Method for producing foundry pig iron by using rare earth elements

Abstract

The invention relates to a method for producing cast iron by using rare earth elements, which comprises the following steps of: firstly, raising the temperature of high-purity cast iron liquid for casting produced by a hydrogen-based smelting reduction process through an electromagnetic heating device outside a furnace, and ensuring that the temperature of the molten iron is greater than or equal to 1450 DEG C; then, filamentous rare earth ferrosilicon alloy is added through a wire feeding technology in the subsequent process of the electromagnetic heating device, and primary desulfurization and deoxidation are carried out; then argon bottom blowing refining is carried out, and impurities and anti-spheroidizing elements are deeply removed; and finally, casting is conducted after slagging-off treatment is conducted. According to the method, other impurity elements of the anti-spheroidizing agent in the high-purity molten iron for casting can be treated, and the phenomenon that the quality of castings is affected by uneven distribution, local segregation and the like of rare earth in cast iron can be effectively avoided.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to the foundry industry and the field of ferrous metal smelting technology, and more specifically, to a method for producing cast pig iron using rare earth elements. Background Art

[0002] Due to their unique electron shells, trace amounts of rare earth elements can play unique roles in many materials. Cast iron is one of the important application fields of rare earths. Ductile iron castings are the largest users of rare earths in cast iron. China's production of ductile iron castings has ranked first in the world, but it is difficult to meet the current process production requirements. There are good reaction thermodynamics conditions between rare earth elements and many elements in cast iron. They have extremely strong affinity with sulfur, oxygen and other interfering elements that affect graphite spheroidization, and can combine into stable compounds, which can remove or reduce their adverse effects on graphite spheroidization in cast iron and promote the transformation of graphite from flake to spherical. However, since the specific gravity of rare earths is similar to that of cast iron and their atomic radius is larger than that of iron, they are not easily diffused in the molten iron. Moreover, the melting points of rare earth sulfides and rare earth oxides are relatively high, and they are easily coated on the surface of the nodulizer, often resulting in uneven distribution of rare earths in cast iron and local segregation, greatly reducing the effective utilization rate and making it difficult to meet the quality and performance requirements of high-precision castings. Making full use of China's rich rare earth resources and vigorously developing high-quality rare earth castings and rare earth steels is one of the important ways to upgrade high-end casting materials and steel materials in China. Therefore, there is an urgent need to develop a method for producing cast pig iron using rare earth elements to stably provide high-end basic raw materials for equipment manufacturing industries such as wind power castings and high-speed rail castings, and also to open up a new technology, new process and new idea for smelting high-purity pig iron for casting. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for producing cast pig iron using rare earth elements, which can process other impurity elements in the anti-nodulizer in high-purity molten iron for casting and can effectively solve the problems that affect the quality of castings such as uneven distribution of rare earths in cast iron and local segregation.

[0004] The specific technical solution of the present application is as follows:

[0005] A method for producing cast pig iron using rare earth elements includes the following steps: First, heat up the high-purity pig iron molten iron for casting produced by the hydrogen-based molten reduction process through an external furnace electromagnetic heating device to ensure that the molten iron temperature ≥ 1450°C; then add filamentous rare earth ferrosilicon alloy through a wire feeding process after the electromagnetic heating device for primary desulfurization and deoxidation; then carry out bottom blowing argon refining for deep inclusion removal and anti-nodulizing element removal; finally, carry out slag skimming treatment and then casting.

[0006] Further, the high-purity pig iron liquid for casting is high-purity molten iron with low titanium, low phosphorus, and low trace elements. The composition of the molten iron includes: Ti ≤ 0.010%, P ≤ 0.020%,

[0007] Cr + V + Mo + Sn + Sb + Pb + Bi + Te + As + B + Al ≤ 0.040%, and the balance is iron and unavoidable impurities.

[0008] Further, the electromagnetic induction heating device outside the furnace is high-frequency automatic regulation. According to the molten iron temperature detected by the automatic temperature measuring device, the power of the electromagnetic induction device is adjusted in real time and dynamically, and the heating power is automatically adjusted according to the temperature difference to ensure that the molten iron temperature ≥ 1450 °C.

[0009] Further, the rare earth ferrosilicon alloy mainly contains 21.0% - 42.0% rare earth, 37.0% - 53.0% silicon, 2.0% - 2.5% manganese, 2.0% - 5.0% calcium, 0.1% - 1.5% titanium, and the balance is iron.

[0010] Further, the cerium content in the rare earth is 60% - 65%.

[0011] Further, the rare earth ferrosilicon alloy is in the form of lumps or filaments. The lump size is 1 - 60 mm; the filament diameter is 10 nm - 1.2 mm.

[0012] Further, the calculation of the addition amount of the rare earth ferrosilicon alloy is as follows:

[0013] Further,

[0014]

[0015] where is the recovery rate of the rare earth alloy between 1400 °C and 1600 °C, and P is the grade of the rare earth alloy.

[0016] Further, where is the actual molten iron temperature in the range of 1300 - 1600 °C, is the normal melting temperature range of the rare earth alloy, is the effective utilization rate of the rare earth alloy per degree Celsius, generally 0.1 - 0.4%.

[0017] Further, the rare earth recovery rate is affected by the molten iron temperature, particle size, and batch addition amount. When the molten iron temperature is 1400 - 1450 °C, the rare earth recovery rate is generally 85 - 95%.

[0018] Furthermore, the device used for bottom-blowing argon refining is an LF furnace. Lime with a particle size of 0.5 - 1.5 mm is added 1 - 1.5 minutes after the start of power-on heating, and the addition amount is 30 - 60% of the total amount of lime. After the added slag-making material is completely melted, the remaining lime is put in, and the sulfur content in the molten iron is controlled to be < 0.020%.

[0019] Furthermore, after the slag skimming operation is completed, the ladle is lifted and rotated to the hydraulic tilting ladle support, and the bottom nozzle is directly above the chute pit; the hydraulic device of the sliding nozzle is started, the nozzle is slowly opened, the flow rate of the molten iron is controlled, and an appropriate amount of nano-level rare earth alloy inoculant is slowly added to the pit according to the test results of chemical analysis, so that the inflowing and outflowing molten iron reaches equilibrium; the molten iron enters the casting mold through the chute and is formed by water cooling;

[0020] Furthermore, the nano-level rare earth alloy contains 15.0% - 55.0% rare earth, 20.0% - 34.0% silicon, 2.0% - 5.0% manganese, 2.0% - 5.0% calcium, 0.1% - 3.0% titanium, and the balance is iron.

[0021] Furthermore, the carbide in the pig iron matrix structure is ≤ 3%, and the balance of pearlite + ferrite > 97%.

[0022] Advantages and effects of the present invention:

[0023] 1. After the pig iron molten iron produced by the hydrogen-based melting reduction process, the present invention uses an electromagnetic induction heating device to heat the molten iron online and controls the molten iron temperature ≥ 1450°C; after the molten iron temperature ≥ 1450°C, rare earth ferrosilicon is added for alloying to initially complete deoxidation, desulfurization and removal of anti-spheroidizing elements;

[0024] 2. Adding rare earth ferrosilicon alloy in the present invention can achieve one-time deep removal of anti-spheroidizing elements, inclusions and degassing treatment. It increases the graphite nuclei in the molten iron, promotes nucleation, promotes the precipitation of carbon, and inhibits the formation of Fe3C during solidification. At the same time, the removal treatment of oxygen, nitrogen and hydrogen in the molten iron is carried out to reduce the gas content in the molten iron, and significantly improve the fluidity and casting performance of the molten iron.

[0025] 3. The present invention can achieve the effects of safe, energy-saving and efficient removal of anti-spheroidizing and other impurity elements of high-purity molten iron for casting by utilizing the process advantages in the front-end process of casting spheroidization. Description of the Drawings

[0026] Figure 1 is the process flow chart of the present invention;

[0027] Figure 2 is the metallographic basic structure diagram (×500) before the present invention is implemented;

[0028] Figure 3It is the metallographic matrix structure diagram (×100) after implementing the present invention. Specific embodiments

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0030] The following further explains and illustrates the technical solutions of the present invention in conjunction with specific embodiments.

[0031] Embodiment 1

[0032] The following further describes the technical solutions of the present invention in conjunction with the accompanying drawings and specific embodiments.

[0033] This embodiment is illustrated by a high-purity pig iron production line with an annual output of 600,000 tons:

[0034] When the iron overflows from the MPR furnace, pressurized tapping starts. At 2 minutes, online temperature measurement starts at 1410 °C, and the electromagnetic heating device adjusts the frequency accordingly to raise the temperature to above 1450 °C; then rare earth ferrosilicon alloy is added with the flow at the end of the electromagnetic heating device; after alloying, bottom blowing argon refining is carried out to deeply remove inclusions and reverse spheroidizing elements; finally, slag skimming treatment is carried out and then casting is performed;

[0035] The molten iron composition is shown in Table 1 below;

[0036] Table 1

[0037] Element C Si Mn P S Ti Pb Sn As Al Sb Bi Content % 4.11 0.001 0.0125 0.0092 0.071 0.001 0.00028 0.00065 0.0029 0.00066 0.0024 0.0040

[0038] The rare earth ferrosilicon alloy has the composition shown in Table 2 below;

[0039] Table 2

[0040] Element RE Si Ca Particle size Ce / RE Content % 40 35 2.5 1 - 10mm 61

[0041] According to the chemical composition of the rare earth ferrosilicon alloy in Table 2, the rare earth RE is 40%, the Ce / RE is 61%, the molten iron temperature is 1450 °C, the absorption rate is 93%, and the weight of the iron liquid is 65.45 tons, then Substituting the values and calculating, the addition amount of the rare earth ferrosilicon alloy is about 60.66 kg.

[0042] The product composition after treatment is shown in Table 3 below;

[0043] Table 3

[0044] Element C Si Mn P S Ti Pb Sn As Al Sb Bi Content % 4.08 0.43 0.0180 0.007 0.009 <![CDATA ≤ 0.0001]]> <![CDATA ≤ 0.0001]]> <![CDATA ≤ 0.0001]]> <![CDATA ≤ 0.0001]]> <![CDATA ≤ 0.0001]]> <![CDATA ≤ 0.0001]]> <![CDATA ≤ 0.0001]]>

[0045] The metallographic basic structure diagram of the finally obtained high-purity cast pig iron ingot is as Figure 3 shown. The metallographic basic structure of the cast pig iron ingot obtained without the steps of electromagnetic induction temperature adjustment, LF refining, and addition of rare earth alloy for alloying is as Figure 2 shown. The rare earth ferrosilicon alloy used in the present invention completes the removal of anti-spheroidizing elements, inclusion removal, and degassing treatment in one go. It increases the graphite core in the molten iron, promotes nucleation, promotes the precipitation of carbon, inhibits the formation of Fe3C during solidification. After implementation, the pearlite is increased from the original 70% to over 90%. At the same time, the oxygen, nitrogen, and hydrogen in the molten iron are removed, reducing the gas content in the molten iron, significantly improving the fluidity and casting performance of the molten iron, and effectively solving the problems such as uneven distribution and local segregation of rare earth in cast iron that affect the quality of castings.

[0046] Although the embodiments disclosed in the present invention are as above, the above content is only the embodiments adopted for the convenience of understanding the present invention and is not used to limit the present invention. Any person skilled in the art within the scope of the present invention can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A method for producing foundry pig iron using rare earth elements, characterized in that: The method comprises the following steps: firstly, the high-purity molten pig iron for casting produced by the hydrogen-based molten reduction process is heated by an electromagnetic heating device outside the furnace to ensure that the temperature of the molten iron is ≥1450°C; then, filamentous rare earth ferrosilicon alloy is added to the electromagnetic heating device through a wire feeding process to perform primary desulfurization and deoxidation; then, bottom blowing argon gas refining is performed to deeply remove inclusions and anti-spheroidizing elements; and finally, slag removal is performed before pouring.

2. The method for producing foundry pig iron using rare earth elements as claimed in claim 1, characterized in that: The high-purity pig iron liquid for casting is high-purity molten iron with low titanium, low phosphorus and low trace elements, and the molten iron composition includes: Ti≤0.010%, P≤0.020%, Cr+V+Mo+Sn+Sb+Pb+Bi+Te+As+B+Al≤0.040%, and the remainder is iron and inevitable impurities.

3. The method for producing foundry pig iron using rare earth elements as claimed in claim 2, characterized in that: The rare earth ferrosilicon alloy mainly comprises 21.0%-42.0% rare earth, 37.0%-53.0% silicon, 2.0%-2.5% manganese, 2.0%-5.0% calcium, 0.1%-1.5% titanium, and the balance is iron; the cerium content in the rare earth is 60%-65%.

4. The method for producing foundry pig iron using rare earth elements as claimed in claim 3, characterized in that: The calculation of the amount of rare earth ferrosilicon alloy added is:

5. The method for producing foundry pig iron using rare earth elements as claimed in claim 4, characterized in that: in is the yield of rare earth alloy between 1400℃ and 1600℃, and P is the grade of rare earth alloy.

6. The method for producing foundry pig iron using rare earth elements as claimed in claim 5, characterized in that: in is the actual molten iron temperature in the range of 1300-1600℃, is the normal melting temperature range of rare earth alloys, It is the effective utilization rate of rare earth alloy per degree Celsius, generally 0.1-0.4%.

7. The method for producing foundry pig iron using rare earth elements as claimed in claim 6, characterized in that: The device used for bottom blowing argon refining is LF furnace. Lime with a particle size of 0.5-1.5 mm is added 1 to 1.5 minutes after the start of power heating. The added amount is 30-60% of the total amount of lime. After the added slag-making material is completely melted, the remaining lime is added to control the S in the molten iron to be less than 0.020%.

8. The method for producing foundry pig iron using rare earth elements as claimed in claim 7, characterized in that: After the slag removal operation is completed, the ladle is hoisted onto the hydraulic tilting ladle support, with the bottom water outlet facing the small pit of the chute; the hydraulic device of the sliding water outlet is started, the water outlet is slowly opened, the flow rate of the molten iron is controlled, and according to the test results, an appropriate amount of nano-grade rare earth alloy inoculant is slowly added to the small pit to balance the inflow and outflow of molten iron; the molten iron enters the cast iron mold through the chute and is water-cooled to form.

9. The method for producing foundry pig iron using rare earth elements as claimed in claim 8, characterized in that: The nano-scale rare earth alloy contains 15.0%-55.0% rare earth, 20.0%-34.0% silicon, 2.0%-5.0% manganese, 2.0%-5.0% calcium, 0.1%-3.0% titanium, and the balance is iron.

10. Pig iron obtained according to the method of claims 1-9, characterized in that: The carbide content in the pig iron matrix is ​​≤3%, and the balance is pearlite + ferrite > 97%.

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