Rare earth alloying inoculant

Abstract

The invention relates to the technical field of casting materials, and particularly discloses a rare earth alloying nucleating agent. According to the rare earth alloying nucleating agent, rare earth elements are added on the basis of a traditional silicon-based nucleating agent, the rare earth elements can react with S, O and N in molten iron to generate rare earth sulfide, oxide and nitride particles, and the particles can serve as nucleation substrates of graphite. The melting point of the particles is higher than the temperature of molten iron, so that the nucleation number of rare earth inoculation is large, the anti-recession time is long, the inoculation effect can be ensured, graphite is finer, and the strength of a casting is improved.

Description

Technical Field

[0001] This application relates to the technical field of foundry materials, and more specifically, it relates to a rare earth alloyed inoculant. Background Art

[0002] Cast iron refers to the general term for cast iron-carbon alloys with a carbon mass fraction of more than 2.06%. It is usually made by melting pig iron, scrap steel, ferroalloys, etc. in different proportions. Generally, it can be divided into gray cast iron, ductile cast iron, vermicular graphite cast iron, malleable cast iron, alloy cast iron, white cast iron, inoculated cast iron, etc. Inoculated cast iron refers to gray cast iron that has been inoculated. Inoculation treatment means adding a small amount of inoculant to the molten iron before pouring to form a large number of highly dispersed refractory particles. These particles become the crystallization nuclei of graphite, promoting the nucleation of graphite, and thus a fine pearlite matrix and small and uniformly distributed flake graphite can be obtained. After inoculation treatment, the matrix structure, graphite flake shape, and eutectic cell of the cast iron are refined. Therefore, the strength and toughness of inoculated cast iron are superior to those of ordinary gray cast iron. Due to the high strength and toughness of inoculated cast iron, and the uniform structure and properties of castings with different wall thicknesses, it is often used to manufacture large castings with high mechanical property requirements and large cross-sectional size changes.

[0003] Ferrosilicon alloy used as an inoculant is usually an iron alloy containing 75% silicon. Using this inoculant can obtain a gray structure, refine graphite flakes, reduce the destructive effect of graphite on the matrix, and its significant feature is small wall thickness sensitivity and uniform structure in each part of the casting. Silicon-barium inoculant is a long-acting inoculant with a strong ability to promote graphitization. It can improve the morphology and distribution of graphite in thin-wall castings, and also has the effect of slowing down inoculation decay. Generally speaking, silicon-barium inoculant has a stronger ability to increase the number of eutectic cells and improve cross-sectional uniformity than ferrosilicon.

[0004] Regarding the above related technologies, the inventor believes that traditional silicon-based inoculants are difficult to fully overcome the harmful effects of sulfur, have poor melting effects in molten iron, and limited inoculation effects, and cannot fully improve the comprehensive performance of castings. Summary of the Invention

[0005] In related technologies, traditional silicon-based inoculants are difficult to fully overcome the harmful effects of sulfur, have poor melting effects in molten iron, and limited inoculation effects, and cannot fully improve the comprehensive performance of castings. To improve this defect, this application provides a rare earth alloyed inoculant.

[0006] This application provides a rare earth alloyed inoculant, adopting the following technical solution: A rare earth alloyed inoculant, the inoculant comprising the following components by weight percentage: silicon 65.0 - 70.0%, calcium 1.5 - 2.5%, manganese 4.0 - 6.0%, chromium 6.0 - 8.0%, rare earth elements 0.8 - 1.2%, and the balance being iron and inevitable trace elements; the inevitable trace elements include aluminum, and the weight percentage of aluminum in the inoculant is < 1.0%.

[0007] By adopting the above technical solution, the present application adds rare earth elements, chromium and manganese to the inoculant. Among them, manganese and chromium are used as alloying elements, and rare earths cooperate with calcium, silicon and iron to play an inoculating role. The addition of rare earth elements can produce the following effects: (1) Rare earth elements can react with sulfur, oxygen and nitrogen in the molten iron to form rare earth sulfide, rare earth oxide and rare earth nitride particles, which can serve as the nucleation substrate for graphite. Since the melting points of these particles are higher than the temperature of the molten iron, the number of nuclei in rare earth inoculation is not only large, but also the anti-decay time is long, thus ensuring the inoculation effect and making the graphite finer. The fine graphite can optimize the internal structure of cast iron, make the carbide distribution more uniform, thereby improving the mechanical properties of cast iron, increasing the tensile strength, yield strength and hardness of cast iron, and at the same time can also inhibit the surface oxidation of cast iron and reduce the generation of fatigue cracks. (2) Rare earth elements can also enhance the corrosion resistance of cast iron, by forming a dense oxide film on the surface of cast iron to prevent the intrusion of corrosive media, thereby extending the service life of cast iron. (3) Rare earth elements can improve the machinability of cast iron, making the surface quality of cast iron better, reducing the cutting force, reducing chips and defects, and improving the efficiency and quality of cutting processing. Through these effects, the application of rare earth in inoculating cast iron can significantly improve the performance and processing quality of cast iron and meet different usage requirements.

[0008] Chromium is a strong carbide stabilizing element, and the addition of chromium can produce the following effects: (1) It can form a dense oxide layer on the surface of cast iron, significantly improving the corrosion resistance of cast iron. (2) Chromium can form chromium carbide compounds with high hardness, thereby increasing the hardness and strength of cast iron. (3) The addition of chromium elements can make the grains of cast iron finer, which not only helps to improve the mechanical properties of cast iron, but also improves its casting performance. The fine grains can reduce the defects on the surface of the casting and improve the surface quality of the casting. (4) Chromium can increase the solidification temperature of the iron-carbon-silicon ternary alloy, reduce the depth of the molten iron, prevent defects from appearing on the surface of the casting, thereby improving the surface quality of the casting. In addition, chromium can stabilize cementite and reduce the formation of non-refined graphite, thereby improving the wear resistance of cast iron.

[0009] Manganese is an alloying element that can counteract the harmful effects of sulfur and improve the melting characteristics of the inoculant in molten iron. The addition of manganese can produce the following effects: (1) It refines the grains of the casting, thereby increasing the hardness and wear resistance of the casting, significantly improving the hardness and strength of the casting, enabling it to withstand greater mechanical stress and wear, and extending the service life of the casting. (2) It improves the toughness of cast iron, making it have better impact and seismic resistance, which is particularly important for castings that need to withstand dynamic loads. (3) Manganese can combine with carbon in cast iron to form cementite, and this structure makes the structure of the casting more dense and uniform. An appropriate amount of manganese can adjust the ratio of ferrite and pearlite in the casting, thereby changing the properties of the casting.

[0010] The inoculant of the present application not only overcomes the harmful effects of sulfur, but also has a relatively low melting point and can dissolve into the molten iron at 1180 - 1200 °C. Therefore, it is easier to play an inoculating role during the casting process. Under the synergistic effect of rare earth elements, chromium, manganese and other elements, the rare earth alloyed inoculant of the present application has both alloying and inoculating functions, has good anti-decay ability, is conducive to obtaining cast iron parts with high strength, high hardness and high cross-sectional uniformity, can fully improve the comprehensive properties of the casting, and thus overcomes the defects of traditional inoculants.

[0011] Preferably, the inoculant comprises the following components by weight percentage: silicon 65.0 - 67.0%, calcium 1.5 - 2.0%, manganese 4.0 - 5.0%, chromium 6.0 - 7.0%, rare earth elements 0.8 - 1.0%, and the balance is iron and unavoidable trace elements.

[0012] Preferably, the inoculant comprises the following components by weight percentage: silicon 66.0 - 68.0%, calcium 1.7 - 2.2%, manganese 4.5 - 5.5%, chromium 6.5 - 7.5%, rare earth elements 0.9 - 1.1%, and the balance is iron and unavoidable trace elements.

[0013] Preferably, the inoculant comprises the following components by weight percentage: silicon 67.0 - 70.0%, calcium 1.8 - 2.5%, manganese 5.0 - 6.0%, chromium 7.0 - 8.0%, rare earth elements 1.0 - 1.2%, and the balance is iron and unavoidable trace elements.

[0014] Preferably, the inoculant is made from the following raw materials: ferrosilicon, ferromanganese, ferrochrome, rare earth ferrosilicon, calcium silicon alloy.

[0015] By adopting the above technical solutions, the present application uses ferromanganese to provide manganese element, ferrochrome to provide chromium element, and rare earth ferrosilicon to provide rare earth element. Rare earth ferrosilicon is a rare earth alloy with a large supply and a low price. Its melting point is 1082 - 1089 °C, and the average specific gravity is 4.7 g / cm³. The rare earth element itself has the effect of promoting white mouth, but when the addition amount of rare earth is less than the "critical addition amount", due to the deoxidation and desulfurization effects of rare earth, rare earth compounds are formed. The formation of rare earth compounds not only makes the rare earth itself lose its original role in promoting the formation of white mouth, but also reduces the role of impurities such as oxygen and sulfur that strongly hinder graphitization. At the same time, rare earth compounds are refractory small particles in the molten iron, and these particles can serve as crystal nuclei for graphitization. The comprehensive result is that the white mouth of cast iron is reduced. Therefore, rare earth ferrosilicon alloy is actually a composite inoculant, which not only has the inoculation effect of ferrosilicon and calcium silicide, but also can purify the molten iron, improve the casting performance, refine the graphite and matrix structure, make the distribution more uniform, reduce the supercooling tendency, and improve the mechanical properties and wear resistance of cast iron. Generally speaking, if it is an inoculant of ferrosilicon type, its addition amount must be appropriately controlled. When the addition amount is too much, not only good results cannot be obtained, but the strength of cast iron will decrease instead. Compared with ferrosilicon, the negative impact of the addition amount of rare earth ferrosilicon on the inoculation effect is not so obvious, so it helps to maintain good strength performance of cast iron.

[0016] Preferably, the ferrosilicon includes FeSi90Al1.5 and FeSi75Al0.5 - A.

[0017] By adopting the above technical solutions, since rare earth ferrosilicon is added in the present application, the dosage of ferrosilicon can be controlled, and the situation of poor strength of castings caused by too high ferrosilicon content can be effectively avoided.

[0018] Preferably, the ferromanganese selected is Mn88C0.2.

[0019] By adopting the above technical solutions, ferromanganese can be used as an inoculant and spheroidizing agent for ductile iron, which can prevent the formation of carbides, promote the precipitation of graphite, thus shortening the spheroidizing time, improving the quality of cast iron, and improving the performance of cast iron. In addition, the addition of ferromanganese can also reduce the blockage of the water inlet of the smelting furnace and effectively extend the service life of the smelting furnace.

[0020] Preferably, the ferrochrome selected is FeCr65C0.06.

[0021] By adopting the above technical solutions, the white mouth tendency of ferrochrome can be effectively neutralized by rare earth elements, which helps to improve the comprehensive performance of castings.

[0022] Preferably, the inoculant is made from the following raw materials by weight: 260-272 parts of FeSi90Al1.5 ferrosilicon, 498-520 parts of FeSi75Al0.5-A ferrosilicon, 41-62 parts of Mn88C0.2 ferromanganese, 90-119 parts of FeCr65C0.06 ferrochrome, 36-53 parts of rare earth ferrosilicon, and 19-46 parts of calcium silicide alloy.

[0023] By adopting the above technical solution, the present application optimizes the raw material composition of the inoculant, which helps to improve the comprehensive performance of the casting.

[0024] In summary, the present application has the following beneficial effects: 1. The rare earth alloying inoculant of the present application adds rare earth elements to the traditional silicon-based inoculant. The rare earth elements can react with S, O, and N in the molten iron to form rare earth sulfide, oxide, and nitride particles, which can serve as the nucleation substrates for graphite. Since the melting points of these particles are higher than the temperature of the molten iron, the number of nuclei in rare earth inoculation is not only large but also the anti-decay time is long, thus ensuring the inoculation effect, making the graphite finer, and thereby improving the strength of the casting.

[0025] 2. The inoculant of the present application not only overcomes the harmful effects of sulfur but also has a relatively low melting point, so it is easier to play an inoculation role during the casting process. Under the synergistic action of rare earth elements, chromium, manganese and other elements, the rare earth alloying inoculant of the present application has both alloying and inoculation functions, has good anti-decay ability, is beneficial to obtaining cast iron parts with high hardness and high cross-sectional uniformity, can fully improve the comprehensive performance of the casting, and thus overcomes the defects of traditional inoculants.

[0026] 3. The rare earth alloying inoculant of the present application can promote graphitization, make the graphite morphology in the cast iron finer and more evenly distributed, and thus improve the mechanical properties of the cast iron.

[0027] 4. The rare earth alloying inoculant of the present application can eliminate or reduce the flaw tendency in the cast iron and avoid problems such as cold shuts and slag inclusions.

[0028] 5. The rare earth alloying inoculant of the present application can refine the grains and improve the matrix structure, significantly improve the mechanical properties of gray cast iron, reduce the wall thickness sensitivity of the casting, and reduce the difference in microstructure and hardness between thin walls and thick walls.

[0029] 6. When producing cylinder blocks and cylinder heads of engines for automobiles or tractors, the rare earth alloying inoculant of the present application can reduce processing defects such as slag inclusions or micro-shrinkage porosity. Detailed Embodiments

[0030] The following further elaborates on the present application in combination with examples and comparative examples. The raw materials involved in the present application can all be obtained through commercial channels. Examples

[0031] Examples 1 - 6 Taking Example 1 as an example, the description is as follows.

[0032] Example 1 In this example, the raw materials for preparing the rare earth alloyed inoculant are as follows: "Ferrosilicon" in accordance with "GB / T2272 - 2009", grade: FeSi90Al1.5, chemical composition (%) : Si, 87.0 - 95.0; Al < 1.5; Ca < 1.5; Mn < 0.4; Cr < 0.2; P < 0.040; S < 0.020; C < 0.20; balance Fe.

[0033] "Ferrosilicon" in accordance with "GB / T2272 - 2009", grade FeSi75Al0.5 - A, chemical composition (%) : Si, 74.0 - 80.0; Al < 0.5; Ca < 1.0; Mn < 0.4; Cr < 0.3; P < 0.035; S < 0.020; C < 0.10; balance Fe.

[0034] "Ferromanganese" in accordance with "GB / T 3795 - 2014", low - carbon ferromanganese, grade: Mn88C0.2, chemical composition (%) : Mn, 85.0 - 92.0; C ≤ 0.2; Si ≤ 1.0 - 2.0; P ≤ 0.10 - 0.20; S ≤ 0.02; balance Fe.

[0035] "Ferrochrome" in accordance with "GB / T 5683 - 2008", ferrochrome grade: FeCr65C0.06, chemical composition (%) : Cr, 60.0 - 70.0; C < 0.06; Si < 1.0; P < 0.03; S < 0.025; balance Fe.

[0036] "Rare earth ferrosilicon alloy" in accordance with "GB / T4137 - 2004", grade: 195023. Chemical composition (%) : RE, 21.0 - 24.0; Si < 44.0; Mn < 2.5; Ca < 5.0; Ti < 2.0; balance Fe.

[0037] "Calcium - silicon alloy" in accordance with "YB / T 5051 - 2007", grade Ca28Si60, chemical composition (%) : Ca < 28.0; Si, 50.0 - 65.0; C < 1.0; Al < 2.4; P < 0.04; S < 0.06.

[0038] This example provides a rare earth alloyed inoculant, which includes the following components by weight percentage: silicon 65.0%, calcium 1.5%, manganese 4.0%, chromium 6.0%, rare earth elements 0.8%, the balance being iron and unavoidable trace elements, and the unavoidable trace element is aluminum, and the weight percentage of aluminum is 0.6%.

[0039] This embodiment provides a preparation method of a rare earth alloyed inoculant, including the following steps: (1) Weigh 260 kg of ferrosilicon FeSi90Al1.5, 498 kg of ferrosilicon FeSi75Al0.5-A, 19 kg of calcium-silicon alloy, 41 kg of ferromanganese, 90 kg of ferrochrome, and 36 kg of rare earth ferrosilicon alloy. After drying, they are respectively crushed into particles with an average particle size of 1 mm; (2) Put the particles obtained in step (1) into a blender and stir at a speed of 10 r / min for 10 min to obtain a rare earth alloyed inoculant.

[0040] As shown in Table 1, the differences between Examples 1-6 mainly lie in the element composition and raw material ratio of the rare earth alloyed inoculant.

[0041] Table 1 Element composition and raw material ratio of rare earth alloyed inoculant Comparative example Comparative example 1 In this comparative example, commercially available ferrosilicon alloy particles (average particle size 1 mm) are selected as the inoculant. The ferrosilicon alloy grade is FeSi75Al0.5-A, which complies with the provisions of "GB / T 2272-2009 Ferrosilicon". According to the regulations, its chemical composition (%) is as follows: Si, 74.0 - 80.0; Al < 0.5; Ca < 1.0; Mn < 0.4; Cr < 0.3; P < 0.035; S < 0.020; C < 0.10; the balance is Fe.

[0042] Comparative example 2 In this comparative example, commercially available silicon-barium inoculant (average particle size 1 mm) is selected. The element composition of the silicon-barium inoculant is as follows: silicon 75%, barium 4.0%, calcium 1.8%, aluminum 1.4%, and the balance is made up to 100% by iron.

[0043] Performance detection test method Use HT200 gray iron castings that meet the provisions of "GB / T 9439-2023 Gray Iron Castings" as the test material. Its chemical composition is: carbon 3.2%, silicon 2.0%, manganese 0.8%, phosphorus 0.04%, sulfur 0.08%, and the balance is iron. Melt the HT200 gray iron castings into molten iron at 1540 °C in an electric furnace for standby. After the molten iron is kept at 1540 °C for 5 min, take an inoculant with a weight equivalent to 0.35% of the total weight of the molten iron, put the inoculant at the bottom of the ladle, cool the molten iron to 1510 °C, then pour it into the ladle. After the reaction is over, skim the slag, and then transfer the ladle to the casting machine for casting.

[0044] Tensile tests were carried out on specimens machined from attached cast test bars with cooling conditions similar to those of the castings. Type B specimens were used for the tensile tests, and the test results of the tensile strength are shown in Table 2.

[0045] Table 2 Tensile Strength Combined with Examples 1-6 and Comparative Examples 1-2 and Table 2, it can be seen that the tensile strengths measured in Examples 1-6 are all higher than those in Comparative Example 1 and Comparative Example 2. This is because the inoculant of the present application provides heterogeneous nucleation cores for the molten iron, achieving the purpose of refining grains, improving the microstructure, and enhancing the material properties. Moreover, the inoculant of the present application has more excellent characteristics than traditional inoculants, such as fast dissolution, high absorption efficiency, and a large number of nucleation cores, etc., which refine the microstructure of gray cast iron and improve properties such as tensile strength and hardness. After inoculation, the mechanical properties of HT200 gray cast iron have reached the level of HT250 gray cast iron.

[0046] The differences between the inoculant of the present application and traditional inoculants are mainly in the following aspects: Firstly, rare earth elements are added to the traditional silicon-based inoculant in the present application, and alloying elements are introduced at the same time. Under the synergistic effect of rare earth elements, chromium, manganese and other elements, the rare earth alloyed inoculant of the present application has both alloying and inoculating functions, has good anti-decay ability, is conducive to obtaining cast iron parts with high hardness and high cross-section uniformity, and can fully improve the comprehensive performance of castings under relatively low addition amounts. For traditional inoculants, sulfur in cast iron is not beneficial to improving strength, while manganese can offset the harmful effects of sulfur, thus improving the melting characteristics of the inoculant in molten iron. The inoculant of the present application not only overcomes the harmful effects of sulfur, but also has a relatively low melting point and can dissolve into the molten iron at 1180-1200 °C, so it is easier to play an inoculating role during the casting process and overcomes the defects of traditional inoculants.

[0047] Secondly, rare earth elements can react with sulfur, oxygen, and nitrogen in molten iron to form rare earth sulfide, rare earth oxide, and rare earth nitride particles, which can serve as the nucleation substrate for graphite. Since the melting points of these particles are higher than the molten iron temperature, the number of nuclei in rare earth inoculation is not only large, but also the anti-decay time is long, thus ensuring the inoculation effect and making the graphite finer. The fine graphite can optimize the internal structure of cast iron, make the carbide distribution more uniform, thereby improving the mechanical properties of cast iron, increasing the tensile strength, yield strength, and hardness of cast iron, and at the same time can inhibit the surface oxidation of cast iron and reduce the generation of fatigue cracks. Manganese can improve the toughness of cast iron, making it have better impact resistance and seismic resistance, which is particularly important for castings that need to withstand dynamic loads.

[0048] In the third aspect, rare earth elements can improve the machinability of cast iron, making the surface quality of cast iron better, reducing the cutting force, decreasing chips and defects, and enhancing the efficiency and quality of machining. As a strong carbide stabilizing element, chromium can make the grains of cast iron finer, which not only helps improve the mechanical properties of cast iron but also its casting properties. The fine grains can reduce the defects on the surface of castings. Chromium can increase the solidification temperature of the iron-carbon-silicon ternary alloy, reduce the depth of molten iron, and prevent defects on the surface of castings. Through the synergistic effect with rare earth elements, the surface quality of castings is improved. Manganese can combine with carbon in cast iron to form cementite, and this structure makes the microstructure of castings denser and more uniform. An appropriate amount of manganese can adjust the ratio of ferrite and pearlite in castings, thereby changing the properties of castings.

[0049] In the fourth aspect, rare earth elements can significantly improve the corrosion resistance of cast iron by forming a dense oxide film on the surface of cast iron to prevent the intrusion of corrosive media. Chromium can also form a dense oxide film on the surface of cast iron. At the same time, chromium can stabilize cementite and reduce the formation of non-refined graphite, and can form chromium carbide compounds with high hardness, thereby increasing the hardness and strength of cast iron and improving its wear resistance. And manganese can refine the grains of castings, improve the hardness and wear resistance of castings, significantly increase the hardness and strength of castings, enabling them to withstand greater mechanical stress and wear. The synergistic effect of the three effectively extends the service life of cast iron.

[0050] The above embodiments are only explanations of this application and not limitations thereof. After reading this specification, those skilled in the art can make modifications to the embodiments of this application that do not contribute creatively as needed, but as long as they are within the scope of the claims of this application, they are protected by the patent law.

Claims

1. A rare earth alloying inoculant, characterized in that: The inoculant comprises the following components in weight percentage: 65.0-70.0% silicon, 1.5-2.5% calcium, 4.0-6.0% manganese, 6.0-8.0% chromium, 0.8-1.2% rare earth elements, and the remainder is iron and inevitable trace elements; the inevitable trace elements include aluminum, and the weight percentage of aluminum in the inoculant is less than 1.0%.

2. The rare earth alloying inoculant according to claim 1, characterized in that: The inoculant comprises the following components in weight percentage: 65.0-67.0% silicon, 1.5-2.0% calcium, 4.0-5.0% manganese, 6.0-7.0% chromium, 0.8-1.0% rare earth elements, and the remainder is iron and inevitable trace elements.

3. The rare earth alloying inoculant according to claim 1, characterized in that: The inoculant comprises the following components in weight percentage: 66.0-68.0% silicon, 1.7-2.2% calcium, 4.5-5.5% manganese, 6.5-7.5% chromium, 0.9-1.1% rare earth elements, and the remainder is iron and inevitable trace elements.

4. The rare earth alloying inoculant according to claim 1, characterized in that: The inoculant comprises the following components in weight percentage: 67.0-70.0% silicon, 1.8-2.5% calcium, 5.0-6.0% manganese, 7.0-8.0% chromium, 1.0-1.2% rare earth elements, and the remainder is iron and inevitable trace elements.

5. The rare earth alloying inoculant according to claim 1, characterized in that: The inoculant is made of the following raw materials: ferrosilicon, ferromanganese, ferrochrome, rare earth ferrosilicon and silicon-calcium alloy.

6. The rare earth alloying inoculant according to claim 5, characterized in that: The ferrosilicon includes FeSi90Al1.5 and FeSi75Al0.5-A.

7. The rare earth alloying inoculant according to claim 6, characterized in that: The ferromanganese is selected from Mn88C0.

2.

8. The rare earth alloying inoculant according to claim 7, characterized in that: The ferrochrome is FeCr65C0.

06.

9. The rare earth alloying inoculant according to claim 8, characterized in that: The inoculant is made of the following raw materials in parts by weight: 260-272 parts of FeSi90Al1.5 ferrosilicon, 498-520 parts of FeSi75Al0.5-A ferrosilicon, 41-62 parts of Mn88C0.2 ferromanganese, 90-119 parts of FeCr65C0.06 ferrochrome, 36-53 parts of rare earth ferrosilicon, and 19-46 parts of silicon-calcium alloy.

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