Method for top and bottom combined blown converter smelting and its application

Abstract

The application discloses a top and bottom combined blowing converter smelting method and application thereof and relates to the technical field of steel smelting. By matching different temperature rising rates and temperature range settings, the process of top and bottom combined blowing converter smelting is divided into four periods, precise temperature control of the four periods is realized, and the smelting principle of rapid temperature rising, slag forming first, temperature rising later and uniform composition is realized, so that efficient smelting of molten steel in the converter is realized, and abnormal phenomena are eliminated. In the low-temperature dephosphorization and high-temperature decarburization zoning treatment mode, the rapid temperature rising mode is adopted in the preheating slag forming period, sufficient time is provided for dephosphorization, the temperature rising rate is slow in the temperature control dephosphorization period, on the one hand, the dephosphorization time is prolonged, and on the other hand, the low temperature is beneficial to the dephosphorization reaction, so that the dephosphorization efficiency and quality are improved; the temperature rising rate is increased again in the slag changing anti-phosphorus returning period, the slag is changed rapidly, and the phosphorus returning phenomenon is prevented; finally, high-temperature rapid decarburization is used to protect the furnace, the steel tapping quality is ensured, and the in-furnace burning loss is avoided.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, and more specifically, to a method for smelting in a top-and-bottom combined blowing converter and its application. Background Technology

[0002] Steel cleanliness is an important indicator for measuring the amount of harmful components in steel. Clean steel refers to steel in which the quantity, size, and distribution of non-metallic inclusions have a significant impact on the properties of the steel. With the increasing demand for clean steel year by year, reducing the FeO content in the final slag has become an important cost control indicator for modern primary smelting furnaces.

[0003] Because oxide slag is a highly complex multi-element system, any change in any parameter or the addition of any material will lead to changes in its parameters, and these changes occur continuously throughout the smelting process. Slag composition plays a crucial role in removing phosphorus (P) and sulfur (S) from molten steel, as well as in process control and slag splashing for furnace protection. Regarding endpoint control, in addition to controlling the content of harmful elements such as P, S, and H in the molten steel, the steel temperature, and the carbon content within reasonable ranges, it is also essential to make the final slag viscous and significantly reduce the FeO content in the final slag to effectively improve the cleanliness of the molten steel from the source.

[0004] However, in the current smelting process, rapid oxidation of Fe, C, Si, and Mn in the molten steel is common in the early stages of smelting, resulting in the production of large amounts of SiO2 and FeO in the slag. At this point, the total slag volume has not yet reached the required level, and the CaO content in the slag is low. This leads to a slow slag formation rate, poor slag fluidity and foaming properties, resulting in a long smelting cycle and excessive oxidation of the molten steel. Other problems include difficulties in dephosphorization during the middle stages of smelting and secondary oxidation of the molten steel during the final furnace turnover process. Furthermore, the overall carbon retention capacity is poor, causing an increase in the H content in the molten steel and ultimately resulting in poor quality steel.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for top-and-bottom blowing converter smelting and its application.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for smelting in a top-and-bottom combined blowing converter, comprising adding the iron to be processed into the top-and-bottom combined blowing converter for smelting, and the smelting process including a preheating slag formation period, a temperature control and phosphorus removal period, a slag transformation and phosphorus reversion prevention period, and a decarburization and furnace protection period.

[0009] When the temperature of molten steel exceeds 1550℃, the smelting process changes from the preheating and slag formation period to the temperature-controlled dephosphorization period; when the temperature of molten steel exceeds 1585℃, the smelting process changes from the temperature-controlled dephosphorization period to the slag transformation and phosphorus prevention period; when the temperature of molten steel exceeds 1590℃, the smelting process changes from the slag transformation and phosphorus prevention period to the decarburization and furnace protection period.

[0010] The heating rate of molten steel during the preheating and slag-forming period is 12-15℃ / min, the heating rate of molten steel during the temperature-controlled descaling period is 2-4℃ / min, and the heating rate of molten steel during the slag-changing and anti-phosphorus-reversion period and the decarburization and furnace protection period is 10-12℃ / min.

[0011] Secondly, the present invention provides an application of the method as described in any of the foregoing embodiments in iron and steel smelting.

[0012] The present invention has the following beneficial effects:

[0013] This invention provides a method for top-and-bottom blowing converter smelting and its application. By coordinating different heating rates and temperature ranges, the smelting process in the top-and-bottom blowing converter is divided into four stages, achieving precise temperature control for each stage. Following the principles of rapid heating, slag formation first, temperature control later, and homogenization, this method achieves efficient smelting of molten steel in the converter and prevents abnormal phenomena. Specifically, the preheating and slag formation stage employs rapid heating to preheat and rapidly form slag within a very short time, providing ample time for dephosphorization. The temperature-controlled dephosphorization stage involves a slow heating rate, extending the dephosphorization time while the low temperature is conducive to the dephosphorization reaction, achieving a dual improvement in dephosphorization efficiency and quality. The slag transformation and phosphorus reversion prevention stage further increases the heating rate for rapid slag transformation, achieving phosphorus fixation in the slag and preventing phosphorus from returning to the molten steel and affecting its quality. Because phosphorus fixation is achieved in the slag during the slag transformation and phosphorus reversion prevention stage, decarburization and furnace protection can be performed in the final stage of smelting to ensure steel quality and avoid furnace burn-out. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A graph showing the relationship between furnace temperature and decarburization rate and dephosphorization distribution ratio provided for this invention;

[0016] Figure 2 The curve relating smelting cycle to furnace temperature provided by this invention;

[0017] Figure 3A graph showing the relationship between slag alkalinity and dephosphorization distribution ratio provided in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0020] First, it's important to clarify that converter steelmaking uses molten iron, scrap steel, and ferroalloys as primary raw materials. Without external energy sources, it relies on the physical heat of the molten iron itself and the chemical reactions between its components to generate heat, thus completing the steelmaking process within the converter. Therefore, the raw material added to the converter during converter steelmaking is the iron to be processed, but once steelmaking operations begin, such as heating and blowing, the liquid inside the furnace becomes molten steel. Because slag formation is required to purify the molten steel during converter smelting, and due to the light weight and low density of the slag, it generally resides on the surface of the molten steel within the converter.

[0021] Converters are classified into several types according to the location where gas is blown into the furnace: top blowing, bottom blowing, and side blowing. Each of the different blowing methods has its own advantages and disadvantages. This invention mainly targets the smelting process of a top-bottom combined blowing converter that combines top blowing and bottom blowing functions.

[0022] Therefore, it can be understood that a top-and-bottom blown converter includes a top lance for top-blown gas, a bottom lance for bottom-blown gas, and the furnace body required for steelmaking. The top lance is located above the furnace body, and its position can be adjusted according to the needs of the smelting process, thereby improving the quality of the steel.

[0023] The position of the lance generally refers to its position, which is the distance between the lance and the surface of the slag inside the furnace. The lower the lance position, the smaller the distance between the lance and the slag and molten steel, and the greater the lance's agitation ability on the molten steel and slag. Conversely, the higher the lance position, the greater the distance between the lance and the slag and molten steel, and the smaller the lance's agitation ability on the molten steel and slag.

[0024] Bottom lances are typically positioned directly at the bottom of the furnace body and their position is not adjustable. The stirring process of the molten steel is generally controlled by adjusting the flow rate of the bottom lances. The number of bottom lances and the angle between each bottom lance and the furnace body vary significantly depending on the design of the top-and-bottom blown converter. In some embodiments of this invention, a common top-and-bottom blown converter with six bottom lances is used as an example to provide a method for smelting steel in a converter.

[0025] In a first aspect, the present invention provides a method for smelting in a top-and-bottom combined blowing converter, comprising adding the iron to be processed into the top-and-bottom combined blowing converter for smelting, and the smelting process including a preheating slag formation period, a temperature control and phosphorus removal period, a slag transformation and phosphorus reversion prevention period, and a decarburization and furnace protection period.

[0026] When the temperature of molten steel exceeds 1550℃, the smelting process changes from the preheating and slag formation period to the temperature-controlled dephosphorization period; when the temperature of molten steel exceeds 1585℃, the smelting process changes from the temperature-controlled dephosphorization period to the slag transformation and phosphorus prevention period; when the temperature of molten steel exceeds 1590℃, the smelting process changes from the slag transformation and phosphorus prevention period to the decarburization and furnace protection period.

[0027] Furthermore, during the temperature-controlled dephosphorization period, the slag mixing is made more uniform and intense through furnace pressure, negative pressure, and flow field control, thereby increasing the dephosphorization rate. The steel heating rate during the preheating and slag-forming period is 12–15℃ / min, the steel heating rate during the temperature-controlled dephosphorization period is 2–4℃ / min, and the steel heating rate during the slag-changing and anti-phosphorus-reversion period and the decarburization and furnace protection period is 10–12℃ / min.

[0028] This invention divides the heating process of molten steel in a converter into four stages. By controlling the heating rate of the molten steel at different temperatures, dephosphorization and decarburization are achieved at different temperature stages. By shortening the preheating and slag-forming period, the temperature-controlled dephosphorization period is extended, ensuring the dephosphorization effect of the molten steel. Simultaneously, dephosphorization is performed on the molten steel at a low temperature, which is beneficial for the dephosphorization reaction. After dephosphorization, the temperature is rapidly increased to form slag, fixing the phosphorus in the slag and preventing phosphorus reversion in the molten steel. Then, decarburization is performed at a higher temperature to protect the furnace, improving the quality of the molten steel at the end of the converter smelting process.

[0029] In an optional embodiment, the iron material to be processed includes molten iron and solid steel material, wherein the solid steel material includes at least one of scrap steel, pig iron, coke, and Fe-C spheres. The molten iron is from ironworks after processing and has a high temperature, while the solid steel material is generally a room-temperature material.

[0030] Currently, the converter steelmaking process does not rely on external energy sources; it generates heat through the physical heat of the molten iron itself and the chemical reactions between its components. Therefore, a relatively high proportion of molten iron needs to be added; for example, in existing technologies, the molten iron content typically accounts for 85-90% of the total mass of the iron to be processed. Since the molten iron itself carries heat and the amount of solid steel added is relatively low, the molten iron can quickly heat the solid steel. However, the increased amount of molten iron leads to increased steelmaking costs. Therefore, reducing steelmaking costs while ensuring a smooth steelmaking process and producing molten steel that meets requirements is another technical problem that urgently needs to be solved in this field. The applicant of this invention proposes the following solution.

[0031] Preferably, the mass of molten iron in the iron material to be treated is ≤75%.

[0032] Preferably, the mass of scrap steel in the iron material to be processed is ≥25%.

[0033] Preferably, the temperature of the molten iron added to the top-and-bottom blown converter is ≥1375°C. The molten iron can be added to the furnace as long as its temperature is ≥1375°C. More preferably, the temperature of the molten iron added to the furnace is 1375–1400°C.

[0034] Preferably, the heat-preserving gas before the molten iron is added to the top and bottom blown converter includes natural gas, hydrogen and air in a volume ratio of 30-50:10-20:40-50%.

[0035] Reducing the quality of molten iron in the iron charge reduces steelmaking costs. However, lower molten iron quality can lead to incomplete melting of solid steel or excessively low temperatures in the molten steel, making it difficult to maintain smelting progress. Therefore, one solution is to increase the inlet temperature of the molten iron when it is added to the top-and-bottom blown converter. For example, this can be achieved by keeping the molten iron warm during transportation. By introducing insulating gas into the molten iron insulation hood used for holding and transporting the molten iron, using a mixture of natural gas, hydrogen, and air in the aforementioned proportions, the inlet temperature can be increased. This reduces the amount of molten iron added, lowers smelting costs, and ensures smelting quality.

[0036] It should be noted that the method of the present invention is applicable to low-cost smelting processes with low iron content, as well as smelting processes with slightly higher iron content, demonstrating wide applicability. The above embodiments merely provide a low-cost smelting solution that does not affect the smelting process and should not be construed as limiting the smelting method of this application.

[0037] In some embodiments, the inventors have determined, through research, the relationship between furnace temperature and dephosphorization distribution ratio, as well as the relationship between furnace temperature and decarburization rate, such as... Figure 1 As shown. By Figure 1 It can be seen that the dephosphorization ratio first increases and then decreases with the increase of furnace temperature, and the dephosphorization effect is best in the range of 1540-1600℃; while the decarburization rate increases with the increase of furnace temperature, but the decarburization rate is relatively slow when the furnace temperature is <1580℃, and the decarburization rate increases rapidly when the furnace temperature is >1580℃.

[0038] Therefore, according to Figure 1 The oxidation reaction rates of C and P in molten steel, and the influence of slag on molten steel under furnace temperature, are represented by a simplified and refined staged temperature control technology, such as... Figure 2As shown, the four-stage simplified and refined staged temperature control technology is as follows: preheating and slag formation period (1420–1550℃), temperature-controlled dephosphorization period (1550–1585℃), slag transformation and phosphorus reversion prevention period (1585–1590℃), and decarburization and furnace protection period (1590–1630℃). Based on the oxidation trends of C and P in the molten steel, the dephosphorization work is mainly concentrated before 1585℃, while rapid decarburization is concentrated above 1585℃. After dephosphorization is completed, an instantaneous slag transformation operation is performed to form a new slag system. Different slag system ratios are used during the slag formation and slag transformation periods to interfere with the dephosphorization distribution ratio of the slag, preventing phosphorus reversion in the molten steel.

[0039] In some embodiments, the present invention provides a top-and-bottom blowing converter smelting method, the operation process of which is as follows:

[0040] S01, Warm-up Period

[0041] In an optional embodiment, a preheating period is included before the slag-forming period. During the preheating period, a mixed gas is used to preheat the solid steel material. The mixed gas includes at least one of hydrogen, oxygen, carbon dioxide, carbon monoxide, natural gas, and nitrogen. Because the amount of molten iron added is small in some embodiments of the invention, the mixed gas can be used to heat the solid steel material during the preheating period to supplement the temperature required for the patented smelting process, ensuring the smooth progress of subsequent smelting processes.

[0042] Preferably, the mixed gas is hydrogen, oxygen, carbon dioxide, carbon monoxide, natural gas, and nitrogen in a volume ratio of 48–52:0.5–1.5:2–5:18–22:18–22:5–10%. When preheating solid steel, the mixed gas is pre-mixed and then directly injected for heating.

[0043] Preferably, the combustion time of the mixed gas is 10-20 minutes. More preferably, it is 15 minutes. Due to the advantages of the above-mentioned mixed gas ratio, the solid steel material can be heated rapidly, and the temperature of the solid steel material can exceed 1100°C within 20 minutes, indicating rapid preheating.

[0044] Preferably, the heating rate of the solid steel material during the preheating period is 60-70℃ / min. After reaching the furnace entry standard, it is put into the furnace together with the molten iron for the next step of processing.

[0045] S02, Preheating and Slag Formation Period

[0046] In an optional embodiment, the heating rate of molten steel during the preheating and slag-forming period is 12–15 °C / min.

[0047] The slag parameters after the preheating and slag-forming period include FeO: 20–25 wt%, MgO: 6–8 wt%, SiO2: 10–13 wt%, and slag basicity: 2.0–3.0. The slag from converter smelting is generally a five-element slag system, including CaO, SiO2, FeO, MgO, and Al2O3. The slag basicity is calculated as the mass ratio of CaO to (SiO2 + Al2O3). Therefore, the remaining percentage values ​​and composition of the slag after the preheating and slag-forming period can also be obtained based on the above-mentioned parameters.

[0048] The purpose of controlling the slag parameters within the above range after the preheating and slag-forming period of smelting is to improve the dephosphorization ratio at the slag-steel interface and achieve rapid dephosphorization.

[0049] Preferably, the molten steel temperature during the preheating and slag-forming period of smelting meets the following condition: 1420℃ < molten steel temperature ≤ 1550℃.

[0050] Preferably, during the smelting process in the preheating and slag-forming stage, oxygen is blown through the top lance at a position of 1.0–1.5 m and a flow rate of 20,000–24,000 Nm³. 3 / min; Argon gas is blown through the bottom gun, with a flow rate of 40-50 Nm³ / min for each bottom gun. 3 / min.

[0051] In an optional embodiment, the smelting process during the preheating and slag-forming period includes adding oxide slag to the top and bottom combined blowing converter, wherein the mass ratio of oxide slag to iron to be treated is 20-30 kg: 1 t, preferably 25 kg: 1 t.

[0052] Oxidized slag can be added from the preheating and slag-forming period. That is, when the temperature of the molten steel exceeds 1420℃, oxidized slag can be added to the molten steel for slag-forming treatment.

[0053] Preferably, the feeding rate of the oxide slag is 450-550 kg / min, and the feeding time is ≤5 min. By adding the oxide slag to the molten steel at a relatively fast speed, combined with the high flow rate of the top lance and rapid stirring at the bottom lance, slag formation can be achieved within 2 minutes, allowing sufficient reaction time for dephosphorization.

[0054] Preferably, the oxidized slag material includes dolomite and / or lime. The main function of the oxidized slag material in this step is to oxidize phosphorus in the molten steel into phosphorus pentoxide and separate it from the molten steel, thereby achieving dephosphorization treatment of the molten steel.

[0055] More preferably, the oxidized slag is a mixture of dolomite and lime in a mass ratio of 2.5–3.5:6.5–7.5. Specifically, the dolomite and lime are added separately when the oxidized slag is added.

[0056] Through long-term research, the inventors discovered that the main reason for the long smelting cycle in current steel converter smelting processes is the slow and delayed addition of slag. Due to this slow and delayed slag addition, the high-flow oxygen supply from the lance in the early stages of smelting results in a thin slag layer, severe oxygen backflow into the furnace, and serious secondary combustion, leading to uneven furnace temperature, localized high temperatures, and intense oxidation reactions. Elements such as Fe, C, Si, and Mn in the molten steel oxidize rapidly, producing large amounts of SiO2 and FeO in the slag. At this point, the total slag volume has not yet reached the required level, the CaO content in the slag is low, the slag formation rate is slow, and the slag fluidity, foaming properties, and phosphorus removal distribution are poor, resulting in a long smelting cycle and over-oxidation of the molten steel. This application addresses this issue by rapidly raising the temperature of the molten steel in the early stages, combined with the rapid addition of oxidizing slag and the purging effect of the top lance, thus preventing over-oxidation of the molten steel. The purging effect of the top lance also accelerates the slag formation time, ensuring that the molten steel does not over-oxidize subsequently while shortening the smelting time and improving smelting efficiency.

[0057] S03, Temperature-controlled phosphorus removal period

[0058] In an optional embodiment, the composition of the molten steel after the temperature-controlled descaling period includes: C ≥ 0.40 wt% and P ≤ 0.025 wt%. The composition of other elements in the molten steel is adjusted according to the requirements of different steel grades. The method provided by this invention can be applied to the converter smelting process of different steel grades, thus only limiting the content of phosphorus and carbon.

[0059] The reason for limiting the phosphorus content in the molten steel at this stage is that dephosphorization is a strongly exothermic reaction, and a lower smelting temperature is beneficial for dephosphorization. Therefore, this invention extends the dephosphorization time by reducing the heating rate during the temperature-controlled dephosphorization period, ensuring complete dephosphorization at a lower steel temperature and avoiding difficulties in dephosphorization during subsequent high-temperature stages. Generally, most steel grades require a phosphorus content of P ≤ 0.025 wt%. Therefore, setting the phosphorus content at the end of this stage within this range eliminates the need to consider phosphorus removal from the molten steel in subsequent operations.

[0060] The carbon content is controlled within the above range at this stage. The gas released by the carbon-oxygen reaction will overflow the slag surface, increasing the foaminess of the slag and facilitating dephosphorization. In addition, it can ensure that the carbon content at the end point is within the specified range.

[0061] Preferably, the molten steel temperature during the temperature-controlled descaling process meets the following criteria: 1550℃ < molten steel temperature ≤ 1585℃.

[0062] Preferably, during the temperature-controlled dephosphorization period of smelting, oxygen is blown through a top lance at a position of 2.2–2.5 m and a flow rate of 14,000–16,000 Nm³. 3 / min; Argon gas is blown through the bottom guns, with bottom guns 1, 3, and 6 having an angle of 4° and a flow rate of 65–75 Nm³. 3 / min; the angle of the No. 2 and No. 4 bottom guns is 2°, and the flow rate is 25~35Nm. 3 / min; the No. 5 bottom gun angle is 8°, and the flow rate is 175~185Nm 3 / min.

[0063] During the temperature-controlled dephosphorization period, the top lance position is raised while the top lance flow rate is reduced to increase the slag surface purging area of ​​the top lance gas, reduce the airflow from penetrating the slag surface and entering the molten steel for oxidation reaction, and reduce the heating rate at this stage. Then, the flow rate of the bottom lance is increased to increase the agitation of the molten steel at the bottom, causing the molten steel to boil, the slag to mix thoroughly, and the slag to rotate clockwise, ensuring a complete dephosphorization reaction and improving dephosphorization efficiency.

[0064] In an optional embodiment, the smelting process during the temperature-controlled dephosphorization period includes adding a cooling agent to the top-and-bottom combined blowing converter. The mass ratio of the cooling agent to the iron to be treated is 10-15 kg:1 t, preferably 10 kg:1 t. The cooling agent can be added when entering the temperature-controlled dephosphorization period, that is, when the temperature of the molten steel exceeds 1550°C.

[0065] Preferably, the cooling agent includes at least one of limestone, solidified pellets, and red ore.

[0066] The inventors discovered that in existing smelting methods, improper temperature control in the early stages of smelting leads to severe secondary combustion in the furnace, resulting in excessively high furnace temperatures and significant burn-off of refractory materials, for example, exceeding 2000℃. This prevents the molten steel from fully absorbing the heat source, and the heat utilization rate is low after the oxidation and exothermic reaction of elements such as C, Si, Mn, and Fe. Furthermore, the low density of scrap steel in existing smelting methods means that both the slag and molten steel are at high temperatures, failing to meet the kinetic and thermodynamic conditions for dephosphorization, making dephosphorization difficult. This invention addresses this issue by controlling the heating rate of the molten steel in the early stages, avoiding excessively high furnace temperatures caused by rapid initial heating, and effectively ensuring the smooth progress of dephosphorization.

[0067] Secondly, by controlling the heating rate during the temperature-controlled dephosphorization period to be low, the temperature of the molten steel is low and rises slowly, providing sufficient time and space for the dephosphorization reaction. In addition, the addition of a cooling agent during the temperature-controlled dephosphorization period to lower the temperature of the molten steel further ensures the smooth progress of the dephosphorization reaction.

[0068] S04, Slag Reversion Prevention and Phosphorus Reversion Period

[0069] In an optional embodiment, the slag parameters after the smelting process during the slag-changing and phosphorus-prevention period include FeO < 15 wt%, MgO: 4–6 wt%, SiO2 < 10 wt%, and slag basicity of 3.0–4.0. Similarly, since the slag produced by converter smelting is all pentagonal slag, the percentage content of the remaining components in the slag can be obtained based on the above parameters.

[0070] Preferably, the molten steel temperature during the smelting process in the slag-prevention and phosphorus-prevention period meets the following requirements: 1585℃ < molten steel temperature ≤ 1590℃.

[0071] Preferably, during the smelting process in the slag-transforming and phosphorus-preventing stage, oxygen is blown through the top lance at a position of 1.8–2.0 m and a flow rate of 18,000–20,000 Nm³. 3 / min; Argon gas is blown through the bottom gun, with a flow rate of 30-40 Nm³ / min for each bottom gun. 3 / min.

[0072] During the slag-changing and phosphorus-prevention period, the top lance position is lowered and the top lance flow rate is increased to stabilize the slag interface. Lime is added for secondary slag conditioning to improve the slag dephosphorization distribution ratio, further reducing the risk of phosphorus reversion. At the same time, the reduced flow rate of the bottom lance also creates negative pressure in the furnace, thereby stabilizing the slag interface and preventing phosphorus reversion.

[0073] Preferably, during the smelting process of preventing phosphorus reversion in the slag-changing stage, lime is added to the top and bottom blowing converter, and the mass ratio of lime to the iron to be treated is 5-8 kg:1 t, preferably 6.5 kg:1 t.

[0074] When the furnace temperature rises above 1585℃, the dephosphorization ratio (P2O5 / P) decreases, and the decarburization rate increases. At this point, the slag surface temperature inside the furnace reaches approximately 2000℃. Utilizing this heat source, adding lime at a ratio of 6.5 kg:1 t through a high-level silo and lowering the top lance position while increasing the top lance flow rate, can instantly accelerate the tumbling and boiling of the steel-slag interface, ensuring full contact and rapid melting of the newly added lime with the slag. By altering the slag basicity, the slag composition is instantly changed within 1 minute without slag discharge, affecting the slag oxidation reaction rate. This achieves rapid dephosphorization not only in the low-temperature zone but also in the high-temperature zone, enabling phosphorus fixation. Reducing iron oxide in the slag lowers iron consumption while increasing the P2O5 saturation in the slag, preventing phosphorus reversion under low-carbon, high-temperature conditions.

[0075] S05, Decarburization Furnace Protection Period

[0076] In an optional implementation, the molten steel temperature during the decarburization and furnace protection period meets the following requirements: 1590℃ < molten steel temperature ≤ 1630℃.

[0077] Preferably, during the decarburization and furnace protection period of smelting, the parameters of the top lance are the same as those during the slag transformation and phosphorus prevention period, and the bottom lance is purged with argon gas. When the molten steel temperature is ≥1600℃, the flow rate of each bottom lance is 115~125Nm. 3 / min.

[0078] By increasing the flow rate of the bottom lance and performing strong stirring with inert gas, the composition of the molten steel is homogenized, residual oxygen is eliminated, and the hydrogen content in the molten steel is reduced. This allows for the actual carbon content of medium and high carbon steel to be greater than 0.15%, and the hydrogen content to be controlled within 5 ppm, resulting in a high degree of molten steel cleanliness.

[0079] Preferably, 1-2 minutes before tapping, carbon powder is added to the top and bottom combined blowing converter to reduce FeO in the slag. The mass ratio of carbon powder to the iron material to be treated is 0.2-0.6 kg:1 t, preferably 0.4 kg:1 t.

[0080] The inventors discovered that in current smelting processes, the carbon content of molten steel is low at the end of converter smelting, generally C < 0.15%, while the FeO content in the slag is high and at a high temperature. During the process from stopping the lance to tapping, the furnace tilting angle is relatively large due to the characteristics of the tooling, which causes a sudden increase in the kinetic conditions of the molten steel in the furnace during the tilting process. This easily leads to secondary oxidation of C in the molten steel, increasing the probability of phosphorus reversion in the slag.

[0081] Furthermore, existing smelting methods suffer from poor overall carbon retention during the smelting process, and the carbon-oxygen reaction capacity of high-temperature molten steel weakens and the dehydrogenation capacity slows down at the end of the smelting process. In addition, the bottom blowing system uses natural gas cooling to prevent local high temperatures at the furnace bottom; however, when natural gas is blown into molten steel and encounters high temperatures (>1580℃), it will rapidly decompose into C and H, inevitably causing an increase in the H content of the molten steel and affecting the cleanliness of the tapped steel.

[0082] The inventors achieved strong stirring of molten steel by adjusting the bottom-blowing gas to argon and increasing the bottom-blowing flow rate, thus maintaining a large heating rate in the SO4 step and shortening the high-temperature time of molten steel during the smelting process. This resulted in molten steel with strong carbon retention and good dehydrogenation capabilities, without causing an additional increase in the hydrogen content of the molten steel, ensuring the quality of the tapped steel.

[0083] The inventors have determined the relationship between slag basicity and FeO content in the slag, as well as the relationship between slag basicity and dephosphorization distribution ratio. Figure 3 As shown in the figure. The dephosphorization distribution ratio (P2O5 / P) refers to the ratio between P2O5 in the slag and P in the molten steel. It characterizes the dephosphorization rate of the molten steel. The larger the dephosphorization distribution ratio, the easier it is for phosphorus to be removed from the molten steel; the smaller the dephosphorization distribution ratio, the more difficult it is for phosphorus to be removed from the molten steel.

[0084] Depend on Figure 3 It can be seen that the relationship between the dephosphorization distribution ratio and slag basicity shows a trend of first increasing and then decreasing with the increase of slag basicity. Within the range of slag basicity of 2 to 5, the dephosphorization distribution ratio is relatively high, and the dephosphorization effect of the molten steel is good. The FeO content in the slag increases with the increase of slag basicity. Therefore, the FeO content in the slag and the dephosphorization effect can be adjusted by controlling the slag basicity to obtain molten steel with low FeO content and good dephosphorization effect in the final slag after smelting.

[0085] For example, when FeO in the slag is 20wt% and the slag basicity is 2-3, the dephosphorization ratio is 150-200. As smelting progresses, the FeO content in the slag will continue to rise. At the end of smelting, when FeO in the slag is 25wt% and the slag basicity is 3-4, the dephosphorization ratio is >200.

[0086] Secondly, the present invention provides an application of the method as described in any of the foregoing embodiments in iron and steel smelting.

[0087] Example 1

[0088] This embodiment provides a method for smelting in a top-and-bottom combined blowing converter, which includes adding the iron to be processed into the top-and-bottom combined blowing converter for smelting. The smelting process includes a preheating period, a preheating slag formation period, a temperature-controlled phosphorus removal period, a slag transformation and phosphorus reversion prevention period, and a decarburization and furnace protection period.

[0089] In this embodiment, the iron charge to be treated is prepared according to the heat distribution standards of molten steel temperature ≥1620℃, C ≥0.12%, and P ≤0.012%. The iron charge to be treated consists of 110t molten iron, 2.5t coke, 13t iron-carbon balls, and 25t scrap steel, with a cold charge ratio of 26.6% and an iron-to-material ratio of 73.3%. The molten iron comes from the ironworks after processing, and its temperature when added to the top and bottom blown converter is 1383℃. The solid steel is generally a room-temperature material, with a temperature of 20-30℃.

[0090] To ensure that the temperature of molten iron added to the top and bottom combined blowing converter is ≥1375℃, the heat preservation gas before the molten iron is added to the top and bottom combined blowing converter is natural gas, hydrogen and air in a volume ratio of 50:10:40%.

[0091] Specifically, the smelting process provided in this embodiment is as follows:

[0092] S01, Warm-up Period

[0093] During the preheating period, a mixed gas combustion process is used to preheat the solid steel. The mixed gas consists of hydrogen, oxygen, carbon dioxide, carbon monoxide, natural gas, and nitrogen in a volume ratio of 50:1:3:20:19:7%. This mixed gas is pre-mixed and then directly injected for heating. After 15 minutes of combustion, the temperature of the solid steel reaches 1117℃, at which point heating is stopped. After the steel is fed into the furnace, the top and bottom lances of the top-and-bottom blowing converter are used to heat the molten steel.

[0094] During the preheating period, oxygen is purged through the top lance at a position of 1.2m and a flow rate of 21000 Nm³. 3 / min; Argon gas is blown through the bottom nozzles, with a flow rate of 45 Nm³ / min for all six nozzles. 3The steel heating rate is 13℃ / min, rapidly raising the steel temperature to around 1420℃ in preparation for the next step of processing.

[0095] S02, Preheating and Slag Formation Period

[0096] When the molten steel temperature exceeds 1420℃, keep the heating rate of the top lance, bottom lance, and molten steel constant, and add oxide slag to the top and bottom combined blowing converter. The mass ratio of oxide slag to the iron to be treated is 25kg:1t. The oxide slag consists of dolomite and lime in a mass ratio of 3:7. When adding the oxide slag, the dolomite and lime are added separately.

[0097] The oxidized slag material is fed at a rate of 500 kg / min over a time of 4 min. Slag is rapidly formed within 2 min after feeding to allow sufficient reaction time for dephosphorization. When the molten steel is rapidly heated to around 1550℃, a slag sample is taken. The slag contains 22 wt% FeO, 6.5 wt% MgO, 12.7 wt% SiO2, and has a basicity of 2.6. The next step can then be carried out.

[0098] S03, Temperature-controlled phosphorus removal period

[0099] When the molten steel temperature exceeds 1550℃, oxygen is blown through the top lance at a position of 2.3m and a flow rate of 14000 Nm³. 3 / min; Argon gas is blown through the bottom guns, with the flow rate of bottom guns 1, 3, and 6 at an angle of 4° being 70 Nm³ / min. 3 / min, the flow rate of bottom guns No. 2 and No. 4 at an angle of 2° is 30Nm 3 / min, the flow rate of the No. 5 bottom gun at an angle of 8° is 180 Nm 3 The heating rate of molten steel is 3℃ / min.

[0100] While adjusting the top and bottom lances, add 6 kg of limestone and 4 kg of solid cooling pellets to the top and bottom combined blowing converter. When the molten steel slowly heats up to around 1585℃, take a steel sample. The molten steel has C = 0.65 wt% and P = 0.0216 wt%, which indicates that the next step can be carried out.

[0101] The phosphorus content in the molten steel sampled before the temperature-controlled dephosphorization period was 0.096%, and the dephosphorization rate during the temperature-controlled dephosphorization period was 77.4%.

[0102] S04, Slag Reversion Prevention and Phosphorus Reversion Period

[0103] When the molten steel temperature exceeds 1585℃, oxygen is blown through the top lance at a position of 2.0m and a flow rate of 20000 Nm³. 3 / min; Argon gas is blown through the bottom nozzles, with a flow rate of 35 Nm³ / min for each nozzle. 3The steel heating rate is 11.5℃ / min.

[0104] While adjusting the top and bottom lances, lime is added to the top and bottom blowing converter at a mass ratio of 6.5 kg to 1 t of iron to be treated. When the molten steel rapidly heats up to around 1590°C, a slag sample is taken. The slag contains 26 wt% FeO, 6 wt% MgO, 9.3 wt% SiO2, and has a basicity of 3.6. The next step can then be performed.

[0105] S05, Decarburization Furnace Protection Period

[0106] Maintain the top lance parameters and molten steel heating rate consistent with step S04 during smelting. When the molten steel temperature reaches ≥1600℃, adjust the flow rate of each bottom lance to 120 Nm³. 3 The process continues at a rate of / min, with argon gas being continuously blown in, and smelting is carried out under strong stirring with a large argon gas flow rate at the bottom gun.

[0107] One minute before tapping, carbon powder was added to the top and bottom blowing converter to reduce FeO in the slag. The mass ratio of carbon powder to the iron to be treated was 0.4 kg: 1 t. After the carbon powder and molten steel were mixed evenly, a slag sample was taken when the molten steel reached a temperature of approximately 1630℃. The molten steel contained 0.21% C, 0.018% P, and 4.3 ppm H; the slag contained 13.7% FeO. The molten steel had a high degree of cleanliness and was ready for tapping, thus completing the smelting process.

[0108] Using the method of this embodiment, and following the same heat distribution standard as this embodiment, the possible batching methods for the iron material to be processed are shown in Table 1.

[0109] Table 1. Batching list of iron materials to be processed

[0110]

[0111]

[0112] As shown in Table 1, this embodiment can be applied to a wider range of batching methods, and the above-described processes in this embodiment can achieve good refining results to decarburize and descale the molten steel. Furthermore, the method in this embodiment can employ both lower-cost smelting methods (e.g., 100t of molten iron with a lower content) and methods with a molten iron content of 130t, making it widely applicable.

[0113] Comparative Example 1

[0114] This comparative example provides a method for top-and-bottom combined blowing converter smelting, the specific steps of which are as follows:

[0115] S01. The iron to be treated is added to the top and bottom combined blowing converter within 0 to 5 minutes for smelting. The iron to be treated is matched according to the same heat matching standard as in Example 1, and the batching table shown in Table 2 is obtained.

[0116] Table 2. Batching list of iron materials to be processed

[0117] Iron volume / t 130 125 120 scrap steel / t 20 25 30 Total load / t 150 150 150

[0118] S02. After the iron material to be processed is completely added to the top and bottom combined blowing converter, the furnace body is leveled. Within 5 minutes, 27 kg / t of lime, 6 kg / t of dolomite, and 10 kg / t of limestone are added as slag-forming materials, and 16 kg / t of cooling materials, solid cooling pellets and 8 kg / t of hematite are added.

[0119] S03. Simultaneously with the addition of slag, the top and bottom lances of the top-and-bottom combined blowing converter begin purging. Oxygen is purged through the bottom lances throughout the smelting process, with a flow rate of 35 Nm³. 3 / min. Oxygen is blown through the top lance at a position of 2m. After the slag-forming and cooling materials are added, the top lance is lowered to 1.6m, and the top lance flow rate is maintained at 18000–20000 Nm³. 3 / min, the slag formation time is 5-8 minutes after the top lance is started blowing.

[0120] S04. After slag formation, raise the lance to 2.2m and reduce the lance flow rate by 16000-18000 Nm. 3 Continue blowing at a speed of 5-8 minutes to dephosphorize the steel. During the dephosphorization period, add 500-1000 kg of solid-cooled pellets. At the end of the dephosphorization period, lower the lance to 1.5 m and deep blow out the steel.

[0121] As shown in Tables 1 and 2, the scheme in this comparative example cannot effectively control the time of dephosphorization and decarburization, which reduces the number of raw material combinations and proportions that can be selected for the iron material to be treated. If coke, iron-carbon balls and pig iron are added to the raw material combination of the iron material to be treated, it will lead to severe over-oxidation of the molten steel.

[0122] Experimental Example 1

[0123] The smelting was carried out according to the methods of Example 1 and Comparative Example 1, and the smelting results are shown in Table 3:

[0124] Table 3 Smelting Effects

[0125]

[0126]

[0127] Table 3 shows that the maximum scrap ratio represents the ratio of the maximum amount of solid steel that can be added to the total amount of the iron material to be treated, applicable to this method. In Example 1, the maximum scrap ratio is higher than in Comparative Example 1, reducing smelting costs from the perspective of raw material costs. The steel material ratio represents the total amount of steel required to produce one ton of molten steel; therefore, a lower steel material ratio indicates a smaller total amount of steel required to produce one ton of molten steel, reducing smelting costs from the perspective of raw material addition. Simultaneously, reduced oxygen and slag consumption further lower smelting costs. The reduced FeO content in the final slag after top-and-bottom blowing furnace smelting improves the smelting effect of the added iron material to be treated, further reducing smelting costs. Furthermore, the method of this embodiment produces steel with higher C content and lower P content, achieving better dephosphorization while retaining a certain amount of carbon to prevent excessively low carbon content and increased difficulty in subsequent processing. The method of this embodiment also significantly reduces the H content of the molten steel, improving the cleanliness of the steel.

[0128] Experimental Example 2

[0129] Based on the method of Example 1, the volume ratio of the mixed gas in step S01 was changed to preheat the solid steel. The formula of the iron to be treated was: 115t molten iron, 10t pig iron, 2t coke, 1t iron-carbon balls, and 22t scrap steel, with an iron ratio of 77%. The volume ratio of the mixed gas in step S01 is shown in Table 4, and the smelting effects obtained are compared in Table 5.

[0130] Table 4. Volume ratio of mixed gas

[0131]

[0132] Table 5. Smelting effects of different mixed gas ratios

[0133]

[0134] As shown in Tables 4 and 5, the method of using mixed gas to preheat solid steel is beneficial to increasing the temperature of the steel material entering the furnace and reducing the heat source utilization rate. Furthermore, it results in lower smelting costs and better quality molten steel. By controlling the proportions of various gases in the mixed gas, a better preheating effect can be achieved while simultaneously reducing smelting costs and improving steel quality.

[0135] Experimental Example 3

[0136] Based on the method of Example 1, the flow rate of the bottom gun in step S03 was changed as shown in Table 6, and smelting was carried out according to the method of Example 1. The smelting effect comparison is shown in Table 7.

[0137] Table 6 Bottom gun flow rate during temperature-controlled dephosphorization period

[0138]

[0139] Table 7. Smelting effect of changing the bottom lance flow rate during temperature-controlled dephosphorization period.

[0140]

[0141] As shown in Tables 6 and 7, the smelting method provided by the present invention can achieve better dephosphorization effect in the same time by controlling the bottom lance flow rate during the temperature-controlled dephosphorization period, ensuring the removal of phosphorus elements in the molten steel. Furthermore, the bottom lance flow rate during the temperature-controlled dephosphorization period provided by the present invention can also save costs, achieving better molten steel smelting effect with lower steel content. The molten steel has a low phosphorus content and a high carbon content, avoiding the situation where the carbon content is too low in order to achieve descaling.

[0142] Test Example 4

[0143] Based on the method of Example 1, the amount of lime added in step S04 and the amount of carbon powder added in step S05 were changed, and smelting was carried out according to the method of Example 1. The smelting effect comparison is shown in Table 8.

[0144] Table 8. Smelting Effects of Changing Lime and Carbon Powder Addition Amounts

[0145]

[0146] As shown in Table 8, the smelting method provided by the present invention controls the amount of lime and carbon powder added during the slag transformation and phosphorus reversion period and the decarburization and furnace protection period. Before adding lime at the beginning of step S04, the FeO content of the slag is high and the slag basicity is low. During the process from step S04 to step S05, after adding lime and carbon powder, the slag rapidly transforms into slag, the FeO content decreases, and the slag basicity increases. Moreover, the phosphorus content in the molten steel by the method in Example 1 (Table 8 4-1) is reduced by 4.33%, effectively avoiding phosphorus reversion in the molten steel and eliminating the need to extend the smelting time.

[0147] Experimental Example 5

[0148] Based on the method of Example 1, the flow rate of the bottom gun in step S05 was changed, and smelting was carried out according to the method of Example 1. The smelting effect comparison is shown in Table 9.

[0149] Table 9. Smelting Effects of Changes in Bottom Gun Flow Rate During Decarburization and Furnace Protection

[0150]

[0151] As shown in Table 9, the smelting method provided by the present invention can effectively remove H and O from molten steel by adjusting the bottom lance flow rate during the decarburization and furnace protection period in step S05, thereby improving the cleanliness of molten steel and ensuring the quality of tapped steel.

[0152] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for smelting in a top-and-bottom blown converter, characterized in that, The process includes adding the iron to be processed into a top and bottom blowing converter for smelting, and the smelting process includes a preheating slag formation period, a temperature control dephosphorization period, a slag transformation and phosphorus prevention period, and a decarburization and furnace protection period. When the temperature of molten steel exceeds 1550℃, the smelting process changes from the preheating and slag-forming period to the temperature-controlled dephosphorization period; when the temperature of molten steel exceeds 1585℃, the smelting process changes from the temperature-controlled dephosphorization period to the slag-changing and phosphorus-prevention period; when the temperature of molten steel exceeds 1590℃, the smelting process changes from the slag-changing and phosphorus-prevention period to the decarburization and furnace protection period. The heating rate of molten steel during the preheating and slag-forming period is 12~15℃ / min, the heating rate of molten steel during the temperature-controlled descaling period is 2~4℃ / min, and the heating rate of molten steel during the slag-changing and phosphorus-preventing period and the decarburization and furnace protection period is 10~12℃ / min. During the preheating and slag-forming stage of the smelting process, oxygen is blown through a top lance at a position of 1.0~1.5m and a flow rate of 20000~24000 Nm³. 3 / min; Argon gas is blown through the bottom gun, with a flow rate of 40~50 Nm for each bottom gun. 3 / min; During the temperature-controlled dephosphorization period of smelting, oxygen is blown through a top lance at a position of 2.2-2.5m and a flow rate of 14,000-16,000 Nm³. 3 / min; Argon gas is blown through the bottom guns, with bottom guns 1, 3, and 6 having an angle of 4° and a flow rate of 65~75 Nm. 3 / min; the angle of the No. 2 and No. 4 bottom guns is 2°, and the flow rate is 25~35 Nm. 3 / min; No. 5 bottom gun angle is 8°, flow rate is 175~185 Nm 3 / min; During the smelting process of preventing phosphorus reversion in the slag-changing stage, oxygen is blown through the top lance at a position of 1.8~2.0m and a flow rate of 18000~20000 Nm³. 3 / min; Argon gas is blown through the bottom nozzles, with a flow rate of 30~40 Nm for each nozzle. 3 / min; the smelting process during the slag-changing and phosphorus-preventing period includes adding lime or limestone into the top and bottom combined blowing converter; the mass ratio of the lime or limestone to the iron material to be treated is 5~8kg:1t; During the decarburization and furnace protection period, the parameters of the top lance are the same as those during the slag transformation and phosphorus prevention period. Argon gas is blown into the bottom lance, and when the molten steel temperature is ≥1600℃, the flow rate of each bottom lance is 115~125 Nm³. 3 / min.

2. The method according to claim 1, characterized in that, The slag parameters after the preheating and slag-forming period and smelting are as follows: FeO: 20~25wt%, MgO: 6~8wt%, SiO2: 10~13wt%, and slag basicity: 2.0~3.

0.

3. The method according to claim 1, characterized in that, During the preheating and slag-forming period of smelting, the molten steel temperature must meet the following requirements: 1420℃ < molten steel temperature ≤ 1550℃.

4. The method according to claim 2 or 3, characterized in that, The smelting process during the preheating and slag-forming period includes adding oxide slag to the top and bottom combined blowing converter, wherein the mass ratio of the oxide slag to the iron to be treated is 20~30kg:1t.

5. The method according to claim 4, characterized in that, The feeding rate of the oxidized slag is 450~550 kg / min, and the feeding time is ≤5 min.

6. The method according to claim 4, characterized in that, The oxidized slag material includes dolomite and / or lime.

7. The method according to claim 4, characterized in that, The oxidation slag material is dolomite and lime in a mass ratio of 2.5~3.5:6.5~7.

5.

8. The method according to claim 1, characterized in that, The composition of the molten steel after the temperature-controlled descaling period includes: C ≥ 0.40 wt% and P ≤ 0.025 wt%.

9. The method according to claim 1, characterized in that, During the controlled temperature dephosphorization period, the molten steel temperature must meet the following requirements: 1550℃ < molten steel temperature ≤ 1585℃.

10. The method according to claim 8 or 9, characterized in that, During the smelting process of the temperature-controlled dephosphorization period, a cooling agent is added to the top and bottom combined blowing converter, and the mass ratio of the cooling agent to the iron material to be treated is 10~15kg:1t.

11. The method according to claim 10, characterized in that, The cooling agent includes at least one of limestone, solidified pellets, and red ore.

12. The method according to claim 1, characterized in that, The slag parameters after the completion of the smelting process during the slag-changing and phosphorus-preventing period include FeO < 15 wt%, MgO: 4~6 wt%, SiO2 < 10 wt%, and slag basicity 3.0~4.

0.

13. The method according to claim 1, characterized in that, During the smelting process of preventing phosphorus reversion in the slag-changing stage, the molten steel temperature must meet the following requirements: 1585℃ < molten steel temperature ≤ 1590℃.

14. The method according to claim 12 or 13, characterized in that, During the decarburization and furnace protection period, the molten steel temperature must meet the following requirements: 1590℃ < molten steel temperature ≤ 1630℃.

15. The method according to claim 12 or 13, characterized in that, Carbon powder or Fe-C balls are added to the top and bottom blown converter 1-2 minutes before tapping. The mass ratio of the carbon powder or Fe-C balls to the iron material to be treated is 0.2-0.6 kg: 1 t.

16. The method according to claim 1, characterized in that, The iron material to be processed includes molten iron and solid steel material, wherein the solid steel material includes at least one of scrap steel, pig iron, coke and Fe-C spheres.

17. The method according to claim 16, characterized in that, The mass of molten iron in the iron material to be processed is ≤75%; The mass of scrap steel in the iron material to be processed is ≥25%.

18. The method according to claim 16, characterized in that, The temperature of the molten iron added to the top and bottom blown converter is ≥1375℃.

19. The method according to claim 16, characterized in that, The heat-preserving gas before the molten iron is added to the top and bottom combined blowing converter includes natural gas, hydrogen and air in a volume ratio of 30~50:10~20:40~50%.

20. The method according to claim 1, characterized in that, The preheating slag-forming period is preceded by a preheating period, in which a mixed gas is used to preheat the solid steel material. The mixed gas includes at least one of hydrogen, oxygen, carbon dioxide, carbon monoxide, natural gas, and nitrogen.

21. The method according to claim 20, characterized in that, The mixed gas consists of hydrogen, oxygen, carbon dioxide, carbon monoxide, natural gas, and nitrogen in a volume ratio of 48~52:0.5~1.5:2~5:18~22:18~22:5~10%.

22. The method according to claim 20, characterized in that, The combustion time of the mixed gas is 10-20 minutes.

23. The application of the method as described in any one of claims 1 to 22 in iron and steel smelting.

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