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CN-117230273-B - Method for smelting low-nitrogen steel by adopting electric arc furnace

CN117230273BCN 117230273 BCN117230273 BCN 117230273BCN-117230273-B

Abstract

The invention discloses a method for smelting low-nitrogen steel by adopting an arc furnace, which comprises the steps of using scrap steel and molten iron as main raw materials in an alternating-current arc furnace, conducting electricity through electrodes to heat and melt the scrap steel in the furnace, supplying oxygen to a furnace wall oxygen gun to divide a burner, low oxygen, medium oxygen, high oxygen and a holding mode, supplying oxygen to a furnace door oxygen gun to divide the low oxygen and high oxygen modes, adopting a furnace bottom electromagnetic stirring technology to reduce the time for melting large scrap steel, adding lime a small amount of lime for multiple times, ensuring the fluidity of steel slag and the temperature control of molten steel in the whole smelting process, carrying out temperature measurement and sampling before tapping, and cutting off power when molten steel in a ladle is turned over to contact air in the tapping process. The tapping N content of the electric arc furnace is stably less than or equal to 25ppm.

Inventors

  • JIN QINGFENG
  • MA JIANCHAO
  • WANG YAO
  • DU XIQIAN

Assignees

  • 江苏省沙钢钢铁研究院有限公司
  • 江苏沙钢集团有限公司

Dates

Publication Date
20260512
Application Date
20230901

Claims (8)

  1. 1. A method for smelting low nitrogen steel using an electric arc furnace, comprising the steps of: The method comprises the steps of feeding raw materials into an alternating current arc furnace, namely, using scrap steel and molten iron as main raw materials, opening a top-open furnace cover, loading the scrap steel from the furnace top, placing a ladle on a ladle turret after the furnace cover is closed, feeding the ladle into the furnace through a furnace rear chute, controlling the iron charging speed to be 5-10 tons/min, decarbonizing CO generated by the arc furnace, and removing part of N element in the raw materials; After closing the furnace cover, conducting electric conduction through the electrode to heat and melt scrap steel in the furnace; oxygen supply operation, namely, oxygen supply of the furnace wall oxygen gun is divided into a burner, a low oxygen mode, a medium oxygen mode, a high oxygen mode and a holding mode, and oxygen supply of the furnace door oxygen gun is divided into a low oxygen mode and a high oxygen mode; The bottom electromagnetic stirring is realized by adopting a bottom electromagnetic stirring technology and generating a magnetic field penetrating through the bottom through a stirring coil, so that stirring is enhanced in the process of smelting scrap steel, forced convection is reduced, layering is reduced, the temperature and chemical components in a molten pool are more quickly and uniformly achieved, and the time for melting large scrap steel is reduced; The slag forming operation comprises the steps of adding lime a small amount of lime for many times, and ensuring the fluidity of steel slag and the temperature control of molten steel in the whole smelting process; the tapping operation comprises the steps of cutting off power when temperature measurement and sampling are carried out before tapping, changing a furnace wall oxygen lance into a holding mode, flowing slag before tapping as much as possible, ensuring that no slag flows out from a tap hole when the furnace returns to a slag discharging position after tapping, and increasing nitrogen content of molten steel when the contact time of molten steel and air is longer and the contact surface area is larger in the tapping process, so that the scattering of the tap hole is avoided, and argon blowing at the bottom of a ladle is avoided when tapping, and the contact of molten steel in the ladle with air caused by the rising of the molten steel is avoided.
  2. 2. The method for smelting low-nitrogen steel by using an arc furnace according to claim 1, wherein the arc furnace is an arc furnace of an alternating current arc power supply system, and the unit power of a transformer is 650kVA/t or more.
  3. 3. The method for smelting low nitrogen steel by using an electric arc furnace according to claim 1, wherein the raw material is charged into the furnace by adding molten iron to the rear wall of the furnace.
  4. 4. The method for smelting low-nitrogen steel by using an electric arc furnace according to claim 3, wherein the temperature of molten iron added in the charging operation of the raw materials is more than or equal to 1250 ℃, and the composition requirements are more than or equal to 4.0% of C, less than or equal to 0.7% of Si, less than or equal to 0.13% of P and less than or equal to 0.03% of S.
  5. 5. The method for smelting low nitrogen steel by using an electric arc furnace according to claim 1, wherein the electric arc furnace is provided with three furnace wall oxygen guns and one furnace door carbon oxygen gun with carbon powder spraying function, and the installation positions of the furnace wall oxygen guns are named as 1# gun, 2# gun and 3# gun in sequence in a clockwise direction; The oxygen supply operation comprises the steps of adopting a furnace wall gun burner mode when smelting starts, switching to a furnace wall gun low-oxygen mode after 4 minutes of operation, then using a medium-oxygen mode for a No. 1 gun and a No. 2 gun, keeping the low-oxygen mode for a No. 3 gun, avoiding using a high-oxygen mode in the whole process, and switching to a keeping mode after the temperature of molten steel reaches 1600 ℃; The furnace door oxygen lance is not opened in the earlier stage of smelting, the low-oxygen mode is started after the raw materials in the furnace are melted down, the furnace door oxygen lance is closed after the temperature of molten steel reaches 1600 ℃, and the furnace door oxygen lance is used for spraying carbon powder according to the condition in the furnace, wherein the total amount is 2-5kg/t, so as to thicken slag and avoid tapping and discharging slag.
  6. 6. The method for smelting low nitrogen steel using an electric arc furnace according to claim 5, wherein the respective mode setting flow ranges of the furnace wall lance and the furnace door lance in the oxygen supplying operation are as follows: 。
  7. 7. The method for smelting low-nitrogen steel by adopting an electric arc furnace according to claim 1, wherein 3-4 batches of lime are added in the whole slag forming operation, when slag flows out from a furnace door, a first batch of lime is added for 2-3 times, the addition amount is 1.0-1.5 tons, when carbon-oxygen reaction occurs after the furnace is cleared, a second batch of lime is added for 2-3 times, the addition amount is 1.0-1.5 tons, when raw materials are completely melted, a third batch of lime is added at the temperature of 1510-1530 ℃, 0.5-0.8 tons are added for 2-3 batches, and if the carbon-oxygen reaction is intense, the slag leakage degree is large, 0.2-0.3 tons of lime is added.
  8. 8. The method for smelting low-nitrogen steel by adopting the electric arc furnace according to claim 1, wherein the current intensity and the stirring frequency of a coil of a furnace bottom electromagnetic stirring system of the electric arc furnace are controlled and adjusted according to stages, and the method comprises the steps of a scrap steel melting period and a temperature uniformity period, wherein the current intensity range is 200-350A, the electromagnetic stirring frequency range is 1-3Hz, the temperature uniformity period, the current intensity range is 300-500A, the electromagnetic stirring frequency range is 2-5Hz, and the electromagnetic stirring is turned off before tapping.

Description

Method for smelting low-nitrogen steel by adopting electric arc furnace Technical Field The invention relates to a method for smelting low-nitrogen steel by adopting an electric arc furnace, belonging to the technical field of steelmaking. Background In most cases, the element N in steel is a detrimental element. Too high an N content reduces the plasticity and toughness of the steel, increases the ageing tendency and brittleness, and impairs the welding and cold bending properties of the steel. With the continued advancement of "dual carbon" targets, electric arc furnace steelmaking will have increased in development. However, according to the past experience, as a primary smelting furnace, an arc furnace has one of disadvantages in that it is difficult to control the N content compared with a converter. Generally, the liquid nitrogen content of the converter end point steel ranges from 15 to 30ppm, and the electric furnace ranges from 50 to 100ppm. The primary furnace N content substantially determines the final product N content level, so how to effectively control the nitrogen content in the electric arc furnace steel is a problem to be solved. The prior patent is searched, chinese patent CN107502702A discloses a clean and rapid smelting method of a full scrap steel electric arc furnace, full scrap steel smelting is adopted, and different types of mediums are sprayed at different smelting stages by utilizing a spray gun buried in the refractory material at the side surface of the bottom of the electric arc furnace, so as to promote the denitrification of molten steel. The method has the limitations that molten steel in the later stage of smelting is insufficient for carrying out severe carbon-oxygen reaction to realize denitrification, the buried spray gun is difficult to maintain, and the production stability is not high. The method disclosed in Chinese patent CN111996334A adopts a full scrap steel electric arc furnace for smelting, optimizes the formation of foam slag in the furnace, and reduces the nitrogen absorption degree of molten steel. The method has the limitations that the electric arc furnace adopts a full scrap steel charging mode, the fluctuation of nitrogen content of raw materials entering the furnace is large, the carbon adding amount in the furnace material is not high, the carbon-oxygen reaction is not severe, the denitrification effect is not ideal, and the stability is not high. Chinese patent CN101899548a discloses a new process for preheating waste steel and making steel by high-efficiency electric furnace, and refers to that the waste steel is melted by induction furnace and then added into electric furnace for smelting, so that the smelting period of electric furnace can be shortened. The induction furnace has the limitations of high energy consumption, long smelting period and mismatching with the production rhythm of the electric furnace. The method disclosed in chinese patent CN108715912a is to control the oxygen content of the steel in the electric arc furnace to be in a slight peroxidation state, so as to reduce the nitrogen absorption phenomenon of the steel in the tapping process. The limitation of the method is that the quality of the subsequent products is affected by the peroxidized molten steel, and the nitrogen content of the molten steel is increased after deoxidation in the refining process. In addition, the electric arc furnace can also reduce the exposure of molten steel, reduce the contact surface with air and reduce nitrogen absorption through the operation of large current, low voltage and short electric arc, but the mode not only prolongs the smelting rhythm, but also can cause the rise of cost indexes such as electrode consumption, electricity consumption and the like. Therefore, this method is not suitable for practical production. Disclosure of Invention In order to solve the problems, the invention discloses a method for smelting low-nitrogen steel by adopting an electric arc furnace, which comprises the following specific technical scheme: A method for smelting low nitrogen steel using an electric arc furnace comprising the steps of: the method comprises the steps of feeding raw materials into an alternating current arc furnace, wherein waste steel and molten iron are used as main raw materials, the waste steel adopts a round material bag, a top-open furnace cover is opened, the waste steel is fed from the furnace top, after the furnace cover is closed, the ladle is placed on a ladle turret, the ladle is fed into the furnace through a chute behind the furnace, the speed of iron charging is controlled to be 5-10 tons/min, CO generated by decarburization of the arc furnace is removed, and part of N element in the raw materials is removed; After closing the furnace cover, conducting electric conduction through the electrode to heat and melt scrap steel in the furnace; oxygen supply operation, namely, oxygen supply of the furnace wall oxygen gun is divided i