Method for smelting ultra-low manganese industrial pure iron from high manganese iron melt

Abstract

This invention discloses a method for smelting ultra-low manganese industrial pure iron from high-manganese molten iron, belonging to the field of iron and steel metallurgy technology. The method includes the following steps: pre-treatment of molten iron with Mn ≤ 0.8% by desulfurization; smelting in a converter to semi-steel (C ≤ 0.06%, Mn ≤ 0.25%); adding the semi-steel to an electric furnace, adding direct reduced iron (DRI) in batches with a weight similar to the semi-steel, melting it by oxygen blowing / electric power supply, utilizing the manganese-free nature of DRI to dilute the molten steel, and using its endothermic melting to create a low-temperature environment of 1540-1550℃, under which efficient oxidation and demanganese removal are achieved, reducing Mn to ≤ 0.02%; finally, deep decarburization, deoxidation, and desulfurization are achieved through VOD vacuum refining. This invention increases the upper limit of manganese content in molten iron for smelting ultra-low manganese industrial pure iron from 0.5% to over 0.8%. Through an innovative synergistic mechanism of "dilution + low-temperature oxidation," it successfully solves the problem of deep demanganese removal from high-manganese molten iron, resulting in a stable process that can produce high-quality industrial pure iron with Mn ≤ 0.02%.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a method for smelting industrial pure iron, and particularly to a method for smelting industrial pure iron with extremely low manganese content (≤0.02%) from molten iron with a high manganese content. Background Technology

[0002] Industrial pure iron is an important soft magnetic material, requiring extremely high purity, especially with strict limits on elements that impair magnetic properties, such as manganese, carbon, sulfur, and phosphorus. Typically, the manganese content must be controlled below 0.03%, or even lower (e.g., below 0.02%). Traditional industrial pure iron smelting processes mainly employ a "converter primary refining → LF furnace refining → RH vacuum treatment" flow. However, the demanganese removal capacity of the converter and subsequent conventional refining processes is limited, and its efficiency is greatly affected by factors such as slag basicity, temperature, and slag formation, resulting in insufficient stability. This leads to stringent requirements on the manganese content of the molten iron entering the furnace in traditional processes, typically needing to be controlled below 0.5%, severely limiting the range of raw material selection and increasing production costs.

[0003] For molten iron with a manganese content higher than 0.5%, it is almost impossible to produce qualified ultra-low manganese industrial pure iron economically and stably using traditional processes. Therefore, developing an industrial pure iron smelting method that can relax the requirements for manganese content in molten iron and efficiently and stably remove manganese has significant practical and economic value. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art in smelting ultra-low manganese industrial pure iron, which has strict requirements on the manganese content of molten iron (≤0.5%), and is difficult and unstable in demanganese removal. The present invention provides a smelting method that can efficiently and stably smelt ultra-low manganese industrial pure iron with a manganese content of ≤0.8% using molten iron with a manganese content of ≤0.02%.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for smelting ultra-low manganese industrial pure iron from high-manganese molten iron includes the following steps: (1) Pretreatment of molten iron: Desulfurization pretreatment is carried out on molten iron with a manganese content of not more than 0.8%; (2) Converter smelting: The pretreated molten iron is added to the converter and oxygen is blown to remove silicon, manganese, carbon, phosphorus and sulfur. When the carbon content in the molten steel is reduced to ≤0.06% and the manganese content is reduced to ≤0.25%, the steel is tapped to obtain semi-steel. (3) Electric furnace dilution and demanganese removal: The semi-steel is added into the electric furnace, and direct reduced iron is added to the electric furnace in batches. Oxygen blowing and power supply are carried out to dilute the manganese content in the molten steel by using direct reduced iron to melt and dilute the manganese content in the molten steel. The heat absorption of direct reduced iron melting and oxygen blowing oxidation are used to create low temperature demanganese removal conditions to reduce the manganese content in the molten steel to below 0.02%. (4) Vacuum refining: The molten steel processed in step (3) is vacuum refined to complete decarburization, deoxidation and deep desulfurization, and molten steel with composition that meets the standard of ultra-low manganese industrial pure iron.

[0006] Further, the composition of the molten iron in step (1) by mass percentage is: C≥4.0%, Mn≤0.8%, Si:0.30-0.60%, P≤0.120%, S≤0.05%; the sulfur content in the molten iron after pretreatment is ≤0.03%.

[0007] Furthermore, in step (3), the amount of direct reduced iron added is controlled to be between 0.8:1 and 1.2:1, representing the ratio of the weight of the molten steel produced after complete melting to the weight of the semi-steel added to the electric furnace. This ratio allows the semi-steel with an initial manganese content of approximately 0.2% to be diluted to an average manganese content of approximately 0.1%, significantly reducing the subsequent demanganese load.

[0008] Furthermore, in step (3), after adding direct reduced iron and melting it, the temperature of the molten steel is controlled at 1540-1550℃; after oxygen blowing for demanganese removal, the demanganese slag is dumped. The lower molten steel temperature (relative to the conventional steelmaking temperature) provides more favorable thermodynamic conditions for demanganese removal (low temperature is conducive to the oxidative demanganese removal reaction).

[0009] Furthermore, in step (3), after the demanganese slag is poured out, slag-forming agents (such as lime and fluorite) are added to the electric furnace and oxygen is blown in. Under the condition of alkalinity of 3-5, dephosphorization operation is carried out to reduce the phosphorus content in the molten steel to below 0.003%.

[0010] Further, in step (3), after dephosphorization, the temperature of the molten steel is raised to 1620-1640℃ and then tapped into the ladle; the carbon content in the molten steel at the time of tapping is ≤0.03% and the manganese content is ≤0.02%.

[0011] Further, the vacuum refining in step (4) is carried out in a VOD furnace, specifically including: decarburizing using oxygen dissolved in molten steel under vacuum conditions to reduce the carbon content to ≤0.003%; then adding aluminum particles for deoxidation, and adding lime and fluorite for slag formation, and carrying out deep desulfurization through strong stirring to reduce the sulfur content to ≤0.003%.

[0012] Furthermore, the amount of lime added is 0.8-1.2 tons per furnace, and the amount of fluorite added is 8%-15% of the amount of lime added.

[0013] Furthermore, the ultra-low manganese industrial pure iron standard requires that the manganese content in the molten steel be ≤0.02%.

[0014] The beneficial effects of this invention are as follows: 1. Expanding the range of applicable raw materials: The upper limit of manganese content in molten iron suitable for smelting ultra-low manganese industrial pure iron has been significantly increased from the traditional 0.5% to over 0.8%, reducing the dependence on scarce low-manganese molten iron resources, making raw material selection more flexible and cost-effective.

[0015] 2. Innovative Demandation Mechanism: Direct reduced iron (DRI) was creatively introduced into the electric furnace process, achieving synergistic demandation through "physical dilution" and "low-temperature oxidation." DRI itself contains almost no manganese, and its melting effectively dilutes the manganese content of molten steel. Simultaneously, its melting process absorbs a large amount of heat, which, combined with oxygen blowing, maintains the molten steel in a relatively low temperature range of 1540-1550℃, providing excellent thermodynamic conditions for the oxidative demandation reaction, resulting in high and stable demandation efficiency.

[0016] 3. A rational process route has been established: an optimized flow has been formed, consisting of "molten iron pretreatment (desulfurization) → converter (desiliconization, manganese removal, carbonization, and phosphorus removal) → electric furnace (dilution and deep demanganese and phosphorus removal) → VOD (deep decarburization, deoxidation, and desulfurization)". Each process has a clear division of labor: the converter undertakes the main oxidation task, the electric furnace focuses on solving the core deep demanganese removal problem using unique conditions, and VOD completes the final purity control. The process is smooth and highly operable.

[0017] 4. Excellent product quality: This method can stably produce high-quality ultra-low manganese industrial pure iron with a manganese content ≤0.02% and extremely low carbon, sulfur and phosphorus content (e.g., C≤0.003%, S≤0.003%, P≤0.003%), which fully meets the requirements for high-end magnetic materials. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto. Example

[0019] Using a 100-ton electric arc furnace, a 50-ton converter, and a VOD refining furnace as the main equipment in a steel plant, this invention's method is employed to smelt ultra-low manganese industrial pure iron. The specific smelting steps are as follows: (1) Hot metal pretreatment: Hot metal supplied by the blast furnace was used. Its composition is shown in Table 1. The manganese content was 0.782% and 0.811%, respectively, both higher than the 0.5% limit of the traditional process. The hot metal was poured into a hot metal ladle for desulfurization pretreatment. After desulfurization, the sulfur content of the hot metal was reduced to 0.028% and 0.025% (as shown in Table 2), meeting the requirement of S≤0.03%, and the temperature decreased slightly.

[0020] (2) Converter smelting: The pretreated molten iron is added to a 50-ton converter. Before adding, 10-14 tons of clean scrap steel are added to the converter as a coolant. The amount of molten iron added is 42-46 tons. After smelting begins, oxygen is blown in at a flow rate of 10,000-12,000 Nm³ / h. While blowing oxygen, lime (approximately 2100 kg in total) and a small amount of fluorite (approximately 150-180 kg in total) are added in 3-4 batches to form slag, and approximately 700 kg of iron ore is added as needed to cool and dephosphorize. Silicon, manganese, carbon, phosphorus, and other elements are removed by blowing oxygen. During the smelting process, the composition of the molten steel is monitored through online monitoring or sampling analysis. When the carbon content in the molten steel drops to 0.055%-0.060%, the manganese content drops to 0.18%-0.21%, and the phosphorus content drops to 0.019%-0.022% (as shown in Table 3), oxygen blowing is stopped, the grate is tilted, and the molten steel (at this time, it is called "semi-steel") is poured into the ladle at a temperature of 1630-1641℃.

[0021] (3) Electric furnace dilution and deep demanganese and dephosphorization: a. Steel addition and charging: The ladle containing the semi-steel is hoisted to the 100-ton electric furnace, and about 51 tons of the semi-steel is added to the electric furnace. After steel addition, the electric furnace electrodes are started and power is supplied to raise the temperature. At the same time, direct reduced iron (DRI) is continuously added. The specific operation is as follows: the DRI is weighed through the high-level silo and lowered into the temporary storage silo through the feed pipe. The feed is then fed into the furnace from the temporary storage silo in a jogging manner. The feed rate and the weighing rate of the high-level silo are adjusted according to the melting rate of the DRI in the furnace. The total amount added is controlled at 60-61 tons (as shown in Table 4), so that the amount of molten steel produced after melting is close to the weight of the added semi-steel (the ratio is about 1:1). b. Oxygen blowing and demanganese: During and after the addition of DRI, oxygen blowing is carried out simultaneously. The oxygen flow rate is 2000-4000 Nm³ / h, and the total oxygen blowing amount is 200-230 Nm³. Oxygen blowing promotes rapid melting of DRI (Diluted Refined Iron) and provides an oxidant to oxidize manganese in the molten steel into the slag. Due to the significant heat absorption during DRI melting, the steel temperature is effectively controlled within the lower range of 1540-1550℃, creating excellent thermodynamic conditions for the oxidative demanganese reaction (MnO formation) (low temperature favors the reaction). Under this synergistic effect of "dilution + low-temperature oxidation," the manganese content in the molten steel is rapidly reduced. c. Slag removal and dephosphorization: When the DRI melts completely and a sample confirms that the manganese content in the molten steel has dropped below 0.02%, the electric furnace is tilted, and the demanganese slag is removed. Then, new slag-forming agents are added to the furnace, mainly lime (1950-2500 kg) and a small amount of fluorite (190-220 kg), controlling the slag basicity at 3-5. Power is continued and oxygen is blown; under high basicity and continuous oxidation conditions, phosphorus is deeply removed. Sampling analysis confirmed that the phosphorus content could be reduced to 0.001-0.0020% (as shown in Table 5), and the manganese content was further reduced to 0.015%-0.018%. d. Heating and tapping: After dephosphorization, power was continued to raise the temperature of the molten steel to 1620-1640℃. At this point, the carbon content of the molten steel was 0.020%-0.030%, and the manganese content was ≤0.02%, meeting the tapping requirements. The final molten steel was tapped into the refining ladle.

[0022] (4) VOD Vacuum Refining: The ladle after tapping from the electric arc furnace is hoisted to the VOD furnace. a. Vacuum Decarburization: The ladle is placed in a vacuum tank and evacuated to a pressure below 100 Pa. Utilizing the original dissolved oxygen in the molten steel (approximately 0.08%), a decarburization reaction is carried out under bottom blowing and vacuum conditions. By controlling the vacuum level and time, the carbon content of the molten steel is reduced to 0.0020%-0.0023% (as shown in Table 6). b. Deoxidation and Slag Forming Desulfurization: After decarburization, based on the oxygen content analysis results of the molten steel, an appropriate amount of aluminum particles is calculated and added for precipitation deoxidation. Then, approximately 1 ton of lime and 0.1 ton of fluorite (approximately 10%) are added for slag formation. Strong stirring is performed for 5-8 minutes to fully remove sulfur and inclusions. Finally, the sulfur content can be reduced to 0.001% (as shown in Table 6). c. Composition Adjustment and Casting: After refining, samples are taken for analysis to confirm that all components are qualified (as shown in Table 7, Mn≤0.02%, C≤0.003%, S≤0.003%, P≤0.003%, etc.). Then, the molten steel is hoisted to the continuous casting machine and cast into industrial pure iron slabs.

[0023] The specific smelting data for the two furnaces are recorded in Tables 1 to 7 below, which intuitively show the changes in key components and operating parameters of each step, fully demonstrating the effectiveness and stability of this method.

[0024] The above embodiments illustrate in detail the specific operation process and parameter control of the method of the present invention. For those skilled in the art, without departing from the principles and spirit of the present invention, various adjustments, substitutions, or improvements can be made to the specific parameters of the above steps (such as oxygen blowing flow rate, feeding batch, temperature range, etc.), equipment selection, etc., and these should all be considered to fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for smelting ultra-low manganese industrial pure iron from high-manganese molten iron, characterized in that, Includes the following steps: (1) Pretreatment of molten iron: Desulfurization pretreatment is carried out on molten iron with a manganese content of not more than 0.8%; (2) Converter smelting: The pretreated molten iron is added to the converter and oxygen is blown to remove silicon, manganese, carbon, phosphorus and sulfur. When the carbon content in the molten steel is reduced to ≤0.06% and the manganese content is reduced to ≤0.25%, the steel is tapped to obtain semi-steel. (3) Electric furnace dilution and demanganese removal: The semi-steel is added into the electric furnace, and direct reduced iron is added to the electric furnace in batches. Oxygen blowing and power supply are carried out to dilute the manganese content in the molten steel by using direct reduced iron to melt and dilute the manganese content in the molten steel. The heat absorption of direct reduced iron melting and oxygen blowing oxidation are used to create low temperature demanganese removal conditions to reduce the manganese content in the molten steel to below 0.02%. (4) Vacuum refining: The molten steel processed in step (3) is vacuum refined to complete decarburization, deoxidation and deep desulfurization, and molten steel with composition that meets the standard of ultra-low manganese industrial pure iron.

2. The method according to claim 1, characterized in that, The composition of the molten iron in step (1) is as follows (by mass percentage): C ≥ 4.0%, Mn ≤ 0.8%, Si: 0.30-0.60%, P ≤ 0.120%, S ≤ 0.05%; The sulfur content in the pretreated molten iron is ≤0.03%.

3. The method according to claim 1, characterized in that, In step (3), the amount of direct reduced iron added is controlled by the ratio of the weight of the molten steel produced after complete melting to the weight of the semi-steel added to the electric furnace being 0.8:1-1.2:

1.

4. The method according to claim 1 or 3, characterized in that, In step (3), after adding direct reduced iron and melting it, the temperature of the molten steel is controlled at 1540-1550℃; after oxygen blowing to remove manganese, the manganese removal slag is poured out.

5. The method according to claim 4, characterized in that, In step (3), after the demanganese slag is poured out, slag-forming agent is added to the electric furnace and oxygen is blown in. Dephosphorization is carried out under the condition of basicity of 3-5 to reduce the phosphorus content in the molten steel to below 0.002%.

6. The method according to claim 5, characterized in that, Step (3) After dephosphorization, the temperature of the molten steel is raised to 1620-1640℃ and then tapped into the ladle; the carbon content in the molten steel at the time of tapping is ≤0.03% and the manganese content is ≤0.02%.

7. The method according to claim 1, characterized in that, The vacuum refining in step (4) is carried out in a VOD furnace, specifically including: decarburizing using dissolved oxygen in molten steel under vacuum conditions to reduce the carbon content to ≤0.003%; then adding aluminum particles for deoxidation, and adding lime and fluorite for slag formation, and carrying out deep desulfurization through strong stirring to reduce the sulfur content to ≤0.003%.

8. The method according to claim 7, characterized in that, The amount of lime added is 0.8-1.2 tons per furnace, and the amount of fluorite added is 8%-15% of the amount of lime added.

9. The method according to claim 1, characterized in that, The standard for ultra-low manganese industrial pure iron requires that the manganese content in molten steel be ≤0.02%.

Images