Synthetic cast iron preparation method based on high-proportion scrap steel

Abstract

The invention relates to the technical field of cast iron production processes, in particular to a synthetic cast iron preparation method based on high-proportion scrap steel, which comprises the following steps: smelting furnace burden at high temperature to obtain synthetic cast iron liquid; when it is judged that preparation of the synthetic cast iron liquid does not reach the standard according to the eutectic supercooling degree, the preset standing time is prolonged; silicon carbide is added into the synthetic cast iron liquid meeting the preset standard, stirring is conducted, and first inoculation iron liquid is obtained; tapping the first inoculation iron liquid, and adding a first inoculant to obtain second inoculation iron liquid; when it is judged that the preparation of the second inoculation iron liquid does not reach the standard according to the eutectic recovery rate, whether the preparation of the second inoculation iron liquid meets the preset standard or not is judged secondarily according to the eutectic solidification rate, or an adjustment strategy when the preparation of the second inoculation iron liquid does not reach the standard is determined according to the relative deviation rate of the carbon equivalent; and the second inoculation iron liquid meeting the preset standard is poured into a casting, and the synthetic cast iron casting is obtained. The preparation efficiency of the synthetic cast iron is improved.

Description

Technical Field

[0001] This invention relates to the field of cast iron production technology, and in particular to a method for preparing synthetic cast iron based on a high proportion of scrap steel. Background Technology

[0002] Cast iron is one of the most widely used basic materials in manufacturing, and its performance directly affects the quality and lifespan of various mechanical equipment. Traditional cast iron smelting primarily uses pig iron as the main furnace charge, supplemented by scrap steel and recycled materials. However, this traditional method has the following significant drawbacks: Pig iron has a high dependence on raw materials and its costs fluctuate greatly: pig iron prices are heavily influenced by the upstream iron ore and coking coal markets, making costs difficult to control. Furthermore, pig iron itself contains many impurities, which can worsen the mechanical and casting properties of cast iron. In contrast, scrap steel is widely available and relatively inexpensive. Increasing the proportion of scrap steel can significantly reduce raw material costs.

[0003] Significant environmental pressure: Pig iron production is a typical high-energy-consuming and high-emission process.

[0004] To overcome these problems, the industry began exploring synthetic cast iron technology, which uses scrap steel as the main furnace charge and adjusts the carbon equivalent by adding carburizing agents to simulate the chemical composition of pig iron. Although the high proportion of scrap steel has obvious advantages, in actual production applications, fluctuations in the high proportion of scrap steel raw materials lead to poor stability of molten iron, making it difficult for the industry to simultaneously meet the dual requirements of cost reduction with high proportion of scrap steel and stable quality of synthetic cast iron.

[0005] Chinese Patent Application Publication No. CN114990419A discloses a method for smelting cast iron from scrap steel, belonging to the field of cast iron production technology. The method includes the following steps: Step S1, Furnace charge preparation: Selecting low-carbon scrap steel with an average carbon content of 0.2%, selecting recycled gray cast iron from the riser and casting gate, and preparing carbon powder and ferrosilicon; Step S2, Furnace loading: The first batch of materials consists of 15% scrap steel + 30% carbon raiser; the second batch consists of 20% scrap steel + 50% carbon raiser; Step S3, Preliminary smelting of the molten metal; Step S4, Molten iron purification: Adding a slag-collecting agent for slag removal, then adding an inoculant to adjust the composition, stirring evenly, and taking samples for testing; Step S5, Fine-tuning the composition of the molten iron based on spectral composition analysis data, with the following order of adjustment: first increasing Mn, then increasing carbon, and finally increasing Si, until the as-cast composition and microstructure standards are met; Step S6, The molten iron continues to heat up, the temperature is measured with a thermocouple thermometer, and then it is unloaded from the furnace.

[0006] It can be seen that the above technical solution does not take into account the metallurgical state of the molten iron after smelting and after inoculation, which affects the tendency of the molten iron to undercool before solidification and the inoculation effect, thus resulting in poor preparation efficiency of synthetic cast iron. Summary of the Invention

[0007] Therefore, the present invention provides a method for preparing synthetic cast iron based on a high proportion of scrap steel, which overcomes the problem in the prior art that does not consider the metallurgical state of the molten iron after smelting and after inoculation, affecting the tendency of supercooling and the inoculation effect before the molten iron solidifies, thus resulting in poor preparation efficiency of synthetic cast iron.

[0008] To achieve the above objectives, the present invention provides a method for preparing synthetic cast iron based on a high proportion of scrap steel, comprising: The furnace charge, which includes scrap steel and silicon carbide of a first preset amount, is added into an electric furnace and smelted at high temperature to obtain synthetic cast iron molten iron. After being allowed to stand at high temperature for a preset standing time, the first cooling curve of the synthetic cast iron molten iron is collected, and the eutectic undercooling is determined based on the first cooling curve. If the preparation of the synthetic cast iron molten iron does not meet the preset standard based on the eutectic undercooling, the preset standing time of the next batch or the value of the first preset addition amount of the next batch shall be increased. Add a second preset amount of silicon carbide to the synthetic cast iron molten iron that meets the preset standard and stir to obtain the first inoculated iron molten iron; The first inoculated iron liquid is tapped, and a first inoculant is added to the iron stream at a third preset amount to obtain a second inoculated iron liquid; the eutectic recovery rate of the second inoculated iron liquid is determined based on the second cooling curve of the second inoculated iron liquid; When the preparation of the second inoculated iron liquid does not meet the preset standard, the preparation of the second inoculated iron liquid is determined a second time based on the eutectic recovery rate of the second inoculated iron liquid. Alternatively, the adjustment strategy for the preparation of the second inoculated iron liquid does not meet the preset standard is determined based on the relative deviation rate of the carbon equivalent of the second inoculated iron liquid. The second inoculated molten iron that meets the preset standard is poured into a casting, and a second inoculating agent is added during the pouring process to obtain a synthetic cast iron casting.

[0009] Furthermore, the process of determining whether the preparation of the synthetic cast iron molten iron meets the preset standard based on the eutectic undercooling of the synthetic cast iron molten iron includes: The eutectic undercooling is compared with the first preset eutectic undercooling and the second preset eutectic undercooling, respectively; If the eutectic undercooling is less than the first preset eutectic undercooling, then the preparation of the synthetic cast iron molten iron is determined to meet the preset standard; If the eutectic undercooling is greater than or equal to the first preset eutectic undercooling and less than the second preset eutectic undercooling, then the preparation of the synthetic cast iron molten iron is determined to be non-compliant with the preset standard, and the preset standing time of the next batch is increased according to the difference between the eutectic undercooling and the first preset eutectic undercooling. If the eutectic undercooling is greater than or equal to the second preset eutectic undercooling, it is determined that the preparation of the synthetic cast iron molten iron does not meet the preset standard, and the value of the first preset addition amount in the next batch is increased according to the difference between the eutectic undercooling and the second preset eutectic undercooling.

[0010] Furthermore, the process of obtaining the eutectic undercooling of the synthetic cast iron molten iron includes: Take a first preset amount of the synthetic cast iron molten iron and pour it into a thermal analysis sample cup with a built-in thermocouple. Record the temperature change curve of the synthetic cast iron molten iron from pouring to solidification, i.e., the first cooling curve. Determine the first actual eutectic temperature from the first cooling curve. Take a first preset amount of the synthetic cast iron molten iron casting spectrum standard test block, and calculate the first theoretical eutectic temperature of the synthetic cast iron molten iron based on the determination of the chemical composition of the synthetic cast iron molten iron. The absolute value of the difference between the first actual eutectic temperature and the first theoretical eutectic temperature is the eutectic undercooling of the synthetic cast iron molten iron.

[0011] Furthermore, several adjustment methods are provided for increasing the value of the first preset addition amount in the next batch, and each adjustment method increases the value of the first preset addition amount in the next batch by a different amount.

[0012] Furthermore, the process of determining whether the preparation of the second inoculated iron melt meets the preset standard based on the eutectic recovery rate of the second inoculated iron melt includes: The eutectic recovery rate is compared with the first preset eutectic recovery rate and the second preset eutectic recovery rate, respectively; If the eutectic recovery rate is less than the first preset eutectic recovery rate, it is determined that the preparation of the second inoculated iron liquid does not meet the preset standard, and the adjustment strategy when the preparation of the second inoculated iron liquid does not meet the preset standard is determined according to the relative deviation rate of carbon equivalent of the second inoculated iron liquid. If the eutectic recovery rate is greater than or equal to the first preset eutectic recovery rate and less than the second preset eutectic recovery rate, then the preparation of the second inoculated iron liquid is determined to meet the preset standard, and the preparation of the second inoculated iron liquid is further determined based on the eutectic solidification rate of the second inoculated iron liquid to meet the preset standard. If the eutectic recovery rate is greater than or equal to the second preset eutectic recovery rate, then the preparation of the second inoculated iron liquid is determined to meet the preset standard.

[0013] Furthermore, the process of obtaining the eutectic recovery rate of the second inoculated iron melt includes: Take the second preset amount of the second inoculated iron liquid and pour it into the thermal analysis sample cup with the built-in thermocouple; Record the temperature change curve of the second inoculated molten iron from liquid to solid state during the cooling process, i.e., the second cooling curve; Identify and read the lowest temperature value of the eutectic transformation stage of the second inoculated iron liquid from the second cooling curve, and record it as the eutectic minimum temperature; Identify and read the highest temperature value that the second inoculated molten iron reaches after supercooling due to the release of latent heat of crystallization from the second cooling curve, and record it as the second eutectic recovery temperature; The second theoretical eutectic temperature of the second inoculated iron liquid is calculated based on its chemical composition. The difference between the second eutectic recovery temperature and the lowest eutectic temperature is calculated and denoted as the first difference. The difference between the second theoretical eutectic temperature and the lowest eutectic temperature is calculated and denoted as the second difference; the ratio of the first difference to the second difference is denoted as the eutectic recovery rate of the second inoculated iron melt.

[0014] Furthermore, if the preparation of the second inoculated iron liquid does not meet the preset standard, based on the comparison result that the eutectic solidification rate of the second inoculated iron liquid is less than the preset eutectic solidification rate, the addition rate of the first inoculator in the next batch is increased according to the difference between the eutectic solidification rate and the preset eutectic solidification rate. The eutectic solidification rate is the ratio of the first difference to the eutectic recovery time, wherein the eutectic recovery time is the time taken for the second inoculated molten iron obtained from the second cooling curve to reach the second eutectic recovery temperature from the lowest eutectic temperature.

[0015] Furthermore, the process of determining the adjustment strategy when the preparation of the second inoculated iron melt does not meet the preset standard based on the relative deviation rate of the carbon equivalent of the second inoculated iron melt includes: The relative deviation rate of carbon equivalent is compared with the preset relative deviation rate of carbon equivalent; If the relative deviation rate of carbon equivalent is less than the preset relative deviation rate of carbon equivalent, the second preset addition amount of silicon carbide in the next batch is increased according to the difference between the preset relative deviation rate of carbon equivalent and the relative deviation rate of carbon equivalent. If the relative deviation rate of carbon equivalent is greater than or equal to the preset relative deviation rate of carbon equivalent, a component runaway alarm will be issued; The relative deviation rate of carbon equivalent is determined based on the carbon equivalent of the second inoculated iron melt and the preset carbon equivalent.

[0016] Furthermore, the furnace charge consists of the following raw materials in the following mass percentages: 60%-80% scrap steel, 20%-40% shot-blasted recycled material, and silicon carbide added at a first preset amount, wherein the particle size of the silicon carbide ranges from 1 to 5 mm.

[0017] Further, the first inoculant is a barium silicon inoculant, and its addition amount is 0.3%-0.5% of the mass of the first inoculated iron liquid, and the particle size range of the first inoculant is 3mm-10mm; the second inoculant is a barium silicon inoculant, and its addition amount is 0.1%-0.2% of the mass of the second inoculated iron liquid, and the particle size range of the second inoculant is 0.2mm-0.8mm.

[0018] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention constructs a closed-loop quality control system that runs through the entire process of smelting, inoculation, and casting. By collecting and analyzing the cooling curves of molten iron at different process stages in real time, it extracts metallurgical state characteristic values ​​such as eutectic undercooling, eutectic recovery rate, eutectic solidification rate, and relative deviation rate of carbon equivalent. Based on these values, it performs multi-level judgment and feedback adjustment. It not only evaluates the eutectic undercooling of molten iron after smelting, but also re-evaluates the inoculation effect after tapping and inoculation. It also provides two refined troubleshooting paths for non-conforming cases: one is to further judge based on the eutectic solidification rate, and the other is to trace the cause of non-compliance based on the relative deviation rate of carbon equivalent. This ensures that various preparation risks are detected and addressed in a timely manner before final casting, thereby improving the preparation efficiency of synthetic cast iron.

[0019] Furthermore, this invention achieves precise identification and differentiated processing of molten iron preparation effects by setting a graded judgment of eutectic undercooling and a dual-threshold graded judgment. Instead of using a single standard, the eutectic undercooling is compared with two preset eutectic undercooling values. Targeted measures can be taken based on the different degrees of defects in the graphitization capacity of the molten iron: when the eutectic undercooling is less than the first preset value, the molten iron is directly judged to be qualified without additional adjustment, ensuring production efficiency; when the eutectic undercooling is between the first and second preset values, it indicates that the graphitization capacity of the molten iron is only slightly insufficient, which can be improved by extending the preset standing time of the next batch; when the eutectic undercooling is greater than or equal to the second preset value, it indicates that the graphitization capacity of the molten iron is severely insufficient, which requires increasing the first preset amount of silicon carbide to supplement carbon and silicon elements, thereby improving the efficiency of process adjustment.

[0020] Furthermore, by measuring the actual temperature and calculating the theoretical temperature through spectral analysis, this invention eliminates the subjectivity and error of human experience-based judgment, making the abstract metallurgical concept of supercooling tendency measurable and comparable, thereby improving the reliability of the assessment.

[0021] Furthermore, the present invention provides multiple adjustment methods for increasing the amount of silicon carbide added, thereby achieving adaptive and precise control of the increase in the amount of silicon carbide added.

[0022] Furthermore, the present invention reflects the kinetic conditions of eutectic cluster growth in the second inoculated iron melt by setting the eutectic solidification rate; when the eutectic solidification rate is less than the preset value, it indicates that the first inoculant is dispersed in the iron melt. By increasing the addition rate of the first inoculant in the next batch, its dispersion in the iron flow is improved, thereby providing more effective crystallization nuclei, promoting faster and more uniform eutectic growth, and thus improving the level of intelligence in the evaluation. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing synthetic cast iron based on a high proportion of scrap steel, as described in an embodiment of the present invention. Figure 2 This is a flowchart illustrating how to determine whether the preparation of the synthetic cast iron molten metal meets a preset standard, as described in this embodiment of the invention. Figure 3 This is a flowchart illustrating how the preparation of the second inoculated iron liquid is determined based on the eutectic recovery rate of the second inoculated iron liquid according to an embodiment of the present invention to determine whether the preparation of the second inoculated iron liquid meets a preset standard; Figure 4 This is a flowchart illustrating the adjustment strategy for determining when the preparation of the second inoculated iron liquid does not meet the preset standard, as described in an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0025] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0026] It should be noted that the data in this embodiment are all derived from a comprehensive analysis and evaluation of historical test data and corresponding historical test results from the three months prior to this test. Those skilled in the art will understand that the method described in this invention can determine the above-mentioned parameters in the following ways: selecting the value with the highest proportion based on the data distribution as the preset standard parameter; using weighted summation to obtain the value as the preset standard parameter; substituting each historical data point into a specific formula and using the value obtained by that formula as the preset standard parameter; or other selection methods, as long as the method described in this invention can clearly define different specific situations in the single-item judgment process through the obtained values.

[0027] Please see Figure 1 , Figure 2 , Figure 3 as well as Figure 4The flowcharts shown are respectively: a flowchart of the method for preparing synthetic cast iron based on a high proportion of scrap steel according to an embodiment of the present invention; a flowchart of determining whether the preparation of the synthetic cast iron molten iron meets the preset standard according to an embodiment of the present invention; a flowchart of determining whether the preparation of the second inoculated iron molten iron meets the preset standard based on the eutectic recovery rate of the second inoculated iron molten iron according to an embodiment of the present invention; and a flowchart of the adjustment strategy when the preparation of the second inoculated iron molten iron does not meet the preset standard according to an embodiment of the present invention.

[0028] This invention provides a method for preparing synthetic cast iron based on a high proportion of scrap steel, comprising: Step S1: A furnace charge consisting of 70% scrap steel, 28% shot-blasted cast iron remelting material of the same type, and 0.2% silicon carbide with a particle size of 2mm (based on the mass of the first preset addition amount of furnace charge) is added into an intermediate frequency induction furnace. After melting at 1510℃, synthetic cast iron molten iron is obtained. After being allowed to stand at a high temperature for a preset standing time of 8 minutes, the first cooling curve of the synthetic cast iron molten iron is collected. The eutectic undercooling is calculated based on the first cooling curve. During the standing period, the furnace temperature is maintained at 1505℃.

[0029] Step S2: If the preparation of the synthetic cast iron molten iron does not meet the preset standard according to the eutectic undercooling, increase the preset standing time of the next batch or increase the value of the first preset addition amount of the next batch. Step S3: Add silicon carbide of a second preset addition amount of 0.1% of the mass of the synthetic cast iron liquid to the synthetic cast iron liquid that meets the preset standard and stir to obtain the first inoculated iron liquid; Step S4: Tap the first inoculated iron liquid and add a third inoculating agent with a preset addition amount of 0.4% of the mass of the first inoculated iron liquid to the iron stream to obtain the second inoculated iron liquid; calculate the eutectic recovery rate of the second inoculated iron liquid based on the second cooling curve of the second inoculated iron liquid; Step S5: If the preparation of the second inoculated iron liquid does not meet the preset standard based on the eutectic recovery rate of the second inoculated iron liquid, the preparation of the second inoculated iron liquid is determined a second time based on the eutectic solidification rate of the second inoculated iron liquid, or the adjustment strategy is determined based on the relative deviation rate of carbon equivalent of the second inoculated iron liquid when the preparation of the second inoculated iron liquid does not meet the preset standard. Step S6: The second inoculated iron liquid that meets the preset standard is poured into a casting, and during the pouring process, a second inoculator accounting for 0.1% of the mass of the second inoculated iron liquid is added to obtain a synthetic cast iron casting.

[0030] It should be noted that the data in this embodiment are all results obtained through preliminary experiments before this test using the method described in this invention. Each preset value can be adjusted according to the specific application, as long as the method described in this invention can clearly define different specific situations in the single-item judgment process through the acquired values. The preset values ​​set in this embodiment are all obtained from preliminary experiments, including the correction coefficients, which were also selected through experimental verification.

[0031] In this implementation example, tapping is a routine operation in the casting industry, which is the process of releasing molten iron from the smelting furnace and transferring it to the ladle.

[0032] Specifically, the process of determining whether the preparation of the synthetic cast iron melt meets the preset standard based on the eutectic undercooling of the synthetic cast iron melt includes: The eutectic undercooling is compared with the first preset eutectic undercooling of 10°C and the second preset eutectic undercooling of 20°C. If the eutectic undercooling is less than the first preset eutectic undercooling, then the preparation of the synthetic cast iron molten iron is determined to meet the preset standard; If the eutectic undercooling is greater than or equal to the first preset eutectic undercooling and less than the second preset eutectic undercooling, then the preparation of the synthetic cast iron molten iron is determined to be non-compliant with the preset standard, and the preset standing time of the next batch is increased according to the difference between the eutectic undercooling and the first preset eutectic undercooling. If the eutectic undercooling is greater than or equal to the second preset eutectic undercooling, it is determined that the preparation of the synthetic cast iron molten iron does not meet the preset standard, and the value of the first preset addition amount in the next batch is increased according to the difference between the eutectic undercooling and the second preset eutectic undercooling.

[0033] Specifically, the first preset eutectic undercooling value ranges from [5℃ to 12℃], and the second preset eutectic undercooling value ranges from [15℃ to 25℃]. Preferably, the first preset eutectic undercooling value is 10℃ and the second preset eutectic undercooling value is 20℃.

[0034] Specifically, eutectic undercooling directly reflects the number of effective crystallization nuclei inside the molten iron. The greater the eutectic undercooling, the fewer the nuclei and the greater the tendency for white iron.

[0035] Specifically, the increase in the preset settling time for the next batch is positively correlated with the difference between the eutectic undercooling and the first preset eutectic undercooling. The positive correlation can be linear or nonlinear. The slope of the linear positive correlation is not specifically limited. It can be understood that the greater the difference between the eutectic undercooling and the first preset eutectic undercooling, the greater the increase in the preset settling time for the next batch.

[0036] Specifically, the process of obtaining the eutectic undercooling of the synthetic cast iron molten iron includes: Take 150g of the synthetic cast iron molten iron and pour it into a thermal analysis sample cup with a built-in thermocouple. At the same time, start the temperature acquisition instrument to record the temperature change curve of the synthetic cast iron molten iron from pouring to solidification, i.e., the first cooling curve. Identify the eutectic plateau region from the first cooling curve and determine the lowest temperature point of the plateau region as the first actual eutectic temperature. When hypoeutectic gray cast iron is cooled, primary austenite is precipitated first and the temperature continues to drop. When the eutectic transformation temperature is reached, austenite and graphite are precipitated in the liquid at the same time. This process is carried out at a constant temperature or near a constant temperature and releases a large amount of latent heat of crystallization, forming a eutectic plateau on the cooling curve. Take a first preset amount of the synthetic cast iron molten iron casting spectrum standard test block, and determine the chemical composition of the synthetic cast iron molten iron: C=3.25%, Si=1.85%, P=0.06%, according to the formula: T 理1 =1153+4.25×Si%-2.5×P%, the first theoretical eutectic temperature of the synthesized cast iron molten iron is calculated; The absolute value of the difference between the first actual eutectic temperature and the first theoretical eutectic temperature is the eutectic undercooling of the synthetic cast iron molten iron.

[0037] Specifically, there are several adjustment methods for increasing the value of the first preset addition amount in the next batch, among which, If the eutectic undercooling difference is less than the first preset eutectic undercooling difference of 6°C, then the value of the first preset addition amount is increased to the corresponding value using the first adjustment coefficient of 1.04. If the eutectic undercooling difference is greater than or equal to the first preset eutectic undercooling difference and less than the second preset eutectic undercooling difference of 11°C, then the value of the first preset addition amount is increased to the corresponding value using the second adjustment coefficient of 1.06. If the difference in eutectic undercooling is greater than or equal to the second preset difference in eutectic undercooling, then the value of the first preset addition amount is increased to the corresponding value using the third adjustment coefficient of 1.08; The eutectic undercooling difference is the difference between the eutectic undercooling and the second preset eutectic undercooling.

[0038] Specifically, the process of determining whether the preparation of the second inoculated iron melt meets the preset standard based on the eutectic recovery rate of the second inoculated iron melt includes: The eutectic recovery rate is compared with the first preset eutectic recovery rate of 0.51 and the second preset eutectic recovery rate of 0.81, respectively; If the eutectic recovery rate is less than the first preset eutectic recovery rate, it is determined that the preparation of the second inoculated iron liquid does not meet the preset standard, and the adjustment strategy when the preparation of the second inoculated iron liquid does not meet the preset standard is determined according to the relative deviation rate of carbon equivalent of the second inoculated iron liquid. If the eutectic recovery rate is greater than or equal to the first preset eutectic recovery rate and less than the second preset eutectic recovery rate, then the preparation of the second inoculated iron liquid is determined to meet the preset standard, and the preparation of the second inoculated iron liquid is further determined based on the eutectic solidification rate of the second inoculated iron liquid to meet the preset standard. If the eutectic recovery rate is greater than or equal to the second preset eutectic recovery rate, then the preparation of the second inoculated iron liquid is determined to meet the preset standard.

[0039] Specifically, the first preset eutectic recovery rate ranges from [0.35, 0.55], and the second preset eutectic recovery rate ranges from [0.65, 0.85]. Preferably, the first preset eutectic recovery rate is 0.51, and the second preset eutectic recovery rate is 0.81.

[0040] Specifically, the eutectic recovery rate reflects the strength of graphitization dynamism stimulated by the inoculation behavior. The higher the eutectic recovery rate, the more nuclei created by the inoculation, the stronger the activity, and the more complete the graphitization.

[0041] Specifically, the process of obtaining the eutectic recovery rate of the second inoculated iron melt includes: Take 80g of the second preset amount of the second inoculated iron liquid and pour it into the thermal analysis sample cup with the built-in thermocouple; Record the temperature change curve of the second inoculated molten iron from liquid to solid state during the cooling process, i.e., the second cooling curve; Identify and read the lowest temperature value of the eutectic transformation stage of the second inoculated iron liquid from the second cooling curve, and record it as the eutectic minimum temperature; Identify and read the highest temperature value that the second inoculated molten iron reaches after supercooling due to the release of latent heat of crystallization from the second cooling curve, and record it as the second eutectic recovery temperature; Based on the chemical composition of the second inoculated iron melt: carbon content C%=3.28%, silicon content Si%=1.92%, phosphorus content P%=0.05%, according to formula T 理2 =1153+4.25×Si%-2.5×P%, the second theoretical eutectic temperature of the second inoculated iron melt is calculated; The difference between the second eutectic recovery temperature and the lowest eutectic temperature is calculated and denoted as the first difference. The difference between the second theoretical eutectic temperature and the lowest eutectic temperature is calculated and denoted as the second difference; the ratio of the first difference to the second difference is denoted as the eutectic recovery rate of the second inoculated iron melt.

[0042] Specifically, the preparation of the second inoculated iron liquid is determined a second time based on the eutectic solidification rate of the second inoculated iron liquid to determine whether it meets the preset standard. If the eutectic solidification rate is less than the preset eutectic solidification rate of 0.6℃ / s, it is determined that the preparation of the second inoculated iron liquid does not meet the preset standard, and the addition rate of the first inoculant in the next batch is increased according to the difference between the eutectic solidification rate and the preset eutectic solidification rate. If the eutectic solidification rate is greater than or equal to the preset eutectic solidification rate, then the preparation of the second inoculated iron liquid is determined to meet the preset standard. The eutectic solidification rate is the ratio of the first difference to the eutectic recovery time, wherein the eutectic recovery time is the time taken for the second inoculated molten iron obtained from the second cooling curve to reach the second eutectic recovery temperature from the lowest eutectic temperature.

[0043] Specifically, the eutectic solidification rate characterizes the intensity and rate of graphitization in molten iron after eutectic supercooling. Essentially, it reflects the overall activity of the nuclei created by the inoculation treatment and the kinetics of graphite growth. The eutectic solidification rate is the temperature rise per unit time; a higher value indicates more graphite nuclei precipitating synchronously and rapidly and releasing latent heat per unit time, resulting in a healthier and faster solidification process. Conversely, a lower value indicates insufficient graphitization motive force and a slow process. Therefore, when the measured eutectic solidification rate is less than the preset value, the molten iron preparation is deemed not to meet the preset standard because a slow solidification rate directly indicates insufficient nucleation numbers or low nucleus activity, leading to a high risk of graphite morphological deterioration. In this case, increasing the addition rate of the first inoculant in the next batch based on the difference aims to increase the nucleation particle input intensity per unit time, thereby inoculating the supercooled molten iron and forcibly stimulating a more intense and synchronous graphitization reaction.

[0044] Specifically, the preset eutectic solidification rate is 0.6℃ / s, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0045] Specifically, the process of determining the adjustment strategy when the preparation of the second inoculated iron melt does not meet the preset standard based on the relative deviation rate of the carbon equivalent of the second inoculated iron melt includes: The relative deviation rate of carbon equivalent is compared with the preset relative deviation rate of carbon equivalent of 2%. If the relative deviation rate of carbon equivalent is less than the preset relative deviation rate of carbon equivalent, the second preset addition amount of silicon carbide in the next batch is increased according to the difference between the preset relative deviation rate of carbon equivalent and the relative deviation rate of carbon equivalent. If the relative deviation rate of carbon equivalent is greater than or equal to the preset relative deviation rate of carbon equivalent, a component runaway alarm will be issued.

[0046] Specifically, the preset relative deviation rate of carbon equivalent is 2%, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0047] The process of obtaining the relative deviation rate of the carbon equivalent includes: The carbon content (C%) and silicon content (Si%) of the second inoculated iron melt were determined using a direct-reading spectrometer. Based on the measured carbon content (C%) and silicon content (Si%) of the second inoculated iron liquid, the actual carbon equivalent of the second inoculated iron liquid is calculated according to the carbon equivalent calculation formula: CE=C%+(1 / 3)Si%. The difference between the actual carbon equivalent and the preset carbon equivalent of 4.3% is calculated and recorded as the carbon equivalent difference. The absolute value of the carbon equivalent difference is recorded as a percentage of the preset carbon equivalent as the carbon equivalent relative deviation rate.

[0048] Specifically, the increase in the second preset addition amount of silicon carbide in the next batch is positively correlated with the difference between the preset relative deviation rate of carbon equivalent and the relative deviation rate of carbon equivalent. The positive correlation can be linear or nonlinear. The linear slope of the linear positive correlation is not specifically limited. It can be understood that the greater the difference between the preset relative deviation rate of carbon equivalent and the relative deviation rate of carbon equivalent, the greater the increase in the second preset addition amount of silicon carbide in the next batch.

[0049] Specifically, the furnace charge consists of the following raw materials by mass percentage: 60%-80% scrap steel, 20%-40% shot-blasted cast iron of the same type as recycled material, and silicon carbide added at a first preset amount, wherein the particle size of the silicon carbide is 1-5 mm.

[0050] Specifically, the first inoculant is a barium silicon inoculant, which is added at a rate of 0.3%-0.5% of the mass of the first inoculated iron liquid, and the particle size range of the first inoculant is 3mm-10mm; the second inoculant is a barium silicon inoculant, which is added at a rate of 0.1%-0.2% of the mass of the second inoculated iron liquid, and the particle size range of the second inoculant is 0.2mm-0.8mm.

[0051] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing synthetic cast iron based on a high proportion of scrap steel, characterized in that, include: The furnace charge, which includes scrap steel and silicon carbide of a first preset amount, is added into an electric furnace and smelted at high temperature to obtain synthetic cast iron molten iron. After being allowed to stand at high temperature for a preset standing time, the first cooling curve of the synthetic cast iron molten iron is collected, and the eutectic undercooling is determined based on the first cooling curve. If the preparation of the synthetic cast iron molten iron does not meet the preset standard based on the eutectic undercooling, the preset standing time of the next batch or the value of the first preset addition amount of the next batch shall be increased. Add a second preset amount of silicon carbide to the synthetic cast iron molten iron that meets the preset standard and stir to obtain the first inoculated iron molten iron; The first inoculated iron liquid is tapped, and a first inoculant is added to the iron stream at a third preset amount to obtain a second inoculated iron liquid; the eutectic recovery rate of the second inoculated iron liquid is determined based on the second cooling curve of the second inoculated iron liquid; When the preparation of the second inoculated iron liquid does not meet the preset standard, the preparation of the second inoculated iron liquid is determined a second time based on the eutectic recovery rate of the second inoculated iron liquid. Alternatively, the adjustment strategy for the preparation of the second inoculated iron liquid does not meet the preset standard is determined based on the relative deviation rate of the carbon equivalent of the second inoculated iron liquid. The second inoculated molten iron that meets the preset standard is poured into a casting, and a second inoculating agent is added during the pouring process to obtain a synthetic cast iron casting.

2. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 1, characterized in that, The process of determining whether the preparation of the synthetic cast iron melt meets the preset standard based on the eutectic undercooling of the synthetic cast iron melt includes: The eutectic undercooling is compared with the first preset eutectic undercooling and the second preset eutectic undercooling, respectively; If the eutectic undercooling is less than the first preset eutectic undercooling, then the preparation of the synthetic cast iron molten iron is determined to meet the preset standard; If the eutectic undercooling is greater than or equal to the first preset eutectic undercooling and less than the second preset eutectic undercooling, then the preparation of the synthetic cast iron molten iron is determined to be non-compliant with the preset standard, and the preset standing time of the next batch is increased according to the difference between the eutectic undercooling and the first preset eutectic undercooling. If the eutectic undercooling is greater than or equal to the second preset eutectic undercooling, it is determined that the preparation of the synthetic cast iron molten iron does not meet the preset standard, and the value of the first preset addition amount in the next batch is increased according to the difference between the eutectic undercooling and the second preset eutectic undercooling.

3. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 2, characterized in that, The process of obtaining the eutectic undercooling of the synthetic cast iron molten iron includes: Take a first preset amount of the synthetic cast iron molten iron and pour it into a thermal analysis sample cup with a built-in thermocouple. Record the temperature change curve of the synthetic cast iron molten iron from pouring to solidification, i.e., the first cooling curve. Determine the first actual eutectic temperature from the first cooling curve. Take a first preset amount of the synthetic cast iron molten iron casting spectrum standard test block, and calculate the first theoretical eutectic temperature of the synthetic cast iron molten iron based on the determination of the chemical composition of the synthetic cast iron molten iron. The absolute value of the difference between the first actual eutectic temperature and the first theoretical eutectic temperature is the eutectic undercooling of the synthetic cast iron molten iron.

4. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 3, characterized in that, There are several adjustment methods for increasing the value of the first preset addition amount in the next batch, and each adjustment method increases the value of the first preset addition amount in the next batch by a different amount.

5. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 4, characterized in that, The process of determining whether the preparation of the second inoculated iron melt meets the preset standard based on the eutectic recovery rate of the second inoculated iron melt includes: The eutectic recovery rate is compared with the first preset eutectic recovery rate and the second preset eutectic recovery rate, respectively; If the eutectic recovery rate is less than the first preset eutectic recovery rate, it is determined that the preparation of the second inoculated iron liquid does not meet the preset standard, and the adjustment strategy when the preparation of the second inoculated iron liquid does not meet the preset standard is determined according to the relative deviation rate of carbon equivalent of the second inoculated iron liquid. If the eutectic recovery rate is greater than or equal to the first preset eutectic recovery rate and less than the second preset eutectic recovery rate, then the preparation of the second inoculated iron liquid is determined to meet the preset standard, and the preparation of the second inoculated iron liquid is further determined based on the eutectic solidification rate of the second inoculated iron liquid to meet the preset standard. If the eutectic recovery rate is greater than or equal to the second preset eutectic recovery rate, then the preparation of the second inoculated iron liquid is determined to meet the preset standard.

6. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 5, characterized in that, The process of obtaining the eutectic recovery rate of the second inoculated iron melt includes: Take the second preset amount of the second inoculated iron liquid and pour it into the thermal analysis sample cup with the built-in thermocouple; Record the temperature change curve of the second inoculated molten iron from liquid to solid state during the cooling process, i.e., the second cooling curve; Identify and read the lowest temperature value of the eutectic transformation stage of the second inoculated iron liquid from the second cooling curve, and record it as the eutectic minimum temperature; Identify and read the highest temperature value that the second inoculated molten iron reaches after supercooling due to the release of latent heat of crystallization from the second cooling curve, and record it as the second eutectic recovery temperature; The second theoretical eutectic temperature of the second inoculated iron liquid is calculated based on its chemical composition. The difference between the second eutectic recovery temperature and the lowest eutectic temperature is calculated and denoted as the first difference. The difference between the second theoretical eutectic temperature and the lowest eutectic temperature is calculated and denoted as the second difference; the ratio of the first difference to the second difference is denoted as the eutectic recovery rate of the second inoculated iron melt.

7. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 6, characterized in that, If the preparation of the second inoculated iron liquid does not meet the preset standard, the addition rate of the first inoculant in the next batch is increased based on the difference between the eutectic solidification rate and the preset eutectic solidification rate. The eutectic solidification rate is the ratio of the first difference to the eutectic recovery time, wherein the eutectic recovery time is the time taken for the second inoculated molten iron obtained from the second cooling curve to reach the second eutectic recovery temperature from the lowest eutectic temperature.

8. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 7, characterized in that, The process of determining the adjustment strategy when the preparation of the second inoculated iron liquid does not meet the preset standard based on the relative deviation rate of the carbon equivalent of the second inoculated iron liquid includes: The relative deviation rate of carbon equivalent is compared with the preset relative deviation rate of carbon equivalent; If the relative deviation rate of carbon equivalent is less than the preset relative deviation rate of carbon equivalent, the second preset addition amount of silicon carbide in the next batch is increased according to the difference between the preset relative deviation rate of carbon equivalent and the relative deviation rate of carbon equivalent. If the relative deviation rate of carbon equivalent is greater than or equal to the preset relative deviation rate of carbon equivalent, a component runaway alarm will be issued; The relative deviation rate of carbon equivalent is determined based on the carbon equivalent of the second inoculated iron melt and the preset carbon equivalent.

9. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 1, characterized in that, The furnace charge consists of the following raw materials in the following mass percentages: 60%-80% scrap steel, 20%-40% shot-blasted recycled material, and silicon carbide added at a first preset amount, wherein the particle size of the silicon carbide is 1-5 mm.

10. The method for preparing synthetic cast iron based on a high proportion of scrap steel according to claim 1, characterized in that, The first inoculant is a barium silicon inoculant, and its addition amount is 0.3%-0.5% of the mass of the first inoculated iron liquid, and the particle size range of the first inoculant is 3mm-10mm; the second inoculant is a barium silicon inoculant, and its addition amount is 0.1%-0.2% of the mass of the second inoculated iron liquid, and the particle size range of the second inoculant is 0.2mm-0.8mm.

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