 is turned off. At this time, the flow rates of oxygen guns #2, #4, and #5 are reduced to 1894 NL / min, 1908 NL / min, and 1806 NL / min, respectively.

[0068] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 33.9 kg / min.

[0069] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was circulated for 11 minutes under high vacuum.

[0070] (3) Continuous casting process: During continuous casting, the ladle is superheated to 19°C, and the argon flow rate at the ladle nozzle is 6.2 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 60mm. Example 8

[0071] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0072] (1) The electric arc furnace smelting process includes the following steps:

[0073] Iron scale carbon balls were continuously added to the furnace as a carbon-rich raw material. Specifically, 1.9 kg of iron scale carbon balls were added per ton of molten steel 3 minutes after the start of energization, 4.0 kg per ton of molten steel 18 minutes after the start of energization, and 3.9 kg per ton of molten steel 26 minutes after the start of energization, for a total of 9.8 kg of iron scale carbon balls per ton of molten steel in this furnace. The iron scale carbon balls were made of a mixture of iron oxide scale and dust collector ash, and their chemical composition was as follows: TFe 69.5%, SiO2 1.59%, CaO 0.69%, MgO 0.12%, Al2O3 0.18%, ZnO 0.25%, Cr2O3 0.17%, TiO2 0.10%, S 0.029%, P 0.017%, C 16.9%.

[0074] The power-on cycle is 35 minutes. After 15 minutes of power-on, oxygen lance #3 is turned off. After 23 minutes of power-on, oxygen lance #6 is turned off. After 30 minutes of power-on, oxygen lance #1 is turned off. At this time, the flow rates of oxygen lances #2, #4, and #5 are reduced to 1985 NL / min, 1929 NL / min, and 1836 NL / min, respectively.

[0075] Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 43.4 kg / min.

[0076] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was circulated for 16 minutes under high vacuum.

[0077] (3) Continuous casting process: During continuous casting, the ladle is superheated to 22°C, and the argon flow rate at the ladle nozzle is 5.8 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 57mm.

[0078] Comparative Example 1

[0079] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0080] (1) The electric arc furnace smelting process includes the following steps:

[0081] No iron sheet or carbon balls are added to the furnace during the electro-smelting process;

[0082] All oxygen lances were turned on normally during the power-on cycle. After 15 minutes of power-on, the flow rates of oxygen lances 1-6 were 836 NL / min, 859 NL / min, 821 NL / min, 887 NL / min, 811 NL / min, and 844 NL / min, respectively. After 23 minutes of power-on, the flow rates of oxygen lances 1-6 were adjusted to 2679 NL / min, 2634 NL / min, 2638 NL / min, 2701 NL / min, 2653 NL / min, and 2697 NL / min, respectively. After 30 minutes of power-on, the flow rates of oxygen lances 1, 3, and 6 were adjusted to 2521 NL / min, 2566 NL / min, and 2513 NL / min, respectively, while the flow rates of oxygen lances 2, 4, and 5 remained unchanged.

[0083] The carbon lance is not turned on until the steel tapping is completed and the smelting begins.

[0084] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 65Pa as quickly as possible. The molten steel was then circulated for 10 minutes under high vacuum.

[0085] (3) Continuous casting process: During continuous casting, the ladle is superheated to 25°C, and the argon flow rate at the ladle nozzle is 4.1 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 46mm.

[0086] Comparative Example 2

[0087] The method for smelting low-NOx automotive steel sheets using an electric arc furnace includes an electric arc furnace smelting process, an RH vacuum refining process, and a continuous casting process; details are as follows:

[0088] (1) The electric arc furnace smelting process includes the following steps:

[0089] No iron sheet or carbon balls are added to the furnace during the electro-smelting process;

[0090] All oxygen lances were turned on normally during the power-on cycle. After 15 minutes of power-on, the flow rates of oxygen lances 1-6 were 864 NL / min, 878 NL / min, 803 NL / min, 865 NL / min, 827 NL / min, and 839 NL / min, respectively. After 23 minutes of power-on, the flow rates of oxygen lances 1-6 were adjusted to 2615 NL / min, 2603 NL / min, 2618 NL / min, 2682 NL / min, 2696 NL / min, and 2681 NL / min, respectively. After 30 minutes of power-on, the flow rates of oxygen lances 1, 3, and 6 were adjusted to 2502 NL / min, 2526 NL / min, and 2531 NL / min, respectively, while the flow rates of oxygen lances 2, 4, and 5 remained unchanged.

[0091] The carbon lance is not turned on until the steel tapping is completed and the smelting begins.

[0092] (2) RH vacuum refining process: Before RH treatment, the equipment sealing was checked and argon was used to boost the gas to reduce the vacuum to 67Pa as quickly as possible. The molten steel was circulated for 14 minutes under high vacuum.

[0093] (3) Continuous casting process: During continuous casting, the ladle is superheated to 19°C, and the argon flow rate at the ladle nozzle is 5.2 m³ / s. 3 / h, operation on the black slag surface inside the crystallizer, with a slag thickness of 51mm.

[0094] The continuous casting billet samples of Examples 1-8 and Comparative Examples 1 and 2 were processed into gas analysis samples (5 sets of samples for each example) and measured using an oxygen and nitrogen analyzer. The specific results are shown in Table 1 below.

[0095] Table 1. Nitrogen content of the boards prepared in each embodiment and comparative example.

[0096]

[0097] Compared to Comparative Examples 1 and 2, Examples 1-8 used inexpensive iron-coated carbon balls as carbon-rich raw materials added to the furnace, controlled oxygen operation with oxygen lances on the furnace wall, and activated carbon lances for carbon injection after tapping. This created favorable conditions for denitrification and prevention of nitrogen absorption, resulting in a significant reduction in nitrogen content in the molten steel.

[0098] The content of all chemical components in the automotive sheet materials prepared in each embodiment and comparative example is shown in Table 2.

[0099] Table 2 Chemical composition of automotive sheet metal prepared in each embodiment and comparative example

[0100]

[0101] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for smelting low-NOx automotive steel sheets in an electric arc furnace, comprising electric arc furnace smelting, RH vacuum refining, and continuous casting processes; characterized in that, The electric arc furnace smelting process includes the following steps: Iron-coated carbon balls are continuously added to the furnace as a carbon-rich raw material, specifically: 1-2 kg of iron-coated carbon balls per ton of molten steel is added after 3-5 minutes of energization, 2-4 kg per ton of molten steel is added after 15-18 minutes of energization, and 2-4 kg per ton of molten steel is added after 25-28 minutes of energization. The chemical composition of the iron-coated carbon balls is: TFe 65-72%, SiO2 1.5-2.0%, CaO 0.5-0.8%, MgO 0.1-0.2%, Al2O3 0.1-0.3%, ZnO 0.2-0.5%, Cr2O3 0.1-0.2%, TiO2 ≤0.2%, S ≤0.1%, P ≤0.1%, C 12.0-18.0%. During the power-on cycle, one oxygen lance is turned off at regular intervals. Five to ten minutes before the end of smelting, all three oxygen lances are turned off, and the flow rate of the open oxygen lances is reduced to 1800-2000 NL / min. Immediately after tapping, the carbon lance is turned on to inject carbon to reduce and thicken the final slag. The carbon lance flow rate is set to 30-50 kg / min. The low-nitrogen automotive steel sheet has the following chemical composition and weight percentage: C≤0.005%, Si≤0.20%, Mn: 0.75~1.00%, P: 0.050~0.080%, S: ≤0.015%, Al: 0.020~0.035%, Ti: 0.010~0.030%, Nb: 0.010~0.020%, N≤0.004%, with the remainder being Fe and unavoidable impurity elements.

2. The method for smelting low-nitrogen automotive steel sheets in an electric arc furnace according to claim 1, characterized in that, The iron-coated carbon balls are made of a mixture of iron oxide scale and dust.

3. The method for smelting low-nitrogen automotive steel sheets in an electric arc furnace according to claim 1, characterized in that, In the continuous casting process, the ladle is superheated to 10-30℃, and the argon gas flow rate at the ladle nozzle is 3-7 m³ / h. 3 / h, operate on the black slag surface inside the crystallizer, and ensure the slag thickness is 40-60mm.

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