Low-carbon ferromanganese and method for producing the same

Abstract

This invention relates to the field of ferroalloy technology and discloses a low-carbon ferromanganese and its preparation method. The chemical composition of the low-carbon ferromanganese, by mass percentage, is: Mn 78%-85%, C≤0.3%, Si 1.2%-2.0%, P≤0.06%, S≤0.04%, with the balance being Fe and unavoidable impurities. The preparation process employs "pretreatment-medium-frequency induction furnace melting-refining and decarburization-composition adjustment-casting and cooling," effectively reducing the carbon content in the ferromanganese while ensuring a high manganese recovery rate and stable mechanical properties of the product. The low-carbon ferromanganese prepared by this invention is suitable for smelting high-strength steel, stainless steel, and other steel products with stringent carbon content requirements. The preparation process is simple, energy-efficient, and environmentally friendly, possessing promising prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of ferroalloy technology, specifically to a low-carbon ferromanganese and its preparation method. Background Technology

[0002] Ferromanganese is an important alloying additive in the steel industry, mainly used to improve the strength, hardness, and toughness of steel. Based on carbon content, ferromanganese can be classified into high-carbon ferromanganese, medium-carbon ferromanganese, and low-carbon ferromanganese. Low-carbon ferromanganese, due to its low carbon content, is widely used in the smelting of high-strength low-alloy steel, stainless steel, heat-resistant steel, and other high-end steels, effectively avoiding problems such as decreased toughness and poor weldability caused by excessive carbon in the steel.

[0003] Existing methods for preparing low-carbon ferromanganese mainly include the "blast furnace primary smelting-converter refining" method and the "electric furnace direct reduction" method. The former suffers from a long process and low manganese recovery rate during converter refining; the latter, while relatively simple, requires expensive low-grade manganese ore and reducing agents, and the carbon content of the finished product is difficult to stably control below 0.3%. Therefore, developing a simple, easily controllable carbon content, and high manganese recovery method for preparing low-carbon ferromanganese has become an urgent need in the ferroalloy industry. Summary of the Invention

[0004] Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a low-carbon ferromanganese and its preparation method, which exhibits good hardness and impact toughness.

[0006] Technical solution

[0007] To achieve the above objectives, the present invention provides the following technical solution: a low-carbon ferromanganese, wherein the chemical composition of the low-carbon ferromanganese comprises: Mn 78%-85%, C≤0.3%, Si 1.2%-2.0%, P≤0.06%, S≤0.04%, with the balance being Fe and unavoidable impurities;

[0008] Among them, Mn ensures the core alloy function of ferromanganese, providing sufficient manganese to improve the mechanical properties of steel. If the Mn content is less than 78%, the amount added needs to be increased to meet the steel's requirements, increasing smelting costs. If it is higher than 85%, it will lead to an increase in the melting point of ferromanganese and increase the difficulty of smelting. C (≤0.3%), strictly control the carbon content to avoid negatively affecting the toughness and weldability of high-end steel. Si (1.2%-2.0%): on the one hand, it acts as a deoxidizer to remove oxygen from the molten metal and reduce oxide impurities. On the other hand, it can improve the fluidity of ferromanganese and facilitate casting. If the Si content is too low, the deoxidation effect will be poor. If it is too high, it will lead to an increase in the hardness and brittleness of ferromanganese. P and S are harmful impurities that can cause cold brittleness and hot brittleness in steel. Therefore, their contents need to be strictly limited. P≤0.05% and S≤0.03% are preferred to further improve product quality.

[0009] Further, the chemical composition, by mass percentage, is preferably: Mn 80%-83%, C 0.15%-0.25%, Si 1.4%-1.8%, P ≤ 0.05%, S ≤ 0.03%, with the balance being Fe and unavoidable impurities.

[0010] Furthermore, it includes the following steps:

[0011] S1. Raw material pretreatment: High-carbon ferromanganese (Mn≥75%, C6%-8%), ferrosilicon (Si≥72%), iron oxide scale (Fe2O3≥60%), and lime (CaO≥85%) are selected as raw materials and crushed to a particle size of 20-50mm. Then, the crushed raw materials are dried at a temperature of 120-180℃ for 2-3 hours to remove moisture. Through crushing and drying, moisture and large impurities are removed from the raw materials, avoiding splashing and porosity during smelting, while ensuring uniform composition of the raw materials. The addition of iron oxide scale can provide an oxygen source to assist the subsequent decarburization reaction and reduce oxygen consumption.

[0012] S2. Induction Furnace Smelting: Pretreated high-carbon ferromanganese, iron oxide scale, and lime are added to an induction furnace at a mass ratio of 80-85:10-15:3-5. The furnace is then energized and heated, and smelted at this temperature for 30-45 minutes to fully melt the raw materials and obtain the initial smelting liquid. The induction furnace has high heating efficiency and precise temperature control, which can quickly melt the raw materials and reduce the volatilization loss of manganese at high temperatures. The addition of lime can react with sulfur and phosphorus in the raw materials to generate slag, thus initially removing some harmful impurities.

[0013] S3. Refining and decarbonization: An oxygen-nitrogen mixture is introduced into the primary molten liquid obtained in step S2, with an oxygen volume fraction of 30%-40% and a flow rate of 0.8-1.2 m³ / s. 3The aeration rate is 50-80 rpm for 20-30 minutes per hour, while simultaneously stirring the molten liquid. Carbon is removed from the molten liquid through oxidation. Samples are taken every 5 minutes to check the carbon content of the molten liquid. Aeration is stopped when the carbon content drops below 0.3%. Using an oxygen-nitrogen mixture instead of pure oxygen slows down the oxidation reaction rate and prevents excessive oxidation of manganese (manganese has a higher oxidation priority than carbon) due to localized high temperatures, thus improving manganese recovery. Simultaneous stirring ensures uniform composition of the molten liquid, guaranteeing a stable carbon content below 0.3%.

[0014] S4. Composition Adjustment: Add pretreated ferrosilicon to the refined melt obtained in step S3. The amount of ferrosilicon added is 1.5%-2.5% of the mass of the refined melt. Heat to 1600-1680℃, maintain the temperature and stir to ensure uniform distribution of silicon. At the same time, the reduction of silicon further removes trace impurities. The addition of ferrosilicon not only adjusts the silicon content, but also removes residual trace oxides in the melt through the reduction reaction, further purifying the melt. Maintaining the temperature and stirring ensures uniform distribution of silicon and avoids component segregation in the finished product.

[0015] S5. Casting and Cooling: The molten metal adjusted in step S4 is poured into a mold preheated to 300-400℃ and cooled in a stepped manner: first, it is cooled naturally in the air. After the surface of the molten metal solidifies, it is transferred to a cooling water tank for water cooling at a temperature of 20-30℃. After cooling to room temperature, it is demolded to obtain the low-carbon ferromanganese product. Natural cooling followed by water cooling can avoid the internal stress generated by the molten metal due to excessive cooling speed, reducing the risk of cracking of the finished product. Preheating the mold can prevent rapid cooling and shrinkage when the molten metal comes into contact with the cold mold, ensuring the integrity of the finished product's shape.

[0016] Furthermore, in step S1, the particle size of the iron oxide scale is controlled to be 25-35mm, the drying temperature is preferably 150℃, and the drying time is preferably 2.5h, to ensure thorough removal of moisture and avoid oxidation of the raw materials.

[0017] Furthermore, in S2, the temperature at which the power is applied and the temperature is increased is 1550-1650℃.

[0018] Furthermore, in step S3, the oxygen volume fraction of the oxygen-nitrogen mixture is preferably 35%, and the ventilation flow rate is preferably 1.0 m³ / s. 3 The stirring rate is preferably 65 r / min per hour to balance the carbon removal efficiency and manganese recovery rate.

[0019] Furthermore, in step S4, the heat preservation and stirring time is 15-20 minutes.

[0020] Furthermore, in step S5, the mold is made of cast iron; and the natural cooling time in the air is 1-2 hours.

[0021] Beneficial technical effects:

[0022] The low-carbon ferromanganese prepared by this invention has a carbon content ≤0.3% and a manganese content ≥78%, with low levels of harmful impurities P and S, which can meet the smelting requirements of high-end steel. By optimizing the refining and decarbonization process, the manganese recovery rate is high, reducing raw material loss. The use of a medium-frequency induction furnace for smelting results in lower energy consumption than the blast furnace-converter process. The use of an oxygen-nitrogen mixed gas reduces the emission of oxidizing waste gas. The process of this invention is simple, the temperature and composition are easy to control, the equipment investment cost is low, and it has good hardness and impact toughness, making it suitable for large-scale production. Detailed Implementation

[0023] 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 are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] Raw material pretreatment: Select high-carbon ferromanganese (Mn 76%, C 7.2%), ferrosilicon (Si 73%), iron oxide scale (Fe2O3 62%), and lime (CaO 86%), crush them to 25mm, and dry them at 150℃ for 2.5h;

[0026] Medium-frequency induction furnace smelting: Add high-carbon ferromanganese: iron oxide scale: lime at a mass ratio of 82:13:4 to medium-frequency induction furnace, heat to 1600℃, hold for smelting for 40 minutes to obtain primary molten liquid;

[0027] Refining and carbon removal: A mixture of oxygen and nitrogen (35% oxygen by volume) is introduced at a flow rate of 1.0 m³ / s. 3 / h, stirring rate 65r / min, aeration for 25min, sample test showed C content of 0.22%, aeration stopped;

[0028] Composition adjustment: Add 2.0% by weight of refined molten ferrosilicon, heat to 1650℃, and stir for 18 minutes;

[0029] Casting and cooling: The molten metal is poured into a preheated cast iron mold at 350°C and allowed to cool naturally for 1.5 hours. Then, it is transferred to a 25°C cooling water tank for 2.5 hours of water cooling before demolding to obtain the finished low-carbon ferromanganese product.

[0030] Example 2

[0031] Raw material pretreatment: Select high-carbon ferromanganese (Mn 78%, C 6.8%), ferrosilicon (Si 75%), iron oxide scale (Fe2O3 65%), and lime (CaO 88%), crush them to 25mm, and dry them at 160℃ for 2h;

[0032] Medium-frequency induction furnace smelting: Add high-carbon ferromanganese: iron oxide scale: lime at a mass ratio of 85:10:3 to medium-frequency induction furnace, heat to 1650℃, hold for smelting for 35 minutes to obtain primary molten liquid;

[0033] Refining and carbon removal: A mixture of oxygen and nitrogen with an oxygen volume fraction of 38% is introduced at a flow rate of 1.1 m³ / s. 3 / h, stirring rate 70r / min, aeration for 22min, sample test showed C content of 0.18%, aeration stopped;

[0034] Composition adjustment: Add 2.2% ferrosilicon by mass of the refined melt, heat to 1680℃, and stir for 16 minutes;

[0035] Casting and cooling: The molten metal is poured into a preheated cast iron mold at 380°C and allowed to cool naturally for 1.2 hours. Then, it is transferred to a 28°C cooling water tank for 2 hours of water cooling before demolding to obtain the finished low-carbon ferromanganese product.

[0036] Example 3

[0037] Raw material pretreatment: Select high-carbon ferromanganese (Mn 77%, C 7%), ferrosilicon (Si 74%), iron oxide scale (Fe2O3 64%), and lime (CaO 87%), crush them to 30mm, and dry them at 155℃ for 2h;

[0038] Medium-frequency induction furnace smelting: Add high-carbon ferromanganese: iron oxide scale: lime at a mass ratio of 83:12:4.5 to the medium-frequency induction furnace, heat to 1620℃, hold for smelting for 40 minutes to obtain the initial smelting liquid;

[0039] Refining and carbon removal: A mixture of oxygen and nitrogen (36% oxygen by volume) is introduced at a flow rate of 1.0 m³ / s. 3 / h, stirring rate 65r / min, aeration for 25min, sample test showed C content of 0.21%, aeration stopped;

[0040] Composition adjustment: Add 2.1% ferrosilicon by mass of the refined melt, heat to 1660℃, and stir for 18 minutes;

[0041] Casting and cooling: The molten metal is poured into a preheated cast iron mold at 360°C and allowed to cool naturally for 1.5 hours. Then, it is transferred to a 26°C cooling water tank for 2.5 hours of water cooling before demolding to obtain the finished low-carbon ferromanganese product.

[0042] Comparative Example 1

[0043] Raw materials: Same as in Example 3 (high-carbon ferromanganese Mn 77%, C 7%, iron oxide scale Fe2O3 64%, lime CaO 87%), with the addition of manganese ore (Mn 40%, to compensate for Mn loss in the blast furnace) and coke (reducing agent);

[0044] Process steps:

[0045] Blast furnace primary smelting: Raw materials are added to the blast furnace in the ratio of "high-carbon ferromanganese: manganese ore: iron oxide scale: lime: coke = 60:20:10:5:5", heated to 1720℃, and smelted for 2.5 hours to obtain primary smelting liquid;

[0046] Converter refining: Pure oxygen is introduced (flow rate 1.8 m³ / h). 3 / h), blow refining for 35 minutes, and stop when the C sample is 0.4% to avoid excessive oxidation of Mn;

[0047] Composition adjustment: Add 2.1% ferrosilicon (consistent with Example 3), stir at 1660℃ for 10 min;

[0048] Casting and cooling: Pour into a room temperature cast iron mold (without preheating) and allow to cool naturally to room temperature.

[0049] Comparative Example 2

[0050] Raw materials: low-grade manganese ore (Mn 35%, replacing the high-carbon ferromanganese in Example 3), graphite electrode (reducing agent), ferrosilicon (Si 74%, consistent with Example 3), lime CaO 87%;

[0051] Process steps:

[0052] Electric furnace smelting: The raw materials were added to the electric arc furnace in the ratio of "manganese ore: graphite: ferrosilicon: lime = 80:8:5:7", and the temperature was raised to 1620℃ (the same as the smelting temperature in Example 3). The furnace was then reduced and smelted for 50 minutes to obtain the initial smelted liquid.

[0053] Refining and impurity removal: Introduce argon gas (flow rate 1.2 m³ / h). 3 Stir for 15 minutes ( / h), then take a sample and test the C content, which is 0.38%.

[0054] Casting and cooling: Pour into a 360°C preheated cast iron mold (same as in Example 3), and directly water cool at 26°C (natural cooling is omitted).

[0055] The mechanical properties of low-carbon ferromanganese were tested in accordance with GB / T GB / T229-2020 "Metallic Materials Charpy Pendulum Impact Test Method" and GB / T231.1-2018 "Metallic Materials Brinell Hardness Test Part 1: Test Method".

[0056] Table 1:

[0057] ;

[0058] As shown in Table 1, the low-carbon ferromanganese prepared by this invention has good hardness and impact toughness. Although Comparative Example 1 used the same high-carbon ferromanganese as Example 3, the blast furnace melting temperature of 1720℃ (higher than Example 3) led to an increase in Mn vapor volatilization, increasing Mn loss; the use of pure oxygen resulted in high oxidation activity, and unlike Example 3, it did not involve reduction via ferrosilicon, resulting in a lower final manganese recovery rate. Comparative Example 2 used low-grade manganese ore, requiring the reduction of high-valence Mn oxides to Mn first, and the gangue in the manganese ore encapsulated Mn, resulting in a lower final Mn content and recovery rate compared to Example 3.

[0059] Table 2: Chemical composition of Examples 1-3 and Comparative Examples 1-2

[0060] ;

[0061] As shown in Table 2, the Mn content of the finished products in Examples 1-3 is within the preferred range of 82.3%-83.1%, the C content is controlled at 0.18%-0.22%, meeting the technical requirement of ≤0.3%, and the P and S contents are ≤0.04% and ≤0.03%, respectively, indicating low levels of harmful impurities. In contrast, the C contents of Comparative Examples 1-2 are 0.4% and 0.38%, respectively, exceeding the specified range, and the P and S contents are also higher than those in the Examples. Furthermore, the manganese recovery rate of the Examples reaches 92.5%-93.1%, which is much higher than the 78.3% of Comparative Example 1 and the 85.6% of Comparative Example 2, proving that the process of the present invention can effectively control chemical composition, reduce impurity content, and improve manganese recovery rate.

[0062] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0063] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0064] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A method for preparing low-carbon ferromanganese, characterized in that, The chemical composition of the low-carbon ferromanganese, by mass percentage, includes: Mn 80%-83%, C 0.15%-0.25%, Si 1.4%-1.8%, P≤0.05%, S≤0.03%, with the balance being Fe and unavoidable impurities; Includes the following steps: S1. Raw material pretreatment: High-carbon ferromanganese, ferrosilicon, iron oxide scale, and lime are selected as raw materials. Among them, the high-carbon ferromanganese contains Mn≥75% and C6%-8%, the ferrosilicon contains Si≥72%, the iron oxide scale contains Fe2O3≥60%, and the lime contains CaO≥85%. They are crushed to a particle size of 20-50mm. Then, the crushed raw materials are dried at a temperature of 120-180℃ for 2-3 hours to remove moisture from the raw materials. S2. Medium-frequency induction furnace smelting: Pretreated high-carbon ferromanganese, iron oxide scale, and lime are added to the medium-frequency induction furnace at a mass ratio of 80-85:10-15:3-5. The furnace is powered on and heated, and the furnace is kept at the temperature for 30-45 minutes to fully melt the raw materials and obtain the initial smelting liquid. S3. Refining and decarbonization: An oxygen-nitrogen mixture is introduced into the primary molten liquid obtained in step S2, with an oxygen volume fraction of 30%-40% and a flow rate of 0.8-1.2 m³ / s. 3 The ventilation rate is 50-80 r / min, with a ventilation time of 20-30 min. The molten liquid is stirred at a rate of 50-80 r / min to remove carbon from the molten liquid through oxidation. The carbon content of the molten liquid is sampled every 5 min during the process. When the carbon content drops below 0.3%, the ventilation is stopped. S4. Composition adjustment: Add pretreated ferrosilicon to the refined melt obtained in step S3. The amount of ferrosilicon added is 1.5%-2.5% of the mass of the refined melt. Heat to 1600-1680℃, keep warm and stir to make the silicon element evenly distributed, and at the same time remove trace impurities through the reduction of silicon. S5. Casting and Cooling: The molten liquid adjusted in step S4 is poured into a mold preheated to 300-400℃ and cooled in a stepped manner: first, it is cooled naturally in the air, and after the surface of the molten liquid solidifies, it is transferred to a cooling water tank for water cooling at a temperature of 20-30℃. After cooling to room temperature, it is demolded to obtain the low-carbon ferromanganese product.

2. The method for preparing low-carbon ferromanganese according to claim 1, characterized in that, In step S1, the particle size of the iron oxide scale is controlled at 25-35mm, the drying temperature is 150℃, and the drying time is 2.5h to ensure thorough removal of moisture and avoid oxidation of the raw materials.

3. The method for preparing low-carbon ferromanganese according to claim 1, characterized in that, In S2, the temperature at which the power is applied and the temperature is increased is 1550-1650℃.

4. The method for preparing low-carbon ferromanganese according to claim 1, characterized in that, In step S3, the oxygen volume fraction of the oxygen-nitrogen mixture is 35%, and the ventilation flow rate is 1.0 m³ / s. 3 The stirring rate is 65 r / min per hour to balance the carbon removal efficiency and manganese recovery rate.

5. The method for preparing low-carbon ferromanganese according to claim 1, characterized in that, In step S4, the heat preservation and stirring time is 15-20 minutes.

6. The method for preparing low-carbon ferromanganese according to claim 1, characterized in that, In step S5, the mold is made of cast iron; the natural cooling time in the air is 1-2 hours.